The mechanisms of the hydrolyses of N-nitrobenzenesulfonamides, N-nitrobenzamides and some other N-nitro amides in aqueous sulfuric acid 1

Cox, Robin A.

doi:10.1039/a700949f

Cited by 14 publications

(4 citation statements)

References 39 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The effect of the Madelung potential from the zeolite framework slightly lowers the activation energy as compared to that obtained from the bare cluster model. The results agree well with previous studies which have investigated in the same reaction for other different molecules such as N -nitrobenzene sulfonamides, isocyanates, β-lactams, carbodiimine, and acetamide . The activation energy for the tautomerization step of these molecules is ∼105−125 kJ/mol.…”

Section: Resultssupporting

confidence: 92%

Density Functional Study of the Mechanism of the Beckmann Rearrangement Catalyzed by H-ZSM-5: A Cluster and Embedded Cluster Study

2005

View full text Add to dashboard Cite

The mechanism of the Beckmann rearrangement (BR) catalyzed by the ZSM-5 zeolite has been investigated by both the quantum cluster and embedded cluster approaches at the B3LYP level of theory using the 6-31G(d,p) basis set. Single-point calculations were carried out at the MP2/6-311G(d,p) level of theory to improve energetic properties. The embedded cluster model suggests that the initial step of the Beckmann rearrangement is not the O-protonated oxime but the N-protonated oxime. The energy barriers derived from the proton shuttle of the N-bound to the O-bound isomer are determined to be approximately 99 and approximately 40 kJ/mol for the embedded cluster and quantum cluster approaches, respectively. The difference in the activation energy is due mainly to the effect of the Madelung potential from the zeolite framework. The next step is the rearrangement step, which is the transformation of the O-protonated oxime to be an enol-formed amide compound, formimidic acid. The activation energy, at the rearrangement step, is calculated to be approximately 125 and approximately 270 kJ/mol for the embedded cluster and quantum cluster approaches, respectively. The final step is the tautomerization step which transforms the enol-form to the keto-form, formamide compound. The energy barrier for tautomerization is calculated to be 123 and 151 kJ/mol for the embedded cluster and quantum cluster approaches, respectively. These calculated results suggest that the rate-determining step of the vapor phase of the Beckmann rearrangement on H-ZSM-5 is the rearrangement or tautomerization step.

show abstract

Section: Resultssupporting

confidence: 92%

Density Functional Study of the Mechanism of the Beckmann Rearrangement Catalyzed by H-ZSM-5: A Cluster and Embedded Cluster Study

2005

View full text Add to dashboard Cite

show abstract

“…Although sulfonylium ions are much more difficult to form than acylium ions 14 and there are no well-established cases for their formation during substitution at sulfonyl centers, 6 the present case is compatible with the similar acylium ion mechanism suggested for the acid-catalyzed hydrolysis of β-lactams 36,37 and the unimolecular ring opening in β-phospholactams. 38 An A1 process has been suggested for the hydrolysis of N-nitrobenzenesulfonamides, 39 whereas the evidence for such a mechanism in the hydrolysis of five-membered γ-sultams is ambiguous, although most of the evidence is consistent with a bimolecular mechanism. 40 The effect of amine basicity on the acid-catalyzed hydrolysis of substituted N-aryl β-sultams is shown by the Brønsted-type plot in Figure 6.…”

Section: Resultsmentioning

confidence: 99%

Reactivity and Mechanism in the Hydrolysis of β-Sultams

et al. 2000

View full text Add to dashboard Cite

β-Sultams show extraordinary rate enhancements of 10 9 -and 10 7 -fold, respectively, compared with the acid-and base-catalyzed hydrolysis of corresponding acyclic sulfonamides. They are about 10 3 -fold more reactive than analogous β-lactams. The alkaline hydrolysis of some β-sultams shows a rate term that is secondorder in hydroxide ion concentration, which is indicative of a stepwise mechanism involving a trigonal bipyramidal intermediate (TBPI). The Brønsted β lg value for the alkaline hydrolysis of N-aryl-β-sultams is -0.58 and the kinetic solvent isotope effect k OHfor N-alkyl-β-sultams is 1.55, indicative of rate-limiting breakdown of the TBPI. The acid-catalyzed hydrolysis of β-sultams is strongly retarded by electron-withdrawing groups R to the sulfonyl group, and it is suggested that the mechanism may involve unimolecular ring opening to generate a sulfonylium ion. The Brønsted β lg value for the acid-catalyzed hydrolysis of N-benzyl-β-sultams is 0.32. The generalacid-catalyzed hydrolysis of N-benzyl-β-sultam by carboxylic acids shows a Brønsted R value of 0.67 and is attributed to a specific acid-nucleophilic mechanism with the formation of a mixed-anhydride intermediate.

show abstract

“…Nitramides: Me 2 NNO 2 : [11,43,44] 14 N Experiments were complicated by the fast decomposition in triflic acid, which prevented us from obtaining a T 1 for the slowly relaxing (sharp) NO 2 signal; we did not attempt any 17 O measurement.…”

Section: And Their Changes)mentioning

confidence: 99%

Site of Protonation of Carboxylic and Non-Carboxylic Amides in the Gas Phase and in Water

et al. 1999

View full text Add to dashboard Cite

The site of protonation of several types of amide bases (carboxylic amides and thioamides, sulfenamides, sulfinamides, sulfonamides, nitrosamides, nitramides, cyanamides, and phosphorous and phosphoric acid triamides) has been investigated through a combination of quantum chemical calculations and heteronuclear NMR measurements. Relative energies of tautomeric ions deriving from protonation at the various sites were determined both in the gas phase (by MP2 calculations) and in water (by the IPCM continuum solvation method). Relevant NMR properties of the involved heteronuclei (nuclear shielding and electric field gradient) were calculated at the GIAO-HF level, and compared with chemical shifts and relaxation rates experimentally measured in 14 N, 17 O, and 31 P spectra. It is shown that such a combination of theoretical and experimental tools allows a dependable prediction of spectral parameters and ultimately of the protonation site of amides. The reliability of common assumptions, like the comparison of spectral parameters of polyfunctional bases and monofunctional models, is also scrutinized and tested.

show abstract

The mechanisms of the hydrolyses of N-nitrobenzenesulfonamides, N-nitrobenzamides and some other N-nitro amides in aqueous sulfuric acid 1

Cited by 14 publications

References 39 publications

Density Functional Study of the Mechanism of the Beckmann Rearrangement Catalyzed by H-ZSM-5: A Cluster and Embedded Cluster Study

Density Functional Study of the Mechanism of the Beckmann Rearrangement Catalyzed by H-ZSM-5: A Cluster and Embedded Cluster Study

Reactivity and Mechanism in the Hydrolysis of β-Sultams

Site of Protonation of Carboxylic and Non-Carboxylic Amides in the Gas Phase and in Water

Contact Info

Product

Resources

About