Hydroxy benzophenone

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... 

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]. 

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" ... 

Decomposition of 2-diazobenrophenone tetr Duoroborate (1) in the presence of these Cu(l) complexes in a neutral medium gives the major products 2,2 -dibenzoyl-diphenyl (2, 70% yield) and 9-fluorenonc (3. --30" yield). Decomposition of (I) with cuprous oxide at pll I gives as the major products benzophenone, 2-hydroxy-benzophenone. and 9-fluorenone. 

It has been observed that many substances showing an intramolecular hydrogen bond are photochemically very stable. The stability of the 2-hydroxy phenyl benzothiazole has been referred to in Section III-C, and some data are given in Table 5. The photochromism detected by flashing nonpolar solutions of 2-hydroxy phenylbenzothlazole (54) does not exclude photostablllty since it is a reversible process. Of prime importance as photostable substances are derivatives of 2-hydroxy-benzophenone (HB) and 2-(2 -hydroxy-phenyl)-benzotrlazole. 

FIGURE 7. Absorption spectra of nonluminescent chelates 2-hydroxy-benzophenone (1) 2-hydroxy-4-methoxy-benzophenone (2) and 2(2 hydroxy-5 methyl-phenyl)benzotriazole (3) in CCI4. 

The following photostabilizers were used 2-hydroxy-benzophenone (I) (Merck, Germany), 2,2 -dihydroxy-benzophenone (II) (Aldrich, Belgium) and 2(2 -hydroxy-5-methylphenyl)benzotriazole (III)... 

Scheme 12.10 The 2-hydroxy benzophenone route of the dissipation of the light energy in the polyolefin stmcture...

Scheme 12.16 The sequence of radical reactions leading to 2-hydroxy benzophenone derivative, the compound with stabilizing effect against the light...

Light stabilizers Absorb UV light to prevent photooxidation Tinuvin 327, 328, 384, 440, etc. (derivatives of 2-hydroxy-benzophenone)... 

A rhodium-catalysed rearrangement of 2-(aryloxy)benzaldehydes to 2-hydroxy-benzophenones proceeds by the simultaneous rhodium-catalysed cleavage of aryloxy C=0 and aldehyde C—H bonds (Scheme 147). " ... 

The most widely used UV absorbers are 2-hydroxy-benzophenones, 2-hydroxy-phenyl-benzotriazoles and 2-cyanodiphenylacrylate. 

Figure 4.3 Chromatogram of a polypropylene extract. Peaks are (a) biphenyl, (b) butylated hydroxytoluene, (c) 4-(dodecyloxy)-2-hydroxy-benzophenone and (d) unknown impurity...

Competitive UV absorption 2-Hydroxy benzophenones 2-Hydroxyphenyl benzotriazoles 2-Hydroxyphenyl-s-triazines Other chemical classes... 

Phenyl-substituted p-hydroxybenzoates (Structure 4) have been used as light Stabilizers in polyolefins for some time. They were shown to operate through a photo-Fries rearrangement to give a more effective 2-hydroxy-benzophenone product by the following reaction sequence (Scheme 4) to give 2-hydroxybenzophenones as products [1,2]. Obviously for such a reaction to occur, the original stabilizer must absorb appreciably in... 

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