Dichloroethane reactions

The off-gases are passed to a lead cooler where some dichloroethane [reaction (3)] and chlorohydrin are condensed. These are separated and delivered to their respective enameled pressure vessels. The residual off-gases are passed through a scrubber where they are neutralized by a circulating 10 per cent sodium hydroxide solution. The unabsorbed ethylene then goes to the blower for recycling. A part of the recycled gas is continuously vented. 

Consider vinyl chloride production (see Example 2.1). In the oxychlorination reaction step of the process, ethylene, hydrogen chloride, and oxygen are reacted to form dichloroethane ... 

A fiowsheet for this part of the vinyl chloride process is shown in Fig. 10.5. The reactants, ethylene and chlorine, dissolve in circulating liquid dichloroethane and react in solution to form more dichloroethane. Temperature is maintained between 45 and 65°C, and a small amount of ferric chloride is present to catalyze the reaction. The reaction generates considerable heat. 

In early designs, the reaction heat typically was removed by cooling water. Crude dichloroethane was withdrawn from the reactor as a liquid, acid-washed to remove ferric chloride, then neutralized with dilute caustic, and purified by distillation. The material used for separation of the ferric chloride can be recycled up to a point, but a purge must be done. This creates waste streams contaminated with chlorinated hydrocarbons which must be treated prior to disposal. 

This problem is solved in the reactor shown in Fig. 10.6. Ethylene and chlorine are introduced into circulating liquid dichloroethane. They dissolve and react to form more dichloroethane. No boiling takes place in the zone where the reactants are introduced or in the zone of reaction. As shown in Fig. 10.6, the reactor has a U-leg in which dichloroethane circulates as a result of gas lift and thermosyphon effects. Ethylene and chlorine are introduced at the bottom of the up-leg, which is under sufficient hydrostatic head to prevent boiling. 

The reactants dissolve and immediately begin to react to form further dichloroethane. The reaction is essentially complete at a point only two-thirds up the rising leg. As the liquid continues to rise, boiling begins, and finally, the vapor-liquid mixture enters the disengagement drum. A very slight excess of ethylene ensures essentially 100 percent conversion of chlorine. 

As shown in Fig. 10.6, the vapor from the reactor flows into the bottom of a distillation column, and high-purity dichloroethane is withdrawn as a sidestream several trays from the column top. The design shown in Fig. 10.6 is elegant in that the heat of reaction is conserved to run the separation and no washing of the reactor... 

Method I. This procedure is used for most ketone reactions. A representative example is the reductive amination of cyclopenta-none [P2P] with hexamethyleneimine [MeNHa] Hexamethyl-eneamine (I.Og, lOmmol) and cylclopentanone (0.84g, lOmmol) were mixed in 1,2-dichloroethane (35mL) and then treated with... 

Methyl-5-aminothia2ole-4-carboxylic acid is diazotized with isoamyl nitrite in the presence of furan in 1.2-dichloroethane to give a mixture of products 163 (53%), 164 (33%). 165 (11%), and 166 (3%) (Scheme 104) (334). This reactivity experiment was carried out to examine the possibility of the occurrence of 4,5-dehydrothiazole (hetaryne). Hetaryne intermediates seem not to be involved as an intermediate in the reaction. The formation of 163 through 166 can be rationalized in terms of the intermediacy of 166a. 

Nucleophilic substitution is one of a variety of mechanisms by which living systems detoxify halogenated organic compounds introduced into the environment Enzymes that catalyze these reactions are known as haloalkane dehalogenases The hydrolysis of 1 2 dichloroethane to 2 chloroethanol for example is a biological nude ophilic substitution catalyzed by a dehalogenase... 

This stage of the reaction proceeds by a mechanism that will be discussed in Chapter 20 Both stages are faster than the reaction of 1 2 dichloroethane with water in the absence of the enzyme... 

