Phenol, reactivity with phenyl

Perhaps the best-known method of preparing aromatic azo compounds involves the coupling of diazonium salts with sufficiently reactive aromatic compounds such as phenols, aromatic amines, phenyl ethers, the related naphthalene compounds, and even sufficiently reactive aromatic hydrocarbons. Generally, the coupling must be carried out in media which are neutral or slightly basic or which are buffered in the appropriate pH range. The reaction may also be carried out in nonaqueous media. While some primary and secondary aromatic amines initially form an A-azoamine, which may rearrange to the more usual amino-C-azo compound, tertiary amines couple in a normal manner. 

Jacquesy et al.556 have succeeded in preparing mefa-bromophenols from phenols using the Br2-HF-SbF5 system. The orf/zo-protonated phenol or alkyl phenyl ether, which is in equilibrium with the neutral precursor, reacts with the reactive Br+ in the HF-SbF5 medium, leading to only mefa-brominated phenols (Scheme 5.59). The ring protonated phenols are unreactive toward electrophilic bromine in the superacid... 

Relatively little basic information has been published regarding the kinetics of phenol-formaldehyde intermediates, especially of phenols, methylol phenols, benzyl alcohol and benzylic ethers with isocyanates. Due to the fact that a typical resole contains both phenolic and benzylic hydroxyl groups, it was of interest to determine their reactivity toward isocyanates in the presence of various catalysts, as well as the effect of substitution on their reactivity. This investigation describes the kinetics of model phenols and model benzyl alcohols with phenyl isocyanate catalyzed with either a tertiary amine (dimethylcyclo-hexylamine, DMCHA) or an organotin catalyst, dibutyltin dilaurate (DBTDL) in either dioxane or dimethylformamide solution. 

The reactivity of the model phenols and benzyl alcohols with phenyl isocyanate was determined in the presence of a tertiary amine (DMCHA) and a tin catalyst (DBTDL) by measurement of the reaction kinetics. The experimental results based on initial equal concentrations of phenyl isocyanate and protic reactants showed that the catalyzed reactions followed second order reaction with respect to the disappearance of isocyanate groups (see Figure 1). It was also found that a linear relationship exists between the experimental rate constant kexp, and the initial concentration of the amine catalyst (see Figure 2). In the case of the tin catalyst, the reaction with respect to catalyst concentration was found to be one-half order (see Figures 3-4). A similar relationship for the tin catalyzed urethane reaction was found by Borkent... 

EFFECT OF SUBSTITUTION ON REACTIVITY OF MODEL PHENOLS WITH PHENYL ISOCYANATE IN DIOXANE AT 25°C... 

The effect of type of catalyst on the reactivity of phenol and benzyl alcohol with phenyl isocyanate can be seen in Table III. In the case of tertiary amine (DMCHA), there is a relatively small difference in the reactivity of both the phenol and benzyl alcohol with phenyl isocyanate. Using DBTDL as catalyst, benzyl alcohol was found to be 26 times more reactive than phenol in the reaction with phenyl isocyanate. 

It is also of interest to point out that DBTDL is about three times more effective a catalyst than DMCHA in the reaction of phenol with phenyl isocyanate. Baker and Gaunt [21] found that ethyl alcohol was 30 times more reactive than phenol in the uncatalyzed reaction with phenyl isocyanate. However, in the presence of a tertiary amine (triethylamine), the reactivity of phenol increased significantly and was found to be similar to that of ethyl alcohol (see Table IV). 

EFFECT OF TERTIARY AMINE CATALYST ON REACTIVITY OF PHENOL AND ETHYL ALCOHOL WITH PHENYL ISOCYANATE21... 

EFFECT OF SOLVENTS ON REACTIVITY OF PHENOL WITH PHENYL ISOCYANATE AT 25°C... 

EFFECT OF CATALYSTS ON THE REACTIVITY OF PHENOL BENZYL ALCOHOL AND ETHYL ALCOHOL WITH PHENYL ISOCYANATE... 

Reaction of phenol derivatives with acyl chlorides in acidic conditions may result in O-acylation or C-acylation, either directly or via a Fries rearrangement. Studies of acylations in acetonitrile using trifluoromethanesulfonic acid (trifllc acid) have shown that O-acylation is favoured at a low acid concentration, while a high acid concentration favours C-acylation. It has also been shown that A-hydroxysuccinimidyl and phenyl esters of benzoic acids are activated by triflic acid and can be used to acylate electron-rich arenes such as ferrocene or pyrene the reactive acylating intermediate is likely to be an acyl triflate or its protonated form. In a polyphosphoric acid medium, the rearrangement of 1,5- 1,8- and 9,10-diacetylanthracenes leads to the formation of the ring-closed product (56). DFT calculations support the conclusion that the reaction involves the intermediacy of 1,9-diacetylanthracene formed under kinetic rather than under thermodynamic control. ... 

The unsaturated phenol is highly reactive and gives rise to coloured products. This decomposition may be repressed by the use of a molar excess of diphenyl carbonate in the ester interchange reaction. In this way, initial esterification and consequent stabilization of the bisphenol A occurs more rapidly. When an excess of diphenyl carbonate is used, the initial products are low molecular weight polycarbonate chains terminated with phenyl carbonate groups. When these low molecular weight polymers are heated above 250°C under... 

Perhaps the best-known method of preparing aromatic azo compounds involves the coupling of diazonium salts with sufficiently reactive aromatic compounds such as phenols, aromatic amines, phenyl... 

Phenol is a reactive substrate and reacts with butadiene smoothly to give octadienyl phenyl ether (30) in a high yield[14]. 

However, heterocycles containing thiophenols have not been reported. It has been observed that the thiophe-nolate ion undergoes nucleophilic attack by the halo/ nitro compounds more easily than the phenolate ion in displacement reactions [37-39]. The experimental result shows that the reactivity of 3-nitro-N-phenyl-phthali-mide with 4-methyl-thiophenolate (reaction 1) is 100 times faster than that of 4-methyl phenolate [40] (reaction 2) ... 

The imide (86) (see (16a) in Section 4.06.5.2) is a reactive acylating reagent under mild conditions. Reaction with aniline or phenol yields diphenylurea (PhNH)2CO or diphenyl carbonate (PhO)2CO respectively. With benzoic acid, 2-phenyl-4-benzoyl-l,3,4-oxadiazoline-5-thione is formed, hence reaction of (86) with benzoic acid and nucleophiles NuH (Nu = NHPh, OPh, SPh) yields amide PhCONHPh, ester PhC02Ph, and thioester PhCOSPh respectively. With diamines R(NH2)2, (86) forms polyureas [-CONHRNH-] <89BCJ539>. 

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