Phenol and Anisole

Run Substrate Temp (°C) Time (h) Products (mass%) Secondary p-Aldehyde o-Aldehyde Products Conv. (%) 

With toluene as substrate formylation proceeded in a high yield (99%) with respect to aldehyde formation and with good para-selectivity (90%) in a reaction time of only 1 hour. The reaction was carried out on phenol under the same reaction conditions. Surprisingly, the reactivity of phenol proved to be much lower than that of toluene and a reaction time of more than 4 hours was required to obtain acceptable yields, albeit with reduced para-selectivity. When the reaction was extended to anisole, only small differences compared to phenol were observed within the first hour of the reaction, but at extended reaction times phenol proved to give better conversions. The results indicate that the reaction is sustained for a longer time with phenol than with anisole. 

Although unreacted substrate can be separated from the reaction mixture and recycled back to the reactor, this adds to the capital costs since reactor size needs to be increased for a given supply market demand. Thus, maximising product yield is one of the factors imperative to minimisation of production costs. 

In an attempt to increase product yields through increased mass transfer, a modified gas-entrainment stirrer was tested, using anisole as substrate. This resulted in decreased yields and conversions (Table 2.2 Run 6), indicating that mass transfer of CO is not a limiting factor in the reaction. 

Aldehydes of 4-nonylphenol are used as precursors for foaming agents in the mining chemical industry, thus presenting an opportunity to utilise the HF/BF3/CO technology. However, the formylation of 4-nonylphenol at 45 C furnished mainly dealkylated 

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Phenol and anisole are among the commonly en countered benzene deriva tives listed in Table 111 Electrophilic aromatic substi tution in phenol is discussed in more detail in Section 24 8... 

The protonation of phenol and anisole in pure fluorosulphuric acid occurs on the para-carbon (Birchall et al., 1964), but the introduction of methyl substituents in the para-position leads to competing ortho-caihon protonation (Hartshorn et al., 1971). So, for example, in the solutions of 5-methoxyhemimellitene, cations [226] and [227] occur in the ratio 2 5 at low temperature. Similar results... 

Perfluoro[AT-fluoro-Af-(4-pyridyl)acetamide], prepared via direct fluorination of the sodium salt of perfluoro[/V-(4-pyridyl)acetamide], readily fluorinates diethyl sodio(phenyl)malonate, 1-morpholinocyclohexene, phenol and anisole under mild conditions.129... 

The essential step is believed to be the escape of the electron from the coulomb-valence force potential well. A subsequent proton transfer from the radical cation to the solvent should depend on its acidity. For example, the transient spectra in Table II show that proton transfer takes place for phenol and anisole, in which cases the radicals were identified as neutral phenoxyl and phenoxymethyl, respectively. On the other hand, irradiating aniline gave both the neutral and protonated... 

Partial rate factors for the meta positions of phenol and anisole have not been determined in perchloric acid media. The unavailability of such data is a handicap in interpreting the rate data on guaiacol and veratrole. To obtain approximate values for/0OH and/P0H for guaiacol, it was assumed that the partial rate factor 0.25, determined for the meta position of anisole in sulfuric acid (IS), closely approximated the corresponding factor in perchloric acid. 

Formylation of the less reactive phenol and anisole with CO in HF-BF3 was found to require at least stoichiometric amount of the acid for effective transformation (50 equiv. of HF, 2 equiv. of BF3, 50 bar CO, 45°C).445 Conversion increases with increasing reaction time but results in decreasing paralortho ratios suggesting a change from kinetic control to thermodynamic control and the reversibility of formylation. Furthermore, the amount of byproducts (mainly diphenylmethane derivatives) originating from reactions between substrates and products also increases. Additional studies in ionic liquids showed that imidazolium cations with increased chain lengths—for example, l-octyl-3-methylimidazolium salts—are effective in the formylation process. This was attributed to the enhanced solubility of CO in the ionic liquid medium. Tris(dichloromethyl)amine, triformamide, and tris (diformylamino)methane have recently been applied in the formylation of activated aromatic compounds in the presence of triflic acid at low temperature (— 10 to 20°C) albeit yields are moderate.446... 

The photocatalytic ability of POM to induce bromide-assisted functionalization process was also studied by Molinari et al. [27] in the bromination of some aromatics and alkenes. They reported the possibility to convert phenol and anisole to the corresponding monobrominated derivates and a wide range of cydoalkenes to dibromides and bromohydrins, the last ones as intermediates for the formation of epoxides. 

