Cyclohexene

Cyclohexene (C6H10, CAS registry No. 110-83-8) is also called tetrahydrobenzene, which is colorless flammable liquid. It is insoluble in water. Inhalation of high concentrations may have a narcotic effect. Cyclohexene is highly flammable, so it should keep away from heat and open flame. It may form peroxides in storage, so it should be stored in the absence of air. It may cause toxic effects if inhaled or absorbed through skin. Inhalation or contact with material may irritate or burn skin and eyes. Fire will produce irritating, corrosive and/or toxic gases.

Cyclohexene can be synthesized by several ways, such as dehydrogenation of cyclohexane, dehydration of cyclohexanol, dehydrohalogenation of halogenated cyclohexane, Birch reduction or partial hydrogenation of benzene. Compared with other methods，the technology of partial hydrogenation of benzene to cyclohexene is of the advantage of safety, high atom-economy, environmentally friendly. The partial hydrogenation of benzene to cyclohexene has been known for more than 100 years.

Cyclohexene is a cyclic olefin, and is a colorless, flammable liquid with a special pungent odor at room temperature. Long-term placement in the air it can be oxidated into peroxide by air. Naturally present in coal tar, soluble in acetone, carbon tetrachloride, benzene, ether, hexane, ethanol and other organic solvents, can form binary azeotrope with lower alcohols, acetic acid, etc. Cyclohexene has the general nature of olefin, decomposes rapidly in the presence of uranium salts under sunlight or ultraviolet rays, is constant as being heated in a sealed tube at 200 ℃ for a long time, forms benzene and naphthalene at 400~500 ℃.
It is obtained by dehydration of cyclohexanol at high temperature in the presence of an acid catalyst in industrial. It is obtained by sulfated dehydration of cyclohexanol in the laboratory.

Figure 1 is the chemical reaction equation of sulfated dehydration of cyclohexanol to obtain cyclohexene.
Cyclohexene is an important chemical raw materials, used for the production of adipic acid, adipic aldehyde, maleic acid, Cyclohexane acid, cyclohexane aldehyde, maleic acid, cyclohexyl carboxylic acid, cyclohexanecarboaldehyde in industry. It is also used as the extraction agent, the stabilizer having a high-octane gasoline. Inhalation can cause mild poisoning.
Here are some of these important compounds prepared by cyclohexene, (1)chlorinated cyclohexane is made, useful as pharmaceutical intermediates, a solvent and rubber additives. (2) cyclohexanone is made from cyclohexene, can be used as intermediates raw materials of medicine, pesticides, perfumes, and dyes, as polymer modifiers. (3) cyclohexyl acetate is made, used as a plastic solvent. (4) cyclohexanone phenol is made, can be used as raw materials medicine and pesticides. (5) aminocyclohexanol is made, can be used as surfactants and emulsifiers. (6) The product can also be used directly as organic intermediates, solvents and additives when spices are prepared. It can be used in the preparation of butadiene in the laboratory.
The above information were edited and collated by Yan Yanyong of Chemicalbook.

Colorless flammable liquid. Insoluble in water, soluble in ether.

Cyclohexene may react vigorously with strong oxidizing agents. Though simple in its chemical structure, there are two potential oxidation sites in cyclohexene, and the usual oxidation reactions generally lead to a mixture of products with different oxidation states and functional groups: oxidation of the C=C bond (site a) can lead to 7-oxabicyclo[4.1.0]heptane, trans/cis-cyclohexane-1,2-diol, or adipic acid; oxidation at the allylic C-H position (site b) may produce cyclohex-2-en-1-ol or cyclohex-2-en-1-one. These products are useful industrial intermediates that have been widely employed in organic synthesis, medicinal chemistry, pesticide chemistry, materials science, etc. Therefore, controllable oxidation reactions for cyclohexene that can selectively afford the targeted products are synthetically valuable for applications in both the academy and industry, thus becoming the aim of synthetic and catalytic chemists in the field.

1. Used in organic synthesis, it is also used as a solvent.
2. Cyclohexene is used as organic synthetic raw materials, such as synthetic raw materials for lysine, cyclohexanone, phenol, polycycloolefin resin, chlorinated cyclohexane, rubber additives, cyclohexanol, etc. It is also used as a catalyst solvent and petroleum extraction agent, high octane gasoline stabilizer.
3. Cyclohexene is used for Preparation of adipic acid, maleic acid, hexahydro benzoic acid and acetaldehyde, preparation of butadiene in the laboratory. It is used as high-octane gasoline stabilizer.

Cyclohexanol is heated to generate cyclohexene in the presence of sulfuric acid catalyst, distilled to obtain crude products. Washed with a fine saturated salt solution, then sodium sulfate solution is used to neutralize traces of acid, then washed with water, layered, dried, filtration, distillation, collecting 82-85 ℃ distillate products to obtain cyclohexene.

In case of fire, high temperature, oxidant, it is flammable, burning produces irritant smoke.

Treasury ventilation low-temperature drying, stored separately from oxidants and acids. Not long storage to prevent polymerization.

Cyclohexene is a hydrocarbon, mostly obtained from the hydrogenation of benzene.

