Difluoromethane

Difluoromethane, also known as difluoromethylene, HFC-32, Methylene Fluoride, or R-32, is an organic compound of the dihalogenoalkane variety[1]. It has the formula CH2F2 and is a colorless gas at ambient conditions, slightly soluble in water, and exhibits high thermal stability[1]. Due to its low melting and boiling points (-136.0°C and -51.6°C, respectively), contact with difluoromethane can result in frostbite[1].

Synthesis

Difluoromethane is primarily synthesized through batch processes, involving the reaction of dichloromethane and hydrogen fluoride (HF) in the liquid phase, using SbCl5 as a catalyst[1]. However, due to the hazardous properties of hydrogen fluoride, a new synthesis method has been developed, allowing for constant flow production of difluoromethane in an isolated chamber[1].

Applications

Difluoromethane is commonly used in endothermic processes such as refrigeration or air conditioning due to its ability to undergo endothermic processes[1]. It is also used as a fire extinguishant[1]. The atmospheric concentration of difluoromethane has been monitored at various latitudes since 2009[1].

Properties and Safety

Difluoromethane has a 100-year global warming potential (GWP) of 675 times that of carbon dioxide and an atmospheric lifetime of nearly 5 years[1]. It is classified as A2L - slightly flammable by ASHRAE, and has zero ozone depletion potential (ODP)[1]. The common refrigerant R-410A is a zeotropic, 50/50-mass-percent mixture of difluoromethane and pentafluoroethane (R-125)[1]. Difluoromethane shows slight maternal and developmental toxicity at concentrations of approximately 50,000 ppm in rats, but not in rabbits[1]. The exposure limitations set on difluoromethane for human use are 1,000 ppm, making exposure to dangerous levels unlikely[1].

Toxicity and Handling Precautions

Difluoromethane is considered hazardous by the OSHA Hazard Communication Standard (29 CFR 1910.1200)[2]. It may cause frostbite, displace oxygen and cause rapid suffocation, and may form explosive mixtures with air[2]. Precautions include keeping it away from heat, hot surfaces, sparks, open flames, and other ignition sources, and storing it in a well-ventilated place[2]. In case of leakage, all ignition sources should be eliminated, and the area should be approached with caution[2]. Liquid difluoromethane can cause burns similar to frostbite[2].

Availability and Specifications

Difluoromethane is sold by the pound/kilogram, with any quantity custom filled[3]. It is shipped as a liquefied gas under its own vapor pressure (205 psig @ 70°F)[3]. Typical specifications include 99.99% purity[3]. Sigma-Aldrich offers difluoromethane with a purity of 99.7%[4].

Citations:

[1] https://en.wikipedia.org/wiki/Difluoromethane

[2] https://www.airgas.com/msds/001054.pdf

[3] https://www.advancedspecialtygases.com/Halocarbon%2032.html

[4] https://www.sigmaaldrich.com/HU/en/product/aldrich/318043

[5] https://pubchem.ncbi.nlm.nih.gov/compound/Difluoromethane