(Benzoic acid, camphor, adrenaline, salicylic acid.)
Certain chemical bodies which have been used in medicine for centuries have been analysed, their structural formulas ascertained, and then the atoms have been put together in the laboratory so perfectly that in many cases the artificial products cannot be distinguished from the natural original ones. Benzoic acid, obtained by subliming gum benzoin, has been in use since the latter part of the sixteenth century, when under the name of fleurs de benzoin, soon anglicised into flowers of benjamin, they were introduced by a French physician, named Blaise de Vigenère, who was secretary to Henri III. [The name benjamin was not a bad corruption after all, as the Arabic term from which the European designations were derived was Luban Jawa, the incense of Java. The Spaniards first dropped the first syllable under the mistaken impression that it was the Arabic article. Old etymologies traced the name to a supposed Ben-jui, or tree of the Jews.] The artificial benzoic acid is obtained by the oxidation of toluene, a hydrocarbon distilled from coal-tar.
Comparatively recent achievements of synthetic chemistry are the artificial production of camphor and of adrenaline, the active principle of the suprarenal gland. The synthetic products can be distinguished from the originals by their behaviour towards polarised light.
Salicylic acid, prepared by acting on carbolic acid by carbon dioxide in the presence of an alkali, became a practical commercial product in 1874, but its discoverer, Kolbe of Leipzig, had prepared it in his laboratory since 1859. The natural product, prepared from willow bark or oil of wintergreen, was worth twelve guineas a pound; the artificial salicylic acid in a few years came to be sold at not so many shillings per pound. Kolbe’s theory was that the compound he devised would decompose within the organism into phenol and carbon dioxide, and thus exercise an anti-putrefactive effect.
Physiological Speculations.
In many other cases the physiological effect of the compound was distinctly foreseen, and latterly the relation between chemical constitution and physiological action has become the objective of much research. It may be reasonably anticipated that before many years have passed it will be possible to predict the physiological powers of a substance from a knowledge of its structural formula, just as already many of its more noteworthy physical properties may be so foretold. Even at present certain trustworthy rules, affording guidance in this respect, have been formulated. Dujardin-Beaumetz and Bardel, dealing with compounds of the aromatic series, have laid down that (a) those containing hydroxyl (OH) are antiseptic; (b) those containing an amino-group (NH2) or an acid amide are hypnotic; and (c) those containing both an amino-group and an alkyl group (CH3, C2H5, etc.) are analgesic.
In order to show how synthetic remedies have been built up from simple products it will be convenient to take a few typical examples in the order of increasing chemical complexity, rather than with strict regard to chronological progression.
Alcohol, Ether, Aldehyde, Acetic Acid.
Ethyl (that is, ordinary) alcohol forms a convenient starting point. It has been already stated that the molecule of this substance is represented by the formula C2H5OH but for centuries before its constitution was unravelled it had been prepared in a more or less pure condition, as it still is, by a process of fermentation followed by distillation. Alcohol can be built up from its elements thus:—When an electric arc burns between carbon rods in an atmosphere of hydrogen, acetylene is formed; acetylene can be made to combine with hydrogen, forming ethane; ethane reacts with chlorine, yielding ethyl chloride; and this acted upon by an aqueous solution of potash gives alcohol as a result. The steps of the process are shown below:—