Cyclohexene is a colorless liquid (cyclic alkene) with a sweetish odor.

Clear, colorless liquid with a sweet odor. Odor threshold concentration is 0.18 ppm (quoted, Amoore and Hautala, 1983).

It occurs in coal tar and is obtained by catalyticdehydration of cyclohexanol and dehydrogenationof cyclohexane. Cyclohexene isused in making adipic acid, maleic acid,and butadiene; in oil extraction; as a stabilizerfor high-octane gasoline; and in organicsynthesis.

Manufacture of adipic acid, maleic acid, hexahydrobenzoic acid, and aldehyde; stabilizer for high-octane gasoline

Alkylation component. In the manufacture of adipic acid, maleic acid, hexahydrobenzoic acid and aldehyde. To prepare butadiene in the laboratory. Has been suggested for the synthesis of maleic acid and as stabilizer for high octane gasoline.

ChEBI: A cycloalkene that is cylohexane with a single double bond.

Cyclohexene is prepared by dehydration of cyclohexanol by thermal reaction of an ethylene–propylene–butadiene mixture (1).

A colorless liquid. Insoluble in water and less dense than water. Flash point 20°F. Vapors heavier than air. Inhalation of high concentrations may have a narcotic effect. Used to make other chemicals.

Highly flammable. Insoluble in water.

Cyclohexene may react vigorously with strong oxidizing agents. May react exothermically with reducing agents to release hydrogen gas. In the presence of various catalysts (such as acids) or initiators, may undergo exothermic addition polymerization reactions. Oxidizes readily in air to form unstable peroxides that may explode spontaneously [Bretherick, 1979 p.151-154].

There are very few toxicological data availableon cyclohexene. Inhalation producesirritation of the eyes and respiratory tract. Itis also an irritant to skin. Its acute toxicityis low; the toxic effects are similar to thoseof cyclohexane. Exposure to high concentrationsor ingestion may cause drowsiness.Single exposures to 15,000 ppm of cyclohexenecould be lethal to rats.

HIGHLY FLAMMABLE: Will be easily ignited by heat, sparks or flames. Vapors may form explosive mixtures with air. Vapors may travel to source of ignition and flash back. Most vapors are heavier than air. They will spread along ground and collect in low or confined areas (sewers, basements, tanks). Vapor explosion hazard indoors, outdoors or in sewers. Runoff to sewer may create fire or explosion hazard. Containers may explode when heated. Many liquids are lighter than water.

Moderately toxic by inhalation and ingestion. A very dangerous fire hazard when exposed to flame; can react with oxidizers. Dangerous; keep away fromheat and open flame. To fight fire, use foam, CO2, dry chemical.

May be used as an intermediate in making other chemicals (e.g., adipic acid, maleic acid, hex- ahydro benzoic acid), oil extraction and as a catalyst solvent.

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. Do NOT induce vomiting.

Cyclohexene was not mutagenic in Salmonella typhimurium with or without metabolic activation.

Biological. Cyclohexene biodegrades to cyclohexanone (Dugan, 1972; Verschueren, 1983).
Photolytic. The following rate constants were reported for the reaction of cyclohexene with OH radicals in the atmosphere: 6.80 x 10^-11 cm³/moleculesec (Atkinson et al., 1979), 6.75 x 10^-11 cm³/moleculesec at 298 K (Sablji and Güsten, 1990), 5.40 x 10^-11 cm³/moleculesec at 298 K (Rogers, 1989), 1.0 x 10^-10 cm³/moleculesec at 298 K (Atkinson, 1990); with ozone in the gasphase: 1.69 x 10^-16 cm³/moleculesec at 298 K (Japar et al., 1974), 2.0 x 10^-16 at 294 K (Adeniji et al., 1981), 1.04 x 10^-16 cm³/moleculesec (Atkinson et al., 1983), 1.04 x 10^-16 at 298 K (Atkinson and Carter, 1984); with NO3 in the atmosphere: 5.26 x 10^-13 cm³/moleculesec (Sablji and Güsten, 1990); 5.3 x 10^-13 cm³/moleculesec at 298 K (Atkinson, 1990), and 5.28 x 10^-13 cm³/moleculesec at 295 K (Atkinson, 1991). Cox et al. (1980) reported a rate constant of 6.2 x 10^-11 cm³/moleculesec for the reaction of gaseous cyclohexene with OH radicals based on a value of 8 x 10^-12 cm³/moleculesec for the reaction of ethylene with OH radicals.
Chemical/Physical. Gaseous products formed from the reaction of cyclohexene with ozone were (% yield): formic acid , carbon monoxide , carbon dioxide, ethylene, and valeraldehyde (Hatakeyama et al., 1987). In a smog chamber experiment conducted in the dark at 25 °C, cyclohexane reacted with ozone. The following products and their respective molar yields were: oxalic acid (6.16%), malonic acid (6.88%), succinic acid (0.63%), glutaric acid (5.89%), adipic acid (2.20%), 4-hydroxybutanal (2.60%), hydroxypentanoic acid (1.02%), hydroxyglutaric acid (2.33%), hydroxyadipic acid (1.19%), 4-oxobutanoic acid (6.90%), 4- oxopentanoic acid (4.52%), 6-oxohexanoic acid (4.16%), 1,4-butandial (0.53%), 1,5-pentanedial (0.44%), 1,6-hexanedial (1.64%), and pentanal (17.05%).
Grosjean et al. (1996) investigated the atmospheric chemistry of cyclohexene with ozone and an ozone-nitrogen oxide mixture under ambient conditions. The reaction of cyclohexene and ozone in the dark yielded pentanal and cyclohexanone. The sunlight irradiation of cyclohexene with ozonenitrogen oxide yielded the following carbonyls: formaldehyde, acetaldehyde, acetone, propanal, butanal, pentanal, and a C₄ carbonyl.
Cyclohexene reacts with chlorine dioxide in water forming 2-cyclohexen-1-one (Rav-Acha et al., 1987).

