Acidic exchange resin

Scheme 2 Triglycerides can be hydrolyzed to give fatty acids and glycerol. This can be catalyzed by solid acid catalysts like zeolites or acid exchanged resins.

Similarly to the hydrolysis of sucrose, acid exchanged resins can be utilized, in one case to give 75% hydrolysis of triglycerides after six hours at 155 °C. It was shown that the Brondsted acid sites catalyze the hydrolysis reaction, which was performed in the liquid phase with continuous steam injection.The same authors reported that polystyrene sulfonic cation-exchange resin, loaded with 13% of the superacid H3M0, gave 74.5% hydrolysis of palm oil at 155 °C in a batch reactor also operated with steam injection. 

Ion exchange resins are also useful for demineralising biochemical preparations such as proteins. Removal of metal ions from protein solutions using polystyrene-based resins, however, may lead to protein denaturation. This difficulty may be avoided by using a weakly acidic cation exchanger such as Bio-Rex 70 (which is a carboxylic acid exchange resin based on a polyacrylic lattice). 

Recently, there have been many new catalysts developed for the hydration of alkenes, although most are more suited for industrial purposes. These catalysts include zeolites such as pentasil,283 mordenite286 and ferrierite,183 as well as those containing heavy metals,287 heteropolyacids288 and sulfonic acid exchange resins.289 It is reported that some of these new catalysts perform as high as 99.6% conversions and 99.4% selectivity, as illustrated in the hydration of propene into 2-propanol (equation 192).290... 

First, the carbonyl group is protected as an acetal under acidic conditions. The most common acid-catalysts are PTSA, CSA, PPTS or, as used in this case, acid exchange resins like Amberlyst 15. An advantage of ion exchange resins is that aqueous work-up is not necessary since the insoluble catalyst can be easily removed by filtration and then recycled. 

Fig. 7A, B. Adsorption kinetics of digoxin on XAD-4 , XAD-7) B acidic exchange resins ( ...

Acidic hydrolysis of MOM ethers is not easy 3% concentrated HQ in aqueous EtOH and trifluoroacetic acid in dichloromethane at room temperature are typical conditions taken from the solo synthesis of Pleuromutilin by Gibbons [Scheme 4.238J.444 At the other extreme are the remarkably easy scission of a phenolic MOM group activated by an adjacent carbonyl in Muxfeldfs synthesis of Terramycin [Scheme 4.239J44-15 and the use of an acidic exchange resin in re-fluxing methanol to cleave a MOM ether and a dioxolane used in a synthesis of 7-deoxypancratistatin [Scheme 4.240].446... 

Exchange Resins. To the dry sulfonic acid exchange resin (l.OOiO.Ol g, 200-400 mesh) was added sodium chloride (0,1M,... 

Sulfonic Acid Exchange Resins from Graft Copolymers... 

The mixture of mercury oxide, boron trifluoride-ether, and trifluoroacetic acid is a particularly effective catalyst for hydration of alkynes 84 mixtures of mercury oxide and boron trifluoride88 and of mercury oxide with sulfuric acid86 have also been used. Addition to acid-sensitive acetylenes is carried out under neutral conditions by means of mercuriacetamide or mercuri-/7-toluenesulfonamide.87 Acid exchange resins loaded with mercury ions can also be used for addition of water to alkynes.88... 

When excess acid is added to the system, H ions (actually hydro-nium ions) compete for adsorption sites (Equation 6) and displace the pesticide cations back into solution as shown in Figure 9 where the pH decreases from 4 to 1 for prometone. Again the process depends upon the pKa of the compound for example, propazine cations are not released until the pH decreases from 2 to 1 (Figure 9). When strongly acid exchange resins were used, the s-triazine cations released were in the hydroxy form, having been hydrolyzed at the resin surfaces (57). 

Another early example of a continuous flow process was disclosed in 1980 by Nakamura and Morikawa [13]. It was demonstrated that recirculating an aqueous DMSO solution of fructose through a bed of strongly acidic exchange resin led to isomerization and dehydration, producing the corresponding furyl aldehyde (Scheme 5). 

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. 

In the DSM proeess, ammoninm sulfate formation is redueed from about 5 kg for eaeh kilogram of eaprolactam to 1.8 kg. Boric acid catalysts can be used for the rearrangement of the oxime to the lactam at 330°C in fixed or fluidized beds, but have not been nsed eonnnercially. Strong acid exchange resins have... 

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