Acidic ion exchange resins

Polymerization. Paraldehyde, 2,4,6-trimethyl-1,3-5-trioxane [123-63-7] a cycHc trimer of acetaldehyde, is formed when a mineral acid, such as sulfuric, phosphoric, or hydrochloric acid, is added to acetaldehyde (45). Paraldehyde can also be formed continuously by feeding Hquid acetaldehyde at 15—20°C over an acid ion-exchange resin (46). Depolymerization of paraldehyde occurs in the presence of acid catalysts (47) after neutralization with sodium acetate, acetaldehyde and paraldehyde are recovered by distillation. Paraldehyde is a colorless Hquid, boiling at 125.35°C at 101 kPa (1 atm). 

Unsaturated aldehydes undergo a similar reaction in the presence of strongly acid ion-exchange resins to produce alkenyUdene diacetates. Thus acrolein [107-02-8] or methacrolein [78-85-3] react with equimolar amounts of anhydride at —10°C to give high yields of the -diacetates from acetic anhydride, useful for soap fragrances. 

The ratio of reactants had to be controlled very closely to suppress these impurities. Recovery of the acrylamide product from the acid process was the most expensive and difficult part of the process. Large scale production depended on two different methods. If soHd crystalline monomer was desired, the acrylamide sulfate was neutralized with ammonia to yield ammonium sulfate. The acrylamide crystallized on cooling, leaving ammonium sulfate, which had to be disposed of in some way. The second method of purification involved ion exclusion (68), which utilized a sulfonic acid ion-exchange resin and produced a dilute solution of acrylamide in water. A dilute sulfuric acid waste stream was again produced, and, in either case, the waste stream represented a... 

Methyl /-Butyl Ether. MTBE is produced by reaction of isobutene and methanol on acid ion-exchange resins. The supply of isobutene, obtained from hydrocarbon cracking units or by dehydration of tert-huty alcohol, is limited relative to that of methanol. The cost to produce MTBE from by-product isobutene has been estimated to be between 0.13 to 0.16/L ( 0.50—0.60/gal) (90). Direct production of isobutene by dehydrogenation of isobutane or isomerization of mixed butenes are expensive processes that have seen less commercial use in the United States. 

The catalysts used in the industrial alkylation processes are strong Hquid acids, either sulfuric acid [7664-93-9] (H2SO or hydrofluoric acid [7664-39-3] (HE). Other strong acids have been shown to be capable of alkylation in the laboratory but have not been used commercially. Aluminum chloride [7446-70-0] (AlCl ) is suitable for the alkylation of isobutane with ethylene (12). Super acids, such as trifluoromethanesulfonic acid [1493-13-6] also produce alkylate (13). SoHd strong acid catalysts, such as Y-type zeoHte or BE -promoted acidic ion-exchange resin, have also been investigated (14—16). 

ButylatedPhenols and Cresols. Butylated phenols and cresols, used primarily as oxidation inhibitors and chain terrninators, are manufactured by direct alkylation of the phenol using a wide variety of conditions and acid catalysts, including sulfuric acid, -toluenesulfonic acid, and sulfonic acid ion-exchange resins (110,111). By use of a small amount of catalyst and short residence times, the first-formed, ortho-alkylated products can be made to predominate. Eor the preparation of the 2,6-substituted products, aluminum phenoxides generated in situ from the phenol being alkylated are used as catalyst. Reaction conditions are controlled to minimise formation of the thermodynamically favored 4-substituted products (see Alkylphenols). The most commonly used is -/ fZ-butylphenol [98-54-4] for manufacture of phenoHc resins. The tert-huty group leaves only two rather than three active sites for condensation with formaldehyde and thus modifies the characteristics of the resin. 

Methyl tert-Butyl Ether (MTBE). Methyl tert-hutyi ether [1634-04-4] is made by the etherification of isobutylane with methanol, and there are six commercially proven technologies available. These technologies have been developed by Arco, IFF, CDTECH, Phillips, Snamprogetti, and Hbls (hcensed jointly with UOP). The catalyst in all cases is an acidic ion-exchange resin. The United States has been showing considerable interest in this product. Western Europe has been manufacturing it since 1973 (ANIC in Italy and Huls in Germany). Production of MTBE in Western Europe exceeded 600,000 tons in 1990. 

