RICERCA ITALIANA     

Oxidative activation of organic molecules through new catalytic and photocatalytic processes

Università degli Studi di Pavia

Abstract

The project aims to introduce new, more environment compatible, synthetic methods for fine chemicals, based on the mild and selective activation of strong chemical bonds by photochemical reactions or catalysis and photocatalysis with oxides and oxometallates The reactions explored include 1) the activation of the C-H bond in alkanes, both for the selective oxidation with molecular oxygen and for alkylation reactions; 2) the activation of aryl C-X bonds for arylation reactions; 3) the mild oxidation at allylic or alpha-carboxy position and 4) new epoxidation and sulfoxidation methods. New materials with catalytic and/or photocatalytic activity will be prepared by heterogeneization of titanium dioxide, of other oxides and of polyoxometallates on mesoporous materials, which are characterized by greater chemoselectivity and higher turn over number, avoiding leaching of metal ions and inactivation.

Principal Investigator

Angelo ALBINI Università degli Studi di PAVIA

Research Objectives

A major challenge to contemporary chemistry is developing new synthetic paths that are more environment friendly. ‘Green’ or sustainable chemistry has emerged as a discipline on its own, explicitly devoted to developing an environmental-conscious chemistry and over the past decade it has indeed demonstrated that new methodologies can be developed that protect human health and the environment. The most innovative aspect is devising new synthetic methods that start from non activated, easily available starting materials and lead through a short reactions sequence to functionalized derivatives under mild conditions, with high selectivity and minimal waste. Significant progress is being made towards this aim through the use of new catalysts. These are transition metal complexes and, while operating with high selectivity and efficiency, are often labile, expensive and toxic. The present collaborative project follows a different path, involving photoinduced reactions and some particular catalytic reactions, based on (mesoporous) oxides, which are stable materials and are active either as catalysts or as photocatalysts (or both). Light is certainly a ‘green’ reagent and there is an extensive literature on photochemistry, but the application of photochemical reactions in a ‘green chemistry’ context certainly deserves a more extended exploration. An emerging topic within photoinduced syntheses involve photocatalytic processes. In this case, a >>>

First Results

It is expected that in the first phase of the project the following targets will bereached. The preparation and characterization of new photocatalysts where (doped) titanium dioxide or a polyoxotungstate are immobilized on a solid support. The development of photocatatyzed functionalization reactions of alkanes, such as controlled oxygenation and alkylation reactions. The preparation of new catalysts on mesoporous silica of on zeolites that are active in thermal allylic and benzylic oxidation reactions. The development of arylation reactions via phenyl cation photochemically generated from electron-donating substituted aryl halides.In the second phase photocatalytic methods will be extended by using the heterogeneous materials prepared in the first phase and by exploiting the chemistry of the first formed hydroperoxides as well as by exploring the oxidative bromination of alkenes and the (stereo)selective oxidation of sulfides. Methods will be developed that apply heterogeneous catalysis to the thermal alpha-hydroxylation of carboxylic acids and the epoxidation of alkenes with molecular oxygen. Photoinduced ionic arylation reaction will be developed starting from precursors different from aryl halides as well as for intramolecular applications. The results obtained will be presented in manuscripts, at least in part in collaboration between the Units, which will be submitted for publication.

Timescale

24 months

National and international background

A sustainable development requires that new materials are produced that are not harmful to the environment and that are produced by methods that are environment-friendly, in that they minimize the use of available feedstock and of energy and reduce the simultaneous production of waste. Indeed the steadily growing demand for new man-made materials for new applications contrasts with the growing awareness that the limited resources available must be used in the best way and the production of waste must be minimized. A resource-saving production is thus especially important for a sustainable development (1). This is an all important challenge for contemporary chemistry. In the last decades, an extensive effort has been done by chemical companies in order to ameliorate the compatibility with the environment of the synthetic processes they are using. Clearly, much can – and must – be done by ameliorating existing technologies, but at the same time new perspectives must be opened by the exploration of new technologies. These must operate , as stated by a IUPAC Party on Synthetic Pathways and Processes in ‘Greeen’ Chemistry (2, 3), under conditions that allow to increase selectivity an minimize co-produced waste, both when actually carrying out the reaction and when separating the desired product (2, 4). On the other hand, a specific discipline, ‘green’ or sustainable chemistry has emerged and has acquired an independent status. During the past >>>