1H NMR and kinetics studies of the reaction of 4-methyl, 4-bromo and 3-trifluoromethyl benzyltriflones with aromatic nitro-compounds (original) (raw)
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Journal of Physical Organic Chemistry, 2007
1 H NMR studies in DMSO-d 6 of the reaction of benzyltriflones, 2, with 4,6-dinitrobenzofuroxan, 4, indicate the formation, with or without the presence of added base, of anionic s-adducts. Spectra obtained from solutions of 2 and 4-nitrobenzofurazan, 6a, in the presence of triethylamine are consistent with products formed by the elimination of trifluoromethylsulfinic acid from s-adducts initially formed by carbanion attack at the 5-position of 6a. Kinetic studies of the latter reaction in methanol allow the determination of rate constants for nucleophilic attack by the carbanions at the 5-position. The low value of b for these reactions together with the failure to observe reaction with 1,3,5-trinitrobenzene suggest that the benzyltriflone anions have unusually large steric requirements.
Organic & Biomolecular Chemistry, 2007
1 H NMR studies are reported of the reactions in [ 2 H 6 ]-DMSO of 4-nitrobenzofurazan, 2a, and its 7-chloro-and 7-methoxy-derivatives, 2b and 2c respectively, with anions derived from nitromethane, 3, nitroethane, 4, and 2-nitropropane, 5. The initial reactions result in r-adduct formation by carbanion attack at the 5-position of 2a-c and in the case of reaction of 2a with 5 the adduct at the 7-position is also observed. These reactions may be followed by base catalysed elimination of nitrous acid to yield anionic alkene derivatives. Kinetic and equilibrium measurements of these reactions were made spectrophotometrically in methanol. The carbon nucleophilicities of the carbanions decrease in the order 3 > 4 > 5, as also found in their reactions with benzhydrylium cations, and are much lower than the nucleophilicities of some cyano-substituted carbanions. Comparison with corresponding r-adduct forming reactions of 1,3,5-trinitrobenzene, TNB, show that here 2 and TNB have similar electrophilicity, although the value of the intrinsic rate coefficient k o = 0.05, for reaction of 2 is rather lower than that, k o = 0.20, for the TNB reactions. Literature data suggest that for reaction with a variety of nucleophiles 2 and TNB show similar electrophilicities. Measurements of the rates of elimination of nitrous acid from some 5-adducts in methanol catalysed by methoxide ions are reported. Values of rate constants may be influenced both by steric requirements at the reaction centre and by the electronic effects of the 7-substituent.
Organic Biomolecular Chemistry 2007 Vol 5 Pp 1646 1654 Peer Reviewed Journal, 2007
1 H NMR studies are reported of the reactions in [ 2 H 6 ]-DMSO of 4-nitrobenzofurazan, 2a, and its 7-chloro-and 7-methoxy-derivatives, 2b and 2c respectively, with anions derived from nitromethane, 3, nitroethane, 4, and 2-nitropropane, 5. The initial reactions result in r-adduct formation by carbanion attack at the 5-position of 2a-c and in the case of reaction of 2a with 5 the adduct at the 7-position is also observed. These reactions may be followed by base catalysed elimination of nitrous acid to yield anionic alkene derivatives. Kinetic and equilibrium measurements of these reactions were made spectrophotometrically in methanol. The carbon nucleophilicities of the carbanions decrease in the order 3 > 4 > 5, as also found in their reactions with benzhydrylium cations, and are much lower than the nucleophilicities of some cyano-substituted carbanions. Comparison with corresponding r-adduct forming reactions of 1,3,5-trinitrobenzene, TNB, show that here 2 and TNB have similar electrophilicity, although the value of the intrinsic rate coefficient k o = 0.05, for reaction of 2 is rather lower than that, k o = 0.20, for the TNB reactions. Literature data suggest that for reaction with a variety of nucleophiles 2 and TNB show similar electrophilicities. Measurements of the rates of elimination of nitrous acid from some 5-adducts in methanol catalysed by methoxide ions are reported. Values of rate constants may be influenced both by steric requirements at the reaction centre and by the electronic effects of the 7-substituent.
Journal Of Chemical Society Of Nigeria, 2019
Rate constants are reported for the reactions of 4-phenoxy-3-nitrobenzotrifluoride 3c, 2-phenoxy-5nitrobenzotrifluoride 4c and 1-phenoxy-2,4-dinitrobenzene 5c activated by trifluoromethyl (CF 3) or nitro (NO 2) groups with n-butylamine, pyrrolidine and piperidine in DMSO. The results are compared with results reported previously for same reactants and with the more strongly ring-activated compounds 4-phenoxy-3,5-dinitrobenzotrifluoride 1c and 2-phenoxy-3,5-dinitrobenzotrifluoride 2c in acetonitrile. A change in reaction medium from acetonitrile to DMSO leads to a reduction in values of k Am /k-1 as the proton-transfer from zwitterionic intermediates to catalysing amine becomes less thermodynamically favourable. Overall, the reactivity order is 5c > 3c> 4c and decreasing ringactivation in the 1-phenoxy compounds 1c-5c leads to lower values of k Am /k-1 resulting in greater susceptibility to base catalysis. Specific steric effects leading to rate-retardation, is noted for the ortho-CF 3 group. The higher reactivity of para-CF 3 group in compounds 3c compared to 4c has been attributed partly to the more effective polar hyperconjugative activation by the CF 3 group in 3c and to a possible participation of unfavourable electrostatic repulsion for the ortho-CF 3 group between the electronegative fluorine atoms in 4c and the incoming nucleophiles.
