What is Methylene Chloride?

Methylene chloride, otherwise known as dichloromethane or DCM, is an organochlorine compound. It’s a colourless substance that can be distinguished by its chloroform-like smell. While it isn’t miscible with water, it can dissolve many polar organic compounds, making it an excellent solvent. Because of this, it’s well-suited to several industrial applications, such as pharmaceutical manufacturing, paint stripping, paint remover manufacturing, and metal cleaning.

Methylene chloride is actually a naturally occurring substance that can be found in oceans, macroalgae, wetlands, and in volcanoes. While it’s considered a pollutant in some ecological niches, the majority of methylene chloride found in the environment is from industrial pollution.

Methylene Chloride Structural Formula

The chemical formula for methylene chloride is CH2Cl2. The molecule of this compound has a tetrahedral structure with the carbon atom at the centre, surrounded by two hydrogen atoms and two chlorine atoms:

As you can see, there is asymmetry in the atomic sizes and relative distances of the surrounding atoms from the centre. Therefore, the molecular structure is often written in a simplified manner, as demonstrated by the illustration below:

The methyl group isn’t labelled in the above diagram, but is instead indicated by the angle rays connecting the two chlorine atoms. The vertex of the angle represents the methyl group at the centre of the molecule. This way of writing the structural formula is for simplicity purposes. It’s particularly useful when working with complex organic compounds in chains. This type of diagram is called a skeletal formula, but is also known as the shorthand formula or line formula.

How Dangerous is Methylene Chloride?

Methylene chloride isn’t as toxic as other types of simple chlorohydrocarbons. Nonetheless, it can have some serious health risks that you must take care to avoid. For example, the high volatility of this liquid makes it dangerous when inhaled, and it can also be easily absorbed through the skin.

Some symptoms of acute overexposure to methylene chloride via inhalation include: 

  • Dizziness
  • Nausea
  • Headaches
  • Loss of focus
  • Fatigue
  • Numbness
  • Feeling of weakness
  • Irritation of the upper respiratory tract

In more serious cases, the consequences of overexposure to this substance include:

  • Suffocation
  • Loss of consciousness
  • Coma
  • Death

The human body metabolises methylene chloride into carbon monoxide. Therefore, overexposure to this substance can lead to carbon monoxide poisoning. Acute exposure to it may also result in optic neuropathy and hepatitis. Meanwhile, prolonged exposure of the skin to methylene chloride may result in dissolving some of the fatty tissues of the skin, leading to chemical burns.

According to the International Agency for Research on Cancer (IARC), methylene chloride has shown carcinogenic effects on experimental animals. Laboratory experiments have shown that it causes cancer of the lungs, liver, and pancreas in animals. Some experimental animals exposed to the chemical also developed breast cancer and salivary gland cancer. While no evidence of the same effects is linked to cancers in humans, the chemical is classified as potentially carcinogenic all the same.

People who have pre-existing heart disease may exhibit abnormal heart rhythms or suffer heart attacks when they’re exposed to DCM. Those who have existing liver problems or nervous system problems may find their condition worsens after exposure to methylene chloride.

What Are Some of the Applications of Methylene Chloride?

Methylene chloride is highly volatile and can dissolve many types of organic compounds. It’s used in several chemical processes during the mass production of products. For example, the food and beverages industry uses it to decaffeinate coffee and tea, as well as to prepare extracts from hops and other natural flavourings.

The high volatility of the compound also makes it very useful as an aerosol spray propellant. This is why dichloromethane is commonly used as a blowing agent when manufacturing polyurethane foams.

Among DCM’s more specialised applications is its use as a heat engine. This is because its low boiling point allows it to extract mechanical energy from temperature differences. One example of this is the drinking bird toy, which works because of its sensitivity to the temperature difference between water and air, which methylene chloride plays a huge role in.

As a solvent for many organic compounds, dichloromethane also has the ability to weld certain types of plastics. One practical example of this is in the sealing of the casing for electric metres. DCM is also a component of plastic welding adhesives that are commercially available and extensively used by hobbyists who build model buildings. Meanwhile, the garment printing industry uses the compound when removing heat-sealed garment transfers.

Barrel of methylene chloride

How to Dispose of Methylene Chloride

The high volatility of this substance makes it difficult to properly dispose of without the risk of environmental contamination or possible associated health problems. Methylene chloride is under the hazardous waste category, but should not be disposed of alongside other types of hazardous waste aside from halogenated solvents.

The storage and disposal of methylene chloride also requires proper labelling of containers. The containers must be tightly sealed to prevent possible leaks, and good ventilation is required for both storage and disposal.

Moreover, the handling, use, cleanup, and disposal of this chemical in large quantities requires personal protective equipment (PPE), which should include a respirator. Workers who regularly handle and dispose of DCM must strictly follow proper safety protocols.

Is Methylene Chloride Soluble in Water?

Methylene chloride is a polar compound because of the way its atoms are arranged. However, it is not miscible with water. This is because its hydrocarbon component prevents it from forming a homogeneous mixture with water. It’s only soluble in water in a very limited sense – more specifically, it’s soluble in water at 25.6 g/L at 15 °C.

That said, DCM is miscible with the following solvents:

  • Ethyl acetate
  • Alcohol
  • Hexanes
  • Benzene
  • CCl4
  • Diethyl ether
  • CHCl3

As long as methylene chloride is properly handled, the associated health risks and environmental impact are negligible, though you must always follow the workplace protocols mandated by your company, and limit your exposure to it as much as possible.

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