HIGHLY ELECTROPHILIC HETEROAROMATICS - THE HYDROLYSIS OF 7-CHLORO-4,6-DINITROBENZOFURAZAN AND 7-CHLORO-4,6-DINITROBENZOFUROXAN IN AQUEOUS-SOLUTION

The hydrolysis of 7-chloro-4,6-dinitrobenzofurazan (4) and 7-chloro-4,6-dinitrobenzofuroxan (5) to give the related 7-hydroxy derivatives has been kinetically investigated in the pH range 1-6 in aqueous solution. The reactions occur 3500 and 10000 times more rapidly, respectively, than the hydrolysi...

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Bibliographic Details
Published inJournal of the Chemical Society, Perkin Transactions 2 no. 3; pp. 337 - 341
Main Authors TERRIER, F, HLAIBI, M, HALLE, JC, LAN, XA
Format Journal Article
LanguageEnglish
Published CAMBRIDGE Royal Soc Chemistry 1993
Royal Society of Chemistry
Subjects
Chemistry
Chemistry, Organic
Chemistry, Physical
Exact sciences and technology
Kinetics and mechanisms
Organic chemistry
Physical Sciences
Reactivity and mechanisms
Science & Technology
MEISENHEIMER COMPLEXES
SUBSTITUTION
4,6-DINITROBENZOFUROXAN
BASE CATALYSIS
SUPERELECTROPHILES
HETEROCYCLES
AMBIDENT NUCLEOPHILIC REACTIVITY
1-OXIDE
ION
SIGMA-COMPLEX FORMATION
Hydrolysis
Nitro compound
Catalytic reaction
Bicyclic compound
Aromatic compound
Aqueous solution
Rate constant
Oxygen nitrogen heterocycle
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Summary:The hydrolysis of 7-chloro-4,6-dinitrobenzofurazan (4) and 7-chloro-4,6-dinitrobenzofuroxan (5) to give the related 7-hydroxy derivatives has been kinetically investigated in the pH range 1-6 in aqueous solution. The reactions occur 3500 and 10000 times more rapidly, respectively, than the hydrolysis of picryl chloride, emphasizing the much higher electrophilic character of the two heterocycles. Strong catalysis of the hydrolysis of 4 and 5 by carboxylate ions is observed, with Bronsted beta values of 0.38 and 0.42, respectively, which support a concerted mechanism. Although the corresponding points (k(H2O)/55.55) show strong negative deviations from the Bronsted plots, the finding of appreciable solvent isotope effects (k(H2O)/k(D2O) ca. 1.75) favours a similar mechanism for the water reactions, i.e. water attack is assisted by a second water molecule which acts as a base catalyst. Differences in the electrostatic effects contributing to the stabilization of the transition states for the water-catalysed and carboxylate ion-catalysed reactions would account for the deviations observed for the k(H2O) points.
ISSN:0300-9580
2050-8239
1364-5471
DOI:10.1039/p29930000337