Abstract
The enthalpies of reaction of neat PBu3 with solid sulfur (−27.1 ± 0.5 kcal/mol), selenium (−20.0 ± 0.6 kcal/mol), and tellurium (−4.9 ± 0.6 kcal/mol) have been measured by solution calorimetry. The enthalpies of reaction of a series of phosphines with sulfur in toluene solution have been measured as follows (values in kcal/mol): PCy3 = −30.9 ± 1.9, PBu3 = −28.9 ± 0.3, PMe3 = −27.1 ± 0.4, PMe2Ph = −26.0 ± 0.5, PMePh2 = −23.8 ± 0.3, PPh3 = −21.5 ± 0.3. These values correlate with literature data for enthalpies of protonation and indicate that P to S σ donation is probably the dominant factor in determining the R3PS bond strength, estimates for which range from 88 to 98 kcal/mol. The enthalpies of S atom transfer to PPh3 by SAsPPh3 and SSbPh3 in toluene solution are −17.7 ± 1.2 and − 21.5 ± 1.0 kcal/mol, respectively. The enthalpy of removal of the central S atom from BzSSSBz by PCy3, yielding BzSSBz and SPCy3, is − 29.0 ± 1.8 kcal/mol. These data are used to establish a range of enthalpies of S atom transfer in these compounds which spans 31 kcal/mol from SSbPPh3 to SPCy3.
