Nanocrystalline sulfated-zirconia

Shinde et al. (2008) have prepared silica gel-supported sodium hydrogen sulfate and demonstrated its application in the synthesis of coumarins. The reactions were conducted in acetonitrile and the reaction time in most of the cases was 1 h, which included the weakly reactive naphthols. Application of nanocrystalline sulfated zirconia in the reaction of meta-substituted phenols has also been investigated (Tyagi et al. 2007) under different conditions. In view of the slow reaction rates observed in nitrobenzene and toluene, the solvent-free conditions were adopted under MW irradiation to obtain high yields (95%-99%), of 7-amino- and 7-hydroxy-4-methylcoumarins in the reaction of m-amino and m-hydroxy phenols with ethyl acetoacetate. A low percentage of catalyst is required and its reusability has been claimed as a novel feature of this synthesis. 

B. Tyagi et al. described the synthesis of 5,7-dihydroxy 4-methyl cou-marin and 7,8-dihydroxy 4-methyl coumarin using nanocrystalline sulfated-zirconia catalyst in solventless system under MWI at 130 °C within 5-20 min in 78-85% yields (08JMCCF241). 

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