1,4-dichlorobenzene production

Continuous chlorination of benzene at 30—50°C in the presence of a Lewis acid typically yields 85% monochlorobenzene. Temperatures in the range of 150—190°C favor production of the dichlorobenzene products. The para isomer is produced in a ratio of 2—3 to 1 of the ortho isomer. Other methods of aromatic ring chlorination include use of a mixture of hydrogen chloride and air in the presence of a copper—salt catalyst, or sulfuryl chloride in the presence of aluminum chloride at ambient temperatures. Free-radical chlorination of toluene successively yields benzyl chloride, benzal chloride, and benzotrichloride. Related chlorination agents include sulfuryl chloride, tert-huty hypochlorite, and /V-ch1orosuccinimide which yield benzyl chloride under the influence of light, heat, or radical initiators. 

Humans are exposed to 1,4-dichlorobenzene mainly by breathing vapors from 1,4-dichlorobenzene products used in the home, such as mothballs and toilet-deodorizer blocks. Reported levels of 1,4-dichlorobenzene in some homes and public restrooms have ranged from 0.29 to 272 parts of 1,4-di chlorobenzene per billion parts (ppb) of air. Outdoor levels of 1,4-dichlorobenzene are much lower, and reported levels in cities range from 0.02 to 20 ppb. Even levels in the air around hazardous waste sites are low reported levels range from 0.03 to 4.25 ppb. 

Hepatic Effects. Hepatic effects have been reported in humans following long-term exposure to 1,4-diehlorobenzene via inhalation. A 60-year-old man and his wife who were exposed to mothball vapor that "saturated" their home for 3-4 months both died of liver failure (acute liver atrophy) within a year of the initial exposure (Cotter 1953). Yellow atrophy and cirrhosis of the liver were reported in a 34-year-old woman who demonstrated 1,4-dichlorobenzene products in a department store and in a 52-year-old man who used 1,4-diehlorobenzene occupationally in a fur storage plant for about 2 years (Cotter 1953). Duration of exposure was not estimated for the 34-year-old woman, but was indicated in the report to be more than 1 year. No estimates of the 1,4-diehlorobenzene exposure levels (other than the use of the term saturated ) were provided in any of these reports, nor was it verified that... 

In 1972, U.S. exports of 1,4-dichlorobenzene were reported to be 4.5x10 kg (9.9 million pounds) (HSDB 1998). Exports of 1,4-dichlorobenzene have expanded through the 1980s at about 1-2% per year due to the growth in production of pol henylene sulfide (PPS) resin overseas (HSDB 1998 NTP 1989). In 1990, the United States exported about 25% (about 33 million pounds) of its 1,4-dichlorobenzene production volume (Chemical Marketing Reporter 1990). Recent export volumes from 1990 to 1995 have remained relatively constant (NTDB 1996). Export volumes of 1,4-dichlorobenzene were 11,925,179 kg (24.1 million pounds), 11,185,034 kg (24.7 million pounds), 10,651,337 kg (23.5 million pounds), 13,390,545 kg (29.5 million pounds), and 11,078,150 kg (24.4 million pounds) for 1990, 1991, 1992, 1993, and 1994, respectively. 

The recognition that PPS had significant commercial potential as an advanced material came in the late 1940s (12). MacaHum s PPS process is based on the reaction of elemental sulfur, -dichlorobenzene, and sodium carbonate in sealed vessels at 275—300°C (12). Typical products produced by the MacaHum process contain more than one sulfur per repeating unit x = 1.2-2.3) ... 

Eig. 1. The key steps for the Phillips PPS process are (/) production of aqueous sodium sulfide from aqueous sodium hydrogen sulfide (or hydrogen sulfide) and aqueous sodium hydroxide 2) dehydration of the aqueous sodium sulfide and NMP feedstocks 5) polymerization of the dehydrated sulfur source with -dichlorobenzene to yield a slurry of PPS and by-product sodium chloride in the solvent (4) polymer recovery (5) polymer washing for the removal of by-product salt and residual solvent (6) polymer drying (7) optional curing, depending on the appHcation and (< ) packaging. 

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. 

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. 

