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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.

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The direct introduction of boron into the framework of germanosilicate zeolites with UTL topology using different organic spiro azo compounds as structure-directing agents (SDAs) was performed. The influence of the SDA's nature, chemical composition and pH of the reaction mixture, and duration of the synthesis on the phase selectivity, limit of isomorphous introduction of boron into the zeolite framework and its location and coordination, and adsorption and acidic properties of prepared borogermanosilicates was investigated in detail. Experimental data provided clear evidence that the properties of the SDAs control the upper limit of the B content in the reaction mixture for successful synthesis of a pure UTL phase. UTL is formed in the pH region having the highest concentration of Ge 8 O 15 (OH) 5 3À (D4R) in water. In synthesized UTL samples the contents of Si and Ge depend particularly on the pH values of the reaction mixtures with similar chemical compositions. With increasing pH of the reaction mixture, the silicon concentration increases, the germanium content predictably decreases, and the boron content shows a local minimum at pH ≈ 9. The concentration of boron in UTL samples is much less dependent on its content in the reaction mixtures. There is a sharp enhancement of the Si/Ge ratio in UTL samples synthesized from boron-rich reaction gels. A tentative assignment of 11 B magic-angle spinning NMR suggests that at lower contents of boron in the structure the boron atoms are located mainly in the T4 and T9 positions. With increasing pH above 11, a sharp increase in the Si/Ge ratio (decreasing the concentration of Ge atoms in D4R) was observed. It favors additional introduction of boron atoms into the T9 position. B-UTL zeolites contain predominantly Lewis acid sites with a small amount of Brønsted acid sites. The concentration of Brønsted acid sites sharply increases for samples prepared at pH lower than 8.

The role of the type of acid site (Broensted vs. Lewis) on the activity and selectivity of molecular sieve catalysts was investigated in ferrocene and toluene acylation. H-, Zn-, Fe-, Al- and La-forms of zeolite Beta, USY and mesoporous molecular sieves (Al)MCM-41, (Al)SBA-15 were tested. It was observed that addition of metal cations acting as Lewis acid sites can increase the acidity of various molecular sieve catalysts. No general relationship between the type of cation and conversion of individual substrate was found. While the highest activity in ferrocene acylation was observed after addition of Zn, in the case of toluene acylation Al-forms of catalysts were the most active. The results indicate that the acid strength of cationic Lewis sites controls their activity in acylation reactions.