"There is no subject more captivating, more worth of study, than science. To understand this great mechanism, to discover the forces which are active, and the laws which govern them, is the highest aim for the intellect of man."

Nikola Tesla


Acids, Bases, Salts and pH


Acids are generally a class of substances that taste sour, such as vinegar, which is a dilute solution of acetic acid. Bases, or alkaline substances such as baking soda, which are characterized by their bitter taste and slippery feel (when in water). The first precise definition of an acid and base was given by Svante Arrhenius, and is referred to as Arrhenius Theory.


Arrhenius concocted the first successful concept of acids and bases. He did this by defining acids and bases according to the effect these substances have on water. The Arrhenius concept of acids and bases is as follows: an acid is a substance that when dissolved in water increases the concentration of the hydrogen ion, H+. A base is a substance that when dissolved in water increases the concentration of the hydroxide ion, OH-.


The hydrogen ion, is not just a bare proton, it is a proton bonded to a water molecule, H2O. This results in a hydronium ion, H3O+.


In Arrhenius's theory, something that is a strong acid is a substance that completely ionizes in aqueous solution to give a hydronium ion, H3O+, and an anion. An anion is a negatively charged ion. An example of a strong acid is perchloric acid:


HClO4(aq) + H2O(l) -> H3O+(aq) + ClO4-(aq)


What is going on above is that we have perchloric acid in an aqueous solution. This perchloric acid ionizes entirely and results in a hydronium ion and a perchlorate anion. Some other examples of strong acids would be: HI, HBr, HCl, HNO3, and H2SO4.


Now on to bases... a strong base (bases are know for not being soluble in water, but are very soluble in a lot of organic solvents) is something that completely ionizes in aqueous solution to give a hydroxide ion and a cation. A cation is a positively charged ion. Strong bases are most of the hydroxides of Group IA elements and Group IIA elements including LiOH, NaOH, KOH, Ca(OH)2, Sr(OH)2 and Ba(OH)2.

Many of the acids and bases that we encounter in our everyday lives are not strong acids, they are considered weak. Weak acids do not completely ionize in solution, but exist in equilibrium.

Acids are substances that are capable of donating a proton, and bases are substances capable of accepting a proton.


Some Common Strong Acids and Bases

Acids

HCl - hydrochloric acid
HNO3 - nitric acid
H2SO4 - sulfuric acid


Bases

NaOH - sodium hydroxide
KOH - potassium hydroxide
Ca(OH)2 - calcium hydroxide


Salts....

Salts (salts are known for being soluble in water and alcohol, but not very soluble in organic solvents) are the product of the reaction between an acid and a base.... this is why acid/base (aka A/B) extractions can take place. The salt produced can be acidic, basic, or neutral.

Strong Acid + Strong Base ---> Neutral Salt + water

Strong Acid + Weak Base ---> Acidic Salt + water

Weak Acid + Strong Base ---> Basic Salt + water

Weak Acid + Weak Base ---> ( Acidic, Basic, or Neutral ) Salt + water


pH is a logarithmic measure of hydrogen ion concentration, originally defined by Danish biochemist Soren Peter Lauritz Sorensen in 1909.

pH is often used to compare solution acidities (or alkalinity). For example, a solution of pH 1 is said to be 10 times as acidic as a solution of pH 2, because the hydrogen ion concentration at pH 1 is ten times the hydrogen ion concentration at pH 2. This is correct as long as the solutions being compared both use the same solvent. You can't use pH to compare the acidities in different solvents because the neutral pH is different for each solvent. For example, the concentration of hydrogen ions in pure ethanol is about 1.58 × 10-10 M, so ethanol is neutral at pH 9.8. A solution with a pH of 8 would be considered acidic in ethanol, but basic in water! Just as a rule of thumb.... Acids are "Low" on the pH scale and bases are "High". Normal pH readings are from 0-14.



Solvents, Solutions, Molarity, Normality and Polarity



A solvent is a substance that dissolves another substance or substances to form a solution (a homogeneous mixture). The solvent is the component in the solution that is present in the largest amount or is the one that determines the state of matter (i.e. solid, liquid, gas) of the solution. Solvents are usually, but not always, liquids. They can also be gases or solids. The material dissolved in the solvent is called the solute. Together, the solvent and solute comprise the solution.

The most common solvent most of us encounter is water (H2O). Liquid solutions having water as a solvent are called aqueous solutions. Water can dissolve many substances, but not all. Liquid solutions that do not have water as a solvent are called non-aqueous solutions. Broad and common classes of non-aqueous solvents are called organic solvents.


Some common slovents

Acetone

Benzene

Dimethylsulfoxide (DMSO)

Ethyl Ether

Ethyl Alcohol

Hexane

Isopropyl Alcohol

Methyl Alcohol

Methylene Chloride (DCM)

Mineral Spirits

Naptha

Petroleum Ether (Ligroin)

Toluene

Water, Distilled (dH2O)

Xylene



Molarity is the concentration of a substance in solution and is expressed as moles of solute per liter of the solution. Thus, a 0.1 molar (abbreviated 0.1 M) solution of sodium chloride contains 5.8443 (58.443 × 0.1) grams of NaCl per liter of solution. So, if you hear someone say a 2M solution, they mean a 2 Molar solution

Normality is the number of equivalents per liter of solution. For acid-base-salt systems, an equivalent is the amount of the substance that will gain or lose one mole of H+ ions. For instance, one mole of sulfuric acid (H2SO4), which has a mass of 98.0795 grams, produces two moles of H+, or two equivalents. Therefore, a one molar solution of sulfuric acid is a two normal (2 N) solution. A 0.1 N solution (containing 0.1 moles of H+) of sulfuric acid contains 4.90397 grams of H2SO4 per liter of solution (<98.0795/2> × 0.1). If someone says to add a 3N solution, they mean a 3 Normal solution.


So what is a Mole?

The mole is one of the seven fundamental units in the International System of Units (SI). The mole is the unit used for measuring the amount of a substance and is defined as the amount of a substance containing the same number of atoms, molecules, or ions as the number of atoms in 12 grams of 12C (C = carbon). Because there are 6.022 × 1023 atoms of carbon in 12 grams of 12C, this number (6.022 × 1023), known as Avogadro's number, is the amount of matter containing 6.022 × 1023 atoms, molecules, or ions.

The mole concept provides a means of calculating how many atoms, ions, or molecules are in a sample by weighing the substance. From the definition of atomic weight, the amount of any element that has a mass (in grams) equal to its atomic weight (available on the periodic table) will contain 6.022 × 1023 atoms. Thus, 4.0026 grams of helium, 32.0064 grams of sulfur, and 200.59 grams of mercury each contain 6.022 x 1023 atoms.

