It is necessary clearly to distinguish such compounds as the amino- (or amido-) acids and acid-amides; in the first case the amino group is substituted in the hydrocarbon residue, in the second it is substituted in the carboxyl group.
The steps in the breaking down of the highly complex nitrogenous proteid compounds contained in the humus of the soil, or applied to the latter by the farmer in the form of dung and organic refuse generally, are many and varied; most frequently the insoluble proteids are changed by various kinds of putrefactive bacteria into soluble proteids (peptones, &c.), these into simpler amido-bodies, and these again sooner or later into compounds of ammonia.
Tafel, Ber., 1886, 19, p. 1924), by distilling the amido-acids with lime, by heating phenols with zinc chloride ammonia (V.
Freund, Ber., 1895, 28, p. 94 6; 1896, 29, p. 2501), crystallizes in long needles, which melt at 181-183° C. The addition of sodium nitrite to an aqueous solution of its hydrochloride converts it into amido-triaz / N N sulphol S< 1.
For this purpose the urine is concentrated and the hippuric acid precipitated by the addition of hydrochloric acid; it is then filtered and boiled for some time with concentrated hydrochloric acid, when it is hydrolysed into benzoic and amido-acetic acid.
Chlor-, brom-, iodoand fluor-benzoic acids are known and can be obtained by oxidizing the corresponding halogen toluenes, or from the amido acids, or by substitution.
Kolbe resulted in the discovery of many new facts and in a better understanding of the relations between the oxyand the amido-acids.