- Nitrosation of dialkylhydroxylamines, and computational and NMR investigations of the interconversion of conformational isomers of N-nitroso-dimethylhydroxylamine
-
The effect of acidity upon the rate of nitrosation of N-benzyl,O- methylhydroxylamine (3) in 1:1 (v/v) H2O/MeOH at 25°C has been investigated. The pseudo-first-order rate constant (kobs) for loss of HNO2 as the limiting re
- Crugeiras, Juan,Maskill, Howard,MacFarlane, William,Menneer, Iain D.,Rios, Ana,Rios, Miguel A.
-
experimental part
p. 162 - 171
(2011/10/08)
-
- N-nitroso-N,O-dialkylhydroxylamines: Preparation, structure, and mechanism of the hydronium ion catalysed solvolytic nitrous oxide extrusion reaction
-
Eleven N-nitroso-N,O-dialkylhydroxylamines, RN(NO)OR′, have been prepared and the mechanisms of their hydronium ion catalysed solvolyses in aqueous solution which liberate nitrous oxide have been investigated. All reactions are first-order in substrate and first-order in hydronium ion, and the second-order rate constants at 25°C vary over a range of less than 140 in spite of considerable variation in substrate structure (R ranges from methyl to 4-methoxybenzyl to 2-adamantyl, for example) and changes in solvent composition (water with up to 50% methanol or 66% acetonitrile). Enthalpies and entropies of activation are qualitatively similar throughout the range (ΔH?= 72-93 kJ mol-1 and ΔS? = -19 to -57 J K-1 mol-1) which, with the product analyses, are accommodated by a mechanism involving pre-equilibrium protonation of the substrates followed by rate-limiting dissociation to give RN2O+ and HOR′. The oxodiazonium ion intermediate, RN2O+, then dissociates further to give the carbenium ion intermediate, R+, or suffers direct nucleophilic displacement of N2O by solvent (the external nucleophile) or by R′OH (the internal nucleophile liberated in the initial fragmentation). The carbenium ion, R+ (if formed), suffers nucleophilic capture either by solvent or by R′OH. When acetonitrile is the co-solvent (rather than methanol) for the N-(2-adamantyl) substrate 3g, the product of the Ritter reaction, 2-acetamidoadamantane, is detected. These nitrous oxide liberating reactions are compared with the nitric oxide liberating reactions of related N-nitrosohydroxylamines, and the origin of the difference between them is identified. The N(1)-nitroso group in the N,O-dibenzyl compound 3c is shown by X-ray crystallography to be essentially coplanar with the C and O atoms also bonded to N(1).
- Bhat, J. Ishwara,Clegg, William,Maskill, Howard,Elsegood, Mark R.J.,Menneer, Iain D.,Miatt, Peter C.
-
p. 1435 - 1446
(2007/10/03)
-
- Nitrosation of Amines in Nonaqueous Solvents. 3. Direct Observation of the Intermediate in Cyclohexane
-
The reactions of N-methylaniline (MeAn) with 2,2-dichloroethylnitrite (DCEN) and 2,2,2-trichloroethylnitrite (TCEN) in cyclohexane, and N-methylmethoxyamine (MMA) with TCEN in the same solvent, all gave the expected N-nitrosamines. Spectrophotometric monitoring of the MeAn/DCEN and MMA/TCEN reactions showed accumulation of the reaction intermediate. These are the first nitrosations of amines by alkyl nitrites in which observation of the intermediate has been possible; this is attributed to the low basicity of these amines (a) having effectively eliminated the possibility of the intermediate decomposing by base catalysis and (b) having decreased the rate of spontaneous decomposition of the intermediate more than the rate of its formation. Because of the scant capacity of cyclohexane to stabilize charge, it is assumed that both the formation and decomposition of the intermediate occur via concerted mechanisms with four-center transition states: formation through nucleophilic attack by the amine on the nitroso group accompanied by transfer of the amine proton to this group, decomposition through simultaneous cleavage of the N-O bond, and protonation of the alkoxide leaving group.
- Boni,Garcia-Rio,Leis,Moreira
-
p. 8887 - 8892
(2007/10/03)
-
- THE FORMATION OF AZOXYALKANES IN REACTIONS OF SOME ORGANOMETALLIC REAGENTS WITH N-nitroso-O,N-DIALKYLHYDROXYLAMINES: THE NONPHOTOCHEMICAL SYNTHESIS OF AN ACYCLIC (E)-AZOXYALKANE
-
Azoxyalkanes were found to be regiospecifically formed in the reactions of some alkyllithium and Grignard reagents with N-nitroso-O,N-dialkylhydroxylamines.Remarkably, although (Z)-stereomers were usually produced, in one case the (E)-isomer was predominant.
- Meesters, A. C. M.,Rueerger, H.,Rajeswari, K.,Benn, M. H.
-
p. 264 - 268
(2007/10/02)
-