Martina Bejblová

Acylation Reactions over Zeolites and Mesoporous Catalysts

Molecular sieves are highly active and selective catalysts with industrial potential for acylation reactions. Zeolites are the catalysts of choice when shape selectivity influences the preferential formation of some products, while high conversions are achieved over mesoporous catalysts with enhanced diffusion rates of reactants and products. In this Minireview, we focus on the understanding of the relationship among the structure of molecular sieve, type and concentration of acid sites and activity/selectivity in various acylations of aromatic and olefinic hydrocarbons. The products of these acylation reactions are important compounds for the pharmaceutical industry, fragrance and flavor materials, dyes, polymers, agrochemicals, and other applications.

Transformations of aromatic hydrocarbons over zeolites

Aromatic hydrocarbons represent an important group of starting materials, intermediates, as well as final products produced in the chemical industry in the range from large processes in petrochemistry up to the synthesis of fine chemicals. This short overview covers the recent achievements in acid-catalyzed transformations of aromatic hydrocarbons with a special focus on alkylation-isomerization-disproportionation reactions in petrochemistry, and acylations or condensations used mainly in synthesis of chemical specialties. In the case of fine chemical synthesis, some zeolite applications in the preparation of important intermediates for pharmaceutical or fragrance products are presented. Advantages and disadvantages of the various types of zeolite are discussed in these reactions from the point of view of their (shape) selective properties, as well as the accessibility of acid sites.

Selective monoacylation of ferrocene with bulky acylating agents over mesoporous sieve AlKIT-5.

Ferrocene acylation with bulky acylating agents (1-adamantoyl, benzoyl, 2-chlorobenzoyl, and cinnamoyl chlorides; and benzoic anhydride) catalyzed by AlKIT-5 mesoporous catalysts was investigated. AlKIT-5 catalysts with varying ratios of Si/Al were synthesized using tetraethoxysilane and aluminum isopropoxide as the structural building blocks and Pluronic F127 as a template under acidic conditions and were characterized in detail by X-ray powder diffraction, magic-angle spinning (MAS) NMR spectroscopy, sorption of nitrogen, energy-dispersive X-ray spectroscopy (EDS), SEM, TEM, and FTIR with pyridine as a probe molecule. The catalytic activity of the prepared AlKIT-5 catalysts in ferrocene acylation was shown to depend on the type of the acylating agent, thus likely reflecting the strength of interactions between the acyl source, the product, and the solid catalysts when the acylation reaction was carried out at 100 degrees C. In all reactions, the AlKIT-5 catalysts afforded exclusively the monoacylated products (100% selectivity) most likely due to deactivation of the second cyclopentadiene ring by attachment of the first acyl group, steric reasons, and some competitive interactions of the monoacylferrocenes with the catalysts. The prepared AlKIT-5 catalysts could be regenerated without any significant loss of the ferrocene conversion.

Synthesis, modification and characterization of MWW framework topology materials

The effect of the synthesis procedure and variables on the resulting chemical and structural properties of molecular sieves of the MWW family was investigated in detail. In addition, dealumination procedure was optimized to decrease the concentration of framework aluminum, which might lead to the connectivity of both originally independent channel systems. MCM-22 was successfully synthesized with Si/Al ratios higher than 12, while at lower ratios MCM-56 was obtained. The molar ratio of organic templates to inorganic cations forwarded the synthesis towards MCM-22 or MCM-49. Much higher stability of MCM-22 was found against steam treatment compared to alkali treatment.

Acylation of cyclohexene derivatives over zeolites

The effect of the structure and acidity of different zeolite catalysts was investigated in Friedel-Crafts acylation of cyclohexene and 1-methylcyclohexene with propionic anhydride. In addition, the effect of chain length of acylating agent (anhydride) was studied in cyclohexene acylation. The highest conversions were achieved with propionic anhydride over zeolite Beta with Si/Al ratio 37.5 (cyclohexene conversion 78.7 %, 1-methylcyclohexene conversion 60.7 %). Selectivities to cyclohexenylethyl ketone were up to 40 %, while selectivities to ethyl-(3-methylcyclohex-2-enyl)ketone were about 90 %. It was found that conversion of cyclohexene over zeolite Beta decreased with increasing chain length of acylating agent.

Zeolites for preparation of acylferrocenes

Abstract The effect of zeolite structure (pore size, channel connectivity) and concentration of active sites on the activity of zeolites in ferrocene acylation with acetic acid derivatives was investigated. The conversion of ferrocene under identical reaction condition increases in the sequence medium-pore zeolites

A computational study of the stretching frequencies of Brønsted acid sites in SAPO STA-7: preliminary comparison with infrared

Abstract The acidity of the Bronsted sites in SAPO STA-7 material is investigated by atomistic simulation techniques. The long-range interactions mainly govern the acidity where as the short-range contributions have only a limited degree of influence. The calculated population of the OH stretching frequencies for a STA-7 sample with 4.8 silicon atoms per unit cell, predicts a broad distribution ranging from 3560 cm –1 to 3585 cm –1 which is confirmed by Infrared Spectroscopy.