Internal reactions in the Grignard‐complex containing compounds with alkoxy‐groups: Part II. Cyclic acetals

Abstract

If one molar equivalent of 2-methyl-, 2-ethyl-or 2-n-propyl-1,3-dioxolane is used for the preparation of Grignard-reagents in benzene, the five-membered hetero-ring is opened with formation of a magnesium halide 2-alkoxyethan-lolate.The steric and electronic effects of the alkyl groups of the Grignard-reagent and those of the dioxolane molecule are discussed.A previous communication 1 dealt with the preparation of Grignardreagents from one gram-atom of magnesium and one mole of an alkyl halide in a boiling solution of one molar equivalent of an acetal in an aromatic hydrocarbon, resulting in cleavage of the acetal and formation of an ether and an a1 koxymagnesium halide :Efforts to carry out these reactions at room temperature were less satisfactory; a large part of the magnesium did not react and the solution contained much less magnesium yielding basic magnesium on hydrolysis than total magnesium, indicating the formation of magnesium halide through side reactions. In some cases a voluminous precipitate was formed, which covered the magnesium in a thick layer.With cyclic acetals of ethane-1 ,Zdiol, the 1,3-dioxolanes, formation of the Grignard-reagent was smooth and almost complete both at room temperature and in boiling solutions. Hence dioxolanes with methyl substitution on carbon atom 4, or on atoms 4 and 5, can be used as solvents for Grignard-reactions and give satisfactory yields. Carlin and Smith have already reported the use of 4-methyl-lY3-dioxan as a solvent for Grignardreactions 2 .