Para-benzoquinone

Reaction conditions Catalyst wt = 0.75 g phenol H2O2 = 3 1, mole reaction time = 8 h Temp = 353 K solvent = acetonitrile PBQ = para benzoquinone CAT = Catechol HQ = hydroquinone TON = moles of phenol converted per mole of copper in the catalyst... 

Fig. 6. Influence of catalyst weight and residence time on phenol conversion (CONV), and formation of catechol (CAT), hydroquinone (HQ) and para-benzoquinone (PBQ) over CuCl Pc-Na-Y (0.26) at 353 K see Table 6 for reaction conditions.

In total syntheses where a homogeneously catalyzed transfer hydrogenation is applied, almost exclusively aluminum(III) isopropoxide is utilized as the catalyst. At an early stage in the total synthesis of (-)-reserpine (65) by Woodward [106], an intermediate with two ketone groups and two C-C double bonds is formed (66) by a Diels-Alder reaction of para-benzoquinone (67) and vinylacry-late (68). The two ketone groups were reduced with aluminum(III) isopropoxide... 

An interesting example is found in the mr transition of ortho and para benzoquinone. The two molecules are dissected as shown below ... 

Since a2 + b2 > 2ab for all positive values of a and b, except a = b 0, we conclude that S, 3 (ortho) > S 3 (para). Consequently, the pi LUMO of ortho benzo-quinone will be lower in energy than the pi LUMO of para benzoquinone. Furthermore, the degeneracy of the oxygen lone pair AO is lifted more in the case of ortho benzoquinone. The final conclusion is that the mr transition is predicted to occur at longer wavelengths in the ortho isomer relative to the para isomer. 

Figure 11. The influence of residual H2O2 on the reaction testing of phenol hydroxylation to catechol (CAT), hydroquinone (HQ), and para-benzoquinone (BQ) [61], Reaction conditions 4 g phenol 50 mL water solvent 0.2 g a-Fe203 catalyst inner standard ethanol reaction temperature 70°C. Aliquots were sampled at different times and analyzed by (a) HPLC and (b) GC to determine the conversions of PHE (A) and yields of CAT + HQ + BQ ( ), CAT ( ), and BQ (T). Aliquots were also analyzed by (c) iodometric titration to determine the conversion of H2O2 (o). [Reproduced by permission of Elsevier from Ma, N. Ma, Z. Yue, Y. H. Gao, Z. J. Mol. Catal. A 2002, 184, 361-370.]...

For the other esters 54 was not directly detectable, but its existence could be inferred from its decomposition products 60 or 61. A-acetyl-para-benzoquinone imine, 60, was detected during the hydrolysis of AlP Its decomposition products, 62 and 63, accounted for >90% of 47, and about 30% of 46c in buffers from pH 3.0 to 8.0 containing 0.5 M KCl. The identity of 60 was confirmed by the equivalence of its decomposition kinetics and reaction products (61-63) observed in solutions of 47, or its 4-ethoxy analogue, to that of authentic 60 throughout the pH range 1.0 to 8.0. It was not possible to directly detect 60 in the hydrolysis of 46c and 46d, but its characteristic decomposition products were detected. ... 

Tris(aziridinyl)-para -benzoquinone Tris(l-aziridinyl)phosphine-oxide Tris(l-aziridinyl)phosphine-sulphide see Thiotepa)... 

Olah et al.902 demonstrated in 1979 that Nafion-H is able to catalyze Diels-Alder reaction of anthracene with a number of dienophile (maleic anhydride [Eq. (5.329)], para-benzoquinone, dimethyl maleate, dimethyl fumarate) in chloroform or benzene... 

Hunter, C. A., Molecular recognition of para-benzoquinone by a macrocylcic host. Chem. Commun. 1991, 749. 

Already in 1994, it was reported that substituted phenols can be oxidized with MT0/H202 to obtain para-benzoquinones [81]. Benzoquinones are interesting compounds due to their ubiquity in nature and biological importance. 

Reaction of the pyrone (361) with para-benzoquinone and laser irradiation in an oxygen atmosphere gave a mixture of products, including the trioxanes (40) and (41) in yields of 28% and 9%, respectively <88JOC4986>. 

Figure 9-3. Para-benzoquinone and four water molecules distributed at die two carbonyl oxygen atoms...

Though extension of the n electron system in a homologous series has, in general, a bathochromic effect, there are some exceptions e.g. the series para-benzoquinone, naphtha-1,4-qui-none and anthra-9,io-quinone, where a hypsochromic effect is observed. 

V.D). When the electron density in the ring is high (as in polyalkyl phenols) and the ortho- and/or para position (with respect to the OH group) is vacant, the formation of ortho- or para-benzoquinone also occurs. Indeed, in the hydroxylation of phenol to catechol and hydroquinone, one of the major side products (and the main cause of the tar formation) is the formation of benzo-quinones and products derived from them. The benzoquinones of polyalkyl-benzenes are starting materials for many products in the photographic and fine chemicals industries. Trukhan et al. 234) reported the oxidation of 2,3,-... 

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