Pyridinium-1-sulfonate complex

Vuillaume PY, Bazuin CG. Self-assembly of a tail-end pyridinium polyamphiphile complexed with n-aUcyl sulfonates of variable chain length. Macromolecules 2003 36 6378-6388. 

Pyridinium-1-sulfonate was prepared according to the procedure of Sisler and Audrieth. The submitter reports that this procedure may be conveniently carried out at 5 times the specified scale. The reagent should be dry and used soon after its preparation. The checkers found that a technical grade of pyridinium-1-sulfonate (sulfur trioxide pyridine complex) purchased from Aldrich Chemical Company, Inc., gave substantially lower yields of product. 

The first studies on the sulfation of organic compounds, amino acids, and proteins have shown that pyridine/sulfur trioxide complex (pyridine/S03 or pyridine/Cl S03H),168-721 concentrated sulfuric acid,173,74 sulfuric acid//V,A -dicyclohexylcarbodiimide,175,761 and chloro-sulfonic acid177 are the most efficient reagents for the sulfation of tyrosine. More recently, alternative methods based on dimethylformamide/sulfur trioxide complex (DMF/S03),152,781 trimethylamine/sulfur trioxide (Me3N/S03),1152,1531 pyridinium acetylsulfate,137,791 and pyr-idinium trifluoroacetylsulfate1801 have been proposed to minimize side reactions which are difficult to control for the chemical sulfation of tyrosine peptides. 

Figure 3.3-1 Incorporation of groups with high affinities for ILs (such as cobaltacenium (i), guanadinium (ii), sulfonate (iv), and pyridinium (v)) or even groups that are themselves ionic liquid moieties (such as imidazolium (iii)) as peripheral functionalities on coordinating ligands increases the solubility of transition metal complexes in ILs.

Pyridine reacts with sulfur trioxide to give the crystalline, zwitterionic pyridinium-1-sulfonate, usually known as the pyridine sulfur trioxide complex. This compound is hydrolysed in hot water to sulfuric acid and pyridine (for its reaction with hydroxide see 8.12.3), but more usefully it can serve as a mild sulfonat-ing agent (for examples see 16.1.1.3 and 18.1.1.3) and as an activating agent for dimethylsulfoxide in Moffat oxidations. 

Salts that melt at temperatures below 100°C form useful ionic liquids (ILs) [29]. Because they lack measurable vapor pressure (even up to 300°C), the ILs can be used as green solvents or reaction media. As a result, they have recently received a lot of attention [30]. Simple ILs usually contain imidazolium, pyridinium, or organic ammonium cations. The anions could be chloride, bromide, or more complex structures such as hexafluorophosphate, trifluoromethyl-sulfonate, bis(trifluoro-methylsulfonyl)imide [31]. 

Complex formation between a polycation and a polyanion is also called polysalt formation or coacervation. If, for example, a solution of poly(sodium styrene sulfonate) (III) is added to an equimolar solution of poly(4-vinyl pyridinium hydrogen bromide), then a stoichiometric complex with respect to the side groups is formed, and this occurs at every mixing ratio (Figure... 

A water-soluble positively charged pillar[6]arene (H5.37) was synthesized by Li and co-workers. H5.37 formed stable host-guest complexes with two anionic naphthalenesulfonate derivatives (G5.123 and G5.124). The association constant determined by fluorescence titration was (2.1 0.3) X10 for G5.122 with two sulfonate moieties (run 152). The K value for G5.122 is 5.5 times higher than that for G5.123 with one sulfonate moiety [run 153, r=(3.8 0.2)xl0 M ] because co-operative electrostatic interactions between two sulfonate anions of G5.122 and cationic pyridinium moieties on the pillar[6]arene rims stabilize the complexation. 

The first is fluorination of cyclopenta[c]thiophene-4,6-dione 106 by treatment with A-fluoro-6-(trifluoromethyl)pyridinium-2-sulfonate (MEC-04B) in ethyl acetate to give l,3-dibromo-5,5-difluorocyclopenta[c]thiophene-4,6-dione 107 in 84 % yield. Then, conversion of the two carbonyl groups to difluoromethylene groups was accomplished via formation of the bis-l,3-dithiolane derivative 108 followed by desulfurative fluorination with hydrofluoric acid-pyridine complex and dibromatin (l,3-dibromo-5,5-dimethylhydantoin) in dichloromethane to afford 1,3-dibromohe xafluorocyclopenta[c]thiophene 109 in a two-step yield of 73 % [Id, 67]. 

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