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Boroxines acids

The general formula for boric acid esters is B(OR)2. The lower molecular weight esters such as methyl, ethyl, and phenyl are most commonly referred to as methyl borate [121 -43-7] ethyl borate [130-46-9J, and phenyl borate [1095-03-0] respectively. Some of the most common boric acid esters used in industrial appHcations are Hsted in Table 1. The nomenclature in the boric acid ester series can be confusing. The lUPAC committee on boron chemistry has suggested using trialkoxy- and triaryloxyboranes (5) for compounds usually referred to as boric acid esters, trialkyl (or aryl) borates, trialkyl (or aryl) orthoborates, alkyl (or aryl) borates, alkyl (or aryl) orthoborates, and in the older Hterature as boron alkoxides and aryloxides. CycHc boric acid esters, which are trimeric derivatives of metaboric acid (HBO2), are known as boroxines (1). [Pg.213]

Hydrocarbon Oxidation. The oxidation of hydrocarbons (qv) and hydrocarbon derivatives can be significantly altered by boron compounds. Several large-scale commercial processes, such as the oxidation of cyclohexane to a cyclohexanol—cyclohexanone mixture in nylon manufacture, are based on boron compounds (see Cylcohexanoland cyclohexanone Eibers, polyamide). A number of patents have been issued on the use of borate esters and boroxines in hydrocarbon oxidation reactions, but commercial processes apparently use boric acid as the preferred boron source. The Hterature in this field has been covered through 1967 (47). Since that time the Hterature consists of foreign patents, but no significant appHcations have been reported for borate esters. [Pg.216]

Trimethyl boroxine [823-96-1] M 125.5, b 80"/742mm, 79.3"/755mm, d 0.902. Possible impurity is methylboronic acid. If present then add a few drops of cone H2SO4 and distil immediately, then... [Pg.488]

Boronic acids readily dehydrate at moderate temperatures (or over P4O10 at room temperature) to give trimeric cyclic anhydrides known as trialkyl(aryl)boroxines ... [Pg.207]

B. 3-(4,4,5,5-Tetramethyl-[l,3,2]dioxaborolan-2-yl)pyridine. A 250-mL, one-necked, round-bottomed flask equipped with a magnetic stirbar and a Dean-Stark trap fitted with a condenser capped with a nitrogen inlet adaptor is charged with tris(3-pyridyl)boroxin-0.85 H20 (3.0 g, 9.1 mmol), pinacol (4.07 g, 34.4 mmol) (Note 6), and 120 mL of toluene. The solution is heated at reflux for 2.5 hr in a 120°C oil bath. The reaction is complete when the mixture changes from cloudy-white to clear. The solution is then concentrated under reduced pressure on a rotary evaporator to afford a solid residue. This solid is suspended in 15 mL of cyclohexane (Note 7) and the slurry is heated to 85°C, stirred at this temperature for 30 min, and then allowed to cool slowly to room temperature. The slurry is filtered, rinsed twice using the mother liquors, washed with 3 mL of cyclohexane, and dried under vacuum to afford 4.59 g (82%) of 3-pyridylboronic acid pinacol ester as a white solid (Note 8). [Pg.46]

Boronic acids (69 and 70) (Fig. 45) with more than one boronic acid functionality are known to form a polymer system on thermolysis through the elimination of water.93 Specifically, they form a boroxine (a boron ring system) glass that could lead to high char formation on burning. Tour and co-workers have reported the synthesis of several aromatic boronic acids and the preparation of their blends with acrylonitrile-butadiene-styrene (ABS) and polycarbonate (PC) resins. When the materials were tested for bum resistance using the UL-94 flame test, the bum times for the ABS samples were found to exceed 5 minutes, thereby showing unusual resistance to consumption by fire.94... [Pg.50]

