The direct reductive amination of 2,5-diformylfuran (DFF) with ammonia to 2,5-bis(aminomethyl)furan (BAF) was demonstrated, for the first time, over the commercial type Nickel-Raney and acid treated Nickel-Raney catalysts. The effects of reaction parameters such as reaction medium, temperature and hydrogen pressure were described. The acid treated Nickel-Raney catalyst exhibited the highest BAF yield in the THF-water mixed reaction medium. The relatively higher Ni0 species composition and larger surface area of the acid treated Nickel-Raney catalyst with specific reaction conditions contributed greatly to the BAF formation. The oligomeric species, such as furanic imine trimers and tetramers confirmed by MALDI-MS analysis were presented as the intermediates of DFF reductive amination.
Amines are important intermediates in the bulk and fine chemical industries including large-scale production of numerous polymers. In addition, they represent interesting building blocks for the synthesis of pharmaceuticals, agrochemicals and food additives [
As shown in reaction Scheme 1, the reductive amination of 2,5-diformylfuran (DFF), a versatile platform chemical derived from catalytic oxidation of bio-mass based 5-hydroxymethylfurfural (HMF) [
However, the direct preparation of BAF from DFF has been not successful in spite of the recent progress of catalytic aminations. It requires the delicate approaches to prevent the formation of by-products of secondary, tertiary and polymeric amine species due to the condensation and/or hydrogenation of the reactive di-aldehyde groups and high nucleophilic amine groups of the product. Moreover, the bridge imine groups which are formed by the condensation of di-amine and di-aldehyde compounds need to be preserved during the reductive amination from the fast hydrogenation to minimize the polyamine type by-product formation [
To the best of our knowledge, there has been no successful report showing the direct reductive amination of DFF to BAF using ammonia, even though other di-amine compounds, such as bis(aminomethyl)cyclohexane and 1,9-nonanediamine have been prepared from the corresponding dialdehydes, cyclohexanedicarboxaldehyde [
In the present study, we report, for the first time, the direct reductive amination of DFF with ammonia to BAF with Nickel-Raney type catalysts under mild conditions. Herein, the reductive amination activity and selectivity variations of the Nickel-Raney catalyst and the acid treated Nickel-Raney catalyst are shown. Besides, the effects of key parameters and oligomeric imine forms of intermediates in the DFF amination are also described.
In this research, Ni-Al alloy (Kanto Chemical Co., Inc., Japan) containing 50 wt% of nickel and 50 wt% of aluminum was used as a precursor to prepare Nickel-Raney catalysts for the reductive amination. This alloy was activated by alkaline leaching of aluminum using the well-known method [
The acid treated Nickel-Raney (AT-Ni-Raney) catalyst was prepared by a further treatment: The Ni-Raney catalyst suspension was acidified until pH 5 by a dilute acetic acid solution, kept on stirring 30 min then washed with distilled water to neutrality, dried under nitrogen flow at 100˚C and finally stored in the desired reaction medium.
For the comparison purpose, hydrogen peroxide treated AT-Ni-Raney (H2O2-AT-Ni-Raney) catalyst was
Scheme 1. Formation and reductive amination of DFF.
prepared from the AT-Ni-Raney by treatment with an aqueous 0.1 wt% H2O2 solution at room temperature for 30 min, then washed with distilled water, dried under nitrogen and finally stored in the desired reaction me- dium.
Materials: DFF (>98%, TCI, Japan), H2 (99.9%, Deokyang, Korea), NH3 (99.9%, Deokyang, Korea) and solvents (THF ≥ 99.9%, Sigma-Aldrich; EtOH ≥ 99.9%, Samchun; 1,4-Dioxane ≥ 99.8%, Sigma-Aldrich) were obtained commercially and used as received.
In a typical reductive amination reaction, DFF (300 mg), catalyst (30 mg), internal GC standard and reaction medium (30 ml) were charged in the high pressure stainless steel reactor equipped with a magnetic stirring and a temperature control system. The air in the reactor was then replaced by hydrogen three times. Thereafter, liquid ammonia (2 ml) in pre-condensed form was introduced at room temperature. Finally, hydrogen was supplied to 10 bar total pressure and the reaction was started at the desired temperature. Liquid samples were taken from reactor during the course of the experiment to analyze conversion and yield. After 6 h of reaction, the reactor was cooled, the pressure was released and the catalyst was separated by centrifugation.
The conversion of DFF and the yield of BAF were determined by GC analysis with internal standard equipped with MEGA-1 column (30 m × 0.32 mm) and flame ionization detector applying a temperature gradient from 60˚C to 200˚C. The desired product was isolated after removal of solvent and purified by column chromatography (silica gel) method. The structure of BAF product was further confirmed by spectroscopies methods (see Figures S1-S3 of Supporting Information).
