Benzophenone ketyl radical

Rapid purification Check for peroxides (see Chapter 1 and Chapter 2 for test under ethers). Pre-dry with CaCl2 or better over Na wire. Then reflux the pre-dried solvent over Na (1 % w/v) and benzophenone (0.2% w/v) under an inert atmosphere until the blue colour of the benzophenone ketyl radical anion persists. Distil, and store over 4A molecular sieves in the dark. 

If the primary chemical process is still abstraction of a hydrogen atom to produce the benzophenone ketyl radical, one would expect to observe some mixed pinacol product arising from coupling of the benzophenone ketyl and acetone ketyl radicals,... 

As seen earlier in this section, the energy released upon formation of the benzophenone ketyl radical is about 104 kcal/mole. This value is almost identical to that released upon formation of f-butyl alcohol from the f-butoxy radical,... 

The ESR detection of benzophenone-ketyl radical coupled with the formation of pinacols as byproducts (in Scheme 9) provides the basis for an electron-transfer mechanism between carbonyl acceptors and various Grignard reagents48 (equation 23). 

Fig. 11 Transient spectra obtained upon the application of a 200-fs laser pulse to a solution of [Ph2C(0H)C02, MV2+] charge-transfer salt showing the simultaneous formation of benzophenone ketyl radical (dashed line) and the reduced methyl viologen (dotted line). The inset is the authentic spectrum of ketyl radical. Reproduced with permission from Ref. 92a.

Tetrahydrofuran was distilled under nitrogen from sodium/benzophenone ketyl radical immediately prior to use. 

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... 

Photoreduction was quenched by high concentrations of biacetyl, slightly retarded by iodonaphthalene, but not affected by azulene or anthracene.113 These observations led to the unsatisfying conclusion that reduction proceeded via a triplet state which could be only selectively quenched. However, later work114 using flash photolysis showed that the benzophenone ketyl radical was generated upon irradiation of solutions of benzophenone and acridine, and that its predominant mode of disappearance was by reaction with... 

In a study of the quenching of benzophenone photoreduction with biacetyl, it was observed that the biacetyl was consumed.116 This phenomenon also is readily explained by chemical quenching, transfer of a hydrogen atom from the benzophenone ketyl radical to biacetyl to form the biacetyl ketyl radical and ultimately the pinacol derived from biacetyl. 

Luminescence is seldom observed from free radicals and radical ions because of the low energy of the lowest excited states of open-shell species, the benzophenone ketyl radical being however a noteworthy exception. There are few reports of actual photochemical reactions of free radicals, but the situation is different with biradicals such as carbenes. These have two unpaired electrons and can exist in singlet or triplet states and they take part in addition and insertion reactions (Figure 4.90). 

The benzophenone ketyl radical reacts rapidly with 02 yielding 02 [reaction (74)]. 

Side-chain aromatic radicals of the type Ph—CR—OH cannot be produced efficiently by reaction of OH with the alcohol because OH tends to add to the aromatic ring more efficiently. They are, therefore, produced by addition of an electron to the carbonyl compound. The pRwalues for the acetophenone and benzophenone ketyl radicals are 9-5 and they are affected by substituents on the aromatic ring as well as by those directly at the radical site. ... 

Hammond, Wamser, Chang, and Baylor [54] studied the photochemistry of the BP/MK pair formally using flash photolysis techniques and showed that electron transfer occurs via triplet exciplexes that can be formed by excitation of either partner, though under normal circumstances MK absorbs the vast majority of the light. Benzophenone ketyl radical was observed as a transient, and a second species present was identified as either the cation radical of MK or its corresponding deprotonated radical. The coupling product of the latter two radicals (16) was observed as a product of steady-state irradiation, and it was formed with a quantum... 

Miyagawa et al. added diethyl aniline (DEA) to the cyclohexane (CHX) solution of benzophenone and measured its CBDEP spectra. They found that the spectra changed dramatically as shown in fig. 5-6 [16]. The whole spectra observed in CXH showed strong emissive patters as shown in fig. 5-7. The spectra are composed of the two signals due to the benzophenone ketyl radical (central part of (a) and (b)) and the neutral radical of DEA. The latter radical has a structure of hydrogen abstracted at the methylene group. 

UV irradiation of poly(4-vinylbenzophenone) [poly(VBP)] in benzene solution, and in the presence of isopropanol as hydrogen donor, gives rise to a more complex picture [12,13]. Indeed, intra- and inter-molecular coupling reactions by the side-chain benzophenone ketyl radicals (K ) markedly change the macro-molecular morphology with the occurrence of cyclic and network structures as well as chain scission processes (Scheme 5). 

This would not mean that free radicals are actual intermediates, but only that the alkyl assumes a significant amount of radical character in the transition state. The stability of the radical type transition state may be increased by pairing between benzophenone ketyl radical and the alkyl radical [46],... 

Irradiation of a system consisting of 2-methyl-1,4-dihydroxynaphthalene and benzophenone leads to formation of benzophenone ketyl radical and 2-methyl-naphthosemiquinone, and 1 a,7a-dihydro-1 a-methyl-1,1 -diphenyl-1 H-cyclopropa-[b]naphthalene-2,7-dione derivatives (4) in the presence of Mg(C104)2 give indenonaphthoquinones (5) (Scheme 1), by photoinduced intramolecular electron transfer in almost quantitative yield. In agreement with Rehm-Weller predictions, the rate constants for electron transfer between the triplet states of various substituted naphthoquinones and N,N-dimethylaniline (DMA) in acetonitrile solution were found to be diffusion controlled. " Using this information, it has been shown that the efficiencies of formation of naphthalene " and DMA are unity. 

Also, there is a misconception concerning solvents distilled from sodium/ benzophenone. For example, tetrahydrofuran (THF) is distilled from sodium/ benzophenone. Prior to obtaining dry THF, the solvent in the distillation pot is a characteristic blue or sometimes purple in color because of the thus afforded benzophenone ketyl radical. It has been assumed by many that the blue color is indicative of water free THF. In fact, this may not be the case. Malhnkrodt-Baker conducted a study that showed that the blue color was an indication of the absence... 

In order to know the net quantum yield for the benzophenone disappearance, 4i(-BP), by hydrogen abstraction in poly(vinyl alcohol), the change in UV spectra of benzophenone at 256 nm in the poly(vinyl alcohol) film was followed during continuous Irradiation of 365 nm UV light. The (-BP) given in Table III is very small for T < T, suggesting the predominant occurrence of backward reaction (k , ) of benzophenone ketyl radical in the... 

Radicals and radical ions provide fruitful subjects of research. Room temperature fluorescence from the arylmethyl radicals Ph3C, Ph2CH- and PhCH2 and theoretical studies of rotational barriers in the benzyl cation, radical and anion as well as the singlet and triplet states of diphenylcarbene are typical examples of such contemporary studies. A very detailed paper considers the problems of the state assignment and reactivity of excited states of p-substituted benzyl radicals.Ketyl radicals containing the enthrone moiety and the 4-(methyl sulphonate) benzophenone ketyl radical anion are related studies in this field. 

The photochemistry of ketyl radicals is currently of interest and has been reviewed.Photolysis of benzophenone ketyl radical in acetonitrile solution has been shown to yield a mixture of 0-protonated benzophenone, formed by electron ejection, and benzophenone, formed by homolytic cleavage of a hydrogen atom. In non-polar solvents the cyclic analogues of benzophenone ketyl radical such as (353) are also reported to undergo hydrogen atom loss and regeneration of the parent ketone upon excitation.Photolysis of triarylmethyl radicals has been described and leads to the production... 

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