Acetylene. Ethane. Ethyl chloride. Ethyl alcohol.
Alcohol is the basis of a number of substances used in medicine. On treating it with a dehydrating agent such as strong sulphuric acid, the elements of water are removed, and two molecules of alcohol unite into one, the resulting product being ether (diethyl oxide). The reaction is rather more complicated than is explained here, but the net result is as stated. The process was described by the German physician, Valerius Cordus, and was incorporated in the “Dispensatory” published after his death by the Senate of Nuremberg, under the title of “Oleum vitriole dulce verum.” As explained in the article on Ether (Vol. I. p. 347), the chemical reaction was, until recent times, a favourite topic for investigation.
When alcohol (C2H5OH) is oxidised, a substance known as aldehyde (CH3CHO) is formed. This was first prepared and described by Fourcroy and Döbereiner, but its constitution was explained by Kolbe. On further oxidation acetic acid (CH3COOH) is formed. The relationship between the alcohol, aldehyde and acetic acid was traced by Liebig.
Chloral Hydrate and Chloroform.
The oxidation of alcohol may be effected by the agency of chlorine, and in that case an intermediate oily product is obtained, in which three of the hydrogen atoms of the aldehyde are replaced by three of chlorine. The compound resulting is chloral (CCl3CHO), and this readily combines with water and forms the familiar chloral hydrate crystals which were first prepared by Liebig in 1832, but only got into the “British Pharmacopœia” (Additions) in 1874. Chloral hydrate treated with caustic potash splits into chloroform and potassium formate. Chloroform was discovered in 1831 by Liebig and Soubeiran, and was admitted into the “London Pharmacopœia” of 1851, four years after Simpson had demonstrated its wonderful anæsthetic property.
Sulphonal.
Returning to acetic acid, it may be stated that by heating its calcium salt two substances, acetone, (CH3)2CO, and calcium carbonate are formed. Also that when alcohol is acted upon by phosphorus pentasulphide, mercaptan, C2H5SH, is obtained. By the reaction of acetone and mercaptan, mercaptol results, and this, when oxidised, becomes the well-known synthetic hypnotic, sulphonal. It is not necessary to give the full formulas of these reactions, as they may be found in the usual chemical manuals; but it may be stated that the full descriptive name of sulphonal is dimethyl-diethylsulphone-methane. The group of sulphones furnishes an illustration of the reasoning on which new synthetic compounds come to be constructed. The theory was that the physiological action of sulphonal was due to, or connected with, its ethyl group. It was supposed, therefore, that by increasing the number of such groups in a molecule the hypnotic effect would be proportionately developed. It was believed that experiments on dogs supported this deduction; but it was not maintained in clinical experience.
Acetanilide and Phenacetin.
Many of the popular synthetic remedies belong to the benzene series. Benzene is obtained from coal-tar, but, as shown by Berthelot, it is possible to prepare it by heating the gaseous hydrocarbon, acetylene, C2H2, in a closed vessel. By this means three molecules of acetylene are condensed into one, C6H6, which is benzene. Benzene acted upon by nitric acid yields nitrobenzene, and this by the action of nascent hydrogen is changed into aniline. Aniline may be regarded as ammonia, NH3, in which one hydrogen atom has been replaced by the phenyl group, C6H5, and, like ammonia, it combines with acids to form salts. Aniline acetate being formed, the elements of water being eliminated in the process, the product is acetanilide, or antifebrin. Acetanilide was first prepared by Gerhardt, in 1853, but its physiological action was only discovered by Cahn and Hepp in the ’eighties. By the substitution of an ethoxy-group for one of the hydrogen atoms of acetanilide, para-ethoxy-acetanilide, commonly called “phenacetin,” is produced.