Nov 9, 2010 - Terpene Thermal Rearrangement ... Highly functionalized molecules: building blocks for fine ... Linalool: used in flavor/fragrance industry,.
Terpene Thermal Rearrangement Chemistry : a Kinetic Study Nick M. Vandewiele, Kevin M. Van Geem, Marie-Françoise Reyniers, Guy B. Marin
Laboratory for Chemical Technology, Ghent University http://www.lct.UGent.be
Terpenes / Terpenoids • Oligomers of isoprene • Highly functionalized molecules: building blocks for fine chemicals Isoprene • Stereo-isomerism / chirality : flavour/odor-active components • Occurence in the extractives of biomass, e.g. Pines • Source of volatile organic compounds, green house gases
Limonene
Steroid skeleton
Vitamin A
9 november 2010 Eur JOC 2006, 15, 3317
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Industrial Production Kraft pulping process • Wood chips conversion into cellulosic fibers • Crude Sulfate Turpentine (CST), byproduct stream, highly concentrated in pinenes (~90%) CST
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Industrial terpenes • Acyclic functionalized terpenes are of industrial importance • Acyclic compounds obtained via rearrangement of bicyclic isomers • Industrial route: gas phase thermal isomerization, relevant due to high selectivity (~80%)
Gajewski et al., Tetrahedron 2002, 58, 6943 9 november 2010
Lemée et al., Synth. Commun. 1995, 25, 1313
Ohloff et al., Tetrahedron 1962, 18,37
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2-Pinanol rearrangement into linalool • Linalool: used in flavor/fragrance industry, precursor of vitamin A • Cis- & trans-2-pinanol, diastereomers: available for experiments • 2-pinanol-to-linalool: last step in route from biomass (pinenes) to linalool
Cis-2-pinanol
Trans-2-pinanol
Can we model the behaviour and mutual differences between the diastereomers in terms of elementary 9 november 2010 reactions?
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Experiments • Isothermal plug flow reactor (4mm ID, • Methane dilution: 64 1.47m length) & 89 mol% CH4 • 59 experiments (35 cis , 24 trans) • Conversion: 7 – 97 % • Analysis: GC + FID (off• T: 485 – 590 °C line sampling) • P: 120 & 440 kPa
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2-Pinanol chemistry: linalool route Linalool H3 C
H3C
OH
Plinol H3 C
OH
OH CH
C H3C H3 C
Cis-2-pinanol
OH
Plinol isomers: lumped
CH3 CH3
Stepwise cyclobutane fragmentation Concerted fragmentation (Woodward-Hoffmann) 9 november 2010
CH3
Pericyclic ene cyclization: concerted reaction through 6membered transition state
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Side-routes Linalool H3C
H3C
Plinol
OH
H 3C
OH
OH CH H3C OH C
H 3C H3C
Cis-2-pinanol
CH3
OH
CH3
[1,5]H-shift
H 3C
Cis-β-terpineol
CH3
O
CH3 CH3
Alternative cyclobutane fragmentation
CH3
H3 C OH CH3 C CH3
H3C
OH
OH
Retro-ene
CH
Isolinalool 9 november 2010
H3C
Not observed Ene 8 cyclization
Stereo-aspects Plinol
Linalool H3C
H3 C
OH
OH
H 3C
OH CH H3 C
OH
C H 3C
H 3C
Trans-2-pinanol
CH3
Stereo-aspects of ene-cyclization not taken into account
OH
Trans-β-terpineol
H3 C
O
CH3
CH3 CH3
CH3 H 3C
OH CH3 CH3
C CH3 CH
H 3C
OH
H 3C
OH
Isolinalool 9 november 2010
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Reactivity / Selectivity Differences Cis-2-pinanol more selective towards linalool than trans-2pinanol
Cis-2-pinanol more reactive than trans-2-pinanol 9 november 2010
Vandewiele et al., submitted to J. of Analytical and Applied Pyrolysis, 2010
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Kinetic modelling: methodology Only elementary reactions considered
Pre-exponential factors fixed to literature values, equal in both models Activation energies estimated Thermodynamic consistency applied Calculated from TD properties of species via Benson group additivity scheme
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Kinetic models: results H3 C
OH
H3C
OH
Cis-2Pinanol H3C
OH CH H 3C OH C
H3C
H3C
OH
CH 3
CH3 CH3
H3C OH CH 3 C CH3 CH
H3 C
OH
H3 C
OH
H3 C
O
CH3 CH3
Trans-2Pinanol
CH3
Kinetic models: good agreement with experimental data for all response 12 variables
