Benzophenone systems

Interestingly, the metallocene-activated C-F activation is not limited to tertiary C F bonds (in contrast to the Na/benzophenone system). Perfluorocyclohexane has been defluorinated in the presence of bis(r/5-cyclopentadienyl)zirconium(IV) chloride or bis(t/5-cyclopentadienyl)-titanium(IV) chloride. This reaction is accompanied by hydrogen transfer from the solvent onto the substrate yielding 1,2,4,5-tetrafluorobenzene as product.210... 

Several other substituted benzophenone systems [li] such as aminobenzophe-nones (Mischler s ketone and others), trimethylsilylbenzophenones, alkylthiobenzo-phenones [156], aryloxy benzophenones [157], maleimidophenoxyl benzophe-nones [158], polycyclic aromatic ketones (such as tetralone derivatives) were shown to exhibit some interesting properties. 

The results of these comparative reactions are given in Table 3 and indicate a trend of improved reduction from molten for the 2-hexanone, acetophenone, and benzophenone systems. This trend increases from AIP to ASB to AIP/ASB mixture. In the benzaldehyde and cyclohexanone system, the use of aluminum sec-butoxide alone gave much poorer reduction than that seen with molten AIP or with 70 30 AIP/ASB. This behavior is as yet unexplained. The most significant observation from the results of these comparative reactions is that the mixed alkoxide catalyst provides a greatly inq)roved reduction yield over the same reactions performed with either AIP or ASB. The inq>lication is that the mixed AIP/ASB catalyst should be employed with previously reported MPV reactions that proceed slowly or poorly using either of these aluminum trialkoxides separately. 

R.B. Fox, T.R. Price, R.F. Cozzens, and J.R. McDonald, Photophysical processes in polymers. IV. Excimer formation in vinylaromatic polymers and copolymers, J. Chem. Phys. 57, 534 (1972). C. David, W. Demarteau, and G. Geuskens, Energy transfer in polymers II Solid polyvinyl naphthalene benzophenone system and copolymers vinylnaphthalene yinylbenzophenone, Eur. Polym. J. 6, 1397 (1970). 

The shifting of the peel and shear relationships with formulation and cure changes can be illustrated with the poly(vinyl ethyl ether)/MCEA/benzophenone system (Fig. 7). At low MCEA levels (0-15 percent) increasing exposure time causes an increase in peel but the film does not have any... 

Adam and Weissman 116, II7) found for a similar reaction occurring in the sodium-benzophenone system that the mean lifetime of the sodium ion in the ion pair is more than a thousand times greater than the mean lifetime of its counterpart in the ion pair complex, the benzophenone anion. For this reason this process has been called atom transfer. ... 

In the even more crystalline polyethers derived from the benzophenone systems rather than sulfone systems, even higher boiling solvents like diphenyl sulfone are required. Thus the polyether from hydroquinone and 4,4 -difluorobenzophenone requires diphenyl sulfone and a temperature of 300-320°C, which approaches the melting point of the polymer (335 C). 

The benzophenone system was also prepared by the reaction of m-hydroxyphenylacetylene with 4,4 -difluorobenzophenone. The S3nithe-sis allowed an independent method of obtaining pure monomer which could be compared with the monomer obtained from the Ullmann ether synthesis. 

DSC studies on all the cured samples indicate incomplete cure with substantial exotherms still evident. Samples of the benzophenone and biphenyl monomeric moieties were cured at 500 F for 16 hours and their DSC s showed no evidence of exotherm in the 250 C region. An exotherm at 350 C (Figure 1) was related to the thermal decomposition of the materials. Thermogravimetric-mass spectral analysis was performed in vacuum on the benzophenone system at the same heating rate as the DSC scan. The ion intensity as a function of temperature is shown in Figure 2 and indicates that thermal decomposition starts at approximately 350 C with the evolution of phenol, biphenol, and water. 

Figure 1. DSC Scan of the Benzophenone System Cured at 500for 16 hours ...

