Polymer Bound Pyrrole Compounds, VII : Xanthobilirubinic Acid Estes and Anides from an Insoluble, Polystyrene-Supported Precursor

Article abstract of DOI:10.1007/BF00811466

A series of xanthobilirubinic acid (XBR) esters (i.e., 1c to 1p) and amides (2a - 2c) have been prepared by a procedure involving detachment of the chromophore previously ester-bound to a functionalized, insoluble polystyrene (1b).Detachment is achieved by treatment with the respective alcohol in aqueous alkali or with the amines, yielding directly the corresponding esters or amides.With primary, short-chained alcohols the ester yields are high (60percent for n-C4H9-OH to 99percent for C2H5-OH), but decrease rapidly with chain length (40percent for n-C10H21-OH and 0percent for C16H33-OH).The The same trends are observed with the amines.These results are interpreted in terms of an (increasingly) unfavourable entropic interaction between the polymer matrix to which the chromophore is bound and the (growing) alcohol chain.The impairment by the long chained nucleophile to reach the transesterification center could also contribute, and, for the most lipophylic alcohols, their low solubility in aqueous alkali is an additional drawback.With secondary and tertiary alcohols, no ester is obtained, in agreement with a B_AC2 mechanism involving a tetrahedral intermediate. Keywords.Xanthobilirubinic acid esters and amides; Alcoholysis; Aminolysis; Polystyrene bound precursor.