Carbon suboxide is a colourless, extremely mobile, refractive, poisonous liquid, of sp. gr. 1.11, with a strong and peculiar smell. It boils at 7°, and freezes at -107°. It is stable only at low temperatures; at ordinary temperatures it polymerises to a red solid, which dissolves in water, forming a solution of the colour of eosin. The change is almost instantaneous at 100°. Carbon suboxide is inflammable, burning with a blue but smoky flame: C3O2 + 2O2 = 3CO2. Its low boiling-point and the high value of its molecular refraction and dispersion, its general resemblance to the metallic carbonyls and ketones, etc., indicate that this remarkable oxide of carbon is, in all probability, the anhydride of malonic acid. Indeed, by the action of water upon it, it is reconverted into malonic acid.
In point of principle, and viewed as chemical operations, the synthesis of vital products is in nowise different from the synthesis of any other group of organic compounds; and the special interest, and even astonishment, at one time created by the artificial preparation of such products has largely died away. The synthetical production of some of the substances formerly known only to be formed by vital action, either in the animal or the plant, has already been incidentally referred to. But it may be convenient to treat the subject of the artificial production of this group of bodies rather more comprehensively and as a sub-section of this chapter on organic synthesis, since their formation by such means constitutes a phase in the development of chemistry, and has undoubtedly exercised a profound influence on scientific thought and on philosophical and even theological doctrine. During the past fifty or sixty years the chemist has been enabled to form the active principles or characteristic products of many plants and animals. He has built up substances which were formerly regarded as capable of being made only by the very process of living. He has prepared compounds which were at one time considered as only producible by changes in organised matter after death.
Since the date of Wöhler’s epoch-making discovery, already referred to[4] urea has been synthetically prepared by many reactions, notably by Regnault and Natanson by the action of ammonia on carbonyl chloride, and by Basarow and Dexter from ammonium carbamate. Both these substances can be formed directly or indirectly from their elements. It may also be obtained by the hydrolysis of lead cyanate:
Pb(CNO)2 + 2H2O = PbCO3 + CO(NH2)2.
[4] Vol. I., p. 163.
The successive steps in its production from inorganic materials by this method are:
K + C + N ➞ KCN ➞ KCNO
➞ Pb(CNO)2 ➞ CO(NH2)2.
Associated with urea as products of metabolism are uric acid, xanthine, and sarcine. Urea was first artificially transformed into uric acid by Horbaczewski, and its synthesis was effected by Behrend and Roosen. Closely related in chemical composition to these substances are theobromine and caffeine, the characteristic principles respectively of cocoa (the fruit of theobroma cacao); and of coffee, tea, maté (the leaves of ilex paraguayensis); “guarana,” obtained from the seeds of the South American plant paullinia sorbilis, and the kola-nut of Central Africa. Strecker, in 1860, showed how theobromine may be converted into caffeine; and Emil Fischer, by similar means, transformed xanthine into theobromine. Since that time xanthine itself has been prepared artificially. Caffeine can now be built up from its elements by a series of transformations effected by a succession of chemists, as follows:
1. Carbon and oxygen give carbonic oxide.—Priestley, Cruickshank.
2. Carbonic oxide and chlorine give carbonyl chloride.—J. Davy.
3. Carbonyl chloride and ammonia give urea.—Natanson.
4. Urea gives uric acid.—Horbaczewski; Behrend and Roosen.
5. Uric acid gives xanthine.—E. Fischer.
6. Xanthine gives theobromine.—Strecker.
7. Theobromine gives caffeine.—E. Fischer.
Synthetic theobromine is now made on the large scale, and introduced as a soda compound, in combination with sodium acetate, into medicine as a diuretic under the name of agurin. Synthetic caffeine is also prepared on a manufacturing scale from uric acid through the medium of the methylxanthines. The close relationship of xanthine to uric acid is of great physiological significance, since there is little doubt that the xanthine bases are the most important sources of uric acid within the organism.