DICHLOROMETHANE: STRUCTURE, PROPERTIES, USES, TOXICITY - CHEMISTRY - 2025

The dichloromethane, also known as methylene chloride, is an organic compound whose chemical formula is CH ₂ Cl ₂. Specifically, it is an alkyl halide derived from methane gas. Unlike methane, this compound is a colorless, polar liquid.

It was initially synthesized in 1839 by the French chemist and physicist Henri Victor Regnault (1810-1878), who managed to isolate it from a mixture of chlorine and chloromethane exposed to sunlight.

Structural formula of dichloromethane. Source: Jü

Dichloromethane is produced industrially by treating methane or chloromethane with chlorine gas at elevated temperatures (400–500 ºC). Together with dichloromethane, chloroform and carbon tetrachloride are produced in the process, which are separated by distillation.

Dichloromethane is used as a solvent that allows the welding of plastic materials and for degreasing metals. It is also used in the decaffeination of coffee and tea, as well as a hop extractor and diluent for color additives and inks to mark fruit.

Dichloromethane is a toxic compound that can cause irritation of the nasal passages and throat by inhalation. Liver damage has been reported in workers exposed to high concentrations of dichloromethane. In addition, it is a mutagenic agent, being suspected of being carcinogenic.

Structure

Molecular structure of dichloromethane. Source: Gabriel Bolívar via MolView.

The first image showed the structural formula of CH ₂ Cl ₂, in which its covalent bonds CH and C-Cl stand out. Above is also its structure represented by a model of spheres and bars. Note with the naked eye that the CH bonds (white spheres) are short, while the C-Cl bonds (green spheres) are long.

The geometry of CH ₂ Cl ₂ is tetrahedral; but distorted by the bulkier chlorine atoms. One end of the tetrahedron is defined by the two chlorine atoms, more electronegative than those of hydrogen and carbon. Therefore, a permanent dipole moment (1.6D) is established in the CH ₂ Cl ₂ molecule.

This allows the dichloromethane molecules to interact with each other through dipole-dipole forces. Likewise, these intermolecular interactions are responsible for this compound existing as a liquid despite its low molecular mass; a liquid that, however, is quite volatile.

Properties

Appearance

Colorless liquid.

Molar mass

84.93 g / mol.

Odor

Sweet, similar to chloroform.

Odor threshold

205-307 ppm.

Density

1.3266 g / cm ³ (20 ° C).

Melting point

- 97.6 ° C.

Boiling point

39.6 ° C.

Water solubility

25.6 g / L at 15 ° C and 5.2 g / L at 60 ° C.

Dichloromethane is hardly soluble in water. Although both molecules, CH ₂ Cl ₂ and H ₂ O, are polar, their interactions are inefficient, possibly due to the repulsion between the chlorine and oxygen atoms.

Solubility in other solvents

Miscible with ethyl acetate, alcohol, hexane, benzene, carbon tetrachloride, diethyl ether, chloroform, and dimethylformamide.

Octanol / water partition coefficient

Log P = 1.19.

Vapor pressure

57.3 kPa (25 ° C). This pressure corresponds to approximately 5.66 atm, reflecting a high vapor pressure.

Vapor density

2.93 in relation to air taken as 1.

Refractive index (πD)

1.4244 (20 ° C).

Viscosity

0.413 cP (25 ° C).

ignition point

Dichloromethane is not flammable, but when mixed with air it forms flammable vapors above 100ºC.

Autoignition temperature

556 ° C.

Stability

It is stable at ambient temperature in the absence of humidity, having a relative stability when compared to its congeners: chloroform and carbon tetrachloride.

It tends to char at high temperatures (300-450 ºC), when its vapors come into contact with steel and metal chlorides.

Decomposition

May decompose on contact with hot surfaces or a flame, emitting toxic and irritating fumes of phosgene and hydrogen chloride.

Corrosion

Dichloromethane attacks some forms of plastics, rubbers, and coatings.

Heat of vaporization

28.82 kJ / mol at 25 ° C.

Surface tension

28.20 dynes / cm at 25 ° C.

Reactivity

Dichloromethane reacts strongly with active metals, such as potassium, sodium, and lithium. Reacts with strong bases, eg potassium tert-butoxide. It is incompatible with caustics, oxidants and chemically active metals.

Additionally, it reacts with liquid oxygen in sodium and potassium alloys and nitrogen tetroxide. In contact with water it can corrode some stainless steels, nickel, copper, as well as iron.

Applications

Most of the uses and applications of dichloromethane are based on its properties as a solvent. Due to this characteristic, dichloromethane is used in the food, transport, medicine production industries, etc.

Food processing

Dichloromethane is used in the decaffeination of coffee beans and tea leaves. It is also used for the extraction of hops for beer, beverages and other food flavorings, as well as for the processing of spices.

Pharmaceutical industry

Dichloromethane is used for the preparation of cephalosporin and ampicillin, in addition to the manufacture of antibiotics, steroids and vitamins.

Photography

It is also used as a solvent in the production of cellulose triacetate (CTA), used in the creation of security films.

Electronic industry

It is an ideal compound for the production of printed circuit boards, being used to degrease the aluminum surface before adding the photoresist layer to the board.

Paints

Dichloromethane is a solvent found in varnishes and paint strippers, used to remove varnishes or paint coatings from various types of surfaces.

Transport

It is used to degrease metal parts and surfaces present in railway equipment, as well as in aircraft components.

Other uses

It is used as a spray propellant (aerosols) and as a blowing agent for polyurethane foam. It is also used as a fluid in some types of Christmas lights.

Toxicity

Acute effects

Inhaling dichloromethane can cause irritation of the upper airways, coughing, wheezing, or shortness of breath.

It can cause reddening of the skin, and if the compound remains on it for a long time, cause chemical burns. In contact with the eyes, dichloromethane produces a severe irritation that can extend to a burn.

In addition, it acts as a neurotoxin generating visual, auditory and psychomotor disturbances; but these effects are reversible when the inhalation of dichloromethane is stopped.

Chronic effects

Dichloromethane can affect the central nervous system, causing headaches, mental confusion, nausea, vomiting, and memory loss.

In animals it produces harmful effects on the liver, kidneys, central nervous system and cardiovascular system.

Regarding carcinogenesis, a significant increase in cancer deaths has not been reported in workers exposed to dichloromethane. However, studies in animals have shown an increase attributable to dichloromethane in the incidence of cancer of the liver and lungs, as well as benign tumors of the mammary glands.

References

1. Morrison, RT and Boyd, R, N. (1987). Organic Chemistry. 5 ^ta Edition. Editorial Addison-Wesley Interamericana.
2. Carey F. (2008). Organic Chemistry. (Sixth edition). Mc Graw Hill.
3. Graham Solomons TW, Craig B. Fryhle. (2011). Organic Chemistry. (10 ^th edition.). Wiley Plus.
4. National Center for Biotechnology Information. (2020). Dichloromethane. PubChem Database., CID = 6344. Recovered from: pubchem.ncbi.nlm.nih.gov
5. Wikipedia. (2020). Dichloromethane. Recovered from: en.wikipedia.org
6. Brumer. (July 14, 2018). Dichloromethane. Recovered from: brumer.com
7. MSDS Online. (2019). Dichloromethane (Methylene Chloride) Hazards & Safety Information. Recovered from: msdsonline.com
8. EPA. (2000). Methylene Chloride (Dichloromethane).. Recovered from: epa.gov