Poly catalyst recovery

We have utilized somewhat less-effective optional approaches to copolymer purification with attendant catalyst recovery. One of these methods involved the replacement of the f-butyl substituents on the 5-position of the phenolate ligands with poly(isobutylene) (PIB) groups, as illustrated in Fig. 14 [39]. Importantly, this chromium(III) catalyst exhibited nearly identical activity as its 3,5-di-t-butyl analog for the copolymerization of cyclohexene oxide and carbon dioxide. The PIB substituents on the (salen)CrCl catalysts provide high solubility in heptanes once the copolymer is separated from the metal center by a weak acid. 

There have been many efforts to commercialize 2,6-dicarboxynaphthalene for the preparation of poly(ethylene-2,6-naphthalate) due to its favorable thermoplastic properties compared with PET. Therefore, there are numerous patents in which 2,6-alkyl-substituted (alkyl = methyl, ethyl, isopropyl) naphthalenes are oxidized to the corresponding aromatic di-acids, applying mostly Co/Mn/Br catalysts with various co-catalysts such as Zr or Pd in acetic acid as the solvent. The major byproduct is formed by the oxidation of the naphthalene ring to give trimellitic acid (TMA) [5a, 8]. Sumikin Chemical has developed a method to prepare 2,6-naphtha-lenedicarboxylic acid by oxidation of 2,6-diisopropylnaphthalene (2,6-DIPN) in the liquid phase with air in a 500 tpy plant. Sumikin uses a newly developed catalyst based on Co/Mn with an addition of a few ppm of Pd giving advantages such as yields higher than 90 %, suppression of TMA production to around 1 %, and thus better catalyst recovery, and reduced consumption of acetic acid. 

A variant on this theme is to attach a transition-metal complex of a smart polymer, the solubility of which can be dramatically influenced by a change in a physical parameter, e.g., temperature [23] (cf. Sections 4.6 and 4.7). Catalyst recovery can be achieved by simply lowering or raising the temperature. For example, block copolymers of ethylene oxide and propene oxide show an inverse dependence of solubility on temperature in water [24]. Karakhanov et al. [25] prepared water-soluble polymeric ligands comprising bipyridyl (bipy) or acetylacetonate (acac) moieties covalently attached to poly(ethylene glycol)s (PEGs) or ethylene oxide/propene oxide block copolymers 9 and 10. 

Polyethylene oxide) and poly(N-alkylacrylamide)s are known to undergo a temperature-dependent phase change whereupon they separate from an aqueous phase at increased temperatures [14]. This inverse temperature dependence, i.e., the occurrence of a lower critical solution temperature, can be related to an entropi-cally favorable decrease in hydrogen bonding between water and the polymer with increasing temperature. In order to exploit this physical property for catalyst recovery, Bergbreiter et al. attached phosphines covalently to commercially available PEO or PEO-b-PPO-b-PEO block copolymers [Schemes 1 and 2 PPO = polypropylene oxide)] [9a],... 

The utilization of polar polymers and novel N-alkyl-4-(N, N -dialklamino)pyridinium sedts as stable phase transfer catalysts for nucleophilic aromatic substitution are reported. Polar polymers such as poly (ethylene glycol) or polyvinylpyrrolidone are thermally stable, but provide only slow rates. The dialkylaminopyridininium salts are very active catalysts, and are up to 100 times more stable than tetrabutylammonium bromide, allowing recovery and reuse of catalyst. The utilization of b is-dialkylaminopypridinium salts for phase-transfer catalyzed nucleophilic substitution by bisphenoxides leads to enhanced rates, and the requirement of less catalyst. Experimental details are provided. 

The homogeneous chiral phosphine/DPEN-Ru catalyst can be immobilized by use of polymer-bound phosphines such as polystyrene-anchored BINAP (APB-BINAP) [57, 98], Poly-Nap [99], and poly(BINOL-BINAP) [100], poly(BINAP) [101]. These complexes hydrogenate T-acetonaphthone and acetophenone with S/C of 1000-10 000 under 8 10 atm H2 to give the corresponding secondary alcohols in 84-98% e.e. The recovered complexes are repeatedly used without significant loss of reactivity and enantioselectivity. Immobilization allows the easy separation of catalyst from reaction mixture, recovery, and reuse. These advantages attract much attention in combinatorial synthesis. 

The compound was used as a catalyst for the hydrogenation of olefins. No rhodium was lost. This type of polymer shows inverse temperature solubility. When the temperature was raised, the polymeric catalyst separated from solution for easy recovery and reuse. This type of smart catalyst will separate from solution if the reaction is too exothermic. The catalytic activity ceases until the reaction cools down and the catalyst redissolves. Poly (A i sop ropy lacrylamide) also shows inverse temperature solubility in water. By varying the polymers and copolymers used, the temperature of phase separation could be varied (e.g., from 25 to 80°C).214 A terpolymer of 2-isopropenylan-thraquinone, A-isopropylacrylamide, and acrylamide has been used in the preparation of hydrogen peroxide instead of 2-ethylanthraquinone.215 The polymer separates from solution when the temperature exceeds 33 C to allow re-... 

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