1-Bromopropane (n-propylbromide or nPB) is an organobromine compound with the chemical formula CH3CH2CH2Br. It is a colorless liquid that is used as a solvent. It has a characteristic hydrocarbon odor. Its industrial applications increased dramatically in the 21st century due to the phasing out of chlorofluorocarbons and chloroalkanes such as 1,1,1-Trichloroethane under the Montreal Protocol.
Industrial routes to 1-bromopropane involve free-radical additions to the corresponding alkenes. In this way, the anti-Markovnikov product is obtained.[1]
A laboratory synthesis involves treating propanol with a mixture of hydrobromic and sulfuric acids:
CH3CH2CH2OH + HBr → CH3CH2CH2Br + H2O
Alternate synthetic routes include treating propanol with phosphorus tribromide or via a Hunsdiecker reaction with butyric acid.[2]
Like many other liquid halocarbons, 1-bromopropane finds use as a liquid or gaseous solvent. It is a solvent for adhesives in aerosol glues that glue foam cushions together. It is a solvent in asphalt production, in the aviation industry for maintenance, and in synthetic fiber production.[3] It is a solvent for degreasing plastics, optics and on metal surfaces, to remove soldering residues from electronic circuit boards.[4] It is an aggressive solvent with a Kauri-butanol value of 129 which is similar to 1,1,1-Trichloroethane[5]
Its increasing use in the 21st century resulted from the need for a substitute for chlorofluorocarbons and perchloroethylene as a dry cleaning solvent, however its use in dry cleaning has been steadily declining and by 2020, its use for dry cleaning is nearly obsolete[6] while perchloroethylene remained the most common solvent in dry cleaning as of 2024.
In the European Union, 1-bromopropane has been classified as reproductive toxicant per Registration, Evaluation, Authorisation and Restriction of Chemicals, which makes it a "substance of very high concern".[7]
As of January 5, 2022, 1-bromopropane has been added to the United States Clean Air Act list of Hazardous Air Pollutants (HAP).[8]
Since 2007, it has been approved for use under the U.S. EPA's Significant New Alternatives Policy (SNAP) as a suitable replacement for ozone depleting chemicals.[9] The U.S. EPA announced that, based on a work plan developed under the Toxic Substances Control Act of 1976, in 2013 it will begin a full risk assessment of 1-Bromopropane.[10]
The North Carolina Department of Labor's Occupational Safety and Health Division issued a Hazard Alert in 6/2014, as it "is not regulated to protect workers, consumers or the environment".[11]
In 2003, the American Conference of Governmental Industrial Hygienists (ACGIH) set the time-weighted average threshold limit value for an 8-hour exposure at 10 parts per million (ppm). In 2014, the ACGIH adopted a lower threshold limit value of 0.1 ppm as an 8-hour time-weighted average. The California Occupational Safety and Health Administration set the permissible exposure limit at 5 ppm in 2010. Though symptoms of overexposure can begin within 2 days of exposure, typically long-term exposure is more harmful.[4]
In 2008, the U.S. CDC recommended that use of 1-bromopropane as a replacement for perchloroethylene may require adjustment and modification of equipment, improved ventilation, and use of personal protective equipment.
In 2013, a peer-review panel convened by the U.S. National Toxicology Program unanimously recommended that 1-bromopropane, be classified as reasonably anticipated human carcinogens.[12]
Extended occupational exposure to 1-bromopropane in higher concentrations than recommended has resulted in significant injury to workers in the United States.[13] Its use as a solvent in aerosol glues used to glue foam cushions has been especially controversial. Reported symptoms of overexposure affect the nervous system and include confusion, slurred speech, dizziness, paresthesias, and difficulty walking, unusual fatigue and headaches, development of arthralgias, visual disturbances (difficulty focusing), and muscle twitching. Symptoms may persist over one year.[14] Other symptoms include irritation of mucous membranes, eyes, upper respiratory tract, and skin, as well as transient loss of consciousness.[4] Loss of feeling in the feet, an example of paresthesia, is colloquially called "dead foot" by workers who suffer from it. Of nationwide "more than 140 cushion workers nationwide, mostly from plants in Utah, Mississippi and North Carolina,[...] that had been exposed to dangerous levels of the chemical, many of them sickened and [are] unable to walk".[15] One worker's long-term exposure resulting in neurological damage was covered in the NY Times.[15] Air sampling for the level of 1-bromopropane and monitoring workers' urine for metabolites are both effective at measuring workers' exposure.[4]
Occupational exposure to 1-bromopropane typically occurs through breathing or skin contact; it is easily absorbed into the blood via the skin. Replacing 1-bromopropane with water or acetone-based adhesives is the preferred NIOSH option for controlling occupational exposure, but other options include engineering controls like isolation and ventilation, administrative controls, and PPE that includes respiratory and skin protection.[4] 1-Bromopropane can penetrate most gloves, but not those made of polyvinyl alcohol or laminates.[3]
Animal studies of 1-bromopropane have showed that it is a carcinogen in those models.[4] Rodents exposed to 1-bromopropane developed lung, colon, and skin cancer at higher rates.[3]
Although 1-bromopropane is naturally produced, it is one of the very short-lived substances that depletes ozone. Because 1-bromopropane is so short-lived, its ozone depletion potential (ODP) is dependent on the latitude where it is released.[16] [17] According to the United States Environmental Protection Agency, the ODP is 0.013-0.018 in U.S. latitudes and 0.071-0.100 in tropical latitudes.