A simple reduction method of azo-compounds to amines using Fe powder in the presence of NH4Cl

Article abstract of DOI:10.1007/s00706-007-0633-2

A series of azo-compounds were reduced to related aromatic amines in the presence of Fe powder and ammonium chloride. This one step protocol led to the formation of products in middle to high yields, especially when electron releasing substituted aromatic azo-compounds were reduced.

Full text of DOI:10.1007/s00706-007-0633-2

Monatshefte fu¨r Chemie 138, 755–757 (2007)
DOI 10.1007/s00706-007-0633-2
Printed in The Netherlands
A Simple Reduction Method of Azo-Compounds to Amines
Using Fe Powder in the Presence of NH4Cl
ꢀ
Akbar Mobinikhaledi , Naser Foroughifar, and Hasan Fathinejad Jirandehi
Department of Chemistry, Arak University, Arak, Iran
Received November 25, 2006; accepted (revised) February 27, 2007; published online May 23, 2007
# Springer-Verlag 2007
Summary. A series of azo-compounds were reduced to
dithionite and its reaction products are environmen-
related aromatic amines in the presence of Fe powder and
ammonium chloride. This one step protocol led to the for-
mation of products in middle to high yields, especially when
electron releasing substituted aromatic azo-compounds were
reduced.
tally important pollutants. Another disadvantage of
this compound, as a reducing reagent, is its decom-
position under heat. Catalytic reduction of azo-com-
pounds is of interest because of the easy preparation
of amines by regio- and stereo-controlled procedures
[8–10].
Keywords. Reduction; Azo-compounds; Amines; Ammo-
nium chloride; Fe powder.
Results and Discussion
Introduction
The aim of this study is reduction of azo-compounds
to corresponding aromatic amines under neutral, en-
vironmentally benign, and simpler conditions. The
process is carried out by simply mixing of an azo-
compound 1, NH4Cl, and Fe powder in water=ethanol
as co-solvent (Fig. 1).
The major advantage associated with this protocol
is formation of amines in middle to high yields, par-
ticularly when electron releasing substituted aro-
matic compounds such as 1d are used. One more
significance of this reduction method is that it can
be carried out at room temperature and also under
heating as compared to sodium dithionite which de-
composes under heat. Aliphatic amines may be ob-
tained similarly by coupling to an enol followed
by reduction. This method also has the advantage
of occurring under mild conditions. It is therefore
of value in some cases as an alternative to the
usual method for making aromatic amines, in which
nitration is followed by reduction which involves vig-
It is well documented that most of primary amines
are biologically active compounds or important
building blocks for the synthesis of biologically
active compounds [1–6]. Reduction of azo-com-
pounds to amines is very important due to both
industrial and synthetic applications. Sodium dithio-
nite is usually employed as the reducing agent for
reduction of aromatic nitro compounds, diazonium
salts, pyridinium compounds, and other nitrogen-
containing functional groups [7]. Reduction of al-
dehydes and ketones has also been reported with a
hot solution of sodium dithionite. Oximes are also
cleaved by the reagent to the parent carbonyl com-
pounds [7]. However sodium dithionite is relatively
unstable and tends to react with oxygen. This means
that an excess amount of sodium dithionite is needed
in processes where it is involved. Also sodium
ꢀ
Corresponding author. E-mail: akbar_mobini@yahoo.com orous and strongly oxidizing conditions. Moreover,

