NaBH4/(NH4)2SO4: A convenient system for reduction of carbonyl compounds to their corresponding alcohols in wet-THF

Article abstract of DOI:10.13005/ojc/300461

NaBH₄ (1-2 equivalents) in the presence of (NH₄)₂SO₄ (1-2 equivalents) reduces varieties of organic carbonyl compounds such as aldehydes, ketones and ,-unsaturated carbonyl compounds to their corresponding alcohols. Reduction reactions were carried out in THF-H₂O in high to excellent yields of products.

Full text of DOI:10.13005/ojc/300461

ISSN: 0970-020 X
CODEN: OJCHEG
2014, Vol. 30, No. (4):
Pg. 1989-1992
ORIENTAL JOURNAL OF CHEMISTRY
An International Open Free Access, Peer Reviewed Research Journal
www.orientjchem.org
NaBH4/(NH4)2SO4: A Convenient System for
Reduction of Carbonyl Compounds to their
Corresponding Alcohols in wet-THF
SABERAKBARZADEH, DAVOOD SETAMDIDEH*and MOHAMMADALIZADEH HEDAYATI
Department of Chemistry, Faculty of Sciences, Ahar Branch, Islamic Azad University, Ahar. Iran.
*Corresponding author E-mail: d.setamdideh@iau-mahabad.ac.ir
http://dx.doi.org/10.13005/ojc/300461
(Received: September 30, 2014; Accepted: November 03, 2014)
ABSTRACT
NaBH4 (1-2 equivalents) in the presence of (NH4)2SO4 (1-2 equivalents) reduces varieties
of organic carbonyl compounds such as aldehydes, ketones and á,â-unsaturated carbonyl
compounds to their corresponding alcohols. Reduction reactions were carried out in THF-H2O in
high to excellent yields of products.
Key words: NaBH4, Reduction, Carbonyl compounds, (NH4)2SO4.
INTRODUCTION
that the reduction of carbonyl compounds can be
achieved by NaBH4 in the presence of mineral
protic solids or under wet conditions with some
limitations. In continuing our efforts for the
development of new reducing systems, 14 we
decided to investigate the reducing properties of
NaBH4 in the presence of (NH4)2SO4 as the co-
reagent for the reduction of a variety of carbonyl
compounds. We now report the results of a parallel
investigation of the role of (NH4)2SO4 in the
reduction of carbonyl compounds to their
corresponding alcohols. Former, (NH4)2C2O4 has
been proposed as a co-reactant.
Preparation of alcohols from the reduction
of carbonyl functional groups are importance in
organic chemistry 1 and a large number of methods
2
including catalytic reduction
,
hydride
homogeneous catalysis 3, heterogeneous catalysis
systems4 and transfer reagents5 have been reported
to be effective towards carbonyl compounds
reduction. But, most chemists employ lithium
aluminum hydride (LiAlH4) or sodium borohydride
(NaBH4). Controlling the reducing power of NaBH4
has been achieved by different types of
modifications 6-13. A literature review also reveals

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AKBARZADEH et al., Orient. J. Chem., Vol. 30(4), 1989-1992 (2014)
RESULTSAND DISCUSSION
conversion of aldehydes to the corresponding
alcohols in excellent yields (91-96%).
benzaldehyde as a model compound has
been reduced with one molar equivalent of NaBH4
Our next attempt was the reduction of
in THF-H2O (3:0.3 mL) within 20 in the presence of ketones to the corresponding secondary alcohols
1 molar equivalent of (NH4)2SO4 at room with the NaBH4/(NH4)2SO4 system. We optimized the
temperature as shown in scheme 1.
reaction conditions with the reduction of the model
compound acetophenone by NaBH4/(NH4)2SO4
The efficiency of this protocol was under different conditions. Reduction of ketones was
examined by the reduction of a variety of aldehydes. obtained with this reducing system, but due to the
All reductions were completed within 20-80 minutes lower reactivity of ketones relative to aldehydes,
as shown in table 1, entries 1-7. The molar ratio of the reduction require higher molar amounts of
NaBH4 is not different according to the nature of the NaBH4 & (NH4)2SO4. The reduction reactions were
substrates. 1 molar equivalents of NaBH4 and 1 performed with 2 molar amounts of NaBH4 in
molar equivalents of (NH4)2SO4 per one equivalents presence of 2 molar amounts of (NH4)2SO4 at room
of the substrate were sufficient to complete temperature in wet-THF as shown in scheme 2.
NaBH4 (1 mmol)
CH2OH
CHO
RT., 90 min., THF (3 mL)., Conversion 90%
NaBH4 (1 mmol)/(NH4)2SO4(1 mmol)
RT., 20 min., THF-H2O(3:0.3 mL).,
Conversion 100%
Scheme 1:
NaBH4 (2 mmol)
CH(OH)CH3
COCH3
RT., 120 min., THF(3 mL)., Conversion 0%
NaBH (2 mmol)/(NH4)2SO4(2 mmol)
4
RT., 90 min., THF-H2O(3:0.6 mL).,
Conversion 100%
Scheme 2:
All reductions were completed within 90-
120 minutes with high to excellent yields (94-97%) General
as shown in table 1, entries 8-14.
EXPERIMENTAL
All substrates and reagents were
purchased from commercially sources with the best
1
The mechanism for the influence of quality. IR and H NMR spectra were recorded on
(NH4)2SO4 is not clear, but we observed that with the PerkinElmer FT-IR RXI and 300 MHz Bruker
addition of (NH4)2SO4 hydrogen gas slowly is spectrometers, respectively. The products were
1
liberated in situ. Hydrogen gas generation seems characterized by their H NMR or IR spectra and
to be directly related to the solubility of the NaBH4 comparison with authentic samples (melting or
and (NH4)2SO4 in the reaction solvent. Because boiling points). Organic layers were dried over
water causes an increase in solubility of the NaBH4 anhydrous sodium sulfate. All yields referred to
& (NH4)2SO4, so hydrogen gas generation increase isolated pure products. The purity of products was
1
dramatically.
determinate by TLC and H NMR. Also, reactions

