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 ΔfH°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, ΔfH°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.
Published Version
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