Hydrogenation of aldehydes and ketones to corresponding alcohols with methylamine borane in neat water

Article abstract of DOI:10.1080/00397911.2014.909489

GRAPHICAL ABSTRACT Chemoselective hydrogenation of various aldehydes and ketones with methylamine borane (MeAB) in neat water was investigated. MeAB is suitable for green organic reactions, for MeAB is a nontoxic, environmentally benign, and easily handled reagent. Aldehydes were selectively and rapidly hydrogenated in excellent yields (86-97%) for 30 min, but hydrogenation of aromatic ketones needed over 20 h at room temperature because of their poor water solubility and steric hindrance. Thus we investigated polyethylene glycol (PEG400) and acidic cation-exchange D072 resin as catalysts to accelerate the hydrogenation reaction of aromatic ketones and achieved excellent yields within several hours. PEG 400 and D072 resin are both suitable for green organic reactions. The D072 resin was reused up to four times without any significance loss in activity.

Full text of DOI:10.1080/00397911.2014.909489

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Hydrogenation of Aldehydes and
Ketones to Corresponding Alcohols with
Methylamine Borane in Neat Water
Yifan Duan a , Ruijiao Bai a , Jun Tian a , Ligong Chen a & Xilong Yan a
a School of Chemical Engineering and Technology , Tianjin
University , Tianjin , China
Accepted author version posted online: 07 May 2014.Published
online: 02 Jul 2014.
To cite this article: Yifan Duan , Ruijiao Bai , Jun Tian , Ligong Chen & Xilong Yan (2014)
Hydrogenation of Aldehydes and Ketones to Corresponding Alcohols with Methylamine Borane in Neat
Water, Synthetic Communications: An International Journal for Rapid Communication of Synthetic
Organic Chemistry, 44:17, 2555-2564, DOI: 10.1080/00397911.2014.909489
To link to this article: http://dx.doi.org/10.1080/00397911.2014.909489
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Synthetic Communications1, 44: 2555–2564, 2014
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2014.909489
HYDROGENATION OF ALDEHYDES AND KETONES TO
CORRESPONDING ALCOHOLS WITH METHYLAMINE
BORANE IN NEAT WATER
Yifan Duan, Ruijiao Bai, Jun Tian, Ligong Chen, and
Xilong Yan
School of Chemical Engineering and Technology, Tianjin University,
Tianjin, China
GRAPHICAL ABSTRACT
Abstract Chemoselective hydrogenation of various aldehydes and ketones with methylamine
borane (MeAB) in neat water was investigated. MeAB is suitable for green organic
reactions, for MeAB is a nontoxic, environmentally benign, and easily handled reagent.
Aldehydes were selectively and rapidly hydrogenated in excellent yields (86–97%) for
30 min, but hydrogenation of aromatic ketones needed over 20 h at room temperature
because of their poor water solubility and steric hindrance. Thus we investigated polyethyl-
ene glycol (PEG400) and acidic cation-exchange D072 resin as catalysts to accelerate the
hydrogenation reaction of aromatic ketones and achieved excellent yields within several
hours. PEG 400 and D072 resin are both suitable for green organic reactions. The D072
resin was reused up to four times without any significance loss in activity.
Keywords Aldehydes; hydrogenation; ketones; methylamine borane; water
Received January 6, 2014.
Address correspondence to Xilong Yan, School of Chemical Engineering and Technology, Tianjin
University, Tianjin, China. E-mail: yan@tju.edu.cn
Color versions of one or more of the figures in the article can be found online at www.tandfonline.
com/lsyc.
2555