Chemical analyses of catalysts were performed by the energy dispersive X-Ray fluorescence (EDXRF) using ARL QUANT’X/Thermo instrument equipped with an X-Ray tube of Rhodium and Si(Li) detector at energy resolution of 155 eV. The surface area measurements were calculated by the Brunauer, Emmett and Teller (BET) method on a Micromeritics ASAP 2040 system. Samples were transferred to the adsorption glass tube with the storage liquid and treated at 200˚C under ultrahigh pure nitrogen flow for 2 h before measurement. The oxidation states of nickel and the surface composition of Ni-Raney catalysts were determined by X-Ray photoelectron spectroscopies (XPS) recording on KRATOS AXIS NOVA instrument.
The surface elemental compositions (wt%) by EDXRF analysis and BET surface areas of the Ni-Raney type catalysts are first compared. As shown in
For the purpose of quantitative estimates of Ni components in the catalysts, XPS of Ni-Raney and AT-Ni- Raney samples were used. As can be seen from
Catalyst | Nickela | Aluminuma | Oxygena | Surface areab |
---|---|---|---|---|
Ni-Raney | 61.8 | 11.4 | 26.5 | 12.2 |
AT-Ni-Raney | 70.3 | 8.5 | 21.0 | 44.7 |
H2O2-AT-Ni-Raney | 64.2 | 10.5 | 24.9 | 45.3 |
aDetermined by EDXRF analysis; bMeasured at liq. N2 temperature, m2/g (BET method, after vacuum pre-treatment at 200˚C for 2 h).
metal 2p3/2 species [
The direct reductive amination scheme of DFF to BAF is depicted in Scheme 2. To avoid the complexity in the DFF reductive amination, a high molar ratio (30:1) of ammonia to DFF was applied in all experiments. The application of an excess amount of ammonia is a common technique to increase the selectivity to primary amine in the reductive amination of aldehydes [
A number of representative DFF reductive aminations results are shown in
Catalyst | Component (%) | ||
---|---|---|---|
Ni0 | NiO | Ni(OH)2 + NiOOH | |
Ni-Raney | 17.5 | 36.5 | 45.9 |
AT-Ni-Raney | 37.7 | 24.1 | 38.2 |
H2O2-AT-Ni-Raney | 0.0 | 40.3 | 59.7 |
Entry | Catalyst | Solvent (vol%) | T (˚C) | PH2 (bar) | BAF yielda (%) |
---|---|---|---|---|---|
1b | Pt/C | Sole, Sol-H2O (90:10) | 100, 120 | 10 | - |
2c | Pd/CaCO3 | Sol, Sol-H2O (90:10) | 120 | 10, 20 | - |
3d | Ru/C | Sol, Sol-H2O (90:10) | 100, 140 | 10 | - |
4 | Ni-Raney | EtOH | 120, 140 | 5, 10, 20 | - |
5 | Ni-Raney | EtOH-H2O (90:10) | 120 | 10, 20 | - |
6 | Ni-Raney | 1,4-Dioxane | 120 | 10 | - |
7 | Ni-Raney | 1,4-Dioxane-H2O (90:10) | 120 | 10 | - |
8 | Ni-Raney | THF | 120 | 10, 20 | - |
9 | Ni-Raney | THF-H2O (90:10) | 120 | 20 | 7.3 |
10 | AT-Ni-Raney | THF | 120, 140 | 20 | - |
11 | AT-Ni-Raney | THF-H2O (95:5) | 120 | 20 | 27.2 |
12 | AT-Ni-Raney | THF-H2O (90:10) | 100 | 20 | 28.3 |
13 | AT-Ni-Raney | THF-H2O (90:10) | 120 | 10 | 42.6 |
14 | AT-Ni-Raney | THF-H2O (90:10) | 120 | 5 | 18.1 |
15 | H2O2-AT-Ni-Raney | THF-H2O (90:10) | 120 | 20 | - |
Reaction conditions: DFF (300 mg), catalyst (30 mg), solvent (30 ml), liquid ammonia (2 ml), 6 h. aDetermined by GC analysis with tetraethylene glycol dimethyl ether as the internal standard; b,c,dUsing 5 wt% Pt/C and 5 wt% Pd/CaCO3 (Strem Chemicals, USA), and 5 wt% Ru/C (Acros, Belgium) catalysts, respectively; eSol = EtOH, 1,4-Dioxane, THF.
