The Beckmann Rearrangement in Concentrated Sulfuric Acid. Studies by Means of NMR and Kinetic Isotope Effect

Kim, Seung-Geon; Kawakami, Takeo; Ando, Takashi; Yukawa, Yasuhide

doi:10.1246/bcsj.52.1115

Cited by 13 publications

(8 citation statements)

References 20 publications

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“…[11] A plausible mechanism involves the formation of an oxime sulfonic acid 6 (Scheme 3), which was isolated and characterized. [19] The intermediacy of imidate 7 could imply a concerted rearrangement, [20] in which the oxygen atom of 2 is the 190 www.chemsuschem.org same as that of 1. Alternatively, [21] the dissociation of the [HSO 4 ] À anion could result in the cationic species 8, which can rapidly undergo a rearrangement to form the 1-aza-cycloheptenium cation 9.…”

Section: Ionic Liquidmentioning

confidence: 99%

ε‐Caprolactamium Hydrogen Sulfate: An Ionic Liquid Used for Decades in the Large‐Scale Production of ε‐Caprolactam

et al. 2008

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Ionic liquids [1] are among the solvents [2] which can be used by molecular designers [3] to fine tune the performance of chemical systems in order to facilitate high atom economy [4] for chemical reactions or facile separation of products from reagents or catalyst, [5] all constituting key parts of green chemistry. [6] In particular, they can provide control at the molecular level of the vapor pressure of the medium, [7] a key issue of process safety and environmental protection. The ultimate success of these solvents depends on whether they will be used commercially in small-or larger-scale applications. Of course, a profitable larger-scale process will convince others to explore and use the same or similar media for different applications. Ionic liquids are starting to leave the academic laboratories and find their way into a wide variety of industrial applications.[8] We have been investigating the mechanism of the Beckmann rearrangement of cyclohexanone oxime (1) to e-caprolactam (2) in sulfuric acid and oleum as described [9] and conclude now that the caprolactam process [10] is in fact the largest-scale industrial technology that has been using an ionic liquid, caprolactamium hydrogen sulfate (3), as the reaction medium for decades. We report here the physical characterization of this ionic liquid, including its remarkable capability to keep the vapor pressure of 12 % dissolved sulfur trioxide below 10 kPa even at 140 8C, allowing its safe use in large-scale processes for decades. The mechanism of the Beckmann rearrangement of cyclohexanone oxime (1) to e-caprolactam (2) has been also investigated in 18 O-labeled sulfuric acid, which revealed that the migration of the oxygen function is intermolecular. The cause of the accelerating effect of excess sulfur trioxide in the Beckmann rearrangement in oleum is discussed.The commercial processes of the Beckmann rearrangement of 1 to 2 are performed in the presence of oleum.[10] The reaction is carried out in the so-called "rearrangement mixture" obtained from mixing oleum with molten 1. As the reaction proceeds to complete conversion of 1 with a remarkable 99.5 % selectivity to 2, an appropriate amount of the rearrangement mixture is removed for neutralization with ammonia to produce the final product 2 and (NH 4 ) 2 SO 4 . The molar ratio of the oleum to 1, calculated as ([, is generally greater than one because the dissolved sulfur trioxide plays an important role by significantly increasing the rate of the reaction.[11] As the Beckmann rearrangement of 1 to 2 is very exothermic, [10] the control of the vapor pressure of SO 3 has therefore been a key safety issue.The reaction medium, traditionally called the rearrangement mixture, can be prepared by dissolving 2 in sulfuric acid or oleum. Importantly, note that the addition of one equivalent of 2 to 100 % sulfuric acid results in the formation of a colorless solid at room temperature, which becomes a viscous liquid around 60 8C. Although its viscosity decreases further by increasing the temperature, it was no...