The well-known photopolymerization of acrylic monomers usually involves a charge transfer system with carbonyl compound as an acceptor and aliphatic tertiary amine, triethylamine (TEA), as a donor. Instead of tertiary amine such as TEA or DMT, Li et al. [89] investigated the photopolymerization of AN in the presence of benzophenone (BP) and aniline (A) or N-methylaniline (NMA) and found that the BP-A or BP-NMA system will give a higher rate of polymerization than that of the well-known system BP-TEA. Still, we know that secondary aromatic amine would be deprotonated of the H-atom mostly on the N-atom so we proposed the mechanism as follows ... 

The reaction between Cell—O radical and vinyl monomers leads to the formation of grafted cellulose. In the presence of photosensitizers generally used as photoinitiators, such as benzophenone and phenylace-tophenone derivatives, the photoinitiator absorbs the UV radiation and transforms to its singlet (S ) and then triplet (T ) states. After that it may decompose into free radicals or transfer its energy to cellulose or any other molecules in the system. Take benzophenone as an example ... 

Phenylbenzisothiazolescan be photochemically transformed to benzophenone derivatives however. depending on the solvent, 1,5-diazocine systems, generated by dimerization of the primarily formed product, can be isolated.36... 

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). 

To distinguish between azobenzene and benzophenone, assuming reference spectra are not available for these compounds, it is a good idea to examine the mass spectra of aromatic ketones, such as acetophenone, butyrophenone, diphenyldiketone, and so forth. Complete identification is assured by obtaining or synthesizing the suspected component and analyzing it on the GC/MS system under the same GC conditions. If the retention time and the mass spectrum agree, then the identification is confirmed. 

Hint To distinguish these compounds without elemental composition or standards for GC retention time, split the GC effluent to a FID, a nitrogen-phosphorus detector, and the mass spectrometer, simultaneously. Using this splitter system, it is easy to determine if the GC peak contains nitrogen. Also, the analyst can differentiate between azobenzene and benzophenone by using the methoxime derivative. 

Photoredox systems involving carbonyl compounds and amines are used in many applications. Carbonyl compounds employed include benzophenone and derivatives, a-diketones [e.g. benzil, cainphoroquinone (85),2W 291 9,10-phenanthrene quinone], and xanthone and coumarin derivatives. The amines are tertiary and must have a-hydrogens [e.g. N,A7-dimethylani 1 ine, Michler s ketone (86)]. The radicals formed are an a-aminoalkyl radical and a ketyl radical. 

Lewin and Cohen (1967) determined the products of dediazoniation of ben-zophenone-2-diazonium salt (10.42, Scheme 10-77) in five different aqueous systems (Table 10-7). About one-third of the yield is 2-hydroxybenzophenone (10.46) and two-thirds is fluorenone (10.45, run 1) copper has no effect (run 2). On the other hand, addition of cuprous oxide (run 3) has a striking effect on product ratio and rate. The reaction occurs practically instantaneously and yields predominantly fluorenone. As shown in Scheme 10-77, the authors propose that, after primary dediazoniation and electron transfer from Cu1 to 10.43 the sigma-complex radical 10.44 yields fluorenone by retro-electron-transfer to Cu11 and deprotonation. In the presence of the external hydrogen atom source dioxane (run 12) the reaction yields benzophenone cleanly (10.47) after hydrogen atom abstraction from dioxane by the radical 10.43. 

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... 

The chemistry involved in LfV-curable resin systems has been extensively investigated and thoroughly surveyed [88-94]. LfV-radiation polymerization, is in principle, completely analogous to the conventional addition polymerization. A photoinitiator is used in UV polymerization. Its function is the same as the free-radical initiator. A conventional initiator possesses a thermally labile bond which is cleaved to form free-radical species, but the photoinitiator has a bond which breaks upon absorption of radiant energy. Benzoin ethers, benzyldialkyl ketals, benzophenone, and acetophenone derivatives are the important LfV-photoinitiators [95-99]. 

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