Boron acetate

The zinc salts have been widely used for this purpose, chloride, ui. i i. in. i6 , JS7 . M. 2 perchlorate, nitrate,thin <0 anate, trifiuoroaeetate, " fluophosphate, fluoborate, as well as the boron compounds boric acid,boron acetate, borate esters. boiCHi trilluorido >m or its ether com plex M . . T. 151. is7.i5s.SM.Mte and metal fluoboratee. and riic alominum compounds aluminum chlwide alone< > or in a mixture with zinc ealte ), alumina, and alununum silicate. . 

Simple sharing of one oxygen atom by two B03 units would give [02B0B02]4 this so-called pyroborate anion has been shown to exist in Co2B2Os. Also, the compound referred to as boron acetate, prepared by the reaction... 

Yan and covrorkers developed titanium enolate acetate aldol reactions as an extension of their boron acetate enolate methodology [13, 14]. Good yields and diastereoselectivity vere reported vhen using camphor-derived N-acyloxazolidinethione 19 (Scheme 2.3, Table 2.4, entries 1-7, and Figure 2.1). The high selectivities vere attributed to additional chelation afforded by the thiocarbonyl of the chiral auxiliary in transition state assembly 20, sho vn in Scheme 2.3. The corresponding camphor-derived oxazolidinone acetate imide provided no stereocontrol, supporting the chelation control hypothesis. 

A mixture of an acid anhydride and a ketone is saturated with boron trifluoride this is followed by treatment with aqueous sodium acetate. The quantity of boron trifluoride absorbed usually amounts to 100 mol per cent, (based on total mola of ketone and anhydride). Catalytic amounts of the reagent do not give satisfactory results. This is in line with the observation that the p diketone is produced in the reaction mixture as the boron difluoride complex, some of which have been isolated. A reasonable mechanism of the reaction postulates the conversion of the anhydride into a carbonium ion, such as (I) the ketone into an enol type of complex, such as (II) followed by condensation of (I) and (II) to yield the boron difluoride complex of the p diketone (III) ... 

Acylation may also be effected with the acetic acid - boron trifluoride complexes BF3.CH3COOH and BF3.2CH3COOH. 

Boron trifluoride method. Fit a 1 litre three-necked flask with a gas inlet tube, a gas outlet leading to an alkali trap (compare Fig. 11,8, laori for the unabsorbed boron trifluoride), and stopper the third neck. Place 68 g. (73 ml.) of pure, anhydrous acetone (1) and 255 g. (236 ml.) of A.R. acetic anhydride in the flask and cool in a freezing mixture of ice and salt. Connect the gas inlet tube through an empty wash bottle to a cylinder of commercial boron trifluoride (2), and bubble the gas through the reaction mixture at such a rate that 250 g. is absorb in about 5 hours (2 bubbles per second). Pour the reaction mixture into a solution... 

The solid appears to be a mixture of the complexes CH,COOH.BF, and 2CH COOH.BF,. The latter appears to be a liquid and is alone soluble in ethylene dichloride the former is a solid. The solid moiioocetic acid complex is obtained by saturating an ethylene dichloride solution of acetic acid with boron trifluoride, filtering and washing the precipitate with the solvent it is hygroscopic and should be protected from moisture. It may be used as required 0-75 mol is employed with 0-26 mol of ketone and 0 6 mol of anhydride. 

Nitric oxide Aluminum, BaO, boron, carbon disulflde, chromium, many chlorinated hydrocarbons, fluorine, hydrocarbons, ozone, phosphine, phosphorus, hydrazine, acetic anhydride, ammonia, chloroform, Fe, K, Mg, Mn, Na, sulfur... 

FLUORINECOMPOUNDS,INORGANIC - BORON - FLUOROBORIC ACID] (Vol 11) Copper(II) acetate [142-71-2]... 

