Methylene Chloride TCI

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Methylene Chloride TCI (dichloromethane, CAS 75-09-2) is supplied as a high-purity reagent for organic synthesis, liquid-liquid extraction, surface preparation, and laboratory cleaning. The product identity is defined by the linear formula CH₂Cl₂, a molar mass of 84.93 g mol⁻¹, a boiling range of 39.8–40.0 °C at 101.3 kPa, a density of 1.325 g mL⁻¹ at 25 °C, and a refractive index n20/D of 1.4242. TCI packaging uses amber glass bottles with fluoropolymer-lined caps in 500 mL and 1 L formats. The TCI catalogue item is the high-purity reagent, not a formulated degreasing solvent; stock-keeping units vary by bottle size and stabilizer option, and the lot-specific certificate of analysis should be checked before use because preservative-free and stabilizer-containing packaging configurations are not interchangeable in downstream catalytic reactions.

What Controls the Purity Profile of TCI Methylene Chloride?

Purity is assessed by gas chromatography with flame ionisation detection, Karl Fischer titration, and gravimetric residue analysis. The critical failure modes are hydrolytic release of free acid, accumulation of higher-boiling stabilizer residues, and water ingress during repeated bottle opening. A representative release profile is presented in Table 1. Gas chromatographic assay typically uses a 30 m × 0.32 mm fused-silica column coated with 5% phenyl methylpolysiloxane; the stationary phase separates chloroform, carbon tetrachloride and 1,2-dichloroethane from dichloromethane. These halocarbon impurities, if present, can quench organometallic catalysts or co-elute with target analytes in GC-MS extract scans. Water is determined by coulometric Karl Fischer titration under ASTM E203-16; water above 0.05% promotes slow hydrolysis and raises the free-acid value. Nonvolatile residue is measured by evaporation of a 100 mL aliquot in a platinum or borosilicate dish under ASTM D1353-13. The ≤0.005% limit is operational because less volatile impurities concentrate in rotary evaporator residues and distort total dissolved solids measurements.

The tabulated values are release criteria, not a guarantee of performance in any specific reaction. For catalytic hydrogenation, olefin metathesis, and radical polymerisation, the stabilizer identity and concentration must be checked on the certificate of analysis because amylene at even low residual levels can poison palladium and platinum surfaces. If a stabilizer-free item is not in stock, the solvent can be washed with sulfuric acid and distilled over calcium hydride under dry nitrogen using Schlenk-type glassware, but this laboratory preparation introduces a distillation step and a separate acid-handling operation.

Liquid-liquid extraction with dichloromethane places the organic phase below the aqueous phase where the density of 1.325 g mL⁻¹ creates a stable lower layer. Continuous extractors for chlorinated solvents require fluoropolymer stopcocks and PTFE sleeves because chlorinated solvents swell and embrittle polyolefin fittings. The low boiling point of 39.8–40.0 °C permits concentration in a rotary evaporator at bath temperatures of 35–40 °C and pressure ramps from 500 mbar to 200 mbar. This reduces thermal damage to thermolabile analytes relative to higher-boiling chloroform or toluene. Compared with technical-grade dichloromethane, TCI product is differentiated by low nonvolatile residue and controlled free halogens; technical solvent grades often carry unspecified stabilizer packages that appear in GC-MS as unresolved complex matter in the C9–C14 range. Recoveries of semivolatile analytes should be verified by matrix spikes under US EPA 3510C or an equivalent validated liquid-liquid extraction protocol. Published data for TCI-specific extraction recoveries in environmental matrices are limited, so matrix-matched validation remains the operative control.

Because dichloromethane is classified as a suspected human carcinogen under GHS H351, the TCI product should be handled only in fume hoods with demonstrated containment. Storage at 15–25 °C in the original amber bottle, with the cap closed under dry air or nitrogen, limits water uptake and photochemical oxidation. Repeated opening of the bottle is a common source of batch-to-batch variance in trace water; after 6 months of intermittent use, coulometric Karl Fischer re-testing is recommended before use in water-sensitive reactions. The product is not classified as flammable, but the vapour is heavier than air and can accumulate in low-lying areas; work areas without ramped ventilation should be avoided. The stabilizer, when present, may be consumed over time because it reacts with acidic species generated by slow degradation; this is another reason to check the certificate of analysis before catalytic work.

