Sulfuryl chloride initiation

The selective replacement of hydroxyl groups in carbohydrates by chlorine has been achieved by the use of sulfuryl chloride.1,74,87,88 The reaction of sulfuryl chloride with maltose89,90 and methyl /3-maltoside24 has been studied. Treatment of maltose with sulfuryl chloride, initially for 2 h at — 70° and then processing at room temperature, gave, after methyl glycosidation and dechlorosulfation, a low yield... 

A more energy-efficient variation of photohalogenation, which has been used since the 1940s to produce chlorinated solvents, is the Kharasch process (45). Ultraviolet radiation is used to photocleave ben2oyl peroxide (see Peroxides and peroxide compounds). The radical products react with sulfuryl chloride (from SO2 and CI2) to Hberate atomic chlorine and initiate a radical chain process in which hydrocarbons become halogenated. Thus, for Ar = aryl,... 

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. 

Besides radical additions to unsaturated C—C bonds (Section III.B.l) and sulfene reactions (see above), sulfonyl halides are able to furnish sulfones by nucleophilic substitution of halide by appropriate C-nucleophiles. Undesired radical reactions are suppressed by avoiding heat, irradiation, radical initiators, transition-element ion catalysis, and unsuitable halogens. However, a second type of undesired reaction can occur by transfer of halogen instead of sulfonyl groups283-286 (which becomes the main reaction, e.g. with sulfuryl chloride). Normally, both types of undesired side-reaction can be avoided by utilizing sulfonyl fluorides. 

By means of oxidation of the initially formed 3,4-disubstituted 5-bromo-2-bromomethylpyrrole, bromine converted 3,4-disubstituted-2-methylpyr-roles and their 5-carboxylic acids into 5-bromo-5 -bromomethyl-2,2 -dipyrrolylmethanes. Similar reaction with sulfuryl chloride led to the analogous chloro species (77MI2). Whereas treatment of 2-aroyl-l,3-dimethylpyrrole-5-acetic esters with NBS brominated the vacant ring carbon, the related oxalate ester gave the 3-bromomethyl derivative (80JMC98). 

Alkanes can be simultaneously chlorinated and chlorosulfonated. This commercially useful reaction has been applied to polyethylene (201—203). Aromatics can be chlorinated on the ring, and in the presence of a free-radical initiator alkylaromatic compounds can be chlorinated selectively in the side chain Ring chlorination can be selective. A patent shows chlorination of 2,5-di- to 2,4,5-trichlorophenoxyacetic acid free of the toxic tetrachlorodibenzodioxins (204). With alkenes, depending on conditions, the chlorination can be additive or substitutive. The addition of sulfuryl chloride can occur to form a 2-chloroalkanesulfonyl chloride (205). 

The first step in preparing the very useful elastomer Hypalon involves treating a mixture of long-chain alkanes, H(CH2) H, where n =50-200, with sulfuryl chloride (S02C 2) in the presence of substances that can initiate radical-chain chlorination, as described in Section 4-5B. The product molecules contain many C-CI bonds and a few C-S02-Cl bonds, the latter of which are subsequently used in a curing step to improve the physical properties. How can the chain mechanism for chlorination with S02CI2 be modified to account for the formation of C-S02-Cl bonds ... 

Sulfuryl chloride, S02C12, decomposes by first-order kinetics, and k = 2.81 X 10 3 min-1 at a certain temperature, (a) Determine the half-life for the reaction, (b) Determine the time needed for the concentration of a S02C12 sample to decrease to 10% of its initial concentration, (c) If a 14.0-g sample of S02C12 is sealed in a 2500-L reaction vessel and heated to the specified temperature, what mass will remain after 1.5 h ... 

Although direct chlorination cannot be applied to methylchlorodisilanes of lower chlorine content as well as permethylated polysilanes because they are highly sensitive to cleavage, peroxide-initiated chlorination with sulfuryl chloride is fairly satisfactory for them. Thus, hexamethyldisilane (120) and 1,2-dichlorotetramethyldisilane (110) are converted to the corresponding monochloromethyl derivatives, although extensive cleavage of the silicon-silicon bond also occurs. 

Another interesting reaction is the treatment of partially protected saccharides with sulfuryl chloride (Scheme 3.2d).10 These reactions proceed by the initial formation of chlorosulfates, which are displaced by the liberated chloride ions. The substitution reaction occurs only at those centres where the steric and polar factors are favourable for an Sn2 reaction. The chlorosulfates that have not been substituted with a chloride can easily be cleaved by treatment with sodium iodide. 

To initiate the chain reaction catalytic amounts of dibenzoyl peroxide are used. Dibenzoyl peroxide undergoes multistep fragmentation to give the phenyl radical (cf. Figure 1.37), which abstracts a Cl atom from sulfuryl chloride and thus generates the initiating radical S02CI. 

Sulfuryl chloride, in the absence of light or free-radical initiators, acts as an electrophile. At 65-85 °C, in the dark, tetrahydrofuran and tetrahydropyran are selectively chlorinated by S02C12 to 2,3,3-trichloro tetrahydrofuran and 2,3,3-trichlorotetrahydropyran, respectively (equation 120)853,854. 

The chlorination of alkyl aromatics by sulfuryl chloride promoted by free-radical initiators, which was originally discovered by Kharasch and Brown990, can be modified by incorporation of transition metal complexes. Matsumoto and coworkers have observed that, upon addition of Pd(PPh3)4, in place of a radical initiator, the side-chain monochlorination of toluene is substantially more selective991. Davis and his colleagues992 have extended this study and report that Pt(0) and Pd(0) are effective initiators for side-chain chlorination of toluene by sulfuryl chloride and dichlorine. Mn, Re, Mo and Fe complexes, on the other hand, behave more like Friedel-Crafts catalysts. Gas-phase chlorination of olefins to allyl chlorides is catalyzed by PdCl2 or by PtCl2993. 

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