Electrochemical study of bromide in the presence of 1,3-indandione. Application to the electrochemical synthesis of bromo derivatives of 1,3-indandione

Article abstract of DOI:10.3390/60700639

The electrochemical oxidation of bromide in the presence of 1,3-indandione (1) in water/acetic acid and methanol/acetic acid mixtures has been studied by cyclic voltammetry and controlled-potential coulometry. The results indicate the participation of 1,3-indandione in the bromination reaction. On the basis of the electroanalytical and preparative results a reaction mechanism including electron transfer, chemical reaction and regeneration of bromide was discussed. The electrochemical synthesis of bromo derivatives of 1,3-indandione (2-3) has been successfully performed at constant current, in an undivided cell, in good yield and purity.

Full text of DOI:10.3390/60700639

Molecules 2001, 6, 639-646
molecules
ISSN 1420-3049
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Electrochemical Study of Bromide in the Presence of 1,3-
Indandione. Application to the Electrochemical Synthesis of
Bromo Derivatives of 1,3-Indandione
D. Nematollahi*, N. Akaberi
Department of Chemistry, Faculty of Science, University of Bu-Ali-Sina, Hamadan, Iran
*Author to whom correspondence should be addressed: E-mail: nemat@basu.ac.ir
Received: 15 November 2000; in revised form 7 June 2001 / Accepted: 8 June 2001/ Published: 30
June 2001
Abstract: The electrochemical oxidation of bromide in the presence of 1,3-indandione
(1) in water/acetic acid and methanol/acetic acid mixtures has been studied by cyclic
voltammetry and controlled-potential coulometry. The results indicate the participation
of 1,3-indandione in the bromination reaction. On the basis of the electroanalytical and
preparative results a reaction mechanism including electron transfer, chemical reaction
and regeneration of bromide was discussed. The electrochemical synthesis of bromo
derivatives of 1,3-indandione (2-3) has been successfully performed at constant
current, in an undivided cell, in good yield and purity.
Keywords: Electrochemical oxidation, cyclic voltammetry, 1,3-indandione, 2-bromo-
1,3-indandione, 2,2-dibromo-1,3-indandione.
Introduction
In previous publications we have shown that electrolysis offers a convenient and simple
technique for the synthesis of organic compounds [1-9]. Although numerous methods are
available for bromination of 1,3-indandione, they usually involve unstable and/or troublesome
reagents such as ascorbic acid for synthesis of 2-bromo-1,3-indandione via reduction of 2,2-

Molecules 2001, 6
640
dibromo-1,3-indandione [10], 5-hydroxy-5-(1,3-indandione-2-yl) barbituric acid and bromine
[11], potassium chlorate and bromine [12], the sodium salt of 1,3-indandione-2-sulfonate [13], 2-
methanoylindandione in the presence of bromine [14], N-bromosuccinimide [15], 2-{[N-
(hydroxymethyl)amino]methylene}-1,3-indandione [16], 2-bromo-2-nitro-1,3-indandione [17],
potassium bromate with potassium bromide in the presence of Dowex [18] or the bromine
complex of poly(styrene-CO-4-vinyl pyridine)[19], none are satisfactory for the preparation of
mono and dibromo derivatives of 1,3-indandione in good yield and purity, under mild conditions
such as an electrolytic procedure using bromide salts. This prompted us to investigate the anodic
behavior of bromide in the presence of 1,3-indandione by cyclic voltammetry, controlled-
potential coulometry and macroscale electrolysis from both electrochemical and organic synthetic
aspects. The present work describes an electrochemical study of the anodic oxidation of bromide
in the presence of 1,3-indandione in water/acetic acid and methanol/acetic acid mixtures and
reports a facile electrochemical method using inexpensive reagents and simple equipment for
synthesis of 2-bromo- and 2,2-dibromo-1,3-indandione in good yield and purity.
Results and Discussion
Electrooxidation of bromide in the presence of 1,3-indandione in water/acetic acid mixture
The electrochemical oxidation of bromide in the presence of 1,3-indandione (1) in water/acetic
acid mixture has been studied using cyclic voltammetry and controlled-potential coulometry. The
cyclic voltammogram of 5 × 10 −3 M of sodium bromide in aqueous acetic acid (40% V/V)
containing 0.1 M potassium nitrate as supporting electrolyte (scan rate: 50mV/s; T= 25 ± 1°C)
exhibits anodic and cathodic peaks at 0.98 V and 0.65V, respectively, which correspond to the two-
electron transformation of bromide to bromine and vice versa (Figure1, curve a).
Figure 1. (a) Cyclic voltammogram of 5 × 10 −3 M sodium bromide, (b) cyclic voltammogram of
5× 10 −3 M sodium bromide in the presence of 5 × 10 −3 M 1,3-indandione, (c) cyclic
voltammogram of 1 × 10 −3 M 1,3-indandione. Working electrode: glassy carbon.

