Trifluoride, boron

Boron trifluoride [7637-07-2] (trifluoroborane), BF, was first reported in 1809 by Gay-Lussac and Thenard (1) who prepared it by the reaction of boric acid and fluorspar at duU red heat. It is a colorless gas when dry, but fumes in the presence of moisture yielding a dense white smoke of irritating, pungent odor. It is widely used as an acid catalyst (2) for many types of organic reactions, especially for the production of polymer and petroleum (qv) products. The gas was first produced commercially in 1936 by the Harshaw Chemical Co. (see also Boron COMPOUNDS). 

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). 

Physical Properties. The physical properties are Hsted in Table 1. The molecule has a trigonal planar stmcture in which the F—B—F angle is 120° and the B—F bond distance is 0.1307 0.0002 nm (13). 

Nuclear magnetic resonance B spectral studies of BF have given a value of 9.4 1.0 ppm for the chemical shift relative to BF3 0(02113)3 as the 

Dissolves with reaction to form complexes and other species. 

Lower LD Boron halides. In M. Grayson (ed) Kirk-Othmer Concise Encyclopedia of Chemical Technology, p 180. New York, Wiley-Interscience, 1985 

NIOSH Chemical Safety Information Boron Tribromide Occupational Safety and Health Guidelines for Chemical Hazards 6pp. US Department of Health and Human Services, Public Health Service, Centers for Disease Control, National Institute for Occupational Safety and Health, Division of Standards Development and Technology Transfer, Cincinnati, OH, 1992 

Physical Form. Colorless gas forms dense white fume in moist air 

In catalysis with and without promoting agents fumigant flux for soldering magnesium 

Toxicology. Boron trifluoride gas is a severe irritant of the lungs, eyes, and skin. 

Chemical Symbol BF3 Synonym Boron fluoride CAS Registry Number 7637-07-2 

DOT Proper Shipping Name Boron trifluoride, compressed 

TC Shipping Name Boron trifluoride TC Classification 2.3 TC Label POISON GAS UN Number UN 1008 

Specific gravity of liquid at boiling point (water = 1) 1.57 1.57 

Compressed Gas Association, Handbook of Compressed Gases Springer Science+Business Media New York 1999 

Chemical Symbol BF3 Synonym Boron fluoride CAS Registry Number 7637-07-2 DOT Classification Nonflammable gas DOT Label Nonflammable gas, Poison Transport Canada Classification 2.3 (8) UN Number UN 1008 

Boron trifluoride is available for commercial and industrial use in technical grades having much the same component proportions from one producer to another. The specification for a typical technical grade is as follows  

Boron trifluoride is used as a catalyst for polymerizations, alkylations, and condensation reactions as a gas flux for internal soldering or brazing as an extinguisher for magnesium fires and as a source of B isotope. 

Boron trifluoride irritates the nose, mucous membranes, and other parts of the respiratory system. Concentrations as low as 1 ppm in air can be detected by the sense of smell. 

A TLV ceiling of 1 ppm (3 mg/m ) for exposures to boron trifluoride has been adopted by the American Conference of Governmental Industrial Hygienists. [1] The U.S. Occupational Safety and Health Administration similarly has adopted a ceiling limit of Ippm (3mg/m ) for exposures to boron trifluoride. [2) 

LABORATORY CHEMICAL SAFETY SUMMARY BORON TRIFLUORIDE  

Substance Boron trifluoride (Boron fluoride, tiifluoroborane) CAS 7637-07-2 

Physical Properties Colorless gas, fumes in moist air bp -100 °C, mp -127 °C Highly soluble in cold water (332 g/100 mL) 

Major Hazards Highly corrosive to skin, eyes, and mucous membranes reacts violently with water to form highly toxic HE. 

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. 

It is commonly available as diethyl etherate (C2H5)2OBF3 and is widely used as catalyst in Friedel-Crafts and other acid-catalyzed reactions in organic chemistry.49 

6NaBF4 B2O3 6H2SO4 — 8BF3 -f- 6NaHS04 -t- 3H2O 

The usual method of preparing boron trifluoride from calcium fluoride, boric oxide, and sulfuric acid is unsatisfactory, since yields are low, much silicon fluoride contaminates the product, and a solid residue which is difficult to remove remains in the generator. 

Using sodium fluoborate or ammonium fluoborate,1 boric oxide, and sulfuric acid, the yields are good, little silicon fluoride is produced, and the residue is water soluble. 

