Chlorinated Hydrocarbon Synthesis

Introduction
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Isopentane is emitted by some types of pine and oak trees, fern and moss. It may also be given off by near-shore marine sediments. Isopentane also occurs in gasoline fumes. It is present in tobacco smoke.
USE: Isopentane is an important commercial chemical. It is used as a solvent and to make other chemicals and polystyrene. Isopentane is an ingredient in many household products such as car care. Isopentane is a hydrocarbon and one of three isomers of pentane. Pentanes are components of some fuels, such as gasoline, and are also used as specialty solvents in the laboratory.

Chlorinated hydrocarbons are widely used as solvents and raw materials for the synthesis of various useful products, such as cleaning agents, pesticides and poly vinyl chloride (PVC). These chlorinated hydrocarbons, however, cause serious environmental problems when they were released into the air or water media. Many technologies have been developed for the safe treatment and destruction of these hazardous materials produced as a waste or by-product. Thermal incineration has been widely used because of high destruction efficiency and ease of operation. However, it requires high operating temperature and generates hazardous pollutants, including incomplete combustion by-products, such as dioxins and NOx.

Catalytic dechlorination of chlorinated hydrocarbons is now recognized as a promising process for the treatment of chlorinated hydrocarbons and recovering useful chemicals, such as hydrocarbons and HCl. Numerous studies have been performed to develop a dechlorination catalyst using noble or transition metals supported on SiO2, Al2O3, zeolites or mesoporous materials, such as MCM-41, as a supports [1–5]. Recently, mesoporous molecular sieves have been attracted much attention as a catalyst support due to its desirable properties such as large surface area, well arranged pore array and narrow pore size distribution. In addition, mesoporous silicas can be functionalized with organic chemicals by silylation and grafting techniques.

In this study, mesoporous silica, SBA-15, was synthesized using a sol-gel method. Three different types of metal catalysts were prepared via the silylation and grafting techniques. In particular, Ni-L-SBA was prepared by the impregnation with LIX-984 after silanization by 3-aminopropyltriethoxy silane (APTES, Aldrich Chemical Co.) of the SBA-15 and Ni-L-CS was prepared using a conventional silica as a support. Ni-E-SBA was synthesized by the direct grafting of the EDTA on SBA-15. The kinetic performances of these catalysts for the dechlorination of chlorinated hydrocarbons were compared with that of commercial catalyst (HP318, IFP Co.). In this study, dechlroination of trichloroethane (TCEa) was selected as a model compound.

Clinical Management
In general, following acute exposure to chlorinated hydrocarbon insecticides, blood chlorinated hydrocarbon levels are not clinically useful; for most compounds it reflects cumulative exposure over a period of months rather than recent exposure. Emesis may be indicated and is most effective if initiated within 30 min postingestion. In addition, an activated charcoal/cathartic may be given. For seizures, diazepam should be administered as an intravenous bolus. Oils should not be given by mouth. Adrenergic amines should not be administered because they may further increase myocardial irritability and produce refractory ventricular arrhythmias. If clothing is contaminated, it should be removed.

Up to now, acetic acid and chlorinated hydrocarbons, which have the low dielectric constant ε, have been extensively employed as solvents for the molecular weight fractionation of CTA. The fractionation efficiency achieved by using the above-mentioned solvents was poor, unfortunately, and the numerous attempts made so far have been met with very limited success. In order to overcome the above-mentioned experimental problem, preliminary experiments on phase separation of CA solution were performed for many solvent/nonsolvent combinations, including those employed in the literature.21–36 Judging from the ease of separation of the two liquid phases and of the solvent recovery, we chose l-chloro-2,3-epoxypropane (epichlorohydrine) as a solvent and hexane as a precipitant. Successive solutional fractionation technique (SSF), originally advocated for use by Kamide and coworkers2,3 was applied:

Sixty grams of TA 2 sample was dissolved in l-chloro-2,3-epoxypropane (6000 cm3) and thermostated at 35 °C. The amount of hexane predetermined by a pilot fractionation was added to the solution, resulting in phase separation. The supenatant phase was isolated by a vacuum line from the vessel and hexane and l-chloro-2,3-epoxypropane in the phase were separated by stepwise evaporation in a rotary evaporator and reused for further fractionation. The fractionation was carried out in a totally closed system. The fractionation apparatus was specially designed and is described in Figure 3.2.2. Finally, 13 fractions were separated in a SSF run, in which the composition of the hexane at each step varied from 44.5 to 33.4 vol% at 35 °C. Equilibrium between the two phases was not difficult to attain so that the fractionation is efficient (see Table 3.3.5). The polymer fractions prepared in this way were vacuum dried at 60 °C for 1 day. No hydrolysis of the acetyl group was detected.

