Polymer-bound quaternary ammonium

A series of epoxides has been efficiently converted to the corresponding thiiranes using a polymer-bound quaternary ammonium thiocyanate 38. The polymeric byproduct of this transformation is the supported cyanate.56... 

Full details are now available of a study of polystyrene-supported quaternary ammonium and phosphonium catalysts (80) for triphase catalysis (TC) in a liquid-solid-liquid mode. Long spacer chains between the quaternary centre and the polymer backbone were found to be unnecessary for TC activity, and phosphonium catalysts were more effective than ammonium thus (80 n = 3, A = P) compared favourably with soluble octadecyltributylphosphonium bromide as a PT catalyst for reactions such as halide to halide interconversions. A test reaction, that of potassium acetate with 1-bromo-octane, has been used to examine the TC activity of silica in the solid-solid-liquid mode. Silica impregnated with a cationic surfactant appears to be as effective as alumina (4,163), whereas silica bearing covalently bound quaternary ammonium groups exhibits increased effectiveness. 

Transformations to polymer-bound amino compounds, which are often useful as ligands for metals ions or other free species (67), employ a wide selection of organic reactions. Quaternary ammonium salts result from heating isolated polymer tosylate with tertiary amine they may also be prepared in one step from (hydroxyethyl)polystyrene and toluenesulfonyl chloride and a two-fold excess of amine. 

Secondary amines, such as pyrrolidine, must be alkylated with care too polar a solvent leads to participation of a second nearby polymer-bound alkylant in the formation of a quaternary ammonium salt, along with the desired immobilized trialkyl amine. The exception, as seen above, is diisopropylamine, which refuses to displace tosylate even in the refluxing pure amine, or in hot dimethyl-formamide or other polar solvent, while metal diisopropylamide is notorious as a powerful non-nucleophilic base. However, carboxamide is not difficult to form from (carboxymethyl)polystyrene, again using toluenesulfonyl chloride as condensing agent this can then be reduced to (diisopropyl-ethylaminoethyl)polystyrene, which is of interest as a polymer-bound non-nucleophilic base. ... 

Deliberate production of (vinyl)polystyrene from (toluenesul-foxyethyl)polystyrene or (haloethyl)polystyrenes was best accomplished by quaternization with N,N-dimethylaminoethanol, followed by treatment with base beta-deprotonation is encouraged in the cyclic zwitterionic intermediate. Reaction was faster and cleaner than with other reagents recommended (64, 76, 77) for eliminations, such as alkoxide, diazabicycloundecene or quaternary ammonium hydroxide this new and efficient procedure may find application elsewhere. Hydrometallation or other additions to polymer-bound olefin may prove useful steps in future syntheses by polymer modification. 

Because of their high lipophobic character, compared with other ammonium salts, quaternary ammonium hydroxides are not readily prepared by liquidrliquid anion exchange. Only with quaternary ammonium hydrogen sulphates is it possible to transfer the ammonium hydroxide into the organic phase in any viable degree of concentration [30] and this procedure remains the cheapest and simplest procedure. Other methods include treatment of quaternary ammonium halides with silver oxide [31] and by anion exchange using polymer bound hydroxide [e.g. 32]. 

Polymer-bound catalysts containing both quaternary ammonium centres and oligo-(oxyethylene) links of the type shown in Scheme 1.10 have been synthesized [34]. There is an increase in catalytic activity resulting from a cooperative effect of the two types of catalyst upon nucleophilic reactions, compared to that of simple quaternary ammonium catalysts and crown ethers. 

The simplest C-C bond formation reaction is the nucleophilic displacement of a halide ion from a haloalkane by the cyanide ion. This was one of the first reactions for which the kinetics under phase-transfer catalysed conditions was investigated and patented [l-3] and is widely used [e.g. 4-12], The reaction has been the subject of a large number of patents and it is frequently used as a standard reaction for the assessment of the effectiveness of the catalyst. Although the majority of reactions are conducted under liquiddiquid two-phase conditions, it has also been conducted under solidrliquid two-phase conditions [13] but, as with many other reactions carried out under such conditions, a trace of water is necessary for optimum success. Triphase catalysis [14] and use of the preformed quaternary ammonium cyanide [e.g. 15] have also been applied to the conversion of haloalkanes into the corresponding nitriles. Polymer-bound chloroalkanes react with sodium cyanide and cyanoalkanes under phase-transfer catalytic conditions [16],... 

