General procedure -SEM-protected imidazoles

Quaternary salts can be made by alkylation of 1-substituted imidazoles. They may also be formed directly from imidazoles treated with an excess of alkylating agent. Begtmp and Larsen predict quatemization in terms of quatemization potentials (Pq) using the relationship 

Standard reaction conditions are 20°C (72 h) in methanol, dichloromethane, acetonitrile or DMF. Under these conditions 1-methylimidazole gives a 30% yield of 1,3-dimethyhmidazolium iodide (using methyl iodide) and a 99% yield of l-benzyl-3-methylimidazolium chloride (using benzyl chloride) [3]. Heating promotes alkylation, but does not seem to have much effect or ease of quatemization, although it does increase yields. 

Imidazole quaternary salts (9) are frequently quite hygroscopic and need to be kept dry if storage is intended. In their synthesis all apparatus must be scrupulously dry, solvents must be dried before use, and reactions and recrystallizations need to be carried out under dry nitrogen. Liquid reagents are best added using a syringe through a serum cap, and Schlenk apparatus is recommended for filtrations. 

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