Molecules 2001, 6
641
A peak current ratio (Ipa/Ipc) of nearly unity, particularly during the repetitive recycling of
potential can be considered as criteria for the stability of bromine produced at the surface of
electrode under the experimental conditions. Figure 1, curve b, shows the cyclic voltammogram
obtained for 5 × 10 −3 M solution of sodium bromide in the presence of 5 × 10 −3 M 1,3-indandione.
The voltammogram exhibits an increase in anodic current and disappearance of the cathodic
counterpart of the anodic peak. Under these conditions a cathodic peak (C) appears proportionally
to the increase of sweep rate, and its height increases progressively with scan rate. Moreover, a plot
of the peak current function (Ipa/v1/2 ) and peak current ratio (Ipa/Ipc) as a function of scan rate is in
good agreement with that of occurrence of a chemical reaction after the electron transfer process
appearing as a decrease in the peak current ratio (Ipa/Ipc) and peak current function (Ipa/v1/2 ) with
increasing scan rate [20].
In addition, controlled-potential coulometry was performed in solution containing 5 × 10 −3
M
sodium bromide and 5 × 10 −3 M of 1,3-indandione at 1.10 V vs. SCE. The monitoring of the
electrolysis progress was carried out by cyclic voltammetry. It is shown that as the electrolysis
proceeds, the height of anodic peak (A) decreases and finally it disappears. These observations
allow us to propose the following mechanism for electrochemical oxidation of bromide in the
presence of 1,3-indandione (Scheme 1).
2Br-
-
2e-
Br2
(1)
O
OH
O
O
1a
1
OH
O
O
Br2
+
Br
Br
H+
+
+
(2)
O
1a
2
Scheme 1
Such a mechanism is also in good agreement with the results already proposed for the
electrochemical halogenation of dibenzoylmethane [21], dimedone [22] and barbituric acid [23].
The interesting feature of this mechanism, is its similarity to the EC mechanism (following
reaction), in respect of the reaction of bromine with 1,3-indandione. On the other hand,
regeneration of bromide ion on the surface of electrode indicates its resemblance to EC’ mechanism
(catalytic reaction). Based on this mechanism, the increase of the Ipa in the presence of 1,3-