Polymer-bound reagent. Reaction of a quaternary ammonium anion-exchange resin (Amberlites) wth NaBH4 results in an immobilized borohydride reducing agent (1), which is somewhat less reactive than NaBH4.4... 

Exchange of potassium or sodium iodide with primary alkyl bromides or chlorides is one of the most thoroughly studied phase transfer reactions173,174. It is normally performed in a two-phase aqueous/organic system utilizing a soluble or a polymer-bound PTC. Starks and collaborators have shown175,176 that primary alkyl chlorides or bromides quantitatively exchange with aqueous sodium iodide in the presence of few mol% of a soluble quaternary ammonium PTC at 108 °C within a few hours (secondary alkyl halides normally yield elimination products under these conditions). The mechanism, which is typical of PTC, comprised two consecutive steps ... 

A high enantioselectivity was attained with chiral quaternary ammonium salts in the reaction of p-toluylchloromethylsulfone and ketones in a two-phase system with a catalyst bound to a polymer matrix. ... 

In a series of papers [30-35], Blum and co-workers reported the hydrogenation of alkenes, alkynes, and arenes in the presence of a hydrated ion-pair [0ct3NMe] [RhCl4(H20)n] . The quaternary ammonium tetrachlororhodate also catalyzes HTR of alkynes, alkenes and a,j6-unsaturated carbonyl compounds with polymethylhydrosiloxane [36, 37]. Recently, heterogenized and therefore recyclable quaternary ammonium halometallates, namely glass-encapsulated catalysts [38] and polymer-bound tetrachlororhodate [39], have been described. Both types of the insoluble catalysts effectively promote various processes including the hydrogenation of alkenes and the HTR of a,/9-unsaturated carbonyl compounds [40]. 

The procedure recommended for amination is that of Pepper et al. (13). Polymers containing quarternary, tertiary, secondary, and primary amines were prepared. In all cases, the dried polymer had to be swelled with a solvent such as THF or dioxane. The amine was then added, which reacted with the chloromethyl groups to produce polymer-bound amine groups. All the steps were carried out under an inert atmosphere. Quaternary ammonium salt groups were obtained by reacting 20 g of polymer swollen in dioxane and 100 ml of cold anhydrous trimethylamine at 0°C. The mixture was kept at 0°C for 2 days with stirring under N . The polymer was then washed sequentially with 2N HC1, 0.1N NaOH, 2N HC1, 2N NaCl, and finally deionized water until the effluent was chloride free. 

For example, the cobalt(II) complex for phthalocyanine tetrasodium sulfonate (PcTs) catalyzes the autoxidation of thiols, such as 2-mercaptoethanol (Eq. 1) [4] and 2,6-di(t-butyl)phenol (Eq. 2) [5]. In the first example the substrate and product were water-soluble whereas the second reaction involved an aqueous suspension. In both cases the activity of the Co(PcTs) was enhanced by binding it to an insoluble polymer, e.g., polyvinylamine [4] or a styrene - divinylbenzene copolymer substituted with quaternary ammonium ions [5]. This enhancement of activity was attributed to inhibition of aggregation of the Co(PcTs) which is known to occur in water, by the polymer network. Hence, in the polymeric form more of the Co(PcTs) will exist in an active monomeric form. In Eq. (2) the polymer-bound Co(PcTs) gave the diphenoquinone (1) with 100% selectivity whereas with soluble Co(PcTs) small amounts of the benzoquinone (2) were also formed. Both reactions involve one-electron oxidations by Co(III) followed by dimerization of the intermediate radical (RS or ArO ). 

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