The Liquid/Solid Alkylation of Alkali Metal Pyrazolates

Abstract

The reactions of the lithium, sodium, potassium and cesium derivatives of 3‐methyl‐5‐carbomethoxy‐pyrazole, of 3‐methyl‐5‐ethyl‐pyrazole and of 3‐methyl‐5‐methoxy‐methylene‐pyrazole with methyl iodide, allyl bromide and benzyl chloride were investigated in 1,2‐dimethoxy‐ethane solution and at a liquid/solid interface (suspension of the pyrazole in a 1:1 mixture of n‐hexane and n‐heptane). Comparison of the ratios of the two nitrogen alkylated products formed from the reaction in solution and at the liquid/solid interface, suggests that the latter ratio is determined by the size of the alkali metal cation and by the presence of a coordination centre placed non‐symmetrically with respect to the mirror plane passing through the nitrogen‐nitrogen bond. It is suggested that a “cation in the way” effect is responsible for the liquid/solid‐interface alkylation results.