Nitrated monochlorobenzene is used as a building block to produce many other products. There is also some commercial nitration of o-dichlorobenzene in the United States and Western Europe. 

The dichlorobenzene isomers have very similar vapor pressures making separation by distillation difficult. Crystallization is generally used in combination with distillation to obtain the pure 1,2 and 1,4-dichlorobenzene isomers. The small quantity of 1,3-dichlorobenzene isomer produced is not generally isolated as a pure product. Environmental concerns have led to the use of improved crystalliza tion systems that contain the products with minimal losses to the environment. 

Commercial chlorination of benzene today is carried out as a three-product process (monochlorobenzene and 0- and -dichlorobenzenes). The most economical operation is achieved with a typical product spHt of about 85% monochlorobenzene and a minimum of 15% dichlorobenzenes. Typically, about two parts of -dichlorobenzene are formed for each part of (9-isomer. It is not economical to eliminate the coproduction of the dichlorobenzenes. To maximize monochlorobenzene production (90% monochlorobenzene and 10% dichlorobenzene), benzene is lightly chlorinated the density of the reaction mixture is monitored to minimize polychlorobenzene production and the unreacted benzene is recycled. 

The principal use of (9-dichlorobenzene is to manufacture 3,4-dichloroaniline, which is a raw material for several herbicides and for the production of 3,4,4 -trichlorocarbaniHde (TCC), a bacteriostat used in deodorant soaps. Some is exported, but the amount is expected to decline as Brazil brings on increased capacity. A modest decline in U.S. consumption between 1989 and 1994 is expected. About 11,400 t were consumed in 1988. 

The production of chlorobenzenes in Eastern Europe is concentrated in the former Soviet Union, Poland, and Czechoslovakia. The estimated capacity is 200—250 thousand metric tons the former Soviet Union has most (230 thousand tons) of this capacity. There is trade between Eastern and Western Europe on monochlorobenzene and the dichlorobenzenes, but the net trade balance is probably even at about 20 thousand metric tons. Eastern Europe exported 20 thousand metric tons of monochlorobenzene principally to Germany, Erance, and the United States. 

Canada has no known basic producers of chlorobenzene. There is one company that isolates small quantities of ortho and para from purchased mixed dichlorobenzenes. Some of the isolated product is exported. The primary portion of Canada s chlorobenzenes comes from the United States. 

Dichlorobenzene is sold as two grades technical chlorobenzene <0.05, trichlorobenzenes <1.0, 1,2-dichlorobenzene 80, and other isomers <19.0 and purified, produced by redistilling the technical product in a very efficient stiU chlorobenzene <0.05, 1,2,4 trichlorobenzene <0.2 and 1,2-dichlorobenzene 98.0. 

Dichlorobenzene. T -Dichlorobenzene s largest and growing oudet is in the manufacture of poly(phenylene sulfide) resin (PPS). Other apphcations include room deodorant blocks and moth control, a market which is static and likely to remain unchanged but combined is currently a larger outlet than PPS. Small amounts ofT -dichlorobenzene are used in the production of 1,2,4-trichlorobenzene, dyes, and insecticide intermediates. Exports have been a principal factor in U.S. production with about 25% exported in 1988. 

Figure 22-8 shows the features of a horizontal center-fed column [Brodie, Au.st. Mech. Chem. Eng. Tran.s., 37 (May 1979)] which has been commercialized for continuous purification of naphthalene and p-dichlorobenzene. Liquid feed enters the column between the hot purifying section and the cold freezing or recovery zone. Ciystals are formed internally by indirect cooling of the melt through the walls of the refining and recovery zones. Residue liquid that has been depleted or product exits from the coldest section of the column. A spiral conveyor controls the transport of solids through the unit. 

The Phillips Corporation have recently introduced interesting copolymers related to PPS. In addition to the use of p-dichlorobenzene and Na2S, a second aromatic dichloro compound is used. For the marketed material PAS-2 this is 4,4 -dichlorodiphenylsulphone whilst for the developmental products PAS-1 and PAS-B the compounds are 4,4 -dichlorodiphenyl and 4,4 -dichlorodiphenyl-ketone. Each of these copolymers is amorphous, so that a high heat deformation resistance requires a high value for. ... 

