Oligomerization of 3,5-dimethyl benzyl alcohol promoted by clay: experimental and theoretical study

The Role of ESR Spectroscopy in Advancing Catalytic Science: Some Recent Developments

Recent progress is surveyed in regard to the importance of molecular species containing unpaired electrons in catalytic systems, as revealed using ESR spectroscopy. The review begins with studies of enzymes and their role directly in biological systems, and then discusses investigations of various artificially created catalysts with potential human and environmental significance, including zeolites. Among the specific types of catalytic media considered are those for photocatalysis, water splitting, the degradation of environmental pollutants, hydrocarbon conversions, fuel cells, ionic liquids and sensor devices employing graphene. Studies of muonium-labelled radicals in zeolites are also reviewed, as a means for determining the dynamics of transient radicals in these nanoporous materials.

Unpaired electrons as probes of catalytic systems

An overview is provided of the importance of molecular species containing unpaired electrons in catalytic systems, as revealed using ESR spectroscopy. The review aims to demonstrate the considerable extent of scientific progress that has been made in this broad topic during the past few decades. Studies of catalytically active surfaces, including zeolites, are surveyed, and the detection of radical species, formed as intermediates in their reactions, using matrix isolation and spin-trapping techniques. Radical cation formation in zeolites is discussed, and the employment of muon spin rotation and relaxation techniques to study the mobility of labelled radicals in various porous and catalytic media. Among the specific types of catalytic media considered are those for photocatalysis, water splitting, degradation of environmental pollutants, hydrocarbon conversions, fuel cells and sensor devices employing graphene. The review concludes with recent developments in the study of enzymes and their reactions, using ESR-based methods.

Synthesis of cycloveratrylene macrocycles and benzyl oligomers catalysed by bentonite under microwave/infrared and solvent-free conditions

Tonsil Actisil FF, which is a commercial bentonitic clay, promotes the formation of cycloveratrylene macrocycles and benzyl oligomers from the corresponding benzyl alcohols in good yields under microwave heating and infrared irradiation in the absence of solvent in both cases. The catalytic reaction is sensitive to the type of substituent on the aromatic ring. Thus, when benzyl alcohol was substituted with a methylenedioxy, two methoxy or three methoxy groups, a cyclooligomerisation process was induced. Unsubstituted, methyl and methoxy benzyl alcohols yielded linear oligomers. In addition, computational chemistry calculations were performed to establish a validated mechanistic pathway to explain the growth of the obtained linear oligomers.

Effects of bentonite on p-methoxybenzyl acetate: a theoretical model for oligomerization via an electrophilic-substitution mechanism

Tonsil Actisil FF, a commercial bentonitic clay, promotes the formation of a series of electrophilic-aromatic-substitution products from para-methoxybenzyl acetate in carbon disulfide. The molecules obtained correspond to linear isomeric dimers, trimers, tetramers and a pentamer, according to their spectroscopic data. A clear indication of the title mechanistic pathway for the oligomerization growth was obtained from the analysis of a set of computational-chemistry calculations using the density-functional-theory level B3LYP/6-311++G(d,p). The corresponding conclusions were based on the computed dipole moments, the HOMO/LUMO distributions, and a natural-populations analysis of the studied molecules.