422 CHEMISTR Y OF THE DIGESTIVE PROCESSES. 
eraldehj'de with hydrocyanic and hydrochloric acids. Isovalcraldehyde 
(C 4 H 9 COH) is prepared, according to the general method, by oxidising amyl 
alcohol with potassium bichromate and sulphuric acid ; purified by forming the 
sodium bisulphite compound, decomposing this and collecting the distillate ; 
this is shaken with ammonia, when isovaleraldehyde-ammonia is thrown down 
in crystalline form. These crystals are washed with water, and then boiled 
with a mixture of strong hydrocyanic and dilute hydrochloric acids, when 
a reaction takes place yielding a body of the composition C 1S 1I.,.X- | , which 
breaks up into leucine and ammonia. 
C 18 H 33 K" 5 + 611,0 = 3(C 6 H 13 N0 2 )+2 NH 3 . 
(leucine) 
Leucine has also been obtained artificially by Hiifner, 1 by heating mono- 
bromocaproic acid with saturated ammonia under pressure to 120°-130° C. 
during four or five hours. 
C 5 H 10 BrCOOH + NH 3 = C 5 H 10 (NH 2 )COOH + HBr. 
Constitution of leucine. — That leucine is an amidocaproic acid is shown 
both by these methods of artificial preparation and by the following- 
reactions : — 
1. Heated under pressure to 140°-150° C, with strong hydriodic acid, it 
yields caproic acid, iodide of ammonium, and iodine. 
G 5 H 10 (NH 2 )COOH + 3 HI = C 5 H n COOH + NH 4 I + 1 2 
(leucine) (caproic acid) 
2. Heated alone, rapidly over its melting-point (170° C), to 180-200° C, 
it yields amylamine and carbon-dioxide. 
C 5 H 10 (NH 2 )COOH = C 5 H n XH 2 + C0 2 
3. When acted upon by nitrous acid, it breaks up in the usual manner of 
amido-acids, all the nitrogen being evolved as such, and oxycaproic or leucic 
acid being simultaneously formed. 
C 5 H 10 (N"H 2 )COOH + HN0 2 = C H 10 (OH)COOH + H,0 + N 2 
(leucine) (leucic or oxycaproic acid) 
These reactions show that leucine is an amidocaproic acid, but there are 
several isomeric amidocaproic acids.- It was thought until quite recently 
that leucine was the amido-acid of normal caproic acid, but it has been recently 
shown to be amido-isobutylacetic acid. 3 The difference in the structure of these 
two compounds would be represented according to the usual convention by the 
two following graphic formulae : — 
CH 3 
CH, 
Normal a-amido- CH 2 Isobutyl-(a) amidoacetic 
[CH 3 CH 3 
caproic acid 
CH acid, or leucine 
CH— XIL 
^COOH 
CH 
CH 
CHNH, 
COOH" 
Pure leucine crystallises in the form of thin white transparent plates, 
forming in mass a snow-white powder, which feel greasy and are not wetted 
1 Ckem. Gentr.-Bl., Leipzig, 1S69, S. 159; Joum. f. vrakt. Chem., Leipzig, 1870, 
Bd. i. S. 6. 
2 According to R. Colin, not one but several leucines are formed in pancreatic digestion ; 
these are probably the isomeric amidocaproic-acids, Ztschr. f. physiol. Chem., Strassburg, 
1894, Bd. xx. S. 203. 
3 Schulze and Likiernik, Ber. d. deutsch. chem. Gesellsch., Berlin, 1891, Bd. xxiv. S. 6G9 ; 
B. Gmelin, Inaug. Diss., Tubingen, 1892. 
