Standard enthalpy of formation of hexamethyldisilane

Abstract

The standard (p°= 0.1 MPa) enthalpy of formation at 298.15 K of liquid hexamethyldisilane was determined by measuring the enthalpy of its reaction with bromine to produce trimethylsilicon bromide. The required Δ_fH°_m[(CH₃)₃SiBr, I]/kJ mol^–1=–330.4 ± 2.7 was determined from its enthalpy of hydrolysis in aqueous hydrobromic acid. The final result, Δ_fH°_m[(CH₃)₆Si₂, I]/kJ mol^–1=–341.1 ± 5.5 differs considerably from previous determinations and the consequences for the thermochemistry of silicon–methyl species are discussed. In particular the enthalpies of formation of the silylenes, SiH₂, SiHMe and SiMe₂, were derived as 266, 201 and 140 kJ mol^–1, respectively, with uncertainties < ±6 kJ mol^–1.