Effect of solvent and temperature on the lithium–iodine exchange of primary alkyl iodides: reaction of t-butyllithium with 1-iodooctane in heptane–ether mixtures

The reaction of 1-iodooctane, a representative primary alkyl iodide, with t-BuLi at 0 °C in solvent systems composed of heptane and four dialkyl ethers in various proportions has been investigated. Coupling and elimination are unavoidable side reactions that accompany lithium–iodine exchange when the reactions are conducted at 0 °C. The exchange reaction, which is slow in pure hydrocarbon solvent, is significantly facilitated by the presence of essentially catalytic quantities of an ether co-solvent. An optimal ether–heptane ratio for each of the ethers surveyed maximizes the extent of lithium–iodine exchange between 1-iodooctane and t-BuLi but in no case does the yield of octyllithium, assayed as octane, exceed ∼90% when reactions were conduced at 0 °C. At lower temperatures, in a solvent system composed of heptane–MTBE (19:1 by volume), side reactions are suppressed and the yield of octyllithium approaches quantitative.