Figure 45 Boronic acids (69 and 70) with multiple boronic acid functionalities that form boroxine ring systems on thermolysis through the elimination of water. (Adapted from ref. 93.)... Figure 45 Boronic acids (69 and 70) with multiple boronic acid functionalities that form boroxine ring systems on thermolysis through the elimination of water. (Adapted from ref. 93.)...
Rhodium(i) complexes are excellent catalysts for the 1,4-addition of aryl- or 1-alkenylboron, -silicon, and -tin compounds to a,/3-unsaturated carbonyl compounds. In contrast, there are few reports on the palladium(n) complex-catalyzed 1,4-addition to enones126,126a for the easy formation of C-bound enolate, which will result in /3-hydride elimination product of Heck reaction. Previously, Cacchi et al. described the palladium(n)-catalyzed Michael addition of ArHgCl or SnAr4 to enones in acidic water.127 Recently, Miyaura and co-workers reported the 1,4-addition of arylboronic acids and boroxines to a,/3-unsaturated carbonyl compounds. A cationic palladium(n) complex [Pd(dppe)(PhCN)2](SbF6)2 was found to be an excellent catalyst for this reaction (dppe = l,2-bis(diphenyl-phosphine)ethane Scheme 42).128... [Pg.389]

Nitrone derivatives of 2-fonny phenylboronie acid have been prepared, and these exist in cyclic, trisubstituted boroxin fonn (35a-d) <83JOM247>. Interestingly, treatment with a 1,2-dio converts them into monomers with a rather unique 1,3-zwitterion structure (36a-d),... [Pg.11]

Cyclotriboroxanes (RBO)3 (also known as boroxines) are formally anhydrides of the corresponding boronic acids RB(OH)2 only mild heating is required to convert these dibasic acids into a wide range of cyclic trimeric anhydrides [eqn (9.18)]. This dehydration process can be adapted for the synthesis of B3O3 rings with different aryl groups on the boron atoms by using two or more arylboronic acids in the appropriate stoichiometric ratio. [Pg.143]

Boroxines result from the condensation of boronic acids. RBfOH). The cyclic Irimeric anhydride of methylboronic acid is (IVfeBO),. Give a balanced equation for the reaction of (MeBO)j with water (See Brown, H. C. Cole, T. E. Organometallics 1985.4. 816.)... [Pg.946]

Two different approaches can be followed to prepare and use the catalyst. The first is to prepare it in situ by mixing (R)- or (S)-diphenylprolinol (DPP) (4) and a borane complex (Scheme 16.2). This route is advantageous because there is no need to use boronic acids (or boroxines) and to remove water to form the catalyst. Another possible way is to use preformed catalysts, some of which are commercially available from suppliers such as Callery. [Pg.307]

The oxazaborolidine is finally made by heating diphenylprolinol (4) under reflux with a suitable alkyl(aryl)boronic acid or, better, with the corresponding boroxine in toluene in the presence of molecular sieves—the water can also be removed by azeotropic distillation. According to the literature, methyl-oxazaborolidine (Me-CBS) can be either distilled or recrystallized. The key point is that the catalyst must be free from any trace of water or alkyl(aryl)boronic acid because those impurities decrease enantioselection. [Pg.309]

SCHEME 9.2 Formation of boroxine frompara-diboronic acid. [Pg.227]

A second peptide coupling employing 2-pyrazine carboxylic acid (24) and TBTU affords 25. Finally the boronic ester moiety is removed under acidic conditions using isobutyl boronic acid. This regenerates pinanediol boronic ester 16, which can be used in another batch run of the process. Crystallization from ethyl acetate gives bortezomib in its anhydride (boroxine) form 26. The overall yield for the route is 35% with a typical purity of > 99% w/w. [Pg.107]

Fig. 9 (a) Reversible synthesis of a bisiminoboronate-guanosine derivative from guanosine and a bisiminoboronic acid, (b) Dynamic polymeric networks based on reversible boroxine formation, (c) Formation of a macrocycle in a [4 + 4 + 2] condensation via simultaneous reversible formation of imine bonds and boronic esters... [Pg.308]

Boronic acids readily undergo self-condensation to give cyclic anhydrides, and either these trisubstituted boroxins (11), or the acids themselves, react spontaneously, but not necessarily completely, in solution, with suitable diols, to give cyclic boronates 12 (see Scheme 1),... [Pg.37]

