Selective Synthesis of Primary Amines by Reductive Amination of Ketones with Ammonia over Supported Pt catalysts

Abstract

Supported platinum catalysts are studied for the reductive amination of ketones under ammonia and hydrogen. For a model reaction with 2-adamantanone, Pt-loaded MoO x /TiO 2 (Pt-MoO x /TiO 2 ) shows the highest yield of primary amine. The catalyst is effective for the selective transformation of various aliphatic and aromatic ketones to the corresponding primary amines, which demonstrates the first example of the selective synthesis of primary amines by this reaction. The yield of the amine increases with increase in the negative shift of the C=O stretching band in the infrared spectra of adsorbed acetone on the catalysts, suggesting that Lewis acid sites on the support material play an important role in this catalytic system. Primary amines are important intermediates in the bulk and fine chemical industries.[1] The reductive amination of carbonyl compounds [2][3][4][5][6] and borrowing-hydrogen type amination of alcohols [7][8][9][10] can be practical synthetic methods of amines. However, amination of carbonyl compounds by NH 3 generally produces secondary amines, [11][12][13][14][15] because primary amines are more reactive than NH 3 , resulting in the conversion of the primary amines to secondary amines. As for the synthesis of primary amines from aldehydes, a few catalysts such as heterogeneous Ru catalysts [16,17] and a homogeneous Rh catalyst [18] are available. The selective synthesis of primary amines by reductive amination of ketones is more challenging. Reductive amination of a ketone with NH 3 and H 2 by Cu- [11] and zeolite [12] based heterogeneous catalysts resulted in selective formation of a secondary amine as a major product together with a primary amine as a minor product. Recently reported homogeneous methods for the selective synthesis of primary amines from ketones with NH 3 did not use H 2 but used less atom-efficient reductants such as HCO 2 NH 4 , [19] the Hantzsch ester, [20] silane, [21] and NaBH 4 . [22] To our knowledge, there are no reports on the selective synthesis of primary amines by the reductive amination of ketones with NH 3 and H 2 . During a course of our efforts on the reductive CÀN bond formation reactions by heterogeneous Pt catalysts, [23,24] we found that Pt and MoO x coloaded TiO 2 (Pt-MoO x /TiO 2 ) was effective for this catalytic reaction. We report herein the first example of the selective synthesis of primary amines by the reductive amination of ketones under 4 bar NH 3 and 2 bar H 2 . We also show the relationship between Lewis acidic nature of the support oxides and the catalytic efficiency.First, we screened Pt catalysts supported on various support materials (MoO x /TiO 2 , Nb 2 O 5 , q-Al 2 O 3 , ZrO 2 , TiO 2 , MgO, SiO 2 , ZSM-5, C, and CeO 2 ) for a model reaction of 2-adamantanone (1 a) in o-xylene under 4 bar NH 3 and 2 bar H 2 . Table 1 summarizes the yields of the corresponding primary amine (2 a), alcohol (3 a), and secondary amine (4 a) with 0.5 mol % of Pt catalysts. The catalytic tests were performed under the same conditions (0.5 mol % Pt with respe...

Hydrodeoxygenation of Fatty Acids, Triglycerides, and Ketones to Liquid Alkanes by a Pt–MoOx/TiO2 Catalyst

“…In our previous IR study of the pyridine adsorbed on these catalysts, we showed that Pt–MoO x /TiO 2 , Pt/TiO 2 , and Pt/Al 2 O 3 were Lewis acidic owing to the exposed cations on the support surface . Also, we reported that the C=O stretching band in the IR spectrum of the acetone coordinated to the Mo n + Lewis acid sites on Pt–MoO x /TiO 2 was observed at lower wavenumbers than Pt/TiO 2 and Pt/Al 2 O 3 . The IR spectra of acetone on these catalysts are shown in Figure A; the spectra at t= 0 s are a result of the acetone adsorbed on the catalyst at 40 °C after adsorption of acetone followed by purging with He flow for 10 min.…”

“…The IR spectra of acetone on these catalysts are shown in Figure A; the spectra at t= 0 s are a result of the acetone adsorbed on the catalyst at 40 °C after adsorption of acetone followed by purging with He flow for 10 min. The C=O stretching band of acetone for Pt–MoO x /TiO 2 is at a lower wavenumber (1690 cm −1 ) than those for Pt/TiO 2 (1709 cm −1 ) and Pt/Al 2 O 3 (1703 cm −1 ), which indicates that the Lewis acid sites on Pt–MoO x /TiO 2 weakens the C=O bond strength more effectively than those on Pt/TiO 2 and Pt/Al 2 O 3 . Then, we studied the reactivity of the acetone on these catalysts under 1 atm H 2 .…”

“…We show the substrate scope and mechanistic studies to demonstrate the catalytic performance and to discuss a possible role of Mo n + Lewis acid sites. It should be noted that spectroscopic characterization results of Pt–MoO x /TiO 2 have been shown in our previous papers, so the structure and acidity of the catalyst are not discussed in this paper.…”

“…In our previous study, we reported that Pt/Nb 2 O 5 showed a 60 times higher TON for hydrodeoxygenation of a fatty acid than Ni‐loaded Hβ zeolite and tungsten‐ or molybdenum‐based catalysts . Recently, we have developed Pt and MoO x co‐loaded on TiO 2 (Pt–MoO x /TiO 2 ) as a generally effective catalyst for the hydrogenation of amides, CO 2 , and sulfoxides . We report herein that Pt–MoO x /TiO 2 is a more efficient catalyst than Pt/Nb 2 O 5 for the selective hydrodeoxygenation of various fatty acids and triglycerides to n ‐alkanes with the same chain length as the substrates in a batch reactor.…”

Selective Synthesis of Furfurylamine by Reductive Amination of Furfural over Raney Cobalt

“…So far, metal complex‐based homogeneous catalysts, such as Rh, Ru, and Ir‐based complexes and heterogeneous catalysts such as Pt, Ru, Rh, Pd, Ni, Co, and Cu have been reported for the reductive amination of carbonyl compounds with ammonia and hydrogen. However, the selectivity to primary amines in reductive amination remains difficult to control because primary amines are more nucleophilic than ammonia and easily react with aldehydes to form secondary amines . In addition, undesired hydrogenation of the carbonyl groups and the unsaturated bonds also limit the selectivity to corresponding primary amines .…”