The primary chemicals associated with taints are solvents or inks, aliphatic aldehydes and ketones, phenols or halogenated phenols, and anisoles (Lord, 2003). 

Fig. 5. Bromination of phenols and anisols using a quaternary ammonium bromide in combination with nitric acid as bromination reagent. Y is OH and OCH3 for phenols and anisols, respectively. X is H or CH3...

Intramolecular oxidation of phenols and anisoles with in rf/ -generated dioxiranes affords spiro-2-hydroxydienones in moderate yields when a tethered carbonyl group is present in the substrate (Scheme 58) <2000JOC4179>. 

The para positions of A,A-dimethylanihne, diphenylamine, phenol, and anisole are electron-rich and accordingly attack 2-alkylthio-l,3-dithiolium cations at C-2, yielding various 2-aryl-1,3-dithiolium cations. A similar reaction occurs with 2,6-bis(/er/-butyl)phenol and with 2-naphthol, and by subsequent deprotonation ketones such as 174 and 175 are obtained. ... 

Excellent reviews on dioxirane-mediated oxidations have appeared. One of the most eharacteristic points is that dioxiranes can be applied to the epoxidation of labile olefins such as enol ethers, enol acrylates, allenes and others. Dioxiranes have also been utilized for phenolic oxidation, but in relatively rare cases. Oxidation of simple phenols and anisoles with dimethyldioxirane (544) provided only a complex mixture, so that hindered phenols are more favorable. On treatment with dimethyldioxirane (4 equiv.) in acetone, 2,4-di(terf-butyl)phenol (216) was oxidized to afford in 79% yield the corresponding o-benzoquinone 220, which reacted with 544 and aq. NaHS03 to give catechol 545. Dimethyldioxirane-promoted oxidation of 545 provided again a quantitative yield of 220. Further oxidation of 220 produced a 52% yield of two epoxides 546 and 547 in a ratio of 1 20. Oxidation of thymol (548) was effected with dimethyldioxirane in acetone to afford fhe four oxidation producfs 549-552 in 10, 20, 10 and 10% yields, respectively (Scheme 102). ... 

The results of the catalytic experiments follow in general the above assumptions. However, some of the expected products are not observed. Conversions and selectivity in the oxidation of the alkylbenzenes studied are presented in Table 1. In all cases hydroxylation in the aromatic ring is observed, mainly to p-isomers. This p-selectivity is due not only to the substrate molecules used but also to the properties of the solvent molecules. It is known that phenol and anisole hydroxylation in methanol and ethanol exhibits substantial p-selectivity while in non-alcoholic solvents, such as acetonitrile and acetone, o-selectivity is found [5,ISIS]. The p/o ratio increases with the bulkiness of the alkyl group but, surprisingly, even 2-propylbenzene is hydroxylated to some extent at the o-position. 

This paper is devoted to the acylation in liquid phase of phenol and anisole by aromatic acetates. Reaction mechanisms are presented and the effect of the solvent polarity which is known to play an important role on the rate and on the selectivity of zeolite catalysed reactions... 

Noteworthy, a technical application and a subsequent emission of mono-to tribrominated phenols to the aquatic environment has not been reported so far. In contrast, brominated phenols and anisols are well-known organohalogens derived from biogenic formation, but exclusively detected in the marine environment (Ballschmiter 2003). Thus, the origin of brominated phenols in the Rhine water samples is still ambiguous. In any case, the prevalence of brominated substances as compared to chlorinated contaminants in the riverine environment is unusual. 

Forbes and co-workers9 have extensively studied the ultra-violet absorption spectra of several series of disubstituted benzene derivatives acetophenones, benzoic adds, benzaldehydes, phenylbenzoates, acetanilides- nitrobenzenes, anilines, fluorobenzenes, chlorobenzenes, phenols and anisoles. They have collected valuable data and interpreted them in terms of the resonance and steric interactions of substituents. Baliab. and co-workers27 have studied the absorption spectra of aryl sulphones and sulphoxides. The absorption spectra of substituted phenylazides28 and phenyl isothiocyanates29 have been discussed by Rao et al. 

Phenol and anisole undergo Friedel-Crafts reactions—orienting ortho and para— because oxygen, being a weaker base than nitrogen, does not complex with the Lewis acid. 

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