Polymer-bound sulfonic acid

Polymer supported persulfonic acids can be prepared by treating polymer-bound sulfonic acids with H2O2 or K2S20g. The resulting resin was found to display an activity of 2.5 mole equivalents per gram of wet resin. This persulfonated resin was successively applied for the oxidation of carboxylic acids, ketones, olefins and for the cleavage of disulfide linkage and of A-formylamino acids. 

The products 58 of this reaction are of high interest as they can be used in a variety of subsequent reactions, Scheme 26. They can be used in next condensation reactions [120,121], which sometimes can be carried out as one-pot procedures [122]. Some examples are shown in Scheme 27. The combination of a-tosylation and reaction with amidines generates different substituted lH-imi-dazoles 60 [123]. Also polymer bound sulfonic acids can be used to trap the hypervalent iodine intermediates and to transfer subsequent steps to solid-phase synthesis [124]. Products of type 61 can be reacted with a variety of different bisnucleophiles to generate polycyclic compounds 62. 

In an opposite manner to bases such as 1 and 2 in terms of reactivity, polymer-supported tosyl chloride equivalent 14 is able to capture alcohols as polymer-bound sulfonates 15, which are released as secondary amines, sulfides and alkylated imidazoles with primary amines, thiols and imidazoles as nucleophiles in a substitution process (Scheme 6) [24]. This technique has further been extended for the preparation of tertiary amines [25] and esters [26]. Excess of amine was scavenged by polymer-supported isocyanate 16 [27, 28] while excess of carboxylic acid was removed by treatment with aminomethylated polystyrene 17. 

Precipitation from poor solvents is routinely used in purification of polymers and in many or most cases is part of the synthetic workup used in making the polymer-immobilized catalysts described throughout this review. Solvent precipitation is also sometimes used incidentally as a way to recover catalysts that are more commonly recovered in some other way. Examples of this are seen in the use of hexane to precipitate the poly(AT-alkylacrylamide)-bound Pd-phosphine complexes 76 and 77 or the poly(JV-terf-butylacry-lamide)-bound sulfonic acid catalyst 78 [115-117], catalysts that are routinely recovered as solids by thermal precipitation (vide infra),... 

Polymer supported reagents, catalysts, protecting groups, and mediators can be used in place of the corresponding small molecule materials (Sherrington, 1991 Sundell and Nasman, 1993). The reactive species is tightly bound to a macromolecular support which immobilizes it. This generally makes toxic, noxious, or corrosive materials much safer. The use of polystyrene sulfonic acid catalyst for the manufacture of methyl r-butyl... 

Several microwave-assisted protocols for soluble polymer-supported syntheses have been described. Among the first examples of so-called liquid-phase synthesis were aqueous Suzuki couplings. Schotten and coworkers presented the use of polyethylene glycol (PEG)-bound aryl halides and sulfonates in these palladium-catalyzed cross-couplings [70]. The authors demonstrated that no additional phase-transfer catalyst (PTC) is needed when the PEG-bound electrophiles are coupled with appropriate aryl boronic acids. The polymer-bound substrates were coupled with 1.2 equivalents of the boronic acids in water under short-term microwave irradiation in sealed vessels in a domestic microwave oven (Scheme 7.62). Work-up involved precipitation of the polymer-bound biaryl from a suitable organic solvent with diethyl ether. Water and insoluble impurities need to be removed prior to precipitation in order to achieve high recoveries of the products. 

Because the hydrophilic sulfonic acid groups are covalently bound to the hydrophobic polymer, they aggregate somewhere in the hydrophobic/hydrophilic transition region, with an average separation of 0.8 nm, compared to 1 nm expected for a totally uniform distribution within the material. ... 

The first type is a standard polysoap derived from a polymerizable surfactant leading to poly(sodium 11-acryloyloxyundecane-l-sulfonate) PSl whereas the second polysoap is an alternating copolymer of maleic acid anhydride and acrylamide leading to a polymer with carboxylic acid groups and hydrophobic n-alkylamide groups PS2 (see Fig. 6.9). The organometaUic catalyst was not covalently bound to the polysoaps in the catalytic experiments. 

So-called optical bleaches, such asBlankophor BA, a substituted amino stilbene sulfonic acid, like auramine O will show enhanced fluorescence in viscous media or when bound to polymers. The strong blue emission tends to give the dyed fabric, especially when viewed under sunlight illumination, an apparent whiteness to the fabric. This stilbene derivative is... 

Gancet, C Preparation of Esters of Carboxylic Acids Directly From Carboxylic Acids and Alcohols Using a Catalyst System Comprising a Sulfonic Acid and a Polymer-Bound Tertiary Amine. European Patent 1,167,337, Jan 2, 2002. 

Obrecht described the reaction of resin-bound thiouronium salt 111 vrith oxophe-nylbutynoic acid tert-butyl ester. Cleavage from the support was effected by S-oxidation to the sulfone followed by displacement vrith an amine [132]. The thiouronium salt pathway is illustrated in Scheme 26. Later, Masquelin et al. developed a condensation of resin-bound thiouronium salts with methylenemalononitriles to provide polymer-bound alkylthiopyrimidines 110 [133]. Pyrimidine derivatives 112... 

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