2-chloro-1,3-butadiene

Chloroprene, 2-chloro-1,3-butadiene, is a colorless, volatile synthetic liquid that has a pungent ether-like odor. Synthesis of chloroprene was first reported by chemists of the E. I. du Pont de Nemours Company in 1931 following studies of acetylene polymerization with the objective of producing synthetic rubber. The chloroprene monomer differs from isoprene, the fundamental monomer of natural rubber, only by substitution of chlorine for the methyl group of isoprene. Chloroprene was observed to polymerize much more quickly than did isoprene. In industrial processes prior to 1960, chloroprene was produced in relatively high yields by reacting vinyl acetylene with hydrogen chloride. Today, chloroprene is produced more efficiently by chlorination of 1,3-butadiene.
When compared with natural rubber the chloroprene synthetic polymer, polychloroprene, was noted to be much denser, more resistant to water and hydrocarbon solvents, less permeable to many gases, and was more resistant to degradation by oxygen, ozone, hydrogen chloride, hydrogen fluoride, and other chemicals. Due to desirable physical and chemical properties, polychloroprene and its latex polymers are produced in quantities exceeding 200 000 metric tons at a limited number of facilities around the world. Chloroprene production is closely tied to demand for polychloroprene.

Chloroprene (2-chloro-l,3-butadiene) was first synthesized by Carothers and Collins (E.I. du Pont de Nemours and Co.) in 1930 during classical studies on acetylene. The compound was found to undergo spontaneous polymerization with the formation of a rubbery material. This product was shown to have good resistance to oil, heat and weathering and commercial manufacture of chloroprene rubber was started in 1932.
Chloroprene is a colourless liquid, b.p. 59℃.

Chloroprene (2-chloro-1,3-butadiene) is a flammable, colorless liquid at room temperature with a characteristic ether-like odor. The Odor Threshold is 0.4 milligram per cubic meter. It is slightly soluble in water and more soluble in organic solvents. It has not been found to occur naturally. Chloroprene is very unstable and reacts in air with oxygen and other compounds to form epoxides, peroxides, and other hazardous compounds.

Clear, colorless liquid with a pungent, ether-like odor. The odor threshold is 0.40 mg/m3 (CHRIS, 1984).

Almost all the chloroprene produced is used for the manufacture of these polychloroprene rubbers. Chloroprene is a volatile, toxic, flammable liquid and is especially susceptible to oxidation and polymerization.

The only commercial use identified for chloroprene is as a monomer in the production of the elastomer polychloroprene (neoprene), a synthetic rubber used in the production of automotive and mechanical rubber goods, adhesives, caulks, flame-resistant cushioning,construction materials, fabric coatings, fiber binding, and footwear. Other uses of this polymer include applications requiring chemical, oil, or weather resistance or high gum strength. The U.S. Food and Drug Administration permits the use of chloroprene as a component of adhesives used in food packaging and also permits the use of polychloroprene in products intended for use with food (IARC 1979, 1999, NTP 1998).

Manufacture of neoprene.

A colorless liquid derivative of butadiene used in the manufacture of neoprene rubber.

Chloroprene can be synthesized by addition of HCl to vinyl acetylene H2C=CHC≡CH +HCl → H2C=CHCCl=CH2, and by dehydrochlorination of dichlorobutenes or 2,2,3-trichlorobutane.

Preparation of chloroprene from butadiene In this method, the following route is used:

In the first step, butadiene is chlorinated in the vapour phase at 330-420 and atmospheric pressure. The main products are 3,4-dichloro-l-butene and 1,4-dichloro-2-butene in approximately equal amounts. The latter material is then isomerized to the former by heating with a copper catalyst such as cuprous chloride. The 3,4-dichloro-l-butene is dehydrochlorinated by treatment with 10% aqueous sodium hydroxide at 85. Chloroprene is isolated by distillation under reduced pressure in the presence of polymerization inhibitors.

A clear colorless liquid. Flash point -4°F. May polymerize exothermically if heated or contaminated. If polymerization takes place inside a container, the container may rupture violently. Less dense than water. Vapors heavier than air. Used to make neoprene rubber.

Highly flammable. Slightly soluble in water.

CHLOROPRENE emits highly toxic fumes of chlorine gas when heated to decomposition. Autooxidizes very rapidly with air and, even at 0°C, produces unstable peroxides that catalyze exothermic polymerization [Bretherick, 5th ed., 1995, p. 507]. This reactivity is greatly slowed by presence of an inhibitor.

Toxic by ingestion, inhalation, and skin absorption. Flammable, dangerous fire risk, explosive limits in air 4.0–20%. Eye and upper respiratory tract irritant. Possible carcinogen.

INHALATION: Fatigue, psychic changes, irritability, oppression in chest, occasionally substernal pain, tachycardia upon exertion. EYES: Can cause conjunctivitis, corneal necrosis and edema of eyelids. SKIN: May cause dermatitis and temporary loss of hair. Rapidly absorbed by skin.

