Acylations heteropoly acids

In this paper we report the use of supported heteropoly acid (silicotungstic acid) and supported phosphoric acid catalysts for the acylation of industrially relevant aromatic feedstocks with acid anhydrides in the synthesis of aromatic ketones. In particular, we describe the acylation of thioanisole 1 with iso-butyric anhydride 2 to form 4-methyl thiobutyrophenone 3. The acylation of thioanisole with acetic anhydride has been reported in which a series of zeolites were used as catalysts. Zeolite H-beta was reported to have the highest activity of the zeolites studied (41 mol % conversion, 150°C) (2). 

Supported Heteropoly Acid Catalysts for Friedel-Crafts Acylation 347... 

When H3PM012O40 was used to catalyze acylation reactions some of the acid dissolved and the reactions were partially promoted by the acid in solution. The H4SiW]204o and H3PW12O40 catalysts, however, did not dissolve under the reaction conditions and were, therefore, effective promoters for liquid phase Freidel-Crafts acylation reactions.Supported and bulk heteropoly acids have also been used to promote vapor phase Freidel-Crafts alkylations and esterifications.. ... 

Kozhevnikov, I. V. Friedel-Crafts acylation and related reactions catalyzed by heteropoly acids. Appl. Cat. A 2003, 256, 3-18. 

In this paper we would like to communicate the details of our investigation in the acylation of 2-MON with acetic anhydride using different solid acid catalysts such as zeolites, clays, pillared clays, unsupported heteropoly acids (HPA) and HPA/KIO, sulphated zirconia euid ion-exchange resins. 

Maximum effort has been directed toward the use of solid acid catalysts. In fact, heterogeneous catalysts can be easily separated from the reaction mixture and reused they are generally not corrosive and do not produce problematic side products. Different classes of materials have been studied and utilized as heterogeneous catalysts for Friedel-Crafts acylations these include zeolites (acid treated), metal oxides, and heteropoly acids already utilized in hydrocarbon reactions. Moreover, the application of clays, perfluorinated resinsulfonic acids, and supported (fluoro) sulfonic acids, mainly exploited in the production of fine chemicals, are the subject of intensive studies in this area. 

The use of HPAs and multicomponenf polyoxometalates as catalysts in liquid-phase reactions was reviewed by Kozhevnikov. Moreover, an interesting minireview was published concerning the Friedel-Crafts acylation of arenes and the Fries rearrangement catalyzed by HPA-based solid acids. The results show that HPA-based solid acids, including bulk and supported heteropoly acids as well as heteropoly acid salts, are efficient and environmentally friendly catalysis for all reacfions analyzed. 

Kaur, J., Griffin, K., Harrison, B., and Kozhevnikov, 1. V. 2002. Friedel-Crafts acylation catalysed by heteropoly acids. J. Catal. 208 448 55. 

Tagawa, T., Amemiya, J., and Goto, S. 2004. Chlorine-free Friedel-Crafts acylation of benzene with benzoic anhydride on insoluble heteropoly acid catalyst. Appl. Catal. A Gen. 257 19-23. 

Friedel-Crafts acylation and Fries rearrangement catalysed by heteropoly acids... 

Izumi et al. pioneered the use of heteropoly acids as catalysts for aromatic acylation. Silica-supported acids H4[SiWi204o] and H3[PWi204o] were found to effectively catalyse the acylation of p-xylene with benzoyl chloride. Cs2.5Ho.5[PWi204o] showed high efficiency in the acylation of activated arenes, such as p-xylene, anisole, mesitylene, etc., by acetic and benzoic anhydrides and acyl chlorides. This catalyst provided higher yields of acylated arenes than the parent acid H3[PWi204o], the latter being partly soluble in the reaction mixture. ... 

The aromatic acylation with carboxylic acids (Eq. 3) instead of acid anhydrides and acyl chlorides has attracted interest, because it is an environmentally benign reaction, resulting in the formation of water as the only by-product. It has been attempted with zeolites and clays as catalysts. Heteropoly acids have proved to be more active catalysts for this... 

Cs" salts catalyse the acylation of toluene, p-xylene and m-xylene with crotonic acid. Some alkylation of aromatic compounds with crotonic acid also takes place. Heteropoly acid was found to be more active than zeolites HY and H-Beta in the acylation. 

Supported heteropoly acids have been shown to be active catalysts for the acylation of aromatic compounds using organic acids as the acylating agents. Their activity being far superior to Ce and La exchanged zeolites, that have previously been reported to be active for these reactions. ... 

The supported heteropoly acid catalysts offer a significant improvement in terms of catalytic activity compared to ion exchanged zeolites. However, there is the need for further improvements before they could be considered commercially viable for acylation of non activated aromatic rings. 

Lan, K., Fen, S., Shan, Z.X. 2007. Synthesis of aromatic cycloketones via intramolecular Friedel-Crafts acylation catalyzed by heteropoly acids. Australian Journal of Chemistry 60(l) 80-82. 

Heteropoly acid, aluminum dodecatungstophosphate AIPW12O40, was found to be an effective catalyst for the Friedel-Crafts acylations using carboxylic acid, acetic anhydride, and benzoyl chloride (Scheme 6.9) [11]. Nonhydroscopic nature and relatively high catalytic activity of this heteropoly acid, for example, as compared with Sc(OTf)3 or In(OTf)3, should be noted. Reactions were conducted under solvent-free conditions. 

Cs2.5 for the acylation. Anisole and /j-xylene are acylated with benzoic anhydride and acetic anhydride in the presence of Cs2.5 without the dissolution of this catalyst. Carboxylic acids are much less reactive as acylating agents than the corresponding anhydrides because of the liberation of water. But when the water is removed, the acylation proceeds smoothly 214). Although the reaction of benzene with acetic acid is attractive in prospect, there is no report of heteropoly compounds as catalysts for this reaction. 

Kaur, J. and Kozhevnikov, I. V. 2002. Efficient acylation of toluene and anisole with aliphatic carboxylic acids catalysed by heteropoly salt CsjgHQ 5PW12O40. Chem. Commun. 2508-2509. 

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