134 BORON TRIFLUORIDE

electrode or ion chromatography (at trace concentrations) with appropriate dilution.

Toxicity

Boron trichloride is highly toxic, causing severe irritation of eyes, skin and mucous membranes.

LCLO inhalation (rat): 20 ppm/7hr.

BORON TRIFLUORIDE

[7637–07–2]

Formula: BF3; MW 67.82; planar sp2 hybridization; F–B–F angle 120°; an electron deficient compound (Lewis acid)

Synonym: boron fluoride

Uses

Boron trifluoride is used as a catalyst in esterification, polymerization and many other organic synthetic reactions. Other applications of this compound include measuring weak neutrons in ionization chambers and in devices to monitor radiation levels in the earth’s atmosphere; and measuring depth for oil drilling. It also is used in fumigation; as a flux for soldering magnesium; to prepare diborane; and in gas brazing.

Physical Properties

Colorless gas; pungent suffocating odor; density 2.975 g/L; fumes in moist air; liquefies at –101°C; solidifies at –126.8°; vapor pressure at –128°C is 57.8 torr; critical temperature –12.2°C; critical pressure 49.15 atm; critical volume 115 cm3/mol; soluble in water with partial hydrolysis; solubility in water at 0°C 332 g/100g; also soluble in benzene, toluene, hexane, chloroform and methylene chloride; soluble in anhydrous concentrated sulfuric acid.

Preparation

Boron trifluoride is prepared by treating borax with hydrofluoric acid; or boric acid with ammonium bifluoride. The complex intermediate product is then treated with cold fuming sulfuric acid.

BORON TRIFLUORIDE ETHERATE 135

Reaction

Boron trifluoride is partially hydrolyzed when dissolved in water. The hydrolysis products are boric acid and fluoroboric acid:

4BF3 + 3H2O → B(OH)3 + 3HBF4

The tetrafluoroborate, BF4¯ anion can form stable salts with pyridinium, tetraalkylammonium and other countercations.

Boron trifluoride is reduced to elemental boron when heated with alkali

metals:

BF3 + 3Na heat → B + 3NaF

The reaction is highly exothermic resulting in incandescence. Similar reduction occurs with alkaline earth metals except magnesium.

Being an electron deficient compound, boron trifluoride forms complexes with Lewis bases and compounds that have unshared pair(s) of electrons. With ammonia, it forms boron trifluoride ammonia. Similar coordination compounds are formed with monoethylamine, BF3–NH2C2H5; diethyl ether, CH3CH2O(BF3)CH2CH3; and methanol, BF3–OHCH3. It forms a solid complex HNO3–2BF3 with concentrated nitric acid.

BORON TRIFLUORIDE ETHERATE

[109–63–7]

Formula: (CH3CH2O)2O•BF3; MW 141.94;

Synonyms: boron fluoride etherate; boron fluoride ethyl ether

Uses

Boron trifluoride etherate is used as a catalyst in many organic reactions; namely, alkylation, polymerization and condensation reactions.

Physical Properties

Fuming liquid; stable at ambient temperatures but hydrolyzed on exposure to moist air; density 1.125 g/mL; refractive index 1.348; solidifies at –60.4°C; boils at 125.7°C; flash point (open cup) 147°F (68.8°C); decomposes in water.

Preparation

Boron trifluoride etherate is prepared by the reaction of vapors of boron trifluoride with that of anhydrous diethyl ether:

BF3 (g) + (C2H5)2O (g) → (C2H5)2O•BF3

Toxicity

The compound is highly toxic by inhalation. Skin contact causes burns.