Chlorinated Hydrocarbons
Chlorinated hydrocarbons are often used to degrease base metal pieces prior to welding. Trichloroethylene (ClCHdouble bondCCl2) is one of the more commonly used agents and has a high vapor pressure at room temperatures (51). The airborne vapors formed near the welding arc are subject to oxidation in a process that is enhanced by UV radiation from the arc to produce the irritant gas phosgene (COCl2; see eqn [5]).

[5]ClCHdouble bondCCl2 + O2 + UV light → COCl2 + HCl + CO
COCl2 gas may appear colorless or as a white to pale yellow cloud. At low concentrations, it has a pleasant odor of newly mown hay, but at high concentrations, the odor may be strong and unpleasant (62). COCl2 is irritating to skin, eyes, nose, throat, and lungs. Overexposure to COCl2 may cause coughing, burning sensation in eyes and throat, difficulty breathing, watery eyes, blurred vision, nausea and vomiting, and pulmonary edema.

Wildlife and Domestic Animal Exposures
The recognition that chlorinated hydrocarbons are a persistent danger to wildlife led to a decrease in their use as agricultural chemicals and to an increase in the use of OPs and CBs. In general, OPs and CBs do not bioaccumulate as do chlorinated hydrocarbons and they are relatively biodegradable. However, they are more acutely toxic than chlorinated hydrocarbons to humans and wildlife. A thorough discussion of the comparative toxicology of OPs and CBs is outside the scope of this entry. ChE inhibitions are generally the same, regardless of the animal; differences between species are often in the overall pharmacokinetics and metabolism. For example, although birds have higher brain AChE activities than mammals, they also have less hepatic MFOs to activate OPs and less A-esterases to hydrolyze them. Much research has been done on the toxicology of OPs to wild birds from sparrows to hawks and eagles. For example, Hill et al. of the US Fish and Wildlife Service studied the toxicity of 19 OPs and eight CBs to 35 species of birds. In general, such studies showed that over 50% of OPs and 90% of CBs have LD50s of <40 mg kg−1 for most birds.

Route of exposure may have much to do with the recovery from OPs. When pigeons were treated orally with an OP, inhibition of blood ChE was rapid, and recovery of activity occurred within a few days. However, when the treatment was conducted dermally, putting the OP on the feet, recovery of enzyme activity took several weeks, implying the presence of a depot for OPs and the possibility that birds can accumulate OPs by flying from site to site. The possibility of bioaccumulation of OPs in a food chain (usually considered to be a characteristic of chlorinated hydrocarbons) was demonstrated by the report of an eagle poisoned by an OP (Warbex) in magpies that, in turn, had obtained the OP by ingesting hair from a steer that had been treated with it for parasites.

Beef cattle, horses (more than sheep), goats, and swine are treated several times each year with OPs to control parasites and some are fed tetrachlorvinphos to prevent fly larvae hatching in their feces. Carbaryl is commonly used for flea and tick control. Oehme states that insecticides are a common cause of poisoning of domestic animals and that “the majority of insecticide problems in domestic animals result from ignorance or mismanagement.” Indeed, there is some epidemiological evidence that animal technicians in pet grooming and veterinary hospitals are exposed to the OP and CB chemicals used to control fleas and ticks while washing the animals. Sheep ‘dipping’ methods have been changed to minimize exposure to the worker.

Azeotropic Drying
Benzene, toluene, xylene and the chlorinated hydrocarbons, such as chloroform, can each be effectively dried by distilling out the relatively low boiling azeotrope that it forms with water. (Ethanol can be dried by the formation of a ternary azeotrope with water and benzene, but usually a desiccant is used.) Azeotropic drying is only possible if the concentration of dissolved water in the saturated organic liquid at room temperature is significantly lower than that in the azeotrope at its boiling point. Distillation of this saturated material will first produce the azeotrope—a low boiling fraction, relatively richer in water than the wet solution—which will distil until no water remains: from that point onwards pure dry solvent will distil at a higher temperature. The azeotrope produces a characteristic appearance as it distils; it is relatively richer in water than the saturated solvent at room temperature, so that, as it is cooled by the condenser, some water separates to give a heterogeneous mixture which will initially look milky because of suspended water globules, but may separate into two layers in the receiver. Distillation is therefore continued until the distillate emerging from the condenser is quite clear. In order to judge this accurately, small quantities are collected separately in a test tube. Once the drying has been achieved, it may be sufficient to use the residual liquid in the boiler flask without further distillation: if, however, further distillation is required, the original condenser and other wet fittings should be changed, or sufficient distillate should be allowed to pass over these surfaces to wash them free of water, before the dry component is collected.

