Highly selective synthesis of nopol over mesoporous and microporous solid acid catalysts

Exploring the effect of acid modulators on MIL-101 (Cr) metal–organic framework catalysed olefin-aldehyde condensation: a sustainable approach for the selective synthesis of nopol

Acid modulated synthesis of MIL-101(Cr) with tunable textural and surface acidic properties for highly selective synthesis of nopol.

ZnAlMCM-41: a very ecofriendly and reusable solid acid catalyst for the highly selective synthesis of 1,3-dioxanes by the Prins cyclization of olefins

The Prins cyclization of styrene (SE) with paraformaldehyde (PFCHO) was conducted with mesoporous ZnAlMCM-41 catalysts for the synthesis of 4-phenyl-1,3-dioxane (4-PDO) using a liquid phase heterogeneous catalytic method. For a comparison study, the Prins cyclization reaction was also conducted over different nanoporous catalysts, e.g. mesoporous solid acid catalysts, AlMCM-41(21) and ZnMCM-41(21), and microporous catalysts, USY, Hβ, HZSM-5, and H-mordenite. The recyclable mesoporous ZnAlMCM-41 catalysts were reused in this reaction to evaluate their catalytic stabilities. Since ZnAlMCM-41(75) has higher catalytic activity than other solid acid catalysts, washed ZnAlMCM-41(75)/W-ZnAlMCM-41(75) was prepared using an efficient chemical treatment method and used with various reaction parameters to find an optimal parameter for the highly selective synthesis of 4-PDO. W-ZnAlMCM-41(75) was also used in the Prins cyclization of olefins with PFCHO and formalin (FN, 37% aqueous solution of formaldehyde (FCHO)) under different reaction conditions to obtain 1,3-dioxanes, which are widely used as solvents or intermediates in organic synthesis. Based on the nature of catalysts used under different reaction conditions, a reasonable plausible reaction mechanism for the Prins cyclization of SE with PFCHO is proposed. Notably, it can be seen from the catalytic results of all catalysts that the W-ZnAlMCM-41(75) catalyst has higher 4-PDO selectivity with exceptional catalytic activity than other microporous and mesoporous catalysts.

Selective synthesis of octahydroacridines and diannelated pyridines over zinc-containing mesoporous aluminosilicate molecular sieve catalysts

We demonstrate a very eco-friendly and single-step catalytic method for the highly selective synthesis of 1,2,3,4,5,6,7,8-octahydroacridine (OHA) by the vapour phase aminocyclization of cyclohexanone (Cy[double bond, length as m-dash]O) with a mixture of formaldehyde (HCHO) and ammonia (NH₃) over mesoporous bimetallic ZnAlMCM-41 (ZnAl-41) molecular sieves as efficient catalysts, which were synthesised by a simple basic hydrothermal method. To find optimum parameters for the synthesis of OHA, different reaction parameters, such as temperature, time on stream (TOS), weight hourly space velocity (WHSV), and feed molar ratios of Cy[double bond, length as m-dash]O : HCHO : NH₃, have been extensively studied. The used ZnAl-41 catalysts were treated by washing and calcination to recover the recyclable catalysts which were then reused in these reactions to study their catalytic abilities. To selectively synthesize a variety of pyridine compounds, the active mesoporous catalysts, namely, ZnAl-41(75) and recyclable ZnAl-41(75), with different reaction parameters, were extensively used in the vapour phase aminocyclization reaction with different aldehydes and cycloketones, and produced excellent product selectivities, e.g., 9-alkyl substituted octahydroacridines (9-ASOHAs) and diannelated pyridines (DAPs), with good ketone conversions. In this catalytic reaction, OHA, 9-ASOHAs and DAPs are the main products and are important as starting materials in the preparation of biologically active compounds, drugs, dyes and alkaloids. It is shown by our remarkable catalytic results that the ZnAl-41(75) catalyst, as an environmentally friendly heterogeneous catalyst, has outstanding catalytic activity in the production of OHA, 9-ASOHAs and DAPs by a single-step synthetic method.

Superior performance of metal-organic frameworks over zeolites as solid acid catalysts in the Prins reaction: green synthesis of nopol

The catalytic performance of a set of metal-organic frameworks [CuBTC, FeBTC, MIL-100(Fe), MIL-100(Cr), ZIF-8, MIL-53(Al)] was investigated in the Prins condensation of β-pinene with formaldehyde and compared with the catalytic behavior of conventional aluminosilicate zeolites BEA and FAU and titanosilicate zeolite MFI (TS-1). The activity of the investigated metal-organic frameworks (MOFs) increased with the increasing concentration of accessible Lewis acid sites in the order ZIF-8<MIL-53(Al)<FeBTC<MIL-100(Cr)<MIL-100(Fe). Unwanted β-pinene-like isomerization takes place on the strong Brønsted acid sites of zeolites BEA and FAU, which showed significantly lower selectivity to the target nopol than the MOFs. Its high activity, the preservation of its structure and active sites, and the possibility to use it in at least three catalytic cycles without loss of activity make MIL-100 (Fe) the best performing catalyst of the series for the Prins condensation of β-pinene and paraformaldehyde. Our report exemplifies the advantages of MOFs over zeolites as solid catalysts in liquid-phase reactions for the production of fine chemicals.