Phenol acylation catalyst deactivation

Advantage can be drawn from the positive effect of phenol on PA transformation into p-HAP to improve the yield and selectivity of p-HAP production.[82 84] Thus, with a HBEA zeolite the yield and selectivity for p-HAP passes from ca. 5 and 28 % respectively with cumene solvent to 24 and 60% with phenol as a solvent .[84] Again sulfolane was shown to have a very positive effect on the selectivity for p-HAP and limits the catalyst deactivation. To explain these observations as well as the effect of P and PA concentrations on the reaction rates, it was proposed that sulfolane plays two independent roles in phenol acylation solvation of acylium ion intermediates and competition with P and PA for adsorption on the acid sites.1831... 

A kinetic study of the acylation of phenol with phenyl acetate was carried out in liquid phase at 160°C over HBEA zeolite samples, sulfolane or dodecane being used as solvents. The initial rates of hydroxyacetophenone (HAP) production were similar in both solvents. However the catalyst deactivation was faster in dodecane, most likely because of the faster formation of heavy reaction products such as bisphenol A derivatives. Moreover, sulfolane had a very positive effect on p-HAP formation and a negative one on o-HAP formation. To explain these observations as well as the influence of phenol and phenyl acetate concentrations on the rates of 0- and p-HAP formation it is proposed that sulfolane plays two independent roles in phenol acylation solvation of acylium ions intermediates and competition with phenyl acetate and phenol for adsorption on the acid sites. Donor substituents of phenyl acetate have a positive effect on the rate of anisole acylation, provided however there are no diffusion limitations in the zeolite pores. 

Studies on catalyst deactivation during phenol acylation with PA in the presence of BEA zeolite were performed by recovering the organic material entrapped into the zeolite following two methodologies ... 

While the first process represents a positive event because acetoxyaceto-phenones are convertible into HAPs and can give further intermolecular phenol acylation affording both ortho- and para-HAP, the second process produces ketene, which, being highly reactive, represents the most important source of coke responsible for heterogeneous catalyst deactivation. 

Solid acid catalysts such as clays and zeolites are also utilized for phenol acylation however, these processes suffer from catalyst deactivation problems and lack C-selectivity. In the acylation of phenol with acetic anhydride, HZSM-5 zeolite shows a very high ort/io-selectivity (48% o-HAP yield, <1% p-HAP yield), although phenyl acetate is isolated in only approximately 20% yield [115]. The SAR value has a remarkable influence on the selectivity of the process when the reaction is carried out in the presence of HZSM-5(30), HZSM-5(150), and HZSM-5(280) zeolites, the o-HAP yields are 42,40, and 15%, respectively, whereas the O-acylation is noticeably increased. These results mean that C-acylation requires higher Brpnsted acidity and that lower acidity leads to phenyl acetate formation. It must be noted that the reaction performed with an amorphous aluminosilicate acid catalyst gives mostly phenyl acetate without isomer selectivity. These results suggest that the C-acylation of phenol occurs in the channels of zeolites and not on the external surface. 

The scheme proposed for the reaction over HFAU was that PA dissociates in phenol (P) and ketene and that o-HAP, which was highly favoured over the para isomer, results partly from an intramolecular rearrangement of PA, partly from acyl group transfer from PA to P whereas p-HAP results from this latter reaction only. In these experiments, the zeolite deactivation was very fast, as a result of coke deposition and zeolite dehydroxylation. Catalyst stability can be considerably improved by operating at lower temperatures and especially by substituting equimolar mixtures of PA and water or P and acetic acid for PA. Much higher HAP yields were obtained by using the P - acetic acid mixture as reactants.[68]... 

Pd nanoparticles supported on PANI-NFs are efficient semi-heterogeneous catalysts for Suzuki coupling between aryl chlorides and phenylboronic acid, the homocoupling of deactivated aryl chlorides, and for phenol formation from aryl halides and potassium hydroxide in water and air [493], PANl-NF-supported FeCl3 as an efficient and reusable heterogeneous catalyst for the acylation of alcohols and amines with acetic acid has been presented [494]. Vanadate-doped PANI-NFs and PANI-NTs have proven to be excellent catalysts for selective oxidation of arylalkylsulfides to sulfoxides under nuld conditions [412]. Heterogeneous Mo catalysts for the efficient epoxidation of olefins with ferf-butylhydroperoxide were successfully synthesized using sea urchin-Uke PANI hollow microspheres, constructed with oriented PANI-NF arrays, as support [495]. Pt- and Ru-based electrocatalyst PANI-NFs—PSSA—Ru—Pt, synthesized by the electrodeposition of Pt and Ru particles into the nanofibrous network of PANI-PSSA, exhibited an excellent electrocatalytic performance for methanol oxidation [496]. A Pt electrode modified by PANI-NFs made the electrocatalytic oxidation reaction of methanol more complete [497]. Synthesis of a nanoelectrocatalyst based on PANI-NF-supported... 

The HBEA(20) deactivation in the reaction between phenol and phenyl acetate has also been studied [118]. In this case, the organic material trapped in the zeolite can be recovered following two methods (i) Soxhlet extraction of the zeolite [Ext] and (ii) extraction of coke by dissolution of the zeolite itself in a 40% solution of hydrofluoric acid [Coke]. The acylation reactions are carried out in two classical solvents, dodecane and sulfolane, and in both cases, a significant lowering of the rate of HAPs formation with time is observed. This deactivation is faster in dodecane ( 1 h) than in sulfolane ( 2h).Whatever the solvent, the two reactants are the main components of the material retained in the catalyst nevertheless, in the case of sulfolane, their contents in Ext and Coke are similar to that of the reaction mixture, whereas when the less polar solvent dodecane is employed, their contents in Ext and Coke are greater than that in the reaction mixture. In addition. 

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