Phenol, selective oxidation with aqueous

Nickel peroxide is a solid, insoluble oxidant prepared by reaction of nickel (II) salts with hypochlorite or ozone in aqueous alkaline solution. This reagent when used in nonpolar medium is similar to, but more reactive than, activated manganese dioxide in selectively oxidizing allylic or acetylenic alcohols. It also reacts rapidly with amines, phenols, hydrazones and sulfides so that selective oxidation of allylic alcohols in the presence of these functionalities may not be possible. In basic media the oxidizing power of nickel peroxide is increased and saturated primary alcohols can be oxidized directly to carboxylic acids. In the presence of ammonia at —20°, primary allylic alcohols give amides while at elevated temperatures nitriles are formed. At elevated temperatures efficient cleavage of a-glycols, a-ketols... 

New materials are also finding application in the area of catalysis reiated to the Chemicals industry. For example, microporous [10] materials which have titanium incorporated into the framework structure (e.g. so-calied TS-1) show selective oxidation behaviour with aqueous hydrogen peroxide as oxidizing agent (Figure 5). Two processes based on these new catalytic materials have now been developed and commercialized by ENl. These include the selective oxidation of phenol to catechol and hydroquinone and the ammoxidation of cyclohexanone to e-caproiactam. 

TS-1 is a material that perfectly fits the definition of single-site catalyst discussed in the previous Section. It is an active and selective catalyst in a number of low-temperature oxidation reactions with aqueous H2O2 as the oxidant. Such reactions include phenol hydroxylation [9,17], olefin epoxida-tion [9,10,14,17,40], alkane oxidation [11,17,20], oxidation of ammonia to hydroxylamine [14,17,18], cyclohexanone ammoximation [8,17,18,41], conversion of secondary amines to dialkylhydroxylamines [8,17], and conversion of secondary alcohols to ketones [9,17], (see Fig. 1). Few oxidation reactions with ozone and oxygen as oxidants have been investigated. 

Unsubstituted cycloamyloses have been used to catalyze a number of reactions in addition to acyl group transfer. Brass and Bender (8) showed that cycloamyloses promoted phenol release from diphenyl and bis(p-nitro-phenyl) carbonates and from diphenyl and bis(m-nitrophenyl)methyl phos-phonates. Breslow and Campbell (10,11) showed that the reaction of anisole with HOCL in aqueous solution is catalyzed by cyclohexaamylose and cycloheptaamylose. Anisole is bound by the cyclodextrins and is chlorinated exclusively in the para position while bound. Cycloheptaamylose has been used to promote regiospecific alkylation followed by the highly selective oxidation shown in reaction (3) (95). In addition cycloheptaamylose effec-... 

The nitrosodisulfonate salts, particularly the dipotassium salt called Fremy s salt, are useful reagents for the selective oxidation of phenols and aromatic amines to quinones (the Teuber reaction). - Dipotassium nitrosodisulfonate has been prepared by the oxidation of a hydroxylaminedisulfonate salt with potassium permanganate, " with lead dioxide, or by electrolysis. This salt is also available commercially. The present procedure illustrates the electrolytic oxidation to form an alkaline aqueous solution of the relatively soluble disodium nitrosodisulfonate. This procedure avoids a preliminary filtration which is required to remove manganese dioxide formed when potassium permanganate is used as the oxidant. " ... 

Selective Oxidation of Alkanes, Alkenes, and Phenol with Aqueous H2O2 on Titanium Silicate Molecular Sieves... 

The activity data confirm that an IR absorption band at 960 cm" is a necessary condition for titanium silicates to be active for the selective oxidation of hydrocarbons with aqueous H2O2 as suggested by Huybrechts et al. (9). However, this band is not a sufficient condition for predicting the activity of the TS-1 catalyst. Although TS-l(B) and TS-l(C) show intensities for the 960 cm- band similar to TS-1 (A), their activities are different First of all, the reaction data reveal that TS-1 (A) is much more active than TS-l(B) for phenol hydroxylation, while both samples show similar activity for n-octane oxidation and 1-hexene epoxidation. Therefore, the presence of the IR band at 960 cm-i in TS-1 catalysts may correlate with the activities for the oxidation of n-octane and the epoxidation of 1-hexene but not for phenol hydroxylation. However, note that the amorphous Ti02-Si02 also has an IR absorption band at 960 cm- and it does not activate either substrate. 