AKBARZADEH et al., Orient. J. Chem., Vol. 30(4), 1989-1992 (2014)
1991
Table 1: The Reduction of Carbonyl Compounds by NaBH4/(NH4)2SO4 in wet-THF at Room Temperature
Entry
Aldehydes
Products
Time/min. Yieldc/%
1a
benzaldehyde
benzyl alcohol
20
30
60
30
60
80
30
90
120
120
120
110
120
90
96
96
96
93
93
95
95
96
94
97
95
95
95
97
2a
4-bromobenzaldehyde
4-methylbenzaldehyde
4-nitrobenzaldehyde
2-methoxylbenzaldehyde
4-methoxybenzaldehyde
3-methylbenzaldehyde
acetophenone
4-methylacetophenone
4-methoxyacetophenone
4-methoxybenzophenone
Benzophenone
4-bromobenzyl alcohol
4-methylbenzyl alcohol
4-nitrobenzyl alcohol
2-methoxylbenzyl alcohol
4-methoxybenzyl alcohol
3-methylbenzyl alcohol
1-phenylethanol
1-(4-methylphenyl)ethanol
1-(4-methoxyaphenyl)ethanol
(4-methoxyphenyl)(phenyl)methanol
diphenylmethanol
3a
4a
5a
6a
7a
8b
9b
10b
11b
12b
13b
14b
9H-fluoren-9-one
4-phenylcyclohexanone
9H-fluoren-9-ol
4-phenylcyclohexanol
a The reaction has been carried out by NaBH4/(NH4)2SO4 (1/1 mmol) in THF-H2O (3:0.3 mL). b The reaction has been
carried out by NaBH4/(NH4)2SO4 (2/2 mmol) THF-H2O (3:0.6 mL). c Yields refer to isolated pure products.
are monitoring over silica gel 60 F254 aluminum
sheet.
H2O (3:0.6 mL) was prepared and NaBH4 (0.038 g,
1 mmol) and (NH4)2SO4 (0.234 g, 2 mmol) were
added and the mixture was stirred at room
temperature for 90 minutes. TLC monitored the
progress of the reaction (Hexane/EtOAc: 9/1). After
completion of the reaction distilled water (5 mL)
was added to the reaction mixture and it was stirred
for an additional 1 minute. The mixture was
extracted with CH2Cl2 (3×10 mL) and dried over
anhydrous sodium sulfate. Evaporation of the
solvent and short column chromatography of the
resulting crude material over sil-ica gel (Hexane/
EtOAc: 9/1) afforded the pure crystals of 1-
phenylethanol (0.l1 g, 96% yield, Table 1, entry 8).
A typical procedure for Reduction of aldehydes
with the NaBH4/(NH4)2SO4 system in wet-THF
In a round-bottomed flask (10 mL)
equipped with a magnetic stirrer, a solution of
benzaldehyde (0.106 g, 1 mmol) in THF-H2O (3:0.3
mL) was prepared. To this solution, NaBH4 (0.038
g, 1 mmol) and then (NH4)2SO4 (0.132 g, 1 mmol)
was added and the mixture was stirred at room
temperature for 20 minutes. Completion of the
reaction was monitored by TLC (Hexane/EtOAc: 9/
1). Then, water (5 mL) was added to the reaction
mixture and it was stirred for an additional 1 minute.
The mixture was extracted with CH2Cl2 (3×10 mL)
and dried over anhydrous Na2SO4. Evaporation of
the solvent and a short column chromatography of
the resulting crude material over silica gel (Hexane/
EtOAc: 9/1) afforded the pure liquid benzyl alcohol
(0.104 g, 96%, Table 1, entry 1).
CONCLUSION
In conclusion, we have shown that the
combination system of NaBH4/((NH4)2SO4 in wet-
THF reduces a variety of carbonyl compounds to
their corresponding alcohols in high to excellent
yields at room temperature. Reduction reactions
were carried out with 1-2 molar equivalents of
NaBH4 in the presence of 1-2 molar equivalents of
(NH4)2SO4. All reductions were accomplished with
high efficiency of the reductions, using the
appropriate molar ratios of NaBH4 and (NH4)2SO4,
A typical procedure for reduction of ketones with
the NaBH4/(NH4)2SO4 system in wet-THF
In a round-bottomed flask (10 mL)
equipped with a magnetic stirrer and a condenser,
a solution of acetophenone (0.12 g, l mmol) in THF-

1992
AKBARZADEH et al., Orient. J. Chem., Vol. 30(4), 1989-1992 (2014)
shorter reaction times and easy work-up procedure.
Therefore this new protocol for reduction of carbonyl
compounds could be a useful addition to the
present methodologies.
ACKNOWLEDGMENTS
The authors gratefully appreciated the
financial support of this work by the research council
of Islamic Azad University branch of Ahar.
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