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Abstract: The reactivity of several phenols toward liquid phase alkylation with cyclohexene in the presence of heterogeneous and homogeneous acid catalyst at 358K is studied. The comparison between Amberlyst 15 and CH3SO3H, as examples of heterogeneous and homogeneous systems, shows a higher activity of the former with different behavior of selectivity between the two systems, anyway, in both systems O-alkylation and ring alkylations occur. A remarkable difference in the selectivity of the ring alkylation between heterogeneous and homogeneous systems is observed: Amberlyst 15 shows a constant ortho/para ratio close to 2, while in the presence of CH3SO3H ortho/para is variable from 3 to 5, suggesting an involvement of the cyclohexyl phenyl ether rearrangement. This is proved also by a direct relationship between the ortho/para ratio and the concentration of the cyclohexyl phenyl ether when CH3SO3H is used as a catalyst. The formation of cyclohexyl aryl ethers is reversible; on the contrary, ring alkylation appears irreversible. The reactivity of the dimethylphenols shows a strong influence of the steric hindrance of the substituent on the electrophilic attack of the cyclohexyl cation, which is poorly influenced by the inductive effect of the methyl group. [Copyright &y& Elsevier]

Abstract: The kinetics of phenol cyclohexylation catalyzed by sulfonic resins is studied taking into account equilibria and side reactions observed in the reaction media. The influence of different sulfonic resins has been tested and only small variation of the catalyst activity, referred to the acid amount, has been observed. Besides, the selectivity is unaffected by varying the type of the catalyst. The effect of reagent concentration on the reaction rate has been also studied, together with the reactivity of the cyclohexyl phenyl ether as intermediate. The etherification equilibrium of cyclohexyl phenyl ether has been analyzed in the presence of methanesulfonic acid, and the adsorption equilibria on a sulfonic resin of reagents and intermediates are measured, too. Starting from the evidences obtained from these studies an Eley–Rideal type kinetic model has been proposed and the fitting of the experimental data allows obtaining the kinetic constant of each stage. Good reliability of the model with the experimental data has been observed, also at high conversion, and the values of the fitting parameters are substantially constant by varying the operative variable, which is a further proof of the goodness of the model. [Copyright &y& Elsevier]

Abstract: The Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam in high yield catalyzed by trifluoroacetic acid in aprotic solvents is described. The influence of the concentration of reagents, intermediates, solvents on reaction rate and selectivity in ɛ-caprolactam is studied. The identification of the key intermediate and its role in the catalysis are reported together with the influence of the acid on the reaction rate. In addition, the study of the hydrolysis reactions of reagent and intermediates highlights what are the parameters that influence the selectivity to ɛ-caprolactam. On the basis of these results a likely catalytic cycle based only on the experimentally verified intermediates is also given. [Copyright &y& Elsevier]

Abstract: Homogeneous and heterogeneous Pd-based catalysts (in the presence of Co(acac)3/ligand/BQ/TBAB and molecular sieve 4A), have been compared in the oxidative carbonylation of phenols. The best yields have been observed in the presence of bulky bidentate N-N ligands such as dmphen and triind. The comparison between homogeneous and heterogeneous systems shows similar behavior in terms of yield and selectivity in DPC, as in 4h of reaction only small differences of activity have been observed. On the contrary, in 20h of reaction only the systems Pd(OAc)2/Co(acac)3/dmphen/BQ/TBAB and Pd(OAc)2/Co(acac)3/triind/BQ/TBAB double the yield in DPC, while with the other systems the conversion is blocked. The beneficial effect of the ligands and of TBAB might be due to their capacity of inhibiting the growing of Pd nanoparticles that are likely to form, thus easing their reoxidation to Pd(II) species. The initial rate of phenol or methyl substituted phenols in CH2Cl2 as a solvent are only slightly influenced, except in the case of bulkier 2,6-dimethylphenol. The conversion vs. time profile evidences that fast catalyst deactivation occurs in any case. [Copyright &y& Elsevier]

Abstract: The influence of some transition metal oxide promoters in the catalyzed Beckmann rearrangement of cyclohexanone oxime was studied by preparing several heterogeneous H2SO4/M/SiO2 catalysts using SiO2 as support and H2SO4 as acid source. A definite effect of each metal has been observed and the best results have been obtained with Cr-, Zr- and Zn-oxides based promoter, which have shown an improved selectivity towards ɛ-caprolactam formation if compared to the H2SO4/SiO2 catalytic system. Moreover, the influence of some organic promoters on the reaction pathway was investigated. Acetic and trifluoroacetic anhydrides gave the best results, even if only the latter allowed the rearrangement even without solid acid catalysts. The transacetylation of the cyclohexanone oxime by using the acetyl caprolactam, which is the product of rearrangement of the acetyl cyclohexanone oxime, was studied for developing a step wise catalytic cycle. Finally, some preliminary results on a homogeneous organic catalyzed process are reported. [Copyright &y& Elsevier]