2556
Y. DUAN ET AL.
INTRODUCTION
Ammonia borane (NH3BH3, AB) has attracted great attention as hydrogen
source for hydrogenation of polar unsaturated compounds.[1–8] Researchers reported
[1]
[7]
=
=
that AB hydrogenation of C N groups and polarized C C groups occurred at
60 ꢀC or at room temperature by a double hydrogen transfer process. Shi et al.
reported hydrogenation of aldehydes and ketones with AB in neat water.[8] Yang
et al. reported hydrogenation of aldehydes and ketones with AB in tetrahydrofuran
(THF) and methanol.[3] Methylamine borane (CH3NH2BH3, MeAB), an AB deriva-
tive, was a promising candidate for organic synthesis and industrial applications,[4]
generally due to solubility in both protic and aprotic solvents and considerable
hydrolytic and thermal stability.[8,9] However, MeAB only has been widely used
as hydrogen storage materials.[9–16] Examples for hydrogenation of unsaturated
compounds with MeAB are relatively rare.[4]
Hydrogenation of carbonyl compounds to alcohols is one of the most impor-
tant and prevalent transformations in organic chemistry.[17–24] In this study we inves-
tigated the hydrogenation of aldehydes and ketones to corresponding alcohols with
MeAB. This is the first report of hydrogenation of carbonyl compounds with MeAB.
Reactions in aqueous media have attracted much attention in synthetic organic
chemistry, because water is one of the most abundant, cheap, and environmentally
friendly solvents.[25–27] Because MeAB is water-soluble, nontoxic, and environmen-
tally benign, it is a good combination to conduct green organic reactions in water
using MeAB as hydrogen donors.
In our experiment, the hydrogenation of aromatic ketones with MeAB at room
temperature proceeds rather at a slow rate. The slow reaction rates resulted from
the poor water solubility and low reactivity of aromatic ketones.[8] To improve the
solubility of aromatic ketones in water, PEG400 was investigated to improve the mis-
cibility of reactants.[28–31] To improve the reducibility of the reaction system, acidic
cation-exchange D072 resin was investigated as acid catalyst.[32–37] In our experiment,
PEG400 and D072 resin efficiently accelerate the hydrogenation reaction. Both
PEG400 and D072 resin are widely applied as efficient catalyst in organic synthesis
and industrial chemical processes. The attractive features of the two catalysts include
their low cost, stability, availability, ease of handling, and suitability for green organic
reactions. D072 resin can be reused for several times with a slight decrease in activity,
and the separation of the catalyst from reagents is very easy.
RESULTS AND DISCUSSION
Water, as a cheap, safe, and nontoxic solvent, is the preferred choice as
medium in organic reactions. First, we discussed the reaction route of hydrogenation
of carbonyl compounds with MeAB in neat water. According to Dong and Berke’s
work, when the reaction was in protic solvent, the amine would be separated from
amine borane;[4] thus methylamine was generated in this hydrogenation reaction.
The reaction was monitored by 11B NMR spectroscopy: The peak of MeAB (at
ꢁ19.44 ppm, 128 MHz)[16] weakens while the peak of B(OH)3 (at 19 ppm, 128 MHz)[38]
appeared with the progression of hydrogenation reaction.
The NMR technique was employed to monitor the carbonyl compounds
hydrogenated to corresponding alcohols. Therefore, we speculated the possible

REDUCTION OF CARBONYL COMPOUNDS WITH MEAB
2557
reaction for hydrogenation of carbonyl compounds by AB in water (Scheme 1).
Further investigations on the reaction mechanism are needed.
As shown in Table 1, several aldehydes and ketones with different structures
under went hydrogenation to alcohols with MeAB in neat water. In these reactions,
the carbonyl group of carbonyl compounds was selectively hydrogenated while other
unsaturated groups such as double bond (entries 2–5, 17), nitro (entry 9), and ester
groups (entry 10) were retained. Aldehydes (entries 1–14) and alicyclic ketones
(entries 15–17) were hydrogenated in a relatively shorter time than aromatic ketones
(entries 18–22) owing to the greater activity of carbonyl groups. Aliphatic aldehyde
(entry 4), a,b-unsaturated aldehydes (entries 2 and 5), heterocyclic aldehydes (entry
3), benzaldehyde (entry 1), and aromatic aldehydes with electron-donating groups
(EDG) or electron-withdrawing groups (EWG) (entries 6–14) were hydrogenated
to alcohols in excellent yields at room temperature for 30 min. Diverse substituents
on the aryl, whether EDG or EWG (entries 6–14), did not show significant effect on
the yield. Hydrogenation of ketones (entries 15–22) also occurred smoothly and gave
corresponding secondary alcohols in excellent yields, but required longer time. The
low reaction rates of ketones arise from their poor water solubility and steric
hindrance. The aromatic ketone with EWG (entry 21) in the aromatic ring was more
reactive than those with EDG (entries 19 and 20).
The solubility is important for the reaction rate. The hydrogenation of
aromatic ketones, which are poorly soluble in water, needed more than 20 h at room
temperature. In Table 2, PEG 400 was investigated to accelerate the reaction. The
use of PEG 400 increases the solubility of reactants, which leads to larger interfacial
area, and lower mass transfer resistance. Thus, a mild and efficient method for the
hydrogenation of aromatic ketones to alcohols with MeAB in PEG 400=H2O was
established. The method provides an opportunity to avoid toxic solvents, metal
catalysts, and high temperature.
Acidic cation-exchange resins are widely used as acid catalysts in liquid-phase
reactions as they are inexpensive, environmentally friendly, and reusable and have
high surface area, large pore volume, and uniform pore size distribution.[35–38]
Sulfonated poly D072 resin was investigated as heterogeneous catalysts to accelerate
the hydrogenation of aromatic ketones.[35–38] Table 3 shows high efficiency of the
reduction system with D072 resin due to its excellent protonation ability. Besides,
the reusability of D072 resin was investigated in the model reaction of hydrogenation
of hypnone. After each run, the catalyst was filtered from reaction mixture and
reused for the next reaction without any activation. As shown in Table 4, the
D072 resin was reused up to four times without significance loss in activity The
catalytic activity of the acidic D072 resin decreases if used a few times. However,
its activity could be regenerated with dilute hydrochloric acid.
Scheme 1. Possible reaction for hydrogenation of carbonyl compounds with MeAB in neat water.

