Determination of carbohydrazide and kinetics of condensation reaction of carbohydrazide with malachite green by spectrophotometry

The kinetics of the condensation reaction of malachite green and carbohydrazide was studied by spectrophotometry in aqueous solution in the temperature range of 15.0-22.0 °C. The reaction was found to be second-order overall, first-order with respect to each reactant. The effect of ionic strength on the reaction has negative salt effect in the range of 0.2-1.0 mol⊖L^-1. A mechanism of the reaction between malachite green and carbohydrazide was proposed, and the rate equation derived from the mechanism can explain all experimental observations properly. Based on this reaction, a method of determining the content of carbohydrazide in the concentration range of (0.02-0.5) × 10^-3 mol⊖L ^-1 was proposed.