1022-07-7Relevant academic research and scientific papers
Evidence of the presence of minor tautomeric forms in selected nitroanilines
Colasurdo, Diego D.,Pila, Matías N.,Laurella, Sergio L.,Allegretti, Patricia E.,Ruiz, Danila L.
, (2021)
Rationale: Nitroanilines can exist in several tautomeric forms: nitro-amino, nitro-imino, and aci-imino. The importance of evaluating minor tautomeric species comes from the fact that even less abundant tautomers have been proved to play important roles in reaction mechanisms. Methods: Electron ionization mass spectra of the pesticide Pendimethalin and four related nitroanilines were recorded at 70 eV to find information about the presence of minor tautomeric forms in the gas phase. The existence of the possible tautomers was evaluated by studying specific fragmentation pathways, which were confirmed by tandem mass spectrometry (MS/MS) experiments. Further supporting information was obtained by studying the structures of some intermediate compounds by theoretical calculations at the B3LYP 6-311++G(d,p) level. Results: The mass spectrum of Pendimethalin suggests the coexistence of the nitroamine tautomer (the most stable form) with four possible less stable tautomers in equilibrium. The fragmentation routes were used to explain analogous peaks in two related compounds. However, the spectra of two other related compounds that cannot follow the proposed route of fragmentation for nitro-imine tautomers do not show the analogous peak. Theoretical calculations were used to correlate the precursor cation with the proposed fragmentation pathway. Conclusions: By the study of mass spectra and proposed fragmentation pathways it can be concluded that, although the nitro-amine is the most abundant species within the system, minor tautomers (nitro-imine and aci-imine) coexist in the gas phase.
RAPID INJECTION NMR: A SIMPLE TECHNIQUE FOR THE OBSERVATION OF REACTIVE INTERMEDIATES
McGarrity, John F.,Prodolliet, Jacques,Smyth, Timothy
, p. 59 - 65 (1981)
A system has been designed for the NMR observation (at 60 MHz) of unstable intermediates, with half-lives of 100 ms, at concentration levels above 1E-2 M.Rapid mixing can be achieved in less than 40 ms and a series of eight spectra acquired in less than 1.08 s.Low temperature operation is straightforward.Reactive intermediates involved in the reaction of methylamine with 2,4,6-trinitroanisole and the acid-catalysed hydrolysis of 1,1-diethoxy-2,3-diphenylcycloprop-2-ene were identified, and in a kinetic application, the rate of hydrolysis of trimethyloxonium tetrafluoroborate was measured.
15N NMR and FTIR studies of 2,4-dinitroanilines and their salts
Gierczyk,Leska,Nowak-Wydra,Schroeder,Wojciechowski,Bartl,Brzezinski
, p. 217 - 225 (2007/10/03)
Twenty-two 2,4-dinitroanilines were synthesised and their pK(a) values were determined. The 2,4-dinitroanilines and their protonated forms were studied by 15N NMR spectroscopy. The relations between the 15N NMR chemical shifts and the pK(a) values of the 2,4-dinitroanilines and their salts were found to be linear. The deprotonation reaction of N-methyl-2,4- dinitroanilines and N-methyl-2,4,6-trinitroaniline by MTBD was successful only for the latter and yielded protonated MTBD molecule and the anion in which the electrons are strongly delocalised. The kinetic parameters of the 2,4-dinitroanilines in reactions with hydroxide ions in mixed solvent DMSO:water (95:5, v/v) were determinated and discussed. (C) 2000 Elsevier Science B.V.
N-denitration of nitramines by dihydronicotinamides
Chapman, Robert D.,O'Brien, Richard A.,Kondracki, Paul A.
, p. 9655 - 9664 (2007/10/03)
N-NO2 bond scission in organic nitramines occurs in high yields by reaction with 1,4-dihydronicotinamides. HMX (3) and tetryl (4) were used as model aliphatic and aromatic nitremines in reactions with 1-benzyl-1,4- dihydronicotinamide (BNAH, 1), resulting in hexamethylenetetramine and N- methylpicramide (5), respectively, as the predominant products. Radical initiation of the electron-transfer denitrohydrogenation mechanism is achieved either by photolysis or chemically by dithionite ion. A polymer- supported analogue of BNAH effects similar, though slower, N-denitration.
