ALDEHYDES 87 



Reconversion into Chloral. 



About 2 gm. of chloral hydrate are placed in a dry test tube and 

 covered with concentrated sulphuric acid and the mixture is warmed 

 gently. Chloral is formed and floats to the surface. 



An aqueous solution heated with zinc to 50 and gradually treated with 

 dilute acid yields aldehyde and paraldehyde which may be distilled off. 



Tests for Chloral and Chloral Hydrate. 



Aqueous solutions in the cold give no reaction with silver nitrate. 

 On adding a few drops of ammonia and boiling, metallic silver is 

 deposited. 



Aqueous solutions reduce Fehling's solution on heating. Traces 

 of chloral may be detected by the carbylamine reaction for chloro- 

 form (p. 61). 



Decomposition of Chloral by Alkali. 



Chloral or chloral hydrate is rapidly decomposed by caustic alkali 

 with the formation of chloroform and alkali formate : 

 CC1 S CH(OH) 2 + NaOH = CHC1 3 + HCOONa + H 2 O. 



The odour of chloroform is noticed at once on gently warming an 

 aqueous solution of chloral with caustic soda. 

 Estimation. 



1. By measuring the volume of chloroform. 



2 5 gm. of chloral hydrate or chloral are placed in a graduated cylinder 

 and excess of sodium hydroxide solution (80-100 c.c.) are carefully added. 

 The tube is kept well cooled at first on account of the violence of the reaction. 

 Afterwards the cylinder is closed and shaken. On standing the liquid be- 

 comes clear and separates into two layers. When cold (at 17) the volume of 

 the lower layer of chloroform is measured. The volume in c.c. multiplied by 

 i -84 gives the number of grams of chloral, or by 2-064 of chloral hydrate, in the 

 sample. 



2. By titrating the acid. 



i-2. gm. are dissolved in water and shaken with barium carbonate to 

 remove any acid. The carbonate is filtered off and washed, Excess of 

 normal caustic soda (100-150 c.c.) is added and the solution titrated with 

 normal acid, using litmus as indicator. 



Each c.c. of alkali neutralised = '1475 g m - chloral or '1655 gm. chloral 

 hydrate. 



Butyric Chloral Hydrate. 



This compound is formed when chlorine is passed into paraldehyde or 

 acetaldehyde. It is a white crystalline substance with peculiar fruity flavour 

 -and melts at 78. 



