1 04 Biological Chemistry. 



/OC 2 H 5 01 



OC< and OC< 



X OC 2 H 5 X C1 



(Note. These substances are not quite analogous in 

 their formulae to esters and acid chlorides of simple 

 carboxylic acids, in that carbonic acid can be regarded as 

 a substance with two hydroxyl groups attached to the 

 same carbon atom ; the simple carboxylic group, on the 

 other hand, contains only one hydroxyl group.) 



The equations representing the formation of urea from 

 the above substances, ethyl carbonate and carbonyl chloride, 

 are the following : 



CO(OC 2 H 6 ) a + 2NH 8 = CO(NH 2 ) 2 + 2C 2 H 5 OH 

 COC1 2 + 4NH 3 = CO(NH 2 ) a + 2NH 4 C1 



Urea is a crystalline substance, melting point 132, which 

 is soluble in alcohol and water, but almost insoluble in 

 ether. On heating to a high temperature with water 

 under pressure, it decomposes into ammonia and carbon 

 dioxide 



CO(NH 2 ) 2 + 2H 2 = C0 2 + 2NH 3 



It also decomposes when treated with sodium hypo- 

 bromite 



CO(NH 2 ) 2 + SNaOBr = C0 2 + N 2 + 3H 2 + SNaCl 



This reaction is employed for estimating the urea in a 

 sample of urine ; a given volume is treated with a solution 

 of the hypobromite, and the nitrogen evolved in the 

 reaction is measured. This process gives, however, only 

 approximately accurate results. 



Urea acts as a base, and forms with acids a series of 

 well-defined salts. The nitrate, CO(NH 2 ) 2 HN0 3 , crystallizes 

 well, and is only sparingly soluble in nitric acid. Advan- 

 tage is taken of this fact to separate urea from urine ; the 

 latter fluid is concentrated and treated with strong nitric 

 acid, when urea nitrate separates out. 



