Boron fluoride, complex from

Acetylcyclohexanone. Method A. Place a mixture of 24-6 g. of cyclohexanone (regenerated from the bisulphite compound) and 61 g. (47 5 ml.) of A.R. acetic anhydride in a 500 ml. three-necked flask, fitted with an efficient sealed stirrer, a gas inlet tube reaching to within 1-2 cm. of the surface of the liquid combined with a thermometer immersed in the liquid (compare Fig. II, 7, 12, 6), and (in the third neck) a gas outlet tube leading to an alkali or water trap (Fig. II, 8, 1). Immerse the flask in a bath of Dry Ice - acetone, stir the mixture vigorously and pass commercial boron trifluoride (via an empty wash bottle and then through 95 per cent, sulphuric acid) as fast as possible (10-20 minutes) until the mixture, kept at 0-10°, is saturated (copious evolution of white fumes when the outlet tube is disconnected from the trap). Replace the Dry Ice-acetone bath by an ice bath and pass the gas in at a slower rate to ensure maximum absorption. Stir for 3 6 hours whilst allowing the ice bath to attain room temperature slowly. Pour the reaction mixture into a solution of 136 g. of hydrated sodium acetate in 250 ml. of water, reflux for 60 minutes (or until the boron fluoride complexes are hydrolysed), cool in ice and extract with three 50 ml. portions of petroleum ether, b.p. 40-60° (1), wash the combined extracts free of acid with sodium bicarbonate solution, dry over anhydrous calcium sulphate, remove the solvent by... 

The behavior of 2-boron fluoride etherate under anhydrous conditions has also been examined in some detail.4 From thiB reaction a crystalline boron fluoride complex was obtained which was spectroscopically characterised as that of the ritf-isomer (XXVII) of A-fert-butylbenzaldoxime. On standing or recrystaUisation from solvent this isomer was converted to the [Pg.326]

A further spectrophotometric method [3, 4] for water soluble boron in soil, boron is extracted from soil with boiling water. Borate in the extract is converted to fluoroborate by the action of orthophosphoric acid and sodium fluoride. The concentration of fluoroborate is measured spectrophotometrically as the blue complex formed with methylene blue and which is extracted into 1, 2-dichloroethane. Nitrates and nitrites interfere they are removed by reduction with zinc powder and orthophosphoric acid. 

Many other compounds have been shown to act as co-catalysts in various systems, and their activity is interpreted by analogous reactions [30-33]. However, the confidence with which one previously generalised this simple picture has been shaken by some extremely important papers from Eastham s group [34], These authors have studied the isomerization of cis- and Zraws-but-2-ene and of but-l-ene and the polymerization of propene and of the butenes by boron fluoride with either methanol or acetic acid as cocatalyst. Their complicated kinetic results indicate that more than one complex may be involved in the reaction mechanism, and the authors have discussed the implications of their findings in some detail. 

The initiation reaction in the polymerization of vinyl ethers by BF3R20 (R20 = various dialkyl ethers and tetrahydrofuran) was shown by Eley to involve an alkyl ion from the dialkyl ether, which therefore acts as a (necessary) co-catalyst [35, 67]. This initiation by an alkyl ion from a BF3-ether complex means that the alkyl vinyl ethers are so much more basic than the mono-olefins, that they can abstract alkylium ions from the boron fluoride etherate. This difference in basicity is also illustrated by the observations that triethoxonium fluoroborate, Et30+BF4", will not polymerise isobutene [68] but polymerises w-butyl vinyl ether instantaneously [69]. It was also shown [67] that in an extremely dry system boron fluoride will not catalyse the polymerization of alkyl vinyl ethers in hydrocarbons thus, an earlier suggestion that an alkyl vinyl ether might act as its own co-catalyst [30] was shown to be invalid, at least under these conditions. 

Elimination of hydrogen fluoride from vinylic fluoride 16. using the triethylamine-boron trifluoride complex, yields the allene 17.96... 

As the inner salts are generally unstable and insoluble, they cannot be manipulated and their structures were therefore inferred from those of the more stable nitrogen analogues. The inner oxonium salt from boron fluoride, when examined at low temperatures, was found to contain a molecule of ether of crystallization which was held very tenaciously and was involved in the complex decomposition of the salt at higher temperatures. The salt from antimony pentachloride did not contain this molecule of ether and decomposed to ethyl chloride and a mixture of alkoxy antimony tetrachlorides. The stannic chloride decomposed in at least two ways,... 

