Amberlyst resins

Amberlyst resin 538 Amberlyst-15 (H+) 762 f. ambident electrophile 456, 478 ambident nucleophile 78 amides... 

Experiments were carried out using isotopically labelled methanol (97% 0) and ethanol (98% purchased from MSD Isotopes. Anhydrous isobutanol was purchased from Aldrich Chemical Co., Inc. and contained the natural abimdances of orygen isotopes, i.e. 99.8% and 0.2% O. Nafion-H was obtained fi om C. G. Processing, Inc. and Amberlyst resins were provided by Rohm and Haas. The 2SM-5 zeolite was provided by Mobil Research Development Corp. H-Mordenite, montmorillonite K-10, and silica-alumina 980 were obtained firom Norton, Aldrich, and Davison, respectively. y-AIumina was prepared from Catapal-B fi om Vista. 

Furodithiino[3,4-A5,6-4 ]l,3-dithiole-2-thione 461, a precursor to an interesting TTF derivative, was synthesized in three steps from the l,3-dithiole-2,4,5-trithione oligomer 458 (Scheme 35) <2004JMC2822>. The final cyclization has also been achieved using amberlyst resin in dichloromethane <2003TL1623>. 

Cation-exchange resins are used as catalysts in the produdion of MTBE (methyl tertiary-butyl ether, 2-methoxy-2-methylpropane) and various other oxygenates and, lately, also in the dimerization of isobutene [30]. Other commercial applications of the cation-exchange resins indude dehydration of alcohols, alkylation of phenols, condensation readions, alkene hydration, purification of phenol, ester hydrolysis and other reactions [31]. The major producers of ion-exchange resins are Sybron Chemicals Incorporated [32] (Lewatit resins), Dow Chemical Company [33] (DOWEX resins), Purolite [28] (Purolite resins), and Rohm and Haas Company [27] (Amberlyst resins). 

The acid-catalysed oxidation of a protected S-methyl cysteine, which gives poor diastereoselectivity when oxidized in conventional solvents, shows density-dependent diastereoselectivity as shown in scheme 6.1 [8], Here, tert-butyl hydrogen peroxide (TBHP) is used as the oxidant and the reaction is catalysed by an Amberlyst resin (a solid acid). By tuning the pressure at which this reaction was carried out, almost 100% selectivity to one diastereomer could be achieved (Figure 6.4). 

Bills et al. (1963) used pre-treated Amberlite resin dispersed in hexane to isolate FFAs from milk. Fat was removed from the resin using hexane, absolute ethanol and methanol and the FFAs were esterified prior to analysis by GC. Needs et al. (1983) extracted lipids from milk by using ether and the FFAs were isolated using a strong basic anion exchange resin (Amberlyst 26, BDH Ltd, Poole Dorset, UK). The FFAs were methylated and resolved by GC. McNeill et al. (1986) also used Amberlyst resin to isolate FFAs in conjunction with silicic acid to remove phospholipids. Extracted FFAs were then analyzed by GC. This method was used by McNeill and Connolly (1989) to quantify FFAs in a number of semi-hard cheeses. 

Figure 15.9 shows the esterification of different saturated carboxylic acids with dicyclopentadiene. In all depicted experiments the carboxylic acid/dicyclo— pentadiene molar ratio is about 4 and the amount of catalyst is 10% by weight of dicyclopentadiene at a reaction temperature of 80°C. In this reaction the Nafion/silica composite catalyst is more active compared to the Amberlyst resin, in particular with respect to the amount of the acid groups on the resin. 

Tungstophosphoric acid (HPW) and its Cs and ammonium salts encapsulated into the channels of MCM-41 molecular sieves were useful for the conversion of phenol and acetone to Bisphenol-A. The Cs-HPW/MCM system was more selective to the p,p -isomer than that of zeolites ZSM-5 and H-Y. The Bisphenol-A is useful industrially in the production of polymeric resins. Various other catalysts such as Amberlyst resins were used for this purpose (equation 20). The latter catalyst gave a 90% selectivity for the p,p -isomer . The MCM-41 encapsulated catalyst was shown to have superior thermal characteristics compared to that of the Amberlyst catalyst. 

Dioxolans 146 can be considered as masked carbonyl functionalities, and are cleaved under acidic conditions. In solution, the olefination of a dioxolan-protected ketone would therefore be a two-step transformation consisting of deprotection and olefination. Using polymer-supported adds, e.g., strongly addic Amberlyst resin 147 and polymer-supported phosphonates 135 (Scheme 25), the two-step transformation involving the carbonyl compound 137 as intermediate could be performed simultaneously in one pot (Scheme 27) [113]. The product 136 was isolated by filtration. This procedure would not work as a one-pot sequence in solution because the acidic catalyst would immediately quench the basic phospho-nate resin. 

Scheme 8.37 Immobilized Amberlyst resins as the key purification step avoiding classical purification.

Esterification of Terpenes - Under standard conditions and temperatures from 40 to 100°C limonene and a-pinene were esterificated with acetic and acrylic acid, respectively, over the Amberlyst resin as well as the Nation composite. The conversion is high, however, the reaction is very unselective and no distinct main product is obtained. It seems that both terpenes rearrange to several different products before the final esterification takes place. Using camphene (2) as a starting material, much better results are obtained (Scheme 3). 

The second group consists of reagents supported by ion exchange resins. Amberlyst resins are often used to support anionic nucleophiles, oxidants or reducing agents. Many of these ion exchange resins are commercially available or easily prepared from the chloride form (Scheme... 

One proviso in terms of comparison is that neither furan product appears to be very stable in acidic/wet reaction media, and significant yield variations are seen depending on the rate of removal of the products from the reaction medium. Amberlyst resins have been studied for these transformations with moderate success (yields from 30-67%). Several studies using zeolites... 

Mesoporous silicas modified with acidic groups [e.g. grafted alkyl or aryl sulfonic acids, or containing heteropolyacids or sulfated zirconia within their large pores) have generally provided higher yields, with several systems achieving over 70% yield. Amberlyst resins have been used in these reaction with some success, and the best systems (75% and 100% yield) both required DMSO as solvent, attributed to its ability to remove water and minimise decomposition reactions of the products. ... 

As mentioned earlier, the most important issue in cellulose hydrolysis is sohd acid operation in water. Cellulose is insoluble in water, but soluble in some ionic Hquids such as l-butyl-3-methyHmidazolium chloride (BMIMCl). The use of ionic hquids thus affords a good accessibihty to dissolved cehulose for conversion at active sites of sohd add catalysts. Amberlyst resins in ionic hquids could effectively depolymerize cellulose (microcrystaUine cehulose and a-cehulose) into ceUo-ohgomers under mild reaction conditions (373 K, <5 h) [147]. 

Sufficiently stable catalyst managed to be received sedimentation ammonium paiamolybdate on Amberlyst resin (70 h works) and polyvinyl alcohol (100 h works). Immobilization of hexacarbonyl molybdenum on ion exchange resin the authors [28] have presented by the following (Scheme 4) ... 

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