Hydroquinone production figures

Reaction Mechanisms. Our analysis of intermediates and reactions reported by other researchers leads to proposed reaction pathways describing the photocatalytic oxidation of 4-chlorophenol in TiOz aqueous suspensions. The photocatalytic oxidation reaction is brought about by OH radicals, which are formed mainly from water decomposition on the Ti02 surface upon UV light irradiation (9-13). The OH radicals can either directly react with the adsorbed organic species on the TiOa surface or diffuse to the solution and then react with the dissolved organic species in the solution phase. Both reactions lead to formation of hydroxylated products such as 4-chlorocatechol, hydroquinone, 4-chlororesorcinol, and hydroxyhydroquinone as the initial products (Figure 6). Eventually, the reaction will mineralize these interme-... 

Hydroperoxidative synthesis 4 (Figure 12.4, middle) accounts for approximately 2.5 x 10 kg of hydroquinone production per year. p-Diisopropylbenzene is synthesized by zeolite-catalyzed Friedel-Crafts reaction of benzene or cumene with propylene or isopropanol. Air oxidation of p-diisopropyl-benzene proceeds at 90-100°C in an aqueous NaOH solution containing organic bases along with cobalt... 

Reaction of phenol with hydrogen peroxide (H2O2) in the presence of strong acids leads to a mixture of hydroquinone and catechol (Figure 12.4, bottom).This hydroxylation process accounts for approximately 1.4 x 10 kg of hydroquinone production per year. The ratio of hydroquinone to catechol is controlled to a finite extent by the acidity of the catalyst. ZSM zeolites, an aluminosilicate zeolite with high silica and low aluminum content, such as TS-1 are also used as the acid catalyst. 

It should be noted that one of these diols, the hydroquinone, did not provide any oligomer in the first step. This was due to the formation of the quinone structure which made it impossible to use hydroquinone directly in the substitution reaction. An alternate method was used to overcome this problem which involved the use of 4-methoxyphenol to obtain the sulfone product, followed by cleavage of the methyl ether to the diol (VIII) with boron tribromide. This set of reactions is outlined in Figure 5. 

FIGURE 12.8. Product distribution resulting at 80% conversion of hydroquinone over (a) iron ox-ide/quartz chips at 300 C and (b) only quartz chips at 480 C with 18 x 10 mmol/min and 3% of oxygen. 

Figure 12.9 shows the products distribution generated from 2,3-dimethyl-hydroquinone cracking with 80% conversion under two different thermal conditions. Despite its two substituted methyl groups, it followed the same trend as found with hydroquinone, i.e. the product distributions were identical in both cases, which again was different from the chemistry of catechol. A peak of the starting material is found at m/z 136 (dimethylbenzoquinone) and possible identities of other peaks are methylpen-tenyne (m/z 80) and butadiene (m/z 54). 

FIGURE 12.14. Three classes of possible products from hydroquinone cracking over 280 to 480 C temperature range (a) Primary, (b) secondary, and (c) tertiary products that are derived by factor analysis. 

FIGURE 12.15. Fractional concentration of three classes of products from hydroquinone cracking, resulting from factor analysis as a function of temperature over (a) iron oxide/quartz chips and (b) only quartz chips, primary (P), secondary I (S), and tertiary (T) products at a feed rate and oxygen concentration of 8xl0-3mmol/min and 3%, respectively. 

The mechanism for the breakdown of phenol after hydroxylation of benzene can be seen in Figure 12.1. Several dihydroxy-substituted phenol derivatives were observed upon irradiation hydroquinone, catechol, and trace amounts of resorcinol (Nickelsen et al., 1993a,b). However, hydroquinone and catechol were both formed at the highest concentration at a low absorbed dose and their concentration decreased with increasing radiation to below detection limits at a dose of 300 krad. At a pH of 9 and a dose of 100 krad, dihydroxy-substituted phenol concentrations increased. When the pH was 5 and 7, the maximum concentrations of these products were found at 50 krads, suggesting a more efficient removal at a lower pH. 

Analysis of the irradiated HPC film which contains hydroquinone A by GPC after dissolution in THF and filtration over a glass-wool membrane (0.2 m) reveals a cross-linking of the yellow products with the HPC matrix since the amount of residual hydroquinone is only 49% (Figure 11). Cross-linked HPC is retained on the glass-wool membrane during the filtration and does not contribute to the GPC chromatogram. This observation is in accordance with what was observed on HYP and, as is shown below, with the behaviour of A adsorbed on filter paper. 

Whereas hydroquinone (p-HOPhOH) in acetonitrile is oxidized via an irreversible two-electron process at +1.18 V versus SCE (Eq. 12.34 and Table 12.2), its dimethyl ether (p-MeOPhOMe) is significantly more resistant with a reversible one-electron oxidation at +1.30 V versus SCE (Figure 12.5).16 The initial oxidation of the latter is followed by a second irreversible one-electron oxidation ( + 1.81 V vs. SCE) that yields a product that is reduced at +0.59 V versus SCE [consistent with the reduction of benzoquinone in the presence of hydronium ions (Table 12.2)] ... 

Hydroquinone (H2Q) is another developing agent and is commonly used in black-and-white processes, usually in conjunction with an auxiliary developing agent such as Metol (A -methyl-p-aminophenol), which is also called Elon, or Phe-nidone (l-phenylpyrazolidin-3-one) (see Figure 6), a heterocyclic agent (see Section 8.2.5). The overall reaction of hydroquinone with silver halide is shown in Eq. (15). In fact hydroquinone undergoes two sequential one-electron transfer steps, with an intermediate semiquinone (S ) and with p-benzoquinone (Q) as the final product. 

The removal of an inhibiting oxidation product was demonstrated by Levenson and Twist [52c] in studies of physical development onto colloidal nuclei. In this case the very early stages of silver ion reduction were followed and it was found that silver ion reduction by Phenidone was initially high but fell after less than 1 min to a much lower rate (of about 1/25 of the initial rate see Figure 13) even though only 30 % of the Phenidone had been consumed. It is suspected that this inhibition is due to the Phenidone radical. The addition of hydroquinone, which did not develop by itself under these conditions, restored the initial rate of development by Phenidone. 

Figures 3 and 4 present the infrared and nmr spectra of the starting hydroquinone dimethyl ether. Can you predict the appearance of the nmr spectrum of the product ...

Aromatic hydroxylation such as that depicted in figure 4,3 for the simplest aromatic system, benzene, is an extremely important biotransformation. The major products of aromatic hydroxylation are phenols, but catechols and quinols may also be formed, arising by further metabolism. One of the toxic effects of benzene is to cause aplastic anaemia, which is believed to be due to an intermediate metabolite, possibly hydroquinone. As a result of further metabolism of epoxide intermediates (see below), other metabolites such as diols and glutathione conjugates can also... 

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