Spectrophotometric Investigation on the Kinetics of Decomposition of Murexide in Acid Solutions

Abstract

The kinetics of the decomposition of murexide in acid solutions were investigated spectrophotometrically by following the absorption at λ=530 mμ. The optical density of murexide at λ= 530 mμ which obeyed Beer's law, decreased irreversibly with time, following a first order law. The corresponding rate constant k, was dependent upon the concentration (C) of the strong acids like HCl, HBr, HNO3, etc. and followed a relationship: k/min-1 = 2.56·10-3·C. k was also dependent upon the concentration of murexide. The effect of neutral salts on k showed that in accord with the data obtained with different acids, the anions of the acids or salts had no significant role in the mechanism responsible for the decomposition of murexide. A hypothesis referring to the formation of an intermediate complex (electrically uncharged in character) which decomposed unimolecularly to give the products, uramil and alloxan, was put forward.

Pre‐equilibrium Approximation for Analysis of Chemical Kinetics in Chromatography: Application to Reversed‐Phase On‐column Kinetics of Decomposition of Murexide

“…The use of Equation (22) for fitting the kinetic data assumes there is no reaction in the stationary phase. If there is a reaction occurring in the stationary phase, then Equation (22) will include an irreversible step in the stationary phase, cf. in Equation (19).…”

“…This work shows the requirement of both on-column and off-column (batch) kinetics to obtain values of all parameters. The use of Equation (22) for fitting the kinetic data assumes there is no reaction in the stationary phase. If there is a reaction occurring in the stationary phase, then Equation (22) will include an irreversible step in the stationary phase, cf.…”

“…Thus, the observed rate of decomposition of murexide in the column is slower than in the mobile phase solution alone due to the term (K M K c [H + ]) in the denominator of Equation (22).…”

“…The retention time of the observed peak of each chromatogram is the sum of the stopped-flow and the elution times, i. e., the reaction time. Equation (22), was fitted to the data in Table 2 by non-linear least-squares regression (Figure 2(C)), to obtain the parameter K c , using the values of K M and k r from the batch method (Table 3). The best-fit value of K c is 8.8 � 0.5.…”

“…The proposed procedure is applied to the kinetics of the decomposition of murexide, [20][21][22] in a reversed-phase C8 column and also a solution of the mobile phase. The net reaction gives uramil (U) and alloxan (A), as shown in Scheme 2(A).…”