The thiolate anion as a nucleophile part X. Reactions of some nitrofluoroaromatics
Journal of Fluorine Chemistry, 1981
The reactions of various nitrofluorobenzenes, C H F N02, 6XY with sodium methanethiolate have been studied in ethylene glycol/pyridine mixture as solvent. All the fluorine atoms, but not the nitrogroups, could be substituted by the methylthio group. The reactions have also been studied with the addition of a deactivating group, either methyl or amino, on the aromatic nucleus. Some of the methylthio groups in the products were oxidized to the corresponding sulfones. The new compounds isolated have been characterized and their spectra (IR, NMR and mass) examined.
Regioselective Hydroxylations of 2-Nitrofluorene in Vivo : A Nuclear Magnetic Resonance Study
Chemical Research in Toxicology, 1997
The time-dependent metabolism of 2-nitrofluorene (2-NF) in vivo has been studied after ip administration to rats. After hydrolysis with-glucuronidase/arylsulfatase, five hydroxylated 2-nitrofluorenes were isolated by HPLC and identified by a combination of data from NMR, UV, and MS experiments. These metabolites were characterized as 6,9-dihydroxy-2-nitrofluorene (I), 9-hydroxy-2-nitrofluorene (II), 6-hydroxy-2-nitrofluorene (III), 7-hydroxy-2nitrofluorene (IV), and 8-hydroxy-2-nitrofluorene (V). The highest amounts of metabolites were found after 24 h of injection, and although the major ones were still present after 48 h, only traces of them could be found beyond that time. A unique feature of the present study was our ability to establish the position of the different hydroxylations that occur in vivo by NMR techniques and, thus, to observe the regioselectivity of the metabolism of the 2-NF in vivo. Furthermore, two conjugated metabolites were identified by 1 H-NMR and ESI-MS as 6-[(hydroxysulfonyl)oxy]-2-nitrofluorene (2-nitrofluorene 6-sulfate) (VI) and 7-[(hydroxysulfonyl)oxy]-2-nitrofluorene (2-nitrofluorene 7-sulfate) (VII).
Chemico-Biological Interactions, 1982
2-Nitrosofluorene (NOF) and N-hydroxy-2-aminofluorene (N-HO-AF)are potent direct-acting mutagens, derived from metabolic ~activation' of the carcinogen, N-acetyl.2-aminofluorene (AAF). To assess the ability of cellular glutathione (GSH) to detoxify these electrophilic derivatives, we examined the reaction of NOF and N-HO-AF with GSH in vitro. Two reaction products were isolated and identified as glutathionyl derivatives of 2-aminofluorene (AF) containing an N-S linkage. Amino acid analysis, infrared and NMR (500 MHz) spectroscopy, fast atom bombardment mass spectrometry and analysis of reaction characteristics and hydrolysis products established their structures as N-(glutathion-g-yl)-2-aminofluorene S-oxide (GS-AFI) and N-(glut athion-S-yl)-2-aminofluorene (GS-AFII). Ascorbic acid, which reduces NOF to N-HO-AF, was used to modify reaction yields. These results indicated that GS-AFI was derived from reaction with NOF and that GS-AFII could be formed from both NOF and N-HO-AF. A reaction scl~eme is proposed in which NOF reacts with GSH to form an intermediate addition product that can rearrange either to GS-AFI or be reduced to GS-AFII. The latter could also be formed by direct reaction with N-HO-AF.
Journal of Fluorine Chemistry, 2002
Dedicated to Professor Lev M. Yagupolskii on the occasion of his 80th birthday.
Canadian Journal of Chemistry, 2005
The reactions of four 4-nitrobenzofurazans (4a4d) substituted at the 7 position with (a) N-ethyl, (b) N-butyl, (c) piperidino, or (d) pyrrolidino groups have been examined with sulfite ions and with hydroxide ions in waterDMSO (80:20, v/v). Addition of sulfite at the 5 position gives σ adducts with equilibrium constants ca. 105 lower than that for the formation of the corresponding adduct from 4-nitrobenzofurazan. These reductions are attributed to the stabilization of the parent molecules 4a4d by conjugative interaction between the 4 and 7 substituents. In alkaline solution, 4a and 4b yield the conjugate bases while 4c and 4d suffer nucleophilic substitution to give 7-hydroxy-4-nitrobenzofurazan. Reactivity here is relatively high because of the iminium ion character of the substrates. Key words: benzofurazans, σ adducts, nucleophilic reactivity, substitution.