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Wallis, John William (1959) Reactions of boron trihalides with certain organic compounds. Doctoral thesis, Northern Polytechnic.
This thesis deals with the interaction of boron halides with nitriles, amides and oximes. Invariably nitriles and amides formed 1:1 co-ordination complexes, the structure and reactions of which have been studied, whilst oximes (only benzophenone oxime was investigated) underwent the Beckmann rearrangement. A literature survey of relevant investigations with other inorganic halides is included.
Hydrolysis of selected nitrile complexes and alcoholysis (except with t-butanol when t-butyl chloride was obtained) of acetonitrile-boron trichloride afforded hydrogen chloride, free nitrile and boric acid or boron esters. Displacement reactions on the acetonitrile-boron trichloride complex showed basic strengths, with respect to boron trichloride as the reference Lewis acid, to be in the order pyridine > tetrahydrofuran and di-n-butyl sulphide > acetonitrile > acyclic ethers.
The presence of the C≡N stretching vibration in the infra-red spectra of nitrile complexes indicated that these compounds are of the co-ordination type; the unexpected shift of this band to a higher frequency as between free nitriles and their complexes is explained in terms of changes in hybridisation of the nitrogen atom. A large increase in the extinction coefficient of the CN band as between nitriles and nitrile complexes is noted and explained.
Hydrolysis of the benzamide-boron trichloride complex afforded benzamide, hydrogen chloride and boric acid, butanolysis yielded benzamide hydrochloride, hydrogen chloride and tributyl borate. Pyrolysis of primary (acetamide, propionamide, and benzamide) and secondary (methylformamide and acetanilide) amide-boron trichloride complexes resulted in hydrogen chloride elimination; propionitrile and benzonitrile were isolated from the propionamide and benzamide complexes.
Frequency shifts of infra-red bands associated with NH and CO bonds as between free amides and their boron-trichloride and -tribromide complexes and the absence of molecular association in the complexes (band frequencies being independent of molecular aggregation) indicated oxygen and not nitrogen donation in the complexes. Nuclear magnetic resonance examination of the dimethylformamide–boron trichloride complex also supported oxygen donation.
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