Today the sulphonation route is somewhat uneconomic and largely replaced by newer routes. Processes involving chlorination, such as the Raschig process, are used on a large scale commercially. A vapour phase reaction between benzene and hydrocholoric acid is carried out in the presence of catalysts such as an aluminium hydroxide-copper salt complex. Monochlorobenzene is formed and this is hydrolysed to phenol with water in the presence of catalysts at about 450°C, at the same time regenerating the hydrochloric acid. The phenol formed is extracted with benzene, separated from the latter by fractional distillation and purified by vacuum distillation. In recent years developments in this process have reduced the amount of by-product dichlorobenzene formed and also considerably increased the output rates. 

Thermolysis of the azido derivative 143 (R = R =H) in refluxing 1,2-dichlorobenzene gave the pyrroloquinoline 144 and the dihydropyrrolo derivative 145 amongst other products (79H1021), whereas its thermal... 

A mixture of this crude product (approximately 302 grams, 0.92 mol) and 480 grams (2.3 mols) of phosphorus pentachloride is heated for 1 hour at 120°-140°C in a 2 liter round-bottomed flask. The resulting clear solution is poured on ice. 4,5-Dichlorobenzene-1,3-disulfonyl chloride separates immediately as a solid. It is collected by filtration and washed with water. While still moist, it is added in portions during about 20 minutes to 1 liter of concentrated ammonia water contained in a 3 liter beaker surrounded by a cold water bath. The reaction mixture is then allowed to stand for 1 hour without cooling after which it is heated on a steam bath for about 30 minutes while air is bubbled through it, in order to remove some of the excess ammonia. It is then filtered, acidified with concentrated hydrochloric acid and chilled. 

The product separates as a gum from which the supernatant liquid is decanted, and the gum is triturated with 250 cc of water in order to induce crystallization. The crude product thus obtained is recrystallized from 3,200 cc of boiling water and then from 40% aqueous isopropyl alcohol yielding 4,5-dichlorobenzene-1,3-disulfonamide as a white solid, MP 228.5° to 229.0°C. 

Chlorination of benzene is an electrophilic substitution reaction in which CL serves as the electrophile. The reaction occurs in the presence of a Lewis acid catalyst such as FeCls. The products are a mixture of mono- and dichlorobenzenes. The ortho- and the para-dichlorobenzenes are more common than meta-dichlorobenzene. The ratio of the mono-chloro to dichloro products essentially depends on the benzene/chlorine ratio and the residence time. The ratio of the dichloro-isomers (0- to p- to m-dichlorobenzenes) mainly depends on the reaction temperature and residence time ... 

Typical liquid-phase reaction conditions for the chlorination of benzene using FeCls catalyst are 80-100°C and atmospheric pressure. When a high benzene/Cl2 ratio is used, the product mixture is approximately 80% monochlorobenzene, 15% p-dichlorobenzene and 5% o-dichlorobenzene. 

A1C1, (0.8 g, 6 mmol) was added to a solution of the chloride 1 (1.6 g, 5.2 mmol) and a nitrile (6 mmol) in 1,2-dichlorobenzene and the mixture was heated at 120-130 C for 20 min. The mixture was cooled, made alkaline with dil aq NaOH and extracted with Et20. The solvents were removed by steam distillation and the residue was chromatographed (silica gel. EtOAc/petroleum ether 1 9) to give the yellow product (deep red if R = Ar). 

The kinetic effect of increased pressure is also in agreement with the proposed mechanism. A pressure of 2000 atm increased the first-order rates of nitration of toluene in acetic acid at 20 °C and in nitromethane at 0 °C by a factor of about 2, and increased the rates of the zeroth-order nitrations of p-dichlorobenzene in nitromethane at 0 °C and of chlorobenzene and benzene in acetic acid at 0 °C by a factor of about 559. The products of the equilibrium (21a) have a smaller volume than the reactants and hence an increase in pressure speeds up the rate by increasing the formation of H2NO. Likewise, the heterolysis of the nitric acidium ion in equilibrium (22) and the reaction of the nitronium ion with the aromatic are processes both of which have a volume decrease, consequently the first-order reactions are also speeded up and to a greater extent than the zeroth-order reactions. 

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