ALDEHYDES 83 



soluble in water and alcohol, and easily decomposed by acids and 

 alkalies. 



On dissolving a little aldehyde ammonia and heating with dilute 

 sulphuric acid, aldehyde is given off. Ammonia is also evolved on 

 heating with dilute caustic soda. 



Aldehyde Sodium Bisulphite. 



On adding 1-2 c.c. of a cold saturated solution of sodium bisulphite 

 to 5-10 drops of aldehyde and shaking vigorously, aldehyde sodium 

 bisulphite crystallises out : 



,OH 



CH 3 . CHO + NaHS0 3 = CH 3 . CH\ 



X S0 3 NA. 



Aldehyde Cyanhydrin. 



Hydrogen cyanide combines with aldehydes forming cyano- 



hydrins : 



,OH 



CH, . CHO + HCN = CH 3 . CH\ 



X CN. 



In this way another carbon atom can be added to organic com- 

 pounds. Compounds containing the CN group are hydrolysed by 

 acids or alkalies and converted into the corresponding acid (see cyano- 

 gen compounds) : 



,OH OH 



CH-.CHx + 2 H 2 = CH 3 .CH< + NH 8 . 



\CN \COOH 



Aldehyde Hydrazone. 



Aldehydes combine with hydrazine and substituted hydrazines,. 

 especially phenylhydrazine, forming hydrazones. 



The calculated quantities of aldehyde (-5 c.c.), phenylhydrazine 

 hydrochloride (-2 gm.) and cryst. sodium acetate (-5 gm.)-are dissolved 

 in about 10 c.c. of water and warmed ; an oil (acetaldehyde phenyl- 

 hydrazone) is formed : 



CH 3 . CHO + H 2 N . NH . C 6 H 5 = CH 3 . CH : N . NH . CH 5 + H 2 O. 



Aldoxime. 



Aldehydes combine with hydroxylamine forming oximes : 



CH 3 . CHO + H 2 NOH = CH 3 . CH : NOH + H 2 O 



(acet)aldoxime. 



The calculated quantity of hydroxylamine hydrochloride is dissolved in 

 water, the equivalent quantity of caustic soda required to liberate the 

 hydroxylamine is added and then the calculated quantity of the aldehyde. 

 The mixture is shaken and allowed to stand until it no longer reduces 

 Fehling's solution. The oxime is extracted with ether, most of the ether dis- 

 tilled off, and the concentrated solution poured into a basin. The crystals 

 which separate are drained on a porous plate and recrystalhsed from hgrom. 



