268 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Properties. 



Tyrosine is a colourless crystalline solid, which is soluble with 

 difficulty in cold water, more easily in hot. It dissolves readily in 

 dilute acids or alkalies from which it separates on neutralising the 

 solution. 



If a small quantity of tyrosine be dissolved in a drop of ammonia 

 on a glass slide and the ammonia be allowed to evaporate, the tyrosine 



crystallises out in charac- 

 teristic bunches of fine 

 needles (Fig. 47). It is 

 insoluble in alcohol and 

 ether. 

 Reactions and Tests. 



(i) Its crystalline form 

 is very characteristic. 

 * (2) It gives a yellow 

 colour on heating with 

 nitric acid ; this becomes 

 orange on making alkaline 

 with ammonia. 



(3) It gives a red 

 colour, even in extreme 

 dilution, on heating with 

 Mi lion's reagent. 



(4) Pirias test. 3 drops of concentrated sulphuric acid are put 

 on a little tyrosine in a dry test tube and it is placed in the boiling 

 water-bath for half an hour. The red liquid is diluted with 10 c.c. of 

 water and neutralised with barium carbonate. The filtrate (from 

 BaSO 4 ) on evaporation to a small volume gives a violet colour with 

 2-3 drops of ferric chloride, showing the presence of phenol. 



(5) When boiled with copper carbonate it gives a blue copper salt 

 like aliphatic amino acids. 



(6) Morners test. A solution of tyrosine gives a green colour on boiling 

 with a solution of formalin in sulphuric acid (i vol. formalin, 45 vols. water, 

 55 vols. cone. H 2 SO 4 ). 



(7) A wine-red colour is formed if tyrosine be added to 3 or 4 drops of 

 formalin in 5 c.c. of concentrated sulphuric acid. The liquid becomes green 

 on adding double the volume of glacial acetic acid and boiling (Denigts). 



