- MECHANISMS AND INTERMEDIATES FOR SQUARIC ACID SYNTHESIS FROM HEXACHLOROBUTADIENE AND MORPHOLINE
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The mechanistic course of the 3-stage synthesis of squaric acid from hexachlorobutadiene and morpholine has been elucidated, and 5 novel intermediates isolated and characterized.
- Paine, Anthony James
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- Kinetic Analysis and Mechanism of the Hydrolytic Degradation of Squaramides and Squaramic Acids
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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.
- Ximenis, Marta,Bustelo, Emilio,Algarra, Andrés G.,Vega, Manel,Rotger, Carmen,Basallote, Manuel G.,Costa, Antonio
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- Structural effects on interconversion of oxygen-substituted bisketenes and cyclobutenediones
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(Graph Presented) Cyclobutenediones 5 disubstituted with HO (a), MeO (b), EtO (c), i-PrO (d), t-BuO (e), PhO (f), 4-MeOC6H4O (g), 4-O2NC6H4O (h), and 3,4-bridging OCH 2CH2O (i) substituents upon laser flash photolysis gave the corresponding bisketenes 6a-i, as detected by their distinctive doublet IR absorptions between 2075 and 2106 and 2116 and 2140 cm-1. The reactivities in ring closure back to the cyclobutenediones were greatest for the group 6b-e, with the highest rate constant of 2.95 ×107 s -1 at 25°C for 6e (RO = t-BuO) in isooctane, were less for 6a (RO = OH, k = 2.57 × 106 s-1 in CH3CN), while 6f- i were the least reactive, with the lowest rate constant of 3.8 × 104 s-1 in CH3CN for 6h (RO = 4-O 2NC6H4O). The significantly reduced rate constants for 6f-i are attributed to diminution of the electron-donating ability of oxygen to the cyclobutenediones 5f-h by the ArO substituents compared to alkoxy groups and to angle strain in the bridged product cyclobutenedione 5i. The reactivities of the ArO-substituted bisketenes 6f-h in CH3CN varied by a factor of 50 and gave an excellent correlation of the observed rate constants log k with the σp constants of the aryl substituents. Computational studies at the B3LYP/6-31G(d) level of ring-closure barriers are consistent with the measured reactivities. Photolysis of squaric acid (5a) in solution provides a convenient preparation of deltic acid (7).
- Fu, Nanyan,Allen, Annette D.,Kobayashi, Shinjiro,Tidwell, Thomas T.,Vukovic, Sinisa,Matsuoka, Takeshi,Mishima, Masaaki
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p. 1768 - 1773
(2008/09/18)
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- Method for producing 3,4-dihydroxy-3-cyclobutene-1,2-dione
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In the formulae, R1 represents alkyl; and R2, R3 and X independently represent halogen. The present invention relates to a method for producing 3,4-dihydroxy-3-cyclobutene-1, 2-dione of general formula (II) by hydrolyzing 3-alkoxy-2, 2, 4, 4-tetrahalogenocyclobutanone derivative of general formula (I).
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- Electro-organic reactions. Part 27. The mechanism of cathodic cleavage of activated esters; oxalates, squarates and oxamates
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Esters of oxalic acid, 3,4-dihydroxy-3-cyclobutene-1,2-dione (squaric acid), and oxamic acid, are reduced cathodically at modest potentials. In aprotic solvent, and on the cyclic voltammetric time scale, the esters are cleaved to the corresponding alkane. For oxalates, the mechanism of cathodic cleavage was investigated thoroughly by voltammetry, coulometry, and detailed product analysis. On the time scale of controlled potential electrolysis the rapid electrogenerated base-catalysed hydrolysis of the esters by adventitious water competes with cathodic cleavage. Similarly, rapid base-catalysed transesterification involving oxalates and added alcohols is observed which provides a practical method of reductively cleaving alcohols to alkanes by co-electrolysis of a mixture of alcohol and readily available oxalate (e.g. diethyloxalate). The leaving group in such cathodic fragmentation is the half-ester anion and the efficiency of reaction depends on the stability of the other, radical, fragment.
- Islam, Nazar-ul,Sopher, David W.,Utley, James H.P.
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p. 959 - 970
(2007/10/02)
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- Synthesis of squaric acid
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Squaric acid is prepared by reacting hexachlorobutadiene with an excess of morpholine in the presence of an aromatic hydrocarbon solvent while maintaining the temperature between 110° C and 120° C, and then converting the resulting 1,1,3-trichloro-2,4,4-trimorpholino-butadiene to 3-morpholinotrichloro-2-cyclobuten-1-one, which in turn is hydrolyzed in the presence of strong acid to produce the desired squaric acid.
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