Bromochloromethane

How Does the Critical-Use Exemption Framework Govern Halon 1011 Recharge Operations?

Bromochloromethane (BCM) charged into handheld extinguishers and fixed total-flooding systems must conform to the chemical composition limits stipulated in ISO 7201-1:2021 Clause 4 and the corresponding purity specifications embedded in NFPA 2001 Annex C, which mandate an assay of ≥99.5 % (mass fraction) with acid content expressed as HCl below 1 mg·kg⁻¹ and non-volatile residue not exceeding 10 ppm. Recharge operations at aeronautical maintenance facilities operating under ICAO Annex 6 Part I critical-use exemptions are executed on closed-circuit evacuation-fill benches equipped with nitrogen-purge capability and dew-point monitoring that maintains system moisture below 10 ppm(v); any excursion above 15 ppm(v) during cylinder preconditioning triggers a mandatory 48-hour heated silica-gel desiccant cycle before agent transfer proceeds. The formulation itself is typically a single-component halon charge without admixture of inert gas propellants, although 0.5–1.2 wt% of a proprietary metal-deactivator additive—commonly a substituted benzotriazole—is incorporated to suppress bronze-valve dezincification observed in 10- to 15-year service-life teardown analyses. Downstream filling workflow involves evacuation of the cylinder to ≤1.33 Pa absolute, mass-flow-metered transfer of BCM through a 0.2 µm PTFE filter at a fill density of 1.48–1.52 kg·L⁻¹ (internal volume basis), followed by nitrogen super-pressurisation to 4.2 MPa at 21 °C and a helium leak test at 1×10⁻⁶ mbar·L·s⁻¹ sensitivity compliant with EN 3-8:2021 Annex D. Finished-product types range from 1 kg portable BC-rated extinguishers to modular 300–500 kg banked suppression units installed in engine nacelles and electronic equipment bays, where the agent’s boiling point of 68 °C ensures rapid vapour-phase dispersion without thermal shock to avionics.

Chloromethylation Reagent in Cimetidine Congener Synthesis

In the preparation of 4-chloromethyl-5-methylimidazole—a penultimate intermediate in the cimetidine route—BCM serves as a monochloromethylating agent under Lewis-acid catalysis, replacing historically employed formaldehyde-hydrogen chloride systems that generate high levels of bis-chloromethyl ether impurity. The process stream operating under ICH Q7 GMP for active pharmaceutical ingredient starting materials employs anhydrous zinc chloride (0.08–0.12 molar equivalents relative to the imidazole substrate) in a dichloromethane co-solvent matrix, with BCM metered at a molar ratio of 1.03–1.07:1 (chloromethylating agent/substrate) over 90–120 minutes while the jacket maintains a temperature of −3 °C to +2 °C; exceeding +5 °C accelerates dialkylation side-reactions that generate the quaternary imidazolium impurity CP-1, which is difficult to purge crystallographically. The biphasic quench uses pre-chilled 10 % aqueous sodium bicarbonate at 0 °C to hydrolyse residual zinc complex without thermally degrading the acid-labile chloromethyl group, and the organic layer is passed through a wiped-film evaporator operating at 2.7 kPa and 45 °C wall temperature to strip BCM for recovery (recovery yield typically 92–94 %). Residual BCM in the crystallised intermediate is controlled to ≤60 ppm to satisfy ICH Q3C Option 1 Class 2 solvent limits, with verification by headspace GC-MS using a DB-624 30 m × 0.32 mm column. The terminal manufactured product is a crystalline free-base intermediate with purity ≥99.0 % (HPLC area), destined for thioether coupling to cimetidine or ranitidine analogues in downstream drug-substance manufacturing suites.

