GB880802A - Improvements in or relating to the manufacture of organoboron compounds - Google Patents

Abstract

An improved process for preparing organoboron compounds comprises reacting an organo-alkali metal compound in an anhydrous inert liquid reaction medium with a triester of boric acid in at least 15 mole per cent. excess of the stoichiometrical amount, with cooling if necessary, to produce the corresponding organoboric acid ester complex. Reaction media mentioned include toluene, tetrahydronaphthalene, diethyl and diisopropyl ethers and tetrahydrofuran. Organo-alkali metal compounds mentioned are lithium, sodium and potassium compounds, the organo group being an acyclic or cyclic hydrocarbon group, saturated or unsaturated, e.g. an aromatic group such as phenyl or a heterocyclic group, e.g. a furyl or thiophene group. The organo group may have one or more substituents inert to the alkali metal substituent, e.g. hydrocarbon, nitro, etherified hydroxy or trifluoromethyl or the group OM where M represents an alkali metal. Specific organo alkali metal compounds mentioned are butyl lithium, alkali metal-alkene and -alkyne derivatives, benzyl sodium and p -potassium, sodium triphenylmethyl, o-aminophenyl lithium, p-nitrophenyl lithium, dibenzylfuryl lithium, thionaphthenyl lithium, phenyl lithium and -sodium. Triesters of boric acid employed in the process may be derived from an aliphatic alcohol, e.g. containing 1 to 5 carbon atoms or a phenol. Organic ester complexes insoluble in the reaction mixture may be extracted with a volatile amine, e.g. propylamine to remove the complex which may then be recovered by evaporating the amine from the solution. The organoboric esters may be obtained from the complexes by treating the latter with anhydrous hydrogen halide, e.g. hydrogen chloride. The organoboric acid ester or the complex thereof may be hydrolysed to the corresponding organoboric acid with water, preferably with a dilute mineral acid solution. Organoboric acids obtained in the process may be converted to the corresponding anhydrides, water being removed azeotropically. The products of the process are chiefly organoboric compounds though some organoborinic may also be formed, mixtures of organoboronic and -borinic acids being separated by washing with light petroleum. Organo alkali metal compounds are prepared by reacting halocarbons with alkali metals or by reacting alkyl alkali metals with aromatic hydrocarbon or heterocyclic compounds which may carry one or more substituents. With an etherified hydroxy group or trifluoromethyl group metallation takes place mainly in the position ortho to the substituent group. With a methyl mercapto group metallation occurs in the methyl group and not in the nucleus. The methyl groups in methyl pyridines are also metallated. The halogenated aromatic or heterocyclic compound may carry a hydroxy group, e.g. as in p-bromophenol. Solvents for use in the preparation of the organo-alkali metal compounds include anhydrous ethers, ligroin, toluene, xylene and tetrahydronaphthalene.