Dibenzyl ketone, photochemistry

The results reported here and in earlier publications in this series suggest that cavity size and limitations to molecular motion play a dominant role in the photochemistry and photophysics of alkyl aryl ketones included in zeolites. In the case of Silicalite the size and polarity of various substituted 8-phenylpropiophenones seem to determine the efficiency of inclusion and ultimately of luminescence. The same factors, relating to size and mobility can be expected to play an important role in the use of zeolites as catalysts for other reactions, whether these are photochemical or thermal processes. In this sense studies with 8-phenylpropiophenones may lead to considerable information on adsorption sites and on the freedom (or lack of it) of molecular motion as well as on the accessibility of these sites to other reactants. Recent work from Turro s laboratory has shown that pyrene aldehyde can be used to probe the nature of inclusion sites in various zeolites (27) dibenzyl-ketones were also used as probes on porous silica (28). 

In homogeneous solutions, the photochemistry of dibenzyl ketone (DBK, 7) and substituted DBK s proceeds through the mechanism illustrated in Scheme III10). The quantum yield for the formation of diphenyl ethylene (DPE, 2) is quite high... 

High intensity irradiation of dibenzyl ketone in hexane/isopropanol mixtures yields 1,2-diphenyl ethane and toluene as the sole products. A study of the photochemical behaviour of dibenzyl ketone adsorbed on zeolites has been carried out and the results found to be dependent upon the Sl/Al composition of the zeolite. A laser flash examination of the behaviour of dibenzyl ketone in Nafion membranes has demonstrated that a modest yield of benzyl cations is formed. A study of the physical photochemistry of the ketone (1) has shown that the excited state is a carbonyl localized singlet state. This ultimately decays to afford a naphthalene localized triplet state. Norrish Type I cleavage does occur from the singlet state to afford products derived from the radicals (2) and (3). The authors report also that the 1-naphthyl methyl radical is formed from the triplet state. A study of the modification of the photochemical behaviour of the a-alkyldibenzyl ketones (4) by complexation in... 

Systems in which carbon-carbon bond cleavage in an aryl substituent leads to products In which the cleaved substituent Is bonded to the arene ring include the alkylated dibenzyl ketones (234). 51 Ramamurthy has compared the photochemistry of these compounds when Irradiated In solution with that obtained when they are irradiated in the presence of 9-cyclodextrin. In the absence of... 

Photodecarbonylation of p-tolyl benzyl ketone Photolysis of dibenzyl ketones with CuClj scavenger Photochemistry of benzyl sulfones... 

Remarkable effects of nuclear spin on the photochemistry of dibenzyl ketone and its derivatives (see Special Topic 6.11) have been reported and substantial isotopic enrichment of 13C in specific products has been achieved under favourable conditions.434 The influence of magnetic fields and of microscopic reactors (micelles, zeolites, etc.) on these reactions was investigated in detail.435... 

PHOTOCHEMISTRY OF DIBENZYL KETONE ADSORBED ON SIZE/SHAPE SELECTIVE FAUJASITE ZEOLITES. STERIC EFFECTS ON PRODUCT DISTRIBUTIONS... 

Photochemistry of Dibenzyl Ketone Adsorbed on Size/Shape Selective Faujasite Zeolites Steric Effects on Product Distributions (N. J. Turro and Z. Zhang)... 

The photochemistry of dibenzyl sulfoxide 10 was briefly reported in the mid 1960s [21,22]. It was said to decompose mainly to benzyl mercaptan (isolated as the disulfide 17) and benzaidehyde 16. Though no mechanism was suggested at the time, it is now clear that these products arise from a standard a-cleavage mechanism, followed by secondary photolysis of the sulfenic ester 13. The careful reader will note that the yield of bibenzyl (19) is very low in comparison to photolysis of dibenzyl ketone. Sulfinyl radicals rarely lose SO, though some net extrusions are discussed later. 

Gibb CLD, Sundaresan AK, Ramamurthy V, Gibb BC. Templation of the excited-state chemistry of a-(n-Alkyl) dibenzyl ketones How guest packing within a nanoscale supramolecular capsule influences photochemistry. J Am Chem Soc 2008 130 4069-80. 

Photochemistry of dibenzyl ketones has been examined in a number of organized media. Photolysis of 3-(4-methylphenyl)-l-phenylacetone (MeDBK) results in a 1 2 1 mixture of three products shown in Scheme 31. Photolysis of the same molecule solubilized in a micelle (hexadecyltrimethylammonium chloride) gives a single product (AB). This remarkable change in product distribution is due to the cage effect brought forth by the micellar structure. The change in product distribution occurs at or above the critical micelle concentration. 

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