Sulphonation reagents

Chlorosulphonic acid, and other derivatives of sulphuric acid, may also be used for the formation of sulphonic acids by sulphonation of aromatic compounds. These sulphonating reagents are more reactive than sulphuric acid itself78,84 and so milder conditions (temperatures of 0-25 °C are typical) may be used with them. In addition, water is not normally involved in the reaction and the separation problems, caused by the use of excess reagents, as is the case with sulphuric acid, are significantly reduced. 

Alkyl sulphamic acids have also been used for the formation of aromatic sulphonic acids, in excellent yields, by heating this sulphonating reagent with an aromatic compound, as shown in equation 1097. 

Sulphur trioxide is a much more reactive sulphonating reagent than either sulphuric acid or its derivatives84. Oleum, sulphur trioxide in concentrated sulphuric acid, is even... 

The yields of y- and <5-sultones obtained from the sulphonation of alkenes depend largely on the nature of the sulphonation reagent and reaction temperature. The sulphur trioxide-Lewis base complexes effect less charring than uncomplexed sulphur trioxide, but the lower reactivity of the former tends to lead to lower yields of sultones under the... 

A variety of sulphonation reagents can be used for the sulphonation reaction SOa/air from sulphur burning and subsequent conversion of the S02/air formed SOs/air from stabilised liquid SO3 or SO3 stripped from 65% oleum with dried process air, 20% oleum and chlorosulphonic acid. 

It is also technically feasible to use liquid sulphuric acid or 20% oleum as a sulphonation reagent. The reactions can be carried out in various types of liquid - liquid contact reactors and are also highly exothermic. 

Woodward has now reported reliable procedures for the preparation of trimethylene and ethylene dithiotoluene-jp-sulphonates, reagents used in the formation of dithians and dithiolans from active methylene compounds, including those adjacent to a carbonyl group activated by prior hydroxy-methylene or enamine formation. Applications include carbon-carbon bond cleavage and ketone transposition (Scheme 148). 

Alkane sulphonation by SOz + Oz and a-sulphonation of N-alkyl-j3-alanines illustrate conventional studies in sulphonic acid synthesis sulphonation at C-1 in cyclopentanesulphonic acid proceeds via a relatively stable mixed anhydride when SO3 is used as sulphonation reagent. ... 

Chemical methods may be employed if the reagent attacks only one of the components. Thus quicklime may be employed for the removal of water in the preparation of absolute ethyl alcohol. Also aromatic and unsaturated hydrocarbons may be removed from mixtures with saturated hydrocarbons by sulphonation. 

Sulphones. Sulphones are usually crystalline solids, and are extremely stable to most oxidising, reducing and hydrol3rtic reagents. 

B. Naphthaquinone method Discussion. Many primary amines develop a blue colour when treated with ortho-quinones the preferred reagent is the sodium salt of l,2-naphthaquinone-4-sulphonic acid. 

Reagents. 1,2-Naphthaquinone-4-sulphonic acid sodium salt. Dissolve 0.4 g of the solid in 100 mL distilled water (solution C). 

Kinetic isotope effects have not been observed in the reaction of 1-naphthol-4-sulphonic-2-acid with 2-methoxydiazobenzene127, imidazole-2,4,5-d3 with 4-diazobenzene sulphonic acid128, or indole-3- / with 4-nitrodiazobenzene12S, nor has base catalysis been observed in those cases where it has been measured in each of these reactions one or both of the reagents is relatively reactive. 

Most methods of oxidation to sulphones involve classical reagents and the standard procedure has been to use a measured amount of oxidation reagent in excess and to determine the unused amount by back-titration, nearly always with iron(II). Sub-classification is most convenient according to the reagent ... 

The well-known fact that enantiomers exhibit different reactivity towards chiral reagents has been used to obtain optically active sulphoxides in a process which is called kinetic resolution. Kinetic resolution of sulphoxides usually involves either oxidation to the corresponding sulphones or reduction to sulphides by means of proper chiral oxidizing or reducing agents. 

The reagent has also been used to desulphonylate vinyl sulphones to give alkenes141-143. The solvent was refluxing 10% aqueous THF and the yields reported were over 80%. 

Three reaction sequences, all of a similar nature, have been published by Fujita and coworkers. The first175 is an alkene synthesis in which only three examples that involve sulphones are given. The most useful of these is a conversion of nerly phenyl sulphone (from neryl chloride) into aCn triene (75%), with the extra carbon atom being supplied by the iodomethylstannane reagent. The reaction proceeds spontaneously, with apparent retention of configuration at the Z alkene, as in equation (72). 

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