Microporous titanium silicate (e.g., TS-1, Ti-(3, Ti-ZSM-12, Ti-mordenite) is an effective molecular-sieve catalyst for the selective oxidation of alkanes, the hydroxyla-tion of phenol, and the epoxidation of alkenes with aqueous H202. The range of organic compounds that can be oxidized is greatly limited, however, by the relatively small pore size (about 0.6 nm) of the host framework. 

The catalytic liquid-phase oxidation of aqueous phenol solution, carried out in a variety of reactor systems, demonstrates that phenol can be transformed to nontoxic compounds at milder reaction conditions than used in the thermal processes. The present study indicates that it is advantageous to conduct the reaction in a trickle-bed reactor with partial wetting of catalyst particles, perhaps with cyclic operation, since a direct contact between the catalyst surface and gas-phase increases the concentration of active sites for phenol oxidation. Furthermore, the reaction selectivity in a trickle-bed reactor is higher than that in a slurry reactor. The main drawback of the investigated process is dissolution of metal ions into the liquid-phase, which calls for more stable catalysts. 

For example, the cobalt(II) complex for phthalocyanine tetrasodium sulfonate (PcTs) catalyzes the autoxidation of thiols, such as 2-mercaptoethanol (Eq. 1) [4] and 2,6-di(t-butyl)phenol (Eq. 2) [5]. In the first example the substrate and product were water-soluble whereas the second reaction involved an aqueous suspension. In both cases the activity of the Co(PcTs) was enhanced by binding it to an insoluble polymer, e.g., polyvinylamine [4] or a styrene - divinylbenzene copolymer substituted with quaternary ammonium ions [5]. This enhancement of activity was attributed to inhibition of aggregation of the Co(PcTs) which is known to occur in water, by the polymer network. Hence, in the polymeric form more of the Co(PcTs) will exist in an active monomeric form. In Eq. (2) the polymer-bound Co(PcTs) gave the diphenoquinone (1) with 100% selectivity whereas with soluble Co(PcTs) small amounts of the benzoquinone (2) were also formed. Both reactions involve one-electron oxidations by Co(III) followed by dimerization of the intermediate radical (RS or ArO ). 

With TS-1 as the catalyst, the oxidation products of phenol are hydro-quinone and catechol (para- and ort/to-hydroxyphenol), with minor yields of water and tar formed as by-products. Numerous early papers are concerned with this reaction (218), and patents (219) have been iiled. In the reaction catalyzed by TS-1, the conversion of phenol and the selectivity to dihydroxy products are significandy higher than achievable by either radical-initiated oxidation or acidic catalysts. The catechol/hydroquinone molar ratio is within the range of 0.5—1.3 and depends on the solvent. When the reaction occurs in aqueous acetone, the ratio is close to 1.3. It is believed that the product ratio is the result of restricted transition-state selectivity as well as mass transport shape selectivity associated with the different diffusivities of the ortho and para products. Hydroxylation at the para-position of phenol should be less hindered relative to that at the ortho-position, and hydroqui-none has a smaller kinetic diameter than catechol, facilitating diffusion. Tuel and Taarit (220) proposed that catechol is mainly produced at the external surface of TS-1 crystals. Thus, the different catechol/hydroquinone ratios obtained when methanol or acetone is used as a solvent could be explained by either rapid or very slow poisoning of external sites by organic deposits, respectively. Accordingly, the authors were able to show that tars were easily dissolved by acetone (i.e., external sites for catechol formation remained available in this solvent) while they were insoluble in methanol. 

The oxidation of phenol ethers 311 bearing an alkyl sulfide side chain followed by treatment with aqueous methylamine selectively affords various dihydrobenzothiophenes 312 (Scheme 3.128) without yielding any sulfoxides as by-products [372]. This procedure has been applied in the total synthesis of the potent cytotoxic makaluvamine F, a sulfur-containing pyrroloiminoquinone marine product [373]. 

A green aqueous-ionic liquid biphasic hydroxylation of benzene was performed using metal dodecanesulfonate salts as catalysts [73]. With 1 equiv. of H O, the phenol selectivity reached 90% at 54 and 60% conversion of benzene and oxidant, respectively. 

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