Fine-Bubble-Based Strategy for the Palladium-Catalyzed Hydrogenation of Nitro Groups: Measurement of Ultrafine Bubbles in Organic SolventsThis 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.
Received: 21. April 2017
Accepted after revision: 11. Mai 2017
06. Juli 2017 (online)
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.
Key wordsmicrobubbles - ultrafine bubbles - hydrogenation - heterogeneous catalysis - green chemistry - nitro compounds
References and Notes
- 1a Kashid MN. Renken A. Kiwi-Minsker L. Chem. Eng. Sci. 2011; 66: 3876
- 1b Kiwi-Minsker L. Renken A. Catal. Today 2005; 110: 2
- 1c Jakobsen HA. Lindborg H. Dorao CA. Ind. Eng. Chem. Res. 2005; 44: 5107 ; and references cited therein
- 2a Parmar R. Majumder SK. Chem. Eng. Process. 2013; 64: 79
- 2b Craig VS. J. Soft Matter 2011; 7: 40
- 2c Agarwal A. Ng WJ. Liu Y. Chemosphere 2011; 84: 1175 ; and references cited therein
- 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
- 4 Mase N. Mizumori T. Tatemoto Y. Chem. Commun. (Cambridge) 2011; 47: 2086
- 5a Mase N. Isomura S. Toda M. Watanabe N. Synlett 2013; 24: 2225
- 5b Nagano T. Kanemitsu M. Motoyama T. Mase N. JP 2013023460, 2013
- 6a Seddon JR. T. Lohse D. J. Phys.: Condens. Matter 2011; 23: 133001
- 6b An H. Liu G. Atkin R. Craig VS. J. ACS Nano 2015; 9: 7596
- 7 The synthesis of a five-membered cyclic carbonate derived from an epoxide in the presence of carbon dioxide micro- and nanobubbles has recently been disclosed; see: Uruno M. Takahashi K. Kimura K. Muto K. Tanigawa M. Hanada K. JP 2016190799, 2016
- 8a Tian X. Nejadnik MR. Baunsgaard D. Henriksen A. Rischel C. Jiskoot W. J. Pharm. Sci. 2016; 105: 3366
- 8b Filipe V. Hawe A. Jiskoot W. Pharm. Res. 2010; 27: 796
- 9a Blaser H.-U. Steiner H. Studer M. ChemCatChem 2009; 1: 210
- 9b Blaser H.-U. Malan C. Pugin B. Spindler F. Steiner H. Studer M. Adv. Synth. Catal. 2003; 345: 103
- 9c Downing RS. Kunkeler PJ. van Bekkum H. Catal. Today 1997; 37: 121
- 10 Pd/C can ignite on exposure to air; see: Committee on Prudent Practices for Handling, Storage, and Disposal of Chemicals in Laboratories, Prudent Practices in the Laboratory, Handling and Disposal of Chemicals . National Academy Press; Washington: 1995
- 11 Although the formation mechanism is not clear, the reaction is considered to proceed through the reductive amination of N-methyleneaniline, formed in situ from aniline and formaldehyde; the latter is in turn generated by dehydrogenation of methanol on the catalyst surface.
- 12 Möbus K. Wolf D. Benischke H. Dittmeier U. Simon K. Packruhn U. Jantke R. Weidlich S. Weber C. Chen B. Top. Catal. 2010; 53: 1126
- 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).
- 14 Takasaki M. Motoyama Y. Higashi K. Yoon S.-H. Mochida I. Nagashima H. Org. Lett. 2008; 10: 1601
- 15 Shimada K. Yoshisato E. Yoshitomi T. Matsumura S. JP 1995242606, 1995
- 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.
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: