Photoinduced reactivity of titanium dioxide

Photocatalysis (by semiconductors, molecules and ions) is used in such diverse applications as water hydrolysis for producing hydrogen as fuel, organic synthesis and the recovery of polluted effluents. This tutorial review discusses the common principles of such applications and their role in green chemistry.

Photocatalysis. A multi-faceted concept for green chemistry

Chemistry of Acyl Radicals

Sulfur compounds represent one of the most common impurities present in the crude oil. Sulfur in liquid fuel oil leads directly to the emission of SO2 and sulfate particulate matter (SPM) that endangers public health and community property; and reduces the life of the engine due to corrosion. Furthermore, the sulfur compounds in the exhaust gases of diesel engines can significantly impair the emission control technology designed to meet NOx and SPM emission standards. The research efforts for developing conventional hydrodesulfurization and alternative desulfurization methods such as selective adsorption, biodesulfurization, oxidation/extraction (oxidative desulfurization), etc. for removing these refractory sulfur compounds from petroleum products are on the rise. Research laboratories and refineries are spending huge amounts of money in finding a viable and feasible solution to reduce sulfur to a concentration of less than 10 mg l−1. This paper reviews the current status in detail of various desulphurization techniques being studied worldwide. It presents an overview of novel emerging technologies for ultra-deep desulfurization so as to produce ultra-low-sulfur fuels.

An evaluation of desulfurization technologies for sulfur removal from liquid fuels

Photocatalysis: a promising route for 21st century organic chemistry

Photocatalytic oxidation of selected aryl alcohols ( 1 – 7 ) has been carried out by using anatase titanium dioxide catalyst. The main oxidation products were the corresponding aldehydes or ketones and acids, in addition to unidentified minor compounds. Kinetic studies revealed a second-order reaction rate for benzyl alcohol, as a model alcohol, photocatalytic oxidation. The suggested mechanism envisages electron–hole pair formation on the catalyst surface followed by oxidation–reduction reactions.

Photocatalytic oxidation of selected aryl alcohols in acetonitrile

Several sulfonamides containing pyrroles ( 2a – c , 6a – d , 8a – d) , pyrrolo[2,3-d] pyrimidines ( 3a – c ), acetanilides ( 11a – c ) and tetrahydrobenzothiophenes ( 13a – c ) were synthesized starting from N 4 -chloroacetylsulfanilamides ( 1a – d ). The structures of synthesized compounds were elucidated by elemental analyses and spectral data. Compounds 2b , 3b , 6b , 8b and 8d exhibited a remarkable antifungal activity compared with the standard fungicide mycostatine.

Novel synthesis and antifungal activity of pyrrole and pyrrolo[2,3-d]pyrimidine derivatives containing sulfonamido moieties.

Synthetic Applications of the Pyrolysis of Meldrum’s Acid Derivatives

Hydrazones 2a-d were prepared from diazotiazation of sulfanilamide or its derivatives followed by coupling with ethyl cyanoacetate. 3-Aminopyrazoles 3a-d were obtained by refluxing of 2a-d with hydrazine hydrate in ethanol. [Bis(-methylthio)methylene]malononitrile (4) was reacted with aminopyrazoles 3a-d in refluxing DMF containing triethylamine to yield the novel pyrazolo[1,5-a]pyrimidines 6a-d. The anilino derivatives 8a-h were obtained by fusion of compounds 6a-d with aromatic amines. When compounds 6a,c,d were subjected to the reaction with hydrazine hydrate, the hydrazino derivatives 9a-c were isolated. Also, the aminopyrazoles 3 were reacted with some electrophiles such as arylidenemalononitriles, ethoxymethylene malononitrile and ethyl ethoxymethylene cyanoacetate to yield the novel substituted pyrazolo[1,5-a]pyrimidines 13, 17 and 19, respectively. Structures of the new compounds were established by their elemental analyses and spectral data. Most of these compounds were also tested in vitro for their antibacterial activity against some gram positive and gram negative bacteria.

Studies on aminopyrazoles: antibacterial activity of some novel pyrazolo[1,5-a]pyrimidines containing sulfonamido moieties

Polynuclear-heterocyclic sulfides (I–IV) were oxidized dominantly to the corresponding sulfoxides and sulfones via TiO2-mediated photocatalytic oxidation in aerated acetonitrile. Also, methylene group in IV and V and active methene groups in VI have been readily oxidized to carbonyl one in a high yield under the same prevailing conditions. A plausible electron transfer mechanism, in which an electronhole pair is generated on the surface of TiO2 by illumination, is suggested for the semiconductor-mediated photocatalysis.

Abd El-Aal M. Gaber

Papers

Photocatalytic oxidation of selected aryl alcohols in acetonitrile

Novel synthesis and antifungal activity of pyrrole and pyrrolo[2,3-d]pyrimidine derivatives containing sulfonamido moieties.

Synthetic Applications of the Pyrolysis of Meldrum’s Acid Derivatives

Studies on aminopyrazoles: antibacterial activity of some novel pyrazolo[1,5-a]pyrimidines containing sulfonamido moieties

TiO2-photocatalytic oxidation of selected heterocyclic sulfur compounds