Alkyl borates

The use of these is described in the patent literature, but again they seem to offer no advantage over the less expensive fatty acids [38]. 

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Alkyl borates. By heating boric acid with excess of the alcohol the water formed in the reaction is removed by fractional distillation as an azeo tropic mixture with the alcohoi, for example ... 

Secondary alcohols (C q—for surfactant iatermediates are produced by hydrolysis of secondary alkyl borate or boroxiae esters formed when paraffin hydrocarbons are air-oxidized ia the presence of boric acid [10043-35-3] (19,20). Union Carbide Corporation operated a plant ia the United States from 1964 until 1977. A plant built by Nippon Shokubai (Japan Catalytic Chemical) ia 1972 ia Kawasaki, Japan was expanded to 30,000 t/yr capacity ia 1980 (20). The process has been operated iadustriaHy ia the USSR siace 1959 (21). Also, predominantiy primary alcohols are produced ia large volumes ia 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 ia the temperature range 150—180°C at a paraffin conversion generally below 20% to a mixture of trialkyl borate, (RO)2B, and trialkyl boroxiae, (ROBO). 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). 

The selectivity to alcohol in LPO may be significantly increased when boric acid, meta-hotic acid, or boric anhydride is present in stoichiometric amounts (2). The boron compounds appear to convert alkyUiydroperoxides to alkyl borates and may also intercept alkylperoxy radicals, converting them to alkylperoxyboron compounds these are later converted to alkyl borates. The alkyl borates are resistant to further oxidation they are hydrolyzed to recover alcohols. 

Steric factors are important ia transesterification reactions. With a given alcohol, primary alkyl borates react at a rate too fast to measure, secondary alkyl borates react at measurable rates, and tert-huty borate reacts very slowly. 

Procedures for shipping boric acid esters depend on the particular compound. Aryl borates produce phenols when in contact with water and are therefore subject to shipping regulations governing such materials and must carry a Corrosive Chemical label. Lower alkyl borates are flammable, flash points of methyl, ethyl, and butyl borates are 0, 32, and 94°C, respectively, and must be stored in approved areas. Other compounds are not hazardous, and may be shipped or stored in any convenient manner. Because borate esters are susceptible to hydrolysis, the more sensitive compounds should be stored and transferred in an inert atmosphere, such as nitrogen. 

Alizarin, 981 Alkyd resins, 1018 Alkyl borates, 302 Alkyl bromides, 270 Alkyl chlorides, 270 Alkyl fluorides, 272 Alkyl halides, 270... 

Selectivity of alcohol formation can be substantially increased by carrying out the autoxidation in the presence of a stoichiometric quantity of boric acid that reacts with the intermediate hydroperoxide to form alkyl borate. This observation gained practical importance in the commercial oxidation of alkanes (see Section 9.5.1). 

The constitution of the fairly strong complex acids formed from alkyl borates and alcohol and of esters of boric acid with polyalcohols with hydroxyl groups in the cis position (Boese-ken) must be similar ... 

Alkyl borates, boron alkyls, and boron halides have all been used to polymerize diazoalkanes. Several authors have claimed that macrozwitterions are formed56 58. ... 

Gharnley, Skinner, and Smith 4 have deduced the average bond dissociation energy D(B - OR) in the esters of boric acid B(OR)3. The heats of formation of four alkyl borates were determined from their heats of hydrolysis. From these, together with some subsidiary data, they found the following values of 5(B-0) in R3BO3 5(B-O) =5(RO-H) x kcal, where x=4 l, 4 3, 5 O5... 

However, the application of these classical procedures for 1-alkenylboronic acid or ester synthesis may suffer from the formation of small amounts of the opposite stereoisomers, or from bis-alkenylation leading to the boronic acid derivatives. Also, formation of trialkylboranes may occur. A recent useful variant utilizes organolithium reagents and triisopropyl borate, followed by acidification with HCl to give directly alkyl-, aryl-, 1-alkynyl-, and 1-alkenylboronic esters in high yields, often over 90% (Scheme 2-6) [27]. Triisopropyl borate was shown to be the best of the available alkyl borates to avoid multiple alkylation of the borates. 

Radicals can be generated at the anode by oxidation of carbanions, alkyl borates, alkoxides, and carboxylates (see Chapter 22, Sec. V) and at the cathode by reduction of protonated carbonyl compounds or onium salts (see Chapter 10). Thereby, a wide choice of different radical structures can be mildly and simply obtained from readily available precursors. These radicals are especially suited for coupling and additive coupling reac-... 

In the oxidation stage of hydroboration-oxidation, alkylboranes are converted into alkyl borates, which are hydrolyzed to alcohols. It has b n suggested that the formation of the borates involves the reagent HOO. ... 

Arylboronic acids.Aryl halides, alkyl borates, and magnesium in THF react under ultrasonication. Hydrolysis of the reaction mixtures provides arylboronic acids. 

X-(Trifluoromethyl)ethenyl boronic acid (72) was conveniently prepared from the reaction of readily available 2-bromotrifluoropropene with alkyl borate and magnesium in one-pot. The Suzuki coupling of 2-amino-3-methoxy-5-bromopyrazine (71) with boronic acid 72 provided styrene derivative, 73 in excellent yield [43]. 

The transmetallation of (R 0)3B with R—M (M=Li, MgX) at low temperature (usually at -78 C) proceeds by initial formation of a relatively unstable teracoordinat-ed complex [RB(OR0i]M, which is in equilibrium with RB(OR )2 and R OM. If the monoalkyl(trialkoxy)borate can be cleanly formed, and if equilibrium favors this complex, the boronic ester will be formed selectively. Otherwise, successive steps will give rise to the di-, tri-, or tetraalkylborates (eq (7)). Triisopropyl borate is shown to be the best of the available alkyl borates to prevent such side reactions thus allowing the syntheses of a number of alkyl, aryl. 1-alkenyl [9]. and 1-alkynylboronates [10] in high yields, often over 90% (eq (8)). 

Light induced electron transfer from an amine to an excited arene leading to a contact radical ion pair is proposed to account for the products observed when 9,10-dicyanoanthracene is irradiated in wet benzene in the presence of an a-aminoketone. The non-polar solvent maintains the proximity of the radical ion pair which would normally then undergo non-productive back electron transfer however, in this case the ion pair reacts, ultimately to furnish 9,10-dihydro-9,10-dicyanoanthracene along with products of fragmentation of the a-aminoketone. Alkyl borate and borohydride salts can also serve as electron donors in the photoreduction of aryl cyanides and aryl halides and an abstract of a report on this topic has appeared. ... 

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