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Determination of the mean enthalpy of dissociation of arsenic–oxygen bonds in some arsenic (III) alkoxides

✍ Scribed by Antonio G. de Souza; Maria G.A. Brasilino; Claudio Airoldi

Publisher
Elsevier Science
Year
1996
Tongue
English
Weight
273 KB
Volume
28
Category
Article
ISSN
0021-9614

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✦ Synopsis

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(NEt2)3(l) + 3ROH(l) = As(OR)3(l); DsolH°m at T = 298.15 K. This series of alkoxides gave the following molar enthalpy of formation DfH°m values: -(758.1 2 9.0) kJ•mol -1 , -(774.3 2 9.0) kJ•mol -1 , -(809.8 2 9.0) kJ•mol -1 , -(828.8 2 8.9) kJ•mol -1 , and -(863.4 2 8.9) kJ•mol -1 , respectively. The standard molar enthalpies of vaporization DvapHm (47.9 2 1.1) kJ•mol -1 , (51.2 2 1.8) kJ•mol -1 , (80.1 2 0.9) kJ•mol -1 , (64.0 2 1.8) kJ•mol -1 and (75.7 2 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 DfHm in the liquid phase, the standard molar enthalpy of formation of these compounds in the gas phase was obtained as -(710.2 2 9.0) kJ•mol -1 , -(723.1 2 9.1) kJ•mol -1 , -(729.3 2 9.0) kJ•mol -1 , -(764.8 2 9.1) kJ•mol -1 , and -(787.7 2 9.0) kJ•mol -1 , respectively. From these values, the mean enthalpy of dissociation of the arsenic-oxygen bond Dm (As-O) was calculated for the sequence of the above alkoxides to give: (320 2 5) kJ•mol -1 , (301 2 5) kJ•mol -1 , (292 2 5) kJ•mol -1 , (293 2 5) kJ•mol -1 , and (294 2 5) kJ•mol -1 . The linear correlation between the standard molar enthalpies of formation of the liquid alkoxides DfHm{As(OR)3,l} and the respective alcohol DfHm(ROH,l), suggests that these thermochemical data can be assessed for a series of normal and iso chain alcohols.

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