The dynamic kinetic resolution of azlactones towards amide formation and the hydrolysis of poly(ethylene terephthalate) by terephthalate-based ionic liquids

Abstract

Solid-liquid phase transfer catalysis was used in the enantioselective ring opening of tetrachlorophthalic anhydride-derived azlactones to provide bis-amide products using dynamic kinetic resolution. Using cinchona alkaloid-based phase-transfer catalysts, benzylation and alkylation of the quinuclidine unit afforded a considerable increase in the stereoselective formation of piperidine-amides and morpholine-amides in moderate enantiomeric excess (up to 64% ee). However, this system proved to be restrictive with regards to catalyst scope, since complex cinchona alkaloid catalysts are relatively insoluble in toluene. A mode of homogenous catalysis using ion-pairs was also examined for the same process. These ion-pair catalysts had many potential benefits over phase-transfer catalysts, such as: higher rate of reaction, a wide variety of usable solvents and the certainty of a controlled amount of active catalyst in solution. Overall, this system gave a lower degree of stereocontrol (up to 50% ee)but the rate of catalytic formation of the para-nitrophenolate ester intermediate was higher. A set of novel betaine catalysts were examined in the dynamic kinetic resolution of azlactones. This system allowed for the rapid introduction of novel nucleophiles without the necessity for isolation of intermediates. The addition of 1,1�-binaphthyl-2,2�-diol-derivatives in catalytic quantities along with the betaine catalyst increased the enantiocontrol facilitated by the system considerably (up to 77% ee, 83% ee at �50�C). A series of alkyl phosphonium and ammonium phase-transfer catalysts were assayed in the neutral hydrolysis of poly(ethylene terephthalate) to form terephthalic acid. The best-performing phase-transfer catalysts were used in tandem with the conjugate base of the product(i.e. disodium terephthalate) to attain high yields of terephthalic acid (up to 71%). A later innovation to form phosphoniumterephthalate ionic liquid catalysts proved to be worthwhile and the resulting yield of terephthalic acid increased considerably in the presence of the catalyst at an extremely low loading (up to 97% yield at 0.5 mol% of catalyst loading). The relative yield of the product was relatively independent of the particle size associated with the starting material. To expand on previously performed work by Dr. Lee Anderson, a set of experiments were conducted using half the concentration of sodium hydroxide in the alkaline hydrolysis of poly(ethylene terephthalate). Using the optimised conditions found by Dr. Anderson,tetrapentyl ammoniumchloride facilitated the consumption of poly(ethylene terephthalate) to yield terephthalic acid (up to 81% yield)