Similarly, a mole of a molecular substance (6.022 × 1023 molecules) is the amount of the substance whose mass (in grams) is equal to its molecular weight. Summing the atomic weights of the atoms composing a molecule derives molecular weight. For example, 70.906 grams (2 × 35.453) of Cl2 contains 6.022 × 1023 molecules (one mole) of Cl2.

Chemists use the same principle to measure the number of ions in a compound. For example, one mole of sodium ions (Na+) has a mass of 22.9898 grams (atomic weight of Na is 22.9898). One mole of NaCl has a mass of 58.443 grams (22.9898 + 35.453).

To make a long story short, a "Mole" is just molecular weight translated into Grams.


Polarity...

The polarity of a bond is the distribution of electrical charge over the atoms joined by the bond. Specifically, it is found that, while bonds between identical atoms (as in H2) are electrically uniform in the sense that both hydrogen atoms are electrically neutral, bonds between atoms of different elements are electrically inequivalent. In hydrogen chloride, for example, the hydrogen atom is slightly positively charged whereas the chlorine atom is slightly negatively charged. The slight electrical charges on dissimilar atoms are called partial charges, and the presence of partial charges signifies the occurrence of a polar bond and on the other had a Nonpolar molecule is a molecule in which there is a symmetrical distribution of electronic charge.


Water is a polar molecule, which means that it has a negatively charged end and a positively charged end. So water molecules attract each other. They also attract other polar molecules. A lot of solvents are Nonpolar molecules, which don't have a separation of charge... so water and a lot of solvents aren't attracted to each other. This is why chemists can do solvent extractions. As a rule of thumb... if a solvent is miscible with water, it is polar... if it is immiscible with water then it's Nonpolar. Just remember.... like dissolves like.

It's also good to learn some chemical nomenclature. Chemical nomenclature is the system of names and rules that chemists use to identify compounds precisely. The systematic method of naming compounds is vital to the study of chemistry, because when a new substance is formulated, it must be named in order to distinguish it from all other substances.

Using this systematic method of naming compounds, the positive part is named and written first, followed by the negative part. The names of the elements in the compound are modified with suffixes and prefixes to identify the different types of compounds.


Misc. chemistry, Drug and Pharmaceutical info


The earliest records of medicinal plants and minerals are those of the ancient Chinese, Hindu, and Mediterranean civilizations. In 2735 BC the Chinese emperor Shen Nung wrote an herbal in which he described the antifever capabilities of a substance known as Ch'ang Shang, since shown to contain antimalarial alkaloids. The school of alchemy that flourished in Alexandria in the 2nd century BC could prepare white lead (lead carbonate) from litharge, arsenic from realgar (arsenic disulfide), and mercury by roasting cinnabar (mercuric sulfide) in a current of air. It is recorded in De materia medica, a book of the 1st century BC, that verdigris (basic cupric acetate) and cupric sulfate were prescribed as medicinal agents. Remarkably, cupric sulfate is still used in medicine today.

Many crude drugs still used now, such as ipecacuanha root (ipecac), were known and employed by the ancients. The Egyptians treated constipation with senna pods and castor oil and employed caraway and peppermint to relieve indigestion. The Greek physician Galen (c. AD 130-c. 200) included hyoscyamus, opium, squill (a plant drug used as an expectorant, cardiac stimulant, and diuretic), and viper toxin among other drugs in his apothecary shop. He also insisted on purity in drugs--i.e. the right variety and age of the botanical specimens.

Pharmaceutical practice improved markedly in the 16th and 17th centuries. In 1546 the first pharmacopoeia, or collected list of drugs and medicinal chemicals with directions for making preparations from them, appeared in Nuremberg (Nürnberg, West Germany). Previous to this time, medical preparations had varied in concentration and even in constituents. Other pharmacopoeias followed, in Basel (1561), Augsburg (1564), and London (1618). Despite its name, the London Pharmacopoeia was mandatory for the whole of England and thus was the first example of a national pharmacopoeia.

In 1617 the Society of Apothecaries, London, was founded, marking the emergence of pharmacy as a distinct profession. King James I authorized the separation of apothecaries from grocers; only a member of the society could keep an apothecary's shop and make or sell pharmaceutical preparations. In 1841 the Pharmaceutical Society of Great Britain, London, was founded, placing the education and training of the pharmacist on a proper scientific basis. Today, pharmaceutical practice and education are carefully supervised throughout the world.

Known as "Hoffman's drops," ether was first employed as an anesthetic in 1842; chloroform followed soon afterward in 1847. Alkaloid compounds were also isolated from plant sources during this period. Narcotine was obtained from opium by a French pharmacist in 1803 and was followed by morphine in 1806, emetine and strychnine (about 1817), brucine and piperine (1819), colchicine and quinine (1820), nicotine (1828), atropine (1833), cocaine (1860), and physostigmine (1867). Many other alkaloids where extracted and synthesized around this period in history (like... amphetamine and mescaline) Isolation of these potent compounds was a milestone in pharmaceutical progress for three reasons. First, accurate doses could now be administered; this had been impossible previously with crude drugs of unknown and variable composition. Second, toxic effects due to impurities in crude drugs could now be eliminated if pure compounds were used; and third, knowledge of the chemical structure of these drugs led to attempts at laboratory synthesis, which led in turn to discovery of valuable related compounds.

Joseph Lister, in England, opened the modern era of antiseptic surgery in 1865 when he used phenol (carbolic acid) to prevent infections. In 1869 the soporific properties of chloral hydrate, the first synthetic hypnotic (sleep-producing drug), were discovered. In 1874 it was found that organic nitrites relax the blood vessels, and, in 1875, salts of salicylic acid were introduced as remedies for fever. The year 1879 witnessed the introduction of saccharin, still in use today as a sweetening agent for diabetic patients. The simple compound acetanilide, introduced in 1886, was one of the first analgesic-antipyretic drugs (i.e., reducing both pain and fever) to be used but was later replaced by the less toxic phenacetin in 1887, by aspirin in 1899, and all of these to some extent by acetaminophen (paracetamol) in 1956. The hypnotic sulfonal (sulfonmethane) was discovered about 1888, followed a few years later by barbital; this latter led to a whole series of barbiturates, of which phenobarbital is the best known.

Cocaine was the only known potent local anesthetic until about 1900, when the much simpler compound benzocaine was introduced. The closely related local anesthetic procaine followed early in the 20th century.


In 1935 it was discovered that sulfanilamide (Prontosil) stopped the growth of bacteria. Over 6,000 derivatives of sulfanilamide--the sulfonamides, or sulfa drugs--were prepared and tested for their antibacterial properties. Today, the sulfonamides have partially been superseded by antibiotics, of which the first was penicillin, first isolated in 1941. In 1959, 6-aminopenicillanic acid was isolated for the first time; this led to production of many semisynthetic types of penicillin such as ampicillin, carbenicillin, cloxacillin, methicillin, oxacillin, and phenethicillin. Also used, as antibiotics are compounds known as cephalosporins, the first of which was isolated in 1961.


