| dc.description | The standard molar enthalpy of formation of arsenic alkoxides in the liquid phase, As(OR)(3) {R = ethyl (Et), n-propyl (Pr-n), i-propyl (Pr-i), n-butyl (Bu(n)), and i-butyl (Bu(i))}, was determined through reaction-solution calorimetry in chloroform based on the reaction: As(NEt(2))(3)(1) + 3ROH(1) = As(OR)(3)(1); Delta(sol)H(m) degrees at T = 298.15 K. This series of alkoxides gave the following molar enthalpy of formation Delta(f)H(m) degrees values: -(758.1 +/- 9.0) kJ . mol(-1), -(774.3 +/- 9.0) kJ . mol(-1), -(809.8 +/- 9.0) kJ . mol(-1), -(828.8 +/- 8.9) kJ . mol(-1), and -(863.4 +/- 8.9) kJ . mol(-1), respectively. The standard molar enthalpies of vaporization Delta(vap)H(m) (47.9 +/- 1.1) kJ . mol(-1), (51.2 +/- 1.8) kJ . mol(-1), (80.1 +/- 0.9) kJ . mol(-1), (64.0 +/- 1.8) kJ . mol(-1) and (75.7 +/- 1.2) kJ . mol(-1), were obtained for the same sequence of alkoxides, by means of differential scanning calorimetry. By combining the preceding values with the standard molar enthalpy of formation of the alkoxide Delta(f)H(m) in the liquid phase, the standard molar enthalpy of formation of these compounds in the gas phase was obtained as -(710.2 +/- 9.0) kJ . mol(-1), -(723.1 +/- 9.1) kJ . mol(-1), -(729.3 +/- 9.0) kJ . mol(-1), -(764.8 +/- 9.1) kJ . mol(-1), and -(787.7 +/- 9.0) kJ . mol(-1), respectively. From these values, the mean enthalpy of dissociation of the arsenic-oxygen bond [D-m](As-O) was calculated for the sequence of the above alkoxides to give: (320 +/- 5) kJ . mol(-1), (301 +/- 5) kJ . mol(-1), (292 +/- 5) kJ . mol(-1), (293 +/- 5) kJ . mol(-1), and (294 +/- 5) kJ . mol(-1). The linear correlation between the standard molar enthalpies of formation of the liquid alkoxides Delta(f)H(m){As(OR)(3),1} and the respective alcohol Delta(f)H(m)(ROH,1), suggests that these thermochemical data can be assessed for a series of normal and iso chain alcohols. (C) 1996 Academic Press Limited | |