AROMATIC NUCLEOPHILIC SUBSTITUTION REACTIONS OF ACTIVATED N-ARYLPYRAZOLES WITH FORMAMIDES
Chiriac, Constantin I.,Lupu, Viorel,Chiriac, Florentina,Ropot, Radu,Tibirna, Mihaela,Truscan, Ion
, p. 549 - 553 (2007/10/03)
Different activated N-arylpyrazoles, as N-(2',4'-dinitrophenyl)-3,5-dimethylpyrazole, N-picryl-3,5-dimethylpyrazole etc., can react with excess formamides, as formamide N-methylformamide and N,N-dimethylformamide, at 165-175 deg C, for 5-6 hours, resulting amines in high yieds.This reaction is influenced by steric hindrance.
Aromatic nucleophilic substitution reactions of 1-dialkylamino-substituted activated benzenes with various amines in dimethyl sulfoxide
Sekiguchi, Shizen,Ishikura, Hiromi,Hirosawa, Yukitoshi,Ono, Nobuyuki
, p. 5567 - 5578 (2007/10/02)
In the reactions of 1-dlalkylamino-2,4,6-trinitro- and 1-dialkylamlno-2, 4-dinitrobenzenes with various amines in dimethyl sulfoxide, 1-dialkylamino group is easily replaced with primary n-alkylamines at room temperature, and in a low yield with pyrrolidine only among secondary amines.
Kinetics of the Reactions of Nitro-substituted N-Alkylacetanilides with Sodium Methoxide in Methanol
Sekiguchi, Shizen,Miyazaki, Chika,Motegi, Masayuki
, p. 1333 - 1338 (2007/10/02)
The sodium methoxide-catalysed methanolysis of N-ethyl (3) or N-methyl-2',4',6'-trinitroacetanilide (4) is found to proceed with initial formation of a 1,3-disubstituted anionic ?-complex (II), which then reverts to the reactant system, relatively slowly giving N-alkyl-4-methoxy-(main product) and N-alkyl-2'-methoxy-4',6'-dinitroacetanilides with the amido group unchanged, via a 1,4-disubstituted anionic ?-complex (III); kinetics and absorption and 1H n.m.r. spectral data are reported.
N-methylpicramide-methoxide ion interactions: proton abstraction versus ?-complex formation
Buncel, Erwin,Hamaguchi, Masashi,Norris, Albert R.
, p. 1615 - 1620 (2007/10/02)
The interaction of N-methylpicramide (NMP) with methoxide ion in dimethylsulfoxide-methanol media and with 1,4-diazabicyclooctane in dimethylsulfoxide have been investigated spectrophotometrically at 25.0 deg C.Dimethylsulfoxide has been found to stabilize the conjugate base of NMP, formed via loss of hydrogen ion from the methylamino group, with respect to the anionic ?-complex generated via addition of methoxide ion to a ring carbon position.As a result, methanol-dimethylsulfoxide solutions rich in dimethylsulfoxide (i. e. 95/5, v/v, DMSO/MeOH) contain the conjugate base of NMP as the sole product of the 1:1 interaction of NMP and methoxide ion.At mole ratios of methoxide ion to NMP>1 a second interaction results, yielding a dianion formed via addition of methoxide ion to one of the H-bearing ring carbon atoms of the conjugate base.Values of absorption maxima and molar absorptivities at the absorption maxima for the conjugate base of NMP and the dianion are reported here for the first time.
1H NMR Studies of Proton Transfer and ?-Complex Formation in the Reactions of N-Substituted Picramides with Oxygen and Nitrogen Bases
Crampton, Michael R.,Gibson, Brenda,Metthews, Raymond S.
, p. 455 - 459 (2007/10/02)
1H NMR measurements of N-substituted picramides in dimethyl sulphoxide-methanol containing sodium methoxide show that the two major modes of 1:1 interaction involve transfer of an amino proton to give the conjugate base or methoxide attack at the 3-position to give a ?-adduct.The proportion of parent reacting by the latter pathway increases as the proportion of methanol in the solvent increases.Some comparative measurements in isopropanol-dimethyl sulphoxide show that relative to methoxide the isopropoxide ion has a greater propensity abstraction than for base addition.Reaction of the substrates with amide ions derived from piperidine or from benzylamine gives ?-complexes by attack at unsubstituted ring positions.In the benzylamide adducts spin coupling is observed between the amino proton and the adjacent ring and methylene protons.