Pre-Emergence Herbicide Backbone Construction via Bromochloromethyl Ketone Intermediates: Synthesis of certain sulfonylurea and triazolopyrimidine herbicide precursors exploits BCM for the introduction of a bromochloromethyl ketone moiety onto a substituted aryl framework under Friedel-Crafts acylation conditions. The reaction is carried out in a glass-lined reactor with an anchor agitator at 80–100 rpm, where BCM is combined with the aromatic substrate and an acyl halide in the presence of anhydrous aluminium chloride (1.05–1.15 equivalents) at a charge ratio of 1.10–1.20 mol BCM per mol synthetic target. Critical to process yield is the control of local exotherms during the 30-minute induction period, as thermal spikes above 15 °C lead to preferred α-halogen scrambling that yields a regioisomeric impurity profile exceeding the 0.4 % specification in the technical-grade active ingredient. Compliance with FAO/WHO Manual on Development and Use of Pesticide Specifications (2016) Section 5.2 requires that the isolated bromochloromethyl ketone intermediate carries a total halogenated volatile organic residue below 500 mg·kg⁻¹, which is achieved by a toluene azeotropic distillation finishing step at 60 °C and 8 kPa until Karl Fischer titration reads ＜200 ppm water. The resulting intermediate is shipped in epoxy-lined steel drums under nitrogen blanket to formulation plants where it is elaborated into dry-flowable or suspension-concentrate herbicidal end-products registered under REACH Annex XVII entries. Large-scale campaigns routinely process 800–1200 kg batches, and in-line Raman spectroscopy is employed to track the disappearance of the BCM C–Br stretching band at 610 cm⁻¹ as the reaction endpoint criterion.

Density-Tuned Fractionation of Kimberlite Indicator Minerals: Exploration laboratories performing heavy-liquid separation of chromian diopside, pyrope garnet, and ilmenite from till samples routinely adjust BCM-based heavy liquids to target densities between 1.95 g·cm⁻³ and 2.20 g·cm⁻³ by volumetric blending with analytical-grade n-heptane or perfluorohexane, using a calibrated Anton Paar density meter to maintain tolerance within ±0.005 g·cm⁻³ to prevent cross-contamination of mineral separates. The separation protocol aligns with ISO 7936:1992 and the ASTM D4371-06(2019) float–sink test method, where a 10–20 g sieve fraction (0.5–1.0 mm) is introduced into a pear-shaped separatory funnel containing 150 mL of the density-adjusted BCM medium; after a 15-minute settling interval, the sink fraction is drained through a PTFE stopcock onto a 45 µm stainless-steel sieve, rinsed with technical-grade acetone, and dried at 60 °C under reduced pressure. A strict environmental health boundary requires that all open-vessel handlings be conducted inside a walk-in fume hood with face velocity ≥0.5 m·s⁻¹ and that personal exposure monitoring remains below the 200 ppm 8-hour time-weighted average threshold adopted from ACGIH guidance for structurally related aliphatic halocarbons. Terminal products are 50–500 g heavy-mineral concentrates packed into inert glass vials for electron-microprobe confirmation, with the spent BCM medium being recovered by simple fractional distillation at atmospheric pressure (68–70 °C cut) and reused for up to six cycles before dissolved humate-derived discoloration necessitates a wash with 5 % sodium hydroxide solution.

Producing Anhydrous ClCH₂MgBr Solutions for Pharmaceutical Research

Contract synthesis organisations manufacture chloromethylmagnesium bromide in diethyl ether or 2-methyltetrahydrofuran solutions by reacting magnesium turnings (particle size 0.5–2.0 mm, activated by iodine vapour at 2 kPa) with BCM at a stoichiometric ratio of 1.08 g-atom Mg per mole BCM, maintaining a steady reflux at 34–36 °C (ether) or 78–80 °C (2-MeTHF) under an argon blanket with oxygen and moisture levels each certified below 3 ppm. The insertion selectivity for the C–Br bond over the C–Cl bond ensures that the Grignard reagent composition is principally ClCH₂MgBr, confirmed by ¹³C NMR (δ 12.8 ppm, CD₃CN) and total base content titration; however, batch records from 20-litre jacketed reactors show that at addition rates exceeding 0.15 mol BCM·h⁻¹ per litre of solvent, Wurtz-type homocoupling yields detectable (＞0.5 area%) 1-chloro-2-bromoethane, reducing the effective molarity of the reagent to below its nominal 0.5 M specification. The commercial product is supplied as a supernatant solution decanted from excess magnesium in septum-capped Sure/Seal™ bottles containing molecular sieves, shipped under UN 3399 (organometallic substance, liquid, water-reactive) and governed by the stability criterion of ≤3 % concentration drop after 28 days storage at −20 °C. Downstream, this Grignard reagent is utilised by medicinal chemistry laboratories for ring-opening epoxide additions and for constructing homoallylic alcohols when treated with aldehydes, making it a terminal speciality reagent rather than a bulk intermediate. No pharmacopoeial monograph applies, but the release certificate includes identity by GC-FID retention index and colorimetric active magnesium titration per ASTM E1068-23, with residual BCM limited to ＜0.1 mol% relative to the Grignard concentration to avoid side reactions in subsequent coupling steps.

