Chlorinated by-products

Dead Sea Works Process. The Dead Sea Works, a subsidiary of Israel Chemicals Ltd., aimounced plans ia 1992 to constmct a 25,000 t/yr magnesium plant at Beer-Sheva, Israel. The plant, to be based on Russian camaHite technology, is designed to use an existing potash plant as the source of camaHte. The chlorine by-product can be either Hquefted and sold, or used ia an existing bromine plant. Waste streams from the camaHite process, as well as spent electrolyte from the electrolytic cells, can be returned to the potash plant. 

Chlorinated by-products of ethylene oxychlorination typically include 1,1,2-trichloroethane chloral [75-87-6] (trichloroacetaldehyde) trichloroethylene [7901-6]-, 1,1-dichloroethane cis- and /n j -l,2-dichloroethylenes [156-59-2 and 156-60-5]-, 1,1-dichloroethylene [75-35-4] (vinyhdene chloride) 2-chloroethanol [107-07-3]-, ethyl chloride vinyl chloride mono-, di-, tri-, and tetrachloromethanes (methyl chloride [74-87-3], methylene chloride [75-09-2], chloroform, and carbon tetrachloride [56-23-5])-, and higher boiling compounds. The production of these compounds should be minimized to lower raw material costs, lessen the task of EDC purification, prevent fouling in the pyrolysis reactor, and minimize by-product handling and disposal. Of particular concern is chloral, because it polymerizes in the presence of strong acids. Chloral must be removed to prevent the formation of soflds which can foul and clog operating lines and controls (78). 

Chlorine. Chlorine is a weU known disinfectant for water and wastewater treatment, however, it can react with organics to form toxic chlorinated compounds such as the tribalomethanes bromodichloromethane, dibromochloromethane, chloroform [67-66-3] and bromoform [75-25-2]. Chlorine dioxide [10049-04-4] may be used instead since it does not produce the troublesome chlorinated by-products as does chlorine. In addition, by-products formed by chlorine dioxide oxidation tend to be more readHy biodegradable than those of chlorine, however, chlorine dioxide is not suitable for waste streams containing cyanide. 

The biggest use of chlorine dioxide is in bleaching wood pulp. In some mills, much of the chlorine and hypochlorite has been replaced by chlorine dioxide to reduce the amount of chlorinated by-products. Chlorine dioxide is also used to bleach textiles, flour, and edible fats and oils. 

In Japan, Toagosei is reported to produce trichloroethylene and tetrachloroethylene by chlorination of ethylene followed by dehydrochlorination. In this process the intermediate tetrachloroethane is either dehydrochlorinated to trichloroethylene or further chlorinated to pentachloroethane [76-01-7] followed by dehydrochlorination to tetrachloroethylene. Partially chlorinated by-products are recycled and by-product HCl is available for other processes. 

Chlorination of Ethylene Dichloride. Tetrachloroethylene and trichloroethylene can be produced by the noncatalytic chlorination of ethylene dichloride [107-06-2] (EDC) or other two-carbon (C2) chlorinated hydrocarbons. This process is advantageous when there is a feedstock source of mixed C2 chlorinated hydrocarbons from other processes and an outlet for the by-product HCl stream. Product ratios of tri- and tetrachloroethylene are controlled by adjusting the CI2 type="subscript">2 EDC ratio to the reactor. Partially chlorinated by-products are recycled to the chlorinator. The primary reactions are... 

Benzyl chloride is manufactured by the thermal or photochemical chlorination of toluene at 65—100°C (37). At lower temperatures the amount of ring-chlorinated by-products is increased. The chlorination is usually carried to no more than about 50% toluene conversion in order to minimize the amount of benzal chloride formed. Overall yield based on toluene is more than 90%. Various materials, including phosphoms pentachloride, have been reported to catalyze the side-chain chlorination. These compounds and others such as amides also reduce ring chlorination by complexing metallic impurities (38). 

The free HCl and Cl generated in the catalytic cycle produce environmentally harmful chlorinated by-products to the extent that more than 3 kg of HCl need to be added to the reactor per tonne of acetaldehyde produced to keep the catalytic cycle going. Modified catalysts such as ones based on palladium/ phosphomolybdovanadates have been suggested as a way of reducing byproduct formation to less than 1% of that of the conventional Wacker process. These catalysts have yet to make an impact on commercial acetic production, however. 

The use of chlorine at such relatively high concentrations may give rise to the production of chlorinated by-products if the water supply contains traces of chemicals which can react with chlorine. Such trace chlorinated chemicals are known to be carcinogenic(4) and their presence in water supplies for possible human consumption should be minimised. 

Starting material Desired product De- chlorinated by-product... 

Benzisothiazoles (51) are available from the reaction of thionyl chloride with o-alkylbenzeneamines (o-toluidines).63 Chlorinated by-products are... 

A modified reaction mechanism to the one suggested by Hurd and Mori is proposed for the preparation of some thieno[2,3- 7][l,2,3]thiadiazole derivatives in order to explain the formation of a chlorinated by-product <1998J(P1)853>. 

Wacker oxidation of l-alkenes. The Wacker oxygenation of 1-alkenes to methyl ketones involves air oxidation catalyzed by PdCl2 and CuCU, which is necessary for reoxidation of Pd(0) to Pd(II).1 This oxygenation is fairly sluggish and can result in chlorinated by-products. A new system is comprised of catalytic amounts of Pd(OAc)2, hydroquinone, and 1, used as the oxygen activator.2 The solvent is aqueous DMF, and a trace of HClOj is added to prevent precipitation of Pd(0). Oxygenation using this system of three catalysts effects Wacker oxidation of 1-alkenes in 2-8 hours and in 67-85% yield. 

Terasaki M, Makino M (2008) Determination of chlorinated by-products of parabens in swimming pool water. Int J Environ Anal Chem 88(13) 911-922... 

King WD, Dodds L, Allen AC Relation between stillbirth and specific chlorination by-products in public water supplies. Environ Health Perspect 108(9) 883-886, 2000... 

Chlorinated Drinking-water Chlorination By-products Some Other Halogenated Compounds Cobalt and Cobalt Compounds... 

I ARC (1991) lARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol, 52, Chlorinated Drinking-Water Chlorination By-Products Some Other Halogenated Compounds Cobalt and Cobalt Compounds, Lyon, pp. 337-359... 

Catalysis. The most important industrial use of a palladium catalyst is the Wacker process. The overall reaction, shown in equations 7—9, involves oxidation of ethylene to acetaldehyde by Pd(II) followed by Cu(II)-catalyzed reoxidation of the Pd(0) by oxygen (204). Regeneration of the catalyst can be carried out in situ or in a separate reactor after removing acetaldehyde. The acetaldehyde must be distilled to remove chlorinated by-products. 

Dih symmetrical porphyrins such as porphin itself,7 H2TPP and H2OEP9 are conveniently prepared from pyrrole and aldehyde by cyclocondensations (Scheme 1). Addition of Zn11 ion often improves the yield.10 The product is often contaminated with chlorin by-product, which can be converted to porphyrin by oxidants such as DDQ,10 or separated by chromatography.11 Bulky substituents tend to lower the yield, and meso o-substituted phenyl groups give rise to atrope isomers. 

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