n8 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



(4) Calcium citrate is not precipitated when calcium chloride is 

 added to a cold neutral solution of a citrate. This salt is less soluble in 

 hot water and hence on boiling the solution calcium citrate is pre- 

 cipitated ; it dissolves again as the solution cools. 



(5) Citric acid does not form an insoluble acid potassium salt when 

 its solutions are treated with potassium chloride and acetic acid. 



Aceto-Acetic Acid or Acetylacetic Acid. 



Ethyl aceto-acetate was prepared in 1863 by Geuther by acting 

 upon ethyl acetate with sodium and acidifying the product with acetic 

 acid. An oil resulted ; it was separated and purified by distillation. 



Ethyl aceto-acetate is a liquid with a fruity smell which boils at 

 182. It is largely used in synthesis in organic chemistry, like malonic 

 ester. 



Aceto-acetic acid can be prepared from the ester by hydrolysis. 

 It is a very unstable, strongly acid, hygroscopic syrup which decom- 

 poses on warming into acetone and carbon dioxide. Solutions of 

 aceto-acetic acid are readily decomposed on distilling with dilute acid 

 or alkali. 



Traces of aceto-acetic acid occur in normal urine 2-4 mg. in 

 24 hours. The amount is increased in starvation, on a diet of protein, 

 and on a diet of fat i.e. whenever there is a shortage of carbohy- 

 drate. The excretion of aceto-acetic acid is lessened if carbohydrate 

 be added to the food. 



The origin of the aceto-acetic acid in the urine appears to be 

 partly from the protein of the food, but mainly from the fat. The 

 work of Knoop and of Dakin has shown that the oxidation of the 

 fatty acids takes place at the yS-carbon atom ; the long chains are 

 broken down with the loss of 2 carbon atoms at a time. This accounts 

 in part for the occurrence of those fatty acids in nature containing 

 an even number of carbon atoms. Butyric acid, if present as such 

 or formed by the oxidation of higher fatty acids by /3-oxidation, is 

 oxidised and converted into aceto-acetic acid or /3-hydroxybutyric 

 acid : 



CH 3 .CH 2 .CH 2 .COOH 



s \ 



H a . COOH - CH 3 . CHOH . CH 2 . COOH. 