Designated Halon 1011 under the fire suppression nomenclature and registered as CAS 74-97-5, bromochloromethane (BCM, CH₂BrCl) is supplied in two primary purity grades: technical grade (99.0% minimum by GC, ASTM D5134) and high-purity grade (99.5% minimum, with individual halogenated homologues limited to <0.2% each). The product is a clear, heavy, non-flammable liquid with a characteristic haloform odour, manufactured via sequential halogenation of methane or by hydrodebromination of dibromochloromethane over a palladium-on-carbon catalyst at 80–120°C and 0.3–0.5 MPa H₂ pressure. Bulk shipments typically employ lined ISO tank containers UN T50; smaller quantities are packaged in HDPE jerricans or epoxy-lined steel drums under nitrogen blanket.

Typical Commercial Specification Ranges
Property	Test Method	Technical Grade	High-Purity Grade
Purity (GC area %)	ASTM D5134	≥99.0	≥99.5
Density at 20°C	ASTM D4052	1.930–1.940 g/mL	1.933–1.937 g/mL
Boiling range	ASTM D1078-05	67.0–69.0°C	67.5–68.5°C
Water content	Karl Fischer ASTM D1364	≤0.05%	≤0.02%
Acidity (as HBr)	ASTM D1613	≤0.001%	≤0.0005%
Non-volatile residue	ASTM D1353	≤0.005%	≤0.002%
Colour (APHA)	ASTM D1209	≤20	≤10

When Halon 1011 Is Deployed in Total-Flood Enclosures — Regulatory Limits and Quenching Kinetics

BCM functions as a fire extinguishing agent through a combination of physical cooling and radical trap mechanisms; its cup-burner extinguishing concentration for n-heptane is 4.2 vol% (ISO 14520), with a design concentration of 5.0 vol% for Class B hazards per NFPA 2001 legacy editions. Complete discharge from a pressurised system occurs within 10 seconds, and the agent achieves peak suppression by interrupting the H· + O₂ branching cycle. Nevertheless, the substance is classified as an ozone-depleting substance with an ODP of 0.12 (Montreal Protocol Annex C, Group II) and a 100-year GWP of 1470 (IPCC AR5). Production for fire extinguishing purposes has been phased out in all non-Article 5(1) parties, and new fixed systems are prohibited under EU Regulation 2024/590. Existing legacy installations in military vehicle engine compartments or aircraft dry bays are permitted only on an emergency-use basis with full containment and recovery, a condition that imposes logistical and operational burdens rendering BCM unsuitable for new fire protection design. Published data for long-term storage stability in pressurised cylinders shows slow hydrohalic acid generation when moisture exceeds 15 ppm, necessitating periodic acidity checks per ISO 7201-1.

Can Bromochloromethane Function as a Drop-in Replacement for Trichloroethylene in Metal Degreasing?

