Oxidation of alkylphenols

Faust, B. C., and J. Hoigne, Sensitized photo-oxidation of alkylphenols by fulvic acid and natural water , Environ. Sci. Technol., 21,957-964(1987). 

A drawback of Schiff base complexes is their low productivity in oxidation catalysis because the salen ligand is highly prone to oxidative destruction. Kinetically more stable phthalocyanine complexes have been widely explored as catalysts for oxidation of alkylphenols. This subject has been recently reviewed by Sorokin [98]. 

SCHEME 14.14 Oxidation of alkylphenols with H O over Ti(lV) dimeric sites [131],... 

Commercial alkylphenol ethoxylates are almost always produced by base-cataly2ed ethoxylation of alkylphenols. Because phenols are more strongly acidic than alcohols, reaction with ethylene oxide to form the monoadduct is faster. The product, therefore, does not contain unreacted phenol. Thus, the distribution of individual ethoxylates in the commercial mixture is narrower, and alkylphenol ethoxylates are more soluble in water. 

Snia Viscosa. Catalytic air oxidation of toluene gives benzoic acid (qv) in ca 90% yield. The benzoic acid is hydrogenated over a palladium catalyst to cyclohexanecarboxyhc acid [98-89-5]. This is converted directiy to cmde caprolactam by nitrosation with nitrosylsulfuric acid, which is produced by conventional absorption of NO in oleum. Normally, the reaction mass is neutralized with ammonia to form 4 kg ammonium sulfate per kilogram of caprolactam (16). In a no-sulfate version of the process, the reaction mass is diluted with water and is extracted with an alkylphenol solvent. The aqueous phase is decomposed by thermal means for recovery of sulfur dioxide, which is recycled (17). The basic process chemistry is as follows ... 

In general, this method is a one-step procedure for the oxidation of a cresol type of molecule to the corresponding phenolic acid. The vigorous reaction conditions clearly limit the type of functional groups that may be present in the molecule. There is no evidence that the reaction has been applied to polynuclear or heterocyclic alkylphenols. 

Aryl alcohol oxidase from the ligninolytic fungus Pleurotus eryngii had a strong preference for benzylic and allylic alcohols, showing activity on phenyl-substituted benzyl, cinnamyl, naphthyl and 2,4-hexadien-l-ol [103,104]. Another aryl alcohol oxidase, vanillyl alcohol oxidase (VAO) from the ascomycete Penicillium simplicissimum catalyzed the oxidation of vanillyl alcohol and the demethylation of 4-(methoxymethyl)phenol to vanillin and 4-hydro-xybenzaldehyde. In addition, VAO also catalyzed deamination of vanillyl amine to vanillin, and hydroxylation and dehydrogenation of 4-alkylphenols. For the oxidation of 4-alkylphenol, the ratio between the alcohol and alkene product depended on the length and bulkiness of the alkyl side-chain [105,106]. 4-Ethylphenol and 4-propylphenol, were mainly converted to (R)-l-(4 -hydroxyphenyl) alcohols, whereas medium-chain 4-alkylphenols such as 4-butylphenol were converted to l-(4 -hydroxyphenyl)alkenes. 

The enzyme p-ethylphenol methylene hydroxylase (EPMH), which is very similar to PCMH, can also be obtained from a special Pseudomonas putida strain. This enzyme catalyzes the oxidation of p-alkylphenols with alkyl chains from C2 to C8 to the optically active p-hydroxybenzylic alcohols. We used this enzyme in the same way as PCMH for continuous electroenzymatie oxidation of p-ethylphenol in the electrochemical enzyme membrane reactor with PEG-ferrocene 3 (MW 20 000) as high molecular weight water soluble mediator. During a five day experiment using a 16 mM concentration of p-ethylphenol, we obtained a turnover of the starting material of more than 90% to yield the (f )-l-(4 -hydroxyphenyl)ethanol with 93% optical purity and 99% enantiomeric excess (glc at a j -CD-phase) (Figure 14). The (S)-enantiomer was obtained by electroenzymatie oxidation using PCMH as production enzyme. 

Oxidation of phenols.1 The reagent oxidizes 1,2- and 1,4-dihydroxyphenols to the quinones in almost quantitative yield at 25° in methanol. 4-Alkylphenols are oxidized to 4-alkyl-4-methoxycyclohexadienones (mixed quinone ketals) in >90% yield. Monohydric phenols can be oxidized to p-quinone diketals on oxidation with 2 equiv. of the reagent in CH,OH at 25°. 

Nonionic surfactants contain (Fig. 23) no ionic functionalities, as their name implies, and include ethylene oxide adducts (EOA) of alkylphenols and fatty alcohols. Production of detergent chain-length fatty alcohols from both natural and petrochemical precursors has now increased with the usage of alkylphenol ethoxylates (APEO) for some applications. This is environmentally less acceptable because of the slower rate of biodegradation and concern regarding the toxicity of phenolic residues [342]. 

