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New Journal of Chemistry
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DOI: 10.1039/C9NJ04725E
(i.e., geraniol (2), geometric isomer of nerol; -citronellol (3), not
allylic primary alcohol; -terpineol (4), tertiary alcohol; borneol (5),
a secondary saturated cyclic alcohol (Figure 12).
hydrogen peroxide. Lacunar sodium phosphotungstate salt was
more active than phosphomolybdate and silicotungstate catalysts.
We demonstrated that the presence of a vacancy in the Keggin
heteropolyanion played essential role for activity of catalyst. The
saturated salt (i.e., Na3PW12O40) was almost inactive; in this case,
alkyl peroxides were the main product. In Na7PW11O39-catalyzed
reactions, nerol epoxide was always the major product (ca. 90 %),
with a lower formation of aldehyde and diepoxide.
Effects of main reaction parameters were investigated. Catalyst
concentration and oxidant load had an impact mainly on reaction
selectivity. Others terpenic alcohols were also oxidized by hydrogen
peroxide in Na7PW11O39-catalyzed reactions. While geraniol has a
similar reactivity to the nerol, -citronellol, -terpineol and borneol
were less reactive.
OH
OH
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OH
OH
geraniol (2)
-citronellol (3)
-terpineol (4)
borneol (5)
Figure 12. Terpenic alcohols evaluated as substrates in Na7PW11O39-catalyzed oxidation
reactions with H2O2
Besides nerol (1), three terpenic alcohols (i.e., geraniol (2), -
citronellol (3), and -terpineol (4) have at minimum a double bond
that may be potentially epoxidized. However, only (2) and (3) could
be oxidized to aldehydes. Conversely, borneol may be oxidized to
camphor, a bicyclic ketone 37. The kinetics curves presented in Figure
13, clearly demonstrate the different reactivity of these substrates.
Conflicts of interest
There are no conflicts to declare.
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Acknowledgements
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nerol
The authors are grateful for the financial support from CNPq
and FAPEMIG (Brasil). This study was financed in part by the
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
- Brasil (CAPES) - Finance Code 001.
-citronelol
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40
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geraniol
-terpineol
borneol
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0
30
60
90 120 150 180 210 240
Time / min
2
3
Figure 13. Effect of terpenic alcohols on the conversion of Na7PW11O39-catalyzed
oxidation reactions with H2O2
aReaction conditions: alcohol (2.75 mmol); H2O2 (2.75 mmol); Na7PW11O39 (0.33 mol %);
temperature (298 K); CH3CN (10 mL)
4
5
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conversion (ca. 14 %); its epoxide and glycol were the main products
obtained. The lowest conversion (ca. 10 %) was attained in borneol
oxidation, with the camphor as only product.
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4. Conclusions
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