In vapour degreasing applications, BCM offers a boiling point of 68°C and a specific heat of 0.53 J/g·K, which enables effective removal of heavy drawing oils without the thermal distortion risk posed by trichloroethylene (boiling point 87°C). Its density of 1.93 g/mL enhances phase separation in two-sump degreasers, and its low surface tension (28.5 mN/m at 20°C, Wilhelmy plate method) allows penetration into 0.1 mm blind holes. However, BCM’s permissible exposure limit ( OSHA PEL) is 200 ppm as an 8-hour TWA, identical to trichloroethylene, yet the substance hydrolyses to corrosive HBr when in contact with aqueous condensate at the degreaser cooling coil interface. This mandates installation of a molecular sieve dryer on the water separator return line and continuous pH monitoring of the solvent phase; a drop below pH 5.0 triggers automatic shutdown per DIN 8964-3. The Montreal Protocol has eliminated emissive use of BCM for surface cleaning in signatory nations, restricting any degreasing application to hermetically sealed, closed-loop systems with zero atmospheric loss and waste solvent destruction via high-temperature incineration (>1100°C, 2-second residence time). These engineering controls, together with the need for titanium or fluoropolymer-lining of vapour zone surfaces to resist HBr attack, make the solvent uncompetitive against modern blended hydrofluoroethers despite the boiling point advantage.

Where bromochloromethane preserves a distinct technical role is in chemical synthesis, specifically as a reagent for introducing a CH₂X moiety under phase-transfer conditions. The following section examines the behaviour of BCM in the preparation of cyclopropanation precursors, a domain where its selectivity profile diverges sharply from that of dichloromethane or dibromomethane.

In the generation of dihalocarbene intermediates from CH₂BrCl under strongly basic conditions, the leaving-group hierarchy governs product distribution. When ground NaOH pellets ( 50% w/w aqueous) are mixed with BCM and a quaternary ammonium catalyst such as Aliquat 336 at 0–5°C in a custom jacketed glass-lined reactor equipped with a retreat-curve impeller, the initial dehydrohalogenation favours loss of HBr over HCl with a kinetic selectivity of approximately 4:1 (k_HBr/k_HCl) as determined by online Raman spectroscopy. The resulting bromochlorocarbene (:CBrCl) reacts preferentially with electron-rich olefins to give bromochlorocyclopropanes, yet prolonged stirring beyond 45 minutes at 10°C promotes a secondary Finkelstein-type halide exchange at the geminal carbon of the cyclopropane ring, leading to dibromocyclopropane enrichment that reduces the synthetic utility of the intermediate. Industrial-scale batches must maintain a strict temperature window of 0±2°C and a stoichiometric ratio of olefin:BCM of 1:1.1 to cap dibromo impurity at <3% GC area. Yield losses on a 500 L pilot batch attributed to uncontrolled temperature excursions averaged 12% across six campaigns at a contract synthesis facility in Visp, with the primary by-product identified as bromoform from over-alkylation. Contrast this with dichloromethane, which under the same conditions generates only :CCl₂, avoiding halogen redistribution but requiring higher activation temperature (40°C) and exhibiting a hazard from thermal runaway due to a more exothermic dehydrochlorination (ΔH_r = −180 kJ/mol vs. −142 kJ/mol for BCM, DSC measurement, Mettler Toledo HP DSC 2+). Dibromomethane, in turn, exclusively yields :CBr₂ and produces the most stable dihalocyclopropane product, yet its boiling point (97°C) restricts its recovery by vacuum distillation post-reaction; BCM’s lower boiling point allows recycling at 120 mbar and 35°C head temperature on a Kühni RPB structured packing column, HETP 0.25 m, cutting solvent regeneration energy by 40% relative to dibromomethane rectification.

Headspace Reactivity and Methylenation By-Products in Base-Catalyzed Systems

A further selectivity consideration arises when BCM is used as a methylenation agent in mixed-phase reactions involving amines or bulky phenoxides. The faster abstraction of the bromine atom by the nucleophile generates chloromethyl carbocation equivalents, which are susceptible to competitive solvolysis by residual water, producing formaldehyde and HCl. In a multipurpose 2000 L glass-lined reactor utilised for O-methylenation of catechol derivatives at 90°C in the presence of K₂CO₃ and BCM, the formation of bis(chloromethyl) ether as a genotoxic impurity exceeded the 1 µg/g threshold of ICH M7 whenever the reaction mass water content surpassed 0.15%. Consequently, the BCM feedstream must be dried in-line through a 3A molecular sieve column to <0.02% H₂O prior to dosing, and the reactor headspace is swept with dry nitrogen at a rate of 2 Nm³/h to evacuate HCl vapour, preventing autocatalytic acceleration of bromide release. This sensitivity to moisture contrasts with the behaviour of dichloromethane alkylations, which tolerate up to 0.5% water without significant oxychloride formation, though at the cost of slower conversion rates.