Drugs may be classified in one of three ways: by chemical group (e.g., alkaloids, mentioned above); pharmacologically (i.e., by the way they work in the body); and according to their therapeutic uses. Pharmacological and therapeutic classifications show considerable divergence, as drugs that act upon the body in different ways may bring about the same desired therapeutic result. Furthermore, classification by therapeutic usage is complicated by the fact that a drug may be used to combat more than one ailment. The antimalarial compound primaquine, for example, may also be employed to relieve arthritis. Some familiar drugs classified by therapeutic use include aspirin, an analgesic, or painkiller; benzocaine, a local anesthetic; magnesium carbonate, an antacid; charcoal, an antiflatulent; penicillin, used against syphilis; calcium lactate, a calcium supplement; hexachlorophene, a deodorant; phenolphthalein, a laxative; levulose, a nutrient; cascara sagrada, a purgative; phenobarbital, a sedative; and thiamine hydrochloride, a vitamin.

Pharmaceutical raw materials may be plant, animal, or other biological products; inorganic elements and compounds; or organic compounds. If the raw material is "official"--that is, if it is the subject of a monograph in a pharmacopoeia or national formulary--then the minimum acceptable degree of chemical purity is specified. Very often, however, because some raw materials at specified levels may begin to decompose after a time, purification far exceeds these minimum requirements. If extra purification is inconvenient, a preservative may be added. If the raw material is not the subject of an official monograph, then physical or chemical specifications or both are drawn up by the manufacturer in accordance with the pharmaceutical requirements of the finished product, on lines similar to the official monographs.

The term crude drug is usually applied to plant or animal organs or whole organisms or exudations of these, either in the fresh state or dried and either ground or unground. Some crude drugs, such as acacia, belladonna, and starch, are official; for these, rigid specifications are available. Plant-derived crude drugs may come from cultivated sources, or they may be collected in the wild. The harvested drug plant must then be cleaned to remove extraneous matter such as sand and dirt. Next, unwanted plants or plant parts are carefully removed. Some crude drugs, such as belladonna, undergo curing, a process that consists either of slow drying or sweating, during which enzymes bring about chemical changes whereby the content of the active ingredient is increased. Alternatively, as with cascara sagrada, the drug is carefully stored for one year, during which time unwanted constituents slowly decompose. The final stage in crude-drug production consists of drying, which is accomplished in air or with artificial heat. Drying aids preservation, stops various chemical reactions that might weaken or destroy the substance, facilitates subsequent grinding, and reduces the weight and bulk. Drugs containing volatile constituents are dried at temperatures near freezing. After drying, some drugs (such as belladonna and ipecac) are reduced to a fine powder.


Inorganic elements and compounds

Production methods for inorganic elements and compounds are not always the same as those for industrial chemicals, since purification is usually carried to a much higher level. Industrial zinc oxide, for example, may contain as much as 10 percent impurities, including small quantities of lead. The pharmaceutical substance, by contrast, must contain at least 99 percent zinc oxide and no lead. For this reason, industrial zinc oxide is manufactured by combustion of zinc in air, whereas pharmacopoeial zinc oxide is produced from zinc sulfate.


Organic compounds

Organic compounds used as pharmaceuticals are either extracted from natural sources or prepared by chemical synthesis (various methods are described below). Physical specifications used in purity control of inorganic and organic pharmaceuticals include particle size, color, odor, solubility, homogeneity, and freedom from particulate impurities. Some common chemical specifications are melting point, boiling point, density, viscosity, and freedom from impurities.


Preparation from natural sources

The alkaloids

As mentioned above, the first pure pharmaceuticals isolated from natural sources were the alkaloids. Although the methods adopted for their extraction from plants vary in detail, all are based on three general characteristics of these compounds. First, most alkaloids are only slightly soluble in water but readily soluble in certain organic solvents such as benzene, chloroform, ether, and light petroleum. Second, alkaloids combine with acids to form salts that are usually freely soluble in water but only slightly so in organic solvents. Third, alkaloids are liberated from their salts by alkalis.

Application of these general principles can be seen in the following generalized outline of extraction methods. The crude drug, ground to a suitable state of subdivision, is mixed with water, a water-soluble alkali such as lime, and some organic solvent that does not mix with water. The mixture separates into two layers: one contains water, lime, and impurities and is discarded; the other contains the alkaloid dissolved in the organic solvent. Fresh water and dilute acid are now added to the mixture. Again there are two layers, but the acid has caused the alkaloids to pass from the organic layer into the aqueous layer. The aqueous layer is now separated, and cooling or concentrating the solution may crystallize the alkaloid salt or salts out. The process described above is used to obtain quinine sulfate from cinchona bark.


Volatile, or essential, oils

Volatile, or essential, oils, also obtained from plants, may be extracted by distillation, steam distillation, expression, or by extraction with fats or organic solvents. In steam distillation, the most common method, the crude drug--either fresh or dried--is used in powder form. Water is mixed with the powder, serving the double purpose of preventing decomposition of plant material by excessive heat and of facilitating volatilization of the essential oil. The powder-water mixture is usually placed in a basket through which the steam penetrates. The distillate consists of a water-oil mixture; the oil forms a separate layer, which is run off. Anise, cinnamon, clove, coriander, fennel, and peppermint oils are all obtained by this method, as is the pharmaceutical substance camphor from camphor wood. Fixed or fatty oils cannot be obtained by distillation, but only by expression or extraction.


Preparation by chemical synthesis

Two or more of the methods discussed below are usually involved in the manufacture of any one drug. There are many different possible routes for the production of pharmaceuticals. It is not often that the simplest possible theoretical pathway is the initial choice of the manufacturer; manufacturers depending on the starting materials and equipment available to them choose many different methods.


Acetylation

This is a special case of acylation, a process in which alcohols, phenols, and primary and secondary amines yield acyl derivatives by displacement of the hydrogen atom of the hydroxy, primary amino, or secondary amino group by an acyl radical. The commonest acyl radical by far is the acetyl radical, CH3CO-. The usual acetylating agent is acetic anhydride, (CH3CO)2O, but glacial acetic acid, CH3COOH, and acetyl chloride, CH3COCl, are also used. With acetic acid and alcohols or phenols, it is usual to use a dehydrating agent, such as concentrated sulfuric acid or anhydrous sodium acetate, in order to eliminate the water formed in the reaction. With acetyl chloride, a base such as dimethylaniline or pyridine is added to remove hydrogen chloride as it is formed.

Acetylation is often used in drug production since it reduces the toxicity of amines. Thus the drug paracetamol is much less toxic than p-aminophenol. Paracetamol is manufactured from p-nitrophenol.


