Complex formation was studied in the systems boric acid (sodium monoborate)3polyol (D-sorbitol, mannitol, dulcitol, xylitol, glycerol)3water, concentrational stability constants of the complexes and ionization constants of bis(polyol)boric acids were estimated. In the systems D-sorbitol, D-mannitol, dulcitol, glycerol3boric acid3water electric conductivity increases sharply to peak at the molar ratio polyol : boric acid = 2 : 1; in the case of dulcitol there appears yet another peak at the molar ratio polyol : boric acid = 1 : 1.In the systems D-sorbitol, D-mannitol, glycerol3sodium monoborate3water three complex anions: [BPolyol 2 ] ! in acidic, [BPolyol] ! , and [B 2 Poyol] 2! in neutral and basic regions of the system were revealed, their stability being dependent on the nature of the polyol and the overall concentration of the solution. In the system dulcitol3sodium monoborate3water only one complex anion [BDulc] ! is formed, and in the system xylitol3 sodium monoborate3water dimeric complex [BXyl] ! is found.The reaction of D-mannitol with boric acid was much investigated, in contrast to D-sorbitol, dulcitol, xylitol, ribitol, and L-arabitol. It was of interest to compare their ability to complex formation with boric acid and borate ions and to isolate the forming compounds. It is believed that in the solutions of boric acid there are formed two types of compounds with polyols: H[BPolyol] and H[BPolyol 2 ] [1,2]. Recent studies with the use of NMR spectroscopy have shown that complex [B 2 Polyol] 2! can be also formed with varied pH in the basic region [3]. So we studied in more detail the reactions of D-mannitol, D-sorbitol, dulcitol, xylitol, and, for reference, glycerol with boric acid and sodium monoborate by the isomolar series method. The characteristcs under study were deviations from the additivities of specific electric conductivity and polarization angles (in the cases of optically active D-mannitol and D-sorbitol; dulcitol, xylitol, and ribitol are optically inactive). As was shown in [4], this method can be successfully used in the investigation of the reaction of boric acid and sodium monoborate with polyhydroxy compounds. Unfortunately we had no specimens of ribitol and L-arabitol at hand. Fig. 1 suggests, reactions of D-sorbitol, D-mannitol, and xylitol with boric acid are of the same type. At all studied total concentrations (c 5 ) deviations from the additivity of specific electric conductivity are positive and show a peak at the molar ratio polyol : boric acid = 2 : 1. This indicates the formation of bis(polyol)boric acids which are more powerful than boric acid. In the pH range of 2 to 5 bis(polyol)boric acid is the only complex in the system. On going to higher temperatures complex formation goes down (shown for xylitol as one example, Fig. 1), but its nature does not change. In the order of stability bis(polyol)boric acids can be arranged in the following series: bis(dulcitol)-boric > bis(D-sorbitol)boric>bis(D-mannitol)boric > bis(xylitol)boric acid (c 5 0.5 M) (Table 1). In the syste...