756
A. Mobinikhaledi et al.
of corresponding diazonium salt with substituted
aromatic compounds and tested for this transforma-
tion (Table 1). All azo-compounds were reduced com-
pletely with Fe=NH4Cl under standard conditions
to readily give the corresponding amines 2a–2j in
middle to good yields (65–95%) and high purity
1
Fig. 1. General reduction of azo-compounds to amines
(95%, based on H NMR spectra). In order to im-
prove the yields, reactions were performed using
different amounts of reagents. The best results were
obtained using a 1:0.1:1 ratio of NH4Cl:Fe:azo-
compound. Using higher amounts of NH4Cl did
not improve the result. All amines were isolated as
hydrochloride salts, which were transferred to free
amines by neutralization with a NaOH solution. The
major advantage of this method is toleration of some
functional groups, such as C¼C bonds and benzyl
the procedure avoids problems associated with sol-
vent use (cost, handling, safety, and pollution). De-
creased reaction times are also realized because of
the increased reactivity of the reactant in the liquid
state.
To extend the scope of the reducing reagent Fe=
NH4Cl for the reduction of azo-compounds, several
azo-compounds 1a–1j were prepared by reaction
Table 1. The reduction of azo-compounds to aromatic amines
Azo-compound
Aromatic amine
Yields=%
Azo-compound
Aromatic amine
Yields=%
1a
2a
85
1f
2f
90
1b
2a
1g
2f
80
90
1c
74
95
1h
1i
2h
2i
65
72
2c
1d
2d
1e
2d
1j
2j
88
82