Addition

This chemical reaction can only take place with unsaturated compounds, but the addition products vary greatly in nature. The mode of addition, where there are two possibilities, is determined by the structure of the unsaturated compound and the mechanism of addition.

The anesthetic drug halothane is manufactured from trichloroethylene (see below Dehydrohalogenation) by an addition reaction with hydrogen chloride. The product is treated with hydrogen fluoride; reaction with bromine then gives halothane.

The manufacture of the anesthetic drug trichloroethylene involves, as a first step, the addition of chlorine to acetylene, followed by dehydrohalogenation.


Alkylation and arylation

Alkylation is a general term for the introduction of an alkyl group into a compound and is more specifically known as methylation, ethylation, propylation, butylation, etc., depending upon the alkyl group inserted. Alkylation of an alcohol or a phenol results in an ether, while alkylation of a thiol gives a sulfide; primary and secondary amines can also be alkylated. The usual alkylating agents are alkyl sulfates and halides. The alcohol, phenol, thiol, or amine is dissolved in sodium hydroxide solution, and dimethyl sulfate, for example, is added to yield the alkylate.

In addition to the above types of compounds, any compound containing "active hydrogen" can be alkylated. Thus, compounds containing a methylene (-CH2-) or a methyne (=CH-) group adjacent to a group such as carbonyl (-CO-) contain active hydrogen.

The important drug codeine, widely used as a cough suppressant and painkiller, occurs naturally as an alkaloid in opium, together with morphine. Demand for codeine is such that much of it is manufactured by methylation of morphine. Morphine is dissolved in potassium hydroxide solution, and the solution is treated with methyl iodide to produce codeine.

The well-known constituent of tea and coffee, caffeine, used as a stimulant drug, is produced either from tea wastes or synthetically from the organic chemicals theophylline or theobromine. These three materials are closely related, and methylation of either theophylline or theobromine or a mixture of the two results in the fully methylated caffeine.

The barbiturates, widely used as sedative-hypnotic drugs, provide many examples of alkylation and arylation (introduction of one or more aromatic radicals, such as phenyl or naphthyl, to a molecule). The general method for their synthesis is as follows. Diethyl malonate (a malonic-acid ester, which contains an active methylene group) is treated with an alcoholic solution of sodium ethoxide, and the monosodium derivative produced is converted by reaction with an alkyl halide into an alkylmalonic ester. This is either used as such in the preparation of the barbiturate, or, as is usually required, a second alkyl group, either the same or different, is introduced in the same way. The alkylmalonic or dialkylmalonic ester is then condensed (see below Condensation and cyclization) with urea, in the presence of sodium ethoxide, to form the sodium salt of barbituric acid. This is either used as such, since sodium barbiturates are usually very soluble in water, or the free barbituric acid is liberated by acidification. Barbiturates containing aromatic groups (phenobarbital and mephobarbital are the only common examples) must be made by a modified route, because of the relative lack of reactivity of aryl halides. For both these drugs, ethyl phenylacetate is condensed with ethyl oxalate to form ethyl oxalophenylacetate, which, when distilled, decomposes to give diethyl phenylmalonate. Ethylation is then effected to yield diethyl ethylphenylmalonate. For the manufacture of phenobarbital, this ester is condensed with urea as in the scheme above.


Amination

Two important methods of amination (the process of adding an amino (-NH2) group to a compound) are reduction and ammonolysis. There are many reduction methods, but the most common is the reduction of the corresponding nitro compound by means of iron and acid. An example of ammonolysis is the preparation of aniline by heating chlorobenzene with excess aqueous ammonia, in the presence of cuprous oxide, at about 200 C (392 F) under pressure. Amination enters into the synthesis of many pharmaceuticals; a good example is amphetamine. Phenylacetone is treated with ammonia and hydrogen in the presence of a nickel catalyst, and reductive amination takes place, forming amphetamine.


Arsonation

Arsonation applied to aromatic compounds is closely analogous to nitration (see below). For example, p-aminophenylarsonic acid (arsanilic acid) is made by heating aniline with concentrated arsenic acid. A method other than arsonation that achieves the same result is Bart's reaction, in which a diazonium salt is coupled with an alkali arsenite, usually in the presence of a catalyst such as copper powder. Sodium phenylarsonate, for example, can be made from benzenediazonium chloride by Bart's reaction. The drug acetarsol is manufactured from phenol by arsonation followed by nitration, reduction, and acetylation.


Carboxylation

This reaction is best exemplified by the manufacture of salicylic acid, used in external preparations as a skin softener. Dry sodium phenoxide is heated with carbon dioxide, under pressure, at about 130 C (266 F); the resulting sodium salicylate is dissolved in water, and the acid precipitated by acidification with hydrochloric acid. Salicylic acid is used in medicine as the free acid, as its acetyl derivative, aspirin (see below Esterification), and as its salts, of which the most important is sodium salicylate, used in the treatment of rheumatism. To obtain the latter product, a weighed amount of salicylic acid is made into a paste with water, and the equivalent quantity of pure sodium bicarbonate is added. The mixture is stirred and warmed until a clear solution is obtained, and this is evaporated to dryness; the sodium salicylate is purified by crystallization from alcohol.


Condensation and cyclization

Condensation is difficult to define, but it involves the linking together of two or more organic molecules (identical or different), with or without the elimination of a simple molecule such as water, ethanol, or a hydrogen halide. Reactions involving condensations that can be defined more precisely, such as esterification, etherification, or polymerization, are usually not described as condensations.

Hexylresorcinol, used for destroying intestinal worms, provides a simple example of a condensation. It is produced by condensing resorcinol with hexanoic acid, in the presence of anhydrous zinc chloride, at about 130 C (266 F). Water is eliminated, and the resulting ketone is reduced by means of zinc amalgam and dilute hydrochloric acid. The sedative meprobamate involves two condensations in its production. Diethyl methyl-n-propylmalonate is reduced with lithium aluminum hydride, LiAlH4, to the corresponding dihydric primary alcohol; this is condensed with carbonyl chloride, COCl2, with elimination of hydrogen chloride to give a dichloroformate; condensation of this with ammonia, again with elimination of hydrogen chloride, gives meprobamate. Cyclization is a special case of condensation; internal condensation takes place in one molecule, with resulting formation of a cyclic molecule. The compound o-iminodibenzyl, from which the antidepressant drugs desipramine and imipramine are produced, illustrates cyclization. The iminodibenzyl is condensed, in the presence of sodamide, NaNH2, with 1-chloro-3-methylaminopropane to give desipramine or with 1-chloro-3-dimethylaminopropane to give imipramine.


Dehydration

This reaction, as the name indicates, involves the loss of the elements of water. If this takes place internally in a molecule, the result is usually an alkene or a cyclic compound. If dehydration takes place between two molecules (condensation), the product is usually an ether.

