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1-Chloro-1,1-difluoroethane, HCFC 142b

1-Chloro-1,1-difluoroethane,  known by trade names including Freon 142b, HCFC-142b, and R142b, is a haloalkane with the chemical formula CH₃CClF₂.  It falls in the category of Hydrochlorofluorocarbon (HCFCs), a class of chemicals known to cause environmental degradation as a pollutant.  It is used as a refrigerant and chemical intermediary in the production of polymers and foams.[1]  Today, it is scheduled for complete phaseout under the Montreal Protocol by 2030 because of its long atmospheric life span and the resulting damage to the ozone of the upper atmosphere. 1-Chloro-1,1-difluoroethane can be toxic to humans in very high concentrations, and therefore would be considered a dangerous industrial chemical only in unventilated areas or fire hazards.  

Properties

Austin Rist

142b was initially listed in the Montreal Protocol as a substitute for Chlorofluorocarbons to be used until 2040. It was described in 1986 as a good replacement for refrigerants used at high temperatures. Unlike other options, 142b has high thermal stability and capacities. The major concern of 142b usage is flammability as it has a lower flame limit of 10% and upper flame limit of 16.3% at standard temperature and pressure.

Of further concern is the general stability of the compound, having been found to have an estimated minimum life in the stratosphere of 138 years. Given the presence of chlorine in the molecule, the long lifetime could contribute to the atmospheric degradation sought to be avoided by the introduction of 142b and similar hydrochlorofluorocarbons (HCFC).

Production

Omar Valdivia-Romo

HCFC is produced from 1,1,1-trichloroethane and anhydrous hydrofluoric acid. This reaction can take place in  either the liquid phase, or using catalysts in either the liquid phase or vapor phase. Swarts-type catalysts based on antimony chlorides and fluorides can be used,or the reaction can take place over chromium oxide, ferric chloride or thorium tetrafluoride catalysts in the vapor phase. The reaction depends on varying hydrogen fluoride concentration, the contact time and reaction temperature for the chlorine exchange to take place.

CCl₂--CH₃ + 2HF ----->CClF₂ + 2HCl.

Freon 142b (HCFC-142b) is sold commercially as a refrigerant for heat pumps and as a chemical intermediary, although its sale and usage is regulated by the UN and numerous nations, including United States. Between 1992 and 2002 HCFC-142b along with HCFC-141b, HCFC-22 and HFC-134a showed rapid growth in the atmosphere with mean rates of 1.1, 1.6, 6.0, and 3.4 ppt/year, respectively. By the 2020 the EPA will have banned all production and importation of Freon 142b in accordance with the Montreal Protocol complete phaseout of R142b by 2020. After that time, equipment that relies on R142b can still be serviced with recycled gas or stockpiles. Because of increasing emissions in recent years, HCFC-142b production is not in equilibrium in the stratosphere. All other CFCs and HCFCs will be completely phased out of production and import by 2030, according to the protocol. Under the same regulations, the import and production of Freon 142b has been banned since 2010 except for quantities needed for servicing equipment, and all HCFC production was banned, again excepting continued servicing needs, in 2015.  AFEAS reportings between 2001 and 2005 does not report emissions from Russia, China, and India which contributed to HCFC 142b emissions because they continue to produce and sell HCFC-142b. As of june 23, 2015 all countries in the UN have ratified the original Montreal Protocol. This phaseout follows several decades of controlled use as an alternative to other CFCs deemed to impose more damaging effects to the environment.

Uses

Cooper Logan

About half of the global 1-Chloro-1,1-difluoroethane was produced in the United States in 2000, and more than half is used as a chemical intermediary in the production of fluoropolymers. In strictly controlled conditions, 1-Chloro-1,1-difluoroethane can react to form vinylidene fluoride, or VF2, and other vinyl polymers that are used as waterproofing in construction and manufacturing of products like cars.  

Industrial use of 1-Chloro-1,1-difluoroethane also relies on its application as a blowing agent. As a blowing agent, 1-Chloro-1,1-difluoroethane is used to spray pressurized polyurethane and as the accelerant in polystyrene foam products, such as styrofoam and packing peanuts.

Freon 142b is used to service cooling equipment today, though production of new equipment using the product is banned, and service providers are required to contain all leaks because the regulation of service providers is manageable compared with sale to consumers. Therefore, this use has become relatively insignificant and unfeasible over time.  Alternatives, such as the non-depleting HFC R-410A, are readily available as alternative refrigerants. However, Freon 142b has been used historically due to the volatility of the gas, allowing it to convert back and forth from liquid and solid phases at low temperatures (-10 C), absorbing and dispersing heat effectively.  This is the property that makes Freon 142b and other CFCs so attractive as refrigerants.  

Environmental considerations

Jiahui(Sophia) Wang

The direct effects of 1-Chloro-1,1-difluoroethane on the environment are minimal, but the unseen environmental impact on the atmosphere is very significant.  Although this gas causes only acute toxicity in mammals, no conclusive research links the chemical to irritation, genotoxicity, carcinogenicity, or reproductive toxicity.

While 1-Chloro-1,1-difluoroethane does not pose a significant health hazard at the vincinity of the release, they have significant long-term atmospheric consequences.  The properties of the compounds, especially volatility and hydrophobicity, are important because they result in the atmosphere becoming the reservoir for accumulated emissions.  Consequently, 1-Chloro-1,1-difluoroethane has an average lifetime in the upper atmosphere of 18 years, with a half life of 12.8 years.  In that time, a molecule of 1-Chloro-1,1-difluoroethane undergoes a series of chemical reactions that upset the homeostasis of the atmosphere.

Greenhouse Effect

Hydrofluorocarbons accumulate in the upper atmosphere over time. Among their properties, they absorb light very strongly in the infrared range (1000-1400 cm-1). The net result on the planet is an increase in the greenhouse effect typically resulting from methane and carbon dioxide. However, despite the influence of the greenhouse effect caused by HFCs, their overall concentration to the atmosphere is dwarfed by carbon dioxide and other emissions, resulting in a comparatively low effect.

Degradation of the Upper Atmosphere

Currently the atmospheric concentrations of some HFCs are growing significantly. Due to the lack of control and regulation on HFC production and usage, it is predicted that the concentrations of HFCs would increase continuously over time. These fluorocarbons are oxidized in the troposphere in reactions analogous to hydrocarbon oxidations. The reactions yield a peroxy radical, carrying the tendency to deplete stratospheric ozone, but on much a slower timescale than that of CFCs (Montzka, 1994), (McCulloch 1999).

Halogen acids as derived product

In water, the parent HFCs will hydrolyze rapidly to form HCl and HF. Reviewed amounts indicates that given the total sources of manmade HCl and HF, contributes only 1% of the total amount of HCl produced by anthropogenic activities and 20% of HF produced. The currently available data shows that halogen acids derived from HFCs is not expected to create heavy environmental impact.