Mesoporous supports for the catalysis of Friedel-Crafts alkylation and cyclialkylation reactions with sulfur-containing aromatics.

摘要

The thesis describes the synthesis of a variety of porous aluminosilicate supports which have been impregnated with zinc chloride and then used as heterogeneous Friedel-Crafts catalysts for the alkylation and cycli-alkylation of sulfur containing aromatics. The liquid phase benzylation of thiophene was adopted as a test reaction for the investigation into the effectiveness of each of the catalysts with the product analysis performed using both quantitative GC and GC-MS. Cyclisation of phenylthio-acetaldehyde diethylacetals to substituted benzolbrack{lcub}it b/{rcub}rbrack thiophenes using a clayzic catalyst was performed in the vapor phase and illustrates a particular application of zinc chloride impregnated acid-treated clays in the synthesis of fine chemicals.; An industrially modified montmorillonite clay, K{dollar}sb{lcub}10{rcub},{dollar} was loaded with ZnCl{dollar}sb2{dollar} and examined under a multitude of experimental conditions in the benzylation of thiophene. The selectivity towards mono-benzylthiophene products was optimised by performing the reaction in nitrobenzene at {dollar}60spcirc{dollar}C. The K{dollar}sb{lcub}10{rcub}{dollar} support, loaded with 2.0 to 2.2 mmol ZnCl{dollar}sb2{dollar} per gram catalyst and activated at {dollar}275spcirc{dollar}C for one hour in air, resulted in a 77% yield of mono-benzylthiophene, 4% di-benzylthiophene and 8 to 11% tar in under 10 min. A degree of regioselectivity towards the formation of 2-benzylthiophene isomer was observed when the reaction time was reduced and further benzylation of the mono-benzyl products was prevented. The heightened ratio of 2- to 3-benzylthiophene isomers was found to depend more on the rate of benzylation of the two mono-benzylthiophene isomers and their subsequent loss through polymerisation and conversion to tar. Isomerisation was observed to occur relatively slowly at higher reaction temperatures, suggesting an equilibrium to a thermodynamically more stable 3-benzylthiophene isomer.; Modification of montmorillonite clay by mineral acid-treatment and loading with ZnCl{dollar}sb2{dollar} provided a series of catalysts with varying pore diameters (0 to 100 A) which could also effectively catalyse the benzylation of thiophene. Use of these micro-/mesoporous catalyst supports resulted in improved yields of mono-benzylthiophene through the suppression of polyalkylation and polymerisation of the thiophene nucleus.; Friedel-Crafts cycli-alkylation reactions of substituted phenylthio-acetaldehyde diethylacetals to their corresponding benzolbrack{lcub}it b/{rcub}rbrack thiophene products was also tested using this same ``clayzic'' catalyst. Under a variety of reaction conditions in the liquid phase, only poor yields were obtained. Suppression of the bimolecular pathways, which generally lead to the production of unwanted by-products including diphenyldisulfide, was possible by carrying out the reaction in the vapor phase over a heated clay catalyst. Excellent yields were thus obtained.; The major drawback of the above clay catalysts was the poor control of pore size. By modification of a montmorillonite clay such that its natural ``cation-exchange-capacity'' was reduced, a series of aluminum-pillared ``charge-reduced'' clays were prepared in an attempt to increase the average spacing between neighbouring pillars and increase the microporosity of the clay. Loading with a Lewis acidic zinc chloride salt produced an active Friedel-Crafts catalyst for the benzylation of thiophene. Lower yields of polyalkylated thiophene and tar were observed.; Incorporation of permanent zinc chloride Lewis acid sites, within the clay structure, was possible by pillaring the clay with mixed zinc and aluminum pillars. The resulting structures would benefit from the catalytic activity of the pillars and the combined micro-/mesopore structure of the pillared clay structure.; A series of synthetic aluminosilicate MCM-41 supports, with cylindrical mesopore s