Diethyl ether (ordinary ether), used as an anesthetic, is produced by indirect condensation of ethanol. A mixture of concentrated sulfuric acid and ethanol is heated to 140 C (284 F), when ether distills over; more ethanol is run into the mixture at the same rate as the ether distills. The ethanol esterifies with the sulfuric acid to form ethyl hydrogen sulfate. This ester, on heating with ethanol at 140 C, gives ether and sulfuric acid back again.

Vinyl ether is also used as an anesthetic and provides a more complex example of dehydration. Ethylene chlorohydrin with sulfuric acid gives 2,2'-dichlorodiethyl ether, and this is dehydrohalogenated (see below) by means of solid potassium hydroxide to produce divinyl ether.


Dehydrohalogenation

This process may be defined as removal of the elements of hydrogen halides with the resultant formation of an unsaturated bond. It is usually affected by means of a base such as calcium oxide or hydroxide. Examples of its application are the production of the anesthetic trichloroethylene and the drug tetrachloroethylene (used for destroying intestinal worms), both involving the elimination of the elements of hydrogen chloride. Acetylene, readily available and comparatively cheap, is used as the starting material. The reaction with chlorine is dangerously explosive under ordinary conditions, but the reaction can be controlled to give acetylene tetrachloride. This readily yields trichloroethylene. In turn, trichloroethylene takes up one molecule of chlorine to form pentachloroethane, and this, treated in the same way as acetylene tetrachloride, produces tetrachloroethylene.


Esterification

The addition of an acid to an alcohol generally results in esterification--that is, the production of an ester plus water. The reaction is reversible, and the rate of the reverse reaction (see below Hydrolysis) will increase as the concentration of water (or ester) increases. Hence, both the anhydrous acid and the anhydrous alcohol are normally used in order to produce good yields. A catalyst such as dry hydrogen chloride speeds up the attainment of equilibrium (but will not affect the point of equilibrium). Concentrated sulfuric acid may be used, but it affects the point of equilibrium since it is a dehydrating agent as well as a catalyst; it may also dehydrate the alcohol and so must not be used in too high a concentration.

Acetylsalicylic acid (2-acetoxybenzoic acid, or aspirin) is the most widely used of all synthetic drugs. It is usually manufactured by the action of acetic anhydride on salicylic acid. As aspirin is only slightly soluble in water, it is easily separated by dilution of the reaction mixture with water. It is readily crystallized from aqueous alcohol, benzene, or light petroleum or from mixtures of these or other solvents with glacial acetic acid (to minimize hydrolysis).


Halogenation

This may involve reactions of addition, substitution, or replacement of a group of atoms. The catalysts used include halogen carriers such as iron, antimony, or phosphorus, all of which exert two valences as halides. They alternately add on and give up halogen to carry on the reaction. Since the halogens form unstable interhalogen compounds, chlorine, bromine, and iodine can also be used as catalysts. Under suitable conditions, substitution of alkenes with halogens takes place, and not addition. The synthetic oral estrogen, chlorotrianisene, for example, is produced from deoxyanisoin by reaction with 4-methoxyphenyl magnesium bromide, followed by subsequent dehydration and substitutive chlorination with a solution of chlorine in carbon tetrachloride. Gamma benzene hexachloride (gammexane), a delousing agent, is manufactured by the addition (not substitution) of chlorine to benzene. The product is a mixture of four of the nine possible stereoisomers, and the gamma isomer, which is the most active as an insecticide, is separated from the others.


Hydrolysis

This term is applied to reactions wherein water affects a double decomposition with another compound, hydrogen going to one component and hydroxyl to the other:


The reversal of esterification is an example of hydrolysis. Catalysts that speed up esterification also accelerate hydrolysis; many enzymes will also catalyze hydrolytic reactions.

A pharmaceutical example is the production of propylene glycol. Propene is oxidized and converted by acid-catalyzed hydrolysis to propylene glycol. The pharmaceutical substance called wool alcohol is made by hydrolysis of wool grease.

Inorganic substances

Helium, nitrogen, oxygen, sulfur, and some inorganic compounds still find a place in medical practice. These are prepared by the general methods used in inorganic chemistry; however, they must comply with pharmacopoeial standards of purity, whereas those used for nonmedical purposes are not usually purified up to these standards.

An example is the manufacture of ferric ammonium citrate, used in iron-deficiency anemias. The first step is preparation of freshly precipitated ferric hydroxide by slow addition, with constant stirring, of a ferric-salt solution (e.g., ferric sulfate) to an alkali solution such as sodium hydroxide:


The ferric hydroxide is collected and washed and, without being dried, is stirred with enough citric acid solution to dissolve almost all of it. A slight excess of ammonia solution is then added, and the residual ferric hydroxide filtered off. The clear, reddish-brown filtrate is evaporated to a syrup, a little ammonia being added occasionally to maintain a slight excess. The syrup is painted on glass plates, dried at a temperature below 40 C (104 F), and scraped off as scales. Ferric ammonium citrate is also produced in the form of granules. The medicinal substance is dark red in color and contains about 21 percent iron. Green ferric ammonium citrate is also made; it contains about 16 percent iron.


Mercuration

This is usually affected by reaction with a solution of mercuric acetate in acetic acid or alcohol; substitution of a hydrogen atom by the acetoxymercuri group, -HgOCOCH3, results. The topical antiseptic acetomeroctol, for example, is prepared by interaction of a complex organic chemical compound with the calculated quantity of mercuric acetate in a 50 percent aqueous ethanolic solution containing 5 percent acetic acid. The mixture is maintained at room temperature for one to two weeks.


Nitration

Medicinal nitro compounds are invariably aromatic carbocyclic or heterocyclic derivatives. These are usually nitrated with a mixture of concentrated sulfuric acid and concentrated or fuming nitric acid (mixed acid). Other nitrating agents include oxides of nitrogen and acetyl nitrate, CH3CO2NO2.

Nitrofurantoin is prescribed as a urinary antiseptic and provides an example of nitration. Furfural is reacted with acetyl nitrate, and the resulting triacetate is treated with pyridine to give 5-nitro-2-furaldehyde diacetate. This is condensed (with elimination of acetic acid) with 1-aminohydantoin to yield nitrofurantoin.


Oxidation

This reaction is widely used in the preparation of chemical compounds. Oxidation may be defined as the loss of electrons or hydrogen or the gain of oxygen; reduction (see below) has the opposite meanings. There are many oxidizing agents available; the choice depends upon the extent to which oxidation is desired. Air, oxygen, ozone, peroxides, chromium trioxide, chlorates, dichromates, permanganates, nitric acid, and sulfuric acid are all common examples. Conversion of the alkaloid nicotine to the vitamin nicotinic acid provides an example of oxidation.