A Simple Reduction Method of Azo-Compounds
757
1
cmꢂ1; H NMR (300MHz, DMSO-d6): ꢁ ¼ 4.92 (bs, NH2),
7.03 (m, 2CHaromatic), 7.17 (m, 1CHaromatic), 7.26 (m,
1CHaromatic), 7.63 (m, 1CHaromatic), 7.91 (m, 1CHaromatic),
9.17 (bs, OH) ppm; 13C NMR (300MHz, DMSO-d6: ꢁ ¼
118.60, 119.31, 120.82, 123.62, 123.48, 125.65, 125.32,
128.35, 129.63, 136.75 ppm.
groups, which are easily destroyed during catalytic hy-
drogenation. Ethanol as co-solvent of water and was
necessary for the reaction due to solubility of reactants.
In conclusion, this study led to the development of
a one-step synthetic strategy of amines involving
reduction of azo-compounds in the presence of Fe
powder and ammonium chloride.
2-Amino-4-fluorophenol hydrochloride (2h, C6H7ClFNO)
Colorless solid, mp>200ꢁC (dec); IR (KBr): ꢀꢀ¼ 3361 (OH),
3217–3184 (NH2), 3023 (CHaromatic), 1626 (C¼Caromatic
)
Experimental Section
cmꢂ1
;
1H NMR (300 MHz, DMSO-d6): ꢁ ¼ 4.79 (bs,
1H NMR spectra were recorded on a Bruker (300 MHz) spec-
trometer. The IR spectra were recorded on a Galaxy FT-IR 300
spectrophotometer. Microanalyses were performed by the
Elemental Analyzer (Elementar, Vario EL III); their results
agreed favorably with calculated values. Reaction courses
and product mixtures were monitored by thin layer chromato-
graphy. All starting materials were obtained from Fluka and
Merck companies.
NH2), 6.08 (m, 1CHaromatic), 6.33 (m, 1CHaromatic), 6.52 (m,
1CHaromatic), 8.91 (bs, OH) ppm; 13C NMR (300 MHz,
DMSO-d6: ꢁ ¼ 100.90, 114.56, 138.53, 140.55, 155.30,
158.37 ppm.
2-Amino-4-ethylphenol hydrochloride (2i, C8H12ClNO)
Colorless solid, mp>200ꢁC (dec); IR (KBr): ꢀꢀ¼ 3261,
3317 (NH2), 3133 (CHaromatic), 2965, 2895 (CHaliphatic),
1
1626 (C¼Caromatic) cmꢂ1; H NMR (300MHz, DMSO-d6):
ꢁ ¼ 1.06 (t, CH3), 2.38 (q, CH2), 4.40 (bs, NH2), 6.21 (m,
1CHaromatic), 6.43–6.50 (m, 2CHaromatic), 8.67 (bs, OH) ppm;
13C NMR (300 MHz, DMSO-d6: ꢁ ¼ 16.55, 28.13, 114.97,
118.23, 118.48, 120.23, 135.41, 139.62ppm.
General Procedure
A mixture of 0.5 g ammonium chloride (0.01 mol), 100 cm3
H2O=EtOH, and 0.01mol appropriate azo-compound was
placed in a 250 cm3 beaker. The mixture was stirred vigor-
ously and 0.11 g Fe powder (2mmol) were added. The tem-
perature was slowly raised to the boiling point of the solvent.
The stirring was continued for a further 15min in an efficient
fume cupboard. By that time the reduction is complete as
indicated by the mixture becoming colorless again. The warm
reaction mixture was then filtered to separate the product.
4-Aminonaphthalen-1-ol hydrochloride (2j, C10H10ClNO)
Colorless solid, mp>200ꢁC (dec); IR (KBr): ꢀꢀ¼ 3317 (OH),
3296–3261 (NH2), 3142 (CHaromatic), 1626, 1515 (C¼Caromatic
)
cmꢂ1
;
1H NMR (300 MHz, DMSO-d6): ꢁ ¼ 4.99 (bs,
NH2), 6.50 (d, 1CHaromatic), 6.61 (d, 1CHaromatic), 7.29 (m,
2CHaromatic), 7.93(m, 2CHaromatic), 9.01(s, OH) ppm; 13C NMR
(300MHz, DMSO-d6: ꢁ ¼ 108.62, 109.31, 118.76, 122.56,
122.82, 124.60, 124.98, 125.58, 137.06, 144.46ppm.
N,N-Dimethylbenzene-1,4-diamine hydrochloride
(2a, C8H13ClH2)
Colorless solid, mp>200ꢁC (dec); IR (KBr): ꢀꢀ¼ 3357–3221
References
(NH2), 3123 (CHaromatic), 2963 (CHaliph), 1615 (C¼Caromatic),
1
1212 (C–N) cmꢂ1; H NMR (300 MHz, DMSO-d6): ꢁ ¼ 2.68
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(s, 2CH3), 5.15 (bs, NH2), 6.42 (d, 1CHaromatic), 6.48 (d,
1CHaromatic), 6.57 (d, 1CHaromatic), 7.23 (d, 1CHaromatic) ppm;
13C NMR (300MHz, DMSO-d6: ꢁ ¼ 40.50, 112.67, 115.56,
117.33, 127.11 ppm.
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4-Amino-2,6-dichlorophenol hydrochloride (2c, C6H6Cl3NO)
Colorless solid, mp>200ꢁC (dec); IR (KBr): ꢀꢀ¼ 3233–
[4] Boyer SK, Pfund RA, Portmann RE, Sedelmeier GH,
Wetter HF (1988) Helv Chim Acta 71: 337
3159 (NH2), 3104 (CHaromatic), 1586 (C¼Caromatic) cmꢂ1
;
1H NMR (300 MHz, DMSO-d6): ꢁ ¼ 5.00 (bs, NH2), 6.55
(m, 2CHaromatic), 8.79 (s, OH) ppm; 13C NMR (300 MHz,
DMSO-d6: ꢁ ¼ 114.06, 123.94, 139.29, 143.40ppm.
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2-Amino-1,3-benzenediol hydrochloride (2d, C6H8ClNO2)
Colorless solid, mp>200ꢁC (dec); IR (KBr): ꢀꢀ¼ 3382 (OH),
3321–3254 (NH2), 3132(CHaromatic), 1613(C¼Caromatic) cmꢂ1
;
¨
MR, Hassall CH, Krohn A, Lawton G, Redshaw S
1H NMR (300MHz, DMSO-d6): ꢁ ¼ 4.98 (bs, NH2), 6.47
(m, 3CHaromatic), 6.96 (bs, 2OH) ppm; 13C NMR (300 MHz,
DMSO-d6: ꢁ ¼ 114.30, 116.06, 129.25, 149.26ppm.
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1-Aminonaphthalen-2-ol hydrochloride (2f, C10H10ClNO)
Colorless solid, mp>200ꢁC (dec); IR (KBr): ꢀꢀ¼ 3325 (OH),
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(2002) Synth Commun 32: 3279
[10] Scriven EFV, Turnbull K (1988) Chem Rev 88: 351
3295–3212 (NH2), 3085(CHaromatic), 1626, 1465 (C¼Caromatic
)