Esterification in sulphuric acid

Abstract

The possible nitrating entities for the esterification of alcohols by nitric acid in sulphuric and perchloric acids have been discussed, and the interpretation of nitration mechanisms by correlation with acidity functions considered. The nitric acid esterification of 2:4-dinitrobenzyl alcohol has been investigated over a wide range of sulphuric acid, but the alcohol proved unsuitable for kinetic study. Results have been obtained for the equilibrium formation of the sulphuric and nitric esters of this alcohol in 75% - 85% H2S04. Kinetic studies have been made on the nitric acid esterification of iso-amyl alcohol in H2SO4 at 0°c. and 25°c. The results have been correlated with acidity functions, but a critical survey of the latter has shown that they are not completely reliable guides to reaction mechanisms. Rates of esterification have been obtained in perchloric acid, and considered in relation to the ionisation of nitrous acid to the nitrosonium ion N0+ in this acid. Correlation of results indicate that the nitronium ion N02 is the nitric acid esterifying agent in HC1O4. Corresponding information on the ionisation of nitrous acid in H2S04 supports the N02 mechanism in sulphuric acid. A tri-aryl carbinol indicator has been measured at 7°C. in H2S04 to give some indication of the effect of temperature on the ionisation of such indicators. A tri-aryl carbinol indicator has also been measured in HC104 at 25°c. as there is at present no existing acidity scale in this acid corresponding to Jo in H2S04. Equilibrium constants for the nitric acid esterification of iso-amyl alcohol have been obtained in H2S04 and HC104, and the rate constants for the hydrolysis calculated. A possible mechanism for the hydrolysis involving proton uptake by the nitrate, and the production of NO2 has been suggested.