2558
Y. DUAN ET AL.
Table 1. Hydrogenation of aldehydes and ketones to alcohols with MeAB in neat watera
Entry
Substrate
Time
Yieldb (%)
93
1
30 min
2
3
30 min
30 min
86
94
4
5
6
30 min
30 min
30 min
86
88
92
7
8
30 min
30 min
30 min
30 min
90
90
95
97
9
10
11
12
30 min
30 min
91
90
13
14
30 min
30 min
92
91
15
16
17
1.5 h
3.5 h
5 h
94
88
85
(Continued )

REDUCTION OF CARBONYL COMPOUNDS WITH MEAB
2559
Table 1. Continued
Entry
Substrate
Time
24 h
Yieldb (%)
93
18
19
20
26 h
29 h
90
91
21
22
20 h
40 h
96
84
aAll reactions were carried out with MeAB (1 mmol), aldehyde, or ketone (1 mmol) in
H2O (2 mL) at room temperature.
bDetected by GC.
Table 2. Hydrogenation of aromatic ketones by MeAB in neat water with PEG 400a
Entry
Substrate
Yieldb (%)
92
1
2
3
87
80
4
5
96
71
aAll reactions were carried out with AB (1 mmol), aldehyde or ketone (1 mmol), and PEG
400 (0.5 mL) in H2O (2 mL) for 8 h at room temperature.
bDetected by GC.

2560
Y. DUAN ET AL.
Table 3. Hydrogenation of aromatic ketones by MeAB in neat water with
D072 resin as catalysta
Entry
1
Substrate
Yieldb (%)
96
2
3
93
92
4
5
99
79
aAll reactions were carried out with MeAB (1 mmol), aldehyde or ketone
(1 mmol), and D072 resin (0.8 g) in H2O (2 mL) for 6 h at room temperature.
bDetected by GC.
Table 4. Recyclability of D072 resina
Consecutive repetition
Yield (%)b
1
2
3
4
5
96
97
95
93
86
aAll reactions were carried out with MeAB (1 mmol), hypnone (1 mmol),
and D072 resin (0.8 g) in H2O (2 mL) at room temperature for 6 h.
bDetected by GC.
CONCLUSION
In conclusion, the present work describes a selective and convenient green pro-
cedure for the hydrogenation of a variety of aldehydes and ketones to corresponding
alcohols using MeAB and neat water as hydrogen source. This hydrogenation
method is applicable to a broad range of carbonyl substrates including aliphatic, aro-
matic, a,b-unsaturated, and heterocyclic aldehydes and ketones. The advantages
offered by this method include excellent yields, mild conditions, operational sim-
plicity, applicability to a wide range of substrates, less pollution of the environment,

REDUCTION OF CARBONYL COMPOUNDS WITH MEAB
2561
and easy application in industrial processes. PEG400 and D072 resin have shown
excellent performance in catalyzing the hydrogenation of aromatic ketones. The
two catalysts are inexpensive and suitable for green organic reaction, and D072 resin
can be reused up to four times without any significance loss in activity.
EXPERIMENTAL
The acidic D072 resin was purchased from Nankai Hecheng S&T Co., Tianjin
(China). Other chemicals were purchased from Guangfu Technology Development
Co., Ltd., Tianjin (China). THF was dried over sodium before use, and liquid alde-
hydes and ketones were purified by distillation before use. Hydrogenation reactions
were monitored by TLC (silica gel GF254s, QingdaoHaiyang) and gas chromato-
graphy (SE-30 capillary column: 60 m ꢂ 0.25 mm, 0.33-mm film thickness). Column
chromatography was performed using 200- to 300-mesh silica gel. NMR spectra
were recorded on Varian Inova 400-MHz NMR spectrometer. Chemical shifts,
quoted in parts per million (ppm), are relative to the internal or external standard:
singlet d ¼ 0 ppm of TMS for1H NMR; the middle of CDCl3 triplet d ¼ 77 ppm for
13C NMR; singlet d ¼ 0 ppm of BF ꢃ Et2O for11B NMR.
Synthesis of MeAB
Powdered NaBH4 (3.787 g, 0.1 mol), CH3NH2 ꢃ HCl (13.504 g, 0.1 mol), and
THF (300 mL, dried over Na) were added to a 500-ml, three-necked, round-
bottomed flask, and the contents were vigorously stirred at room temperature under
nitrogen atmosphere. The reaction was monitored by 11B NMR spectroscopy. Upon
completion (18 h), the reaction mixture was filtered. The solvent was removed under
reduced pressure to obtain MeAB, and the product was vaccuumed overnight
to eliminate the residual THF. Yield 95%. Purity by 11B NMR exceeds 99%
(128 MHz, –19.44 ppm). The MeAB samples were also characterized by x-ray
diffraction (XRD) and FT-IR spectrometer (Figs. 1 and 2). The reaction involved
Figure 1. XRD pattern of the MeAB sample.

