Short Answer
There is no chemical difference. Methylene chloride and dichloromethane are two names for the same compound: CH2Cl2, CAS 75-09-2, molecular weight 84.93. "Dichloromethane" is the systematic name, built from the parent name methane with two chlorine substituents, and it is the name used in formal nomenclature and in most safety data sheets. "Methylene chloride" is the older industrial and commercial name, derived from the methylene group, and it remains common in paint stripping, metal cleaning and pharmaceutical purchasing documents. Confusion usually arises from the abbreviation: DCM correctly stands for dichloromethane, whereas DMC denotes dimethyl carbonate, CAS 616-38-6, which is a completely different, non-chlorinated solvent.
Identity and Physical Properties
| Parameter | Typical value |
|---|---|
| Systematic name | Dichloromethane |
| Industrial synonym | Methylene chloride (DCM) |
| Chemical formula | CH2Cl2 |
| CAS number | 75-09-2 |
| Molecular weight | 84.93 g/mol |
| Boiling point | Approximately 39.6 C |
| Density at 20 C | Approximately 1.33 g/cm3 (sinks in water) |
| Flammability | Volatile, non-flammable in air under normal conditions |
| Solubility | Low in water; miscible with most organic solvents |
The technical data sheet should always carry the CAS number as well as the name, because the two names are used interchangeably in trade and only the CAS number removes the ambiguity between dichloromethane and dimethyl carbonate. Key control parameters are assay by gas chromatography, water by Karl Fischer titration under ASTM E203, colour under ASTM D1209, and acidity plus non-volatile residue.
Main Applications
Typical uses include paint removers and surface preparation, extraction in the pharmaceutical and food testing industries, reaction and crystallisation solvent in fine chemical synthesis, metal cleaning and degreasing, polycarbonate and polyurethane processing aids, adhesives and aerosol formulations, and physical foaming of certain plastics. Formulations are usually tailored to flash off quickly without leaving residue, so the solvent is normally specified with tight limits on non-volatile matter and acidity.
Frequently Asked Questions
Q: Is methylene chloride the same as dichloromethane?
A: Yes, they are the same compound, CH2Cl2, with CAS number 75-09-2. Dichloromethane is the systematic name and methylene chloride is the traditional industrial name used in trade and purchasing documents.
Q: What does DCM mean, and is it the same as DMC?
A: DCM is the accepted abbreviation for dichloromethane. DMC normally refers to dimethyl carbonate, CAS 616-38-6, a different non-chlorinated solvent, so always confirm the CAS number before ordering.
Q: Why is dichloromethane described as non-flammable?
A: Under normal ambient conditions its vapour does not form a flammable mixture in air, and it has no measurable flash point, so it is handled as a non-flammable solvent. It still evaporates readily, so vapour control and ventilation are required for health reasons.
Q: Which properties make it suitable for extraction?
A: High density, so it forms the lower layer; low boiling point, so the solvent can be stripped off gently; and broad solvency for organic compounds, which gives good recovery of the target substance.
Q: How is dichloromethane quality checked?
A: Assay by gas chromatography, water by Karl Fischer titration under ASTM E203, colour under ASTM D1209, and acidity and non-volatile residue by titration and evaporation. These four or five parameters normally appear on every certificate of analysis.
Q: Can dichloromethane be stored in aluminium equipment?
A: Wet dichloromethane can attack aluminium and some reactive metals, and it hydrolyses slowly to form acidic species, so stainless steel, glass-lined or fluoropolymer-lined equipment is preferred, with dry nitrogen blanketing for long term storage.
