2.5- Diphenyl-p-benzoquinone

Salcomine is a useful catalyst for the selective oxygenation of 2,6-disubstituted phenols to the corresponding p-benzoquinones when dimethylformamide is used as the solvent laborious procedures are avoided and high yields of pure p-benzoquinones are obtained. Following the procedure described above, the authors have prepared 2,6-diphenyl-p-benzoquinone (m.p. 134—135°, yield 86%) and 2,6-dimethoxy-p-benzoquinone (m.p. 252°, yield 91%) from the appropriate phenols. 

Tenax is also suitable for use in the cryogenic trap of thermal desorbers. One of the disadvantages of Tenax is its decomposition in oxidative conditions, such as in the presence of ozone and nitrogen oxides. As a result of reaction with ozone, acetophenone and benzaldehyde are generated, and 2,6-diphenyl-p-benzoquinone in the reaction with nitrogen oxides. 

Diphenyl- -Benzoquinone II. In a 1-L oblong flask 50 g (0.2 mol) of 2,6-diphenylphenol were placed in 150 mL of dimethylformamide with 2 g (0.006 mol) of bis(salicylidene)-ethylene di-iminocobalt (II) (Salcomine) as a catalyst. The flask was connected with a gas burette, while the temperature was kept at 40°-45°C. The whole system then was flushed and filled with oxygen and shaken for 3 hr. The reaction was completed as shown by a sudden stop in the oxygen-uptake (4.81). The reaction mixture was poured onto 600 mL of crushed ice and 30 mL of 4N HC1. The immediately formed orange-red precipitate was filtered and washed three times with water. The crude 2,6-diphenyl-p-benzoquinone was recrystallized from 1-butanol, (48 g, 93% ) mp 136.2°-136.8°C. 

A solution of 80 g of Na2S204 in 400 mL of water was added to a solution of 40 g of 2,6-diphenyl-p-benzoquinone in 500 mL of chloroform. The mixture was stirred for 1 hr at 40°C. The initially formed, deep red color turned light yellow over this period. The reaction mixture was filtered and the residue washed with water and cold ethanol. Recrystallization from hexane gave 2,6-diphenylhydroquinone(III), (33 g, 82%) mp 180.2°-181°C). 

A total synthesis of xylerithrin was also reported, starting from 4,5-dimethoxy-3,6-diphenyl-o-benzoquinone and a />tosyl derivative of phenylacetic methylester [99], via 2-oxo-3-(p-hydroxyphenyl)-4,7diphenyl-5,6-dihydroxybenzofuran. 

Cationic-oxidative polymerization reactions have been developed to synthesize PPS under less severe conditions. For example, PPS has been obtained by a cationic-oxidative polymerization of thiophenol or diphenyl disulfide at room temperature. However, the resulting PPS has a low molecular weight due to premature precipitation. The cationic-oxidative polymerization reaction has been performed electrolytically [109] [Eq. (24)], with Lewis acids [110] [Eq. (25)], with 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ) [111] [Eq. (26)], and with O2 in the presence of a catalytic amount of VO(acac)2 [112] [Eq. (27)]. 

Because it is devoid of the active, endogenous secondary acceptors and donors, the Dl/D2/C d b559 complex can serve as an extremely valuable experimental system for the elucidation of the mechanism of photoinhibition. Since the complex contains the active primary donor and acceptor, it can catalyze secondary electron transport if both an artificial secondary donor such as diphenyl carbazide (DPC) or a quinone acceptor such as 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinone (DBMIB) and an artificial secondary acceptor such as silicomolybdate (SiMo) or ferricyanide (FeCy) are provided, as shown in Fig. 3 (B). 

Charge-transfer spectra between substituted diphenyl sulphides with chloranil, tetracyanoethylene, and 2,3-dichloro-5,6-dicyano-p-benzoquinone,182 and between tetracyanoethylene and a variety of substituted benzenes,183 have been reported. 

The direct oxidative coupling of tertiary amines and diall l- or diphenyl-substituted phosphonates has been developed by Prabhu and Wan. Thus, DDQ (2,3-dichloro-5,6-dicyano-p-benzoquinone) ° ° or MoOs-catalysed C-phosphorylation of N-atyl tetrahydroisoquinolines (232) gave the corresponding a-aminophosphonates (233) in moderate to excellent yields (Scheme 78). 

Polyquinolines form another class of heteroaromatic polymers exhibiting photoconductivity. The interest in the synthesis of polyquinolines has increased rapidly during the last decade because of their excellent oxidative and thermal stability. When doped with alkali metal donor compounds like sodium naphthalide or sodium anthracide, several polyquinolines show electrical conductivity as high as 10 S/cm [336,337], When doped with electron-donor compounds such as TNF or 2,3-dichloro-5,5-dicyano-l,4-benzoquinone some poly-quinolines show distinct photoconductivity. One such polyquinoline is poly(4-phenyl-2,6-(p-phenoxy)-quino-line) (54b) [338,339]. It is obtained by the acid catalysed self-condensation reaction of 4-amino-4 -acetyl-3-benzoyl diphenyl ether (54a). 

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