Aluminium catalysis, alkylation with

Cyclopentadienyl ligands have become extremely important in catalysis for metal such as Ti, Zr, and Hf (Chapter 10) and in academic studies of related elements such as Ta. Ethylene polymerisation with the use of CpiTiCE (alkylated with aluminium alkyl compounds) has been known for many decades, but the intensive interest in derivatives of these compounds started in the early 1980 s following the discovery of MAO (methaluminoxane - see chapter 10) which boosted metallocene catalyst activities by several orders of magnitude. Commercial interest focussed on ethylene copolymers (LLDPE where more homogeneous comonomer incorporation resulted in greatly improved copolymer properties) and in enantiospecific polymerisations for propene, styrene, etc. 

The alkylation can also be carried out by processes which do not pollute the environment. As already stated, the conventional process is operated with AICI3 catalysis, and the NaCl formed in the course of production, the aluminium hydroxide sludge and residual benzene must be removed before the effluent is discharged. In the alkylation with HF, virtually no waste appears in the effluent, since the HF... 

The most valuable and comprehensive kinetic studies of alkylation have been carried out by Brown et al. The first of these studies concerned benzylation of aromatics with 3,4-dichloro- and 4-nitro-benzyl chlorides (these being chosen to give convenient reaction rates) with catalysis by aluminium chloride in nitrobenzene solvent340. Reactions were complicated by dialkylation which was especially troublesome at low aromatic concentrations, but it proved possible to obtain approximately third-order kinetics, the process being first-order in halide and catalyst and roughly first-order in aromatic this is shown by the data relating to alkylation of benzene given in Table 77, where the first-order rate coefficients k1 are calculated with respect to the concentration of alkyl chloride and the second-order coefficients k2 are calculated with respect to the products of the... 

The detail of the structure of the polymerisation centre present in suppported Ziegler-Natta catalysts for a-olefin polymerisation has been the subject of much research effort (e.g./-/2) The catalyst consists of a solid catalyst MgC /TiC /electron donor and a co-catalyst, an aluminium alkyl complexed with an electron donor. Proposed mechanisms for the polymerisation involve a titanium species attached to magnesium chloride with the olefin coordinated to titanium. The detail of the site at which the titanium species is attached is an important area of study in understanding the mechanism of catalysis and several recent papers 10-12) have investigated the surface structure of magnesium chloride and the attachment of TiCl4, in particular the interaction of titanium species with the 100 and 110 planes of a and (3- magnesium chloride. 

Carboxylic acid anhydrides or halides normally require the presence of a Lewis acid (often boron trifluoride) for Friedel-Crafts acylation of furans, though trifluoroacetic anhydride will react alone. Aluminium-chloride-catalysed acetylation of furan proceeds 7 x lO times faster at the a-position than at the P-position. 3-Alkyl-furans substitute mainly at C-2 2,5-dialkyl-furans can be acylated at a P-position, but generally with more difficulty. 3-Bromofuran is efficiently acetylated at C-2 using aluminium chloride catalysis. ... 

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