Epichlorohydrin is traditionally manufactured from allyl chloride in two steps, beginning with the addition of hypochlorous acid, which affords a mixture of two isomeric alcohols:[5][6]
In the second step, this mixture is treated with base to give the epoxide:
In this way, more than 800,000 tons (1997) of epichlorohydrin are produced annually.[7]
Glycerol routes
Epichlorohydrin was first described in 1848 by Marcellin Berthelot. The compound was isolated during studies on reactions between glycerol and gaseous hydrogen chloride.[8]
Reminiscent of Berthelot's experiment, glycerol-to-epichlorohydrin (GTE) plants have been commercialized. This technology capitalizes on the availability of cheap glycerol from biofuels processing.[9] In the process developed by Dow Chemical, glycerol undergoes two substitution reactions when treated with hydrogen chloride in the presence of a carboxylic acidcatalyst. This is the same intermediate formed in the allyl chloride/hypochlorous acid process, and is likewise then treated with base to form epichlorohydrin.[10]
Other routes
Routes that involve fewer chlorinated intermediates have continued to attract interest. One such process entails epoxidation of allyl chloride.[11]
Applications
Glycerol and epoxy resins synthesis
Epichlorohydrin is mainly converted to bisphenol A diglycidyl ether, a building block in the manufacture of epoxy resins.[12] It is also a precursor to monomers for other resins and polymers. Another usage is the conversion to synthetic glycerol. However, the rapid increase in biodiesel production, where glycerol is a waste product, has led to a glut of glycerol on the market, rendering this process uneconomical. Synthetic glycerol is now used only in sensitive pharmaceutical, and biotech applications where quality standards are very high.[13]
Minor and niche applications
Epichlorohydrin is a versatile precursor in the synthesis of many organic compounds. For example, it is converted to glycidyl nitrate, an energetic binder used in explosive and propellant compositions.[14] The epichlorohydrin is reacted with an alkali nitrate, such as sodium nitrate, producing glycidyl nitrate and alkali chloride. It is used as a solvent for cellulose, resins, and paints, and it has found use as an insect fumigant.[15]
Polymers made from epichlorohydrin, e.g., polyamide-epichlorohydrin resins, are used in paper reinforcement and in the food industry to manufacture tea bags, coffee filters, and sausage/salami casings as well as with water purification.[16]
Epichlorohydrin is classified by several international health research agencies and groups as a probable or likely carcinogen in humans.[18][19][20] Prolonged oral consumption of high levels of epichlorohydrin could result in stomach problems and an increased risk of cancer.[21] Occupational exposure to epichlorohydrin via inhalation could result in lung irritation and an increased risk of lung cancer.[22]
^Jun Li; Gongda Zhao; Shuang Gao; Ying Lv; Jian Li; Zuwei Xi (2006). "Epoxidation of Allyl Chloride to Epichlorohydrin by a Reversible Supported Catalyst with H2O2 under Solvent-Free Conditions". Org. Process Res. Dev. 10 (5): 876–880. doi:10.1021/op060108k.
