Fries Nafion

The availability of Nafion on silica has not only lowered the cost of the resin but also has made it versatile (Sun et al., 1997 Harmer et al., 1998). A number of industrially important reactions have been attempted, with considerable success, with these catalysts. Consider the Fries rearrangement of phenyl acetate to p-acetyl phenol (/t-hydroxy acetophenone). This has been accomplished by Hoelderich and co-workers (Heidekum, 1998). In the ca.se of alkylation of benzene with benzyl alcohol, Amberlyst-15 and p-toluene sulphonic acid are ineffective and Nafion on silica works well at 80 °C. 

Fries rearrangement—that is, the transformation of phenolic esters to isomeric hydroxyphenyl ketones—is related to Friedel-Crafts acylations.392,393 Olah et al.394 have found a convenient way to perform the Fries rearrangement of a variety of substituted phenolic esters in the presence of Nafion-H in nitrobenzene as solvent [Eq. (5.153)]. A catalytic amount of Nafion-H is satisfactory, and the catalyst can be recycled. In contrast, Nafion-silica nanocomposites, in general, exhibit low activities in the Fries rearrangement of phenyl acetate to yield isomeric hydroxyacetophe-nones.239,395 In a recent study, BF3-H20 was found to be highly efficient under mild conditions (80°C, 1 h) to transform phenolic esters of aliphatic and aromatic carboxylic acids to ketones (71-99% yields).396 In most cases the para-hydroxyphenyl isomers are formed with high (up to 94%) selectivity. 

Figure 32 Phenyl phenylacetates examined for photo-Fries rearrangement within zeolites and Nafion membranes.

Nafion-silica composites were compared with zeolites such as H-Beta, H-USY and H-ZSM-5, in the Fries rearrangement of phenyl acetate (see earlier). The highest conversion was observed with H-Beta [88]. 

Fry has used a similar system for the enzymatic reduction of pyruvate to L-lactate. In this case, the one-electron transfer redox catalyst, methyl viologen, and the lipoamide dehydrogenase are coimmobilized within a Nafion cation-exchange layer on the surface of a reticulated vitreous carbon electrode. As production enzyme, L-lactate dehydrogenase (LDH) was employed [48], which was later stabilized considerably in the form of cross-... 

Heating a phenol ester in the presence of Nafion-H gave good yields of the hydroxy phenyl ketone.This Fries rearrangement gave a mixture of the ortho and para hydroxy compounds in a 1 2-2.5 ratio (Eqn. 22.19). A study of the rearrangement of phenyl benzoate over a number of solid acid catalysts indicated that Nafion-H was more effective than montmorilIonite or amorphous aluminum silicate for this reaction. " ... 

Olah, G. A., Arvanaghi, M., Krishnamurthy, V. V. Heterogeneous catalysis by solid superacids. 17. Polymeric perfluorinated resin sulfonic acid (Nafion-H) catalyzed Fries rearrangement of aryl esters. J. Org. Chem. 1983,48, 3359-3360. 

Olah and coworkers have shown that Nafion-H, a perfluorinated resinsulfonic acid, acts as an efficient catalyst for the Fries rearrangement of aryl benzoates. For example, meta-chlorophenyl benzoate undergoes Fries rearrangement in the presence of Nafion-H... 

Nafion-H-silica nanocomposite (13% Nafion-H) catalyzed Fries rearrangement of phenyl acetate at high temperatures gives phenol, ort/zo-acetylphenol, para-acetylphenol and para-acetylphenyl acetate in a ratio of 45 5 24.5 25.5 (equation 69). The rearrangement in the presence of added phenol gives exclusively the para-acetylphenol, showing that the Fries rearrangement under these conditions is intermolecular in nature. ... 

The activity of Nafion composites of greater surface area was investigated in different organic reactions, e. g. Friedel-Crafts alkylation and acylation, the Fries rearrangement, the dimerization of a-methylstyrene, esterification reactions, and isobutane alkylation. 

The Fries rearrangement of phenyl acetate to o- and p-hydroxyacetophenone is also a very valuable reaction in the pharmaceutical industry. Nafion-silica composites containing 13 and 40% (w/w) Nafion were also studied in this reaction and compared with pure Nafion and with zeolites such as HBEA, HUSY, HZSM5, and HY. The Nafion-silica composites resulted in better conversion than the pure analog, but in this study the BEA zeolite resulted in the highest conversion and a relatively high selectivity. Unfortunately, no reactions rates were given so no conclusions can be drawn about the intrinsic activity of the different catalysts [17]. 

Silica composite materials constituted by Nafion entrapped in a highly porous silica matrix (13% and 40% Nafion) are utilized as catalysts for the Fries rearrangement of PA. The conversions of the reactions performed in cumene are 10% and 16%, respectively, and the selectivity with respect to para- and ortho-HAF ranges from 20% up to 56%, phenol being the main side product accompanied by deposition of carbonaceous materials these... 

Table 5.15 Nafion-promoted Fries rearrangement of PBs in nitrobenzene at reflux for 12 h...

Heidekum, A., Harmer, M. A., and Hoelderich, W. F. 1998. Highly selective Fries rearrangement over zeolites and Nafion in silica composite catalysts a comparison. /. Catal. 176 260-263. 

Chamoumi and Brunei investigated the liquid phase rearrangement of 1,2-epoxyalkenes over various zeolites [96]. H-Offretite gave the best selectivity for the formation of octanal in the reaction with 1,2-epoxyoctane. The esterification of resorcinol with benzoic acid derivatives is followed by a Fries rearrangement to give benzophenones [97]. The reaction is catalysed by Amberlyst-15 ion-exchange resin or Nafion-17 acidic exchange resin. 2,4-Dihydroxybenzophenone has been synthesised in 88% yield by this method. 

M.C. Laufer et al. published the synthesis of hymecromone from resorcinol and EAA in toluene using a nanocatalyst, namely, Nafion resin/silica nanocomposite materials with yield between 81% and 96% (03MI315). The reaction of resorcinol with acrylic acid gives 7-hydroxy-3,4-dihydrocoumarin 36 and [l,2-k5,4-l>]dipyran-2,8-dione 37. The mechanism involves esterification followed by ring closure that ring closure is faster than the Fries rearrangement. Also in this reaction, SAC 40 and SAC 80 led to the best results (Scheme 23) (03MI315). 

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