| Popis: |
The synthesis and standard heats of formation of some substituted arylboroxines are reported. Two new aryl-boroxines, p-tert-butylphenylboroxine and p-trifluoro-methylphenylboroxine, have been prepared and characterized. The effect of substituting the phenyl ring of triphenyl-boroxine by, p-fluoro, p-chloro, p-bromo, p-methoxy, p-methyl and o-methyl groups was considered in terms of resonance stabilization of the boroxines and the strength of the (aryl) carbon to boron bond. While para-substitution increases the stability of the arylboroxines, ortho substitution decreases it by steric effects. Three substituted aryldichloroboranes were synthesized and thermochemically studied. In ortho-tolyldichloroborane δ-overlap between the ortho-hydrogen and chlorine atoms of the dichloroboryl group is proposed to explain the enhanced stability of this compound. Steric effects in mesityl-dichloroborane appear to be dominant and destabilize this compound. Several substituted aryldihydroxyboranes were prepared. Three of them, para-tolyl, ortho-tolyl and para-carboxy-phenyldihydroxyboranes were studied thermochemically. Solution reaction calorimetry and combustion calorimetry of some phosphorus compounds are reported and standard heats of formation of these compounds were determined. Several simple aliphatic diols were combusted in a static bomb calorimeter and their standard heats of formation were derived. |
