Efficient microwave-assisted preparation of squaric acid monoamides in water
作者:Carlos López、Manuel Vega、Elena Sanna、Carmen Rotger、Antoni Costa
DOI:10.1039/c3ra41369a
日期:——
Squaric acid monoamides (SQAMs) were prepared via microwave-enhanced direct reaction of amines with squaric acid in yields ranging from 41 to 92%. These compounds are strong acids, with pKa values ranging from 0.9 to 2.0 as determined by spectrophotometric titration in representative cases.
Synthese von Glutaconaldehyden aus Quadrats�ure-Pyridiniumbetainen
作者:J. Gr�nefeld
DOI:10.1002/prac.19933350308
日期:——
The pyridinium ring of squaric acid betaines (2) is opened by hydroxide ions. Electronegative substituents (R = Cl, CN) at C-3 promote this reaction. The stereochemistry of the resulting 5-(2-hydroxy-3,4-dioxocyclobut-1-en-1-yl) aminopenta-2,4-dienales (3) is confirmed by NMR-spectroscopy. Treatment of 3 with sodium hydroxide results in further hydrolysis to the sodium salts of glutaconaldehydes (5) and 3-amino-4-hydroxycyclobut-3-ene-1,2-dione (6). These products are also directly obtained from the nicotinic acid derivates 2d (R = COOEt) and 2e (R = CONH2), in the latter case cyclisation of the glutaconic acid derivate to the known 3-formylpyrid-2-one (10) is observed.
Kinetic Analysis and Mechanism of the Hydrolytic Degradation of Squaramides and Squaramic Acids
作者:Marta Ximenis、Emilio Bustelo、Andrés G. Algarra、Manel Vega、Carmen Rotger、Manuel G. Basallote、Antonio Costa
DOI:10.1021/acs.joc.6b02963
日期:2017.2.17
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