Aromatic carboxylic acids are obtained in good to excellent yield essentially free of diaryl ketones by carboxylation of aromatics with a carbon dioxide-Al(2)Cl(6)/Al system at moderate temperatures (20-80 degrees C). To optimize reaction conditions and study the reaction mechanism, experimental variables including temperature, amount of Al(2)Cl(6)/Al, various Lewis acids, role of metal additive, carbon dioxide pressure, etc. were studied. The carboxylation reaction was found to be stoichiometric rather than catalytic, with aluminum chloride forming a dichloroaluminate of carboxylic acids. Although the carboxylation takes place using AlCl(3) itself, the presence of metal additives, especially Al, increased the yield and selectivity of carboxylic acids. Because it was not possible to distinguish between two possible mechanistic pathways of the reaction on the basis of the experimental results, theoretical calculations using density functional theory (DFT) were also carried out. One possible pathway involves an initial complex between benzene and Al(2)Cl(6), with subsequent formation of organoaluminum intermediates (PhAlCl(2) and PhAl(2)Cl(5)). The other proceeds through the formation of various complexes of CO(2) with aluminum chloride (AlCl(3))(n), n = 1-4. The calculations have shown that the organometallic pathway, leading eventually through the formation of phenylaluminum dichloride, is endothermic by 33 kcal/mol. In contrast, the preferred CO(2)-AlCl(3) complex forms in an exothermic reaction (-6.0 kcal/mol) as does CO(2)AlCl(2)(+). On the basis of both experimental and calculational findings, the most feasible reaction mechanism proposed involves superelectrophilic aluminum chloride activated carbon dioxide reacting with the aromatics in a typical electrophilic substitution.

Recent advances in the application of heterogeneous catalysis combined with microwave irradiation in the synthesis of heterocyclic compounds are reviewed. While a detailed summary of the different catalysts applied in the synthesis of heterocycles is provided, the work mainly focuses on the heterocyclic compounds and their synthesis and not the preparation or characterization of the catalyst. Due to the large number of N-containing heterocycles, the synthesis of these compounds dominates this account, however, the preparation of other heteroatom containing compounds is also covered in detail. The literature data are summarized based on the size of cycles and the number of heteroatoms in the compounds. Since the major goal of the work is to highlight the environmentally benign and sustainable nature of the combined microwave-assisted heterogeneous catalytic methods, the green aspects of the individual synthetic approaches will be emphasized.

Isoparaffin-olefin alkylation was investigated using liquid as well as solid onium poly(hydrogen fluoride) catalysts. These new immobilized anhydrous HF catalysts contain varied amines and nitrogen-containing polymers as complexing agents. The liquid poly(hydrogen fluoride) complexes of amines are typical ionic liquids, which are convenient media and serve as HF equivalent catalysts with decreased volatility for isoparaffin-olefin alkylation. Polymeric solid amine:poly(hydrogen fluoride) complexes are excellent solid HF equivalents for similar alkylation acid catalysis. Isobutane-isobutylene or 2-butene alkylation gave excellent yields of high octane alkylates (up to RON = 94). Apart from their excellent catalytic performance, the new catalyst systems significantly reduce environmental hazards due to the low volatility of complexed HF. They represent a new, "green" class of catalyst systems for alkylation reactions, maintaining activity of HF while minimizing its environmental hazards.

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Recent advances in the application of microwave-assisted heterogeneous catalytic synthesis approaches are reviewed with additional inputs on the energy efficiency and scale-up of microwave-assisted synthesis.

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