NUCLEAR MAGNETIC RESONANCE STUDY OF THERMAL DECOMPOSITION OF ETHYLENEDINITRILOTETRAACETIC ACID AND ITS SALTS IN AQUEOUS SOLUTIONS

Aqueous and deuterium oxide solutions of ethylenedinitrilotetraacetic acid (H4EDTA), disodium ethylenedinitrilotetraacetate (Na2H2EDTA), and tetralithium ethylenedinitrilotetraacetate (Li4EDTA) were degassed to remove dissolved oxygen and then heated at 200 °C in sealed NMR tubes for periods ranging from one hour to over 300 hours. Periodic examination of the contents using proton NMR showed that decomposition occurred rapidly in the order H4EDTA > Na2H2EDTA > Li4EDTA. Approximate rates for the degradation processes have been determined. The longest half-life, that for O.1M Li4EDTA solution, is approximately 13 hours at 200 °C. The NMR results suggest a primary, pH dependent, stepwise loss of (–CH2CO2-) groups from EDTA4- to form (-O2CCH2)NHCH2CH2N(CH2CO2-)2, NH2CH2CH2N(CH2CO-2)2, and (CH2NHCH2CO-2)2. A slower, secondary decomposition produced products not yet identified. © 1969, American Chemical Society. All rights reserved.