DFT Study of the Arbuzov Reaction Mechanism between Ethyl Halogenides and Trimethoxyphosphine

The mechanism of the reaction between ethyl chloride or ethyl bromide with trimethoxyphosphine in a non-polar (ε = 1) and polar medium (methanol, ε = 32.7) was studied within the density functional theory (DFT) using MOLPRO program. It was shown that the reaction occurs in 2 stages: first, a nucleophilic attack of the carbon atom by phosphorus occurs, followed by the interaction of methyl of one of the methoxy groups with the halide. The limiting stage in all cases is the second stage of the reaction, the barrier of which is approximately 1.5 times higher than the barrier of the first. The reaction barriers are lower for the reaction of ethyl bromide, while the stabilization energies of the intermediate complexes and products are almost the same for chloride and bromide. Temperature in general has little effect on the reaction profile, with the exception of entropic destabilization of the initial complex. At the same time, the usage of a polar solvent accelerates the reaction process, lowering the barriers and stabilizing the intermediates, and can be recommended for carrying out the reaction.