Comparative Physicochemical and Environmental Profile of Halomethanes
Parameter	Bromochloromethane	Dichloromethane	Chloroform	Bromoform	Dibromomethane
Boiling point (°C)	68	39.6	61.2	149.5	97
Density at 20°C (g/mL)	1.934	1.327	1.483	2.889	2.477
Dynamic viscosity at 25°C (mPa·s)	0.95	0.41	0.54	1.80	0.98
Dielectric constant (ε at 25°C)	7.1	8.9	4.8	4.4	6.7
ODP (CCl₃F = 1)	0.12	0.0	0.0	<0.1	0.0
GWP (100-year, CO₂ = 1)	1470	9	16	14	1.7
OSHA PEL (ppm, 8h-TWA)	200	25	50	0.5	—

Compared to dichloromethane, BCM exhibits higher boiling point and density, reducing evaporative loss in open-top process vessels by approximately 40% under identical ambient conditions. However, the presence of bromine elevates both ozone depletion potential and GWP to levels that exclude the molecule from any open-system application. Dibromomethane surpasses BCM in density and carbene selectivity but demands 20–30% longer batch cycle times due to elevated boiling point and higher viscosity, which retards pump transfer rates in multi-ton campaigns. Bromoform, while delivering the highest halogen content, solidifies at 8.3°C and frequently clogs unheated transfer lines in temperate climate manufacturing sites, requiring jacketed piping with 15°C warm glycol tracing.

Storage stability requires strict exclusion of atmospheric moisture and light. BCM is filled into stainless steel 316L or Hastelloy C-276 tanks with a nitrogen pad maintained at 0.2–0.5 bar(g). Prolonged contact with carbon steel produces pitting corrosion at water contents exceeding 50 ppm, driven by cathodic debromination and FeBr₂ formation. The substance must not be stored or mixed with strong bases, alkali metals, or primary amines; uncontrolled reaction with sodium amide, documented in a runaway incident in a 100 L batch reactor at 98°C, generated a pressure spike exceeding the 10 bar design limit within 8 seconds, traced to dibromocarbene polymerization. Transport classification under 49 CFR 172.101 is UN 1887, PG III, with subsidiary risk of chronic aquatic toxicity under GHS Category 3. Pre-drying with type 4A molecular sieves to <20 ppm H₂O is enforced for all synthesis-grade material before introduction into moisture-sensitive organometallic transformations.

HS Code	629414
Chemical Formula	CH2BrCl
Molecular Weight	129.38 g/mol
Cas Number	74-97-5
Appearance	colorless liquid
Melting Point	-86.5 °C
Boiling Point	68 °C
Density	1.934 g/cm³ at 25 °C
Refractive Index	1.481 at 20 °C
Solubility In Water	0.9 g/100 mL
Vapor Pressure	15.8 kPa at 20 °C
Flash Point	35 °C (closed cup)
Odor	sweetish, chloroform-like

Packing	Steel drum containing 250 kg of Bromochloromethane, with UN hazardous material labels and secure sealing for safe transport.
Container Loading (20′ FCL)	Container Loading (20′ FCL): Secure bromochloromethane drums upright, label as UN2512 (Class 6.1), and segregate from foodstuffs.
Shipping	Bromochloromethane (UN 1888) is a toxic, clear liquid classified as Hazard Class 6.1, Packing Group III. Ship in tightly sealed, properly labeled containers. Avoid contact with foodstuffs. Ensure adequate ventilation and segregate from oxidizing materials. Handle with care to prevent leaks or spills.
Storage	Bromochloromethane should be stored in tightly sealed, corrosion-resistant containers (e.g., glass or lined steel) in a cool, dry, well-ventilated area away from heat, ignition sources, and direct sunlight. Keep separated from strong oxidizers, acids, and alkalis. Ensure proper labeling and secondary containment to prevent leaks and environmental contamination.
Shelf Life	Bromochloromethane has a typical shelf life of 2–5 years when stored in a cool, dark, dry place.

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