Color Code—Red: Flammability Hazard: Store ina flammable liquid storage area or approved cabinet awayfrom ignition sources and corrosive and reactive materials.May form peroxides in storage. Prior to working with thischemical you should be trained on its proper handling andstorage. Before entering confined space where this chemicalmay be present, check to make sure that an explosive concentration does not exist. Cumene must be stored to avoidcontact with oxidizers, such as permanganates, nitrites, peroxides, chlorates, and perchlorates, since violent reactionsoccur. Store in tightly closed containers in a cool well-ventilated area away from heat. Sources of ignition, such assmoking and open flames, are prohibited where Cumene isused, handled, or stored in a manner that could create apotential fire or explosion hazard. Metal containers involving the transfer of=gallons or more of this chemical shouldbe grounded and bonded. Drums must be equipped withself-closing valves, pressure vacuum bungs, and flamearresters. Use only nonsparking tools and equipment, especially when opening and closing containers of thischemical.chemical you should be trained on its proper handling andstorage. Before entering confined space where this chemicalmay be present, check to make sure that an explosive concentration does not exist. Store in tightly closed containersin a cool, well-ventilated area away from strong oxidizers(such as chlorine, bromine, and fluorine). Sources of ignition, such as smoking and open flames, are prohibitedwhere cyclohexene is handled, used, or stored. Metal containers involving the transfer of=gallons or more of cyclohexene should be grounded and bonded. Drums must beequipped with self-closing valves, pressure vacuum bungs,and flame arresters. Use only nonsparking tools and equipment, especially when opening and closing containers ofcyclohexene. Wherever cyclohexene is used, handled, manufactured, or stored, use explosion-proof electrical equipment and fittings.

UN2256 Cyclohexene, Hazard Class: 3; Labels: 3-Flammable liquid.

Free cyclohexene from peroxides by washing with successive portions of dilute acidified ferrous sulfate, or with NaHSO3 solution, then with distilled water, drying with CaCl2 or CaSO4, and distilling under N2. Alternative methods for removing peroxides include passage through a column of alumina, refluxing with sodium wire or cupric stearate (then distilling from sodium). The diene is removed by refluxing with maleic anhydride before distilling under vacuum. Treatment with 0.1moles of MeMgI in 40mL of diethyl ether removes traces of oxygenated impurities. Other purification procedures include washing with aqueous NaOH, drying and distilling under N2 through a spinning band column, redistilling from CaH2, storing under sodium wire, and passing through a column of alumina, under N2, immediately before use. Store it at <0o under argon. [Coleman & Johnstone Org Synth Coll Vol I 83 1955, Carson & Ipatieff Org Synth Coll Vol II 152 1943, Woon et al. J Am Chem Soc 108 7990 1986, Wong et al. J Am Chem Soc 109 3428 1987.] [Beilstein 5 IV 218.]

The release of cyclohexene into the air occurs in the form of waste streams from manufacturing units. Cyclohexene has a vapor pressure of 89mm Hg at 25°C, indicating that it exists as a vapor form in the environment and is degraded by reactions with photochemically induced hydroxyl radicals, ozone, and nitrate radicals. The half-life for these reactions in the air is 6, 2, and 4 h, respectively.
Estimated Koc of 850 indicates that cyclohexene has low mobility in the soil. Cyclohexene has Henry’s law constant of 4.55×10^-2atm-m³ mol^-1. Based on this Henry’s law constant, volatilization is expected to be the major process of removal of cyclohexene from moist soil and water, if released into it.

Vapor may form explosive mixture with air. The substance can form explosive peroxides. The sub- stance may polymerize under certain conditions. Incompatible with oxidizers (chlorates, nitrates, peroxides, permanganates, perchlorates, chlorine, bromine, fluorine, etc.); contact may cause fires or explosions. Keep away from alkaline materials, strong bases, strong acids, oxoa- cids, epoxides.

The Initial Threshold Screening Level (ITSL} for Cyclohexene is 10,000 μg/m3 based on an 8 hour averaging time.

Dissolve or mix the material with a combustible solvent and burn in a chemical incinera- tor equipped with an afterburner and scrubber. All federal, state, and local environmental regulations must be observed.