9 november 2010
Cyclobutane Fragmentation A = 1014 s-1
Ea (kJ/mol)
Cis
206±2
Trans
211±2
Linalool H3C
OH CH
C H3C
H3C
OH
Small Δ Ea : reactivity, selectivity difference
CH 3
CH3 CH3
H3C OH CH 3 C CH3
A = 1014 s-1
Ea (kJ/mol)
Cis
225±2
Trans
225±2
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CH
H
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Biradical Rearrangements H3 C
OH
A = 1013.8 s-1 Ea (kJ/mol)
H3C
Cis
88±6
Trans
88±6
OH CH H 3C OH
A = 1011.2 s-1 Ea (kJ/mol)
C H3C
H3C
OH
CH 3
Cis
67±6
Trans
67±6
CH3 CH3
H3C OH CH 3 C CH3 CH
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H3 C
OH
Same kinetics for both models despite connectivity & stereodifferences 14
Pericyclic Ene - cyclizations H3 C
OH
H 3C OH
H3C
OH
A = 108 s-1
Ea (kJ/mol)
Cis
122±2
Trans
122±2
Ene – cyclizations: Same kinetics for both reactions
CH 3 C CH3
H3 C
OH
H3 C
OH
H3 C
O
CH3 CH3
9 november 2010
Fast invisible
CH3
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Conclusion • Kinetic models: – Elementary reactions – Describe chemistry and kinetics of cis/trans 2-pinanol
• Reactivity and selectivity disparities: – Determined by one elementary reaction
• Substituents of the bicycloheptane system – influence initial cyclobutane fragmentation – negligible effect on downstream reactions Generalization to other terpenes?
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Acknowledgements • Aäron Vandeputte • Special Research Fund UGent B/10681/02 – BOF09/DOC/374 • Long Term Structural Methusalem Funding by the Flemish Government - grant number BOF09/01M00409. • Fund for Scientic Research - Flanders (FWO)
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Questions?
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Backup: generalization Mechanism: Substituents of the bicycloheptane system have little or no influence on isomerization chemistry of thermal rearrangements
OH O
HO
O OH
OH
OH HO
HO
Kinetics: Substituents of the bicycloheptane system influence the initial cyclobutane fragmentation, but have no influence on downstream reactions? 9 november 2010
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Backup: kinetic parameters Table 1: Pre-exponential factors and fitted activation energies for the two possible cyclobutane rupture reactions (A and B), for the biradical rearrangements (C, D and E), for the ene cyclizations (F and G) and the retro-ene reaction (H) used in the kinetic models of cis- and trans-2-pinanol
Reaction
Cis-2-pinanol Log10A (s-1)
Ea (kJ mol-1)*
A B C D E
14.0 14.0 13.8 11.2 13.8
206±2 225±2 88±6 67±6 88†
F G H
Log10 A (s-1) 8.0 8.0 11.3
Trans-2-pinanol Log10A Ea (kJ mol-1)* (s-1) 14.0 211±2 14.0 225±2 13.8 88±6 11.2 67±6 13.8 88† Ea (kJ mol-1) 122±2 122±2 100#
*
95% confidence level
†
Kinetic parameters of the subsequent biradical rearrangement E were taken equal to the fitted parameters of
the analogous rearrangement reaction C #Kinetic parameter not estimated
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Duplication of reaction channels
Ohloff et al., Tetrahedron 1962, 18,37
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Kinetic models: results
5
90
Reconstructed weight fraction (%)
3
40
100
Reconstructed weight fraction (%)
Kinetic models: good agreement with experimental data for all response variables
80 70 60 50 40 30
30
20
10
Reconstructed weight fraction (%)
Reconstructed weight fraction (%)
20
2
1
10
4
0
0 0
10
20
30
40
50
60
70
80
90
100
0
3
2
10
20
30
40
Analytical weight fraction (%)
Analytical weight fraction (%)
Linalool
Cis-2-pinanol
1
100
0
1
2
3
0
1
2
3
4
5
Isolinalool
B-terpineols Reconstructed weight fraction (%)
5
Ketone compound
4
80 70 60 50 40 30
30
20
10
20 3
10 0
0 0
2
10
20
30
40
50
60
70
80
90
Analytical weight fraction (%)
Trans-2-pinanol
1
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40
90
Analytical weight fraction (%)
Analytical weight fraction (%)
Reconstructed weight fraction (%)
0
Reconstructed weight fraction (%)
0
100
0
10
20
30
Analytical weight fraction (%)
Plinol 22
0 0
1
2
3
4
Analytical weight fraction (%)
5
40
