Dihydroxybenzophenones

Dihydroxybenzophenones are used for the syntheses of dyes, polymers, and medicines. They are prepared by the condensation of resorcinol with benzoic acids. Catalysts used for this transformation are sulfonic resins (99), boron trifluoride (100), or zinc chloride in the presence of POCl (101). 

Thermotropic polycarbonates have been prepared from mixtures of 4,4 -dihydroxybiphenyl and various diphenols (10). Nematic melts were found for copolycarbonates prepared from methyfliydroquiaone, chlorohydroquiaone, 4,4 -dihydroxydiphenyl ether, and 4,4 -dihydroxybenzophenone. Slightly crystalline polycarbonates have been prepared from mixtures of hydroquinone and BPA (T = 154°C, =313°C, AH = 11.0 J/g (2.63 cal/g)), and... 

Nitrobenzotrichloride is also obtained in high yield with no significant hydrolysis when nitration with a mixture of nitric and sulfuric acids is carried out below 30°C (31). 2,4-Dihydroxybenzophenone [131 -56-6] is formed in 90% yield by the uncatalyzed reaction of benzotrichloride with resorcinol in hydroxyHc solvents (32) or in benzene containing methanol or ethanol (33). Benzophenone derivatives are formed from a variety of aromatic compounds by reaction with benzotrichloride in aqueous or alcohoHc hydrofluoric acid (34). 

Resorcinol monobenzoate Benzoate Converted in sunlight to a dihydroxybenzophenone. Used in cellulosics. 

Dihydroxy- 4-methoxybenzophenone OH 0 OH CH.O-( )-C -( Substituted dihydroxybenzophenone Stronger than the monohydroxy compound but some absorption in the visible range. 

Further improvement in light stability may be achieved by addition of small quantities of ultraviolet absorbers. Typical examples include phenyl salicylate, 2,4-dihydroxybenzophenone, resorcinol monobenzoate, methyl salicylate and stilbene. 

Clearly a wide range of phenols and amines are possible. Where appropriate multi-ringed phenols are used such as 4,4-dihydroxybenzophenone or bisphenol A then three-dimensional cross-linked polymers will be obtained. Amines may be aliphatic such as methylamine or aromatic such as aniline. 

UV absorbers have been found to be quite effective for stabilization of polymers and are very much in demand. They function by the absorption and harmless dissipation of the sunlight or UV-rich artificial radiation, which would have otherwise initiated degradation of a polymer material. Meyer and Geurhart reported, for the first time in 1945 [10], the use of UV absorber in a polymer. They found that the outdoor life of cellulose acetate film was greatly prolonged by adding phenyl salicylate (salol) [10]. After that, resorcinol monobenzoate, a much more effective absorber, was introduced in 1951 [11] for stabilization of PP, but salol continued to be the only important commercial stabilizer for several years. The 2,4-dihydroxybenzophenone was marketed in 1953, followed shortly by 2-hydroxy-4-methoxybenzophenone and other derivatives. Of the more commonly known UV absorbers, the 2-hydroxybenzophenones, 2-hy-droxy-phenyl-triazines, derivatives of phenol salicylates, its metal chelates, and hindered amine light stabilizers (HALS) are widely used in the polymer industry. 

Kelsey et al. reported that die cyclic ketal of 4,4,-dihydroxybenzophenone (DHBP) can polymerize with 4,4,-difluorobenzophenone in DMAc at 150°C (Scheme 6.16).85 The polymerization afforded soluble amorphous polyketal that was quantitatively converted to PEK. Because of relatively lower reaction temperature, the PEK had minimal defect structures and thus possesses higher crystallinity and higher Tg, and has better physical properties than its counterpart made under higher temperatures. 

Difluoro monomers, 341 Difunctional monomers, 12 Dihalide monomers, modified with functional groups, 357 Dihalides, activated, 346, 356-359 Dihydroxybenzophenone (DHBP), 342-343, 420... 

BHA, BHT, PG, TBHQ and tocopherols) a variety of stationary phases, mobile phases and detectors can be used [711]. Common antibacterials such as carba-dox, thiamphenicol, furazolidone, oxolinic acid, sul-fadimethoxine, sulfaquinoxaline, nalidixic and piromidic acid can be analysed by GE-RPLC-UV (at 254 nm). Collaborative studies have been reported for the HPLC determination of the antimicrobial sodium benzoate in aqueous solutions [712], Plastics devices used for field collection of water samples may contain polymer additives (such as resorcinol monobenzoate, 2,4-dihydroxybenzophenone or bisphenol A) or cyanobac-terial microcystins [713],... 

