Synlett 2017; 28(16): 2184-2188
DOI: 10.1055/s-0036-1588869
letter
© Georg Thieme Verlag Stuttgart · New York

Fine-Bubble-Based Strategy for the Palladium-Catalyzed Hydrogenation of Nitro Groups: Measurement of Ultrafine Bubbles in Organic Solvents

Nobuyuki Mase*
a  Applied Chemistry and Biochemical Engineering Course, Department of Engineering, Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johoku, Hamamatsu, Shizuoka 432-8561, Japan
b  Graduate School of Science and Technology, Shizuoka University, 432-8561, Japan
c  Green Energy Research Division, Research Institute of Green Science and Technology, Shizuoka University, 432-8561, Japan   Email: [email protected]
,
Yuki Nishina
a  Applied Chemistry and Biochemical Engineering Course, Department of Engineering, Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johoku, Hamamatsu, Shizuoka 432-8561, Japan
,
Shogo Isomura
a  Applied Chemistry and Biochemical Engineering Course, Department of Engineering, Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johoku, Hamamatsu, Shizuoka 432-8561, Japan
,
Kohei Sato
a  Applied Chemistry and Biochemical Engineering Course, Department of Engineering, Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johoku, Hamamatsu, Shizuoka 432-8561, Japan
,
Tetsuo Narumi
a  Applied Chemistry and Biochemical Engineering Course, Department of Engineering, Graduate School of Integrated Science and Technology, Shizuoka University, 3-5-1 Johoku, Hamamatsu, Shizuoka 432-8561, Japan
b  Graduate School of Science and Technology, Shizuoka University, 432-8561, Japan
c  Green Energy Research Division, Research Institute of Green Science and Technology, Shizuoka University, 432-8561, Japan   Email: [email protected]
,
Naoharu Watanabe
b  Graduate School of Science and Technology, Shizuoka University, 432-8561, Japan
› Author Affiliations
This work was supported in part by a Grant-in-Aid for Scientific Research (B) (No. 15H03844) for scientific research from the Japan Society for the Promotion of Science.
Further Information

Publication History

Received: 21 April 2017

Accepted after revision: 11 May 2017

Publication Date:
06 July 2017 (online)


Abstract

Fine bubbles of hydrogen were employed as a new reaction medium for the autoclave-free gas–liquid–solid multiphase hydrogenation of nitro groups on a multigram scale. Furthermore, ultrafine bubbles were examined by nanoparticle-tracking analysis in organic solvents.

Supporting Information

 
  • References and Notes

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  • 3 Fine bubbles (FBs) include microbubbles (MBs) and nanobubbles (NBs). The term NB is used to describe gas-filled spherical bubbles that have diameters of less than 1000 nm. An alternative and equivalent term, also used in the literature, is ‘ultrafine bubbles’ (UFBs). Since the International Standards Organization is currently evaluating standards for UFBs (ISO/TC281), we use the term ‘UFB’ in this communication; see: Alheshibri M. Qian J. Jehannin M. Craig VS. J. Langmuir 2016; 32: 11086
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      Although UFBs appear to be specific to water and aqueous solutions according to a first report,6a ‘surface UFBs’ have been observed in solvents such as formamide, ethylammonium nitrate, and propylammonium nitrate, but not in propylene carbonate or dimethyl sulfoxide.6b To date it is thought that bubbles generated in nonaqueous solutions are not stable and disappear rapidly:
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  • 13 Hydrogenation of Nitroarenes 1 by a H2-FB-Based Strategy; General Procedure The hydrogenation was carried out in a 100 mL vial equipped with an FB generator, without additional stirring. Nitroarene 1 (10 mmol) was dissolved in AcOEt (80 mL) and the solution was warmed to 30 °C. By using the FB generator (MA3-FS), H2-FB were introduced into the reactor in the presence of Pd on alumina spheres (0.5% Pd, 2–4 mm, 0.3 mmol, 3 mol%) at a H2 flow rate of 5 mL/min. Samples of the reaction mixture were removed periodically to permit monitoring of the progress of the reaction by GC analysis. When the hydrogenation reaction was complete, the AcOEt was evaporated in vacuo to afford the desired aniline 2 with good to excellent purity. GC analyses: SHIMADZU GC-2010, capillary column: GL Sciences TC-17; He = 0.80 MPa, H2 = 0.50 MPa, air = 0.50 MPa, flow rate: 1.4 mL/min, T inj = 250 °C, T det = 250 °C, T i = 100 °C, T f = 250 °C, rate = 10 °C/min; Nitrobenzene (1a, CAS Reg. No.: 98-95-3; t R = 5.3 min), aniline (2a, CAS Reg. No: 62-53-3; t R = 5.5 min) (see Supporting Information).
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  • 16 The reactivity in H2O was lower than that in AcOEt despite the larger number of UFBs observed in H2O (Table 1, entry 1 vs. 7). Because the reaction rate of the hydrogenation was proportional to the concentration of dissolved hydrogen, the reactivity decreased in H2O, in which H2 gas has a low solubility. In addition, the solubility of the hydrophobic substrate should also affect the reaction rate and, consequently, the reactivity in H2O would be reduced.