Epichlorohydrin (abbreviated ECH) is an
organochlorine compound and an
epoxide
In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale ...
. Despite its name, it is not a
halohydrin. It is a colorless liquid with a pungent, garlic-like odor, moderately soluble in water, but
miscible with most
polar organic solvent
A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...
s.
It is a
chiral
Chirality is a property of asymmetry important in several branches of science. The word ''chirality'' is derived from the Greek (''kheir''), "hand", a familiar chiral object.
An object or a system is ''chiral'' if it is distinguishable from i ...
molecule generally existing as a
racemic mixture of right-handed and left-handed
enantiomers. Epichlorohydrin is a highly reactive
electrophilic compound and is used in the production of
glycerol
Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
, plastics,
epoxy glues and resins, epoxy diluents and
elastomers.
Production
Epichlorohydrin is traditionally manufactured from
allyl chloride
Allyl chloride is the organic compound with the formula C H2=CHCH2 Cl. This colorless liquid is insoluble in water but soluble in common organic solvents. It is mainly converted to epichlorohydrin, used in the production of plastics. It is a chl ...
in two steps, beginning with the addition of
hypochlorous acid
Hypochlorous acid (HClO, HOCl, or ClHO) is a weak acid that forms when chlorine dissolves in water, and itself partially dissociates, forming hypochlorite, ClO−. HClO and ClO− are oxidizers, and the primary disinfection agents of chlorine sol ...
, which affords a mixture of two
isomeric
In chemistry, isomers are molecules or polyatomic ions with identical molecular formulae – that is, same number of atoms of each element – but distinct arrangements of atoms in space. Isomerism is existence or possibility of isomers.
Is ...
alcohols:
:
In the second step, this mixture is treated with base to give the
epoxide
In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale ...
:
:
In this way, more than 800,000 tons (1997) of epichlorohydrin are produced annually.
Glycerol routes
Epichlorohydrin was first described in 1848 by
Marcellin Berthelot
Pierre Eugène Marcellin Berthelot (; 25 October 1827 – 18 March 1907) was a French chemist and Republican politician noted for the ThomsenBerthelot principle of thermochemistry. He synthesized many organic compounds from inorganic substa ...
. The compound was isolated during studies on reactions between glycerol and gaseous
hydrogen chloride
The compound hydrogen chloride has the chemical formula and as such is a hydrogen halide. At room temperature, it is a colourless gas, which forms white fumes of hydrochloric acid upon contact with atmospheric water vapor. Hydrogen chloride ga ...
.
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. In the process developed by
Dow Chemical, glycerol undergoes two
substitution reaction
A substitution reaction (also known as single displacement reaction or single substitution reaction) is a chemical reaction during which one functional group in a chemical compound is replaced by another functional group. Substitution reactions ar ...
s when treated with hydrogen chloride in the presence of a
carboxylic acid catalyst
Catalysis () is the process of increasing the rate of a chemical reaction by adding a substance known as a catalyst (). Catalysts are not consumed in the reaction and remain unchanged after it. If the reaction is rapid and the catalyst recyc ...
. This is the same intermediate formed in the allyl chloride/hypochlorous acid process, and is likewise then treated with base to form epichlorohydrin.
:
Other routes
Routes that involve fewer chlorinated intermediates have continued to attract interest. One such process entails
epoxidation
In organic chemistry, an epoxide is a cyclic ether () with a three-atom ring. This ring approximates an equilateral triangle, which makes it strained, and hence highly reactive, more so than other ethers. They are produced on a large scale ...
of allyl chloride.
Applications
Glycerol and epoxy resins synthesis
Epichlorohydrin is mainly converted to
bisphenol A diglycidyl ether
Bisphenol A diglycidyl ether (commonly abbreviated BADGE or DGEBA) is an organic compound used as constituent of epoxy resins. The compound is a colorless solid (commercial samples can appear yellow) that melts slightly above room temperature.
P ...
, a building block in the manufacture of
epoxy resins.
It is also a precursor to monomers for other resins and polymers. Another usage is the conversion to synthetic
glycerol
Glycerol (), also called glycerine in British English and glycerin in American English, is a simple triol compound. It is a colorless, odorless, viscous liquid that is sweet-tasting and non-toxic. The glycerol backbone is found in lipids known ...
. However, the rapid increase in
biodiesel
Biodiesel is a form of diesel fuel derived from plants or animals and consisting of long-chain fatty acid esters. It is typically made by chemically reacting lipids such as animal fat ( tallow), soybean oil, or some other vegetable oil ...
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.
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. 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
Cellulose is an organic compound with the formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell w ...
, resins, and paints, and it has found use as an insect fumigant.
Polymers made from epichlorohydrin, e.g., polyamide-epichlorohydrin resins, are used in paper reinforcement and in the food industry to manufacture
tea
Tea is an aromatic beverage prepared by pouring hot or boiling water over cured or fresh leaves of ''Camellia sinensis'', an evergreen shrub native to East Asia which probably originated in the borderlands of southwestern China and north ...
bags,
coffee
Coffee is a drink prepared from roasted coffee beans. Darkly colored, bitter, and slightly acidic, coffee has a stimulating effect on humans, primarily due to its caffeine content. It is the most popular hot drink in the world.
Seeds of ...
filters, and sausage/salami casings as well as with
water purification
Water purification is the process of removing undesirable chemicals, biological contaminants, suspended solids, and gases from water. The goal is to produce water that is fit for specific purposes. Most water is purified and disinfected for hu ...
.
An important biochemical application of epichlorohydrin is its use as crosslinking agent for the production of
Sephadex Sephadex is a cross-linked dextran gel used for gel filtration. It was launched by Pharmacia in 1959, after development work by Jerker Porath and Per Flodin. The name is derived from separation Pharmacia dextran. It is normally manufactured in a bea ...
size-exclusion chromatographic resins from
dextrans.
Safety
Epichlorohydrin is classified by several international health research agencies and groups as a probable or likely carcinogen in humans. Prolonged oral consumption of high levels of epichlorohydrin could result in stomach problems and an increased risk of cancer. Occupational exposure to epichlorohydrin via inhalation could result in lung irritation and an increased risk of lung cancer.
References
{{Authority control
Organochlorides
Solvents
IARC Group 2A carcinogens
Epoxides
Male reproductive toxicants
Commodity chemicals