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: thomas.schaub@basf.com

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