242 PRACTICAL ORGANIC CHEMISTRY b.p. 198° and d , 1-21. It has a very irritating odour, and its vapour causes copious watering of the eyes. Benzoyl chloride has similar properties to acetyl chloride, but is much less reactive, e.g., it is only slowly hydrolysed by cold water to benzoic acid and hydrochloric acid. It is largely used as a reagent for identifying alcohols and primary and secondary amines (see below). For reactions of benzoyl chloride, see p. 364. 3,5-Dinitrobenzoic Acid. (NO 2 ) 2 C 6 H 3 COOH. Required: Benzoic acid, 50 g.; cone, sulphuric acid, 230 ml; fuming nitric acid, 73 ml. Dissolve 50 g. of benzoic acid in 230 ml. of concentrated sul-phuric acid in a litre flask fitted with a ground-glass reflux water-condenser. (Rubber or cork must not be used.) Now add a few ml. of the fuming nitric acid down the condenser, shake the flask well and keep it cool by immersion in ice-water. Continue the intermittent addition of nitric acid (about 10 ml. at a time) with continuous shaking and cooling: a great deal of heat is evolved on
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