Thermal decomposition of ethylenediaminetetraacetic acid in the presence of 1,2-phenylenediamine and hydrochloric acid

Abstract

Considerando os produtos de reação do ácido etilenodiaminotetraacético (EDTA) com 1,2-fenilenodiamina (o-PDA), um novo processo para a decomposição térmica do EDTA é proposto. O meio ácido forte e a presença de o-PDA facilitam a decomposição de EDTA, como evidenciado pela temperatura relativamente baixa de reação. Em adição aos passos descritos na literatura, um processo de rearranjo está presente na reação de decomposição. Os intermediários rearranjados condensam com o-PDA, formando um inesperado composto biologicamente ativo 2,2,4-trimetil-3H-5-hidro-1,5-benzodiazepina, proporcionando a possibilidade de explorar um mecanismo de decomposição alternativo para este quelante amplamente utilizado.Based on the reaction products of ethylenediaminetetraacetic acid (EDTA) with 1,2-phenylenediamine (o-PDA), a novel thermal decomposition pathway of EDTA is proposed. The strong acidic medium and the presence of o-PDA facilitate the decomposition of EDTA as evidenced by the relatively lower reaction temperature. In addition to the steps described in literatures, rearrangement process is involved in the decomposition reaction. The rearranged intermediates condense with o-PDA, forming an unexpected biologically active compound 2,2,4-trimethyl-3H-5-hydro-1,5-benzodiazepine, thus provides the possibility to explore an alternative decomposition mechanism for this widely used chelator.Keywords: ethylenediaminetetraacetic acid, heterocycle, reaction mechanism, thermal decomposition, thermochemistry IntroductionEthylenediaminetetraacetic acid (EDTA) is one of the most extensively used chelating agents in chemistry, biochemistry, medicine, environmental sciences, and paper industry.1-6 As a scavenger for metal oxides or a stabilizer for metal ions, EDTA is also used at elevated temperatures to prevent scale deposits in high-pressure boilers or nuclear reactors owing to its thermal stability. Nevertheless, the behaviour of EDTA in waste water effluents 8,9 and natural aquatic systems 10 has incurred lots of threats to the natural environment. EDTA not only increases the total nitrogen contents, but also remobilizes most toxic heavy metals from solid matter into water solution and thus extends their biological life cycles. 11Hence, great attention has been paid to the study on decomposition mechanism 12-17 and treatment technique 18 for this aminopolycarboxylic acid complexing agent. Both EDTA and its disodium salt are stable to heat even at 423 K.19 EDTA begins to decompose at about 463 K and nearly 50% breaks down at 483 K in the presence of metal ions. 12 Stepwise decarboxylations and hydrolysis procedures of the ethylene C-N link of EDTA have been suggested by earlier researchers. 13,14 As shown in Figure 1, the decomposition mode may differ greatly with temperature changes. 14,15 Other factors such as acidity and reaction medium can also influence the decomposition of EDTA. For example, Vol. 17, No. 5, 2006 when ammonia was used as a reaction medium and reactant in a high pH system, both ammonolysis and hydrolysis of EDTA oc...

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Synthesis of Nanocrystalline Gd2O2NCN from a Versatile Single‐source Precursor

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