Changes in the relative contribution of specific and general base catalysis in cationic micelles. The cyclization of substituted ethyl hydantoates
The rate-surfactant profiles for the HO-- and AcO--catalyzed ring closure of two ethyl hydantoates, E2 and E3, to hydantoins with three cetyltrimethylammonium salts (CTAX, X = Br-, Cl-, or AcO-) are m
Blagoeva,Toteva,Ouarti,Ruasse
p. 2123 - 2130
(2007/10/03)
On the disappearance of the gem-dimethyl effect: The base-catalysed cyclization of ethyl hydantoates
Buffer catalysis and solvent kinetic isotope effects in the cyclization of methyl-substituted ethyl hydantoates with ω-N-methyl (MUE) and ω-N-phenyl groups (PUE) have been studied in an attempt to elucidate the changes in mechanism and eventual reversal o
Atay, Ergun,Blagoeva, Iva B.,Kirby, Anthony J.,Pojarlieff, Ivan G.
p. 2289 - 2297
(2007/10/03)
Change of Rate Determining Step Induced by the gem-Dimethyl Effekt
The base-catalysed cyclisation to the hydantoin of 2,2,3-trimethyl-5-phenylhydantoate (2; R1 = R2 = Me) is slower than that of the 2,3-dimethyl compound, even though the acceleration expected from the gem-dimethyl effect is observed for the acid-catalysed
Blagoeva, Iva B.,Tashev, Denis T.,Kirby, Anthony J.
p. 1157 - 1158
(2007/10/02)
General Acid-Base Catalysed Cyclisation Reactions of a Strained ω-Phenylhydantoic Acid
In relation to model studies on the carboxylation of biotin, the nucleophilic reactivity of a weakly basic urea towards COOH and COO- was characterised by means of the ring-closure of (3) to (4).Owing to the strain introduced by the two methyl groups the reaction was rapid over the whole pH range, being reversible at pH>9.Three general acid-base-catalysed reactions and one uncatalysed reaction were identified, corresponding to a change of the predominant form of catalysis and/or reactive form of the substrate with changing pH.The additional barrier for anionic nucleophilic attack on COO- versus attack on COOH was estimated as ca. 9 kcal mol-1.A comparison between the reactivity of the phenylureido and methylureido anion towards COO- indicated better nucleophilicity by phenylureido anion, despite its lower basicity.The results obtained with the model compound (3) illustrated the possibility of a change to a different rate-determining step for intramolecular reactions of compounds activated by ground-state strain.
Blagoeva, Iva B.
p. 127 - 134
(2007/10/02)
Photochemical decomposition of phenazone derivatives. Part 7: Mechanism of decomposition in aqueous solutions
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Marciniec
p. 180 - 182
(2007/10/02)
Photochemical decomposition of phenazone derivatives. Part 5: Isolation and identification of decomposition products in aqueous solution
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Marciniec
p. 30 - 33
(2007/10/02)
(13)C Nuclear Magnetic Resonance Studies on the Conformation of Substituted Hydantoins
A number of hydantoins were synthesized and their (13)C n.m.r. spectra were studied using special solvents and shift reagents.Some interesting features of their conformation were deduced.In the case of hydantoins derived from phenylalanine evidence was fo
Fujiwara, Hideji,Bose, Ajay K.,Manhas, Maghar S.,Veen, James M. van der
p. 1573 - 1577
(2007/10/02)
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