Polymerization

Polymerization reactions may be broadly divided into addition polymerization and condensation polymerization (polycondensation). The term polymerization strictly refers to addition polymerization but is often used to include all types of polymerization reactions. Addition polymerization may be defined as the joining together of two or more molecules of a compound in such a way that the molecular weight of the polymer produced is a multiple of that of the original compound. Addition polymerization is usually induced either by heat, pressure, or a catalyst or by a combination of these.

A pharmaceutical example is the preparation of paraldehyde, used as a sedative drug. A small proportion of concentrated hydrochloric acid is added to acetaldehyde, causing three molecules of the liquid to polymerize to form a molecule of paraldehyde, a saturated heterocyclic system. The reaction involves the mutual saturation of three unsaturated carbonyl groups.

Condensation polymerization involves a similar joining together of molecules, but this time a simple molecule, such as water, is condensed out. Heating glycol with a dehydrating agent, for example, can make Diethylene glycol. Higher polyethylene glycols can be made similarly, such as polyethylene glycol 400, with a molecular weight of about 400, and polyethylene glycol 4000, with an average molecular weight of about 3,400. These two polymers are employed in the preparation of a water-soluble ointment base.


Rearrangement

The term is traditionally applied to any reaction that involves a change of connectivity (sometimes including hydrogen), and violates the so-called "principle of minimum structural change". According to this oversimplified principle, chemical species do not isomerize in the course of a transformation, e.g. substitution, or the change of a functional group of a chemical species into a different functional group is not expected to involve the making or breaking of more than the minimum number of bonds required to effect that transformation. For example, any new substituents are expected to enter the precise positions previously occupied by displaced groups. The simplest type of rearrangement is an intramolecular reaction in which the product is isomeric with the reactant (one type of "intramolecular isomerization"). The definition of molecular rearrangement includes changes in which there is a migration of an atom or bond (unexpected on the basis of the principle of minimum structural change), as in the reaction


CH3CH2CH2Br + AgOAc -> (CH3)2CHOAc + AgBr

The definition also includes reactions in which an entering group takes up a different position from the leaving group, with accompanying bond migration. An example of the latter type is the "allylic rearrangement":

(CH3)2C=CHCH2Br + OH -> (CH3)2C(OH)CH=CH2 + Br-

A distinction is made between "intramolecular rearrangements" (or "true molecular rearrangements") and "intermolecular rearrangements" (or "apparent rearrangements"). In the former case the atoms and groups that are common to a reactant and a product never separate into independent fragments during the rearrangement stage (i.e. the change is intramolecular), whereas in an "intermolecular rearrangement" a migrating group is completely free from the parent molecule and is re-attached to a different position in a subsequent step, as in the Orton reaction:

PhN(Cl)COCH3 + HCl -> PhNHCOCH3 + Cl2 -> o- and p-ClC6H4NHCOCH3 + HCl


Reduction, also called Hydrogenation

This reaction, the opposite of oxidation, has wide applications in the production of pharmaceuticals. Examples of reducing agents are aluminum amalgam, hydrogen and a catalyst, lithium aluminum hydride, metal and acid, sodium and alcohol, stannous chloride, and zinc dust and water etc. Reduction is employed in the synthesis of racemic menthol, an anti-itching agent. It is produced by the catalytic hydrogenation of the aromatic analogue, thymol, or of the saturated ketone, menthone, or of the unsaturated ketone, pulegone.


Sulfation

This consists of direct linkage of a sulfate group to carbon, yielding an acid sulfate, ROSO2OH, or a sulfate, ROSO2OR. The most usual sulfating agents are concentrated sulfuric acid, oleum, sulfur trioxide, chlorosulfonic acid, or sulfamic acid, NH2SO3H.

The surface-active agent sodium lauryl sulfate, for example, is produced from commercial lauryl alcohol (mainly dodecanol) by reaction with chlorosulfonic acid. The resulting lauryl hydrogen sulfate is neutralized with sodium hydroxide.


Sulfonation

This consists of direct linkage of the sulfonic acid group, -SO2OH, or salts thereof, or of the sulfonyl halide group, -SO2X, to a carbon or nitrogen atom. The latter are known as N-sulfonates or sulfamates. The same reagents are employed as are used for sulfation, above.

In the production of sulfonamides, the intermediate 4-acetamidobenzenesulfonyl chloride is made from acetanilide and chlorosulfonic acid. Most sulfonamides are made by the condensation of this intermediate with the appropriate primary amine, followed by removal of the acetyl group by alkaline hydrolysis. The hydrolysis is not usually difficult in practice, as the -CO-NH- bond is more easily broken than the -SO2-NH- linkage. After the alkaline hydrolysis, the sulfonamide is precipitated by neutralization.


Complex chemical conversions

Ascorbic acid (vitamin C) provides an example of a complex synthesis. It is manufactured from d-glucose; this is converted by means of microbiological oxidation to a keto acid, which is catalytically reduced to l-idonic acid. Microbiological oxidation converts this to 2-oxo-l-gulonic acid. The 2-oxo-l-gulonic acid is converted to its methyl ester, which is isomerized and cyclized to l-ascorbic acid.


Preparation of dosage forms

Before describing individual types of dosage forms, some consideration of the process of size reduction or comminution is necessary. The degree of comminution varies according to the particular drug and the method of extraction used. Thin leaves and certain substances such as aloes or tolu need no treatment. Others may be cut, crushed, broken into small pieces, or sliced thin. Finally, the drug may be powdered or ground to one of five different degrees of fineness. A number of grinding machines are employed for powdering, the most important being the disintegrator, edge-runner mill, ball mill, and end-runner mill.


Solutions

Many pharmaceuticals are simply solutions of a medicament in water, alcohol, ether, glycerin, or some other solvent. Various flavoured waters (e.g., chloroform or peppermint water) may also be used as solvents. After mixing, many solutions require additional treatment such as sterilization or addition of antimicrobial agents, stabilizers, or buffers.

Spirits are solutions of a volatile substance in alcohol or a mixture of water and alcohol. Elixirs are clear, sweetened hydroalcoholic (alcohol and water solvent) liquids for oral use, usually containing potent or nauseous drugs. Simple elixirs are prepared by solution, while those made from plant drugs are produced by maceration or percolation (described below). Tinctures, solutions of a nonvolatile substance in alcohol or a mixture of water and alcohol, are manufactured by simple solution, maceration, or percolation.

In maceration, the drug, suitably prepared, is placed, together with the extracting solvent (known as the menstruum), in a closed vessel and left for a defined period, usually three to seven days, with occasional shaking. The product is then filtered, the residue on the filter (known as the marc) is pressed to avoid loss, and the mixed filtrates are clarified, either by subsidence (settling out) or filtration.