2562
Y. DUAN ET AL.
Figure 2. Infrared spectra of the MeAB sample.
for the production of MeAB can be expressed in Eq. (1).
THF
CH3NH2 ꢃ HCl þ NaBH4ꢁꢁꢁ! CH3NH2BH3 þ H2 þ NaCl
ð1Þ
CH3NH2BH3: white solid; 11B NMR (128 MHz, CD3OD): d ¼ ꢁ19.44 ppm; 1H
NMR (400 MHz, CD3OD): d ¼ 1.41 (q, J ¼ 92.8 Hz, 3H), 2.33 (s, 3H); 13C NMR
(100 MHz, CD3OD): d ¼ 33.23 ppm.
General Procedure for the Hydrogenation of Carbonyl
Compounds to Alcohols
A mixture of carbonyl compound (1 mmol) and MeAB (1 mmol) in neat water
(2 mL) was stirred at room temperature for an appropriate time. The reaction was
monitored by TLC and gas chromatography (GC). After completion, the reaction
mixture was extracted with ethyl acetate (3 ꢂ 10 mL). Then, the organic extracts were
concentrated by rotary evaporation, and the residue was purified by silica-gel
column chromatography (elution by using petroleum ether=ethyl acetate ¼ 5:1)
to obtain the alcohol product.
General Procedure for the Hydrogenation of Aromatic
Ketones to Alcohols with PEG400
A mixture of aromatic ketone (1 mmol), neat water (2 mL), and PEG400
(0.5 mL) was stirred at room temperature for 10 min. Then, MeAB (1 mmol) was
added, and the stirring was continued. The reaction was monitored by TLC and
GC. After completion, the reaction mixture was extracted with ethyl acetate (3 ꢂ
15 mL). Then, the organic extracts were concentrated by rotary evaporation,
the residue was purified by silica-gel column chromatography (elution by using
petroleum ether=ethyl acetate ¼ 5:1) to obtain the alcohol product.

REDUCTION OF CARBONYL COMPOUNDS WITH MEAB
2563
General Procedure for the Hydrogenation of Aromatic Ketones to
Alcohols with D072 Resin as Catalyst
A mixture of aromatic ketone (1 mmol), MeAB (1 mmol), and D072 resin
(0.8 g) in neat water (2 mL) was stirred at room temperature for an appropriate time.
The reaction was monitored by TLC and GC. After completion, D072 resin was
separated by filtration, and the reaction mixture was extracted with ethyl acetate
(3 ꢂ 10 mL). Then, the organic extracts were concentrated by rotary evaporation,
and the residue was purified by silica-gel column chromatography (elution by using
petroleum ether=ethyl acetate ¼ 5:1) to obtain the alcohol product.
General Large-Scale Procedure for the Hydrogenation of
Benzophenone to Diphenylmethanol with MeAB
MeAB (2mol) and D072 resin (1.6kg) was added to a 5-L flask containing a mix-
ture of benzophenone in neat water (2 L) and vigorously stirred for 17 h at room tempera-
ture. TLC showed the reaction was completed. The crude product was analyzed directly
byGC, andthepurityofbenzophenonewas99.2%.D072resinwasseparatedbyfiltration
and the reaction mixture was extracted with ethyl acetate. The combined organic extracts
were dried over anhydrous magnesium sulfate and concentrated to recover ethyl acetate.
The residue was purified by recrystallization to obtain the product (mp 66.0–67.2 ꢀC).[39]
SUPPLEMENTAL MATERIAL
Supplemental data for this article can be accessed on the publisher’s website.
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