Acids, carboxylic heteropoly

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. 

Solid heteropoly compounds are suitable oxidation catalysts for various reactions such as dehydrogenation of O- and N-containing compounds (aldehydes, carboxylic acids, ketones, nitriles, and alcohols) as well as oxidation of aldehydes. Heteropoly catalysts are inferior to Mo-Bi oxide-based catalysts for the allylic oxidation of olefins, but they are much better than these for oxidation of methacrolein (5). Mo-V mixed-oxide catalysts used commercially for the oxidation of acrolein are not good catalysts for methacrolein oxidation. The presence of an a-methyl group in methacrolein makes the oxidation difficult (12). The oxidation of lower paraffins such as propane, butanes, and pentanes has been attempted (324). Typical oxidation reactions are listed in Table XXXI and described in more detail in the following sections. 

Heteropoly acids can also act as oxidation catalysts both in the vapor and liquid phase. In the vapor phase they are effective dehydrogenation catalysts for saturated carboxylic acids and aldehydes readily converting isobutyric acid to methacrylic acid (Eqn. 10.19). Methacrylic acid is produced in 70% selectivity at 72% conversion over (NH4)3PMoi204q at 260°C. This reaction takes place only when there is a substituent a to the carbonyl group of the reactant. 

There have been several attempts to obtain oxygenated products from lower alkanes (C2 - C5) by using heteropoly catalysts. It has been reported that the hydrogen form of H3PM012O40 catalyzes the oxidation of lower alkanes to aldehydes and carboxylic acids [8] and that the substitution of for Mo modified the catalytic activity and selectivity [1, 9 - 12]. 

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. 

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... 

It is concluded that acidic oxides that possess a certain extent of basic property are favorable for promoting the condensation reaction a more basic property is required than in the case of the reaction with carboxylic acid. The acidic oxides such as H-zeolite, Si-Al, B, Mo-P, and W-P oxides, and heteropoly compounds are lacking in a basic property as catalyst for the reaction. On the other hand, alkali and alkaline earth metal oxides and amphoteric oxides combined with K2O are lacking in acidic property. 

Reports of the photosensitivity of polyoxometalates date to at least 1916 [24]. Early work on the photochromism and photochemistry of alkylammonium polymolybdates by Yamase and co-workers [25-30] and the photooxidation of alcohols by heteropoly acids by Papaconstantinou and coworkers [31] gave some indication of the potential of such chemistry. Papaconstantinou reported that alcohols and carboxylic acids are photooxidized under aerobic conditions by heteropoly acids in water with clean transformation of the primary and secondary alcohols to the corresponding carbonyl compounds, equation (1) [32]. The products were not identified for the other substrates. The rate law was reported for a couple... 

Typic2il examples of acid-catalysis of heteropoly compounds are as follows Dehydration of methanol, - > ethanol, - - propanol - - - -"- "- > and butanol, conversion of metanol or dimethyl ether to hydrocarbons, etheration to form methyl /-butyl ether, esterifications of acetic acid by ethanol and pentanol, decomposition of carboxylic acid and formic acid, alkylation of benzene by ethylene and isomerization of butene, o-xylene and hexane. ... 

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. 

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