Phthalic anhydride radical anion

Fig. 27. Molar mass dependence of [rj] for a fractionated comb macromolecule. The fractionation was made with a SEC/LALLS/VISC set-up. The comb macromolecule consists oi a polyimidazole backbone prepared by free radical polymerization. The imidazol side groups acted in a melt with phenylglycidylether and phthalic anhydride as multifunctional initiator for the anionic growth of polyester chains. The straight lines correspond to the behavior of unattached polyester chains and the comb polymers at low and high molar masses respectively [136]...

Phthalic anhydride forms a persistent anion-radical on reduction, exemplified by the isobenzofuran-l,3-semidione (20). The ESR spectrum of 20 was observed by several groups at about the same time and analyzed with comparable results. The splittings indicated for 20 are those of... 

Voltammetric data for ester reductions are available for several aromatic esters [51-54], and in particular cyclic voltammetry shows clearly that in the absence of proton donors reversible formation of anion radical occurs [51]. In dimethylfonnamide (DMF) solution the peak potential for reduction of methyl benzoate is —2.29 V (versus SCE) for comparison dimethyl terephthalate reduces at —1.68 V and phthalic anhydride at —1.25 V [4]. Half-wave potentials for reduction of aromatic carboxylate esters in an unbuffered solution of pH 7.2 are linearly correlated with cr values [51] electron-withdrawing substituents in the ring or alkoxy group shift Ei/o toward less negative potentials. Generally, esters seem to be more easily reducible than the parent carboxylic acids. Anion radicals of methyl, ethyl, and isopropyl benzoate have been detected by electron paramagnetic resonance (epr) spectroscopy upon cathodic reduction of these esters in acetonitrile-tetrapro-pylammonium perchlorate [52]. The anion radicals of several anhydrides, including phthalic anhydride, have similarly been studied [55]. 

Carboxylic AcidPerivatives. Detailed investigations into the electrolytic reduction of carboxylic acid derivatives (esters, anhydrides, amides) in nonaqueous solutions and the procedures for producing the respective radical anions have been described in the report by iDyasov and his co-workers f39]. They obtained radical anions from esters of aromatic carboxylic acids (benzoates, phtha-lates, isophthalates) and from phthalic anhydride and analyzed their EPR spectra. The production of radical anions of acrylates and methacrylates by electrochemical generation and the effect of proton donors on their stability was also described [11]. 

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