哌啶氧铵盐对醇氧化反应的活性和选择性

Reactivity and Selectivity in the Oxidation of Alcohols by Oxoammonium Salts

系统地研究了12种具有不同4-位取代基(R=H、CH_3O、Cl)及反离子(X=Cl、BF_4、ClO_4、Br或Br_3)的2,2,6,6-四甲基哌啶氧铵盐对醇的氧化反应,发现这些氧铵盐都能以很高的收率将一级醇氧化为醛,二级醇氧化为酮.氧化反应的活性与4-位取代基及反离子有关.当反离子相同时,反应活性的顺序为Cl>CH_3O>H;当4-位取代基相同时,反应活性的顺序为Cl^->>BF_4^->ClO_4^->Br^-.氧化反应的选择性主要与反离子有关,当反离子为Cl^-时,主要氧化一级醇;当反离子为BF_4^-、ClO_4^-、Br^-或Br_3^-时,主要氧化二级醇.

Systematic study was performed on the oxidation of alcohols by twelve 2, 2, 6, 6-tetramethylpiperidine oxoammonium salts bearing different 4-substituents (R=H, CH_3O, Cl) and counter-ions (X^-=Cl^-, BF_4^-, ClO_4^-, Br^-or Br_3^-). All of these oxoammonium salts can oxidize primary alcohols to aldehydes and secondary alcohols to ketones with very high yield. The reactivity of the oxidants is related with both the 4-subsbituent and the counter-ion with the sequence of Cl>CH_3O>H for the salts with the same counter-ion and Cl^->>BF_4^->ClO_4^->Br^-for the salts with the same 4-substituent. The selectivity of the oxidants is mainly determined by the counter-ions. The oxidant oxidizes preferably primary alcohols when the counter-ion is Cl^-, but oxidazes secondary alcohols selectiyely when the counter-ions are BF_4^-, ClO_4^-, Br^-or Br_3^-.