A.J. Hoefnagel

Zeolite catalysed synthesis of coumarin derivatives

The direct synthesis of coumarin derivatives from m-substituted phenols and α,β-unsaturated carboxylic acids catalysed by solid-acid catalysts, such as zeolite H-Beta or Amberlyst-15, in toluene as solvent was studied. The conversion involves esterification followed by alkylation (ring closure). Ring closure of the ester is promoted both by an appropriate substituent on the aromatic ring and by Michael activation of the β-carbon of the ester. These influences were studied by variation of the reactants. 7-Hydroxy-3,4-dihydrocoumarin is formed in high yield when resorcinol and propenoic acid are used as reactants.

Direct fries reaction of resorcinol with benzoic acids catalyzed by zeolite H-beta

Abstract The esterification reaction of resorcinol with benzoic acid, followed by the Fries rearrangement towards benzophenones in a one-pot liquid phase operation was examined with several catalysts. Zeolite H-beta and ion-exchange resins (Amberlyst-15, Nafion-117) were found to be the best catalysts for both equilibrium reactions. More insight in the Fries rearrangement was obtained by carrying out the reaction with a series of substituted phenols and substituted benzoic acids, especially with zeolite H-beta as the catalyst. The esterification reaction of resorcinol with hindered benzoic acids (2-Me- and 2,6-diMe-benzoic acid) is relatively rapid and an intermediate acylium ion is suggested. Here the rate of the rearrangement to the benzophenones is catalyst dependent; with zeolite H-beta the rearrangement of resorcinol-2-Me-benzoate is fast (yield > 90%) and the rearrangement of resorcinol-2,6-diMe-benzoate is slow because of the pore dimensions of the zeolite (shape effect). With Amberlyst-15 as the catalyst both rearrangements are fast. n-Butylbenzene, p -Cl-toluene and n-decane are found to be good solvents in this one-pot reaction. The industrial chemical 2,4-dihydroxybenzophenone can be prepared in a 88% yield by a recycling procedure starting from benzoic acid and resorcinol with zeolite H-beta as the catalyst and with n-butylbenzene as the solvent. In contrast to the existing process the present approach is a clean method.

Zeolite Catalyzed Aromatic Acylation and Related Reaches

Abstract The development of catalytic procedures in aromatic acylation is a priority because the current industrial methods apply stoichiometric or excess amounts of metal chlorides or mineral acids as “catalysts”. The paper reviews zeolite catalysis in this field and subsequently focusses on the acylation of phenols. Here, two reaction steps are involved: esterification and the so-called Fries rearrangement; both reactions are catalyzed by H-zeolites. The Fries rearrangement has been studied over various zeolites using phenyl acetate as a standard reactant. For the combined reaction especially the system resorcinol/benzoic acid has been examined with several catalysts. Zeolite H-Beta was found to be the best catalyst. When more bulky reactants are involved the new MCM-41 zeolitic material is a promising catalyst.

Selective Alkylation of Methylbenzenes with Cyclohexene Catalyzed by Solid Acids

The synthesis of mixtures of cyclohexyltoluenes from cyclohexene and toluene, catalyzed by solid-acid catalysts, such as zeolites (H-USY, H-BEA, H-Mor) or activated clays (e.g. Filtrol-24), was studied. The ortho/meta/para ratio of these mixtures strongly depends on the structure of the catalysts involved. With zeolite H-USY and Filtrol-24 as the catalysts the meta/para ratio is found to be about 2:1, in agreement with the thermodynamic equilibrium, and the ortho-isomer is absent. As H-USY appeared to be a good isomerization catalyst for the cyclohexyltoluenes, the mechanism might involve ortho/meta/para-alkylation followed by isomerization. In this way a new route has been developed to the expensive intermediate 3-methylbiphenyl. The reaction of cyclohexene with xylenes or mesitylene, catalyzed by the zeolite H-USY or the clay Filtrol-24, gives mixtures of cyclohexylxylenes or cyclohexylmesitylene, respectively.

