Patent GB-814647-A (GB)
Title: A process for the manufacture of organoboron compounds
Inventor: YATES JOHN
IPC: C07F5/02
Filed: 1956-03-28
Abstract: A process for preparing organoboron compounds comprises reacting an organoalkali metal compound with a boron trihalide or with a triester of boric acid in an anhydrous, inert liquid reaction medium, with cooling if necessary, to produce the corresponding organoboron halide or organoboric acid ester complex.  The organoboric acid ester complex is optionally converted to the organoboric acid ester by reaction with anhydrous hydrogen halide and the organoboron halide or organoboric acid ester complex or organoboric acid ester is hydrolysed to the corresponding organoboronic or organoborinic acid. The organo-alkali metal compounds employed are preferably lithium, sodium or potassium compounds and the organic group may be acyclic or cyclic hydrocarbon which may be saturated or unsaturated or heterocyclic, e.g. furyl or thiophene, and may be substituted with hydrocarbon, nitro, etherified hydroxyl, trifluoromethyl groups and the group OM where M represents an alkali metal.  Organo alkali metal compounds mentioned as starting materials include butyl lithium, ethyl sodium, alkali metal alkyne derivatives, benzyl sodium, benzyl potassium, dibenzylfuryllithium and thionaphthenyl lithium, sodium triphenylmethyl, o - aminophenyllithium, p - nitrophenyllithium phenyl lithium and phenyl sodium.  Boron trihalides mentioned include boron trichloride and trifluoride.  Boron triesters mentioned include those derived from phenols and alcohols.  Suitable reaction media include diethyl ether, ligroin, toluene or oxylene.  Where organoboron halides are employed as starting materials the reaction mixture may be decanted or filtered, volatile impurities may be distilled off and the residue purified by further distillation or recrystallization.  Where a boric acid triester is employed as starting material and an organoboric ester complex insoluble in the reaction medium is obtained the reaction mixture may be filtered and the complex extracted from the residue with isopropylamine, the latter being evaporated to recover the complex.  Where a soluble organoboric acid ester complex is produced the extraction with isopropylamine may be applied to the residue remaining after distilling off volatile constituents from the reaction mixture.  The organoboric acid ester may be obtained by reacting the organoboric acid ester complex with an anhydrous hydrogen halide, e.g. hydrogen chloride.  The organoboron halide, organoboric acid ester complex or the ester may be hydrolysed to the corresponding organoboric acid by reaction with water.  Where a triester of boric acid has been employed as starting material aqueous mineral acid is preferably employed for the hydrolysis. In examples: phenyl boronic acid is obtained by reacting trimethyl borate with phenyl lithium (I)-(III), and phenyl sodium (IV) or by reacting phenyl sodium with boron trichloride (V) and hydrolysing the products with dilute sulphuric acid; diphenylborinic acid is obtained as a by-product in (II) and is reacted with monoethanolamine to obtain 2-amino-ethyl diphenyl-borinate; phenyl thiomethyl boronic acid (VI), 2 : 5-dimethoxy- and 2 : 6-dimethoxy phenyl boronic acid (VII), benzyl - 2 - boronic acid (VIII), dibenzfuryl-2-boronic acid (IX), dibenzthionyl-1-boronic acid (X) and thionaphthenyl-2-boronic acid (XI) respectively are obtained by reacting the lithium derivatives of methyl phenyl sulphide, 2 : 5- and 2 : 6-dimethoxy benzene, benzofuran, dibenzofuran, dibenzothiophene and thionaphthene with methyl borate and hydrolysing the products.  Organo-alkali metal compounds used as starting materials may be prepared by reacting an halohydrocarbon which may be substituted, e.g. with an hydroxyl group, with an alkali metal in an indifferent solvent or by reacting an alkylalkali metal, e.g. butyl lithium or amyl sodium with an aromatic hydrocarbon or heterocyclic compound which may carry one or more substituents, e.g. etherified hydroxyl, methyl mercapto and aromatic hydrocarbons or heterocyclic compounds may carry a nuclear halogen or hydroxy group as e.g. in p-bromophenol.