Sulphur trioxide/pyridine complex

Sulphonation Pyrrole, furan and thiophene undergo sulphonation with the pyridine-sulphur trioxide complex (CsHsN+SOs ). 

Deoxygenation of sulphoxides to sulphides has been achieved using sodium iodide/pyridine sulphur trioxide complexes in yields of excess of 80% (equation 14)188. 

Baumgarten 80, 1204 showed the pyridine-sulphur trioxide complex to be converted rapidly by alkali into the yellow compound (144). This could be hydrolysed to glutacondialdehyde, and as a source of this compound the reaction has found synthetic use os, xhe quaternary salt from pyridine and ethyl chlorosulphonate is similarly split by alkali, to glutacondialdehyde and sulphamic acid oe. 

The sulphonic acids are usually prepared by the action of sulphuric acid upon a compound. The concentration of the acid and the temperature of reaction are varied according to the reactivity of the compound. Often oleum is used or even chiorosulphonic acid. Alternatively sulphur trioxide complexed to pyridine or dioxan can be used with reactive substrates. Aminosulphonic acids such as sulphanilic and naphthionic acids are most conveniently prepared by heating the sulphate of the amine at ISO C. 

Sieh and Dunham have described an analytical procedure for the estimation of the active sulphur trioxide in pyridine-sulphur trioxide (131) complex. The hydrolysis of the latter when added to water, is completed in one hour. However, when the complex is dissolved in 0.1% water in pyridine solution, complete hydrolysis takes place in 5 minutes. This increased rate of hydrolysis allow the estimation of the complex by Karl Fischer titration with good precision. The reaction was extended to the determination of the active sulphur trioxide in the trimethylamine-sulphur trioxide complex182. A solid adduct of S03 and dimethylformamide has been used as a titrant for the conductiometric titration of aliphatic, aromatic and cyclic amines183. 

Sulfation of gums is carried out to replace hydroxyl groups from the polysaccharide with sulfate moieties (-SO ). The reactants used for sulfate derivitization were mainly chlorosulfonic acid in pyridine (Py), piperidine N-sulfonic acid, or sulphur trioxide complexes with pyridine, triethylamine or DMF. The solvents used were usually for-mamide (FA), DMF, DMSO and pyridine. ITowever, due to the structural complexity of polysaccharides, one sulfation method resulting in predictable derivatives of a certain polysaccharide was not easily applicable to another polysaccharide [11]. The general scheme of sulfation is shown in Figure 10.3. 

The picolineSj when sulphonated under conditions like those used for pyridine, appear to give lower yields ofmonosulphonicacids 272, 275, 278, 279 a-, j8- and y-Picoline give, respectively, 2-methylpyridine-5-, 3-methylpyri-dine-5 and 4-methylpyridine-3-sulphonic acid s. 4-Ethylpyridine gives 4-ethylpyridine-3-sulphonic acid so. Both pyridine and j8-picoline have been sulphonated by heating their sulphur trioxide complexes with sulphuric acid and mercury28i. 

Sulphur trioxide pyridine complex [26412-87-3] M159.2, m 155-165 , 175 . Wash the solid with a little CCI4 then H2O to remove traces of pyridine sulphate, and dry over P2O5 [B 59 1166 1926, S 59 1979]. 

A c.d. correlation confirmed that (+ )-5-carotene (20) has the same absolute stereochemistry at C-6 as (-f )-a-carotene (21). Lutein (22) was also shown to have this absolute stereochemistry at C-6 by c.d. correlation with natural zein-oxanthin (23). In order to do this, the allylic alcohol group was removed by Corey s method using the sulphur trioxide-pyridine complex followed by... 

Partial synthesis of carotenoid sulphates is effected from carotenols by reaction with a sulphur trioxide/pyridine complex prepared from chlorosulphinic acid and pyridine, followed by sodium salt formation by... 

All carotenoid sulphates have been prepared by partial synthesis from the corresponding carotenols by reaction with a sulphur trioxide/pyridine complex prepared from chloro-sulphonic acid and pyridine [8-10], followed by sodium salt formation by addition of NaOH or, for alkali-labile carotenoids, NaCl [11], Scheme 1. The presumed mechanism is that S-0... 

Alkyl sulphuric acids are known to be as acidic as sulphuric acid itself and to form inorganic salts readily [13]. In the general procedure [11], the sulphur trioxide/pyridine complex, in excess, and the respective carotenol are mixed at -10°C and the reaction, monitored by TLC, is allowed to proceed at room temperature. The reaction is quenched either by the addition of 10% aqueous NaOH to ca. pH 9, or by the addition of an aqueous NaCl solution. The carotenoids are extracted with ethyl acetate (or for disulphates with chloroform-methanol) from the aqueous hypophase and separated by TLC. 

With dinitrogen pentoxide pyridine gives 1-nitropyridinium nitrate sa and with nitronium fluoborate the corresponding fluoborate is formed Pyridine forms a 1 1 complex with phosphorus pentachloride Sc with sulphur dioxidei29 (43) and with sulphur trioxide o (44). The last is useful as a sulphonating agent (p. 80), and is formed from its components in carbon tetrachloride, from pyridine and fuming sulphuric acid, and from pyridine and chlorosulphonic acid. Its reactions are discussed later (p. 177). 

With sulphur trioxide in sulphur dioxide at —10°, pyridine, 2,6-lutidine and 2,6-di-isopropylpyridine give addition complexes (p. 162). In contrast,... 

The chromium trioxide-pyridine complex is a highly selective oxidant for alcoholic groups [28]. A mechanism similar to that discussed above seems possible, the selectivity being due to lowered reactivity of chromium trioxide in the pyridine complex. The remarkably smooth and selective oxidation of alcohols by chromium trioxide-sulphuric acid (Jones reagent) in acetone solution [2g] has not been explained. 

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