Benzophenones irradiation

The dimerization of ketones to 1,2-diols can also be accomplished photochemi-cally indeed, this is one of the most common photochemical reactions. The substrate, which is usually a diaryl or aryl alkyl ketone (though a few aromatic aldehydes and dialkyl ketones have been dimerized), is irradiated with UV light in the presence of a hydrogen donor such as isopropyl alcohol, toluene, or an amine. In the case of benzophenone, irradiated in the presence of 2-propanol, the ketone molecule initially undergoes n — k excitation, and the singlet species thus formed crosses to the T, state with a very high efficiency. 

In the case of benzophenone, irradiated in the presence of 2-propanol, the ketone molecule initially undergoes n n excitation, and the singlet species thus formed crosses to the Ti state with a very high efficiency. 

Direct (457.9 nm) or photosensitized (by benzophenone) irradiation of (216) gives rise to the exclusive formation of (217). In contrast to this, irradiation of the isomer of (216) in which the epoxide oxygen iss> to the benzene ring yields a mixture of products, of which the major constituent is (218) ca 25%). The difference in reactivities of these isomers was explained in terms of the stereoelectronic effect of the epoxide ring. 

Benzophenone irradiation Ketones from cyclic sulfoxides... 

A soln. of cis- or trfln5-l,3-dihydro-l,3-diphenyl-2-thiaphenalene 2-oxide in benzene containing benzophenone irradiated with 366 m/ light -> l-benzoyl-8-benzyl-naphthalene. Y 80%. A. G. Schultz, C. D. DeBoer, and R. H. Sdilessinger, Am. Soc. 90, 5314 (1968). 

Benzophenone/irradiation Azomethines from sec. amines and from 2 prim, amine molecules... 

Benzophenone/irradiation Photochemical 1,4-addition Carbohydrate derivs. 

Benzophenone irradiation Carboxylic acid amides from nitriles... 

Benzophenone/irradiation Cyclobutane ring by photochemical cycloaddition... 

When buta-1,3-diene 3 is irradiated in the presence of a photosensitizer (e.g. benzophenone), the isomeric divinylcyclobutanes 6 and 7 are formed via the intermediate diradical species 4 and 5 respectively in addition the [4 + 2] cycloaddition product 4-vinylcyclohexene (see Diels-Alder reaction) is obtained as a side product ... 

Photo-induced grafting onto wood cellulose with several vinyl monomers using phenyl acetophenone and benzophenone derivatives as photosensitizers has been reported [72]. A fast increase in grafting was observed for short irradiation times, whereas longer ones resulted in a decreased percent grafting. 

The parent system oxonin (1) is generated by benzophenone sensitized irradiation with a Hanovia light source3 5 or direct irradiation6 of the monoepoxide of cyclooctatetraene (9-oxabicyclo[6.1.0]nona-2,4,6-triene, 6). 

Intramolecular arylations can also be carried out photochemically. Huisgen and Zahler (1963 a) prepared fluoren-9-one by irradiation of benzophenone-diazonium salts in dilute sulfuric acid. The classical Pschorr synthesis of phenanthrene-9-carb-... 

Thus irradiation of benzophenone in toluene gives the photoreduction product 19, benzpinacol, and bibenzyl [equation (59)] of which only 19... 

In weaker acid systems, other reactions involving the triplet state supervene to the exclusion of dimerization. Photolysis of 85 in 3-3% sulfuric acid, 96-5% acetic acid, and 0-2% water gave as products tri-phenylmethane (93), 9-phenylfluorene (94), 6is-9-phenylfluorenyl peroxide (95) and benzophenone (96). When benzene was present, tetra-phenylmethane (97) was also formed in addition to the other products. When the triphenylmethyl cation is irradiated in 3-3% H2SO4, 80 1% HOAc, 16-4% toluene, and 0-2% H2O, the products observed were... 

Category 5. Hydrogen Atom Abstraction. When benzophenone is irradiated in isopropyl alcohol, the initially formed Si state crosses to the Ti state, which abstracts hydrogen from the solvent to give the radical 7. Radical 7 then abstracts another hydrogen to give benzhydrol (8) or dimerizes to benzpinacol (9) ... 

Intermolecular photocycloadditions of alkenes can be carried out by photosensitization with mercury or directly with short-wavelength light.179 Relatively little preparative use has been made of this reaction for simple alkenes. Dienes can be photosensitized using benzophenone, butane-2,3-dione, and acetophenone.180 The photodimerization of derivatives of cinnamic acid was among the earliest photochemical reactions to be studied.181 Good yields of dimers are obtained when irradiation is carried out in the crystalline state. In solution, cis-trans isomerization is the dominant reaction. 

Figure 16. Surface grafting of polypropylene film strips after 10 sec. irradiation measured as light absorption after dipping in aqueous crystal violet solution. The presoaking solutions contain 0.2 M benzophenone (all) and 1.3 M acrylamide (1), 0.8 M (2),...

Acylimidazoles in the presence of benzophenone lead to oxetanes on irradiation with a medium-pressure mercury lamp [8]... 

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