Determination of organic hydroxyl groups by nuclear magnetic resonance spectroscopy by using trimethylsilyl derivatives

Abstract

A nuclear magnetic resonance spectroscopic method is presented for the determination of hydroxyl values in mixtures of organic compounds. A nine-fold enhancement of sensitivity is obtained by the formation of trimethylsilyl derivatives, which makes the method especially useful for the determination of low hydroxyl values. The method can be applied to the rapid determination of the hydroxyl values of fatty acids, esters, polymerised fatty acids, polyesters, tertiary alcohols and certain phenols. O-Nitrophenols and highly hindered phenols fail to give correct results, as do hydroxy-compounds of low relative molecular mass, which give volatile trimethylsilyl derivatives. Epoxides and non-enolised ketones do not interfere in the determination. Certain shortcomings of methods for the determination of hydroxyl values based on acetylation and differential titration are discussed.