Reactions of hydroxyglycines. New synthetic routes to 4-phenylquinazoline derivatives

Abstract Reaction of hydroxyglycine with 2-aminobenzophenones gives 1,2-dihydro-4-phenyl-quinazoline-2-carboxylic acids in high yields and under mild conditions. These can be smoothly converted into the corresponding 3,4-dihydro isomers and into quinazoline derivatives via rearrangement and oxidation by air, respectively. The X-ray crystallographic structure of 6-chloro-1,2-dihydro-1-methyl-4-phenylquinazoline-2-carboxylic acid shows the carboxylate group at C(2) and the methyl group at N(1) to be in axial positions.

Substituent effects in π-(Tricarbonylchromium) arenes

Abstract The thermodynamic dissociation constants of a series of 38 substituted π-(tricarbonylchromium)benzoic acids in 50% aqueous ethanol at 25°C have been determined. The results require revision of some literature values. The p K a * -values of the π-(tricarbonylchromium)benzoic acids were correlated with the electronic substituent parameters in terms of the Yukawa-Tsuno equation. The reaction constant (ρ) decreases from 1.4 for the benzoic acids to 0.8 for the π-(tricarbonylchromium)benzoic acids, reflecting the decreased ability of the complexed aromatic system to transmit electronic substituent effects. For the alkylsubstituted π-(tricarbonylchromium)benzoic acids, conformational effects of the Cr(CO) 3 group can account for some of the anomalies observed. The substituent parameters, σ meta and σ para , of the π-(Cr(CO) 3 )phenyl group as a substituent were derived from the dissociation constants of the complexed phenylbenzoic acids.

Synthesis of 7-hydroxycoumarins catalysed by solid acid catalysts

Syntheses of substituted 7-hydroxycoumarins via reactions of 1,3-dihydroxybenzene with ethyl acetoacetate (Pechmann reaction) and with propenoic acid and propynoic acids are reported, in which the production of environmentally harmful waste streams is minimized by the use of solid acid catalysts.

Shape Selectivity in the Zeolite-Catalyzed Fischer Indole Synthesis

Abstract It was found that zeolite beta is a highly shape-selective catalyst for the Fischer indole synthesis of 2-benzyl-3-methylindole from phenylhydrazine and 1-phenyl-2-butanone. A selectivity of 83% for this isomer was obtained at full conversion. Combined results from catalytic experiments and sorption measurements indicated that the formation of the isomeric 2-ethyl-3-phenylindole is suppressed as a consequence of restricted transition state selectivity.

Substituent effects. Part 11. Anomalous dissociation constants of benzoic acids in water–organic solvent mixtures. An extended Hammett equation comprising the hydrophobic constant as an additional parameter

Thermodynamic dissociation constants of benzoic acids show deviations from the Hammett equation in ethanol–water and, more strongly, in t-butyl alcohol–water, with maxima at about 40% ethanol–water (16 mol%) and 32% t-butyl alcohol–water (8 mol%). The extended equation Δ=ρσ+hπ, where π is Hanschs hydrophobic constant, covers the experimental data very well; h varies from 0 to – 0.16. Similar behaviour is exemplified for other systems. In the solvents 80% methyl Cellosolve and 65% dimethyl sulphoxide the Hammett equation is followed closely. Some practical implications and an attempt at rationalization are given. Related data from the literature, including recent work of Fan and Jiang, are discussed briefly.

New zeolite-catalyzed ring-closure reaction of benzilic acid

Abstract The formation of the reactive carboxydiphenylmethyl cation from benzilic acid under Bronsted acidic conditions gives rise to a variety of compounds depending on the reaction conditions. When applying Amberlyst-15 as the catalyst, fluorene-9-carboxylic acid is obtained together with a considerable amount of side products. With zeolite H-Beta as the catalyst, a new intramolecular rearrangement takes place leading to 3-phenyl-1,2-dihydrobenzofuran-2-one in high selectivity. In fact, aromatic hydroxylation takes place; accordingly 3-phenyl-1,2-dihydrobenzofuran-2-one can be converted into several (2-hydroxyphenyl)-benzeneacetic acid derivatives. Aromatic solvents were found to enter the benzilic acid rearrangement and give triphenylderivatives, of which the yields are decreasing in the expected order, namely: toluene>p-chlorotoluene>chlorobenzene>o-dichlorobenzene.