Sulfonic acid scavengers

MP borohydride catches one equivalent of the titanium catalyst, while the polystyrene-bound diethanolamine resin (PS-DEAM) can scavenge the remaining titanium catalyst. The borohydride reagent also assists in the reductive animation reaction. Final purification of the crude amine product is achieved with a polystyrene-bound toluene sulfonic acid resin scavenger that holds the amine through an ion exchange reaction, while impurities are washed off. The pure amine can be recovered with methanol containing 2M ammonium hydroxide. 

The stability of the Cgg -cation can be increased by adding trifluoromethane-sulfonic acid CF3SO3H to the TCE/(TBA)PFg solutions [8]. Under these conditions the life-time of the cation is estimated to be at least some hours. Cgg" is probably stabilized by CF3SO3H because of acid s ability to scavenge water and nucleophiles that would react readily with the cation. The elevated lifetime of the cation made it... 

Commercially available acidic resins, as well as ion exchangers, that are used for scavenging amines or other basic compounds contain an acidic functionality, which interacts with the counter basic moiety, thus forming an easily removable salt. Some representative examples are those of benzoic acid (5) and sulfonic acid (6) resins (Fig. 4). 

In glucosides, hemiacetal hydroxyl activation/substitution can be achieved using a sulfonic anhydride and a nucleophile, plus a base as acid scavenger.12 The reaction is catalysed by dibutyl sulfoxide (Bu2S=0), and shows evidence of sulfur-covalent catalysis. Using benzenesulfonic anhydride [(PhS0)20], it is proposed to involve initial formation of a sulfonium sulfonate (6), the S(IV) centre of which then reacts with... 

Recently, Djuric, Sauer and coworkers described the application of a silica-bound p-toluene sulfonic acid (Si-SCX) cartridge for scavenging of DMAP used in the synthesis of acylsulfonamides [51], Reactions were delivered to a packed SPE, allowing gravity elution to effectively remove the DMAP, providing the desired products in high purity by LC/MS (Scheme 8.38). 

Scheme 8.38 Scavenging of DMAP using a silica-bound p-toluene sulfonic acid (Si-SCX) cartridge.

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