Acetic anhydride adds to acetaldehyde in the presence of dilute acid to form ethyUdene diacetate [542-10-9], boron fluoride also catalyzes the reaction (78). Ethyfldene diacetate decomposes to the anhydride and aldehyde at temperatures of 220—268°C and initial pressures of 14.6—21.3 kPa (110—160 mm Hg) (79), or upon heating to 150°C in the presence of a zinc chloride catalyst (80). Acetone (qv) [67-64-1] has been prepared in 90% yield by heating an aqueous solution of acetaldehyde to 410°C in the presence of a catalyst (81). Active methylene groups condense acetaldehyde. The reaction of isobutfyene/715-11-7] and aqueous solutions of acetaldehyde in the presence of 1—2% sulfuric acid yields alkyl-y -dioxanes 2,4,4,6-tetramethyl-y -dioxane [5182-37-6] is produced in yields up to 90% (82). 

The iodination reaction can also be conducted with iodine monochloride in the presence of sodium acetate (240) or iodine in the presence of water or methanolic sodium acetate (241). Under these mild conditions functionalized alkenes can be transformed into the corresponding iodides. AppHcation of B-alkyl-9-BBN derivatives in the chlorination and dark bromination reactions allows better utilization of alkyl groups (235,242). An indirect stereoselective procedure for the conversion of alkynes into (H)-1-ha1o-1-alkenes is based on the mercuration reaction of boronic acids followed by in situ bromination or iodination of the intermediate mercuric salts (243). 

Mercuration. Mercury(II) salts react with alkyl-, alkenyl-, and arylboranes to yield organomercurials, which are usehil synthetic intermediates (263). For example, dialkyhnercury and alkyhnercury acetates can be prepared from primary trialkylboranes by treatment with mercury(II) chloride in the presence of sodium hydroxide or with mercury(II) acetate in tetrahydrofuran (3,264). Mercuration of 3 -alkylboranes is sluggish and requires prolonged heating. Alkenyl groups are transferred from boron to mercury with retention of configuration (243,265). 

Lead borate moaohydrate [14720-53-7] (lead metaborate), Pb(B02)2 H20, mol wt 310.82, d = 5.6g/cm (anhydrous) is a white crystalline powder. The metaborate loses water of crystallization at 160°C and melts at 500°C. It is iasoluble ia water and alkaHes, but readily soluble ia nitric and hot acetic acid. Lead metaborate may be produced by a fusion of boric acid with lead carbonate or litharge. It also may be formed as a precipitate when a concentrated solution of lead nitrate is mixed with an excess of borax. The oxides of lead and boron are miscible and form clear lead-borate glasses in the range of 21 to 73 mol % PbO. 

Conversion to acetates, trifluoroacetates (178), butyl boronates (179) trimethylsilyl derivatives, or cycHc acetals offers a means both for identifying individual compounds and for separating mixtures of polyols, chiefly by gas—Hquid chromatography (glc). Thus, sorbitol in bakery products is converted to the hexaacetate, separated, and determined by glc using a flame ionisation detector (180) aqueous solutions of sorbitol and mannitol are similarly separated and determined (181). Sorbitol may be identified by formation of its monobensylidene derivative (182) and mannitol by conversion to its hexaacetate (183). 

Coumarone—Indene Kesins. These should be called polyindene resins (17) (see Hydrocarbon resins). They are derived from a close-cut fraction of a coke-oven naphtha free of tar acids and bases. This feedstock, distilling between 178 and 190°C and containing a minimum of 30% indene, is warmed to 35°C and polymeri2ed by a dding 0.7—0.8% of the phenol or acetic acid complex of boron trifluoride as catalyst. With the phenol complex, tar acids need not be completely removed and the yield is better. The reaction is exothermic and the temperature is kept below 120°C. When the reaction is complete, the catalyst is decomposed by using a hot concentrated solution of sodium carbonate. Unreacted naphtha is removed, first with Hve steam and then by vacuum distillation to leave an amber-colored resin. It is poured into trays, allowed to cool, and broken up for sale. 

