Benzenes chlorinated

The chlorination of benzene can theoretically produce 12 different chlorobenzenes. With the exception of 1,3-dichlorobenzene, 1,3,5-trichlorobenzene, and 1,2,3,5-tetrachlorobenzene, all of the compounds are produced readily by chlorinating benzene in the presence of a Friedel-Crafts catalyst (see Friedel-CRAFTS reactions). The usual catalyst is ferric chloride either as such or generated in situ by exposing a large surface of iron to the Hquid being chlorinated. With the exception of hexachlorobenzene, each compound can be further chlorinated therefore, the finished product is always a mixture of chlorobenzenes. Refined products are obtained by distillation and crystallization. 

Chlorobenzenes were first synthesized around the middle of the nineteenth century the first direct chlorination of benzene was reported in 1905 (1). Commercial production was begun in 1909 by the former United Alkali Co. in England (2). In 1915, the Hooker Electrochemical Co. at Niagara EaUs, New York, brought on stream its first chlorobenzenes plant in the United States with a capacity of about 8200 metric tons per year. 

The Dow Chemical Company started production of chlorobenzenes in 1915 (3). Chlorobenzene was the first and remained the dominant commercial product for over 50 years with large quantities being used during World War I to produce the military explosive picric acid [88-89-1]. 

The Dow Chemical Company in the mid-1920s developed two processes which consumed large quantities of chlorobenzene. In one process, chlorobenzene was hydrolyzed with ammonium hydroxide in the presence of a copper catalyst to produce aniline [62-53-3J. This process was used for more than 30 years. The other process hydrolyzed chlorobenzene with sodium hydroxide under high temperature and pressure conditions (4,5) to product phenol [108-95-2]. The LG. Earbenwerke in Germany independentiy developed an equivalent process and plants were built in several European countries after World War II. The ICI plant in England operated until its dosing in 1965. 

In the 1930s, the Raschig Co. in Germany developed a different chlorobenzene-phenol process in which steam with a calcium phosphate catalyst was used to hydrolyze chlorobenzene to produce phenol (qv) and HCl (6). The recovered HCl reacts with air and benzene over a copper catalyst (Deacon Catalyst) to produce chlorobenzene and water (7,8). In the United States, a similar process was developed by the BakeHte Division of Union Carbide Corp., which operated for many years. The Durez Co. Hcensed the Raschig process and built a plant in the United States which was later taken over by the Hooker Chemical Corp. who made significant process improvements. 

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With the discontinuation of some herbicides, eg, 2,4,5-trichlorophenol [39399-44-5] based on the higher chlorinated benzenes, and DDT, based on monochlorobenzene, both for ecological reasons, the production of chlorinated benzenes has been reduced to just three with large-volume appHcations of (mono)chlorobenzene, o-dichlorobenzene, and -dichlorobenzene. Monochlorobenzene remains a large-volume product, considerably larger than the other chlorobenzenes, in spite of the reduction demanded by the discontinuation of DDT. 

The chlorobenzene operations in the United States were developed primarily for the manufacture of phenol, aniline, and DDT. However, with the process changes in the production of phenol and aniline, the phase-out of DDT production, and changes in the herbicide and solvent markets, the U.S. production of chlorinated benzenes has shmnk by more than 50% since the total production peaked in 1969. U.S. production of monochlorobenzene peaked in the 1960s and decreased to a low of 101 million kg in 1986 with an 11% and 9% increase, respectively, in 1988 and 1989. 

Special additives are often included in a carrier formulation to provide specific properties such as foam control, stabiUty, and fiber lubrication during dyeing. Most important are the solvents used to solubilize the soHd carrier-active chemicals. These often contribute to the general carrier activity of the finished product. For example, chlorinated benzenes and aromatic esters are good solvents for biphenyls and phenylphenols. Flammable compounds (flash point below 60°C) should be avoided. 

Monohalogen paraffins like methyl chloride and ethyl chloride are in class 11 along with multihalogen paraffins and olefins without ac tive hydrogen such as carbon tetrachloride and perchloroethylene. Chlorinated benzenes are also in class 11 because they do not have halogens on the same carbon as a hydrogen atom. 

Continuous chlorination processes permit the removal of mono-chlorohenzene as it is formed, resulting in lower yields of higher chlorinated benzene. 

Mutations at the active site of CYPlOl (cytochrome P450j,j jj) from a strain of Pseudomonas putida made possible the monooxygenation of chlorinated benzenes with less than three substituents to chlorophenols, with concomitant NIH shifts for 1,3-dichlorobenzene (Jones et al. 2001). Further mutations made it possible to oxidize even pentachlorobenzene and hexachlorobenzene to pentachlorophenol (Chen et al. 2002). Integration of the genes encoding cytochrome PTSO. into Sphingobium chlorophenolicum enabled this strain to partially transform hexachlorobenzene to pentachlorophenol (Yan et al. 2006). 

Pollmann K, S Beil, DH Pieper (2001) Transformation of chlorinated benzenes and toluenes by Ralstonia sp. strain PS 12 tecA (tetrachlorobenzene dioxygenase) and tecB (chlorobenzene dihydrodiol dehydrogenase) gene products. Appl Environ Microbiol 67 4057 063. 

Miller, M. M., Ghodbane, S., Wasik, S. R, Tewari, Y. B., Martire, D. E. (1984) Aqueous solubilities, octanol/water partition coefficients and entropies of melting of chlorinated benzenes and biphenyls. J. Chem. Eng. Data 29, 184-190. 

Liu, K., Dickhut, R.M. (1994) Saturation vapor pressures and thermodynamic properties of benzene and selected chlorinated benzenes at environmental temperatures. Chemosphere 29, 581-589. 

Smith, A.D., Bharath, A., Mullard, C., Orr, D., McCarthy, L.S., Ozbum, G.W. (1990) Bioconcentration kinetics of some chlorinated benzenes and chlorinated phenols in American flagfish, Jordanella floridae (Goode and Bean). Chemosphere 20, 379-386. 

Auger A process for chlorinating benzene to chlorobenzene, catalyzed by metallic iron. Invented by V.E. Auger in 1916 and operated in France and Italy in the early 20th century. 

A convenient one-pot system was developed also for the conversion of highly chlorinated benzenes to less chlorinated ones at room temperature, with reasonable conversion rates using the system [(dppf)PdCl2]/NaBH4/TMEDA/THF [67]. Degradation to benzene could not be achieved. Removal of chlorines in meta-position was preferred over those in ortho- or para-positions. The effectiveness of the method has been tested on the PCB mixtures Aroclor 1242,1248, and 1254 at 67 °C. 

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