Trialkyl borates

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). 

Arylboronic acids have traditionally been prepared via the addition of an organomagnesium or organolithium intermediate to a trialkyl borate. Subsequent acidic hydrolysis produces the free arylboronic acid. This limits the type of arylboronic acids one can access via this method, as many functional groups are not compatible with the conditions necessary to generate the required organometallic species, or these species may not be stable intermediates. 

In recent years, a variety of aryl boronic acids are commercially available, albeit in some cases they may be expensive for large scale purposes. During our work in the mid-1990 s boronic acid (II) was not commercially available and so two different protocols were used to prepare this acid. The first approach involved the transmetallation with n-butyl lithium of aryl bromide (I) and trapping the lithio species generated with trialkyl borate followed by an acid quench. Aryl bromide (I) is easily prepared by reaction of o-bromobenzenesulfonyl chloride with 2-propanol in the presence of pyridine as a base. The second approach was a directed metallation of isopropyl ester of benzene sulfonic acid (VII), to generate the same lithio species and reaction with trialkyl borate. The sulfonyl ester is prepared by reaction of 2-propanol with benzenesulfonyl chloride. From a long-term strategy the latter approach is... 

An alternative approach to reduce the levels of impurity (VII) would be to have a "transient" existence of the lithio species, so that it reacts instantaneously with trialkyl borate to form the aryl boronate, prior to being quenched by any extraneous proton source to form (VII). Thus, the preparation of boronic acid (II) was improved by changing the order of the reagents. The slow addition of n-butvl lithium also controls the exotherm of the reaction. There was no reaction observed between n-butyl lithium and triisopropyl borate (to form any butyl boronic acid), nor was there any formation of 2-butyl derivative of (VII) formed by reaction between butyl bromide and the lithio species. The reaction is veiy fast and as soon as the addition of n-butyl lithium is completed the reaction is finished. This indicates a rapid transmetallation and instantaneous boronation of the lithio species. The reaction is very much a... 

The alkyl migration takes place with retention of configuration of the alkyl group which leads to the formation of a trialkyl borate, an ester, B(OR)3. 

Cragg and Weston (11) in their review of the mass spectra of boron compounds have shown the great amount of work being done with cyclic boron compounds. This trend has continued. Straight-chain trialkyl-borates fragment by C—0 cleavage reactions accompanied by hydrogen transfers. 

The C-2 selective nucleophilic substitution reactions of 2,3-epoxy alcohols mediated by trialkyl borates the first endo-mode epoxideopening reaction through an intramolecular metal chelate. Org. Lett. 2003, 5, 1789-1791. 381... 

Menthol catalyses the enantioselective reduction of ketones by NaBH4 in diglyme proton- and auto-catalytic possibilities are investigated, and trialkyl borate species generated during the reaction may also play a role in catalysis.302... 

Trialkyl borates, generated in situ from sodium borohydride and an alcohol, catalyse reduction of ketones with borohydride. With (-)-menthol as the initiating alcohol, the... 

Borate esters of fluorinated alcohols, simply prepared by the free-radical addition of trialkyl borates to fluorinated alkenes, are cleaved by chlorine to yield fluorinated acid chlorides (equation 141)949. 

Arylboronate esters are made by a two-step process First, we convert the aryl halide to the aryllithium compound (Chapter 10). Addition of a trialkyl borate (often trimethyl borate) allows the organolithium compound to form a carbon-boron bond and expel an alkoxide group. 

So far we have shown all reactions taking place on the monoalkyl borane. In fact, these compounds are unstable and most hydroborations actually occur via the trialkyl borane. Three molecules of alkene add to the boron atom three oxidations and three migrations transfer three alkyl groups (R = 2-methylcyclopentyl) from boron to oxygen to give the relatively stable trialkyl borate B(OR)3, which is hydrolysed to give the products. 

All the reactions of the hydrocyanation process are catalyzed by zero-valent nickel phosphine or phosphite complexes. These are used in combination with Lewis acid promoters such as zinc chloride, trialkyl boron compounds, or trialkyl borate ester. The ability of the precatalyst to undergo ligand dissociation... 

The traditional synthesis of organoboron compounds from organic halides is based on the reaction of trialkyl borates with Grignard or lithium reagents. However, the cross-coupling reaction of diboron solves the difficulties associated with the use of Mg/Li compounds. The cross-coupling reaction of diborons... 

Oxidation of trialkyl borates and of trialkoxyboroxines. Trialkyl borates, B(0R)3, prepared by reaction of primary and secondary alcohols with borane-dimethyl sulfide, are oxidized by PCC to aldehydes and ketones in good yield. This indirect oxidation of alcohols does not involve formation of water, which could be detrimental in some cases. Of even greater interest, carboxylic acids can be converted into aldehydes by reaction with borane-dimethyl sulfide to form a tri-alkoxyboroxine followed by oxidation with PCC (equation I). 

Trialkyl borates, 398 Tri t-butyltodomethyltin, 475-476 Tri-f-butylsilyl perchlorate, 78 Tri- -butyltin hydride, 476-477 Tributyltin hydride-Silica gel, 477 Tri- U-carbonylhexacarbonyldiiron, 477-478, 519... 

The most important of the simple trialkylboranes is triethylborane (TEB). It has been produced commercially since the 1960s. At ambient temperatures, triethylborane is a clear, colorless liquid (bp 95 °C) that is pyrophoric, and burns with a green flame (3). However, unlike most aluminum and magnesium alkyls, TEB is monomeric and is virtually unreactive with water. It is produced commercially by reaction of diborane (B H ) with ethylene or by alkylation of a trialkyl borate by triethylaluminum as illustrated in eq 4.18 and 4.19, respectively. 

Crotylboronic esters (2-butenylboronates) are thermally stable and isolable compounds at room temperature and undergo nearly quantitative additions to aldehydes. The required crotylboronic esters may be prepared by reaction of the crotyl potassium reagents derived from cis- or trans-2-butene with n-butyllithium and potassium tert-butoxide followed by addition of the appropriate trialkyl borates. ... 

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