Low-temperature chlorination

Under typical Hquid-phase chlorination conditions the maximum conversion to benzyl chloride of about 70% is reached after reaction of about 1.1 moles of chlorine per mole of toluene (39). Higher yields of benzyl chloride have been claimed 80% for low temperature chlorination (40) 80—85% for light-catalyzed chlorination in the vapor phase (41) and 93.6% for continuous chlorination above 125°C in a column packed with glass rings (42). 

The following rate expression has been determined for the low temperature chlorine catalyzed decomposition of ozone. 

LTC [Low temperature chlorination] A general term for processes for making 1,2-dichloroethane from ethylene and chlorine by processes operated below the boiling point of the product (83°C). See also HTC. 

Low-temperature chlorination of dibenzothiophene with elemental chlorine produces a chlorine adduct at the sulfur atom which is readily decomposed to dibenzothiophene 5-oxide. However, nuclear chlorination of dibenzothiophene has still not been studied. 2-Chlorodibenzo-thiophene has been prepared by the Sandmeyer reaction on 2-amino-dibenzothiophene and this route has now been extended to give... 

SCHEME 27. Ballard, Fairclough, Hough, and Richardson s study of the selective low-temperature chlorination of sucrose with sulfuryl chloride (1973). 

Nanocrystalline MgO and CaO with high surface area are able to absorb large amounts of chlorine, which undergo dissociative chemisorption. These can serve as rather selective, catalytic alkane chlorination reagents, which suggests that trapped Cl atoms are involved in the reaction.295 Liquid-phase low-temperature chlorination of alkanes is also possible in the presence of various alkenes as inductors and AIBN [azobis(isobutyronitrile)] 296... 

In the case of D-glucose-derived hydroxyglycal ester 8, low temperature chlorination affords an approximate 1 8-mixture of the cw-dichloride of a-D-waHHo-configuration (10) and the a-D-g/wco-benzoxonium salt (11), of... 

Kuzina S.I., Demidov S.V., Denisov N.N., Mikhailov A.I. Synchronic reactions of free radicals formation at low-temperature chlorination of aromatic and olefinic carbohydrates. Izv. AN, Ser. Chem., 1999, 335. 

Further studies of electrophilic substitution using the 2,3-dihydrothiazolo analogue (320) show that regioselective bromination can be effected in the 7-position (347) at low temperature. Chlorination with sulfuryl chloride, however, occurs exclusively in the 5-position. The 5-chloro derivative (348) can be further nitrated in the 7-position. By analogy, bromination of quinoline analogues (349) occurs in the azine ring, in the 5-position. The [3,2-a]pyrimidine analogue (350 R=H) similarly yields the 7-bromide. The activation by... 

Inovy Direct chlorination, low temperature chlorination Ethylene, chlorine Well established system and extensively licensed converts lower purity C2 in gaseous stream 24 1993... 

The low-temperature chlorination of FC(0)NF2 is also a convenient method for the synthesis of C12NF. Alternatively, FNCI2 can be obtained from CIF and CIN3 in perfluorinated ether. Irradiation of FNCI2 with a high-pressure Hg lamp leads to the formation of m-N2F2. 

If chlorination is carried out below 65 C in the presence of a diluent that swells but does not dissolve the polymer, the formation of products with chlorines on all adjacent carbons is promoted. Dannis and Ramp (30) have shown that products prepared by this technique have higher T values and greater heat resistance than products prepared at higner chlorination temperatures. The change in T as a result of increased chlorine content in such low-temperature chlorinations is shown in Figure 25. The high T shown for poly(vinyl dichloride) is not that of poly(vinylidene chrorlde). 

Figure 25. Dependence of glass transition temperature on chlorine content in low-temperature chlorination of PVC.

Prolonged low-temperature chlorination of benzo[6] thiophene in the presence of iodine gives an octachloro compound, in which chlorine has added across the 2,3-bond and substituted all hydrogen atoms.341 Heating this to 240°C gives hexachlorobenzo[b]thiophene,341 which can be reduced catalytically to 4,5,6,7-tetrachlorobenzo[b]thiophene.342... 

If less chlorine is used, this method gives 1-chloroethyl ethyl ether as main product, which is more easily separated from by-products by distillation than in the case of Henry synthesis (see page 232). Similarly chlorination of tetra-hydrofuran under UV-irradiation at —30° to —40° gives 2-chloro- and 2,5-dichloro-tetrahydrofuran,513 and that of dioxan in CC14 at —5° to —10° gives 2,5-dichlorodioxan.514 However, no definite product was isolated on low-temperature chlorination of diisopropyl ether.515... 

Procedures for commercial chlorinations ofpoly(vinyl chloride) vary. Low-temperature chlorinations are conducted on aqueous dispersions of the polymers that are reacted with chlorine gas in the presence of swelling agents, like chloroform. These are light catalyzed reactions, usually carried out at about 50 °C. They result in substitutions of methylene hydrogens. ... 

The major source of chlorine is from electrolysis processes as a by-product of the electrolytic manufacture of caustic soda or by electrolysis of fosed sodium chloride or magnesium solution. Chlorine gas is dried by cooling and passing through concentrated sulphuric acid before being liquefied by compression at low temperature. Chlorine gas may be used to prepare in-situ diluted NaOCl solutions for bleaching of AD pastes. 

Low temperature chlorination. In one process, an aqueous dispersion of poly(vinyl chloride) (containing a swelling agent such as chloroform) is heated to about 50°C, illuminated and treated with chlorine. Under these conditions, substitution occurs mainly at the unsubstituted methylene groups so that s-dichloroethylene units are formed. Commercial chlorinated poly (vinyl chloride) has a chlorine content of about 66-67% and is thus, in effect, a copolymer of vinyl chloride and s-dichloroethylene (poly-s-dichloroethylene would have 73% Cl) ... 

In the low-temperature chlorination the heat of the exothermic reaction is removed by indirect cooling of the reactor to temperatures below the b.p. of EDC, e.g.20 - 70 °C. The advantages are low formation of byproducts and less problems with construction materials, the disadvantage is the high energy input for the rectification of the EDC. 

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