Hydrogen abstraction, benzophenone

Hydroxy Benzophenone 4-Hydroxy Benzophenone Hydrogen Abstraction Processes Photocrosslinking ... 

Electron Transfer Processes - A study of the benzophenone/acetonitrile/t-butylamine system has shown that electron transfer occurs from the amine to the excited state benzophenone. Hydrogen abstraction processes within this system ultimately yield the CH2CN radical. When this species is generated in the presence of a diarylethene such as that shown in Scheme 1 then addition affords reasonable yields of the adducts (16). The mode of addition is dictated by the stability of the radical formed on addition to the ethene bond. Addition can also occur to alkenes such as (17) when the adduct (18) is obtained. SET processes also provide a novel synthetic path to 5,6-dihydro-4/f-l,2-oxazines. These reactions involve the DCA-sensitized transformations of the y,5-unsaturated oximes (19). The reactions are carried out in acetonitrile solution with irradiation through Pyrex for no longer than 30 min. This treatment yields the products (20) in reasonable yields. The likely mechanism for the process involves the formation of the intermediate (21) which cyclizes to yield the final products. The reaction is to some extent substituent dependent and when the oxime (19, R = H, R = R = R = Me) is irradiated under the same conditions for 3 h no reaction is... 

Besides other linear polycondensates, poly(ester-imide)s with benzophenone structures were claimed [273] as useful for producing photographic images by exposure through a photographic mask. The varnishes were dried at 80 °C, giving on a copper substrata a 1.2 my layer. Exposure is made with a 1000 W UV lamp. The exposed areas, crosslinked by benzophenone hydrogen abstraction, are insoluble and the unexposed areas of the film are removed with N-methyl-pyrrolidone. 

Instead of using thermal energy to trigger the hydrogen abstraction mechanism, photo-induced reactions can be also be used to successfully crosslink acrylic PSAs [74-76], In this case, photoactive compounds, such as for example those containing benzophenone, anthraquinone or triazine nuclei are compounded with the polymer or copolymerized as one of the monomers. After drying, the adhesive... 

Hydroxy Benzophenone O- CH2CH2OCH2CH2OCH3 Methoxyethoxyethoxy Hydrogen Abstraction Processes Photocrossslinking" ... 

We saw earlier that when benzophenone is photoreduced in the presence of optically active 2-butanol, the alcohol recovered from the reaction loses no optical activity/541 This was presented as evidence that there could be no appreciable reversibility of the initial hydrogen abstraction since this should lead to racemization of the unreacted alcohol. However, if one uses relabeled benzhydrol and examines the initially produced benzpinacol for the presence of the label, one finds that the product pinacol contains no 14C. This would indicate that there must be some type of rapid transfer of the hydrogen radical from the ketyl radical produced upon abstraction from benzhydrol,... 

The decomposition of methanesulphonyl azide in isopropyl alcohol could be effected by selective irradiation of 2-acetonaphthone instead of benzophenone 21>. Since 2-acetonaphthone triplets are incapable of hydrogen abstraction from isopropyl alcohol 22>, initiation must occur via transfer of excitation energy to the azide. A marked difference was observed from benzophenone sensitization in that the reaction was extremely slow, gave a nitrogen yield of only 68%, and produced a yellow solution 21>. 

Several mechanisms have been postulated in order to account for ketone-sensitized photodehydrochlorination. Benzophenone and acetophenone have been suggested to act as singlet sensitizers via a collisional deactivation process (13). An alternative mechanism proposed for benzophenone involves abstraction of a methylene hydrogen from PVC by the triplet ketone (Equation 2), followed by 3 scission of a... 

Moro-Oka et al. (1976) have reported that the oxidation of 9,10-dihydroanthracene by K02 solubilized in DMSO by 18-crown-6 gives mainly the dehydrogenated product, anthracene. Under the same conditions, 1,4-hexadiene is dehydrogenated to benzene. The authors proposed a mechanism in which the superoxide ion acts as a hydrogen-abstracting agent only. The oxidations of anthrone (to anthraquinone), fluorene (to fluorenone), xanthene (to xanthone) and diphenylmethane (to benzophenone) are also initiated by hydrogen abstraction. 

No, because the molecule carries a built in quencher around with it. Each benzophenone triplet formed will be quenched at a rate much faster than hydrogen abstraction from solvent. 

There is still considerable interest in the products of irradiation of hydrogen abstracting ketones for example, Plank96 has reported that benzophenone in ether gives benzophenone pinacol in higher yield when naphthalene is added. It was suggested that the pinacol is formed from some intermediate which is photochemically destroyed in the absence of a quencher. Challand97 has isolated products from addition of ether to acetophenone. 

It has been shown that the benzophenone sensitized decomposition of benzoyl peroxide is due in part to formation of the benzophenone ketyl radical, which induces decomposition.98,99 Hydrocarbon sensitized peroxide decomposition is discussed in Section IV.A.4. The formation of benzonitrile from the benzophenone sensitized irradiation of benzalazine, which was originally attributed to hydrogen abstraction by benzophenone,100 actually results from a photooxidation.101... 

There are many reports in the literature describing photodegradation sensitized by aromatic ketones and quinones. Beachell and Chang (24) showed that triplet excited benzophenone accelerates degradation of polyurethanes by hydrogen abstraction. Harper and McKellar (25) showed the same effect with benzophenone on opolypropylene, and Amin and Scott (26) on polyethylene. Rabek and Ranby (27) have demonstrated that triplet excited quinones enhance... 

The exact values for the rate constants for hydrogen abstraction by triplet benzophenone are not yet entirely certain. Three groups338-338 have reported a value of 108M-1 sec-1 for abstraction from 2-propanol in concentrated 2-propanol, while the combination of the data of three other groups333,338 339 for dilute benzene solutions yields a value of only 105M-1 sec-1. This discrepancy could well reflect a solvent effect such as that found in studies of the reactivity of alkoxy radicals.340 However, the hundredfold difference between the reported rates for attack of triplet benzophenone on toluene338,338 undoubtedly reflects experimental problems, because both values were measured in aromatic solvents. 

A quenching study at one concentration of 2-propanol (2.6Af) in benzene indicates that the rate constant for hydrogen abstraction is about 1 x 106Af 1 sec-1,451 similar to that for benzophenone. A fact long known is that sulphonate substituents in the 2 and 6 positions do not affect quantum yields of photoreduction, whereas in the 1 and 5 positions they cut O from 1.0 down to 0.01-0.05.216... 

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