Properties of boron trifluoride

Studies on the interaction between hydrogen fluoride and boron trifluoride have been documented. According to Sharp °, reaction to produce HBF4 is unlikely unless an electron donor is present to solvate the proton. McCaulay et investigated the 

HF/BF3 system and did not find any sign of interaction in the absence of a base. Vapour pressure measurements involving individual xylene isomers indicated all the isomers react rapidly and reversibly with HF/BF3 to form a complex in which the mol ratio of boron trifluoride to hydrocarbon is one. They postulated that the reaction of complex formation is the sum of two reaction steps [Eq (2.4)]. 

Hughes et a/. investigated the solubility of boron trifluoride (bp -99°C) in hydrogen fluoride over a wide temperature range (Table 2.1). The rapid increase in solubility with decreasing temperature below the critical temperature (between 4.4 and -26°C) suggests possible HF/BF3 coordination. 

Kilpatrick et postulated the equilibrium reaction (Eq 2.5) from the addition of BFsto HF. 

This follows from the auto-protolysis reaction equilibrium of hydrofluoric acid [(Eq2.6)], which is displaced to the right by boron trifluoride by the reaction (Eq 2.7). 

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The BF4 ion has a regular tetrahedral configuration. The most important property of boron trifluoride is its great capacity to act as an electron pair acceptor (Lewis acid). Some examples of adducts are ... 

This process achieves the extraction of m-xylene by means of HF—BFj. It exploits the complexing properties of boron trifluoride on. aromatic compounds, and the particular ability of m-xylene to fonn the most stable complex. Subsequently, this isomer, added to a mixture of Cg aromatics which does not conCrin it, displaces the other components from their respective complexes, and the composition of the medium depends on the values of the equilibrium constants, or m-xylene, 2 for o-xylene, 0.14... 

For a review of the addition complexes and catalytic properties of boron trifluoride, see Annual Reports of the Chemical Society, 1942, page 128 also the papers of Nieuwland and coworkers in /. Am. Chem. Soc., 1931 and following years. 

The product of this reaction, a Lewis acid-Lewis base complex called infonnally boron trifluoride etherate, may look unusual but it is a stable species with properties different from those of the reactants. Its boiling point (126°C) for exanple, is much higher than that of boron trifluoride—a gas with a boiling point of — 100°C—and diethyl ether, a liquid that boils at 34°C. 

The interaction between nitromethane, the etherate of boron trifluoride and silver oxide gives rise to an extremely dangerous reaction. However, it is difficult to interpret it. Can it be explained by the unstable property of silver tetrafluoroborate or the destabilising effect of boron trifluoride on nitromethane ... 

Cyclodehydration of a-(thioaroylthio)- or a-(thiocarbamoylthio)carboxylic acids (96) with acetic anhydride in the presence of catalytic amounts of boron trifluoride etherate, or with a mixture of acetic anhydride and triethylamine (1 1), leads to the 2-aryl- or 2-amino-l,3-dithiolium-4-olates (97) listed in Table VIII.Chemical properties, dipole moments, NMR, IR, and UV spectra, and charge distribution calculations are consistent with a mesoionic structure. " ... 

Although only cardol in CNSL has bifunctionality, attempts have been made to modify cardanol to the same effect. Thus reaction of (15 1)-cardanol with phenol in the presence of boron trifluoride afforded the 1,8-bis(hydroxyphenyl)pentadecane structure (ref. 261). Reaction then with a molar proportion of epichlorhydrin and polymerisation resulted in final products considered to be superior in properties to and cheaper than those derived from bisphenol A. The corresponding fully saturated cardbisphenol compound has been converted to a water soluble bis Mannich base by reaction with diethanolamine and formaldehyde (ref. 262) of value for cathodic electrodeposition. In another case of a related bis diethanolamine product, it was found necessary to react the hydroxyl groups with the monoisocyanate resulting from treatment of tolylenediisocyanate (TDI) with a molecular proportion of cardanol (ref. 263) in order to obtain a suitable binder for... 

To a 1-liter, four-necked flask equipped with an agitator, thermometer, addition funnel, and condenser are added 186 gm (1.0 mole) of 2,6,8-trimethyl-4-nonanol, and 0.55 gm (0.03 mole) of boron trifluoride. The reaction mixture is purged with nitrogen and then 116gm (2.0 moles) propylene oxide is added over a 1-hr period at 75°-80°C with constant agitation. The acid catalyst is neutralized with methanolic caustic to pH 8.5. Then 0.3 gm sodium hydroxide is added and the temperature raised to 150 -160°C ethylene oxide is added (369 gm = 8.4 mole) at 0-15 lb pressure to a cloud point (1% in water) at 36°C. The final product has surfactant properties. 

Toxicity Boron trifluoride (and organic complexes such as Bp3-etherate) are extremely corrosive substances that are destructive to all tissues of the body. Upon contact with moisture in the skin and other tissues, these compounds react to form hydrofluoric acid and fluoroboiic acid, which cause severe burns. Boron trifluoride gas is extremely irritating to the skin, eyes, and mucous membranes. Inhalation of boron trifluoride can cause severe irritation and burning of the respiratory tract, difficulty breathing, and possibly respiratory failure and death. Exposure of the eyes to BF3 can cause severe burns and blindness. This compound is not considered to have adequate warning properties. Boron trifluoride has not been found to be carcinogenic or to show reproductive or developmental toxicity in humans. Chronic exposure to boron trifluoride gas can cause respiratory irritation and damage. 

The interaction of 2-alkyl-A -thiazolines (196) and aryl isocyanates in the presence of catalytic amounts of boron trifluoride etherate, or methyl isocyanate, produces cyclic 2 2 adducts (197), e.g. 6, 8a -dimethyl-3-methylcarbamoyl-5 -oxospiro(thiazolidine-2,7 -perhydrothiazolo[3,2-c]pyri-midine). This contrasts with the formation of the simple 2 1 adducts (198) in the absence of the catalyst (see these Reports, Vol. 2, p. 627). The 2 2 adducts may have one of several possible structures their formulation as (197) is based on their spectral properties and the results of their... 

The boron atom in boron trifluoride is hybridized to the sp planar configuration and consequently is coordinatively unsaturated, ie, a Lewis acid. Its chemistry centers around satisfying this unsaturation by the formation with Lewis bases of adducts that are nearly tetrahedral sp [ The electrophilic properties (acid strengths) of the trihaloboranes have been found to increase in the order BF < BCl < BBr < BI (3,4). 

Cationic polymerization of coal-tar fractions has been commercially achieved through the use of strong protic acids, as well as various Lewis acids. Sulfuric acid was the first polymerization catalyst (11). More recent technology has focused on the Friedel-Crafts polymerization of coal fractions to yield resins with higher softening points and better color. Typical Lewis acid catalysts used in these processes are aluminum chloride, boron trifluoride, and various boron trifluoride complexes (12). Cmde feedstocks typically contain 25—75% reactive components and may be refined prior to polymerization (eg, acid or alkali treatment) to remove sulfur and other undesired components. Table 1 illustrates the typical components found in coal-tar fractions and their corresponding properties. 

It is especially important to investigate the molecular structure of coordination compounds in the vapor phase because the relatively weak coordination interactions may be considerably influenced by intermolecular interactions in solutions and especially in crystals. It has been shown that the geometrical variations can be correlated with other properties of the molecular complexes ). In particular the structural changes in the F3B N(CH3)3 and CI3B N(CH3)3 molecules ) relative to the respective monomeric species unambiguously indicated boron trichloride to be a stronger acceptor than boron trifluoride. Data on the geometry and force field have also been correlated ). 

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