AB initio quantum chemical study of the reaction mechanism of ethynide ion formation in the C2H2/MOH/DMSO system (M = Li, Na, K)

The reaction mechanism of the formation of alkali metal ethynides C2H2 + MOH → C2HM + H2O (M = Li, Na, K) is studied for the gas phase (MP2/6-311++G**//RHF/6-31+G*) and also with regard to the solvent effect of dimethyl sulfoxide (DMSO) included within the continuum model. Among all acetylene complexes with alkali metal hydroxides considered (C2H2·MOH (M = Li, Na, K)), only the complex with KOH is thermodynamically stable in DMSO solution. The formation of this structure results in activation of the acetylene molecule towards electrophilic attack. The formation of alkali metal ethynide in solution is also thermodynamically favorable only in the system with potassium hydroxide of a whole series of metals considered. Further, the ethynide ion can interact in KCCK·HOH systems.