Acidity of boron halides

The order of acidity of boron halides is BF, < BCI3 < BBr. Is there anything unexpected in this order0 Suggest possible explanations. 

As has already been mentioned, boron halides are electron-deficient molecules. As a result, they tend to act as strong Lewis acids by accepting electron pairs from many types of Lewis bases to form stable acid-base adducts. Electron donors such as ammonia, pyridine, amines, ethers, and many other types of compounds form stable adducts. In behaving as strong Lewis acids, the boron halides act as acid catalysts for several important types of organic reactions (see Chapter 9). 

Hydroelectric turbines, virtual two-way SMA devices in, 22 349-350 Hydroentanglement, 17 507-508 Hydrofinishing, 15 216 Hydroflumethiazide, molecular formula and structure, 5 162t Hydrofluoric acid (HF), 4 579t. See also Hydrogen fluoride North American capacity of, 14 15t production of, 14 15 silicon solubility in, 22 491-492 in sodium fluoride manufacture, 22 825 solubility of boron halides in, 4 140t solubility of metal fluoroborates in, 4 152t... 

Orthopedic devices, 3 721-735 joint replacement, 3 727-735 Orthopedic marrow needles, 3 743-744 Orthophosphate (PO4), in soil, 11 112 Orthophosphates, 18 830-841 20 637 magnesium, 18 839 manufacture of, 18 853-855 Orthophosphate salts, 18 836 Orthophosphoric acid, 18 815, 817-826 condensation of, 18 826 properties of, 18 817-819 solubility of boron halides in, 4 140t orf/zo-phthalic resins, 20 101, 113 formulation of, 20 102 Orthorhombic crystal system, 8 114t Orthorhombic phosphorus pentoxide, 19 49 Orthorhombic structure, of ferroelectric crystals, 11 95, 96 Orthorhombic symmetry, 8 114t Orthosilicate monomers, in silicate glasses, 22 453... 

Bidentate boranes with an o-phenylene backbone constitute some of the simplest examples of polydentate Lewis acids with rigid backbones. They can be prepared by the reaction of boron halides with a 1,2-dimetallated benzene derivative. Thus, the reaction of 1,2-bis(chloromercurio)benzene (5) with boron trichloride affords 1,2-bis(dichloroboryl)benzene (6, Scheme 3). ... 

Alternatively, the compound can be prepared by heating boric oxide or boric acid with ammonium chloride or an alkali metal cyanide. Purified product can be obtained by high temperature reaction of boron halide with ammonia ... 

From Boron Halides. Using boron halides is not economically desirable because boron halides are made from boric acid. However, this method does provide a convenient laboratory synthesis of boric acid esters. The esterification of boron halides with alcohol is analogous to the classical conversion of carboxylic acid halides to carboxylic esters. Simple mixing of the reactants at room temperature or below in a solvent such as methylene chloride, chloroform, pentane, etc, yields hydrogen halide and the borate in high yield. 

Approach Q was used to synthesize a series of selective dopamine agonists (1997JMC1585, 1998USP5597832). Amines 270 with paraformaldehyde in an alkaline medium and then in an acidic medium produced benzothieno[3,2-c]qumolines 271, which were transformed into the target products 272 (as the corresponding salts) by deprotection under the action of boron halides. Compounds 272 possess the... 

By considering the energies of the interacting p orbitals, explain why tri-methylborate 2.103 is much less Lewis acidic than boron halides 2.104. 

The four boron trihalides are quite reactive and undergo similar reactions with a variety of other chemicals. Most of these reactions are based on the strong Lewis acidity of the halides. The boron trihalides form complexes with ethers (equation 16) and other Lewis bases based on N, S, P, and As atoms. 

Cyclohexylbenzene has been prepared by the hydrogenation of biphenyl and of cyclohexenylbenzene over nickel, by the reaction of cyclohexyl chloride or bromide with benzene in the presence of aluminum chloride, and by the addition of benzene to cyclohexene in the presence of aluminum chloride, sulfuric acid, or boron halides. ... 

It must be mentioned, however, that the order of activity of a series of initiators or coinitiators may differ depending on the identity of the other component, monomer, solvent, or the presence of competing reactions. For example, the activity of boron halides in isobutylene polymerization is observed to be BF3 > BCI3 > BBrs with water as the initiator, while the order of acidity is BBra > BCI3 > BF3. This is due to hydrolysis of the boron halides to inactive products increasing in the same order as their acidities. 

Further manifestations of stabilisation by the overlap of a filled with an unfilled orbital are the effects of X-substituents on an empty p orbital on a metal. Thus trimethylborate 2.6 is much less Lewis acidic than boron halides 2.7, because the oxygen lone pairs overlap more efficiently with the empty p orbital on the... 

Boric Acid.9 Hydrolysis of boron halides, hydrides, etc., affords the acid, B(OH)3, or its salts. The acid forms white, needle-like crystals in which B(OH)3 units are linked together by hydrogen bonds to form infinite layers of nearly hexagonal symmetry the layers are 3.18 A apart, which accounts for the pronounced basal cleavage. 

Group III.—Boron. It has only recently been conclusively shown that the stoicheiometry of the boric acid-tartaric acid complex is 1 1. Kinetic results from T-jump experiments indicate attack by an alcohol-oxygen lone-pair at the electron-deficient boron. Other references to reaction mechanisms of three-co-ordinate boron compounds deal with hydrolysis and methanolysis of boron halides, with disproportionation of boranes, and with Sh2 radical reactions of alkylboranes. ... 

The Suzuki coupling of arylboronic acids and aryl halides has proven to be a useful method for preparing C-aryl indoles. The indole can be used either as the halide component or as the boronic acid. 6-Bromo and 7-bromoindolc were coupled with arylboronic acids using Pd(PPh3)4[5]. No protection of the indole NH was necessary. 4-Thallated indoles couple with aryl and vinyl boronic acides in the presence of Pd(OAc)j[6]. Stille coupling between an aryl stannane and a haloindole is another option (Entry 5, Table 14.3). 

The main chemical products produced from these minerals are (a) boron oxides, boric acid and borates, (b) esters of boric acid, (c) refractory boron compounds (borides, eu .), (d) boron halides, (e) boranes and carbaboranes and (f) organoboranes. The main industrial and domestic uses of boron compounds in Europe (USA in parentheses) are ... 

At about die same time, die application of the Suzuki coupling, the crosscoupling of boronic acids widi aryl-alkenyl halides in die presence of a base and a catalytic amount of palladium catalyst (Scheme 9.12),16 for step-growth polymerization also appeared. Schliiter et al. reported die synthesis of soluble poly(para-phenylene)s by using the Suzuki coupling condition in 1989 (Scheme 9.13).17 Because aryl-alkenyl boronic acids are readily available and moisture stable, the Suzuki coupling became one of die most commonly used mediods for die synthesis of a variety of polymers.18... 

The boron halides are made either by direct reaction of the elements at a high temperature or from boron oxide. The most important is boron trifluoride, BF, an industrial catalyst produced by the reaction between boron oxide, calcium fluoride, and sulfuric acid ... 

The Si-O-B fragment can be formed from different starting materials that generally include chlorosilanes or silanols and boron halides or boric acid derivatives. For the preparation of the cyclic six-, eight-, ten- and twelve-membered borasiloxanes 83-89 four synthetic approaches are known so far, starting from either... 

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