An introduction to a range of inorganic solids as heterogeneous catalysts in aromatic bromination reactions is given in Chapter 1. These solids involve silica, alumina, zeolites, clays, and heteropolyacids. Aromatic bromination over these solids is discussed. Regioselectivity towards the <I>para</I>-isomer of various alkylbenzenes is the main theme but the advantages and disadvantages of each brominating system are also discussed. In Chapter 2 the bromination of phenyl acetate (PA) is tested using zeolites, clays and AlCl<SUB>3</SUB> as catalysts. Zeolite NaY was found to be the most efficient catalyst for the <I>para-</I>selective bromination of PA in the presence of dichloromethane. Use of NaY zeolite allows the bromination of PA to give almost exclusively the <I>para</I>-isomer in quantitative yield. Additionally, the effect of the counterions, activation temperature of the zeolite, and solvent on the reaction were also investigated. In Chapter 3 the bromination of PA <I>via</I> a solvent-free process has been investigated. Additives (<I>i.e.</I> acetate anhydride, NaHCO<SUB>3</SUB> and NaOCOCH<SUB>3</SUB>) as HBr scavengers can markedly increase the selectivity for <I>para</I>-isomer. In particular, a mixture of zinc acetate and bromine is shown to be an efficient reagent for <I>para</I>-selective bromination. In Chapter 4 the separation of 4-bromophenyl acetate (4-BPA) is studied. 4-BPA can readily be separated in pure form from industrial distillation residues by selective sorption into ZSM-5 from a cyclohexane solution of the residues and subsequent desorption with acetone. Additionally, the effect of the zeolite parameters, solvent, and temperature on selective adsorption of 4-BPA, as well as re-generation of the used zeolite, have been investigated. In Chapter 5 transbromination of bromo-substituted phenols and phenyl acetates has been discussed using large-pore zeolites and AlCl<SUB>3</SUB> as catalysts. The reactions involve intermolecular transbromination. HZSM-5 zeolite shows shape selectivity for the <I>para</I>-isomer.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:637254 |
| Date | January 1998 |
| Creators | He, P. |
| Publisher | Swansea University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
Page generated in 0.002 seconds