Part A. Preparation of High-purity Boron Trifluoride 

Three hundred grams of sodium fluoborate J and 50 g. of anhydrous boric oxide are ground together, and the mixture is placed in a liter flask equipped with a standard conical joint. About 300 ml. of concentrated sulfuric acid is added, and the flask is swirled to mix the solid and liquid thoroughly. The flask A (Fig. 3) is then connected to the system, using on the conical joint B a grease made by saturating a hot 1 4 mixture of paraffin and vaseline with 

Colorless, fuming gas with pungent suffocating odor bp, -100.4°C.1,2 

Soluble in water with some decomposition forming fluoroboric and boric acids somewhat soluble in concentrated sulfuric acid and nitric acid soluble in benzene, dichlorobenzene, chloroform, carbon tetrachloride, and carbon disulfide.1,2 

Alkali Metals or Alkaline Earth Metals (not Magnesium). Interaction without cooling causes incandescence.2 

The gas irritates the skin, eyes, and respiratory system at high concentrations it may burn the skin. Prevent inhalation of gas. Prevent contact with skin and eyes.2 TLV-STEL-C 1 ppm (2.8 mg/m3).3 

Seal cylinder and return to supplier. In the fume hood, surplus gas or leaking cylinder can be slowly added to a flask containing water. Precipitate the fluoride in solution by adding calcium chloride solution (10%). Let stand overnight. Filter off precipitate and send to a landfill. Wash the filtrate into the drain.4 

---

Boron trifluoride is a colourless, reactive gas which can be prepared by heating boron tnoxide and fluorspar with concentrated sulphuric acid. 

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 ... 

In each case the configuration around the boron changes from trigonal planar to tetrahedral on adduct formation. Because of this ability to form additional compounds, boron trifluoride is an important catalyst and is used in many organic reactions, notably polymerisation, esterification, and Friedel-Crafts acylation and alkylations. 

Both boron and aluminium chlorides can be prepared by the direct combination of the elements. Boron trichloride can also be prepared by passing chlorine gas over a strongly heated mixture of boron trioxide and carbon. Like boron trifluoride, this is a covalent compound and a gas at ordinary temperature and pressure (boiling point 285 K). It reacts vigorously with water, the mechanism probably involving initial co-ordination of a water molecule (p, 152). and hydrochloric acid is obtained ... 

The covalently bonded oxygen atom still has two lone pairs of electrons and can act as an electron pair donor. It rarely donates both pairs (to achieve 4-coordination) and usually only one donor bond is formed. A water molecule, for example, can donate to a proton, forming H30, and diethyl ether can donate to an acceptor such as boron trifluoride ... 

Other catalysts which may be used in the Friedel - Crafts alkylation reaction include ferric chloride, antimony pentachloride, zirconium tetrachloride, boron trifluoride, zinc chloride and hydrogen fluoride but these are generally not so effective in academic laboratories. The alkylating agents include alkyl halides, alcohols and olefines. 

The boron trifluoride is absorbed in sodium hydroxide solution. Similarly p-toluidine p-CH3C,H4NHj 3uelds />-fluorotoluene p-CH3CgH4F. 

The controlled thermal decomposition of dry aromatic diazonium fluoborates to yield an aromatic fluoride, boron trifluoride and nitrogen is known as the Schiemann reaction. Most diazonium fluoborates have definite decomposition temperatures and the rates of decomposition, with few exceptions, are easily controlled. Another procedure for preparing the diazonium fluoborate is to diazotise in the presence of the fluoborate ion. Fluoboric acid may be the only acid present, thus acting as acid and source of fluoborate ion. The insoluble fluoborate separates as it is formed side reactions, such as phenol formation and coupling, are held at a minimum temperature control is not usually critical and the temperature may rise to about 20° without ill effect efficient stirring is, however, necessary since a continuously thickening precipitate is formed as the reaction proceeds. The modified procedure is illustrated by the preparation of -fluoroanisole ... 

The acylation of ketones with acid anhydrides may be effected by means of the acid reagent boron trifluoride, for example ... 

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) ... 

Methylene ketones, such as cyciopentanone and cyciohexanone, are also readily acylated by boron trifluoride thus cyciohexanone (I) affords 2-acetylcycIo-hexanone (II) ... 

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. 

