Aromatic heterocyclic compounds, solid-phase

The interstellar dust was shown to contain quinone derivatives as well as oxygen-rich condensed aromatic compounds the quinones were present in both hydrated and carboxylated form. Very little nitrogen was present in the compounds detected. The cometary material, however, contained condensed nitrogen heterocycles. Hardly any oxygen was detected in the solid phase of the cometary dust it possibly evaporates from the tail of the comet in the form of water or oxidized carbon compounds. The authors assume that these analytical results could lead to a reconsideration of the current biogenesis models (Kissel et al 2004 Brownlee, 2004). 

While UOi+ forms a very large number of complexes with oxygen-donor ligands of all types, particular effort has been devoted to carboxylic acids, from the simplest (formic, acetic, oxalic acids) to polyfunctional, aromatic and heterocyclic acids. One motive for investigating these compounds is the possible role of simple carboxylic acids as reductants [3, 5] of excited UVI, generating U,v which can then reduce Puiv to PuIn which is more readily separable than Pulv from UVI in the treatment of nuclear waste. Another significant role has been proposed for carboxyl-functionalized polymers which show potential in the solid-phase extraction of UV1 from dilute solution [13]. 

More and more, solid catalysts like zeolites, clays or resins are used instead of traditional catalysts. Thus, zeolites are good catalysts for the acylation of non-heterocyclic aromatic compounds, both in the gas phase [2] and in the liquid phase [3]. The acylation of thiophene and of furan can also be carried out in the gas phase with M-5 catalysts [4]. Lasdo and co-woikers have shown that modified clays like montmorillonite doped with ZnCl2 can catalyse the reactioi of arenes with substituted benzoyle chlorides in good yields [5] (70 to 100%). Delmas and co-workers have reported the acylation of furan by carboxylic acids with nafion-H [6] (sulfonic resin) and duolite [7] (ion exchanged phosphonic resin). One of the advantages of these catalysts is the safety of environment. Actually, the use of homogeneous catalysts causes problems of corrosion, waste and troublesome workups [8,9]. 

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