Confirmed carcinogen. Poison by ingestion, intravenous, and subcutaneous routes. Moderately toxic by inhalation. An experimental teratogen. Experimental reproductive effects. Human mutation data reported. Human exposure has caused dermatitis, conjunctivitis, corneal necrosis, anemia, temporary loss of hair, nervousness, and irritabhty. Exposure to the vapor can cause respiratory tract irritation leading to asphyxia. Other effects are central nervous system depression, drop in blood pressure, severe degenerative changes in the liver, kidneys, lungs, and other vital organs. A very dangerous fire hazard when exposed to heat or flame. Explosive in the form of vapor when exposed to heat or flame. To fight fire, use alcohol foam. Auto-oxidlzes in air to form an unstable peroxide that catalyzes exothermic polymerization of the monomer. Incompatible with liquid or gaseous fluorine. When heated to decomposition it emits toxic fumes of Cl-. See also CHLORINATED HYDROCARBONS, ALIPHATIC .

The major use of chloroprene is in the production of artificial rubber (Neoprene, duprene); polychloroprene elastomers. Chloroprene is extremely reactive, e.g., it can polymerize spontaneously at room temperatures; the process being catalyzed by light, peroxides, and other free radical initiators. It can also react with oxygen to form polymeric peroxides and because of its instability, flammability, and toxicity, chloroprene has no end-product uses as such.

If this chemical gets into the eyes, remove anycontact lenses at once and irrigate immediately for at least15 min, occasionally lifting upper and lower lids. Seek medical attention immediately. If this chemical contacts theskin, remove contaminated clothing and wash immediatelywith soap and water. Seek medical attention immediately. Ifthis chemical has been inhaled, remove from exposure,begin rescue breathing (using universal precautions, including resuscitation mask) if breathing has stopped and CPR ifheart action has stopped. Transfer promptly to a medicalfacility. When this chemical has been swallowed, get medical attention. Give large quantities of water and inducevomiting. Do not make an unconscious person vomit

Chloroprene is reasonably anticipated to be a human carcinogen based on evidence of carcinogenicity from studies in experimental animals.

Chemical/Physical. Anticipated products from the reaction of chloroprene with ozone or OH radicals in the atmosphere are formaldehyde, 2-chloroacrolein, OHCCHO, ClCOCHO, H2CCHCClO, chlorohydroxy acids, and aldehydes (Cupitt, 1980).
Chloroprene will polymerize at room temperature unless inhibited with antioxidants (NIOSH, 1997). Chloroprene is resistant to hydrolysis under neutral and alkaline conditions (Carothers et al., 1931).
Chloroprene is subject to hydrolysis forming 3-hydroxypropene and HCl. The reported hydrolysis half-life at 25 °C and pH 7 is 40 yr (Kollig, 1993).

Color Code—Red: Flammability Hazard: Store ina flammable liquid storage area or approved cabinet awayfrom ignition sources and corrosive and reactive materials.Prior to working with chloroprene you should be trained onits proper handling and storage. Before entering confinedspace where this chemical may be present, check to makesure that an explosive concentration does not exist.Chloroprene must be stored to avoid contact with peroxidesand other oxidizers, such as permanganates, nitrates, chlorates, and perchlorates, since violent reactions occur. Storein tightly closed containers in a cool, well-ventilated area attemperatures below 10℃/50
F. Sources of ignition, such assmoking and open flames, are prohibited where chloropreneis handled, used, or stored. Metal containers involving thetransfer of 5 gallons or more of chloroprene should begrounded and bonded. Drums must be equipped with selfclosing valves, pressure vacuum bungs, and flame arresters.
Use only nonsparking tools and equipment, especially whenopening and closing containers of chloroprene. A regulated,marked area should be established where this chemical ishandled, used, or stored in compliance with OSHAStandard 1910.1045.

UN1991 Chloroprene, stabilized, Hazard Class: 3; Labels: 3-Flammable liquid, 6.1-Poisonous material.

Chloroprene is not generally available from chemical supply firms. Concentrated chloroprene is extremely reactive unless stored cold, under inert gas, and in presence of oxidation inhibitors and free radical scavengers. With pure chloroprene multiple undesirable reactions can occur, including spontaneous dimerization, polymerization, oxidation, epoxide formation, and nitration. Due to its reactivity, handling and transportation of chloroprene are carefully regulated; shipment of uninhibited chloroprene is forbidden by statute.
Chloroprene is not known to occur naturally. It is not widely distributed in the environment due its reactivity and its use at a limited number of facilitiesworldwide. Industrial productionof chloroprene is accomplished in sealed reactor systems with very limited fugitiveemissions.Polymerizationprocesses are designed to be sealed, but must be opened to remove and manipulate formed polymer. Such opening causes most environmental release of chloroprene, the majority of which enters the atmosphere. From National Library of Medicine Toxics Release Inventory 2010 data, more than 270 000 pounds of chloroprene was released into the environment. Of that amount more than 97% was released into air at one site in Louisiana, USA.

Can form unstable peroxides; chloroprene may polymerize on standing with fire or explosion hazard. May form explosive mixture with air. Reacts with liquid or gaseous fluorine, alkali metals; metal powders, oxidizers, creating a fire or explosion hazard. Attacks some plastics, rubber, and coatings. May accumulate static electrical charges, and may cause ignition of its vapors.

The Initial Threshold Screening Level (ITSL) for chrloroprene is 20 μg/m3 with annual averaging time.

Incineration, preferably after mixing with another combustible fuel. Care must be exercised to assure complete combustion to prevent the formation of phosgene. An acid scrubber is necessary to remove the halo acids produced.