Sulfur trioxide, chlorination

Iodine Acetaldehyde, acetylene, aluminum, ammonia (aqueous or anhydrous), antimony, bromine pentafluoride, carbides, cesium oxide, chlorine, ethanol, fluorine, formamide, lithium, magnesium, phosphorus, pyridine, silver azide, sulfur trioxide... 

Chemical Properties. The chemistry of the sulfur chlorides has been reviewed (141,142). Sulfur monochloride is stable at ambient temperature but undergoes exchange with dissolved sulfur at 100°C, indicating reversible dissociation. When distilled at its atmospheric boiling point, it undergoes some decomposition to the dichloride, but decomposition is avoided with distillation at ca 6.7 kPa (50 mm Hg). At above 300°C, substantial dissociation to S2 and CI2 occurs. Sulfur monochloride is noncombustible at ambient temperature, but at elevated temperatures it decomposes to chlorine and sulfur (137). The sulfur then is capable of burning to sulfur dioxide and a small proportion of sulfur trioxide. 

Using sulfur trioxide plus chlorine, or sulfur dioxide plus chlorine, sulfur monochloride yields thionyl chloride [7719-09-7] SOCI2. Various nucleophilic reactions can displace the chlorine atoms of sulfur monochloride ... 

When the batch is completed, a slight excess of oleum and chlorine is added to reduce to a minimum the residual SCI2. Because thionyl chloride combines readily with sulfur trioxide to form the relatively stable pyrosulfuryl chloride, it is necessary to maintain the concentration of sulfur trioxide in the reaction mass at a low level hence, the addition of oleum to sulfur chloride rather than the reverse. When all of the reactants are added, heat is appHed to the jacket of the reactor and the batch is refluxed until most of the sulfur dioxide, hydrogen chloride, and chlorine are eliminated. The thionyl chloride is then distilled from the reactor. 

At present, thionyl chloride is produced commercially by the continuous reaction of sulfur dioxide (or sulfur trioxide) with sulfur monochloride (or sulfur dichloride) mixed with excess chlorine. The reaction is conducted in the gaseous phase at elevated temperature over activated carbon (178). Unreacted sulfur dioxide is mixed with the stoichiometric amount of chlorine and allowed to react at low temperature over activated carbon to form sulfuryl chloride, which is fed back to the main thionyl chloride reactor. 

Other burners are used for low capacity operations. A cascade or checker burner, ia which molten sulfur flows down through brick checkerwork countercurrent to a flow of air, is used ia small units with a sulfur trioxide converter to condition gases entering electrostatic precipitators at boiler plants operating on low sulfur coal. A small pan burner, which is fed with soHd, low carbon sulfur, is used to produce sulfur dioxide for solution ia irrigation water to control the pH and maintain porosity ia the soil. The same type of burner is used to disiafect wastewater ia this case sulfur dioxide is used iastead of chlorine. 

This method is also used with alcohols of the stmcture Cl(CH2) OH (114). HaloaLkyl chlorosulfates are likewise obtained from the reaction of halogenated alkanes with sulfur trioxide or from the chlorination of cycHc sulfites (115,116). Chlorosilanes form chlorosulfate esters when treated with sulfur trioxide or chlorosulfuric acid (117). Another approach to halosulfates is based on the addition of chlorosulfuric or fluorosulfuric acid to alkenes in nonpolar solvents (118). 

Arsenic trifluoride (arsenic(III) fluoride), AsF, can be prepared by reaction of arsenic trioxide with a mixture of sulfuric acid and calcium fluoride or even better with fluorosulfonic acid. Chlorine reacts with ice-cold arsenic trifluoride to produce a hygroscopic soHd compound, arsenic dichloride trifluoride [14933-43-8] ASCI2F35 consisting of AsQ. and AsF ions (21). Arsenic trifluoride forms a stable adduct, 2AsF2 SSO, with sulfur trioxide and reacts with nitrosyl fluoride to give nitrosonium hexafluoroarsenate(V) [18535-07-4] [NO][AsFg]. 

Strong dehydrating agents such as phosphorous pentoxide or sulfur trioxide convert chlorosulfuric acid to its anhydride, pyrosulfuryl chloride [7791-27-7] S20 Cl2. Analogous trisulfuryl compounds have been identified in mixtures with sulfur trioxide (3,19). When boiled in the presence of mercury salts or other catalysts, chlorosulfuric acid decomposes quantitatively to sulfuryl chloride and sulfuric acid. The reverse reaction has been claimed as a preparative method (20), but it appears to proceed only under special conditions. Noncatalytic decomposition at temperatures at and above the boiling point also generates sulfuryl chloride, chlorine, sulfur dioxide, and other compounds. 

Other chlorinated solvents such as tetrachloroethylene or chloroform may be used in place of carbon tetrachloride. Caution The reaction of sulfur trioxide with chlorinated solvents has been reported to give phosgene and other toxic products. Adequate venting of all by-product gases is essential. 

Chlorine monoxide reacts violently [1], and sulfur trioxide very violently [2], with dipheny lmercury. 

MRH Carbon monoxide 6.15/65, chlorine dioxide 5.69/75, sulfur dioxide 4.56/74, sulfur trioxide 5.06/70... 

Very frequently, chlorine, bromine, or iodine is present at a carbon atom carrying two fluorine atoms and this promotes hydrolysis of one of the fluorines, together with the other halogen. Acyl fluorides can be intercepted if the hydrolysis is carried out in anhydrous media.<,25,2< Perfliioro-l-iodopropane with sulfur trioxide gives periluoropropanoyl fluoride (20).25... 

Zefirov and coworkers have developed procedures for chlorosulfamation of alkenes and alkynes using reagents of the type R2NSO2OCI formed by insertion of sulfur trioxide into the nitrogen-chlorine bond in yV-chloroamines (R2NCI).106... 

Chlorosulfuric Acid. Chlorosulfuric acid, the monochloride of sulfuric acid, is a strong acid containing a relatively weak sulfur-chlorine bond. It can be prepared by the direct combination of sulfur trioxide and dry hydrogen chloride gas.6 The reaction is very exothermic and reversible, making it difficult to obtain chlorosulfuric acid free of S03 and HCl. Upon distillation, even in good vacuum, some... 

Chlorine is the as-determined chlorine (ASTM D-2361 ASTM D-4208), Sp is the as-determined pyrite sulfur (ASTM D-2492), S03ash is the as-determined sulfate (sulfur trioxide, S03) in ash (ASTM D-1757), and C02 is the as-determined carbon dioxide in coal (ASTM D-1756). All other terms are as given in the earlier formulas, and all values are expressed as percentages. 

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