Abstract
Alkali salts of some aromatic hydroxycarboxylic acids are effective in increasing the solubility of pyrazinamide in water and the use of sodium p-aminosalicylate (PAS-Na) results in the formation of a yellow solution of pyrazinamide-PAS-Na complex. It has been found from examination of absorption spectrum in the visible range that the coloration is due to the formation of a 1 : 1 molecular compound of pyrazinamide and PAS-Na in aqueous solution. It was also found that sodium o-, m-, and p-hydroxybenzoates also form 1 : 1 molecular compound with pyrazinamide. There is a linear relationship between increased solubility of pyrazinamide per mole of aromatic hydroxycarboxylic acid added and equilibrium constant of the molecular compound thereby formed. The equilibrium constants obtained in the present series of work were larger than the values calculated from the solubility increase and some considerations were made on the reason for this difference.
