What is Methylene Chloride Used For?

Methylene chloride can dissolve organic compounds, making it very useful as an industrial solvent for many industrial processes. In the food industry, for example, it’s used in the process of extracting caffeine from coffee beans. It’s also used in processing the extracts from hops and other flavourings.

Various industrial processes are dependent on methylene chloride as a reagent or solvent. These include paint stripping, manufacturing pharmaceutical products, producing paint removers, and cleaning or degreasing metals. There are also some specialised uses this chemical has based on its chemical and physical properties. For example, it can function as a heat engine for the drinking bird toy.

About Methylene Chloride

Methylene chloride is a volatile chemical compound that’s highly miscible with many organic solvents. Also known as dichloromethane (DCM), this compound is a colourless and highly volatile liquid at room temperature. The compound is commercially manufactured together with other important industrial organic compounds, like methyl chloride, chloroform, and carbon tetrachloride.

What Products Contain Methylene Chloride?

Although methylene chloride is used in various industrial applications, a few products actually contain the compound as an active ingredient or component. Some of the products that contain this compound include:

  • Paint Strippers: Many paint stripper brands have methylene chloride as the main ingredient
  • Adhesives: The substance is present in various types of adhesives, such as acrylic cement used by many hobbyists
  • Other products: Other products that have at least trace amounts of dichloromethane include automotive care products, lubrication oil, lithography products, and some general cleaning products. The substance is also used in cleaning medical equipment, particularly those with components that are heat sensitive

Methylene chloride also occurs naturally in oceans, near volcanoes, and in algal blooms. However, the overwhelming majority of the substance found in the environment is from industrial emissions.

How is Methylene Chloride Produced?

The main method used to manufacture methylene chloride is via the chlorination of methane. During this process, methane is mixed with chlorine at 400–500°C. A series of reactions progressively occur that eventually lead to the formation of methylene chloride, as shown in the balanced equations below:

CH4 + Cl2 → CH3Cl + HCl

CH3Cl + Cl2 → CH2Cl2 + HCl

CH2Cl2 + Cl2 → CHCl3 + HCl

CHCl3 + Cl2 → CCl4 + HCl

As you can see, the series of reactions doesn’t only produce methylene chloride, but also other byproducts, including chloromethane, dichloromethane, chloroform, carbon tetrachloride, and hydrogen chloride. The process isn’t 100% efficient but it produces other useful compounds.

What Are Methylene Chloride’s Physical, Chemical & Molecular Properties?

Methylene chloride is one of the simplest organohalogen compounds that has several industrial applications. These applications are largely owed to the molecular geometry of the substance, which gives rise to other physical emergent properties such as volatility, solubility, and boiling point.

It has a boiling point of 39.6°C and decomposes at 720°C under 760 mmHg of atmospheric pressure, which is equivalent to 1 atmosphere or 101.3 kPa. Meanwhile, it has the following solubilities in water at different temperatures:

  • 25.6 g/L (15°C)
  • 17.5 g/L (25°C)
  • 15.8 g/L (30°C)
  • 5.2 g/L (60°C)

The vapour pressure of the substance, which is related to its volatility, also varies at different temperatures:

  • 0.13 kPa (−70.5°C)
  • 2 kPa (−40°C)
  • 19.3 kPa (0°C)
  • 57.3 kPa (25°C)
  • 79.99 kPa (35°C)

Molecular Geometry

The molecular geometry of any compound can be determined by the way the atoms bond with each other. At the same time, we can determine the bond angle, hybridization, and polarity based on the molecular geometry of the compound.

In order to determine the molecular geometry of methylene chloride, we first need to write the Lewis structure. This gives us an idea of the electron pairs and positions of the atoms. The chemical formula and the Lewis structure of the compound is shown in the figure below:

You must determine the central atom to which all other atoms are attached. In this case, the central atom is the carbon of the methyl group. The second step is to calculate or count the number of sigma bonds, which is the same as the number of atoms directly bonded to the central atom.

The third step is to calculate the number of lone pairs based on the following formula:

After calculating the number of lone pairs, you can then calculate the steric number by adding the number of sigma bonds and number of lone pairs. In the case of methylene chloride, the steric number is four. You can now refer to the table below to determine the geometrical shape of the molecule:

As you can see, the geometry of methylene chloride is tetrahedral with bond angles at approximately 109°. The outer atoms tend to be an equal distance from one another. The asymmetry here is in the respective distances of the chlorine and hydrogen atoms from the central carbon atom.

Hybridization of Bonds

When chemicals react to form new compounds, the outermost electrons are the ones involved in bond formation. The orbitals of these electrons become hybrids, which determine the geometry of the molecules and their bonding properties. Refer to the table below to know the orbital hybridization of the tetrahedral molecule of methylene chloride:

As a tetrahedral molecule, the orbital hybridization of methylene chloride is sp3. This is a combination of one s orbital and three p orbitals, resulting in the bedding of the dumbbell orbitals, forming a tetrahedral shape with a common centre. See the illustration below:

Source

Is Methylene Chloride Used in Paint Strippers?

Some brands of paint strippers contain methylene chloride as an active ingredient. These are fast-working paint strippers that can remove pain in a matter of minutes. However, they carry serious health risks. They’re potentially carcinogenic and easily irritate the eyes and skin. You need to wear protective clothing and an air respirator when using this type of paint stripper products.

Red paint getting stripped from wood
Methylene chloride is a common ingredient in paint strippers

Is Methylene Chloride Toxic?

The toxicity level of methylene chloride is not as high as other types of chlorohydrocarbons. However, precautions should still be taken. It is highly volatile and can easily be inhaled, as well as irritate the lungs and skin. People who have prolonged exposure to it can experience the following symptoms:

  • Nausea and vomiting
  • Dizziness
  • Fatigue
  • Weakness
  • Numbness

In more severe cases, people may become suffocated and lose consciousness, resulting in coma or even death. The reason for this is the fact that the body metabolises methylene chloride into carbon monoxide, which can lead to poisoning.

This substance is conclusively linked to cancer in laboratory animals. However, the International Agency for Research on Cancer (IARC) has not found any evidence that it causes cancers in humans. This is why it’s only classified as potentially carcinogenic.

Is Methylene Chloride in Decaffeinated Coffee?

The organic solvent properties of methylene chloride make it very useful as a decaffeination agent – but don’t worry, it’s not considered a health risk when used in this way. In fact, product regulation agencies allow up to ten parts per million of residual trace amounts of this substance.

In actual practice, the coffee industry produces only one part per million residual amounts of methylene chloride in coffee beans. This is due to the fact that the high heat involved in the roasting process eliminates almost all traces of the substance since it’s highly volatile.

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