248 CONSTITUTION OF TYROSINE. [BOOK II. 



It was formerly believed that tyrosine was a derivative of salicylic 

 acid 1 . V. Barth, however, in 1865, shewed that when it is fused 

 with caustic alkalies, it yields, instead of salicylic acid, its isomer 

 paroxybenzoic acid, besides acetic acid and ammonia, thus : 



C 9 H U N0 3 +H 2 + = C 7 H 6 3 + C 2 H 4 O 2 + NH 3 . 



V. Barth, thereupon, advanced as a probable theory, that tyrosine 

 might be considered as ethylamidoparoxybenzoic acid CH 3 .(NHC 2 H 5 ). 

 OH . CO . OH. He subsequently, however, advanced the view that 

 tyrosine is a para-oxyphenylamidopropionic acid 2 ; this opinion has 

 received confirmation both from Beilstein and Kuhlberg, and from 

 Erlenmeyer and Lipp 3 . 



Under the influence of putrefactive processes tyrosine yields primarily 

 para-hydrocumaric acid (paroxyphenylpropionic acid), HO . C 6 H 4 . CH 2 . 

 CH 2 . CO . OH, and secondarily by the decomposition of the latter body, 

 paroxyphenylacetic acid : HO . C 6 H 4 . CH 2 . CO . OH, besides parakresol. 



The following equations exhibit, according to Baumann, the successive 

 processes of decomposition and oxidation of tyrosine 4 . 



(1) HO . C 6 H 4 . CH 2 . CH(NH 2 ) . CO . OH + H 2 = 



Paroxyphenylamido-propionic acid, or 

 Tyro sin 



NH 3 + HO . C 6 H 4 . CH 2 . CH 2 . CO . OH. 



v : ^ / 



Hydroparacumarie acid 



(2) HO . C 6 H 4 . CH 2 . CH 2 . CO . OH = CO 2 + HO . C 6 H 4 . CH 2 . CH 3 . 



^ . f ^ 



Paraethylphenol 



(3) HO . C 6 H 4 . CH 2 . CH 3 + O 2 = H 2 + HO . C 6 H 4 . CH 2 . CO . OH. 



Paroxyphenylacetic acid 



(4) HO . C 6 H 4 . CH 2 . CO . OH = CO 2 + HO . C 6 H 4 . CH 3 . 



Parakresol 



(5) flO . C 6 H 4 . CH 3 + O a = H 2 + HO . C 6 H 4 . CO . OH. 



Paroxybenzoic acid 



(6) HO . C 6 H 4 . CO . OH = CO 2 + HO . C 6 H 5 . 



Phenol 



Physical and Chemical Properties of Tyrosine. 



Crystalline Tyrosine crystallises in fine needles, which occur 



form. singly as well as in characteristic double broom-like 

 bundles and in rosettes. 



1 Odling, Lectures on Animal Chemistry, London, 1866, see p. 125. 



2 Barth, Ann. d. Chem. u. Pharm., Vol. CLI. p. 100. 



3 Erlenmeyer u. Lipp, 'Ueber kiinstliches Tyrosin,' Ber. d. deutsch. c) 

 Gesellschaft, Vol. xv. p. 1544. 



4 Baumann, Berichte d. deutsch. chem. Gesellsch, Vol. xn. p. 1453. Drechsel, 

 ' Chemie der Absenderungen und der Gewebe.' Hermann's Handbuch, Vol. v. i. 