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Section: Ionic Liquidmentioning

confidence: 99%

ε‐Caprolactamium Hydrogen Sulfate: An Ionic Liquid Used for Decades in the Large‐Scale Production of ε‐Caprolactam

et al. 2008

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“…The reaction is acid catalyzed under a variety of conditions and many mechanistic aspects of the reaction have long been firmly established [1][2][3][4][5][6][7][8]. Of particular interest from a practical point of view, but not exhaustively investigated, appears to be the rearrangement in aqueous sulfuric acid, where a large increase of rates has been observed in the range 80-100 wt% [6,7].…”

Section: Introductionmentioning

confidence: 99%

On the Beckmann rearrangement of ketoximes: A kinetic study in trifluoromethanesulfonic acid

Marziano¹,

Ronchin²,

Tortato³

et al. 2004

Int J of Chemical Kinetics

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The formation and the destruction of an intermediate involved in the Beckmann rearrangement of 2,4,6-trimethylacetophenone oxime have been studied in concentrated trifluoromethanesulfonic acid by kinetic and spectroscopic measurements. Observed (k obs ) and thermodynamic rate constants (k o ) have been estimated and the values compared with the ones obtained in perchloric, sulfuric, and methanesulfonic acids. In the range 80-100 wt% of sulfuric acid, combined analysis of k obs and k o rates shows a specific catalysis due to [H 2 SO 4 ] species. In trifluoromethanesulfonic acid, lower rate constants, compared to the values in sulfuric acid, have been observed which differ at 99 wt% by a factor of 10 3 ca. The catalytic effect of different strong acids, the structure of the intermediate inferred from Raman and NMR spectra, and the role of the ion-pairs involved in the reaction are discussed. C

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“…The first step proceeds in the presence of a base to allow the formation of the free hydroxylamine that, then, attacks the C=O group of the ketone. On the other hand, Beckmann rearrangement is generally carried out in mineral acid, i.e ., H 2 SO 4 or oleum , for which safety and/or disposal problems must be taken into account especially in the industrial practice . Furthermore, the resulting amides are protonated, thus, dilution with H 2 O or neutralization of the acid (typically with aqueous ammonia) is required to recover the pure product .…”

Section: Introductionmentioning

confidence: 99%

Density Functional Study of the Reaction Mechanism of Two Oxiimine Alcohol Formations and Their Novel Rearrangements

Kaya

2016

Helvetica Chimica Acta

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In this study, the reaction mechanisms of isonitrosoacetophenone (inapH) with ethanolamine (ea) and 1‐phenylethanolamine (pea) have been investigated theoretically using B3LYP/6‐311G(d,p) method to explain why the formation and unexpected rearrangement products occur or not occur. While the reaction between isonitrosoacetophenone (inapH) with ethanolamine gives oximine alcohol (Ib), the reaction of 1‐phenylethanolamine with inapH results in the formation of oximine alcohol with a different substituent (Ia) and amido alcohol (IIa), which is the unexpected rearrangement product. The rearrangement driving forces of compounds from Ia to IIa are calculated as ca. 28 and 23 kJ/mol in the gas and EtOH phases, respectively. These driving forces have been calculated ca. 46 and 45 kJ/mol for the rearrangement of compound Ib to obtain IIb in the same phases, respectively. This high driving force shows that the compound IIb cannot be obtained from rearrangement of compound Ib as described experimentally in the literature. In addition, as the DFT functionals poorly describe dispersion effects, dispersion correction for reaction heat and free‐energy barrier was estimated using the wB97X‐D/6‐311G(d,p). In general, the relative free energies of all molecules calculated from wB97XD method are lower than performed from B3LYP level. The changes of thermodynamic properties for all molecules with temperature ranging from 100 to 500 K have been obtained using the statistical thermodynamic method.

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The Beckmann Rearrangement in Concentrated Sulfuric Acid. Studies by Means of NMR and Kinetic Isotope Effect

Cited by 13 publications

References 20 publications

ε‐Caprolactamium Hydrogen Sulfate: An Ionic Liquid Used for Decades in the Large‐Scale Production of ε‐Caprolactam

ε‐Caprolactamium Hydrogen Sulfate: An Ionic Liquid Used for Decades in the Large‐Scale Production of ε‐Caprolactam

On the Beckmann rearrangement of ketoximes: A kinetic study in trifluoromethanesulfonic acid

Density Functional Study of the Reaction Mechanism of Two Oxiimine Alcohol Formations and Their Novel Rearrangements

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