Sodium borohydride - Ammonium carbonate: An effective reducing system for aldehydes and ketones

Article abstract of DOI:10.1007/s00706-005-0376-x

Reduction of aldehydes and ketones to the corresponding alcohols was achieved in a simple procedure using the system sodium borohydride and ammonium carbonate. This system needs lower excesses of reducing agent and leads to significantly shortened reaction times. Springer-Verlag 2005.

Full text of DOI:10.1007/s00706-005-0376-x

Monatshefte f€ur Chemie 136, 2041–2043 (2005)
DOI 10.1007/s00706-005-0376-x
Sodium Borohydride – Ammonium
Carbonate: An Effective Reducing
System for Aldehydes and Ketones
Farajollah Mohanazadeh1;ꢀ, Mostafa Hosini2,
and Mahmoud Tajbakhsh2
1
Institute of Industrial Chemistry, Iranian Research Organization
for Science and Technology, Tehran, Iran
2
Institute of Chemistry, Mazandaran University, Babolsar, Iran
Received March 14, 2005; accepted (revised) April 24, 2005
Published online December 2, 2005 # Springer-Verlag 2005
Summary. Reduction of aldehydes and ketones to the corresponding alcohols was achieved in a simple
procedure using the system sodium borohydride and ammonium carbonate. This system needs lower
excesses of reducing agent and leads to significantly shortened reaction times.
Keywords. Sodium borohydride; Ammonium carbonate; Aldehydes; Ketones; Reduction.
Introduction
Most reductions of carbonyl and other functional groups are now achieved with
reagents that transfer a hydride ion from aluminum or boron [1–8]. Sodium boro-
hydride and lithium aluminum hydride are not only the most familiar reagents, but
also display a range in selectivity, with sodium borohydride as a mild reducing
agent. Several factors affect its reactivity. These include the nature of the metal
cation present [9] and the ligands of the complex hydride [10].
In this paper, we wish to report a new system for the reduction of aldehydes and
ketones with sodium borohydride in the presence of ammonium carbonate. The
present method is mild and effective, uses an inexpensive reagent, needs only
rather short reaction times compared with sodium borohydride alone, and thus
offers significant advantages.
Results and Discussions
In a typical procedure 1–3 mmol ammonium carbonate and sodium borohydride
(see Table 1) are added to the solution of 1 mmol carbonyl compound in 15 cm3 of
ꢀ
Corresponding author. E-mail: mohannazadeh@irost.org

2042
F. Mohanazadeh et al.
Table 1. Reduction of aldehydes and ketones with the system sodium borohydride – ammonium
carbonate
Entry
Educt
Mol ratio
Educt
Timea
min
Yieldb
%
NaBH4
(NH4)2CO3
1
2
benzaldehyde
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
3
4
1
0
1
0
1
0
1
0
1
1
1
1
1
2
2
2
2
2
2
2
3
4
4
25
2
83
80
75
76
75
75
65
60
78
68
76
72
85
72
77
75
79
84
86
80
73
67
benzaldehyde
3
4-bromobenzaldehyde
4-bromobenzaldehyde
4-chlorobenzaldehyde
4-chlorobenzaldehyde
4-dimethylaminobenzaldehyde
4-dimethylaminobenzaldehyde
4-acetylbenzaldehydec
4-methylbenzaldehyde
2-chlorobenzaldehyde
3-hydroxybenzaldehyde
cinnamaldehyded
4
17
2
5
6
17
5
7
8
25
3
9
10
11
12
13
14
15
16
17
18
19
20
21
22
3
2
2
5
benzophenone
3
acetophenone
2
4-chlorobenzophenone
4-methylacetophenone
benzyl methyl ketone
benzylidine acetonee
benzoin
2
4
3
5
2
camphorf
220
40
anthraquinone
a
b
The course of reaction was checked by TLC; isolated pure product; 4-acetylbenzyl alcohol
c
d
was obtained; cinnamyl alcohol was obtained; 3-hydroxy-1-phenyl-1-butene was obtained;
f
e
isoborneol was obtained
solvent. The mixture is stirred at room temperature for the time specified in Table 1.
The reaction mixture is filtered through a pad of celite and the filtrate is concen-
trated to give the pure alcohol (Scheme 1).
The rate of reduction increases as the concentration of ammonium carbonate is
increased. For example, the reaction time for reduction of 1 eq 4-chlorobenzaldehyde
with 1 eq sodium borohydride in the presence of 0, 0.5, and 1 eq ammonium
carbonate was 17, 5, and 2 minutes. The same holds for other examples. In all
cases a significant shortening of the reaction time was reached.
Scheme 1

Sodium Borohydride – Ammonium Carbonate
2043
Whereas the reaction with aldehydes proceeds readily with only 1 eq sodium
borohydride and ammonium carbonate, it is preferable to use 1–4 eq of these
reagents in the case of ketones (Table 1). This system also reduces unreactive
ketones. A comparison of the results presented in this article with that reported
earlier clearly indicates that sodium borohydride – ammonium carbonate is a more
effective reagent than sodium borohydride – amberlyst-15 (Hþ) [11]. For exam-
ple, 1 eq camphor is reduced by 40 eq sodium borohydride in presence of am-
berlyst whereas 3 eq sodium borohydride reduce 1 eq camphor in presence of 3 eq
ammonium carbonate. It should be mentioned that reduction of camphor produces
the exo isomer only.
This method is also very effective for the reduction of aldehyde and ketone
functionalities without interfering with sensitive groups, such as chloro, bromo,
conjugated double bond, methoxy, and amino, present in the same molecule. Selec-
tive reduction of aldehyde in the presence of ketone was demonstrated by conver-
sion of 4-acetylbenzaldehyde to 4-acetylbenzyl alcohol (Table 1).
Experimental
1H NMR spectra were recorded on a Varian EM 360A NMR spectrometer using TMS as internal
standard. IR spectra were taken on a Perkin-Elmer 267 spectrophotometer. Thin layer chromatography
was performed on silica gel (Machery Nagel Co, Plygram Sil G=uv). Comparison of spectral data
1
(IR, H NMR, 13C NMR) and thin layer chromatography with authentic samples confirmed structure
and purity of the reported products.
Conversion of Benzaldehyde to Benzyl Alcohol, Typical Procedure
In a round bottomed 50cm3 flask equipped with a condenser and magnetic stirrer, a mixture of 0.106g
benzaldehyde (1mmol) in 15 cm3 ethanol was prepared. Sodium borohydride (0.038g, 1 mmol) and
0.096 g (NH4)2CO3 (1mmol) were added to this solution. The mixture was stirred at room temperature
for 4 min. Reaction progress was monitored by TLC. After completion of the reaction the mixture
was filtered through a pad of celite and the filtrate concentrated under reduced pressure to give the
pure product.
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