Simple, mild, and efficient method for the reduction of 1,4-benzoquinones to hydroquinones by the action of NaN3

Article abstract of DOI:10.1080/00397910600639760

A simple, mild, and efficient method is presented for the reduction of 1,4-benzoquinones to hydroquinones by the action of NaN₃ under neutral conditions in the presence of water. Copyright Taylor & Francis Group, LLC.

Full text of DOI:10.1080/00397910600639760

Synthetic Communicationsw, 36: 2293–2297, 2006
Copyright # Taylor & Francis Group, LLC
ISSN 0039-7911 print/1532-2432 online
DOI: 10.1080/00397910600639760
Simple, Mild, and Efficient Method for
the Reduction of 1,4-Benzoquinones to
Hydroquinones by the Action of NaN3
Fatih Algi
Department of Chemistry, Middle East Technical University,
Ankara, Turkey and Department of Chemistry, Onsekiz Mart University,
Canakkale, Turkey
Metin Balci
Department of Chemistry, Middle East Technical University,
Ankara, Turkey
Abstract: A simple, mild, and efficient method is presented for the reduction of
1,4-benzoquinones to hydroquinones by the action of NaN3 under neutral conditions
in the presence of water.
Keywords: Azides, 1,4-benzoquinones, phenols, quinones, reductions
During the course of a program aimed at opening new libraries of benzo-
quinone-containing heterocycles, we became interested in a convenient
method to selectively reduce the quinone moiety into hydroquinone.
Although a number of methods[1] for the conversion of benzoquinones to
hydroquinones are presently available, new and simpler methods that are
devoid of side reactions, if possible, are still welcome. Furthermore, most
of the existing methods suffer from some drawbacks: low yields, high costs
for the catalyst[2] used, difficulties in controlling the reaction when starting
quinones that contain other reducible and/or labile groups as a result of
very active metal hydrides,[3] strong Lewis acids/bases,[4] complex
Received in the UK 14 July 2005
Address correspondence to Metin Balci, Department of Chemistry, Middle East
Technical University, 06531, Ankara, Turkey. E-mail: mbalci@metu.edu.tr
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F. Algi and M. Balci
organometallic reagents,[5] and multicomponent reagents[6] used as reductants
that have limited functional group tolerance. In this article, we report a simple,
mild, and efficient method for the reduction of 1,4-benzoquinones to hydro-
quinones by the action of NaN3 (Scheme 1).
To rationalize the phenomena, benzoquinone was chosen as a model
substrate. In an initial attempt, it was treated with NaN3 in acetone at room
temperature. The reaction provided the corresponding hydroquinone, albeit
in low yield (ca. 20%, NMR). Dimethoxyethane gave similar results as the
solvent. To increase the yield, it was necessary to load excess NaN3
(5 equiv). Moreover, the addition of water as a cosolvent caused a slight
increase in the rate of the reaction. Thus, a mixture of acetone–water (9:1)
was taken as the solvent system, which resulted in an increased yield of up
to 75%. Finally, these optimizations were chosen as the standard conditions.
To test the scope and limitations of this method, a variety of quinones
including benzannulated quinones (Table 1, entries 2, 3), alkyl (Table 1,
entries 4, 7, 8), aryl (Table 1, entry 5), and halogen (Table 1, entry 6) as a sub-
stituent were subjected to a reaction under the standard set of conditions to
afford hydroquinones, which were characterized on the basis of physical
and spectral (1H and 13C NMR, IR, elemental analysis) data. The results are
summarized in Table 1.
In most cases, moderate to good yields were achieved with only one
exception. Interestingly, the reaction of anthraquinone (Table 1, entry 3) did
not proceed even upon heating at a reflux temperature for a prolonged
period of time, in which the starting material remained essentially unaltered.
This peculiar behavior was attributed to the relatively higher redox potential
(DV ¼ 0.57 V) of anthraquinone when compared to benzoquinone.[9]
It is noteworthy to mention that bromomethyl quinone (Table 1, entry 7)
was converted to azidomethyl hydroquinone in one step under these con-
ditions. To the best of our knowledge, this is one of the rare examples that
demonstrate the unique behavior of such anions as the azide, where it acts
simultaneously as a reductant and nucleophile in a reaction.
2-(Azidomethyl)benzene-1,4-diol (Table 1, entry 7): Dark red oil;
1H NMR (400MHz, CDCl3) d 6.78–6.67 (m, 3H), 5.39 (bs, OH, 1H), 5.12
(bs, OH, 1H), 4.34 (s, -CH2, 2H); 13C NMR (100 MHz, CDCl3) d 149.3, 148.0,
122.8, 117.0, 116.7, 116.4, 50.7; IR (CHCl3, cm21): 3377, 2923, 2839,
Scheme 1.

Sodium Azide Reduction of Quinones
2295
Table 1. Reduction of 1,4-benzoquinones to hydroquinones by NaN3
Mp(8C)
Entry
Quinones(1)a
Hydroquinones(2)b Yield %
Found
173
Reported
1
75
171[5a]
2
3
4
5
6
7
70
NRd
85
175
176[7b]
—
—
125
125[5a]
98[5a]
111[7]
85
97
95
114
e
—
65
—
(continued)

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F. Algi and M. Balci
Table 1. Continued
Mp(8C)
Entry
8
Quinones(1)a
Hydroquinones(2)b Yield %
Found
Reported
78
97
96[8]
aAll of the reactions were carried out in 0.071 M in quinone.
bAll of the products are known except Entry 7 and were characterized by physical
(mp) and spectral (1H and 13C NMR, IR) data.
c This value indicates the isolated yield after purification as the average of two runs.
dNR: No reaction.
eDark red oil (for detailed spectral data, see Ref. 10).
2098, 1651, 1504, 1448, 1329, 1259, 1182, 1099, 861, 805. Anal. calcd.
for C7H7N3O2: C, 50.91; H, 4.27; N, 25.44. Found: C, 50.80; H, 4.18; N,
25.23.
In summary, a simple, mild, and efficient method is presented here for the
conversion of 1,4-benzoquinones to hydroquinones by the action of readily
available NaN3 under neutral conditions in the presence of water. This
method can find applications in synthetic chemistry wherein there is a
demonstrated need for the selective reduction of quinones. Efforts to shed
light on the mechanism and application to the synthesis are currently under
way in our laboratories.
REPRESENTATIVE PROCEDURE FOR THE REDUCTION
OF QUINONES (1) TO HYDROQUINONES (2) WITH NaN3
NaN3 (25 mmol) was added in one portion to a solution of 5 mmol of benzo-
quinone in 70 mL of acetone–water (9:1) mixture at room temperature. After
completion (5–12 h, TLC), the reaction mixture was concentrated in vacuum,
in which saturated NH4Cl was added. The mixture was extracted with ether
(3 Â 100 mL). Combined organic layers were washed with brine and dried
over MgSO4, and the solvent was removed to give analytically pure
products that were crystallized from hexane–ether or further purified by
flash column chromatography (SiO2, ethylacetate/hexane, 15:85) to remove
colored impurities.
Precaution: Although we did not have any problem with handling of
azides, it should be noted that they are hazardous and potentially explosive
when heated.

Sodium Azide Reduction of Quinones
ACKNOWLEDGMENTS
2297
¨
The authors are indebted to the Turkish Academy of Sciences (TUBA) and the
Middle East Technical University for their financial support of this work.
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