Heating boronic acids or treatment with P4Oi0 at room temperature results in loss of H20 to form boroxines, a much-studied class of cyclic organoboranes. [Pg.172]

Secondary alcohols (C1Q—C14) for surfactant intermediates are produced by hydrolysis of secondary alkyl borate or boroxine esters formed when paraffin hydrocarbons are air-oxidized in the presence of boric acid [10043-35-3] (19,20). Union Carbide Corporation operated a plant in the United States from 1964 until 1977. A plant built by Nippon Shokubai (Japan Catalytic Chemical) in 1972 in Kawasaki, Japan was expanded to 30,000 t/yr capacity in 1980 (20). The process has been operated industrially in the USSR since 1959 (21). Also, predominantly primary alcohols are produced in large volumes in the USSR by reduction of fatty acids, or their methyl esters, from permanganate-catalyzed air oxidation of paraffin hydrocarbons (22). The paraffin oxidation is carried out in the temperature range 150—180°C at a paraffin conversion generally below 20% to a mixture of trialkyl borate, (RO)3B, and trialkyl boroxine, (ROBO)3. Unconverted paraffin is separated from the product mixture by flash distillation. After hydrolysis of residual borate esters, the boric acid is recovered for recycle and the alcohols are purified by washing and distillation (19,20). [Pg.460]

Ebelman and Bouquet prepared the first examples of boric acid esters in 1846 from boron trichloride and alcohols. Literature reviews of this subject are available. B The general class of boric acid esters includes the more common orthoboric acid based trialkoxy- and triaryloxyboranes, B(0R)3 (1), and also the cyclic boroxins, (ROBO)3, which are based on metaboric acid (2). The boranes can be simple trialkoxyboranes, cyclic diol derivatives, or more complex trigonal and tetrahedral derivatives of polyhydric alcohols. Nomenclature is confusing in boric acid ester chemistry. Many trialkoxy- and triaryloxyboranes such as methyl, ethyl, and phenyl are commonly referred to simply as methyl, ethyl, and phenyl borates. The lUPAC boron nomenclature committee has recommended the use of trialkoxy- and triaryloxyboranes for these compounds, but they are referred to in the literature as boric acid esters, trialkoxy and triaryloxy borates, trialkyl and triaryl borates or orthoborates, and boron alkoxides and aryloxides. The lUPAC nomenclature will be used in this review except for relatively common compounds such as methyl borate. Boroxins are also referred to as metaborates and more commonly as boroxines. Boroxin is preferred by the lUPAC nomenclature committee and will be used in this review. [Pg.433]

Example 5.5. Oxidation of paraffins to secondary alcohols. Alcohols can be produced by oxidation of paraffins with air or oxygen at moderate temperatures (typically 120 to 180° C) in the presence of boric-acid esters or boroxines [16-18], These intercept the alkyl peroxide, the first oxidation product, preventing it from generating free radicals that would cause further degradation including scission of carbon-carbon bonds and produce aldehydes, ketones, and acids (see also Section 9.6.2). The peroxy borates so formed then are hydrolyzed to yield the alcohol. The carbon atoms at the chain ends are largely immune to oxidation, so the product consists predominantly of isomeric secondary alcohols. The reaction does not stop at... [Pg.108]

The reaction is not "clean." Hydroperoxide decomposition yields aldehyde and ketone. Moreover, at other than quite low conversion, further oxidation leads to scission of carbon-carbon bonds and formation of acids [63], However, if a boric-acid ester or boroxine is added, secondary alcohol can be obtained in good yield (see Example 5.5 in Section 5.4). [Pg.285]


See other pages where Boroxines acids is mentioned: [Pg.45]    [Pg.46]    [Pg.47]    [Pg.20]    [Pg.652]    [Pg.65]    [Pg.138]    [Pg.72]    [Pg.86]    [Pg.638]    [Pg.226]    [Pg.226]    [Pg.100]    [Pg.307]    [Pg.307]    [Pg.39]    [Pg.273]    [Pg.423]    [Pg.423]    [Pg.424]    [Pg.434]    [Pg.435]    [Pg.102]   
See also in sourсe #XX -- [ Pg.15 ]




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