Chlorinated Solvents
Chlorinated solvents, also known as organochlorines, are chemicals primarily used as raw materials in the production of other products. They may be produced as byproducts or intermediates in the synthesis of other chlorinated materials. See our list of chlorinated solvents for seven examples.

Uses & Benefits
1,1-Dichloroethane
Currently, 1,1-Dichloroethane is used in the manufacture of high-vacuum resistant rubber and for extraction of temperature-sensitive substances. Use of 1,1-Dichloroethane for the production of the solvent 1,1,1-trichloroethane ceased in the late 1990s.

1,2-Dichloroethane
1,2 Dichloroethane, commonly known as EDC, is a clear, colorless, oily, synthetic flammable liquid chlorinated hydrocarbon. More than 90 percent of the world’s production of vinyl chloride monomer (VCM) uses EDC. During the process of producing VCM, quantities of 1,2-dichloroethane are completely consumed. VCM is reacted to produce the versatile polymer polyvinyl chloride, or PVC.

EDC also is used in the production of other organic compounds, including polyethylene amines used for chemical synthesis. EDC was also used as a lead scavenger to prevent the buildup of lead deposits in leaded gasoline, but that use has likewise been discontinued.

1,4-Dichlorobenzene
Today, 1,4-dichlorobenzene, also called para-dichlorobenzene, is mainly used to produce other chemicals such as polyphenylene sulfide (PPS) resin, a high-performance thermoplastic. Synthetic fibers and textiles derived from PPS are resistant to chemical and thermal attack.

Historically, para-dichlorobenzene has been used as a space deodorant for refuse containers and toilets, and as a fumigant to help control moths, mold and mildew. Those applications have declined in recent years.

1,2-Dichlorobenzene
Similar in atomic structure to 1,4 dichlorobenzene, 1,2-dichlorobenzene is also known as ortho-dichlorobenzene. It is mainly used as a raw material in the synthesis of agricultural chemicals. It has also been used as a solvent and in dye synthesis. Use of 1,2-Dichlorobenzene as an insecticide for termites and locust borers has been discontinued, as has its use by the U.S. Forest Service to combat widespread bark beetle outbreaks.

Trans-1,2-dichloroethylene
Trans-1,2-dichloroethylene is generated as a byproduct in the synthesis of vinyl chloride monomer (VCM). It can also be produced commercially, in a mixture with the isomer cis-1,2-dichloroethene, to produce chlorinated solvents and other compounds. The trans isomer has been used as a solvent in electronics cleaning, precision cleaning, and other specific metal cleaning applications. Both cis and trans isomer are found in the environment as a result of the anaerobic degradation of the solvents trichloroethylene and perchloroethylene.

1,1,2-Trichloroethane
1,1,2-Trichloroethane is used in the synthesis of 1,1-dichloroethylene (vinylidene chloride), which is used to in semiconductor manufacture. It is also used to produce various polymers including polyvinylidene chloride, the basis for cling food wrap until the early 2000s. It is also used in the production of other chlorinated products and to manufacture high vacuum resistant rubber.

1,2-Dichloropropane
1,2-Dichloropropane is obtained as a byproduct of the production of epichlorohydrin, which is produced on a large scale. It is used in the production of the solvent perchloroethylene and other chlorinated chemicals. It had been used as a soil fumigant and industrial solvent, but those uses have been discontinued.

What are chlorinated solvents?
Chlorinated solvents are chemicals primarily used as raw materials in the production of other commercial products. They may be produced as byproducts or intermediates in the synthesis of other chlorinated materials.

What are some of the past and present uses of chlorinated solvents?
1,2-Dichloropropane was used as a soil fumigant and as an industrial solvent. 1,1,2-Trichloroethane is used to produce high vacuum resistant rubber. The U.S. Forest Service used 1,2-Dichlorobenzene to fight bark beetle outbreaks. 1,4-Dichlorobenzene also has been used as a deodorizer and as a fumigant to help control moths, mold and mildew.

How might someone be exposed to chlorinated solvents?
Occupational exposure to chlorinated solvents can occur through inhalation or skin contact. The National Institute for Occupational Safety and Health offers resources on managing chemical safety in the workplace.