Benzeneboronic anhydride reactant: Three hundred thirty‐six milliliters (312 g., 3 moles) of methyl borate intermediate: benzeneboronic acid product: benzeneboronic anhydride reactant: methanol

The esters of orthoboric acid, although known for more than 100 years (58), have only recently become commercially available. This paper presents process development data; the synthesis and properties of a new series of hydrolytically stable borates; the variation in boiling point, density, index of refraction, and viscosity with temperature; a summary of reactions and uses; and physical evidence that tetracoordinate boron is involved in the reactions of borate esters. A number of methods for preparing borate esters have been described. They in clude: reaction of an alcohol (or phenol) with boron trichloride (48, 134) (Equation 1); boron acetate (8, 146) (Equation 2); boric acid (47, lp) (Equation 3); boron oxide (188) (Equation 4) ; or sodium borohydride (36) (Equation 5) ; and transesterification with a lower boiling borate ester (170, 204) (Equation 6). When water is a product of the esterification, it has been removed by azeotropic distillation with an excess of the alcohol (14, 92, 164) o r a n mer t medium (149) ; or by dehydration with sulfuric acid (45,197), copper sulfate (56, 93), or boron oxide (120,126,172,197) (Equation 7). 3ROH + BC13 -> (RO)3B + 3HC1(1) 6ROH + (CH3COO)4B20 -> 2(RO)3B + 4CH3COOH + H20(2) 3ROH + H3B03 -> (RO)3B + 3H20 (3) 6ROH + B203 -> 2(RO)3B + 3H20 (4) 3ROH + NaBH4 + H+ -> (RO)3B + 4H2 + Na +3ROH + (RO)3B -> 3(RO)3B + 3ROH (6) 3ROH + B203 -> (RO)3B + H3B03 (7) Stanley (180) has claimed the preparation of borate esters as an intermediate step in the conversion of alkylenes into alcohols.The alkylene is converted to the alkyl sulfate, alkyl phosphate, or alkaryl sulfonate by absorption into acid or acid ester; the borate ester formed on subsequent reaction with boric acid is then distilled and hydrolyzed to the alcohol: 3S02(OEt)2 + H3B03 -> 3S02(OEt)OH 4-(EtO)8B 1 H3B°3 > 3H2S04 + (EtO)8B (8) 129 Downloaded by UNIV OF CALIFORNIA SAN FRANCISCO on December 8, 2014 |

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