Acetaldehyde reacts with phosphoms pentachloride to produce 1,1-dichloroethane [75-34-3] and with hypochlorite and hypoiodite to yield chloroform [67-66-3] and iodoform [75-47-8], respectively. Phosgene [75-44-5] is produced by the reaction of carbon tetrachloride with acetaldehyde in the presence of anhydrous aluminum chloride (75). Chloroform reacts with acetaldehyde in the presence of potassium hydroxide and sodium amide to form l,l,l-trichloro-2-propanol [7789-89-1] (76). 

Acetylene and hydrogen chloride historically were used to make chloroprene [126-99-8]. The olefin reaction is used to make ethyl chloride from ethylene and to make 1,1-dichloroethane from vinyl chloride. 1,1-Dichloroethane is an intermediate to produce 1,1,1-trichloroethane by thermal (26) or photochemical chlorination (27) routes. 

A general one-step method for preparation of primary and secondary nitroparaffins from amines by oxidation with y -chloroperbenzoic acid in 1,2-dichloroethane has been reported (68). This method is particularly useful for laboratory quantities of a wide variety of nitroparaffins because a large number of amines are readily available from ketones by oxime reduction and because the reaction is highly specific for nitroparaffins. 

When catalysts are used in a highly exothermic reaction, an active phase may be diluted with an inert material to help dissipate heat and moderate the reaction. This technique is practiced in the commercial oxychlorination of ethylene to dichloroethane, where an alumina-supported copper haUde catalyst is mixed with a low surface area inert diluent. 

Oxychlorination of Ethylene to Dichloroethane. Ethylene (qv) is converted to dichloroethane in very high yield in fixed-bed, multitubular reactors and fluid-bed reactors by reaction with oxygen and hydrogen chloride over potassium-promoted copper(II) chloride supported on high surface area, porous alumina (84) ... 

Oxychlorination of ethylene to dichloroethane is the first reaction performed in an integrated vinyl chloride plant. In the second stage, dichloroethane is cracked thermally over alumina to give vinyl chloride and hydrogen chloride. The hydrogen chloride produced is recycled back to the oxychlorination reactor. 

Methane, chlorine, and recycled chloromethanes are fed to a tubular reactor at a reactor temperature of 490—530°C to yield all four chlorinated methane derivatives (14). Similarly, chlorination of ethane produces ethyl chloride and higher chlorinated ethanes. The process is employed commercially to produce l,l,l-trichloroethane. l,l,l-Trichloroethane is also produced via chlorination of 1,1-dichloroethane with l,l,2-trichloroethane as a coproduct (15). Hexachlorocyclopentadiene is formed by a complex series of chlorination, cyclization, and dechlorination reactions. First, substitutive chlorination of pentanes is carried out by either photochemical or thermal methods to give a product with 6—7 atoms of chlorine per mole of pentane. The polychloropentane product mixed with excess chlorine is then passed through a porous bed of Fuller s earth or silica at 350—500°C to give hexachlorocyclopentadiene. Cyclopentadiene is another possible feedstock for the production of hexachlorocyclopentadiene. 

Addition Chlorination. Chlorination of olefins such as ethylene, by the addition of chlorine, is a commercially important process and can be carried out either as a catalytic vapor- or Hquid-phase process (16). The reaction is influenced by light, the walls of the reactor vessel, and inhibitors such as oxygen, and proceeds by a radical-chain mechanism. Ionic addition mechanisms can be maximized and accelerated by the use of a Lewis acid such as ferric chloride, aluminum chloride, antimony pentachloride, or cupric chloride. A typical commercial process for the preparation of 1,2-dichloroethane is the chlorination of ethylene at 40—50°C in the presence of ferric chloride (17). The introduction of 5% air to the chlorine feed prevents unwanted substitution chlorination of the 1,2-dichloroethane to generate by-product l,l,2-trichloroethane. The addition of chlorine to tetrachloroethylene using photochemical conditions has been investigated (18). This chlorination, which is strongly inhibited by oxygen, probably proceeds by a radical-chain mechanism as shown in equations 9—13. 

