What Is Methylene Chloride (CAS 75-09-2)?
Methylene chloride, also called dichloromethane or DCM, is a clear, colorless and highly volatile liquid with a mild, ether-like odor. Its CAS registry number is 75-09-2 and its molecular formula is CH2Cl2. The product is manufactured mainly by the chlorination of methane or methanol and is supplied in technical and high-purity grades, each matched to a different process duty.
DCM is only slightly soluble in water but is miscible with a wide range of organic solvents, including alcohols, ketones, esters and aromatic hydrocarbons. That combination of strong solvency, a low boiling point and non-flammable behavior is why the material has become a benchmark solvent for paint removal, precision cleaning and extraction operations.
Key Benefits of Methylene Chloride
Process engineers select methylene chloride for reasons that go well beyond simple solvency:
Powerful solvency: it dissolves resins, oils, greases, waxes, adhesives and many polymers that resist aqueous cleaners.
Fast evaporation with low residue: with a boiling point near 39.6 °C the solvent flashes off quickly and leaves almost no film, protecting downstream adhesion, plating and inspection steps.
Non-flammable: DCM has no flash point under normal ambient conditions, which lowers fire and explosion risk in storage, transport and open-bath operation.
Compatibility with common metals: it is non-corrosive to carbon steel, stainless steel and aluminium under normal handling conditions.
Formulation flexibility: it can be blended with alcohols, ketones and esters to adjust evaporation rate, viscosity and selectivity.
Cost efficiency: large-scale production keeps the cost per kilogram low, which matters in high-volume stripping and degreasing lines.
Because the solvent penetrates coatings quickly and carries dissolved material away, cycle times in stripping and cleaning lines are shorter than with slower-evaporating alternatives, and equipment downtime is reduced.
Physical and Chemical Properties
| Property | Typical value |
|---|---|
| CAS number | 75-09-2 |
| Molecular formula | CH2Cl2 |
| Molar mass | 84.93 g/mol |
| Appearance | Clear, colorless liquid |
| Odor | Mild, sweet, ether-like |
| Density at 20 °C | About 1.33 g/cm³ |
| Boiling point | About 39.6 °C |
| Melting point | About −96.7 °C |
| Solubility | Slightly soluble in water; miscible with most organic solvents |
| Flammability | Non-flammable under normal conditions |
| Transport classification | UN 1593, class 6.1 toxic substance |
The figures above describe standard commercial material and serve as a general reference. Tighter assay and impurity tolerances are agreed with the supplier for each specific application.
Industrial Applications
Paint stripping and thinning. Methylene chloride is the classic active ingredient of heavy-duty strippers used to remove paint, varnish, lacquer and powder coatings from wood, metal and masonry. It swells and lifts the film so that it can be scraped away without damaging the substrate, and it is used as a thinner in industrial coating formulations where controlled drying is required.
Precision cleaning and degreasing. Metal parts, moulds, tooling, electronic assemblies and optical components are cleaned in DCM baths to remove oils, fluxes, mould-release agents and particulates. The fast, residue-free drying is critical wherever a leftover film would interfere with bonding, soldering, plating or optical inspection.
Extraction. The solvent is used to extract active pharmaceutical ingredients, natural flavours, fragrances and caffeine, and to recover valuable compounds from process streams. Its selectivity and easy recovery by distillation make it economical in closed extraction loops.
Coatings, adhesives and polymer processing. DCM serves as a carrier and diluent in adhesive and sealant systems, as a processing solvent for cellulose esters and other polymers, and as a swelling and bonding aid in plastics assembly work.
Safe Handling and Storage
Although methylene chloride is less acutely toxic than several other chlorinated solvents, exposure must be controlled. Vapour is heavier than air and can accumulate in pits, tanks and low-lying areas, so adequate general ventilation plus local exhaust at the point of use is essential. Occupational exposure limits such as the OSHA permissible exposure limit of 25 ppm as an 8-hour time-weighted average are applied in most plants.
Recommended personal protection includes chemical-resistant gloves, splash goggles or a face shield, and respiratory protection with organic vapour cartridges where limits may be exceeded. Nitrile gloves offer only limited resistance to DCM and should be replaced frequently. The solvent should not be heated to high temperatures, because thermal decomposition releases hydrogen chloride and trace amounts of phosgene. Store it in clearly labelled, tightly sealed containers away from strong oxidizers, strong alkalis, open flames and hot surfaces, and handle waste through an approved solvent recovery or incineration route.
Frequently Asked Questions
Q: What is the CAS number of methylene chloride?
Methylene chloride, also known as dichloromethane, has the CAS registry number 75-09-2 and the molecular formula CH2Cl2.
Q: What are the main benefits of methylene chloride?
It combines powerful solvency with fast evaporation and low residue, is non-flammable, is compatible with common metals, blends easily with other organic solvents and remains cost-effective at high volumes.
Q: Is methylene chloride flammable?
No. Under normal ambient conditions DCM has no flash point, which removes the fire and explosion hazards associated with many other organic solvents.
Q: What is the boiling point of methylene chloride?
Methylene chloride boils at about 39.6 °C, which is why it evaporates quickly and leaves almost no residue on cleaned surfaces.
Q: What is methylene chloride used for?
Its main uses are paint stripping and thinning, precision cleaning and degreasing of metal and electronic parts, extraction of active compounds and flavours, and as a carrier solvent in coatings, adhesives and polymer processing.
Q: Is methylene chloride corrosive to metals?
No. It is non-corrosive to carbon steel, stainless steel and aluminium under normal handling conditions, so it can be used in metal cleaning and stripping equipment without causing pitting or rust.
Q: How should methylene chloride be stored?
Keep it in tightly sealed, clearly labelled containers in a cool, well-ventilated area away from strong oxidizers, strong alkalis, ignition sources and hot surfaces, and never heat it to the point of thermal decomposition.