3.5- Dinitrobenzoyl chloride hydrolysis

The benzoyl compounds frequently occlude traces of unchanged benzoyl chloride, which thus escapes hydrolysis by the alkali it is therefore advisable, wherever possible, to recrystallise the benzoyl derivatives from methanol, ethanol or rectified spirit, since these solvents will esterify the unchanged acid chloride and so remove the latter from the recrystallised material. Sometimes the benzoyl compound does not crystallise well this difficulty may be frequently overcome by the use of p-nitrobenzoyl chloride or 3,5-dinitrobenzoyl chloride (Expt 6.161), which usually give highly crystalline derivatives of high melting point. Benzoyl compounds are readily hydrolysed by heating with about 70 per cent sulphuric acid (alkaline hydrolysis is very slow for anilides). 

The acid chloride is available commercially, but it is preferable to prepare it from the acid as and when required since 3,5-dinitrobenzoyl chloride tends to undergo hydrolysis if kept for long periods, particularly if the stock bottle is frequently opened. The substance may, however, be stored under dry light petroleum. 

Dinitrobenzoyl chloride releases hydrochloric acid upon hydrolysis, so avoid contact of this reagent with your skin. If contact occurs, immediately flood the area with water and rinse it with 5% sodium bicarbonate solution. Wear latex gloves when handling this reagent. 

If the alcohol formed on hydrolysis is not volatile with steam, it can be extracted with ether and converted to a 3,5-dinitrobenzoate (see p. 150) either directly, or after the evaporation of ether. If both the alcohol and the acid are soluble in water and are not volatile with steam, the hydrolyzate is divided into two portions in the first the acid is identified (by precipitation with S-l-naphthylmethylthiuronium chloride) and in the second the alcohol is identified (by reaction with 3,5-dinitrobenzoyl chloride (see p. 150). For the latter case the direct identification of the acid and the alcoholic components previous to hydrolysis is suitable. 

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