Regioselective t-butylation of m-cresol over mesoporous Al-MCM-41 molecular sieves

Mesoporous Al-MCM-41 molecular sieves (Si/Al = 40, 100, 200) have been synt hesised hydrothermally using sodium silicate and aluminium sulphate as the sources for silicon and aluminium, and cetyltrimethylammonium bromide (CTAB ) as the structure directing template. They have been characterised by XRD, TGA and FTIR techniques. An intense peak in the XRD patterns at low angle proves the mesoporous nature of these materials. t-Butylation of m-cresol w ith t-butyl alcohol has been studied over these materials between 250 and 4 00 degreesC. Reactants feed ratio plays a key role in deciding in-cresol co nversion and product selectivity. When m-cresol to t-butyl alcohol mole rat io is set at 1:1, m-cresol conversion is not observed over all the catalyst s. However, when the feed ratio is changed to 1:2, m-cresol conversion is m ore than 30% with the formation of only one ring alkylated product, namely 2-t-butyl-5-methyl phenol. Presuming the zero conversion at the feed ratio 1:1 is due to prevention of adsorption of t-butyl alcohol by m-cresol on th e Bronsted acid sites, t-butyl acetate has been tested as the alkylating ag ent in the place of t-butyl alcohol. Selection of I-butyl acetate as a prob e in this alkylation is based on its effectiveness to get in to adsorption better than t-butyl alcohol through its steric free carbonyl as the actual site of adsorption. This ester gives m-cresol conversion at the feed ratio I:I thus confirming prevention of adsorption of t-butyl alcohol at the feed ratio 1:1 as the possible cause of nil conversion. The study of time on st ream has been carried out to compare the activity of the catalysts and the results are discussed.