Toluene acylation liquid-phase

As reported in the literature, the acylation of aromatic hydrocarbons can be carried out by using zeolites as catalysts and carboxylic acids or acyl chlorides as acylating agents. Thus toluene can be acylated by carboxylic acids in the liquid phase in the presence of cation exchanged Y-zeolites (ref. 1). The acylation of phenol or phenol derivatives is also reported. The acylation of anisole by carboxylic acids and acyl chlorides was obtained in the presence of various zeolites in the liquid phase (ref. 2). The acylation of phenol by acetic acid was also carried out with silicalite (ref. 3) or HZSM5 (ref. 4). The para isomer has been generally favoured except in the latter case in which ortho-hydroxyacetophenone was obtained preferentially. One possible explanation for the high ortho-selectivity in the case of the acylation of phenol by acetic acid is that phenylacetate could be an intermediate from which ortho-hydroxyacetophenone would be formed intramolecularly. 

Several BEA zeolites have been tested as catalysts for the liquid-phase acylation of toluene with AAN (Table 4.7). [S]-Named zeolites are hydro-thermally prepared using amorphous silica as the silicon source, whereas [T]-named zeolites are prepared by using tetraethylorthosilicate (TEOS) as the silicon source with different SAR. The acylation process represents a very selective route to 4-methylacetophenone 18 small amounts of ortho- and mete-methylacetophenone 19 and 20 are produced in less than 2% of the total yield of the acetylated products. For the [S]-type BEA zeolites, the acidity values are in good agreement with the catalytic activity, following the order [S]-BEA(32) > [S]-BEA(26) > [S]-BEA(54) [S]-BEA(76). In the [T]-BEA series, the catalytic activity decreases when the SAR increases, regardless of the increase of hydrophobicity. The conclusion is that low SAR lead to better yields in acetophenones (APs). However, the poisoning... 

Recently, it was demonstrated that the acylation of toluene and anisole with C2 -Cl 2 aliphatic carboxylic acids in liquid phase is efficiently catalysed by Cs2,5Ho,5[PWi204o]. The acylation of toluene was carried out at a molar ratio PhMe/RCOOH = 50 and 110 C in the presence of ca. 10 wt% Cs2.5Ho.5[PWi204o] (Table... 

However, for liquid phase reactions, it is very difficult to correlate the results wiHi BrOnsted or Lewis acidity as the reaction conditions used are different from those used for characterization. When the Diels-Alder reaction is conducted in a solvent, it appears that the maximum for the activity of HY zeolites is obtained for a Si/Al ratio of 15. This maximum was also observed for esterification of carboiQ lic acids (14), methylthiolation of phenol with dimethyldisulfide (15), acylation of toluene with benzoic acids (15) or dehydration of fhictose (15), and in solvents such as alcohols, water or hydrocarbons. If we assume that Lewis species are transformed to Brdnsted ones in the presence of water as solvent, this would thus mean that the Diels-Alder reaction is preferentially catalyzed by BrSnsted species, the maximum observed at Si/Al=15 for HY zeolites being a good balance between the niunber 6ind the strength of the protonic species. 

Other liquid phase applications of zeolites on the laboratory scale have been reported, including a shape selective /7flr -acylation of toluene with carboxylic acids [15], and the production of 4,4 -diisopropylbiphenyl from biphenyl and propene is catalysed by the naturally occurring zeolite, mor-denite [16]. The latter reaction shows similar pore-imposed selectivity to the chlorination of biphenyl mentioned above. 

Ordinary solid acids such as SiOz —AI2O3 and zeolites are almost or completely inactive for acylation reactions. However, a solid superacid, Zr02 — S04 (cf. Section 3.9) was recendy found to exhibit high activity for the acylation of chlorobenzene or toluene with benzoyl chloride or o-chlorobenzoyl chloride in liquid phase. This was ascertained by separation of the solid superacid from the reaction mixture during a reaction in which the solid superacid acted as the perfect heterogeneous catalyst. 

The simplicity of the two-phase modification of the Gabriel synthesis of primary amines, via the N-alkylation of potassium phthalimide, makes the procedure considerably more convenient than the traditional method, which normally requires the use of anhydrous dipolar aprolic solvents. The reaction can be conducted under solid liquid conditions using potassium hydroxide in toluene [25], or with preformed potassium phthalimide [26, 27] (cf ref. 28). As is normal for acylation reactions, relatively mild conditions are required for the preparation of the A-ethoxycarbonyl derivative [29], whereas a reaction temperature of 100°C is generally used for N-alkylation (Table 5.16). The reaction time for the soliddiquid two-phase system can be reduced dramatically with retention of the high yields, when the reaction mixture is subjected to microwave irradiation [30]. 

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