However, our discussion will be restricted to oxidation of simple alkylated monohydric phenols (2-methoxy-4-alkylphenols), serving as models for noncondensed lignin units. In creosol (I) one ortho position and the para position is blocked, and coupling occurs at the 0-carbon atom under the conditions used. Other coupling mechanisms could not be detected (Figure 7). 

Further to its ability to perform allylic and benzylic oxidations,149 /-butylpcroxy-iodane (6) effects radical oxidation of 4-alkylphenols to give 2,5-cyclohexadien-l-ones under mild conditions in good yields.150 o,o-Coupling dimers as side products and inhibition of the reaction by added galvinoxyl radical scavenger support a radical oxidation mechanism. 

In the United States in 1999 for surfactant applications, 340 million lb of ethylene oxide were consumed in the production of alkylphenol ethoxylates, and 600 million lb were consumed... 

Nonionic surfactants are increasingly popular active ingredients. The majority of nonionic surfactants are ethylene or propylene oxide derivatives of alkylphenols or fatty alcohols, although fatty acids, fatty amines, and alka-... 

The lithium and thallium (I) salts of i satin-3-oxime (isatin oximates) were employed in the development of ion-selective electrodes for these cations. Transition metal complexes of isatin derivatives can also be employed as catalysts for the oxidative self-coupling of alkylphenol s639,640. 

As already shown in Scheme 120, both chromium and molybdenum compounds were used for phenolic oxidation. In addition, inexpensive chromium reagents such as Cr02Cl2 and Na2Cr207 2H20 have been used for the conversion of alkylphenols to the corresponding alkylquinones (30-84%) . However, they are scarcely used for phenolic oxidation. 

Similarly, TTN-mediated oxidation of 4-aUcylphenols in MeOH provided 4-alkyl-4-methoxycyclohexa-2,5-dienones (see Scheme 74). Thallium perchlorate [11(0104)3] was also apphed to the oxidation of phenols 816 and 817 leading to cyclohexadienones 818 and 819, respectively, each in 80% yield (Scheme 163) . However, when 4-alkylphenols such as 27 and 820 were treated with T1(C104)3-60% HCIO4 in CH2CI2 they gave 2-alkyl-p-benzoquinones 290 and 821 in 70 and 66% yields, respectively (Scheme 163). ... 

SCHEME 163. Oxidation of 4-alkylphenols with thallium perchlorate... 

A large amount of phenols is released in wastewater and can be lost to waste streams. A rapid increase in the distribution and abundance of plastic debris in the ocean around the world was reported, and the adverse influence of plastic s phenol residues has been of great interest Polluted water disinfection, enzymatic oxidation of chlorinated phenols, decomposition of alkylphenol polyethoxylates and combustion of phenols can lead to the formation of highly toxic compounds. High adsorption of phenols on sludge and sediments requires that their distribution in these systems also be followed. All of these facts have promoted extensive research on phenolic compounds and their fate in the environment. 

Alkylphenols (APs), particularly nonylphenols (NPs) and to a lesser extent octylphenols (OPs), are extensively used for the production of alkylphenol polyethoxylates (NPEOs), a class of non-ionic surfactants that has been largely employed for more than 40 years in textile and paper processing and in the manufacture of paints, coatings, pesticides, industrial detergents, cosmetics and spermicidal preparations, as well as various cleaning products. NPs are also used in the manufacturing processes of many plastics and as monomers in the production of phenol/formaldehyde resins. Smaller quantities of NPs are employed in the production of tri(4-nonylphenyl) phosphite as an anti-oxidant for rubber and in the manufacture of lubricating oil additives. 

Table 16.3-12. Oxidations of 4-alkylphenols catalyzed by 4-ethylphenol oxidoreductase,27].

More recently, the direct formation of hydroxybenzaldehydes by the oxidation of the corresponding alkylphenols was reported. However, the oxidation of 4- and 2-methylphenol respectively into p- and o-hydroxybenzaldehydes remains difficult, leading very often to heavies. For instance, the catalytic systems used for the... 

So, we have discovered new and original catalytic conditions which allow an easy transformation of alkylphenols into the corresponding hydroxybenzaldehydes. Hence, 4-methylphenol is oxidized into p-hydroxybenzaldehyde by oxygen or air, in water / acetic acid media, in the presence of catalysts like Pd/C or Pd-Sn/C (66 % selectivity for total conversion). The former catalysts are not able to yield o-hydroxybenzaldehyde from 2-methylphenol. However, good performances are reach with a Pd-Pt/C catalyst (60 % selectivity for total conversion). 

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