Kinetic Analysis and Mechanism of the Hydrolytic Degradation of Squaramides and Squaramic Acids

详细信息    查看全文

• 作者：Marta Ximenis ; Emilio Bustelo ; Andrés G. AlgarraManel Vega ; Carmen Rotger ; Manuel G. Basallote ; Antonio Costa
• 刊名：Journal of Organic Chemistry
• 出版年：2017
• 出版时间：February 17, 2017
• 年：2017
• 卷：82
• 期：4
• 页码：2160-2170
• 全文大小：657K
• ISSN：1520-6904

文摘

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^–4 M^–1 s^–1) are 2–3 orders of magnitude faster than those for the second step (k₂ ≈ 10^–6 M^–1 s^–1). Experiments at different temperatures provide activation parameters with values of ΔH^⧧ ≈ 9–18 kcal mol^–1 and ΔS^⧧ ≈ −5 to −30 cal K^–1 mol^–1. DFT calculations show that the mechanism for the alkaline hydrolysis of squaramic acids is quite similar to that of amides.