How many of you have heard of para-chlorobenzotrifluoride (PCBTF)? Or to give it a more systematic name, 1-chloro-4-(trifluoromethyl)benzene.1 In a previous article,2 I described the hazard of the xylene-ethylbenzene hydrocarbon mixture often used as a solvent in varnishes and glues. This solvent system is being phased out to be replaced by PCBTF (figure below), a compound whose own health and environmental effects seem to be poorly documented. This is an interesting story in itself.
Volatile hydrocarbons, such as xylenes, when released to the atmosphere contribute to the formation of photochemical smog. This is a particular concern in the state of California, which has led to the push for replacements that do not contribute to smog.
PCBTF has been commercially-produced since the 1960s, but initially only as an intermediate in the production of other chemicals. It was in the 1990s that PCBTF was first marketed as a solvent.3 The producer at the time, Occidental Chemical, petitioned the U.S. Environmental Protection Agency (EPA) for exemption from regulations pertaining to volatile organic compounds (VOCs) on the grounds that PCBTF did not contribute significantly to photochemical smog nor was it a significant greenhouse gas nor an ozone-depleting gas in the stratosphere. In the troposphere, PCBTF is transformed with an estimated half-life of 67 days by reaction with photochemically-produced hydroxyl radicals to give mainly 2-chloro-5-trifluoromethylphenol.4 The EPA subsequently approved the request for VOC regulation exemption, though Occidental Chemical ceased manufacture, and China seems to be the major producer now.
PCBTF is a colourless liquid that boils at 139°C and the vapour has a characteristic aromatic odour. Sold under the brand names of Oxsol 100 and SMC Spec 900, the great advantage of PCBTF as a solvent is its capacity to dissolve large quantities of non- and low-polarity molecules. The figure commonly cited is that 20 g of PCBTF will dissolve 22 g of printers’ ink.5 Also, the solvent has a low surface tension, so ink, paint and varnish solutions will easily penetrate cracks and crevices.
The upside seems to be that very small proportions of the solvent are needed to dissolve the pigment or varnish formulation, therefore the levels of VOC as the solvent evaporates will be comparatively less. The downside is that very little data seems to be available in terms of toxicity. The material safety data sheets (MSDS) listed online by the different vending companies are very uninformative. Even the U.S. Department of Labor documentation shows no toxicological information.6 The best source is the U.S. National Toxicological Program report which notes that studies have shown PCBTF to have the following effects on humans:5
Exposure induces skin, eye, and respiratory irritation, depression of central nervous system, and dermatitis due to defatting of the skin. Other symptoms include coughing, wheezing, a burning sensation, laryngitis, shortness of breath, headache, nausea, vomiting, lung irritation, chest pain, and edema. PCBTF is destructive to mucous membrane tissues.
So here is a compound that is being used as an industrial solvent in more and more contexts, but whose effects on health and the environment seem to be comparatively poorly documented.
References (websites accessed January 2014)
- This compound has six different names: p-chlorobenzotrifluoride;
(p-chlorophenyl)trifluoromethane; p-(trifluoromethyl)chlorobenzene; p-trifluoromethylphenyl chloride; and p-chloro-α,α,α-trifluorotoluene.
- G. Rayner-Canham, Chem13 News, February 2014,
pages 6 – 7.
- K. Wolf and M. Morris, Assessment, Development and Demonstration of Alternatives for Five Emerging Solvents, http://www.cdph.ca.gov/programs/hesis/Documents/emergingsolvents.pdf.
- Chemical Information Profile for 1-Chloro-4-(trifluoromethyl) benzene, National Toxicology program, https://ntp.niehs.nih.gov/ntp/noms/support_docs/pcbtf060409.pdf.
- 1-chloro-4-trifluoromethylbenzene Exposure Limits and Health Effects, https://www.osha.gov/dts/chemicalsampling/data/CH_228360.html.