Abstract: Beckmann rearrangement of cyclohexanone oxime to ɛ-caprolactam has been studied in heterogeneous liquid/solid system at room temperature and pressure. In this first part preparation, characterization and reactivity of impregnated strong acids on solid support have been investigated, with particular attention to H2SO4/SiO2 catalysts. The influence of many preparative variables on catalyst''s microstructure and reactivity has been studied. Surface characterization suggests a progressive filling of the silica pores as the amount of acid increases without a sensible modification in the silica porosity. Conversion and selectivity in Beckmann rearrangement are directly related to the amount of acid loaded on the solid catalyst as well as to the kind of support. Measurement of kinetic parameters together with the apparent activation energy of few kJ mol-1 and the inspection of Carberry and Weeler-Weisz number suggest that diffusion phenomena affect the kinetics. Comparing liquid/liquid and liquid/solid systems, Beckmann rearrangement occurs only with really strong acid and employing aprotic solvent. On the contrary, oxime hydrolysis occurs also with solid or liquid acid catalysts with low protonation ability which generally do not allow the rearrangement under mild conditions. Fast catalyst deactivation has always been observed, suggesting a relation with oxime hydrolysis by which neutralization of the acid phase on catalyst surface occurs. [Copyright &y& Elsevier]

Abstract: The reactivity of a nitrosating agent (N2O3) on oxidations of alcohols and the methyl group of acetophenone were tested. Active electrophylic surface nitrosonium ions (NO+) was detected on H2SO4/SiO2 catalysts by Raman spectroscopy, suggesting a surface ionic mechanism of oxidation in agreement with the one proposed in acid aqueous solutions. Alcohols are selectively oxidized to ketones and aldehydes in high yield, useful for synthetic applications, at 25°C in 1,2-dichlorethane and using commercial sulfonated styrene divinyl benzene resins (Amberlyst 15®) as catalysts. In addition, nitrous acid ester has been observed as intermediates according to an ionic mechanism by surface NO+. Under the same reaction conditions, acetophenone is selectively oxidized to benzoyl cyanide in high yield and selectivity. The comparison with oxidation carried out in aqueous solution of HNO2, where benzoyl formic acid was obtained, suggests that the differences in the final products are likely due to the specific stabilizing effect of each solvent. Moreover, the reactivity of the intermediates isolated in aqueous systems implies that α-nitroso-acetophenone is a probable reaction intermediate also in aprotic heterogeneous systems. [Copyright &y& Elsevier]

Abstract: Selective oxidations by nitrous acid in aqueous sulfuric acid towards alkyl side chains of enolizable ketones are reported. The conversion reagents–products in different experimental conditions is explored and the reaction path of the compounds involved as intermediates is tested. Side-chain oxidations are particularly successful for substrates with one site or with equivalent sites of oxidation. Thus, 95% of benzoylformic acid from acetophenone and 60% of 1,2-cyclohexanedione from cyclohexanone are obtained at ∼78 and at ∼40% H2SO4, respectively. Kinetic (k obs) and thermodynamic (k°) rate constants of acetophenone are also determined, the latter by using the acidity dependence of the rates, the equilibria involving the reacting species and the departure from the ideality of the catalytic acid system. Details of the process between enolizable ketones and electrophilic species in concentrated aqueous acid solutions are discussed. [Copyright &y& Elsevier]

Abstract: The cationic complexes trans-[Pd(COOR)(H2O)(PPh3)2](TsO) have been synthesised by reacting cis-[Pd(H2O)2(PPh3)2](TsO)2·2H2O with CO in ROH (R=Me and Et), practically under room conditions, or by methathetical exchange of trans-[Pd(COOMe)Cl(PPh3)2] with Ag(TsO) (R= n-Pr, iso-Pr, n-Bu, iso-Bu, sec-Bu). They have been characterised by IR, 1H NMR and 31P NMR spectroscopies. The X-ray investigation of trans-[Pd(COOMe)(TsO)(PPh3)2] reveals that the palladium center is surrounded in a virtually square planar environment realized by two PPh3 trans to each other, the carbon atom of the carbomethoxy ligand and an oxygen atom of the p-toluensulfonate anion, with two crystallization molecules of CHCl3. The Pd–O–S angle, 151.9 (3)°, is very wide, probably due to the interaction of one CHCl3 molecule with the complex inner core. The carbomethoxy derivatives react with R′OH yielding the corresponding R′ carboalkoxy derivative (R′=Et, n-Pr and iso-Pr); ethene does not insert into the Pd–COOMe bond; decarbomethoxylation occurs when treated with TsOH/H2O in MeOH at 50°C. All the carboalkoxy are precursors for the catalytic carboalkoxylation of ethene if used in combination of PPh3 and TsOH, better in the presence of some water. Experimental evidences are more in favor of the so-called “hydride” mechanism rather than the “carbomethoxy” mechanism. [Copyright &y& Elsevier]