Boronic anhydride

The purpose of the ethylene glycol is to intercept the boronic anhydride (80), which otherwise forms polymers that are difficult to oxidize. As we shall see in 18-23 and 18-24, it is possible to stop the reaction after only one or two migrations have taken place. 

The product consists of a mixture of (3,4,5-trifluorophenyl)boronic acid and varying amounts of (3,4,5-trifluorophenyl)boronic anhydride. 

Trimethylborate is a colourless transparent liquid which boils at 68.7°C. It is used as gaseous welding flux and as a parent component for some boron derivatives, such as sodium and potassium boranes, trimethoxy-boroxol, etc. E.g., trimethoxyboroxol can be rather easily formed when trimethylborate interacts with boron anhydride. 

Siloxane diarsine oxide boron anhydride. Disilane. 

Bisseret recently reported the conversion of dibromoalkenols, a new class of benzofuran precursors, into 2-phosphonylated and 2-aryl benzo furans [174]. For example, reaction of dibromalkenol 213 with phenyl boronic anhydride provides 2-phenylbenzofuran in 80% yield. The proposed mechanism for this transformation starts with a Suzuki coupling of the more reactive E vinyl bromide and the boronic anhydride followed by a second Pd-catalyzed coupling between the Z vinyl bromide and the alcohol oxygen. 

I) Reduction of Boron Anhydride (or Acid) with Carbon. The overall reaction is written ... 

Crystals from water. Spontaneous conversion to CaH,BO, benzene boronic anhydride or phenylboroxide on standing in dry air, although the best method is by azeotropic dehydration with toluene, mp 215-216° (anhydride). Ka 13-7. Dipole moment 1.72 (dioxane). Soly in water at 25° 2,5%, benzene 1.75%, xylene 1.2%, ether 30.2%, methanol ... 

Methylation and conversion to the boronic acid 232 followed by precipitation from dichloromethane with hexanes yielded the boronic anhydride 233. The isoquinoline portion 234 was synthesized from homochiral 86 by selective demethylation, benzylation and subsequent... 

Boron Nitride Nanoparticles of boron nitride powders (a-BN) can be obtained by choosing the proper terms of elemental boron combustion in gaseous or liquid nitrogen or boron anhydride (B2O3) combustion by the mode called SHS with a reduction stage [43]. In the first case, the agglomerates of BN nanoparticles can be separated by means of chemical dispersion (chemical-thermal method of the... 

Despite their Hmited structure determination capabilities, ultraviolet and infrared spectroscopy were determinant characterization techniques in the early days of boronic acid research [332]. Notable IR absorptions are the strong H-bonded OH stretch (3300-3200 cm ), and a very strong band attributed to B-O stretch (1380-1310 cm ). IRis particularly diagnostic of the presence of boronic anhydrides. Upon anhydride (boroxine) formation, the OH stretch disappears and a new strong absorption appears at 680-705 cm [68]. 

Recently, Davies et al. have observed that boronic acids, esters and boronic anhydrides are partners in Suzuki coupling reactions with various P-chlorovinylamidini-um salts to give the desired P-arylvinylamidinium salts. Among boron partners, boronic anhydrides give better yields (up to 88%). Reduction is a competing reaction pathway (Equation 83) [115]. 

Achiral (a-bromo-sec-alkyl)boronic esters are readily accessible via radical bromi-nation of sec-alkylboronic esters [36]. Bromination of boronic anhydrides (trialkyl-boroxines) is much more facile and is a recommended alternative [37]. Dropwise addition of bromine to triisopropylboroxine under fluorescent room lights produced bromo derivative 44 essentially quantitatively (Scheme 8.9). Addition of ethylene glycol produced the boronic ester 45, which was easily distilled [37]. 

Compounds containing the B—O linkage, such as borates, boronates boronites, boronic anhydrides, borinic acids, and boronic acids, are characterized by intense absorption at 1380-1310 cm involving the stretching... 

In CANDU reactors, different systems are used to control and stop the reactor [3]. Soluble poisons (boron anhydride, gadolinium nitrate) can be diluted in the heavy-water moderator circuit. Stainless-steel rods can be inserted in order to reduce the moderation efficiency. Finally, control and shutdown rods are made of cadmium mbes sandwiched between stainless steel tubes. All the control rod systems are vertically introduced in the core, when the fuel elements are horizontal. 

The synthesis of tertiary alcohols from trialkylboranes and CO at 100-150 °C has been improved in the presence of ethylene glycol - (eq 19). The purpose of the ethylene glycol is to trap the intermediate boronic anhydride, which can form a polymer that is difficult to oxidize. 

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