Typical reactions using either 1,2-dichloroethane or 1,2-dichloropropane to produce carbon tetrachloride and tetrachloroethylene by the chlorinolysis reaction are shown in equations 21—23. Continued removal of tetrachloroethylene and recycling of carbon tetrachloride can result in a net zero production of carbon tetrachloride. Most chemical producers using chlorinolysis for the production of perchloroethylene in the future will take advantage of the per/tet equiUbrium to maximize perchloroethylene to avoid carbon tetrachloride ipiod.uction.From 1,2-dichloroethane ... 

Oxychlorination. This is an important process for the production of 1,2-dichloroethane which is mainly produced as an intermediate for the production of vinyl chloride. The reaction consists of combining hydrogen chloride, ethylene, and oxygen (air) in the presence of a cupric chloride catalyst to produce 1,2-dichloroethane (eq. 24). The hydrogen chloride produced from thermal dehydrochlorination of 1,2-dichloroethane to produce vinyl chloride (eq. 25) is usually recycled back to the oxychlorination reactor. The oxychlorination process has been reviewed (31). 

The first large-scale commercial oxychlorination process for vinyl chloride was put on-stream in 1958 by The Dow Chemical Company. This plant, employing a fixed-tube reactor containing a catalyst of cupric chloride on an active carrier, produced 1,2-dichloroethane from ethylene. The high temperatures involved in the reaction were moderated by a suitable diluent. The average heat output from the reaction is 116 kJ/mol (50,000 Btu/lb mol). 

In a typical oxychlorination reaction, preheated gas streams at temperatures of 180—200°C are fed onto a fixed- or fiuidized-catalyst bed containing 2—10% copper impregnated on an activated alumina. The reaction occurs during a 15—22 s residence time on the catalyst bed at a temperature of 230—315°C. Typical yields to 1,2-dichloroethane range from 92—97%. 

The properties of 1,1-dichloroethane are Hsted ia Table 1. 1,1-Dichloroethane decomposes at 356—453°C by a homogeneous first-order dehydrochlofination, giving vinyl chloride and hydrogen chloride (1,2). Dehydrochlofination can also occur on activated alumina (3,4), magnesium sulfate, or potassium carbonate (5). Dehydrochlofination ia the presence of anhydrous aluminum chloride (6) proceeds readily. The 48-h accelerated oxidation test with 1,1-dichloroethane at reflux temperatures gives a 0.025% yield of hydrogen chloride as compared to 0.4% HCl for trichloroethylene and 0.6% HCl for tetrachloroethylene. Reaction with an amine gives low yields of chloride ion and the dimer 2,3-dichlorobutane, CH CHCICHCICH. 2-Methyl-l,3-dioxaindan [14046-39-0] can be prepared by a reaction of catechol [120-80-9] with 1,1-dichloroethane (7). 

Dichloroethane is produced commercially from hydrogen chloride and vinyl chloride at 20—55°C ia the presence of an aluminum, ferric, or 2iac chloride catalyst (8,9). Selectivity is nearly stoichiometric to 1,1-dichloroethane. Small amounts of 1,1,3-tfichlorobutane may be produced. Unreacted vinyl chloride and HCl exit the top of the reactor, and can be recycled or sent to vent recovery systems. The reactor product contains the Lewis acid catalyst and must be separated before distillation. Spent catalyst may be removed from the reaction mixture by contacting with a hydrocarbon or paraffin oil, which precipitates the metal chloride catalyst iato the oil (10). Other iaert Hquids such as sdoxanes and perfluorohydrocarbons have also been used (11). 

