Elementary Reactions in the Cationic Oligomerization of 2-Alkoxy-1,3,2-Dioxaphospholane with Alkyl Iodide as Initiator

Abstract

Elementary reactions in the oligomerization reaction of 2-alkoxy-1, 3, 2-dioxaphospholanes by alkyl iodides were studied. The initial reactions were ring-opening reactions leading to open-chain phosphonate and isomerization reactions with loss of an external alkyl group leading to cyclic phosphonate. The ratio of these two elementary reactions was 2.7: 1.0 in the reaction of 2-methoxy-1, 3, 2-dioxaphospholane with methyl iodide at 70°C. The reaction with ethyl iodide was much slower compared to that with methyl iodide. This suggests the slow propagation of the polymerization of 1, 3, 2-dioxaphospholanes by methyl iodide. The isomerization reaction could be a chain-transfer reaction in the growing chain. This might be the reason why high polymers could not be obtained from 2-methoxy-1, 3, 2-dioxaphospholane. The reaction of 2-t-butoxy-1, 3, 2-dioxaphospholane with methyl iodide was exclusively the isomerization process via the Arbuzov reaction, with removal of the external t-butyl group, which led to isobutylene. In the reaction of 2-neopentoxy-1, 3, 2-dioxaphospholane with methyl iodide, the only product resulted from the addition of methyl iodide to the dioxaphospholane ring, followed by ring opening.