256 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



Properties. 



Benzole acid forms glistening crystals which melt at 121 -5 and 

 boil at 249 



On heating, it melts and gives off white vapours with characteristic 

 smell and suffocating effect upon the throat ; the vapours condense as 

 a crystalline sublimate. 



It dissolves easily in hot water and crystallises out on cooling ; it is 

 only slightly soluble in cold water (i part in 400). 



It dissolves in alcohol and ether and other organic solvents. 

 It forms salts with alkalies, dissolving in caustic alkalies and 

 alkali carbonates, in lime water, etc. ; on acidifying these solutions, it is 

 precipitated. 



A neutral solution gives a precipitate of a pale brown colour with 

 ferric chloride. 



It is easily nitrated : nitrobenzoic acid is formed on evaporating a 

 little benzoic acid in a porcelain basin with nitric acid. 



It is converted into benzene by heating with soda lime. 

 It forms esters, e.g. ethylbenzoate (p. 73) is formed if benzoic 

 acid be heated with a little alcohol and a few drops of concentrated 

 sulphuric* acid. The ester has a peculiar aromatic odour and boils at 

 213. 



Benzoyl Chloride, C 6 H 5 . CO . Cl. 



This compound is formed by the action of phosphorus penta- 

 chloride upon benzoic acid : 



C 6 H 5 . COOH + PC1 6 = C 6 H 6 COC1 + POC1 3 + HC1. 



Benzoic acid and a slight excess of phosphorus pentachloride are placed 

 in a distilling flask ; the reaction proceeds at the ordinary temperature and 

 the vapours of hydrogen chloride are passed into soda. As soon as the 

 reaction is complete the contents are distilled in a fume cupboard ; phos- 

 phorus oxychloride passes over at 107, benzoyl chloride at about 198. It is 

 purified by redistillation. 



Benzoyl chloride is a colourless oily liquid with a peculiar pungent smell. 

 It is slowly decomposed by water into benzoic acid and more readily by 

 alcohol into ethyl benzoate. 



Benzoic Anhydride, (QH 5 . CO) 2 O. 



The anhydride of benzoic acid is prepared like other anhydrides by the 

 action of benzoyl chloride upon sodium benzoate : 



C 6 H 6 COC1 + C 6 H 5 COONa = C 6 H 5 . CO . O . CO . C 6 H 5 + 'NaCl. 



It is a colourless crystalline substance melting at 42 and resembles acetic 

 anhydride. 



