HYDROXY-, KETO- AND DIBASIC ACIDS 113 



Pyruvic Acid. 



The work of recent years shows that pyruvic acid and other 

 ketonic acids are very probably intermediate products in the catabolism 

 of fatty acids and proteins. Pyruvic acid may be a stage in the 

 transformation of sugar into alcohol and carbon dioxide and into 

 lactic acid : 



CH 3 CH 3 CH 3 CH 3 



CHOH - CO -> CHO - CH 2 OH 



I I + 

 COOH COOH CO 2 . 



Preparation. 



Pyruvic acid is usually prepared from tartaric acid. A mixture of 500 gm. 

 of tartaric acid and 780 gm. of potassium bisulphate is dist. lied from a 2 li. 

 copper retort provided with a condenser; the receiver is cooled with ice. 

 The distillate is redistilled in vacua using a fractionating column. A yield of 

 about 60 per cent, is obtained. 



Properties. 



Pyruvic acid is a liquid which freezes at 9 and boils at 168 under atmos- 

 pheric pressure, or at 59-60 at 12 mm. pressure. It smells very like acetic 

 acid. It has the propeities of an acid and of a ketone and forms a character- 

 istic hydrazone. 



Test. 



Hurtley has described the following delicate test for pyruvic acid. The 

 test depends upon the formation of a red colour on oxidising the phenyl- 

 hydrazone of pyruvic acid. The reaction is positive at a dilution of i in 

 10,000 and can be obtained at a dilution of i in 100,000. 



10 c.c. of pyruvic acid (i per cent.) are treated with 10 c.c. of phenyl- 

 hydrazine hydrochloride solution (6-41 gm. in 500 c.c. acid = 5 gm. pyruvic 

 acid) ; about 2 c.c. of persulphuric acid (25 gm. K 2 S 2 O 8 are ground up with 

 50 gm. H 2 SO 4 and left for i hour, then poured upon ice and diluted to 500 

 c.c.) are added avoiding an excess and then 5 c.c. concentrated hydrochloric 

 acid. A red colour develops. 



Malonic Acid. 



This acid is found in beetroot as its calcium salt. It was origin- 

 ally prepared by the oxidation of malic acid with potassium bi- 

 chromate and sulphuric acid, but is usually made by the cyanide 

 synthesis from chloracetic acid, 



Potassium chloracetate is boiled with potassium cyanide; the product is 

 hydrolysed with hydrochloric acid and the solution evaporated to dryness. 

 The residue is extracted with ether, and the malonic acid obtained by dis 

 lation of the ether. 



Malonic acid is a colourless, crystalline solid which melts at 

 132, and is readily soluble in water, alcohol and ether. On heat- 

 ing to 140-150 it loses carbon dioxide and is converted into acetic 

 acid ; 



