Chlorosulfonation, mechanism

CSPE. Chlorosulfonated polyethylene (CSPE), a synthetic mbber manufactured by DuPont, is marketed under the name Hypalon. It can be produced as a self-curing elastomer designed to cure on the roof. The membrane is typically reinforced with polyester and is available in finished thicknesses of 0.75 to 1.5 mm. Because CSPE exhibits thermoplastic characteristics before it cures, it offers heat-weldable seams. After exposure on the roof, the membrane cures offering the toughness and mechanical set of a thermoset. The normal shelf life of the membrane for maintaining this thermoplastic characteristic is approximately six months. After the membrane is fully cured in the field, conventional adhesives are needed to make repairs. 

A solution of sulfur trioxide [7446-11-9] dissolved in chlorosulfonic acid [7990-94-5] CISO H, has been used as a smoke (U.S. designation FS) but it is not a U.S. standard agent (see Chlorosulfuric acid Sulfuric acid and sulfur trioxide). When FS is atomized in air, the sulfur trioxide evaporates from the small droplets and reacts with atmospheric moisture to form sulfuric acid vapor. This vapor condenses into minute droplets that form a dense white cloud. FS produces its effect almost instantaneously upon mechanical atomization into the atmosphere, except at very low temperatures. At such temperatures, the small amount of moisture normally present in the atmosphere, requires that FS be thermally generated with the addition of steam to be effective. FS can be used as a fill for artillery and mortar shells and bombs and can be effectively dispersed from low performance aircraft spray tanks. FS is both corrosive and toxic in the presence of moisture, which imposes limitations on its storage, handling, and use. 

Linear polyethylene (high density) was introduced in the late 1950s, with the development of coordination catalysts. Chlorosulfonation of these base resins gave products that were superior to the eadier, low density types in both chemical resistance and mechanical properties and with distinct advantages in mbber processibiUty (6,7). 

Si, and stannic tetrachloride. An effective smoke agent, whether it be mechanically dispersed from an aircraft spray tank or vaporized thermally, is a mixt of S trioxide and chlorosulfonic acid (FS smoke agent) which upon hydrolysis forms sulfuric and hydrochloric acid dispersions. Of course, all such formulations are highly corrosive, and, if not outright toxic, then conducive to pulmonary edema... 

Although sulfonyl chlorides add readily to unactivated olefins, with vinylic monomers telomeric and/or polymeric products were observed. This difficulty has been overcome by carrying out the addition in the presence of catalytic amounts of CuCl2, so as to provide a general and convenient synthesis of /5-chlorosulfones (Asscher-Vofsi reaction)63. For the copper-catalyzed system a redox-transfer mechanism has been suggested in which the... 

The chlorosulfonation of organic molecules with chlorine and sulfur dioxide is called the Reed reaction In scope and range of products obtained, the reaction is similar to 14-1. The mechanism is also similar, except that there are two additional main propagation steps ... 

The prime installation method is mechanically fastened but fully adhered and ballasted applications can also be used. CSPE exhibits strong resistance not only to weathering but also to a broad range of chemicals and pollutants it is also inherently ozone-resistant. It can be produced in many colors and the sheet widths are typically 5—6.5 ft (1.5—1.65 m). The physical characteristics of a CSPE sheet have been described (17) (see Elastomers, SYNTHETIC—CHLOROSULFONATED POLYETHYLENE). 

Exercise 29-6 Radical-induced chlorination of polyethene in the presence of sulfur dioxide produces a polymer with many chlorine and a few sulfonyl chlo-- ide (—S02CI) groups, substituted more or less randomly along the chains. Write suitable mechanisms for these substitution reactions. What kind of physical properties would you expect the chlorosulfonated polymer to have if substitution is carried to the point of having one substituent group to every 25 to 100 CH2 groups How may this polymer be cross-linked (A useful product of this general type is marketed under the name of Hypalon.)... 

SYNTHESIS To a solution of 64.8 g of o-cresol and 56 g dimethyl sulfoxide in 300 mL EtjO, cooled with an external ice bath with vigorous stirring, there was added 40 mL chlorosulfonic acid dropwise over the course of 30 min. The cooling bath was removed, and the two phase mixture was mechanically stirred at room temperature for 12 h. The Et20 phase was then discarded, and the deep red residue that remained was thoroughly triturated under 300 mL IP A, producing a suspension of pale pink... 

In a 500 cc. round-bottom flask, fitted with a mechanical stirrer, is placed 290 g. (2.49 moles) of chlorosulfonic acid (Note 1). The flask is surrounded by a cooling bath and cooled with running water to about 12-150. To the chlorosulfonic acid is added gradually 67.5 g. (0.5 moles) of acetanilide. This requires about fifteen minutes if the temperature is maintained at approxi mately 15°. Since large volumes of hydrogen chloride are evolved, the reaction should be conducted in a good hood. After all of the acetanilide has been added, the mixture is heated to 6o° for two hours to complete the reaction (Note 2). 

To mechanically stirred, cooled (0°C) chlorosulfonic acid (70 mL, 1.05 mol) was added the crude acetamidosulfonamide (29.7 g, 0.114 mol 93 7 trans/cis) portionwise at a rate to maintain the internal temperature <20°C. The dark sulfonylation reaction mixture was heated to 50°C for 12 h, or until the reaction was judged to be complete by HPLC. During the reaction hydrogen chloride (0.114 mol) was evolved. 

Chlorosulfonated polyethylene (Hypalon) 250 Excellent resistance to oxidizing chemicals, ozone, weathering. Relatively good resistance to oils, grease. Poor resistance to aromatic or chlorinated hydrocarbons. Good mechanical properties. 

Aromatic sulfonyl chlorides (51) are conveniently prepared by treatment of the aromatic compound with an excess of chlorosulfonic acid (Scheme 29). The reaction occurs via the sulfonic acid (step 1) which is then chlorinated by the excess reagent (step 2) (Scheme 29). The mechanism probably involves the chlorosulfonic acid acting as the electrophile, as shown for the reaction with benzene (23) in Scheme 30.5... 

The generally accepted mechanism of the Ramberg-Backlund reaction (Scheme 39) involves the deprotonation of the a-chlorosulfone by the base to give the sulfonyl carbanion (92). The latter undergoes an intramolecular nucleophilic attack on the a-carbon atom with elimination of the chloride anion and formation of the episulfone (93), which is unstable and extrudes sulfur dioxide to yield the alkene (Scheme 39).6 The Ramberg-Backlund reaction, unlike the Julia reaction, yields mainly the (Z)-alkene from acyclic starting materials. 

The chemical name for Hypalon is chlorosulfonated polyethylene and it has excellent resistance to heat, ozone and oxidising chemicals and has good abrasion resistance. It can be compounded for outstanding resistance to oxidising chemicals, such as sodium hypochlorite solutions in sulfuric acid saturated with chlorine and concentrated phosphoric acid. It is one of the few synthetic rubbers that can be mixed in any colour without loss in mechanical properties. 

Protective crack-resistant coatings, based on chlorosulfonated polyethylene (CSPE), are widely known due to their unique crack- and corrosion-resistant properties as compared to other rubbers. These coatings also have high ozone, weather, and wear resistance, as well as excellent mechanical and dielectric characteristics. 

A. Swinarski, A. Grodzicki and J. Glowinska, Mechanism of the chlorosulfonation of aromatics using chlorosulfonic acid, Int. Chem. Eng., 1974, 14, 300-303. 

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