Epichlorohydrin (abbreviated ECH) is an
organochlorine compound and an
epoxide. Despite its name, it is not a
halohydrin
In organic chemistry a halohydrin (also a haloalcohol or β-halo alcohol) is a functional group in which a halogen and a hydroxyl are bonded to adjacent carbon atoms, which otherwise bear only hydrogen or hydrocarbyl groups (e.g. 2-chloroethanol ...
. It is a colorless liquid with a pungent, garlic-like odor, moderately soluble in water, but
miscible with most
polar
Polar may refer to:
Geography
Polar may refer to:
* Geographical pole, either of two fixed points on the surface of a rotating body or planet, at 90 degrees from the equator, based on the axis around which a body rotates
*Polar climate, the cli ...
organic
Organic may refer to:
* Organic, of or relating to an organism, a living entity
* Organic, of or relating to an anatomical organ
Chemistry
* Organic matter, matter that has come from a once-living organism, is capable of decay or is the product ...
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 molecule generally existing as a
racemic mixture
In chemistry, a racemic mixture, or racemate (), is one that has equal amounts of left- and right-handed enantiomers of a chiral molecule or salt. Racemic mixtures are rare in nature, but many compounds are produced industrially as racemates. ...
of right-handed and left-handed
enantiomer
In chemistry, an enantiomer ( /ɪˈnænti.əmər, ɛ-, -oʊ-/ ''ih-NAN-tee-ə-mər''; from Ancient Greek ἐνάντιος ''(enántios)'' 'opposite', and μέρος ''(méros)'' 'part') – also called optical isomer, antipode, or optical anti ...
s. Epichlorohydrin is a highly reactive
electrophilic
In chemistry, an electrophile is a chemical species that forms bonds with nucleophiles by accepting an electron pair. Because electrophiles accept electrons, they are Lewis acids. Most electrophiles are positively charged, have an atom that carr ...
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 in two steps, beginning with the addition of
hypochlorous acid, 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. ...
alcohols:
:
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.
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
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 chlorid ...
.
Reminiscent of Berthelot's experiment, glycerol-to-epichlorohydrin (GTE) plants have been commercialized. This technology capitalizes on the availability of cheap glycerol from
biofuel
Biofuel is a fuel that is produced over a short time span from biomass, rather than by the very slow natural processes involved in the formation of fossil fuels, such as oil. According to the United States Energy Information Administration ...
s processing. In the process developed by
Dow Chemical, glycerol undergoes two
substitution reactions when treated with hydrogen chloride in the presence of a
carboxylic acid
In organic chemistry, a carboxylic acid is an organic acid that contains a carboxyl group () attached to an R-group. The general formula of a carboxylic acid is or , with R referring to the alkyl, alkenyl, aryl, or other group. Carboxyli ...
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 of allyl chloride.
Applications
Glycerol and epoxy resins synthesis
Epichlorohydrin is mainly converted to
bisphenol A diglycidyl ether, a building block in the manufacture of
epoxy resin
Epoxy is the family of basic components or Curing (chemistry), cured end products of epoxy resins. Epoxy resins, also known as polyepoxides, are a class of reactive prepolymers and polymers which contain epoxide groups. The epoxide functional ...
s.
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 oi ...
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 wa ...
, 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 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.
An important biochemical application of epichlorohydrin is its use as crosslinking agent for the production of
Sephadex size-exclusion chromatographic resins from
dextran
Dextran is a complex branched glucan ( polysaccharide derived from the condensation of glucose), originally derived from wine. IUPAC defines dextrans as "Branched poly-α-d-glucosides of microbial origin having glycosidic bonds predominantly C- ...
s.
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