Although all four tocopherols have been synthesized as their all-rac forms, the commercially significant form of tocopherol is i7//-n7i a-tocopheryl acetate. The commercial processes ia use are based on the work reported by several groups ia 1938 (15—17). These processes utilize a Friedel-Crafts-type condensation of 2,3,5-trimethylhydroquinone with either phytol (16), a phytyl haUde (7,16,17), or phytadiene (7). The principal synthesis (Fig. 3) ia current commercial use iavolves condensation of 2,3,5-trimethylhydroquiQone (13) with synthetic isophytol (14) ia an iaert solvent, such as benzene or hexane, with an acid catalyst, such as ziac chloride, boron trifluoride, or orthoboric acid/oxaUc acid (7,8,18) to give the all-rac-acetate ester (15b) by reaction with acetic anhydride. Purification of tocopheryl acetate is readily accompHshed by high vacuum molecular distillation and rectification (<1 mm Hg) to achieve the required USP standard. 

In the case of ethylene, it is necessary to use high temperatures and pressures as well as active catalyst to effect esterification (82). Yields of 40—50% based on ethylene were obtained with boron trifluoride—hydrogen fluoride mixtures as catalysts at 150°C. 2-Butene under pressure at 115—120°C with an excess of glacial acetic acid containing 10% H2SO4 gave as much as a 60% yield of I -butyl acetate (83). 

The vapor-phase esterification of ethanol has also been studied extensively (363,364), but it is not used commercially. The reaction can be catalyzed by siUca gel (365,366), thoria on siUca or alumina (367), zirconium dioxide (368), and by xerogels and aerogels (369). Above 300°C the dehydration of ethanol becomes appreciable. Ethyl acetate can also be produced from acetaldehyde by the Tischenko reaction (370—372) using an aluminum alkoxide catalyst and, with some difficulty, by the boron trifluoride-catalyzed direct esterification of ethylene with organic acids (373). 

Dichlorodicyanoquinone (DDQ), CH2CI2, H2O, 40 min, it, 84-93% yield.This method does not cleave simple benzyl ethers. This method was found effective in the presence of a boronate. The following groups are stable to these conditions ketones, epoxides, alkenes, acetonides, to-sylates, MOM ethers, THP ethers, acetates, benzyloxymethyl (BOM) ethers, and TBDMS ethers. 

Cyclic carbonates and cyclic boronates have also found considerable use as protective groups. In contrast to most acetals and ketals the carbonates are cleaved with strong base and sterically unencumbered boronates are readily cleaved by water. 

The monothioacetal is also stable to 12 N hydrochloric acid in acetone (used to remove an TV-triphenylmethyl group) and to hydrazine hydrate in refluxing ethanol (used to cleave an A -phthaloyl group). It is cleaved by boron trifluoride etherate in acetic acid, silver nitrate in ethanol, and tiifluoroacetic acid. The monothioacetal is oxidized to a disulfide by thiocyanogen, (SCN)2- ... 

BBr3, CH2CI2, -10°, 1 h -> 25°, 2 h, 80-100% yield. Benzyl carbamates of larger peptides can be cleaved by boron tribromide in trifluoro-acetic acid, since the peptides are more soluble in acid than in methylene chloride. ... 

Selectivity in formation of protective groups may also be achieved by a proper choice of reaction conditions and catalyst. Thus formation of the 3-monothioketal from 3,6-diketones is achieved by dilution of the ethane-dithiol-boron trifluoride reaction mixture with acetic acid. 3-Monocyanohydrins are obtained in good yield from 3,20-diketo-(5a)-pregnanes by diluting the exchange reaction with ethanol. Similarly, dilution of the... 

Thioketals are readily formed by acid-catalyzed reaction with ethane-dithiol. Selective thioketal formation is achieved at C-3 in the presence of a 6-ketone by carrying out the boron trifluoride catalyzed reaction in diluted medium. Selective protection of the 3-carbonyl group as a thioketal has been effected in high yield with A" -3,17-diketones, A" -3,20-diketones and A" -3,l 1,17-triones in acetic acid at room temperature in the presence of p-toluenesulfonic acid. In the case of thioketals the double bond remains in the 4,5-position. This result is attributed to the greater nucleophilicity of sulfur as compared to oxygen, which promotes closure of intermediate (66) to the protonated cyclic mercaptal (67) rather than elimination to the 3,5-diene [cf. ketal (70) via intermediates (68) and (69)]." " ... 

Thioketals are prepared efficiently from dithiols, but not from monothiols. However, 6-ketones do not react with ethanedithiol/boron trifluoride in the presence of a diluent such as acetic acid. 

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