Potassium superoxide carboxylic acids

By employing anionic techniques, alkyl methacrylate containing block copolymer systems have been synthesized with controlled compositions, predictable molecular weights and narrow molecular weight distributions. Subsequent hydrolysis of the ester functionality to the metal carboxylate or carboxylic acid can be achieved either by potassium superoxide or the acid catalyzed hydrolysis of t-butyl methacrylate blocks. The presence of acid and ion groups has a profound effect on the solution and bulk mechanical behavior of the derived systems. The synthesis and characterization of various substituted styrene and all-acrylic block copolymer precursors with alkyl methacrylates will be discussed. 

Although the potassium superoxide route can be universally applied to various alkyl methacrylates, it is experimentally more difficult than simple acid hydrolysis. In addition, limited yields do not permit well-defined hydrophobic-hydrophilic blocks. On the other hand, acid catalyzed hydrolysis is limited to only a few esters such as TBMA, but yields of carboxylate are quantitative. Hydrolysis attempts of poly(methyl methacrylate) (PMMA) and poly(isopropyl methacrylate) (PIPMA) do not yield an observable amount of conversion to the carboxylic acid under the established conditions for poly(t-butyl methacrylate) (PTBMA). This allows for selective hydrolysis of all-acrylic block copolymers. 

Two alternatives to conventional acid/base hydrolyses for cleaving esters are Sn2 displacement of the carboxylate group by reactive nucleophiles and nucleophilic attack at the carbonyl carbon. In this latter context we investigated the reaction of S-b-MM with potassium trimethylsilanolate, a so-called potassium superoxide equivalent (15). One advantage that this reagent has over potassium... 

Oxidative cieavage. a-Keto, a-hydroxy, and a-halo ketones, esters, and carboxylic acids are cleaved in fair to high yield by excess potassium superoxide solubilized in benzene with 18-crown-6 (25°, 12 hours). The reaction resembles the behavior of some dioxygenases in several aspects. 

The crown catalyzed reaction of potassium superoxide in dry benzene with a-keto-, a-hydroxy-, and a-haloketones, esters and carboxylic acids yields carboxylic acids as formulated in equation 8.9 [12]. The observation that 1-hydroxy-1-carboxy-cycloheptane and a-cyclohexylmandelic acid fail to react under conditions which convert related substrates to acids suggests that a hydrogen alpha to the reactive site is a requisite (see Table 8.5). 

A variety of chalcones are cleaved by potassium superoxide [13] according to equation 8.10 to yield a mixture of two, and sometimes three, carboxylic acids. Labeling experiments indicate that the superoxide transfers an electron to the enone followed by reaction of the resulting radical with molecular oxygen. An overall mechanism has been postulated for this reaction [13]. The results of a number of chalcone cleavage reactions are presented in Table 8.6. 

Potassium superoxide in the presence of 18-crown-6 has been shown to cleave 1,2-diones oxidatively, as well as a-hydroxy- and a-halogeno-ketones, -esters, and -carboxylic acids, in fair to excellent yields. 

Ketones are oxidatively cleaved in 87—96% yield using potassium superoxide (KO2) and a phase-transfer catalyst. The oxidative cleavage of a-ketols, R COC(OH)R R, has been found to proceed smoothly with alkaline hydrogen peroxide in aqueous methanol, affording high yields of ketones R COR and carboxylic acids R C02H. Oxidation of enolizable ketones to a-nitrato-ketones can be achieved using thallium(iii) nitrate in acetonitrile. ... 

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