Dichloroethane is also one of the iatermediate products of high temperature thermal chlorination of ethane or ethyl chloride. In ethane chlorination, the reaction proceeds through ethyl chloride as an iatermediate (12). 1,1-Dichloroethane itself is usually an iatermediate ia the productioa of viayl chloride and of 1,1,1-tfichloroethane by thermal chlorination or photochlofination (13). 

Pyrolysis. Pyrolysis of 1,2-dichloroethane in the temperature range of 340—515°C gives vinyl chloride, hydrogen chloride, and traces of acetylene (1,18) and 2-chlorobutadiene. Reaction rate is accelerated by chlorine (19), bromine, bromotrichloromethane, carbon tetrachloride (20), and other free-radical generators. Catalytic dehydrochlorination of 1,2-dichloroethane on activated alumina (3), metal carbonate, and sulfate salts (5) has been reported, and lasers have been used to initiate the cracking reaction, although not at a low enough temperature to show economic benefits. 

Nucleophilic Substitution. The kinetics of the bimolecular nucleophilic substitution of the chlorine atoms in 1,2-dichloroethane with NaOH, NaOCgH, (CH2)3N, pyridine, and CH COONa in aqueous solutions at 100—120°C has been studied (24). The reaction of sodium cyanide with... 

Dichloroethane is produced by the vapor- (28) or Hquid-phase chlorination of ethylene. Most Hquid-phase processes use small amounts of ferric chloride as the catalyst. Other catalysts claimed in the patent Hterature include aluminum chloride, antimony pentachloride, and cupric chloride and an ammonium, alkaU, or alkaline-earth tetrachloroferrate (29). The chlorination is carried out at 40—50°C with 5% air or other free-radical inhibitors (30) added to prevent substitution chlorination of the product. Selectivities under these conditions are nearly stoichiometric to the desired product. The exothermic heat of reaction vapori2es the 1,2-dichloroethane product, which is purified by distillation. 

Trichloroethane is also a coproduct in the thermal and photochemical chlorination of 1,1-dichloroethane to produce 1,1,1-trichloroethane. Vapor chlorination favors the 1,1,1-isomer, whereas reaction in the Hquid phase may give much higher ratios of 1,1,2-trichloroethane. V-type 2eohtes have been used in vapor-phase chlorination of 1,1-dichloroethane to produce 1,1,2-trichloroethane in high selectivity (100). 

Oxychlorination of Ethylene or Dichloroethane. Ethylene or dichloroethane can be chlorinated to a mixture of tetrachoroethylene and trichloroethylene in the presence of oxygen and catalysts. The reaction is carried out in a fluidized-bed reactor at 425°C and 138—207 kPa (20—30 psi). The most common catalysts ate mixtures of potassium and cupric chlorides. Conversion to chlotocatbons ranges from 85—90%, with 10—15% lost as carbon monoxide and carbon dioxide (24). Temperature control is critical. Below 425°C, tetrachloroethane becomes the dominant product, 57.3 wt % of cmde product at 330°C (30). Above 480°C, excessive burning and decomposition reactions occur. Product ratios can be controlled but less readily than in the chlorination process. Reaction vessels must be constmcted of corrosion-resistant alloys. 

Halogenation. Coumarin reacts with bromine under moderate conditions to give 3,4-dibromocoumarin [42974-18-5] (24). The 3-bromocoumarin [939-18-4] and 3,6-dibromocoumarin [58309-97-0] are formed under more drastic conditions (25). 3-Chlorocoumarin [92-45-5] is formed by reaction with chlorine in dichloroethane (26) or without solvent (27). 

The reaction is carried out over a supported metallic silver catalyst at 250—300°C and 1—2 MPa (10—20 bar). A few parts per million (ppm) of 1,2-dichloroethane are added to the ethylene to inhibit further oxidation to carbon dioxide and water. This results ia chlorine generation, which deactivates the surface of the catalyst. Chem Systems of the United States has developed a process that produces ethylene glycol monoacetate as an iatermediate, which on thermal decomposition yields ethylene oxide [75-21-8]. 

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