Boron Trifluoride

Nov 20, 2021 | SCIENCE, Chemistry

Boron Trifluoride

Boron trifluoride is capable of forming complexes with dimethyl, such as boron-trifluoride–dimethyl ether. These complexes are typically formed to allow for the easy handling of boron trifluoride (NIOSH 1977). Boron trifluoride might also form complexes when combined with water, phenol or phosphoric acids, piperidines, dimethylanilines, methanol, and diethyl ether (NIOSH 1975).  Boron trifluoride is combined with dimethyl or ethyl ether in the ether complexes. They are capable of dissociating under the right conditions of temperature and pressure.

Boron Trifluoride

AEGL derivations

Boron trifluoride-dimethyl ether is derived as part of the AEGL chemistry by breaking down the complex into trifluoride-born elements.

Boron trifluoride can be described as a colorless, unpleasant gas with an intense and oppressive aroma (Budavari. 1996 ) and pleasant Torkelson (et al., 1961 ). There are both chemical and physical data on boron trifluoride and boron-trifluoride -dimethyl ether (when they are available). In moist conditions, the gas forms a white mist or cloud ( NIOSH 1976 Hoffman, 1981), indicating that boron trifluoride is transformed to dihydrate BF3 when it reacts with humidity.

According to some theories, boron fluoride forms the following products in water: Fluoroboric acids (HBF), monohydroxyfluoboric and OH (HBF OH), boron trifluoride (HBF(OH), dihydroxyfluoboric and OH (HBF(OH), boric acid) (H NIOSH 1976). Boron fluoride reacts slowly with water to form hydrogen fluoride. However, it has been suggested that hydrogen fluoride may be quickly complex with other species if it develops.

NIOSH 1976 Dunn (1980) showed that boron trifluoride dihydrate is highly corrosive to rabbit eyes and skin. The eye was affected by the topical application of undiluted Boron Trifluoride Diahydrate (0.1 mL), which caused complete corneal discoloration, necrosis of the conjunctivae, and nictating membranes, as well as a complete opacity. Tap water was ineffective at reducing the corrosive activity. Toxic skin corrosion was caused when undiluted boron fluoride dihydrate was applied to the skin (0.5mL) for 24 hours under a semi-occlusive patch.

Technical and Chemical Data on Boron Trifluoride

ParameterValue Reference
SynonymsTrifluoroborane; boron trifluoride-dimethyl ether (1:1); boron trifluoride-dimethyl etherate; fluoride boron-dimethylether (1:1)

NIOSH 2011

Lewis 1996

CAS registry no.7637-97-2353-42-4
Chemical formula


C2H6O.BF3 (BF3-dimethyl ether)

Molecular weight


113.89g (BF3-dimethyl ether)

Molecular weight


113.89g (BF3-dimethyl ether)

Budavari et al.1996

Lewis 1996

Physical stateGas-Liquid (BF3- dimethyl ether)Budavari et al.1996
Melting point

-128.37 degrees celsius

-14 degrees celsius (BF3-dimethyl ether)

AIHA 1999

Lewis 1996

Boiling Point

(760 mm Hg)

-100.4 degrees CelciusBudavari et al.1996
Vapor density (air=1)3.077 g/LBudavari et al.1996
Solubility in Water332 g/100 g at 0 degrees CelciusBudavari et al.1996
Valor pressureGreater than 1 Torr at 20 degrees Celcius.ACGIH 1991
Conversion factors

1 ppm = 2.76 mg/m3

1 mg/m3 = 0.36 ppm (v/v)

1 ppm = 4.65 mg/m3 (BF3 – dimethyl ether)

ACGIH 1991



AEGL-1 values assume no irritation. Ten rats were exposed to boron trifluoride at 25 mg/m3 for four hours. They did not experience any abnormalities, while rats exposed to 74 mg/m3 showed histopathologic changes and tracheal bifurcation. ( Bowden 2005). For calculating AEGL-1 values, the starting point was 25 mg/m3. The irritant effects at 74 mg/m3 can be more severe than those seen in the threshold values for AEGL-1 values.

The total uncertainty factor was 10. Because irritation is a direct effect of contact and does not vary widely among species, an interspecies uncertainty factor was 3 applied. Because the mechanism of irritation does not vary in subpopulations, an intraspecies uncertainty factor was 3 applied. Because the point of departure for mild irritation is a non-effect level, all AEGL durations were given the same AEGL value –National Center for Biotechnology Information (

We did not have enough data to calculate AEGL-2 numbers. To obtain reasonable estimates of AEGL-2, the AEGL-3 value was divided by 3, verified by Rusch et al. Let’s support the steep dose-response graph by dividing AEGL-3 values by 3. during 1986. The threshold for lethality was used to calculate AEGL-3 values. 

Rusch et al. (1986) determined a 4-h LC [lethal concentration 50% lethality] of 1,210 mg/m3. The exposures involved liquid aerosols containing boron fluoride dihydrate. The concentrations reported are based on boron trifluoride. Using individual death data, a 4-h BMCL was calculated using log-prohibit analysis and the EPA Benchmark Dose software version 1.4.1c [2007]. ( EPA 2012. ).

The AEGL-3 values were calculated from the 4-h BMCL (554 mg/m3). Because boron trifluoride can be corrosive and irritating, the interspecies uncertainty factor was calculated at 3. The mechanism of action should not differ greatly between species. Rusch and coworkers (2012) noted that. The intraspecies uncertainty was set at three since irritation mechanisms between subpopulations will likely differ little. 