A process to convert butenes to acetic acid has been developed by Farbenfabriken Bayer AG (137) and could be of particular interest to Europe and Japan where butylenes have only fuel value. In this process a butane—butylene stream from which butadiene and isobutylene have been removed reacts with acetic acid in the presence of acid ion-exchange resin at 100—120°C and 1500—2000 kPa (about 15—20 atm) (see Acetic acid and its derivatives, acetic acid). Both butenes react to yield j -butyl acetate which is then oxidized at about 200°C and 6 MPa (about 60 atm) without catalyst to yield acetic acid. 

Catalysts used are usually acids such as sulfuric acid, -toluenesulfonic acid, sulfonic acid ion-exchange resins, and others. The water from the reaction of the citric acid and the alcohol is continuously removed as the azeotrope until no more water is formed. At this point, the reaction is usually complete and the solvent and any excess alcohol is distilled off under mild vacuum. The catalyst is neutralized using carbonate or sodium hydroxide, leaving a cmde product. If a pure product is desired, the ester can be distilled under high vacuum. 

In order to produce high yields of ester in this manner it is necessary to remove the by-product ammonia (or amine) either by heating or combining with mineral acid, eg, H2SO4 or HCI. Recent work has shown that acidic ion-exchange resins can be used in place of mineral acids for converting sensitive unsubstituted amides (76). The stmctural relationships involved in esterification of amides are shown in Table 2 (77). 

Commercially, sulfonic acid ion-exchange resins are used in fixed-bed reactors to make these tertiary alkyl ethers (14). Since the reaction is very selective to tertiary olefins and also reversible, a two-step procedure is also used to recover commercially pure tertiary olefins from mixed olefin process streams. The corresponding tertiary alkyl ether is produced in the olefin mixture and then easily separated from the unreacted olefins by simple fractionation. The reaction is then reversed in a second step to make a commercially pure tertiary olefin, usually isobutylene or isoamylene. 

Methyl-te/t-butyl ether, a gasoline additive, is made from isobutene and methanol with distillation in a bed of acidic ion-exchange resin catalyst. The MTBE goes to the bottom with purity above 99 percent and unreacted materials overhead. 

A primary amine, protected by reaction of the amine with cyclopentadiene and formaldehyde (H2O, rt, 3 h), is cleaved by trapping cyclopentadiene with A -methylmaleimide (H2O, 2.5 h, 23-50°, 61-97% yield), CUSO4 (EtOH or MeOH, 70°, 74-99%), or Bio-Rad AG 50W-X2 acid ion-exchange resin, 82-98% yield. ... 

As a catalyst sulfuric acid is most often used phosphoric acid, boron trifluoride or an acidic ion exchange resin have also found application. 1,1-disubstituted alkenes are especially suitable substrates, since these are converted to relatively stable tertiary carbenium ion species upon protonation. o ,/3-unsaturated carbonyl compounds do not react as olefinic component. 

Propargylsilanes can also be employed in the Sakurai reaction. For example the enone 6, containing a propargylsilane side chain, undergoes an intramolecular Sakurai reaction, catalyzed by an acidic ion-exchange resin—e.g. Amberlyst-15—to give stereoselectively the bicyclic product 7 in good yield ... 

Ethyl-ter-butyl ether (ETBE) is also produced by the reaction of ethanol and isobutylene under similar conditions with a heterogeneous acidic ion-exchange resin catalyst (similar to that with MTBE) ... 

Using sulphonic acid ion-exchange resins in ether solvent, selective removal of the trimethylsilyl group from oxygen in bistrimethylsilylated terminal alkynols can be achieved. This method is particularly suitable for low-molecular-weight compounds, where water solubility would make efficient extraction from an aqueous layer difficult. 

The polymer may behave as a weak acid ion exchange resin. Branched copolymers have also been proposed as an approach to achieving "smoother" release patterns for polypeptide systems (40). 

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