AROMATIC KETONES AND QUINONES

Initiators that operate on the basis of the first mechanisms are commonly different acetophenone derivatives (6) and are mainly used in clear lacquers. The second mechanism employs derivatives of aromatic ketones and quinones... 

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... 

Aromatic ketones and quinones continue to attract interest as initiators of photocuring. Several commercially available aromatic carbonyl compounds have been examined in detail and their photochemistry, photophysics and photopolymerisation efficiencies 125... 

AhR-mediated activity results Dioxin-like activity is a useful marker of compounds that are able to activate the AhR receptor, which had been shown to be involved in numerous health effects such as impairment of immunity and nervous system or reproduction (Mukeijee 1998). There have been several studies describing AhR-mediated effects of the PMi (Wenger et al. 2009) and PMio (Clemons et al. 1998 Ciganek et al. 2004 Brown et al. 2005) aerosol size fractions. The TEQ calculated from the data of 28 PAHs (25 parent PAHs, retene, biphenyl and triphenylene) represents by average 7.5 and 95% of the dioxin-like activity associated with the particulate and gaseous fractions, respectively. Most of the activity could be produced by dioxins and furans, but also by partly oxygenated PAHs, such as polycyclic aromatic ketones and quinones that were also shown to activate AhR and to be produced by combustion pollution sources (Misaki et al. 2007). The results, furthermore, confirm that a significant portion of the AhR-mediated activity was produced by compounds present in the gas-phase at many polluted localities as it have been shown previously (Klein et al. 2006 Novak et al. 2009). 

Photolytic decomposition of peroxides is not v y efBcient in crosslinking. An enhancement effect on the extent of photocrosslinking of polyolefins in the presence of peroxides is displayed by aromatic hydrocarbons such as naphthalene. These transfer the exdtation energy absorbed to a peroxide. This procedure, however, does not represent an important improvement when compared with that refored to earlier, namely the photoreduction of pdyethylene with aromatic ketones and quinones [84. From aromatic ketones and quinones, particulariy bena>phenone [32], chlorinated benzophenones, benzoyl-l-( dohexanol [82], a, -dimethot - hen acdr henone, 2,4,6-trimethyl benzoyl phenyl phosphinic ethyl ester [85], anthrone [86], anthraqui-none [87], naphthoquinone, benzoquinone, and their d vatives have all been examined. 

Photoreactions of aromatic ketones and quinones take place both in vacuum and in air. The subsequent reactions of alkyl radicals with oxygen significantly affect cross-linking since parent ketones are regenerated from ketyl radicals and simultaneously, hydrogen peroxyl radicals are formed. 

Davidson, R.S. and Steiner, P.R., Mechanism of the photoinduced decarboxylation of carboxylic acids sensitized by aromatic ketones and quinones,/. Chem. Soc., Perkin Trans. 2, 1357, 1972. 

Reaction with Organic Compounds. Aluminum is not attacked by saturated or unsaturated, aUphatic or aromatic hydrocarbons. Halogenated derivatives of hydrocarbons do not generally react with aluminum except in the presence of water, which leads to the forma tion of halogen acids. The chemical stabiUty of aluminum in the presence of alcohols is very good and stabiUty is excellent in the presence of aldehydes, ketones, and quinones. 

The basic structure of humic substances involves a backbone composed of alkyl or aromatic units crosslinked mainly by oxygen and nitrogen groups. Major functional groups attached to the backbone are carboxylic acids, phenolic hydroxyls, alcoholic hydroxyls, ketones, and quinones. The molecular structure is variable as it is dependent on the collection of DOM available in seawater to undergo the various polymerization, condensation, and oxidation reactions and reaction conditions involved in humification, as well as the ambient physicochemical reaction conditions, such as temperature and light availability. 

The most common triplet state electron acceptors are ketones and quinones, whereas aromatic hydrocarbons, often bearing one or more cyano groups, are the most frequently used singlet state electron acceptors. For the generation of radical cations from a given donor it is important that the exothermidty of the electron transfer reaction can be adjusted to fall within an appropriate range, typically... 

Photoinitiator systems from hydrogen abstraction or electron transfer usually contain two components a photoinitiator (typically an aromatic ketone) and a co-initiator with a weak covalent bond. Some examples for this system include benzophenones (1), thioxanthones (2), benzyls (3), camphor-quinones (CQs) (4), and ketocoumarins (5), which can be used in the presence of H donors (alcohols, THE, and thiols) or electron donors (such as amines) (Table 2). One of the drawbacks of photoinitiation requiring electron transfer is back electron transfer that limits their practical utility. For this reason, the acidity of the C-H bond of the co-initiator is of great importance. A few initiators are also able to undergo cationic and radical photoinitiation such as iodium and sodium salts and arene complexes. ... 

Quinones [124] and aromatic ketones such as flavones, [116] fluorenone, anthra-quinone, and similar compounds [121] dissociate by competing and consecutive losses of CO and C2H2. Multiple CO losses may also occur subsequent to the RDA reaction of flavones. [116,125] As these molecules all have large 71-electron... 

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