Benzophenones, hydroxy

UV absorbers (UVA) act by absorbing UV light hence retarding the photolysis of hydroperoxides. Their activity is also associated with hydrogen bonding between the 2-hydroxy group and the carbonyl chromo-phore [22]. Typical examples are based on 2-hydroxy-benzophenones and 2-hydroxybenztriazoIes (e.g., Table lb, AO 23 and AOs 24-26). 

The UV absorber (UVA) class (e.g., 2-hydroxy-benzophenones and benzotriazoles, see AO 23-27 in Table lb) are stable to UV light and have high extinction coefficients in the region 330-360 nm. They operate pri-... 

Hydroxy-propiophenon 2 -Hydroxy-chalcon 5-Chlor-2-hydroxy-benzophenon 2-Hydroxy-1 -formyl-naphthalin... 

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

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

Hydroxy Benzophenone N(CH3)2 3-N,N -Dimethylamino Phenoxy Electron Abstraction, Followed by Proton Migration Photocrosslinking" ... 

Hydroxy Benzophenone P-Naphthoxy Energy Transfer Processes Self-Stabilized Polymers" ... 

The photodegradation of synthetic polymers can be considerably reduced upon addition of ultraviolet stabilizers. The UV stabilizers (preferably derivatives of o-hydroxy-benzophenone or of 2-(2 -hydroxys -methylphenyl)benzotriazole (Tinuvin) transform the absorbed light energy into thermal energy thus preventing all sorts of photochemically initiated reactions. For review articles see the papers of Otter-stedt (.l), Heller and Blattmann ( 2, 2), Kloepffer (jl, j ), Gysling (JS) and Trozzolo (19 ) ... 

There is some controversy regarding the decay mechanism of 2-hydroxy benzophenone. Scheme 1 summerizes all of the possible decay paths which involve proton transfer in the excited state... 

The apparatus used for picosecond flash spectroscopy on these systems has been described before(8 10). Figure 3a and b show typical transient absorption data obtained on 2-hydroxybenzophenone and the copolymer. Summary of these spectral data are given in Table 3. The transient observed at the shortest delay time (7ps) is the first excited singlet in all systems. The spectral data (at delay times > 50ps) permit placement of upper limits on triplet yields in CH2CI2 for both 2-hydroxy benzophenone itself and the copolymerized chromophore. 

Nanosecond flash kinetic spectroscopy was also carried out on 2-hydroxy benzophenone and the copolymer (11). No transients could be detected in the nanosecond time scale, suggesting that the ground state enol [S (lb) in scheme 1] has a lifetime less than 1 x 10 9 sec. These results strongly imply that processes (3) and (4) are responsible for the deactivation of singlet energy in these systems. A small, non zero triplet yield is postulated in the copolymer both to account for the photodegradation data and the transient spectral data. Triplet... 

Table III. Transient Spectral data on 2-hydroxy benzophenone, and its copolymer.(9)...

Quantum yields and lifetimes of emission (fluorescence) as well as other principal rates of deactivation have been measured on 2-hydroxy benzophenone and 2-hydroxyphenyl benzotriazole derivatives. Polymerizable UV screening agents have been prepared and copolymerized with acrylics in order to obtain transparent films containing nonfugitive UV screening agents. Preliminary results of studies of photodegradation on these copolymers are also reported here. 

Benorylate (315) [4 -(acetamido)phenyl-2-acetoxybenzoate] is another example. It is the ester between two well-known antiinflamatory drugs, aspirin and paracetamol, and is employed in rheumatoid arthritis therapy. In view of the chemical structure with three photolabile groups (two esters and one amide), its possible phototoxicity has been investigated. From the preparative irradiations, it has been concluded that the PFR takes place with breaking of the central C—O bond to yield 5-acetamido-2 -acetoxy-2-hydroxybenzophenone (316). This product undergoes transacetylation to 5 -acetamido-2 -acetoxy-2-hydroxy-benzophenone (318) (Scheme 80) [300]. 

Cellulosic plastics are used in a niunbei of outdoor applications with signs being one of the principal areas of use. This plastic can be stabilized reasonably well with the aryl esters of salicyclic acid. It is of interest to note that these esters undergo a photochemical rearrangement in the plastic to derivatives of hydroxy benzophenone. The hydroxy benzophenones may be added initially to effect stabilization. 

Aliphatic aldehydes and ketones and also aliphatic-aromatic ketones can be converted into the corresponding hydrocarbons alkyl-phenols can be obtained from phenolic-aldehydes and -ketones p-hydroxy-benzophenone yields p-benzylphenol benzoin and benzil yield dibenzyl anthraquinone yields anthracene dihydride. 

Blends of iso- and terephthalates give amorphous, transparent resins, mosdy yellow in color. Heat-deflection temperatures are higher than those of 100% PC resins and depend on the iso- to terephthalate ratio. For example, a resin with a 1 1 ratio has a value of 160°C. These resins are flame retardant mechanical and electrical properties are similar to those of PC resins. The notched Izod impacts are lower at 150—300 J/m (4.7—5.6 fflbf/in.), even in thick sections. Long-term uv radiation stabilities are excellent, but yellowness increases during initial exposure owing to photo-Fries rearrangements (80), wherein 0-hydroxy-benzophenone units are produced along the polymer chains. 

Zeolites H-BEA and H-Y were found to be the most active catalysts, however all catalysts readily form the phenyl benzoate (Table 4.1). In the conditions of the reaction, the formation of phenyl benzoate (PB) occurs rapidly via O-acylation of phenol. Direct C-alkylation of phenol with benzoic anhydride (B) and Fries rearrangement of phenyl benzoate results in the formation of 2- and 4-hydroxy-benzophenones (2-HPB and 4-HPB) (Scheme 4.3). 

Tricyclische Diorgano-phosphorane werden bei der Umsetzung von Dichlor-organo-phosphanen mit Salicylaldehyd bzw. 2-Hydroxy-benzophenon in Gegenwart von Tri-ethylamin in 80% Ausbeute erhalten" ... 

Table III shows results obtained when three UV stabilizers, alone or in combination, were used in 5- and 12-mil films for protecting the blue wool fabrics. The hindered-amine stabilizer (UV-3) was not tested because it was ineffective in 8-mil films (Table II). In 5-mil-thick films, the trends in AE values for the hydroxybenzotriazole (UV-1B), hydroxy-benzophenone (UV-2), and the zinc acetate (UV- 1) stabilizers were the same as they were when these stabilizers were incorporated into 8-mil-thick films. However, after maximum exposure time, the AE values were somewhat higher than those observed with 8-mil films. Similar trends were observed with films of 12-mil thickness. Only the hydroxy-benzophenone (UV-2) had AE values less than 1.0 after 550 kj/m2 exposure. The relative effectiveness of a hydroxybenzotriazole (UV-1B), a hydroxybenzophenone (UV-2), and combinations of each of these stabilizers as a function of film thickness are shown in Figure 3. All films, even those containing no stabilizers, were most effective in protecting the wool fabrics from color change when they were 8-mil thick. Again, no advantage was observed in using combinations of stabilizers instead of a single stabilizer in the film.

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