Boron fluoride compound with

In order to achieve high yields, the reaction usually is conducted by application of high pressure. For laboratory use, the need for high-pressure equipment, together with the toxicity of carbon monoxide, makes that reaction less practicable. The scope of that reaction is limited to benzene, alkyl substituted and certain other electron-rich aromatic compounds. With mono-substituted benzenes, thepara-for-mylated product is formed preferentially. Super-acidic catalysts have been developed, for example generated from trifluoromethanesulfonic acid, hydrogen fluoride and boron trifluoride the application of elevated pressure is then not necessary. 

Notable examples of general synthetic procedures in Volume 47 include the synthesis of aromatic aldehydes (from dichloro-methyl methyl ether), aliphatic aldehydes (from alkyl halides and trimethylamine oxide and by oxidation of alcohols using dimethyl sulfoxide, dicyclohexylcarbodiimide, and pyridinum trifluoro-acetate the latter method is particularly useful since the conditions are so mild), carbethoxycycloalkanones (from sodium hydride, diethyl carbonate, and the cycloalkanone), m-dialkylbenzenes (from the />-isomer by isomerization with hydrogen fluoride and boron trifluoride), and the deamination of amines (by conversion to the nitrosoamide and thermolysis to the ester). Other general methods are represented by the synthesis of 1 J-difluoroolefins (from sodium chlorodifluoroacetate, triphenyl phosphine, and an aldehyde or ketone), the nitration of aromatic rings (with ni-tronium tetrafluoroborate), the reductive methylation of aromatic nitro compounds (with formaldehyde and hydrogen), the synthesis of dialkyl ketones (from carboxylic acids and iron powder), and the preparation of 1-substituted cyclopropanols (from the condensation of a 1,3-dichloro-2-propanol derivative and ethyl-... 

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 analogy between the trivalent boron compounds and car-bonium ions extends to the geometry. Although our arguments for a preferred planar structure in carbonium ions are indirect, there is electron diffraction evidence for the planar structure of boron trimethyl and the boron trihalides.298 Like carbonium ions, the boron and aluminum analogs readily form a fourth covalent bond to atoms having the requisite non-bonding electrons. Examples are the compounds with ammonia, ether, and fluoride ion.297... 

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 first study with an oxygen compound which was sufficiently rigorous to provide evidence on the question of co-catalysis was that of Farthing and Reynolds [61]. They showed that 3,3-bischloromethyl oxetan could be polymerised in methyl chloride solution by boron fluoride only in the presence of water. Tater, Rose [62] obtained kinetic evidence for the need for a co-catalyst in the system oxetan—boron fluoride—methyl chloride, and he interpreted the low reaction rate when no water was added as due to residual water he also showed that water and a hydroxyl-terminated polymer could act as co-catalysts. 

The gas phase polymerization of diisobutylene with boron fluoride also did not occur unless a third component was present. The addition of water or acetone caused the mixture to react rapidly, the boron fluoride combining instantaneously with the vapor of the third component in approximately equimolecular quantities. Certain substances, oxygen, hydrogen sulfide, and hydrogen chloride, did not produce a rapid polymerization of diisobutylene these substances did not combine with the boron fluoride. In each of these cases, the final addition of water to the nonreacting mixture resulted in rapid polymerization. Ammonia formed an addition compound with the boron fluoride in approximately equimolecular quantities, but did not bring about the polymerization of the diisobutylene until water vapor was added, after which rapid reaction occurred (Evans and Weinberger, 85). 

Compounds with H H—H Hydrogen H—Be—H Beryllium hydride H—B—H Boron hydride H 1 H—C—H 1, Methane H—N—H Ammonia H— H Water H—F Hydrogen fluoride... 

Monammino-boron Fluoride, BF3.NH3, is a white solid which may be sublimed without decomposition in a closed tube. The vapour of the substance is stated by Mixtcr 1 to attack glass it is decomposed on exposure to moist air, and dissolves in water with formation of oxy-fluoborate. It is probable that these compounds of boron trifluoride and ammonia are mixtures of the same type as those formed from boron trichloride described by Joannis. 

Boron can complete its octet if another atom or ion with a lone pair of electrons forms a bond by providing both of the electrons. A bond in which both electrons come from one of the atoms is called a coordinate covalent bond. For example, the tetrafluoroborate anion, BF4 (38), forms when boron trifluoride is passed over a metal fluoride. In this anion, the formation of a coordinate covalent bond gives the B atom an octet. Another example of the formation of a coordinate covalent bond is the compound formed when boron trifluoride reacts with ammonia ... 

Of equal importance with these two reactions, but unfortunately much less clear, is the mechanism of oxonium ion formation since it will determine the importance of these intermediates in the polymerizations. The scheme proposed by Meerwein and described above was based entirely on careful product analysis of reactions carried out without extreme precautions to exclude moisture. While it seems reasonable enough, it may require modification as more information becomes available. The question of the role of water in the formation may perhaps be an academic one in the case of the epoxides because even rigorously dry ethylene oxide appears to react with boron fluoride at — 80° (4) to form compounds of the type... 

The location of the catalyst is a problem in all attempts at kinetic measurement in these systems. It is well known that boron fluoride forms 1 1 complexes with most oxygenated compounds and 1 2 complexes when hydroxyl groups are present. The ternary complexes are to be regarded as a form of oxonium salt in which the third molecule is held by hydrogen bonding, so in the present reaction mixtures, equilibria of the type... 

Cyanogen fluoride is a moderately endothermic compound, with AHyfg) +35.8 kJ/ mol, or 0.79 kJ/g. Polymerisation of cyanogen fluoride is rapid at ambient temperature and explosive in presence of hydrogen fluoride [1], Cyanogen fluoride develops more pressure than would acetylene when initiated in the liquid phase at —41 °C by a squib. At —80°C either hydrogen fluoride of boron trifluoride may initiate violent decomposition. The pure vapour is insensitive to sparks or igniters, but mixtures with air are more powerful than those of acetylene [2],... 

Joining silver pieces with silver solder requires temperatures of 316-760°C. At these temperatures, impurities in the silver solder, such as antimony and cadmium, are released. The flux may contain fluoride compounds, such as potassium fluoride and boron trifluoride, or other boron compounds. 

Lewis acids such as boron trihalides will also form stronger bonds with fluoride than with the other halogens, and can be used to abstract fluoride selectively from halogenated compounds. Some examples of Friedel-Crafts alkylations with fluoro-haloalkanes in which only fluoride is displaced are sketched in Scheme 4.14. As shown by the last example, however, hydride migrations can readily occur under such strongly acidic reaction conditions. 

Boron fluoride, for catalysis, 1 23 compound with hexamethyldi-silazane, 5 58 high-purity, 1 2l Boron fluoride-trimethylamine, 5 26... 

Trimetaphosphimic acid, 6 79 Trimethylamine, coordination compounds with boron fluoride and chloride, 5 26, 27 purification of, 2 159 Trimethylamine-sulfur dioxide, 2 159... 

As a result of the formal positive charge of the oxygen atom this compound of boron fluoride with alcohol is a much strong-... 

Diboron tetrafluoride can be prepared from BF3 and elemental boron at 1850°C, a reaction that first produces BF (a compound that can be isolated by condensation at -196°C), which reacts with BF3 to give B2F4 and unstable higher boron fluorides such as B Fi2. 

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