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Transition metal-catalyzed Dehydroperoxidationof Alkyl hydroperoxides
Jessica N. Hamann,a Marko Hermsen,a Anna-Corina Schmidt,a Joaquim H. Teles,b
R. Paciello,b A. Stephen K. Hashmi,a,c Thomas Schauba,b*aCatalysis Research Laboratory (CaRLa), Im Neuenheimer Feld 584, 69120 Heidelberg, Germany
bBASF SE, Synthesis and Homogeneous Catalysis, Carl-Bosch-Str. 38, 67056 Ludwigshafen, Germany cInstitute for Organic Chemistry, Heidelberg University, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany
*email: [email protected]
CaRLa (Catalysis Research Laboratory) is being co-financed by the University of Heidelberg andBASF SE.
Introduction
Proposed Mechanism
Chromium(VI) Catalysts
Kinetic Studies
Acknowledgement
Catalytic Activity
UV/Vis Spectroscopy
NMR Spectroscopy
Nylon 6 is produced via the ring-opening polymerization of ε-caprolactam, whereby themonomer is based on cyclohexanone. In the first step, cyclohexane is oxidized to cyclohexylhydroperoxide in a radical chain reaction, using O2 at elevated temperatures. The formedhydroperoxide decomposes subsequently to a ~1:1 mixture of cyclohexanone andcyclohexanol. In further steps, cyclohexanone reacts with hydroxylamine to thecorresponding cyclohexane oxime and via an acid catalyzed Beckmann rearrangement, thedesired ε-caprolactam is formed.1
Target
In order to minimize the number of process steps in the production of ε-caprolactam,development of applicable catalysts for the selective decomposition of the hydroperoxidesolely to the ketone and one equivalent water would be a very attractive target. Cr-, V-, Co-or Mn-catalysts have been investigated concerning the selective dehydroperoxidation andseems to be the most promising.2,3
Cr(VI) catalysts are known for the selective decomposition of cyclohexyl hydroperoxide.2,4
Homogeneous and heterogeneous catalyst systems were investigated with respect to thefavored formation of cyclohexanone. The focus was put on mechanistic studies usingdifferent spectroscopic methods.
Catalyst Conditions Conversion CyO
CrO3*py 100 °C, 60 min 99 % 91 %
CyOOH
CyOH
CyO
internal standard
before
after 60min@100°C
CyO
The new C=O vibration at ~ 1700 cm-1
indicates the formation of CyO
Based on our experimental observations and calculations a decomposition mechanism via thereactive Chromium (VI) alkylperoxo complex is proposed. Induced by an intramolecular H-atom transfer, the corresponding cyclohexanone is released. The dehydroperoxidationprecedes without radical species and chromium remains in the oxidation state (VI)
The proposed mechanismwas investigated by DFTcalculations. The obtainedresults are presented onthe Poster by MarkoHermsen. Take a look at it!
The formed intermediate decomposesfast with further reaction time.
The same behavior is known in theliterature for a tert-butyl-peroxychromium complex.5
2 min
10 min
48 h
Stoichiometric reaction of CyOOH and CrO3 @ 5 °C
CrO3 system
At different temperatures, kinetic studies were performed to gain insight into the order ofreaction.
ΔG# @ 323 K = 102.77 kJ / mol
The addition of stoichiometric amounts of CrO3 to pureCyOOH leads to the formation of the cyclo-hexylperoxychromium intermediate. Downfield shift of the ring-proton signal and thedisappearance of the OH-signal is observed.
NMR-shift exp. calc.
Pure substrate
OOH 5.83 6.62
OOCH 3.72 3.84
Coordinated
species
CrO2(OH)(OOCy)
OH 11.64 11.82
OOCH 4.09 4.19
Comparison of the observed NMR shifts and the relevant calculated shifts.
Pure CyOOH @ -20°COOH
OOCH
Addition of CrO3 @ -20°C
1) a) J. Hermolin, US 4465861, 1984. b) K. Pugi, US 3530185, 1970. c) A. Kuessner, G.Herrmann, US 3917708, 1975. d) J. D. Druliner, S. D. Ittel, P. J. Krusic, C. A. Tolman, US4326084, 1982. e) M. T. Musser, Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH,Weinheim, 2000.2) a) D. Loncarevic, J. Krstic, J. Dostanic, D. Manojlovic, Z. Cupic, D. M. Jovanovic, Chem. Eng. J.2010, 157, 181-188. b) M. Wang, J. Ma, C. Chen, X. Zheng, Z. Du, J. Xu, J. Mater. Chem. 2011,21, 12609-12612.3) A.-C. Schmidt, M. Hermsen, F. Rominger, R. Dehn, J. H. Teles, A. Schäfer, O. Trapp, T. Schaub,Inorg. Chem. 2017, 56(3), 1319-1332.4) a) M. Constantini, E. Fache, L. Gilbert, FR 2 744 719-A1, 1996. b) W. Buijs, R. Raja, J. MeurigThomas, H. Wolters, Catalysis Letters 2003, 91, 253-259.5) S. Boitsov, J. Songstad, J. Muzart, J. Chem. Soc., Perkin Trans. 2, 2001, 2318-2323.
References