A study of hydrogen-bonded species of acetic acid in water

Abstract

Hydrogen-bonded species viz monomers, linear dimers, cyclic dimers, polymers and free ions existing in an aqueous solution of acetic acid were quantitatively determined at 32°C in the concentration range of 0-100 %w/w. The extent of the presence of each hydrogen-bonded species at some ranges of concentration was determined from three equilibrium constants namely equilibrium constant of the formation of a cyclic dimer from two monomeric acid units (KC) , a linear dimer from two monomeric acid units (K1) , a polymer of i+1 unit from a monomer unit added to i unit polymer (K). The three equilibrium constants were obtained using the non-linear least squares fit method of the proton chemical shifts. These values of K, K1 and KC are equal to 54.4 mf-1, 141.7 mf-1 and 262.5 mf-1 respectively and are statistically accepted in the concentration range of 0-85 %w/w. Results led to a significant conclusion concerning the type of the predominant hydrogen-bonded species occurred at some concentration ranges as shown below. Range of concentration (%w/w)Predominant species 1.6 X 10-3 – 8.0 X 10-3Monomer 6.0 – 20.0Cyclic dimer 10.0 – 25.0Cyclic dimer and linear dimer 50.0 – 85.0Polymeric species