The use of copolymers is essentially a new concept free from low-MW additives. However, a random copolymer, which includes additive functions in the chain, usually results in a relatively costly solution yet industrial examples have been reported (Borealis, Union Carbide). Locking a flame-retardant function into the polymer backbone prevents migration. Organophosphorous functionalities have been incorporated in polyamide backbones to modify thermal behaviour [56]. The materials have potential for use as fire-retardant materials and as high-MW fire-retardant additives for commercially available polymers. The current drive for incorporation of FR functionality within a given polymer, either by blending or copolymerisation, reduces the risk of evolution of toxic species within the smoke of burning materials [57]. Also, a UVA moiety has been introduced in the polymer backbone as one of the co-monomers (e.g. 2,4-dihydroxybenzophenone-formaldehyde resin, DHBF). 

Shell Chemical Company), exhibits a maximum at 300 nm, corresponding to that of the model chromophore anisole. The fluorescence intensity decreases monotonically with increasing concentration of 2,4-dihydroxybenzophenone (DHB) and, furthermore, decreases with time on continued excitation (274 nm) in the spectrophotometer. The fluorescence loss with time may be resolved into two exponential decays. Initially, a relatively rapid fluorescence loss is observed within 20 sec, followed by a slower loss. Loss constants for the initial (k ) and secondary (kj) exponential decays for 1.5 ym films (on glass slides) containing varying concentrations of DHB are provided in Table I (entries 1-3). The initial loss constants are seen to decrease more markedly with increasing DHB concentration than the secondary constants. 

Dihydroxybenzophenone was obtained from Aldrich Chemical Co. and used as received. 

With this purpose, several different types of solid acid catalysts have been investigated for the acylation of aromatics, but the best performances have been obtained with medium-pore and large-pore zeolites (3-9). In general, however, the use of acylating agents other then halides, e.g., anhydrides or acids, is limited to the transformation of aromatic substrates highly activated towards electrophilic substitution. In a previous work (10), we investigated the benzoylation of resorcinol (1,3-dihydroxybenzene), catalyzed by acid clays. It was found that the reaction mechanism consists of the direct 0-benzoylation with formation of resorcinol monobenzoate, while no primary formation of the product of C-benzoylation (2,4-dihydroxybenzophenone) occurred. The latter product formed exclusively by... 

Very early in the study of photosensitization it was discovered that salicylaldehyde, 2,4-dihydroxybenzophenone, and 2-hydroxy-4-methoxy-benzophenone do not sensitize piperylene isomerization, indicating that enolization is much faster than quenching by the diene.37 Later it was shown that 2-hydroxybenzophenone would sensitize the dimerization of isoprene in concentrated solution, but that the reaction was much less efficient than when benzophenone was used as a sensitizer (Table I).36... 

A reaction flask was charged with 2,5-dichloro-2, 4 -dihydroxybenzophenone (100 mmol), 2H-dihydropyrane (2400 mmol), and 100 ml of toluene. While the mixture was stirring, it was treated with cation exchange resin Amberlist 15 (3.0 g) and then stirred an additional 5 hours at ambient temperature. At this point the cation exchange resin was removed and the filtrate washed with aqueous solutions of sodium hydroxide and brine The mixture was dried using MgSOzt, concentrated, the residue recrystallized from toluene, and 21.2 g of product isolated. 

The initial product of this route, a 2,2 -dihydroxybenzophenone, is usually cyclized thermally, often in the presence of an acid. However, some intermediate ketones cyclize spontaneously for instance, 2,2, 4,4 -tetrahydroxybenzophenone cyclized during oximation, giving 3,6-dihydroxyxanthone oxime. 

An improved product is reported to be obtained in higher yield if the cyclization of dihydroxybenzophenones is carried out at 210 °C in glycerol containing a trace of potassium hydroxide 3-hydroxy-4-methylxanthone was obtained in 50% overall yield from salicylic acid and 2-methylresorcinol, for example (75CJC2054). 

A biogenetic flavour is apparent in the formation of dihydroxybenzophenones by the reaction of o-hydroxybenzoate esters with the trianion of heptane-2,4,6-trione (81JOC2260). Acylation of the trianion occurs at 0-25 °C to give a tetraketone which cyclizes under mildly basic conditions to the corresponding benzophenone. A second ring closure takes place when the benzophenone is treated with sodium methoxide, leading to the xanthone (Scheme 188). 

Using potassium hexacyanoferrate(III), the oxidation of 2,3 -dihydroxybenzophenone affords a mixture of 2- and 4-hydroxyxanthones, the proportions of which vary with the... 

The oxidation of the 2, 5 -dihydroxybenzophenone (517) by DDQ also gives two products a xanthone (520) and the major component, a spirocyclohexenedione (521). Their formation may involve the diradicals (518) and (519 Scheme 191). Thermal rearrangement of the cyclohexenedione leads to the xanthone (81JCS(P1)770). 

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