Carbon-boron clusters ( carboranes ) have been shown to react with Cr-coordinated halo-arenes. For example, reaction of 2 equiv. of LiC2BjoHio(CH3) with para-difluorobenzene-tricarbonylchromium complex in refluxing THF results in the displacement of both fluoride substituents from the arene ring to yield the para-phenylene compound, albeit in just 9 % yield owing to the effect of the steric bulk of the carborane [55]. 

The use of ethers as cocatalysts for the cationic polymerisation of alkenyl monomers induced by Lewis acids has received little systematic attention and the mechanism through which these compounds operate is not well understood. The complex diethyl-ether-boron fluoride has been extensively used as a very convenient cationic initiator, but mostly for preparative purposes. As in the case of alcohols and water, ethers are known to act as inhibitors or retarders in the cationic polymerisation of olefins, if used obove cocatalytic levels, because they are more nucleophilic than most rr-donor monomers. Imoto and Aoki showed that diethyl ether, tetrahydrofuran, -chloro-diethyl ether and diethyl thioether are inhibitors for the polymerisation of styrene-by the complex BF3 EtjO in benzene at 30 °C, at a concentration lower than that of the catalyst, but high enough (0.5 x 10 M) to quench the active species formation for a time. Their action was temporary in that the quenching reaction consumed them, and therefore induction periods were observed, but the DP s of the polystyrenes were independent of the presence of such compounds, as expected from a classical temporary inhibition. 

A C2-nonsymmetric FeNx3(BC6H5)(BF) complex was obtained via a "re-boronating" reaction from the initial FeNx3(BC6H5)2 clathrochelate attacked by triethyloxonium boron fluoride, and the complex obtained was chromatographically isolated (Scheme 10). 

When boric acid is added to a solution of Nb-, Ta-, W-, Mo-, or Zr fluoride complexes, the boron displaces the fluoride (formation of BFT) from the Nb, Ta, and W complexes, causing the precipitation of these metals, while Zr and Mo remain in solution, since their fluoride complexes are more stable [5]. 

The tar-acid-free and tar-base-free coke oven naphtha can be fractionated to give a narrowboiling fraction (170°C-185°C [340°F-365°F]) containing coumarone and indene. This is treated with strong sulfuric acid to remove unsaturated components and is then washed and redistilled. The concentrate is heated with a catalyst (such as a boron fluoride/phenol complex) to polymerize the indene and part of the coumarone. Unreacted oil is distilled off, and the resins obtained vary from pale amber to dark brown in color. They are used in the production of flooring tiles and in paints and polishes. 

High yields of aldehydes and ketones from alcohols under mild conditions can be obtained with lead tetraacetate in pyridine . Also with lead tetraacetate, in the presence of boron fluoride, 21-acetoxylation of certain steroids can be achieved efficiently at room temp. -Allylpalladium chloride complexes have found interesting synthetic applications... 

Although in the recent years the stereochemical control of aldol condensations has reached a level of efficiency which allows enantioselective syntheses of very complex compounds containing many asymmetric centres, the situation is still far from what one would consider "ideal". In the first place, the requirement of a substituent at the a-position of the enolate in order to achieve good stereoselection is a limitation which, however, can be overcome by using temporary bulky groups (such as alkylthio ethers, for instance). On the other hand, the ( )-enolates, which are necessary for the preparation of 2,3-anti aldols, are not so easily prepared as the (Z)-enolates and furthermore, they do not show selectivities as good as in the case of the (Z)-enolates. Finally, although elements other than boron -such as zirconium [30] and titanium [31]- have been also used succesfully much work remains to be done in the area of catalysis. In this context, the work of Mukaiyama and Kobayashi [32a,b,c] on asymmetric aldol reactions of silyl enol ethers with aldehydes promoted by tributyltin fluoride and a chiral diamine coordinated to tin(II) triflate... 

Xylenes react reversibly to form complexes with boron trifluoride (BF3) in the presence of liquid hydrogen fluoride (HF). This fact can be utilized in the separation of w-xylene from its isomers, because the m-xylene complex is much more stable than the others and also more soluble in hydrogen... 

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