General Description
A clear colorless liquid with a petroleum-like odor. Density 5.7 lb/gal. Flash point-65°F. Boiling point 93°F. May polymerize exothermically if heated or contaminated. If polymerization takes place inside a closed container, the container may rupture violently. Less dense than water and insoluble in water. Vapors heavier than air.
Reactivity Profile
ISOPRENE may react vigorously with strong oxidizing agents. May react exothemically with reducing agents to release hydrogen gas. May undergo exothermic addition polymerization in the presence of various catalysts (such as acids) or initiators. Undergoes autoxidation upon exposure to the air to form explosive peroxides. Mixing isoprene in equal molar portions with any of the following substances in a closed container caused the temperature and pressure to increase: chlorosulfonic acid, nitric acid (70%), oleum, sulfuric acid (90%) [NFPA 1991].
Air & Water Reactions
Highly flammable. Insoluble in water.
Hazard
Highly flammable, dangerous fire and
explosion risk. Irritant. Possible carcinogen.
Health Hazard
Vapor produces no effects other than slight irritation of the eyes and upper respiratory tract. Liquid may irritate eyes; like gasoline.
Physical properties
Colorless, volatile, extremely flammable liquid with an petroleum-like odor. An odor threshold concentration of 48 ppbV was reported by Nagata and Takeuchi (1990).
Uses
Isoprene occurs in nature and it is produced by many plants. Its polymers are the main component of natural rubber. The most important application of isoprene is to manufacture polymers and copolymers. Polyisoprene, a synthetic rubber made from isoprene, is used in a wide variety of rubber applications including medical equipment, baby bottle teats/nipples, toys, shoe soles, tires, elastic films, threads for golf balls or textiles, adhesives, paints, and coatings. Copolymer butyl rubber, made from isobutene with a small amount of isoprene, has excellent impermeability to gases and is used in inner tubes. Another copolymer styrene-isoprene rubber is used in pressure sensitive adhesives. Isoprene is also used as a chemical intermediate.
Uses
The majority of isoprene produced commercially is used to make synthetic rubber (cis-polyisoprene), most of which is used to produce vehicle tires. The second- and third-largest uses are in the production of styrene-isoprene-styrene block polymers and butyl rubber (isobutene-isoprene copolymer) (IARC 1994).
Uses
The primary use of isoprene is the manufacture of polyisoprene,
or ‘synthetic’ natural rubber, which is subsequently
used to make tires. Other major uses of isoprene include the
production of styrenic thermoplastic elastomer block copolymers
(styrene–isoprene–styrene) and butyl rubber (isobutene–
isoprene copolymer). Isoprene is also used to manufacture
other chemicals, intermediates, and derivatives, which are
subsequently used to manufacture vitamins, pharmaceuticals,
flavorings and fragrances, and epoxy hardeners.
Definition
ChEBI: A hemiterpene with the formula CH22C(CH3)CH2CH2; the monomer of natural rubber and a common structure motif to the isoprenoids, a large class of other naturally occurr
ng compounds.
Preparation
Isoprene is obtained from propylene by the followin,g route:
In the first step, propylene is dimerized to 2-methyl-l-pentene by passage
over a catalyst of tri-n-propylaluminium at about 200??C and 20 MPa (200
atmospheres). This product is then isomerized to 2-methyl-2-pentene by
heating at 150-300??C in the presence of a silica-alumina catalyst. The final
step in the process is the pyrolysis of the olefin to isoprene at 650-800??C in
the presence of a free radical initiator such as hydrogen bromide. The
isomerization step is necessary because pyrolysis of 2-methyl-l-pentene gives
much poorer yields of isoprene than pyrolysis of 2-methyl-2-pentene.
Production Methods
Rubber results from the polymerization of isoprene to form polyisoprene. The resultingstructure dictates the properties of the rubber. Natural rubber has a cis 1,4 structure.This means that the carbon atoms that form the chainattach to the same side ofthe chain at the 1 and 4 positions. The cisstructure gives rubber its elasticity. Polyisoprene alsoexists in a trans 1,3 configuration. In the trans configuration, the addition takes place onopposite sides of the carbon chain.
Natural rubber occurs in a colloidal milky suspension called latex, which is obtained fromnumerous plants. The most important of these is the para rubber tree, Hevea brasiliensis. Naturalrubber is harvested by cutting a v-shape incision into a plant and allowing latex to drain intoa container containing a preservative. About 50mL of latex is obtained on a daily basis. Latexis transported to collection stations where it is processed for shipment. Processing can includepreservation, coagulation, and concentrating before being sent to rubber factories.
Flammability and Explosibility
Extremelyflammable
Carcinogenicity
Isoprene is reasonably anticipated to be a human carcinogen based on sufficient evidence of carcinogenicity from studies in experimental animals.
Environmental Fate
At 25 ℃, isoprene has a high vapor pressure of 733 hPa, a low
water solubility of 642 mg l-1, and a Henry’s law constant of
7781 Pam3 mol-1. Isoprene’s log Kow is 2.42 while its log Koc
is 1.83. Isoprene’s vapor density relative to air is 2.4. Because of
its high vapor pressure at ambient temperature, isoprene will
partition largely into the atmosphere, with negligible amounts
partitioning to soil and water. Due to a short half-life in air
(0.5 h by reaction with nitric oxide, 1.2–4 h by reaction with
hydroxyl radicals, and 19 h by reaction with ozone), wet
deposition of isoprene from air is not expected to play
a significant role in its atmospheric fate. Although laboratory
testing demonstrates that isoprene has the potential to biodegrade,
microbial metabolism is unlikely to contribute significantly
to the removal of isoprene from the environment due to
rapid volatilization from terrestrial and aquatic media.
Isoprene has a low bioaccumulation potential and is not
expected to bioaccumulate.
Purification Methods
Reflux it with sodium then distil it from sodium or NaBH4 under nitrogen, and pass it through a column containing KOH, CaSO4 and silica gel. tert-Butylcatechol (0.02% w/w) is added, and the isoprene is stored in this way until redistilled before use. The inhibitor (tert-butylcatechol) in isoprene can be removed by several washings with dilute NaOH and water. The isoprene is then dried over CaH2, distilled under nitrogen at atmospheric pressure, and the fraction distilling at 32o is collected. Store it under nitrogen at -15o. [Beilstein 1 H 252, 1 IV 1001.]
Toxicity evaluation
The acute effects of isoprene are related to irritation, central
nervous system depression, and asphyxia at high concentrations.
The mutagenic and genotoxic effects of isoprene seen in
in vivo and in vitro studies, as well as the carcinogenic effects
of isoprene in experimental animals (principally mice), are
believed to be due to the formation of isoprene diepoxide.
