422 CHEMISTS. Y OF THE DIGESTIVE PROCESSES. 



eraldehyde with hydrocyanic and hydrochloric acids. Isovaleraldehyde 

 (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 18 H 33 N 5 , which 

 breaks up into leucine and ammonia. 



Ci 8 H 33 N 5 + 6H 2 = 3(C 6 H 13 M) 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 + jtfH 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. 



C 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 U NH 3 + 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 (NH 2 )COOH + HM) 2 = C 5 H 10 (OH)COOH + H 2 + N 2 



(leucine) (leucic or oxycaproic acid) 



These reactions show that leucine is an amidocaproic acid, but there are 

 several isomeric amidocaproic acids. 2 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 f orniulse : 



Normal a-amido- 

 caproic acid 



CH 3 



CH 2 



CH 2 Isobutyl-(a) amidoacetic 



CH 2 acid, or leucine 



CH 



COOH 



CH Q CH : 



CH 

 CH, 



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 Chem. Centr.-BL, Leipzig, 1869, ' S. 159; Journ. f. prakt. 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., Strassbnrg, 

 1894, Bd. xx. S. 203. 



3 Schulze and Likiernik, Bcr. d. detitsch. chem. Gesellsch., Berlin, 1891, Bd. xxiv. S. 669 ; 

 B. Gmelin, Inaug. Diss., Tubingen, 1892. 



