- Kinetics, Mechanism, and Thermodynamics of Glyoxal-S(IV) Adduct Formation
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The reversible addition of glyoxal (ethanedial) and S(IV) to form glyoxal monobisulfite (GMBS) was studied spectrophotometrically over the pH range of 0.7-3.3.Far from equilibrium, the rate of GMBS formation is given by d/dt = (k1,appα1) + k2,appα2), where = + + , = + -> + 2->, α1 = ->/, and α2 = 2->/.The apparent rate constants, k1,app = 0.13 M-1 s-1 and k2,app = 2.08E3 M-1 s-1, are pH independent functions of the dehydration equilibrium constants of (CH(OH)2)2 and CHOCH(OH)2, and intrinsic rate constants for the reaction of HSO3- and SO32- with unhydrated and singly hydrated glyoxal.Glyoxal dibisulfite (GDBS) and GMBS were shown to dissociate with a rate given by d/dt = -1 + k"-1KD3 + (k'-2K'a2 + k"-2K"a2KD3)/+>>t + -3 + k-4Ka3/+>>t, where k-1 and k-2 correspond to the release of bisulfite and sulfite, respectively, from unhydrated and hydrated GMBS species; k-3 and k-4 correspond to the release of bisulfite and sulfite from GDBS; KD3 is the dehydration constant for GMBS; K'a2, K"a2, and Ka3 are acid dissociation constants.Stability constants for the formation of GMBS and GDBS were determined to be cK1 = ->/(-) = 2.81E4 M-1 and cK2 = -)2>/(->->) = 1.45E4 M-1 at 25 deg C and μ = 0.2 M.
- Olson Terese M.,Hoffmann, Michael R.
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- New Synthesis of 2,4,6,8-Tetramethyl-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione Using Etidronic Acid as a “Green” Catalyst
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Abstract: A new method has been developed for the synthesis of2,4,6,8-tetramethyl-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione in 62% yieldusing etidronic acid [1-hydroxyethane-1,1-diylbis(phosphonic acid), HEDP] as a“green” catalyst. A plausible stepwise mechanism of the reaction has beenproposed and partially confirmed by NMR data and studying model processes. Theeffects of the reaction medium and HEDP on particular species involved in thereaction, namely N,N′-dimethylurea, 4,5-dihydroxy-1,3-dimethylimidazolidin-2-one,and 2,4,6,8-tetramethyl-2,4,6,8-tetraazabicyclo[3.3.0]octane-3,7-dione, havebeen studied by 1H and 13CNMR spectroscopy in D2O, neutral and acidified solutions(acetic acid-d4), andsolutions containing 1 equiv of HEDP.
- Panshina, S. Yu.,Ponomarenko,Bakibaev,Malkov
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p. 2067 - 2073
(2021/02/09)
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- Photochemistry of 2-azido-1-methylimidazole in aqueous solutions. Observation of the 1-methyl-2-imidazolylnitrenium ion
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Irradiation of 2-azido-1-methylimidazole (12) in aqueous solution gives products from two reaction channels. One pathway involves a ring opening typical of azidoheterocycles. The observed products are glyoxal bis-hydrate, the methylammonium ion, and cyanamide; a glyoxal bis-oxime is presumed to be the intermediate initially formed in the ring opening. The other pathway leads to products that retain the five-membered ring, the 2-amino-4,5-dihydro-4,5-dihydroxy-1-methylimidazolium ion 3, its monophosphate ester 6 when the irradiation is carried out in phosphate buffer, and glutathione adducts 7 and 8 when glutathione (GSH) is present. These products have been previously observed in the reactions of 2-hydroxylamino-1-methylimidazole in aqueous solution, and arise from reaction of the 1-methyl-2-imidazolylnitrenium ion (2+) with water, phosphate, and GSH. This pathway is therefore proposed to involve formation of the cation 2+ via protonation of the singlet 1-methyl-2-imidazolylnitrene 13 formed upon irradiation of the azide. A single transient species undergoing exponential decay with λmax at 230-235 nm is observed with flash photolysis. This transient is assigned to 2+ on the basis of the pH dependence of the yields of products, and especially because of the correspondence of k2(GS-):ks ratios measured directly with flash photolysis and by competition kinetics starting from the hydroxylaminoimidazole. The cation 2+ has a lifetime in water of 100 ms, and shows a high selectivity for GSH with k2(GS-) = 3 × 107 M-1 s-1. There is evidence that this class of nitrenium ion is formed upon reductive metabolism of 2-nitroimidazoles. Thus this class of drugs is capable of producing a relatively long-lived electrophile in biological systems.
- Gadosy, Timothy A.,McClelland, Robert A.
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p. 1459 - 1465
(2007/10/03)
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- Les acetals du glyoxal et de l'acetaldehyde
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During the synthesis of glyoxal by nitric acid oxidation of acetaldehyde, we have observed the formation of two substances C6H10O4.Structural studies by NMR and mass spectroscopy show that they are cis exo and trans isomers of 3,7-dimethyl-2,4,6,8-tetraoxabicyclooctanes.
- Platzer, Nicole,Lefebvre, Bernard,Temmen, Jean,Mattioda, Georges
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