A steep dose-response curve supports an intraspecies uncertainties factor of 3. This is because 9/10 rats died from 1,010 mg/m3, and 10 rats died from 1,540 mg/m3. This indicates that there is little variation in the response among populations. Rusch et al. The Rusch et al. (1986) study was supported by Kasparov & Kirii (1972), a study that reported a 4-h Lc of 1,180 mg/m3 for rats. The concentration-time relationship equation Rusch et al. Used (CNXT =k) to scale time. C = concentration and t = time duration. Generally, n ranges between 0.8 and 3.5 (ten Berge et al. 1986 ).

Insufficient data made it impossible to calculate a value of n empirically. A default value of 1 was used for extrapolating between shorter and longer exposure times. A value of 3 was used to extrapolate between shorter and longer exposure periods. Based on the uncertainty involved in extrapolating data from a 4-h exposure to a 10-min AEGL, the 10-min value was equal to the 30-min value. 

These are the AEGL values of boron trifluoride. Although the gas is stable when dry, boron fluoride reacts with moisture to form dihydrate ( NIOSH 1976 Hoffman 1981 ). All AEGL values must be reported in mg/m3.  


Anhydrous boron trifluoride has an internal boiling point of 100.3 degrees Celsius and a critical temperature of -12.3 degrees Celsius. It can only be kept refrigerated between these temperatures. Because of the possibility that a refrigeration system malfunction could lead to pressures rising to 49.85 bar (4.95 MPa span), storage or transport vessels must be able to withstand internal pressure.

Boron trifluoride can be corrosive. For equipment handling, Boron Trifluoride, stainless steel, Monel, and Hastelloy are suitable metals. It corrodes steels, including stainless steel, when it comes into contact with moisture. It reacts with polyamides. Polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, and polypropylene show satisfactory resistance. Fluorocarbon-based grease should be used for equipment since boron trifluoride reacts to hydrocarbon-based greases.


The boron trihalides have a monomeric structure, unlike the gallium and aluminum trihalides. They are subject to rapid halide exchange reactions.

BF3 + BCl3 – BF2Cl + BCl2F

The mixed halides can only be obtained through this exchange process.

Boron trifluoride, a versatile Lewis acid, forms adducts when combined with Lewis bases such as fluoride or ethers.

CsF + BF3 – CsBF4

O(C2H5)2 + BF3 – BF3*O(C2H5)2

As non-coordinating anions, tetrafluoroborate salts can be used frequently. It is easy to handle the adduct with diethyl ether, Boron Trifluoride Diethyl Estate, or simply Boron Trifluoride Eetherate (BF3*O(Et2)2). It is, therefore, a common laboratory source for BF3. Another common adduct is dimethyl sulfide ((BF3*S), Me)2]. It can also be used in liquid form.

There was no data to prove that inhaled boron fluoride is toxic to humans. According to Torkelson and colleagues, a worker could smell boron trifluoride at levels of 4.1 mg/m3 (1.5% ppm). 1961). There were no studies on acute toxicology with rats, mice, dogs, and guinea pigs, but they were available. Exposure concentrations were usually expressed in terms of nominal concentrations.

Torkelson and colleagues compared exposure concentrations with nominal concentrations to find that actual concentration varied from 2.7-56% ( Torkelson and co. 1961 Rusch et al. 1986 Bowden 2005 ). There were very few studies that identified endpoints other than mortality. There was no data available to assess the possibility of boron trifluoride causing developmental, reproductive toxicity, or cancer in animals. Boron trifluoride did not cause mutations in Salmonella typhimurium strains (source: NCBI). 


Boron trifluoride reacts when it is mixed with water to make fluoroboric and boric acids. The reaction begins by forming H2O–BF3, which is then lost HF and gives fluoroboric Acid with Boron Trifluoride.

4 BF3 + 3 H2O – 3 HBF4 + B(OH)3

Heavy trihalides undergo no analogous reactions. This is likely due to the lower stability ions BCl –

4 BBr-

Fluoroboric Acid is highly acidic, so it can be used to isolate electrophilic Cations like diazonium Ions.

Organic Uses

Boron trifluoride is most importantly used as a reagent in organic synthesis, typically as a Lewis acid. Examples include initiation of polymerization reactions of unsaturated compounds, such as polyethers, and as a catalyst in some isomerization, acylation, alkylation, esterification, dehydration, condensation, Mukaiyama aldol addition, and other reactions [citation needed]

Medical Application

Skin Burns

Boron Trifluoride is hydrolyzed very quickly and yields hydrofluoric Acid. The skin will then burn like from HF. ( International Chemical Safety Cards. Eye contact, skin contact, or inhalation


Necrotizing enteritis and kidney damage National Institute for Occupational Safety and Health 121.10 Antidote and emergency treatment New Window. Rinse your eyes with plenty of water and lift your upper lids periodically. (Sourced from

Niche uses

There are also other uses that boron trifluoride is less commonly used for:

  • In ion implantation as a dopant
  • For epitaxially-grown silicon, p-type dopant
  • In sensitive neutron detections in ionization rooms and devices to monitor radiation levels on the Earth’s surface
  • In the fumigation process with methyl bromide
  • As a flux to solder magnesium.
  • To prepare diborane boron trifluoride is used


Louis Jacques Thenard & Joseph Louis Gay–Lussac found Boron trifluoride back in 1808. They were trying out fluoric acid, also known as hydrofluoric or “fluoric acid,” by combining calcium and verified arachidic acid. Fluoric gases were created when the resulting vapors failed in their attempt to etch through the glass. 


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