Silicon compounds, chlorosulfonation

Silicon compounds containing reactive aryl groups may be chlorosulfonated without loss of the silicon atom by the use of chlorosulfonic acid. Thus, tetraphenoxysilane 451 reacted with excess chlorosulfonic acid at 75-85 C (2j hours) to give the sulfonyl chloride 452. Subsequent reduction of 452 with zinc afforded 4-hydroxyphenylthiol 453 (72% yield, 99.6% purity) this provides an excellent synthetic route to this compound (Equation 140). ... 

Most compounders use a combination of physical and chemical antiozonants and achieve excellent protection in this way. For more severe ozone-resistance problems, there are, of course, a number of specialty elastomers that are saturated and therefore completely ozone-resistant ethylene/propylene rubber, chlorinated and chlorosulfonated polyethylene, ethylene/vinyl acetate, ethylene/acrylic esters, butyl rubber, SEES, plasticized PVC, butyl acrylate copolymers, polyepichlorohydrin and copolymers, polyetherester block copolymer, polyurethane, and silicone. 

Within solvent release type thermosetting sealants, there are Neoprene, hutadiene-styrene, chlorosulfonated polyethylene, EPDM, and silicones. Solvent release types constitute the largest variety of sealants and are composed of three parts (1) the liquid portion of the compound which is the basic non-volatile polymer/elastomeric vehicle, (2) the pigment component, and a (3) solvent or thinner component used to ease the process and to control the thickness. The sealant is cured and its required viscosity is controlled by the evaporation of solvent. 

The mechanism involves initial nucleophilic attack by the trimethylsilyl compound on the electrophilic sulfur atom of trimethylsilyl chlorosulfonate 459 with loss of trimethylsilyl chloride. In the second step, the initially formed trimethylsilyl sulfonate is hydrolysed to the corresponding sulfonic acid (Scheme 14). Chlorosulfonic acid reacts as a nucleophile with certain trimethylsilylmethyl compounds with regioselective cleavage of the silicon-carbon (sp hybridized) bond. For instance, trimethylsilylmethyl chloride 461 with chlorosulfonic acid afforded the compound 462, which on heating gave the compounds 463-465 (Scheme 15). °... 

The solvolytic behaviour of 25 lead(iv), tin(iv) and silicon(iv) compounds in chlorosulfonic acid has been examined conductometrically. ... 

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