Abstract
Oxidizing abilities of the COD(Cr) method using IC2Cr207 and the COD(Mn) method using K, MnO, for organic compounds have been examined and compared using benzoic acid, L-glutamic acid, tartaric acid and chloride ion. The Std. COD (Cr) ([H]=18 M) method conforming to the JIS (Japanese Industrial Standards) gave the highest oxidation efficiency (0. E. hereafter) to benzoic acid. In contrast, the Mod. COD(Cr) ([H+]=2.4 M) sho wed the weakest. To obtain the same O. E. as Mod. COD(Mn) ([1-1+]=2.4 M), the COD(Cr)method required the [1-11-] of 9-10 M. At the acid concentration higher than ca.15 M ([H+]), the COD(Cr) method gave strong 0. E. The 0. E. of the COD(Mn) method becam e stronger as the [1-1+] increased (untill ca.2.5 M), but decreased rapidly after that (ex.0%at ca. [H+]-, --6 M in the case of chloride ion). The effect of temperature for the COD(Cr)method was clear-cut the higher the temperature, the higher the O. E., although the Std. COD(Mn) method gave no clear temperature dependence. The heating time effect was also clear for the COD(Cr) methods, i. e., the longer the time, the higher the O. E. However, the COD(Mn)methods gave characteristic decomposition curves with maximum values in the region of 30-60 min. O. E. for both COD methods was studied from the point of view of redox-potential. Calculated apparent formal potentials explained the difference in O. E. of both COD methods lEers" ([H]=18 M) =1, 34 V, EM Std ([H+] =1 M) =1.27 V; Ec, "d([H+]=2.4 M) =1.18 V, {Emni" ([H]=2.4 M) =1.31 V}. Experimetal potentials were measured at 25° C and 50 °C, and these experimental potentials also showed relatively good agreemen t with the O. E. of both COD(Cr) and COD(Mn) methods (Fig.6).