In percolation, the powdered drug is first moistened with the extracting solvent, allowed to stand for a defined period, and then carefully packed in a conical or cylindrical vessel with a perforated false bottom and a tap at the base known as a percolator. Sufficient extracting solvent is added to saturate the drug, and, when liquid begins to drip from the percolator, the tap is closed and sufficient solvent added to form a layer above the drug. Maceration is then allowed to proceed for a defined period (usually 24 hours), followed by slow percolation, more solvent being added as necessary, until the desired volume of percolate is obtained, which is then clarified by subsidence or filtration.

Fluidextracts are solutions, in alcohol, water, ether, or a mixture of these; of the active part of a vegetable drug so prepared that one cubic centimetre of extract has the same strength as one gram of the dry drug. More concentrated than tinctures, fluidextracts are made by percolation or maceration.


Solid dosage forms

Solid dosages, such as tablets, have many advantages over other types: greater stability, less risk of chemical interaction between different medicaments, smaller bulk, accurate dosage, and ease of production.

Powders intended for internal use are usually mixtures of two or more ingredients. If two ingredients are present in unequal quantities, then the lesser ingredient (usually the drug) is mixed with an equal weight of the greater ingredient. Next, the resulting mixture is combined with an equal weight of the greater ingredient in steps until the mixture is complete. This process of geometric dilution (or trituration) is essential in order to produce a homogeneous powder. Powders may be sold in a bulk form or in individual packets. Granules, a dosage form related to powders, are particularly suitable for the preparation of solutions or mixtures of drugs, such as antibiotics, that are unstable in the presence of water. Cachets, occasionally used for administration of powdered drugs with an unpleasant taste, consist of shells made of gelatinized starch paste, the powder being placed inside, and the cachet swallowed. More common today is the hard capsule, in which the powder is enclosed in a shell of hard gelatin. Semiliquid and liquid drugs are often enclosed in a soft capsule with a soft gelatin shell.


Pills

Before the machine-made compressed tablet, pills were a very popular solid dosage form, being prepared at the dispensing bench by the pharmacist. Today pills are rarely prescribed, though some popular types are manufactured by machine. The powdered ingredients are mixed together with a binding agent, such as acacia or tragacanth, and are then made into a plastic mass by incorporation of any liquid drugs and addition of an inert liquid. The resulting mass, known as a pill mass, is then rolled into spheres and coated with talc, gelatin, or sugar.


Tablets

Tablets, by far the most common method of administration of drugs, are only rarely made by compression of the drug alone (e.g., potassium bromide tablets). Usually, the drug is mixed with suitable diluents, such as dextrin, lactose, salt, starch, or synthetic substances, designed to ensure disintegration of the tablet in the body. To prevent sticking in the machine, a lubricant such as liquid paraffin, stearic acid, talc, or a synthetic substance is usually added. Furthermore, it is essential that the tablet machines are fed with the drug mixture in a free-flowing form to ensure complete filling of the molds. To achieve this, the drug mixture is customarily granulated by mechanically forcing pellets of the mixture through a sheet of perforated metal. The granulated mixture is fed into the tablet machine, which feeds the correct dose into a cavity, the mixture then being compressed by means of a punch that fits into the cavity. To be successful, the tablet maker must choose correct diluents and lubricants, prepare suitable granules, and obtain the right degree of compression in the tablet machine. Excessive compression may mean that the tablet will not disintegrate in the body; insufficient compression results in fragile tablets that may break, causing inaccurate dosage. Coatings of various types may be applied to the tablet--to protect the ingredients from deterioration, to hide the taste of certain drugs, to control the release of the drug from the tablet, or to produce a more attractive tablet. For sugarcoatings, a concentrated sucrose syrup containing suspended starch, calcium or magnesium carbonate, or other suitable substance is applied, each successive layer being dried before the application of the next. After the final layer is dried, it is highly polished to give an elegant finish. Sugarcoatings provide both protection and a sweet taste. The chief drawback to sugarcoating is the long time involved. This led to the development of film coating, in which a very thin transparent film, usually a cellulose derivative, is applied. Enteric coating is designed to resist solution in the stomach and to dissolve in the more alkaline intestinal fluid. Many substances have been used for enteric coatings, one of the more recent being cellulose acetate phthalate (cellacephate). In the manufacture of layered tablets, incorporating two or more drugs, a compressed tablet is fed to a second machine where another layer is compressed around it. In this way, drugs normally incompatible may be formulated in the same tablet.


Other solid dosages

Troches, also known as lozenges or pastilles, disintegrate or dissolve in the mouth, slowly releasing the active drug. The base usually consists of a mixture of sugar and gum or gelatin. Lozenges are generally manufactured by compression techniques, while pastilles are fabricated by fusion and the use of molds. Dry extracts are prepared by the methods described above for fluidextracts, followed by evaporation either to a pilular consistency or to dryness. Dry extracts are usually granulated through a sieve and may be used for the preparation of tablets. Suppositories are solid, uniformly medicated masses designed for introduction into the rectum. Various bases are used in their preparation, but theobroma oil is the most common. Solid at room temperature, it melts a few degrees below body temperature. Suppositories are manufactured by the use of molds, together with fusion of the suppository mass or cold compression. Pessaries are suppositories intended for introduction into the vagina, while bougies are designed for insertion into the urethra, nostrils, or ears.


Dispersions

Aerosols were formerly defined as colloidal systems consisting of very finely subdivided liquid or solid particles dispersed in a gas. Today the term aerosol, in general usage, has become synonymous with a pressurized package. For pharmaceutical purposes aerosols may be divided into two types. Space sprays disperse the medicament as a finely divided spray with particles not exceeding 50 microns (0.05 millimeter, or 0.002 inch) in diameter. Surface-coating aerosols produce a coarse or wet spray and are used to coat surfaces with a residual film. Propellants used in aerosols are of two main types: liquefied gases and compressed gases. The former consist of easily liquefiable gases such as halogenated hydrocarbons. The drug is dissolved in the liquefied gas or in a mixture of the gas and a suitable solvent. When these are sealed into the container, the system separates into a liquid and a vapor phase and soon reaches an equilibrium. The vapor pressure pushes the liquid phase up the standpipe and against the valve. When pressing down, the liquid phase, opens the valve is expelled into air at atmospheric pressure and immediately vaporizes, leaving an aerosol of the drug. The pressure inside the container is maintained at a constant value as more liquid changes into vapor. When compressed gases are used as the propellant, the pressure falls steadily as the contents of the aerosol are used, and for this reason liquefied gases are used whenever possible. Pharmaceutical aerosols include solutions, suspensions, emulsions, powders, and semisolid preparations. The products include inhalation aerosols, spray-on bandages, creams, and ointments. The application of these latter to wounds and burns is obviously advantageous, as rubbing is eliminated, and the fine film produced promotes rapid absorption. Inhalation aerosols often include a metering valve, so that measured quantities of drug may be administered; these are rapidly replacing old hand sprays.

