Characterisation and mechanistic studies of the acylation of anisole catalysed by zeolite BEA

Tools

Bonati, M.L.M., 2006. Characterisation and mechanistic studies of the acylation of anisole catalysed by zeolite BEA. PhD, Nottingham Trent University.

Preview

Text
10183425.pdf - Published version
Download (32MB) | Preview

Official URL: http://gateway.proquest.com/openurl?url_ver=Z39.88...

Abstract

This thesis presents a study on the acylation of anisole catalysed by zeolite BEA. Zeolite BEA samples were prepared by aqueous ion exchange and characterised by XRD, ICP, TPD-MS and FTIR. These samples are shown to possess different amounts of Brønsted and Lewis acid sites. For example, H-BEA has the highest amount of Brønsted acid sites and Na-BEA the lowest. Catalytic activity in the liquid phase acylation of anisole was highest for H-BEA and lowest for Na-BEA. These results indicate that the reaction should be Brønsted catalysed. However, no straightforward correlation was found between Brønsted acidity and catalytic activity when all the ion- exchanged samples were taken into account.

Investigations by TPD-MS and FTIR of the adsorption of acetic anhydride on BEA suggest that most of the acetic anhydride undergoes decomposition to acetic acid and ketene. Adsorption and catalytic data shows that there is an inverse correlation between the initial rate of acylation and the amount of ketene desorbed intact for a number of catalysts. These results have been interpreted as evidence of the involvement of ketene in the acylation reaction and a mechanism was proposed whereby ketene is formed from acetic anhydride interacting with BEA and then ketene attaches onto the aromatic ring of anisole to give p-MAP. However, subsequent catalytic experiments using deuterium- exchanged reagents and NMR to analyse the product, have shown that ketene can not be the species attaching to the aromatic ring of anisole.

The adsorption studies also indicate stronger bonding of acetic acid/acetic anhydride than the product, p-MAP. Further studies on the hydrolysis of acetic anhydride catalysed by BEA also suggest that neither acetic anhydride nor acetic acid deactivate the catalyst. Thus, multiply acylated products may well be the species responsible for the deactivation and ketene might be responsible for their formation.

Further investigations on the nature of the active sites have shown that the acylation reaction is Brønsted catalysed in the case of H-BEA, but Lewis catalysed when Cu- BEA is used.

Item Type:

Thesis

Creators:

Bonati, M.L.M.

Date:

2006

ISBN:

9781369316261

Identifiers: