title: Kinetic Analysis and Mechanism of the Hydrolytic Degradation of Squaramides and Squaramic Acids.
abstract: The hydrolytic degradation of squaramides and squaramic acids, the product of partial hydrolysis of squaramides, has been evaluated by UV spectroscopy at 37 °C in the pH range 3-10. Under these conditions, the compounds are kinetically stable over long time periods (>100 days). At pH >10, the hydrolysis of the squaramate anions shows first-order dependence on both squaramate and OH-. At the same temperature and [OH-], the hydrolysis of squaramides usually displays biphasic spectral changes (A → B → C kinetic model) with formation of squaramates as detectable reaction intermediates. The measured rates for the first step (k1≈ 10-4M-1s-1) are 2-3 orders of magnitude faster than those for the second step (k2≈ 10-6M-1s-1). Experiments at different temperatures provide activation parameters with values of ΔH⧧≈ 9-18 kcal mol-1and ΔS⧧≈ -5 to -30 cal K-1mol-1. DFT calculations show that the mechanism for the alkaline hydrolysis of squaramic acids is quite similar to that of amides.
authors.affiliation: Department of Chemistry, Universitat de les Illes Balears , Palma 07122, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Ximenis
authors.affiliation: Department of Materials Scientist, Metallurgic Engineering and Inorganic Chemistry, Universidad de Cádiz , Puerto Real, 11510 Cádiz, Spain.
authors.forename: Emilio
authors.initials: E
authors.lastname: Bustelo
authors.affiliation: Department of Materials Scientist, Metallurgic Engineering and Inorganic Chemistry, Universidad de Cádiz , Puerto Real, 11510 Cádiz, Spain.
authors.forename: Andrés G
authors.identifier: 0000-0002-5062-2858
authors.initials: AG
authors.lastname: Algarra
authors.affiliation: Department of Chemistry, Universitat de les Illes Balears , Palma 07122, Spain.
authors.forename: Manel
authors.initials: M
authors.lastname: Vega
authors.affiliation: Department of Chemistry, Universitat de les Illes Balears , Palma 07122, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Rotger
authors.affiliation: Department of Materials Scientist, Metallurgic Engineering and Inorganic Chemistry, Universidad de Cádiz , Puerto Real, 11510 Cádiz, Spain.
authors.forename: Manuel G
authors.identifier: 0000-0002-1802-8699
authors.initials: MG
authors.lastname: Basallote
authors.affiliation: Department of Chemistry, Universitat de les Illes Balears , Palma 07122, Spain.
authors.forename: Antonio
authors.identifier: 0000-0002-9418-7798
authors.initials: A
authors.lastname: Costa