Scheme 2. Direct reductive amination of DFF to BAF.
mediums, as shown in Entries 11-14. Without water addition to the reaction medium, both the Ni-Raney catalyst and the AT-Ni-Raney catalyst gave no BAF yield even at various amination conditions (Entries 8 and 10). The highest BAF yield of 42.6% for the AT-Ni-Raney catalyst which has higher surface area and Ni0 composition as shown in
It is very interesting to observe that BAF formation in the DFF reductive amination depends on the reaction medium, metal component and composition of the catalysts. To understand the key parameter of the DFF amination reaction, water content, reaction temperature, hydrogen pressure and reaction time effects were examined for the AT-Ni-Raney catalyst in THF-water mixed medium. As presented in
In addition to the water addition, reaction medium and reaction temperature, the hydrogen pressure and reaction time effects were examined. As illustrated in
The water addition effects to the reaction medium in the reductive amination of other type of aldehydes have been revealed in previous literatures. It has been demonstrated that the presence of a proper water concentration leads to a markedly lower tendency for the formation of undesired by-products and thus, to an increased selectivity to primary amines as described in the previous amination of 1,8-octanedial [
Ni-Raney type catalysts. With other metallic reductive amination catalyst components and mediums, BAF formations were not observed even with the water addition. The formation of primary diamine BAF in our amination system can be rationalized partially by the solvation effect of amine groups with water molecules, which may lower the condensation rate between aldehyde groups and the primary amine. In fact the primary alkylamines are considered as more basic than ammonia. With the presence of water in the reaction system in which primary alkylamine and ammonia are presented, alkylammonium ion is expected to be formed from primary amine with the chemical equilibrium. When primary diamine BAF is formed in the DFF reductive amination system, the following reaction is expected to form di-ammonium species (Scheme 3). The equilibrium effectively protects BAF from the condensations with dialdehyde DFF, since the alkylammonium ion of BAF is a no longer nucleophile.
As described above, the Ni-Raney catalysts are unique in the DFF reductive amination to BAF in the THF- water medium. The effectiveness of the Ni-Raney catalysts can be attributed to the proper and selective hydrogenation ability toward the imine groups of different types. The two types of imine groups are expected to be formed in the early stage of amination reaction by the imination of DFF as described in Scheme 4: The terminal imine groups which are attached to the furan ring and the bridge type internal imine groups which connect two furan moieties. In the reaction system, the hydrogenation activity of the Ni-Raney catalysts, compared with other precious metal amination catalysts, may catalyze selectively the terminal imine hydrogenation to form BAF preferably rather than the internal type imine hydrogenation to leave the internal imines for the trans-imination. The difference in the hydrogenation activities of Ru and Pd catalysts for the two types of imines was also proposed to explain the product selectivity variations of benzaldehyde reductive amination [
Regarding the reaction intermediates involved in the DFF reductive amination, we note that the full DFF conversion is achieved quickly while only a small amount of BAF appeared in the early stage of amination as shown in
Scheme 3. BAF in equilibrium with water, leading to di-ammonium species.
Scheme 4. Imination of DFF to two types of imine groups.
unidentified by-products. In the case of reductive amination of cyclohexanedicarboxaldehyde, similar type intermediate of macrocyclic polyimine of ~494 molecular weight was observed that corresponds to a cyclic intermediate of two molecules of the cyclohexanedicarboxaldehyde (A) with two molecules of the product diamine (B). This A2B2 oligomer was tended to be the most prevalent species. Besides, the other cyclic A3B3, A4B4, A5B5 species and a series of linear species having molecular weight up to about 1000 were also detected [
Now, we discuss a reaction scheme for the formation of BAF from DFF by adopting the effects of reaction parameters, the proper hydrogenation activity of the Ni-Raney catalysts and the imine oligomeric intermediates of the DFF reductive amination system. In the reaction scheme, as shown in
In conclusion, 2,5-bis(aminomethyl)furan was prepared by the direct reductive amination of 2,5-diformylfuran with ammonia in one step approach. The Ni-Raney catalysts showed reductive amination activities in THF- water mixed medium. The BAF yield of 42.6% was achieved when the acid treated Ni-Raney catalyst was applied under the optimal reaction conditions. It is proposed that the combination of THF-water mixed medium and the Ni0 component of the Ni-Raney catalysts plays a crucial role in the DFF reductive amination to BAF. Moreover, XPS, BET surface area and EDXRF analysis also support that the BAF formation is related with the Ni0 component of the Ni-Raney catalysts. The oligomeric imine trimer and tetramer species, confirmed by MALDI-MS analysis, are suggested as main intermediates in the direct reductive amination of DFF to BAF.
The authors acknowledge the Korea Research Institute of Chemical Technology (KRICT), Daejeon, Korea for supporting this work.
Ngoc-ThucLe,AreumByun,YohanHan,Kee-InLee,HyungrokKim, (2015) Preparation of 2,5-Bis(Aminomethyl)Furan by Direct Reductive Amination of 2,5-Diformylfuran over Nickel-Raney Catalysts. Green and Sustainable Chemistry,05,115-127. doi: 10.4236/gsc.2015.53015