Sulfur trioxide bonding

Sulfur trioxide reactivity can also be moderated through the use of SO adducts. The reactivity of such complexes is inversely proportional to their stabihty, and consequentiy they can be selected for a wide variety of conditions. Whereas moderating SO reactivity by adducting agents is generally beneficial, the agents add cost and may contribute to odor and possible toxicity problems in derived products. CeUulosic material has been sulfated with SO.—trimethyl amine adduct in aqueous media at 0 to 5°C (16). Sulfur trioxide—triethyl phosphate has been used to sulfonate alkenes to the corresponding alkene sulfonate (17). Sulfur trioxide—pyridine adduct sulfates oleyl alcohol with no attack of the double bond (18). 

Sulfonated polyalkenes were prepared by using a triethyl phosphate—sulfur trioxide complex as the sulfonating reagent along with a solvent at low temperature. Sulfonation takes place at the a-position of the double bond with no cross-linking (222). 

Sulfamation is the formation (245) of a nitrogen sulfur(VI) bond by the reaction of an amine and sulfur trioxide, or one of the many adduct forms of SO. Heating an amine with sulfamic acid is an alternative method. A practical example of sulfamation is the artificial sweetener sodium cyclohexylsulfamate [139-05-9] produced from the reaction of cyclohexylamine and sulfur trioxide (246,247) (see Sweeteners). Sulfamic acid is prepared from urea and oleum (248). Whereas sulfamation is not gready used commercially, sulfamic acid has various appHcations (see SuLFAMiC ACID AND SULFAMATES) (249—253). 

The acid is rather slow to react with aUphatic hydrocarbons unless a double bond or other reactive group is present. This permits straight-chain fatty alcohols such as lauryl alcohol [112-53-8] C22H2 0, to be converted to the corresponding sulfate without the degradation or discoloration experienced with the more vigorous reagent sulfur trioxide. This is important in shampoo base manufacture (see Hairpreparations). 

Most of the material presented in this section are reactions of sulfur trioxide. This compound is ambivalent and frequently forms a carbon-sulfur bond (true sulfonation), but it can form a carbon-oxygen bond as well. Examples of both types of bonding are included... 

Two-component methods represent the most widely applied principles in sulfone syntheses, including C—S bond formation between carbon and RSOz species of nucleophilic, radical or electrophilic character as well as oxidations of thioethers or sulfoxides, and cheletropic reactions of sulfur dioxide. Three-component methods use sulfur dioxide as a binding link in order to connect two carbons by a radical or polar route, or use sulfur trioxide as an electrophilic condensation agent to combine two hydrocarbon moieties by a sulfonyl bridge with elimination of water. 

In the first step an S03 molecule is inserted into the ester binding and a mixed anhydride of the sulfuric acid (I) is formed. The anhydride is in a very fast equilibrium with its cyclic enol form (II), whose double bonding is attacked by a second molecule of sulfur trioxide in a fast electrophilic addition (III and IV). In the second slower step, the a-sulfonated anhydride is rearranged into the ester sulfonate and releases one molecule of S03, which in turn sulfonates a new molecule of the fatty acid ester. The real sulfonation agent of the acid ester is not the sulfur trioxide but the initially formed sulfonated anhydride. In their detailed analysis of the different steps and intermediates of the sulfonation reaction, Schmid et al. showed that the mechanism presented by Smith and Stirton [31] is the correct one. 

Sulfate monoesters can react by dissociative paths, and this is the favored path. Whether such reactions are concerted or involve a very short-lived sulfur trioxide intermediate has been the subject of debate. ° Benkovic and Benkovic reported evidence suggesting that the nucleophile is present (though there is little bond formation) in the transition state for the reaction of amines with p-nitrophenyl sulfate. Alkyl esters of sulfuric or sulfonic acids normally react with C-0 cleavage only when this is disfavored, as in aryl esters, does one see S-0 cleavage. Sulfate diester... 

The only other X=Y bond involved in additions to MCP derivatives is the S=0 double bond of sulfur trioxide. Actually, the reactions of MCP (1) and BCP (3) with S03 afford exclusively the y-sultones 608 and 609 (Scheme 85) [160], formal products of [3 + 2] additions of TMM species to S=0 double bond. However, by analogy with larger methylene- and cycloalkylidenecycloalkane derivatives which give stable P-sultones at low temperature, it is presumed that... 

The complexes of sulfur trioxide with various nucleophiles (dioxane, pyridine etc.) are mild sulfonating reagents. Unlike other complexes of sulfur trioxide, dimethyl sulfide-sulfur trioxide readily adds to conjugated multiple bonds. Consequently, not only the sulfo group but also the dimethyl sulfide group add at the multiple bond. The reactions of dimethyl sulfide-sulfur trioxide complex with butadiene, isoprene and 2,3-dimethylbutadiene take place as conjugated l,4- -additions of dimethyl sulfide and sulfonate groups at the double bonds of the diene (equation 103).124... 

Replacement of an allylic hydroxyl without saturation or a shift of the double bond was achieved by treatment of some allylic-type alcohols with triphenyliodophosphorane (PhjPHI), triphenyldiiodophosphorane (PhsPIj) or their mixture with triphenyl phosphine (yields 24-60%) [612]. Still another way is the treatment of an allylic alcohol with a pyridine-sulfur trioxide complex followed by reduction of the intermediate with lithium aluminum hydride in tetrahydrofuran (yields 6-98%) [67 J]. In this method saturation of the double bond has taken place in some instances [675]. 

In Group VIA (16) the same phenomenon is encountered. Selenium trioxide is thermodynamically unstable relative to sulfur trioxide and tellurium trioxide. The enthalpies of formation of SF6, SeF6, and TeFft are -1210. — 1117, and — 1320 kj mol 1, respectively. This indicates comparable bond energies for S—F and Te—F bonds (317 and 330 kj mol-1, respectively), which are more stable than Se—F bonds (285 kj mol 1). 

The most common synthetic methods involving formation of three or more bonds and leading to polyheteroatom systems are of the [2 + 2+2] type. Condensations employing a wide range of different two-atom fragments have been reported, and examples involving the use of sulfur trioxide, nitriles, ketones, isocyanates, ketenes, thioketenes and cyanates as the two-atom components are known. Of these, the reactions of sulfur trioxide and isocyanates are probably the more important, and a few illustrative examples are given here. 

The /J-sultones 3 are readily formed by the addition of sulfur trioxide to polyfluorinated al-kenes.45,46 They are the building blocks of DuPont s Nation membranes.52 Possible mechanisms for the rearrangement have been proposed,45,46,53,54 which all involve initial attack of the nucleophile at the sulfur atom with ring opening at the S-O bond. 

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... 

There are several methods reported in the literature for transforming vicinal diols into ct-diketones while avoiding the risk of C-C bond cleavage.26 Examples include the standard Swem conditions (dimethyl sulfoxide and oxalyl chloride followed by triethylamine), or the use of DMSO activated by acetic anhydride, pyridine-sulfur trioxide complex, or dicyclohexylcarbodiimide (Mq/J-att oxidation). Diones are also obtained by treatment with benzalacetone as a hydride acceptor in the presence of catalytic amounts of tris(triphenylphosphine)ruthenium dichlonde [(PPh RuCFl.27 Recent developments include the use of w-iodoxyben/.oic acid28 or the oxoammonium salt of 4-acctamidoletramethylpipcridine-1-oxyl and y -toluencNulfonic acid.29... 

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... 

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