The Liquid/Solid Alkylation of Alkali Metal Pyrazolates

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.