The Influence of Methyl Group Substitution on the Odour of Aliphatic Nitriles

As part of an investigation into structure/odour correlations, we decided to synthesise a matrix of nitriles consisting of three series; viz, unsubstituted, 2-methyl substituted, and 3- methyl substituted; with five members (i.e., C8 to C12 chains) in each series, in order to determine the effects, if any, of methyl substitution on odour.

All of the nitriles in question were synthesised from readily available starting materials as shown in figure 1. The unsubstituted series were prepared by dehydration of the corresponding oximes; the 2-methyl nitriles from the corresponding methyl ketones using tosyl methyl iso-cyanide (TosMIC) according to the method of van Leusen; and the 3-methyl nitriles by condensation of the corresponding methyl ketone with cyanoacetic acid followed by decarboxylation and hydrogenation of the resultant cyanoacid. All of the materials produced in this way possessed physical and spectroscopic properties consistent with those expected for the desired structures.

The fifteen nitriles were distilled and/or chromatographed to a high degree of purity and evaluated at various concentrations by a number of perfumers. The resultant odour descriptions are shown in Table I from which it is clear that both chain length and methyl group substitution pattern affect the odour character and strength of aliphatic nitriles.

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