The synthesis and thermochemistry of some organoboron compounds and adiabatic calorimetry

Abstract

Some acyloxy and aryloxyboranes have been prepared with a view to determining the relative thermodynasic stabilition of triacyloxyboranes and oxybis(diacylexyboranes) with respect to the disproportionation [formula]. In contrast to literature reports a triacyloxyborone structure was never obtained, but the existence of a higher polymer (when n=C5H11) was noted. This behaviour has been rationalised in terms of the molecular structures involved. [formula] have been determinedby means of solution phase reaction calorimetry together with evaporation date, to be respectively -6.99.6+-2.5, -7.15.3+-2.9. -722.1+-2.9 and -825.9+-2.6 and -517.3+-2.5, -540.2+-2.5, -561.0+-2.9, 565.8+-4.4 and -602.1+-2.9 kj mole-1. The concept of ring strain has been discussed and the ring strains of B-1-butyl and 3-phenyl heterocyclics, with respect to their acyclic diethexy-n-batylborone and diethoxyphenylborane analogues, detemined to be [formula]. It has been shown that diethoxyphenylborane is not a good strainless reference molecule and that the ring strains of the E-phenyl heterocyclics given here should be increased by ca. 41 kj mole-1. An automatic adiabatic solution reaction calorimeter suitable for slow reactions has been developed and a value for the heat of solution THAM in 0.1N NCL at 298X of -29.75+-0.21 kj mole-1 for a series of ten runs obtained (cf. -27.744 +-0.003 kj mole-1, lit). It has been used for reactions of up to two hours duration. Possible standard slow reactions have been investigated and the use of the reaction between potassium peroxydisulphate and aqueous potassium iodids (K2S2o8(o) +3KI(aq) -> 2h2SO4(aq) + KI3(aq) is recommended as a slow test reaction for solution reaction calorimeters.