Photocatalytic synthesis

Rao, K.V.S., Srinivas, B., Subrahmanyam, M., and Prasad, A.R. (2000) A novel one step photocatalytic synthesis of dihydropyrazine from ethylenediamine and propylene glycol. Chemical Communications (16), 1533-1534. 

Fig. 11.3 Reaction mechanism of photocatalytic synthesis of pipecolinic acid (PCA) from L-lysine.

In the field of thiochemistry, the photocatalytic synthesis of mercaptans represents an interesting chemical route. Schoumacker et al. [60] performed the synthesis of propan-1-thiol by addition of H2S on propene in contact with illuminated Ti02 or CdS catalysts, according to a reaction mechanism implying photogenerated SH radicals. 

Scheme 55 Photocatalytic synthesis of L-pipecolinic acid 190 and D-pipecolinic acid 192.

Several other photocatalytic environmentally friendly processes may also be considered. Photocatalytic synthesis of chemicals may serve as a clean alternative route to traditional synthetic methods (see section 6.5). Palmisano et al. reviewed various types of organic reactions that could be achieved by heterogeneous photocatalysis... 

Cozzoli, P.D., R. Comparelli, E. Fanizza, M.L. Curri, A. Agostiano and D. Laub (2004a). Photocatalytic synthesis of silver nanoparticles stabilized by Ti02 nanorods A semiconductor/metal nanocomposite in homogeneous nonpolar solution. Journal of the American Chemical Society, 126(12), 3868-3879. 

Scheme 6.42 Schematic illustrating the photocatalytic synthesis of l- and D-pipecolinic acid (160 and 162, respectively).

Nasution, H. W. Pumama, E. Riyani, K. Gunlazuardi, J. Effect of copper species in a photocatalytic synthesis of methanol from carbon dioxide over copper-doped titania catalysts. World. Appl. Sci. J., 2009, 6,112-122. 

In 1977 Schrauzer and Guth published a seminal communication [1] in which the photocatalytic synthesis of ammonia from nitrogen and water was described. The process involved irradiation with UV-visible light in the presence of a titanium dioxide-based photocatalyst (Section II.A) and was described as the basis for a prototype solar cell for photochemical ammonia synthesis [2]. The photocatalytic process is represented by reaction 1. 

Despite many studies there is available, at this time, no unequivocal report of artificial photocatalytic synthesis of ammonia from nitrogen and water on heterogeneous catalysts. The chemical reaction 1, shown at the beginning of this chapter, remains speculative 17 years after it was initially reported. No rational start has yet been made on determining a mechanism for the reported nitrogen fixation process, despite the fact that a clear demonstration and understanding of any such process would be of great importance. Despite 17 years of research, the reported yields of ammonia from artificial photosynthesis remain at or near the limits of detection by routine analytical methods. As we stated earlier in this chapter, the concept of a major discovery that remains forever on the borderline of detectability is internally contradictory. The current state of the field is one where serious scientific skepticism is appropriate. 

Photolysis of solutions of C6o(OH)ig at low solute concentration leads to [C6o(OH)i8] by electron transfer from Me2C(OH) radicals or from hydrated electrons, and this has enabled the reduction potential of the C6o(OH)ig/ [C6o(OH)ig] couple to be estimated. The kinetics of the photoreduction of hexanal using RhCl(PMe3)2CO as catalyst have been measured and the feasibility of a photocatalytic synthesis of hexanol from pentane, CO, and H2 in the presence of rhodium complexes has been demonstrated. Irradiation of a chiral bimolecular crystal of acridine and R-(-)- or S-(+)-2-phenylpropionic acid induces photodecarboxylation followed by stereoselective condensation to give a mixture of three optically active products, and the 3-0-S-methyl dithiocarbo-nate derivatives of oleanolic and ursolic methyl esters have been used as models for the photodeoxygenation of alcohols. ... 

Photocatalytic Synthesis Group, IMPACT Institute, University of Twente, P.O.Box 217, 7500AE Enschede, The Netherlands... 

The first study of a PVPR was carried out a few years ago by Camera-Roda and Santarelli (2007), and, recently studies have gone on to investigate the possible application of PVPR in the field of photocatalytic synthesis of fine chemicals, lill now, studies of PVPR have not been numerous nonetheless, the potential applications appear to be of real interest and this area of research is expected to grow rapidly. 

In conclusion a PVPR apphed to the photocatalytic synthesis of organic compounds displays the following interesting features ... 

Abstract The configurations and performance of photocatalytic membrane reactors (PMRs) assembled with membranes (also photocatalytic type) and/or suspended photocatalyst are described. Examples of the application of PMRs in water/wastewater treatment as well as in photocatalytic synthesis are shown. An outUne of the modeling of PMRs is presented with a brief economic analysis future trends in PMRs are also discussed. 

Key words photocatalytic membrane reactors, photocatolytic membrane reactor performance, water/wastewater treatment, photocatalytic synthesis. 

Research in the field of photocatalytic synthesis in a PMR is still at a preUm-inary stage, despite the great potentiality of photocatalytic processes, especially when they are coupled with a membrane separation system. 

Photocatalytic synthesis of quinaldines from nitrobenzenes (13) and ethanol with Au loaded Ti02 nanoparticles has been reported by Swaminathan et al. Initially, nitrobenzenes were reduced to anilines and ethanol was oxidized to acetoaldehyde in the photoinduced Ti02 redox reactions. They were dehydrocondensed and intermolecularly cyclyzed to give quinolines (14) and quinaldines (15). 

Li H, Zhang Y, Chang G, Liu S, Tian J, Luo Y, Asiri AM, Al-Youbi AO, Sun X. Environmentally friendly photocatalytic synthesis of potphyrin/Ag nanoparticles/reduced graphene oxide ternary nanohybrids having superior catalytic activity. ChemPlusChem 2012 77 545-50. 

In the context of this chapter, however, it is rather surprising that photocatalysis has found only little industrial application so far. Beside the attempts which have been made to apply photocatalysis in information recording, solar energy conversion, or environmental protection the photocatalytic synthesis of high-price organic compounds is of interest. 

Scheme 7.39 Visible-light photocatalytic synthesis of a trans-substituted cyclohexene.

The photochemical generation of quinolines and benzimidazoles from anilines (a reaction known since more than 100 years, compare Section 6.1.1.1) has been further extended to the use of mesoporous, iV-doped Ti02 under both UV and visible light. " An arenesulfonic acid functionalized mesoporous silica decorated with titania has been claimed for the one-pot photocatalytic synthesis of quinolines. ... 

Mesoporous titania films were successfiJly employed as a support for noble metal nanopartides as well as directly as photocatalysts [77-79]. A titaniaacid from L-lysine [79]. The reaction rate in the microreactor was 70 times larger than that in a batch reactor with titania nanopartides with almost the same selectivity and enantiomeric excess. 

K.V.S. Rao, M. Subrahmanyam, A novel one step photocatalytic synthesis of 2-methyl quinoxaHne from o-phenylenediamine and propylene-glycol over Ti02/zeoHte mediated system, Chem. Lett. (2002) 234-235. 

Scheme 40 Photocatalytic synthesis of piperonal from piperonyl alcohol. ...

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