Use and Manufacturing

1 Chemical Reactivity

Reacts vigorously with active metals (lithium, sodium, potassium) and with strong bases (potassium tert-butoxide) (Sax, 1984)

2 GHS Classification

Signal: Warning

GHS Hazard Statements

H351: Suspected of causing cancer [Warning Carcinogenicity]

Precautionary Statement Codes

P201, P202, P281, P308+P313, P405, and P501

3 Methods of Manufacturing

The predominant method of manufacturing methylene chloride; employs as a first step the reaction of hydrogen chloride; and methanol; to give methyl chloride;. Excess methyl chloride; is then mixed with chlorine; and reacts to give methylene chloride;, chloroform;, and carbon tetrachloride; as coproducts. This reaction is usually carried out in the gas phase thermally but can also be done catalytically or photolytically. Parallel reactor trains operating on different feeds, CH4-CH3Cl or CH3Cl-CH2Cl2, are known. At low temperature and high pressure, the liquid-phase process is capable of giving high selectivities to methylene chloride;.

4 Potential Exposure

The principal route of human exposure to methylene chloride is inhalation of ambient air.Occupational and consumer exposure to methylene chloride in indoor air may be much higher, especially from spray painting or other aerosol uses. People who work in these places can breathe in the chemical or it may come in contact with the skin.Methylene chloride has been detected in both surface water and groundwater samples taken at hazardous waste sites and in drinking water at very low concentrations.

5 Purification Methods

Shake it with portions of conc H2SO4 until the acid layer remains colourless, then wash with water, aqueous 5% Na2CO3, NaHCO3 or NaOH, then water again. Pre-dry with CaCl2, and distil it from CaSO4, CaH2 or P2O5. Store it away from bright light in a brown bottle with Linde type 4A molecular sieves, in an atmosphere of dry N2. Other purification steps include washing with aqueous Na2S2O3, passage through a column of silica gel, and removal of carbonyl-containing impurities as described under Chloroform. It has also been purified by treatment with basic alumina, distillation, and stored over molecular sieves under nitrogen [Puchot et al. J Am Chem Soc 108 2353 1986]. Dichloromethane from Japanese sources contained MeOH as stabiliser which is not removed by distillation. It can, however, be removed by standing over activated 3A Molecular Sieves (note that 4A Sieves cause the development of pressure in bottles), passed through activated Al2O3 and distilled [Gao et al. J Am Chem Soc 109 5771 1987]. It has been fractionated through a platinum spinning band column, degassed, and distilled onto degassed molecular sieves Linde 4A (heated under high vacuum at over 450o until the pressure readings reached the low values of 10-6 mm, ~1-2hours ). Stabilise it with 0.02% of 2,6-di-tert-butyl-p-cresol [Mohammad & Kosower J Am Chem Soc 93 2713 1971]. [Beilstein 1 IV 35.] Rapid purification: Reflux over CaH2 (5% w/v) and distil it. Store it over 4A molecular sieves.