Benzoquinone epoxides

Formaldehyde and formic acid are the two primary intermediates formed during the conversion of EG to CO2. Phenol, hydroquinone, benzoquinone, and benzoquinone epoxide arc a few of the intermediates formed during the initial stage of BZ oxidation. EG has been used as a surrogate waste in detailed investigations of the MEO process [13] since studies of its partial oxidation by Ag(n) had been previously published [22-24], BZ has been studied [ 13] since it will be aprimary constituent of mixed waste generated by the DWPF [17]. 

BZ was al so partially oxidized by Ag(II) in a small H-cell with stationary platinum electrodes. Compounds identified in anolyte extracts included phenol, hydroquinone, benzoquinone, benzaldehyde, benzoic acid, methyl benzoate, benzonitrile, benzonitrile aldehyde, and 4-nitro butylnitrile. The yellow color of the anolyte was probably due to benzoquinone, which had a relatively high concentration. A compound which was tentatively identified as benzoquinone epoxide ( 11403) was present at the highest concentration and is believed to be a product of the oxidation of benzoquinone. Numerous nitrated aromatics were also detected and include nitrobenzene, dinitrobenzene isomers, nitrophenol isomers, and dinitnophenol isomers. Intermediates are summarized in Table 3 and classified as I. BZ substrate II. nitrated BZs HI. phenols, quinones, and epoxides IV. nitrated phenols V. BZ substituted with aliphatic and aromatic... 

An analogous reaction has been studied by Pelizzetti, Mentasti, and Baiocchi [33]. They used Mn(lll), Ce(IV), and Ag(Il) to oxidize 4,4 -biphenyldiol to 4,4 -biphenoquinone. Following the conversion of hydroquinone to benzoquinone, benzoquinone would probably converted to benzoquinone epoxide. Unfortunately, little information exists pertaining to this reaction. 

As the oxidation of BZ approached completion, the predominant species found in the anolyte included acetone, acetic acid, and methanol. The reaction path leading from benzoquinone epoxide to acetone, acetic acid, and methanol has not been established. However, the reaction path leading from acetic acid to CO2 is believed to be represented by Equations 32 through 35. 

An interesting approach to the synthesis of highly oxygenated cyclohexane derivatives has been developed by Ichihara. Benzoquinone epoxides and epox-ycyclohexenones were obtained by the thermal retro Diels-Alder reaction of epoxide 511, obtained from quinones and dimethylfulvene without isolation of the primary adduct. Intermediate 512 (R = Ac), obtained in this way from hydroxymethyl-benzoquinone, was converted into the natural compound sene-poxide (514) as shown in Scheme 6. Reductive, regioselective cleavage of the diepoxide 513 was achieved by treatment with hydrazine hydrate. The stereoselective total synthesis of crotoepoxide (515) from cyclohexenone 512 (R = Ms), and of other natural compounds with related structure, was described. ... 

Direct phase-transfer catalysed epoxidation of electron-deficient alkenes, such as chalcones, cycloalk-2-enones and benzoquinones with hydrogen peroxide or r-butyl peroxide under basic conditions (Section 10.7) has been extended by the use of quininium and quinidinium catalysts to produce optically active oxiranes [1 — 16] the alkaloid bases are less efficient than their salts as catalysts [e.g. 8]. In addition to N-benzylquininium chloride, the binaphthyl ephedrinium salt (16 in Scheme 12.5) and the bis-cinchonidinium system (Scheme 12.12) have been used [12, 17]. Generally, the more rigid quininium systems are more effective than the ephedrinium salts. 

The kinetics of oxidation of aldehydes by the Fenton reagent [Fe(II)-H202-0H-] have been studied.89 It has been suggested that different reactivities of PhIO in iron(III)-porphyrin-catalysed alkene epoxidation may be due to the formation of a more reactive iron(IV)-0-IPh complex.90 The iron(m) complex of tetrakis(3,5-disulfonato-mesityl)porphyrin catalyses the oxidative degradation of 2,4,6-trichlorophenol to 2,6-dichloro-l,4-benzoquinone with KHSO5 as the oxygen atom donor a peroxidase-type oxidation is thought to be involved.91... 

The aim of this section is to demonstrate how reaction calorimetry in combination with IR-ATR spectroscopy can be used for the determination of kinetic and thermodynamic parameters. Several examples of chemical reactions will be discussed, each highlighting a different aspect in the application of reaction calorimetry. The reactions considered are the hydrolysis of acetic anhydride, the sequential epoxidation of 2,5-di-ferf-butyl-l,4-benzoquinone and the hydrogenation of nitrobenzene. The results discussed in this section were obtained using a new calorimetric principle presented below. 

Example 2 sequential epoxidation of 2,5-di-tert-butyl-1,4-benzoquinone... 

The sequential epoxidation of 2,5-di-ferf-butyl-1,4-benzoquinone with ferf-butyl hydroperoxide is shown in Scheme 8.2. In the experiments discussed below, Triton-B was added to the mixture as a catalyst, and the basic reaction model is written as Equations 8.24 ... 

Fig. 8.7 Application of protocol A1 for the sequential epoxidation of 2,5-di-ferf-butyM, 4-benzoquinone at 17 and 30°C using the combined evaluation algorithm [20], Mean values from all experiments at each temperature are shown. Absorbance in the lower plots corresponds to a single wave number (1687 cm"1) from the reaction spectrum.

Table 8.1 Reaction parameters Ari, /o, f a, i and Ea,2 for the sequential epoxidation of 2,5-di-ferf-butyl-1,4-benzoquinone determined by the protocols A1, A2, A3 and B1, B2, B3 [20].

Table 8.3 Kinetic (k, k 2, ordjb, ord p) and thermodynamic (ArH, Ar hfc) parameters for the sequential epoxidation of 2,5-di-ferf-butyM,4-benzoquinone based on six measurements at 30°C at different hydroperoxide concentrations using the protocols C1, C2, C3 [20], The reaction model in Equations 8.25 was applied.

The examples presented in Section 8.3 demonstrate this synergy in an approach using calorimetry and IR-ATR spectroscopy. For the hydrolysis of acetic anhydride, the combination of the two analytical techniques enabled a differentiation between the heat effect due to the chemical reaction and that due to a physical phenomenon - in this case, mixing. Due to this separation of the physical heat effect, a more reliable value for the chemical heat effect was obtained. For the sequential epoxidation of 2,5-di-fert-butyl-l,4-benzoquinone, the importance of selection of an appropriate kinetic model has been demonstrated. For complex reaction systems, several models can be postulated. The appropriateness of these models can then be tested on the basis of experimental data. Combined analytical techniques provide an enriched data set for this purpose as has been demonstrated for this example. After the selection of the most appropriate model, the corresponding parameters can be used... 

Oxidation of 4-alkylamino-5-methoxy-l,2-benzoquinones yields 4-alkyaminopyran-2-ones probably through sequential Baeyer-Villiger ring expansion, epoxide formation and ring contraction (95TL6669). 

The discussion above emphasizes that the allyl-Ni reagents are quite selective for carbon halogen bonds, especially allyl, vinyl, and aryl halides. At the same time, modest reactivity as nucleophiles toward reactive carbonyl derivatives has been reported.Simple aldehydes, the more reactive ketones (such as cyclopentanone and benzoquinone), and certain epoxides will undergo 1,2-addition of the aUyl ligand to the carbonyl group. Esters, amides, and, most remarkably, acyl halides are inert toward the allyl Ni reagents under conditions where the reagents do not decompose thermally (<80 °C or so). 

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