A catalytic synthesis of calix[4]pyrroles and N-confused calix[4]pyrroles by reaction of dialkyl or cycloalkyl ketones with pyrrole was performed using Preyssler, sodium30-tungsto pentaphosphate, [NaP5W30O110]14- and Wells-Dawson heteropolyacids as acidic catalysts. The process occurred under mild, eco-friendly and environmental friendly conditions and as a reusable, green catalyst at room temperature for 6 hours. The results showed that the yield for this synthesis is excellent with the use of Preyssler and Wells-Dawson type tungstophosphoric heteropolyacid, H6[P2W18O62], catalysts. The synthesis reaction of calix[4]pyrroles and N-confused calix[4]pyrroles was developed using different solvents and the best yields were obtained in chloroform.
The Preyssler, Wells-Dowson and Keggin heteropolyacids are efficient and eco-friendly solid acid catalysts for the acylation of electron-rich aromatic compounds with acid anhydrides. The performance of different forms of heteropolyacids was compared. In all the cases, the best results were obtained using the Preyssler heteropolyacid as the catalyst. In the presence of 25 mol% (with respect to H+ equivalency) Preyssler catalyst, highly para-selective acetylation of anisole occurs using two equivalents of acetic anhydride, in 15 min at room temperature. The isolated yield of the p-methoxyacetophenone product is 98%.
A simple, clean and environmentally benign route to the enantioselective synthesis of (S)-2-(6-methoxynaphtalen-2-yl)propanoic acid, (S)-Naproxen 3 is described by using Preyssler heteropolyacid, H14[NaP5W30O110], as a green and reusable catalyst in water and in the presence of 1-(6-methoxynaphthalen-2-yl)propan-1-one 1, D-mannitol 2. The products were obtained in very good yields.
An efficient method for the preparation of 6,7-dimethoxyisatin and its derivatives was developed with good yield by using Preyssler-type heteropolyacid (HPA) as acid catalyst under green conditions. The comparison between Keggin type heteropolyacids, H3[PW12O40], H4[SiW12O40] and H4[SiMo12O40], H3[PMo12O40] and mineral acids with Preyssler's anion shows that the latter possess better catalytical activity than the other heteropolyacids and no degradation of the structure was observed.
Synthesis of acetaminophen at green condition and room temperature in the presence of the Preyssler type heteropolyacids has been investigated in order to contribute toward clean technology, which is the most important need of the society. All of the catalysts are recyclable and reusable.
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