Room-temperature tandem conversion of cyclic alkenes into 1,2-diols using molecular oxygen and β-MnO heterogeneous catalyst
In the cyclic alkene epoxidation reactions using molecular oxygen as oxidant, aldehyde is generally added as co-oxidant to assist transition metal catalyst to activate the oxygen molecule, oxidizing cyclic alkene and producing the corresponding epoxide; however, the added aldehyde would be converted...
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Published in | Green chemistry : an international journal and green chemistry resource : GC Vol. 25; no. 22; pp. 9262 - 9271 |
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Main Authors | , , , , , , , , |
Format | Journal Article |
Published |
13.11.2023
|
Online Access | Get full text |
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Summary: | In the cyclic alkene epoxidation reactions using molecular oxygen as oxidant, aldehyde is generally added as co-oxidant to assist transition metal catalyst to activate the oxygen molecule, oxidizing cyclic alkene and producing the corresponding epoxide; however, the added aldehyde would be converted into byproduct carboxylic acid. Herein, we report the room-temperature tandem conversion of cyclic alkenes into 1,2-diols through the application of byproduct carboxylic acid as a catalyst for epoxide hydration reaction, realizing effective utilization of the byproduct and saving energy consumption. Four kinds of nanosized MnO
2
specimens, including α-, β-, δ-, and γ-MnO
2
, were hydrothermally synthesized and applied as heterogeneous catalysts for the room-temperature tandem conversion of cyclohexene into 1,2-cyclohexanediol using molecular oxygen as oxidant and isobutyraldehyde as co-oxidant. The characterization results demonstrated that the obtained β-MnO
2
sample had the maximum Mn
4+
/Mn
3+
ratio of 1.42 and the minimum O
ads
/O
Latt
ratio of 0.34, consistent with its least oxygen vacancies evidenced by EPR measurement. Accordingly, the β-MnO
2
sample revealed the quickest alkene epoxidation reaction rate and could achieve a 99.2% cyclohexene conversion within 1 h, and meanwhile, a 73.6% 1,2-cycloheanediol yield could be attained within 24 h. A plausible mechanism for the tandem conversion of cyclohexene into 1,2-cyclohexanediol over the β-MnO
2
heterogeneous catalyst was proposed and further verified by quenching experiments and DFT calculations. Furthermore, the synthesized β-MnO
2
catalyst sample could be reused more than ten times, and meanwhile, the tandem conversion way could be expanded to most of the cyclic alkene substrates, which demonstrated that the β-MnO
2
catalyst was an active and stable heterogeneous catalyst for tandem conversion of cyclic alkenes into 1,2-diols.
Tandem conversion of cyclohexene into 1,2-cycloheanediol was attained by applying the generated by-product carboxylic acid as catalyst 2, realizing the effective utilization of isobutyric acid, shortening reaction time, and saving energy consumption. |
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Bibliography: | https://doi.org/10.1039/d3gc02863a Electronic supplementary information (ESI) available. See DOI |
ISSN: | 1463-9262 1463-9270 |
DOI: | 10.1039/d3gc02863a |