Another aspect of my early research in Budapest was in nitration chemistry, specifically the preparation of nitronium tetrafluoroborate, a stable nitronium salt. 1 was able to prepare the salt in a simple and efficient way from nitric acid, hydrogen fluoride, and boron trifluoride. 

Concerning my research during my Dow years, as I discuss iu Chapter 4, my search for cationic carbon intermediates started back in Hungary, while 1 was studying Friedel-Crafts-type reactions with acyl and subsequently alkyl fluorides catalyzed by boron trifluoride. In the course of these studies I observed (and, in some cases, isolated) intermediate complexes of either donor-acceptor or ionic nature. 

Nitration has also been effected with the complexes from dinitrogen tetroxide and Lewis acidsin the case of boron trifluoride the complex appears to be a mixture of nitronium and nitrosonium tetrafluoroborates. ... 

When mixed with Lewis acids, dinitrogen pentoxide yields crystalline white solids, which were identified as the corresponding nitronium salts by their infra-red spectra. The reaction with boron trifluoride can be formulated in the following way... 

Nitronium tetrafluoroborate was first prepared by adding a mixture of anhydrous hydrofluoric acid and boron trifluoride to a solution of dinitrogen pentoxide in nitromethane. Nitric acid can be used in place of dinitrogen pentoxide, and by replacing boron trifluoride by other Lewis-acid fluorides Olah and his co-workers prepared an extensive series of stable nitronium salts. ... 

Cations like that present in (iv) exist in solutions of aromatic hydrocarbons in trifluoroacetic acid containing boron trifluoride, and in liquid hydrogen fluoride containing boron trifluoride. Sulphuric acid is able to protonate anthracene at a mero-position to give a similar cation. ... 

The relative basicities of aromatic hydrocarbons, as represented by the equilibrium constants for their protonation in mixtures of hydrogen fluoride and boron trifluoride, have been measured. The effects of substituents upon these basicities resemble their effects upon the rates of electrophilic substitutions a linear relationship exists between the logarithms of the relative basicities and the logarithms of the relative rate constants for various substitutions, such as chlorination and... 

The cr-complexes (iv) are thus the intermediates corresponding to the substitution process of hydrogen exchange. Those for some other substitutions have also been isolated in particular, benzylidyne trifluoride reacts with nitryl fluoride and boron trifluoride at — ioo°C to give a yellow complex. Above — 50 °C the latter decomposes to hydrogen fluoride, boron trifluoride, and an almost quantitative yield of tn-nitrobenzylidyne trifluoride. The latter is the normal product of nitrating benzylidyne trifluoride, and the complex is formulated as... 

This catalyst should really be purchased rather than made because its use in underground chemistry is limited and is hardly watched at all if not ever. This may change considering its potential as a precursor to the NaBHsCN in Strike s 1 method of choice. There are a lot of ways to make this catalyst, but the least involved is the one using boron trifluoride. What the method calls for is an apparatus called an autoclave. You know how using a vacuum causes the absence of pressure to make things boil at a lower temperature Well, an autoclave is a device that causes an... 

From these results it appears that the 5-position of thiazole is two to three more reactive than the 4-position, that methylation in the 2-position enhances the rate of nitration by a factor of 15 in the 5-position and of 8 in the 4-position, that this last factor is 10 and 14 for 2-Et and 2-t-Bu groups, respectively. Asato (374) and Dou (375) arrived at the same figure for the orientation of the nitration of 2-methyl and 2-propylthiazole Asato used nitronium fluoroborate and the dinitrogen tetroxide-boron trifluoride complex at room temperature, and Dou used sulfonitric acid at 70°C (Table T54). About the same proportion of 4-and 5-isomers was obtained in the nitration of 2-methoxythiazole by Friedmann (376). Recently, Katritzky et al. (377) presented the first kinetic studies of electrophilic substitution in thiazoles the nitration of thiazoles and thiazolones (Table 1-55). The reaction was followed spec-trophotometrically and performed at different acidities by varying the... 

Boron trifluoride (BF3) F 20. B- F F Boron has three bonded pairs Trigonal planar Trigonal planar ... 

Boron trifluoride is a trigonal planar molecule There are six electrons two for each B—F bond associated with the valence shell of boron These three bonded pairs are farthest apart when they are coplanar with F—B—F bond angles of 120°... 

Verify that the formal charges on boron and oxy gen in boron trifluoride etherate are correct... 

---