The precipitation of polyanions by long-chain aliphatic ammonium salts. 5. The influence on precipitation of changes in the amine structure

Abstract

The precipitation of alginate, heparin, hyaluronate, keratosulphate and pectinate from aqueous solution by aliphatic ammonium ions containing paraffin chains from [CH2]6 to [CH2]18, and with several types of cationic group, has been studied. The efficiency of precipitation increases in a regular and marked manner with increase of chain length. This effect can be accounted for if the insoluble complexes are assumed to be "oily" particles, and a free-energy change of about 1.2 RT is associated with the transfer of CH2 from the aqueous phase to the particle. The concentration of organic cation required to precipitate a polyanion depends on the structure of the polyanion. Polyanions with high charge densities are precipitated more readily than less-densely charged polyanions. It is concluded that precipitation of polyanions by primary ammonium salts is unlikely to be a micellar phenomenon. The occurrence of a flocculation end point can be accounted for by applying the Law of Mass Action to the reaction equation, involving single ions. A qualitative hypothesis of the reaction mechanism is proposed.