Influence of the spatial structure of the alkyl chain on the composition of the product of the direct neutralization reaction between aliphatic carboxylic acids and zinc hydroxide

Article abstract of DOI:10.1016/0020-1693(96)05019-0

A study was launched to clarify the influence of the spatial structure of the alkyl chain on the products of the direct neutralization reactions between zinc hydroxide and several non-cyclic saturated carboxylic acids in the presence of an excess of either the carboxylic acid or zinc hydroxide. The species formed were identified on the basis of their FT-IR spectra in the mid-IR region. Straight-chain acids produced the corresponding zinc bis-carboxylates with polymeric sheet structure under all circumstances. The species present in the products of the branched-chain carboxylic acids depended strongly on the nature of the component in excess and the bulk of the alkyl group. Besides the starting materials the reaction mixtures contained two carboxylate species in various ratios. One of them was the zinc bis-carboxylate of the branched-chain carboxylic acid, characterized by an additional νC=O band at around 1630 cm^-1, above the usual two strong carboxylate stretching bands. The other species was the corresponding complex Zn₄O(RCOO)₆. The conditions of formation of these three forms of zinc carboxylates were formulated on the basis of the decreasing possibility of interaction between the neighbouring alkyl chains to form a polyethylene subcell in the sequence of: Zn(RCOO)₂ (polymeric sheet) > Zn(RCOO)₂ (intermediate form) > Zn₄O(RCOO)₆ (tetranuclear complex).