ALKYLATION OF PHENOL WITH 1-PROPANOL AND 2-PROPANOL OVER CATALYSTS DERIVED FROM HYDROTALCITE-LIKE ANIONIC CLAYS

Vapour phase alkylation of phenol with 1-propanol and 2-propanol was c arried out in a fixed-bed flow reactor over calcined magnesium alumini um hydrotalcites (MgAl-CHT) with Mg/Al atomic ratios 2, 3 and 4. MgAl 3.0-CHT showed higher phenol conversion (similar to 80% at 350 degrees C) in the alkylation of phenol with l-propanol. Both O- and C-alkylat ions were found to be taking place without any skeletal isomerization of the propyl moiety, suggesting an S(N)2 type mechanism. Isomorphous substitution of Mg2+ by Cu-2 or Ni2+ in the hydrotalcite framework res ulted in the predominant C-alkylation to give 2-n-propylphenol (60-70% ) with nearly 40-50% phenol conversion at 350 degrees C. When 2-propan ol was used as an alkylating agent, the phenol conversion decreased ov er all these catalysts and the alkylation was noticed exclusively at C -centers. Comparison of the product selectivity at constant phenol con version revealed that CuAl 3.0-CHT is more selective for 2-n-propylphe nol and 2-isopropylphenol in the reaction of phenol with 1-propanol an d 2-propanol respectively. The participation of a pair of acid-base si tes in the calcined hydrotalcites for the alkylation reaction has been proposed. The acid-base properties of these catalysts have been exami ned by the decomposition of cyclohexanol as a test reaction. Analysis of the spent catalysts revealed that CU2+ in CuO gets reduced into Cu1 + and metallic copper during the reaction in the case of CuAl-CHT, whi le MgO and NiO phases of MgAl-CHT and NiAl-CHT are retained.