Sprays, solutions of drugs in aqueous or oily solutions, are applied by means of an atomizer to the mucous membranes of the nose or throat. Oily solutions are no longer considered desirable, and the ideal spray is an aqueous solution isotonic (equal in osmotic pressure) with nasal secretions and of the same pH.

Since some drugs are insoluble in all solvents suitable for medicinal use, they must be administered either as a solid dosage form or as a suspension. Suspensions are chemically more stable than solutions. Apart from aerosols, pharmaceutical suspensions almost always consist of a finely divided solid dispersed in a liquid. The state of subdivision varies from colloidal particles to particles that only slowly subside on standing. Suspensions should not cake on standing, and the solid phase should readily redisperse on shaking; suspensions should pour fairly easily, so the viscosity must not be too high. Gels are special suspensions, namely, those of hydrated drugs in an aqueous medium, in which the particle size is colloidal or nearly colloidal. Lotions, such as calamine lotion, are suspensions for external use only. Magmas and milks are thick, viscous, aqueous suspensions of insoluble inorganic compounds; the particle size is usually larger than in gels. Bentonite magma, for example, is produced by hydration of bentonite, a colloidal hydrated aluminum silicate, and is used as a suspending agent, as, for example, in calamine lotion. Milk (cream) of magnesia, a magnesium hydroxide mixture, is an aqueous suspension of magnesium hydroxide. Mixtures, in the wider sense, are any combination of drugs prescribed and dispensed for internal use but, in the narrow sense, are official mixtures of standard composition. Official mixtures are liquid preparations of one or more solid drugs dissolved or suspended in water; they often contain a thickening or suspending agent such as tragacanth. Thus, most mixtures may be regarded as a special type of suspension.

Mucilages are thick, viscous, aqueous solutions of gums, frequently containing a preservative such as chloroform or benzoic acid. As they are colloidal in nature, they fall between true solutions and suspensions. Acacia and tragacanth mucilages are the best-known examples and are used to aid in suspending insoluble solids in liquids.

Emulsions (emulsions can drive a chemist crazy and are normally avoided at all costs) consist of one liquid dispersed in another. Pharmaceutically, they are intended for internal use and consist of small globules dispersed in water. Oil-in-water emulsions will mix with water, whereas water-in-oil emulsions only mix with oils. However well two immiscible liquids are mixed together, on standing they will separate into two layers. To prevent separation, an emulsifying agent is used. Emulsifying agents can be divided into three groups: finely divided solids such as bentonite and magnesium aluminum silicate; natural emulsifying agents such as cholesterol, gelatin, acacia, methylcellulose, pectin, and tragacanth; and synthetic emulsifying agents such as the anionic sodium lauryl sulfate, the cationic benzalkonium chloride, and the nonionic polyethylene glycol 400 monostearate. A preservative such as chloroform is usually added to emulsions. The production of emulsions depends on the emulsifying agent used. Equipment includes a wide variety of agitators, colloid mills, homogenizers, and ultrasonic devices.


Radioactive dosage forms

A radiopharmaceutical is a medical product incorporating a radioactive isotope. Radiopharmaceuticals are widely used for various diagnostic tests and to a lesser extent as therapeutic agents. Radioactive iodine in the form of sodium iodide has been extensively used in the diagnosis of thyroid disorders. The iodine isotopes used are iodine-131 and iodine-125, orally administered as a sodium iodide solution; the thyroid uptake of radioactive iodine is measured with a measuring instrument placed close to the thyroid gland. Vitamin B12 containing cobalt-57, cobalt-58, or cobalt-60 is employed for the diagnosis of pernicious anemia. Chlormerodrin injection containing mercury-203 is used for renal (kidney) scanning and brain scanning.


Common terms, abbreviations, their definition and other good things to know.



Alkaloid = A class of bitter-tasting, basic organic compounds with nitrogen-containing rings, which are normally obtained from plants. Alkaloids often have powerful effects on living things. Examples are cocaine, nicotine, strychnine, caffeine, and morphine. This term also refers to synthetic substances. If the suffix of substance is "ine", "ane", "one", "ene" or something similar than it is an alkaloid.

Amide = an amide is an organic compound that contains a carbonyl group bound to nitrogen. The simplest amides are formamide (HCONH2) and acetamide (CH3CONH2).

Amine = an amine is an organic compound that contains a nitrogen atom bound only to carbon and possibly hydrogen atoms. Examples are methylamine, CH3NH2; dimethylamine, CH3NHCH3; and trimethylamine, (CH3)3N.

Amorphous = A solid that does not have a definite shape.

Anhydrous = Without Water (this term refers to liquids)

Anhydride = Without Water (this term is used for solids most of the time)

Anode = the electrode at which oxidation occurs in a cell. Anions migrate to the anode.

Anodize = to coat a metal with a protective film by electrolysis.

Aqueous (aq) = aqueous solution. A substance dissolved in water.

Aromatic Ring (Ar) = An exceptionally stable planar ring of atoms with resonance structures that consist of alternating double and single bonds, e. g. benzene.

Aromatic Compound = A compound containing an aromatic ring. Aromatic compounds have strong, characteristic odors.

Atmosphere (atm) = A unit of pressure, equal to a barometer reading of 760 mm Hg. 1 atmosphere is 101325 pascals and 1.01325 bar.

Auto-Ignition Temperature = Minimum temperature at which the vapor/air mixture over a liquid spontaneously catches fire.

Azeotrope = azeotropic mixture; azeotropy. Is a solution that does not change composition when distilled. For example, if a 95% (w/w) ethanol solution in water is boiled, the vapor produced also is 95% ethanol, and it is not possible to obtain higher percentages of ethanol by distillation. There are ways to get around this though.

Boiling Point (b.p.) = standard boiling point; normal boiling point. The temperature at which the vapor pressure of a liquid is equal to the external pressure on the liquid. The standard boiling point is the temperature at which the vapor pressure of a liquid equals standard pressure.

Buffer = pH buffer; buffer solution. A solution that can maintain its pH value with little change when acids or bases are added to it. Buffer solutions are usually prepared as mixtures of a weak acid with its own salt or mixtures of salts of weak acids. For example, a 50:50 mixture of 1 M acetic acid and 1 M sodium acetate buffers pH around 4.7.

Carbon (C) = an element with atomic number 6. Carbon is a nonmetal found in all organic compounds (it's everywhere!). Carbon occurs naturally as diamond, graphite, and buckministerfullerene.

Catalyst = catalyze, catalysis. A substance that increases the rate of a chemical reaction without being consumed or produced by the reaction. Catalysts are used to speed up or slow down a reaction, without changing the position of equilibrium. Enzymes are catalysts for many biochemical reactions. Many noble metals are used