When Drying and Stabilizer Selection Determine Suitability in Organometallic Work

Organometallic transformations impose more stringent drying requirements than bulk release tests. Dichloromethane intended for Grignard reagents, alkyllithium compounds, Friedel–Crafts catalysts, or low-valent transition-metal complexes is dried by passage through an anhydrous solvent purification system with activated alumina and copper catalyst columns under dry nitrogen, or by reflux over calcium hydride followed by distillation in Schlenk-type glassware. The target water content after drying is <10 ppm by coulometric Karl Fischer; this is a process threshold rather than a purchase specification. Amylene-stabilized dichloromethane is a problematic feed for this drying sequence because 2-methyl-2-butene boils at 38.6 °C, too close to dichloromethane for complete separation by simple distillation. The olefinic stabilizer can form π-allyl complexes or compete for open coordination sites on palladium, platinum, and ruthenium centres. If amylene-free material is not available, the stabilizer is removed by stirring with concentrated sulfuric acid, separating the acid layer, washing with water and sodium bicarbonate, drying over activated 4A molecular sieves, and distilling under inert gas. This procedure is exothermic and must be performed in a fume hood with continuous ice-bath cooling of the wash vessel. Residual olefin is confirmed by headspace GC-MS before catalyst loading; an absence of the amylene molecular ion in extracted-ion chromatograms is the operational endpoint.

Vapour Degreaser Chemistry, Thermal Stability, and Equipment Compatibility

Vapour degreasing is not an intended use of TCI high-purity methylene chloride. Industrial vapour degreasing grades are formulated with acid-scavenging stabilizers and high-temperature inhibitors that suppress decomposition on hot vapour-generating surfaces. Reagent-grade dichloromethane without such additives may generate hydrogen chloride and traces of phosgene at metal surfaces above 120 °C; the risk is highest on overheated immersion heaters or in unvented vapour baths. Equipment compatibility is limited to stainless steel, glass, PTFE, and PVDF. Aluminium, zinc, magnesium, sodium, potassium, and strong alkalis are incompatible and can induce dehalogenation. The OSHA standard 29 CFR 1910.1052 establishes an 8-hour time-weighted average permissible exposure limit of 25 ppm, a 15-minute short-term exposure limit of 125 ppm, and an action level of 12.5 ppm. Fume hood containment should be verified under ASHRAE 110-2016; exposure monitoring is performed with pump-and-sorbent tubes analyzed by thermal desorption GC-MS or with calibrated photoionization detectors.

On solvent recovery units using wiped-film evaporators, the wall temperature must be held below 120 °C to avoid chloride release from dichloromethane decomposition; operators monitor the recovered distillate for free chloride by Argentometric titration or ion chromatography. This field observation is not unique to TCI material and applies to all high-purity chlorinated methanes. In laboratory rotary evaporators, the condenser should be vented to the fume hood, and the water bath should not exceed 40 °C during prolonged concentration of dichloromethane extracts.

Chloroform replacement is not a direct density-for-density substitution

Dichloromethane has a density of 1.325 g mL⁻¹ at 25 °C and a dielectric constant of 8.93; chloroform has a density of 1.492 g mL⁻¹ at 25 °C and a dielectric constant of 4.81. These values are not trivial interchangeables: chloroform’s higher density and lower dielectric constant alter phase separation, emulsion behaviour, and partition of moderately acidic or basic analytes. The boiling point difference of 21.4 °C means that dichloromethane concentrates faster and at lower bath temperature, but the lower boiling point also increases losses during prolonged extraction. The TCI high-purity product reduces the stabilizer-derived background that can otherwise interfere with trace-level quantification, but it does not reproduce chloroform’s selectivity for certain alkaloid or polar lipid fractionations. Method transfer from chloroform to dichloromethane therefore requires revalidation of extraction recovery, chromatographic retention, and detector background. Published data for this specific replacement in preparative natural-product isolation is limited; a matrix-spike recovery study remains the appropriate verification for each sample type.

Trace aromatic impurities and stabilizer residues in dichloromethane absorb in the low-ultraviolet region. The UV transmittance cutoff of high-purity dichloromethane is near 233 nm; for HPLC methods with UV detection below 235 nm, a spectrophotometric or HPLC-grade dichloromethane should be specified because the TCI reagent item intended for synthesis may not carry the additional absorbance guarantees of chromatography solvents. This distinction is operational, not a purity defect: the nonvolatile residue and water limits remain valuable for extraction and reaction use, while low-wavelength UV background must be measured lot-by-lot if no chromatographic grade is available.

Cleaning of sintered-glass frits and laboratory glassware with dichloromethane is limited to nonpolar residues. The solvent should not be combined with hot-air drying guns or heated nitrogen above 60 °C because residual liquid in confined glass frits can thermally decompose and release hydrogen chloride. If highly fluorinated or silicone greases are present, dichloromethane may leave a low-level residue that is better removed by a two-step rinse with hexane or acetone. This operational boundary arises from the solvent’s swelling behaviour and chlorinated-methane degradation chemistry, not from a specific TCI product deficiency.