Molecules 2001, 6
642
indandione (Figure 1, curve b) is related to regeneration of bromide in surface of electrode [20]
(Scheme 1, Eq. 2). The overbromination of 2 can be performed in the presence of excess amounts
of bromide as shown in Scheme 2.
O
OH
Br
Br
O
O
2
2a
OH
O
O
O
Br
Br
H+
Br +
Br2
+
Br
+
2a
3
Scheme 2
According to Scheme 2, the initial product in bromination of 1,3-indandione (2), the keto
form of 2-bromo-1,3-indandione, is converted into the enol form (2a), which then reacts with a
13
second molecule of bromine. Compounds 2 and 3 were identified by their IR, 1H-NMR and C-
NMR spectra, determination of bromine content and melting point. The bromine content in these
compounds (2 and 3) can be determined by the simple method described in the Experimental
section. The result shows good agreement between found and required values. A characteristic
feature of the electrolysis is that high current density is required to terminate the reaction in short
time for the mili mole scale experiment. The purity of 2 and 3 were unsatisfactory at lower
current densities (Table 2) and byproduct(s) were obtained, one of which might be corresponding
dimer product. Such a dimer is observed in electrooxidation of acetylacetone [24].
Electrooxidation of bromide in the presence of 1,3-indandione in methanol/acetic acid mixture
Similar to those of the previous case the cyclic voltammogram representative of the behavior of
sodium bromide in MeOH/AcOH (3% V/V) containing 0.1 M KNO3 at 25 °C exhibits one anodic
and corresponding cathodic peak which is corresponding to the transformation of bromide to
bromine and vice versa within two-electron process. Fig. 2, curve a, shows the cyclic
voltammogram obtained for 5 × 10 −3 M solution of bromide in the presence of 5 × 10 −3 M 1,3-
indandione in scan rate 50 mV/s. Under these conditions, the cathodic peak disappeared and
voltammogram exhibits an irreversible process, but with decreasing the timescale of experiment, by
increasing the sweep rate, the cathodic counterpart (C) of anodic peak (A) become increasingly
apparent (Fig. 2 curves b-d). A plot of peak current function (Ipa/v1/2 ) vs. scan rate confirms the

Molecules 2001, 6
643
reaction between bromine and 1,3-indandione, appearing as a decrease in peak current function
(Ipa/v1/2 ) with increasing scan rate (Fig. 3). The reaction mechanism and other observations are
similar to those of the previous case and we assume such a behavior as an indication of a chemical
reaction between bromine and 1,3-indandione according to Scheme 1.
Figure 2. Cyclic voltammograms of 5 × 10 −3 M NaBr in the presence of 5 × 10 −3 M 1,3-indan-
dione in various potential scan rate at glassy carbon electrode in MeOH/AcOH
,
(3%)(V/V). Scan rate from (a) to (d), is: 50, 100, 300 and 500 mV/s respectively.
Supporting electrolyte: 0.10 M KNO3. T = 25 ± 1 o C.
34
30
26
22
0
150
300
450
v (mV/s)
Figure 3. The variation of anodic peak current function (Ipa/v1/2 ) (µΑ.s1/2.mV-1/2)
vs. scan rate.
Conclusions
The results of this work show that bromide is oxidized electrochemically to bromine and then
reacts with. 1,3-indandione to form α-bromo compounds. The reaction mechanisms for anodic
oxidation of bromide in the presence of 1,3-indandione are presented in Schemes 1 and 2. We also
describe a new facile route for synthesis of 2-bromo and 2,2-dibromo-1,3-indandione, that is

Molecules 2001, 6
644
characterized by: (I) bromination without use of molecular bromine; (II) good control of the rate of
release of bromine; (III) selective bromination at the α-position of olefinic active methylene
compounds and (IV) selective formation of the monobromo or dibromo derivatives in good yields
with slight changes in electrolysis conditions. The procedure utilizes inexpensive reagents, simple
equipment, and undivided cell,s it is easily carried out, and workup is simple.
Experimental
Cyclic voltammetry and controlled-potential coulometry were performed using an Autolab
model PGSTAT20 potentiostat/galvanostat. The preparative electrolyses were performed using an
Iran Electronic Industries 8303 DC power supply. The working electrode used in the voltammetry
experiments was a glassy carbon disc and a platinum wire was used as counter electrode. The
working electrode potentials were measured versus the SCE electrode (all electrodes from AZAR
electrode). Reagent grade 1,3-indandione (Aldrich) and Pro-Analysis grade sodium bromide (E.
Merck) were used as received. Proton and carbon spectra were recorded on a JEOL NMR-
Spectrometer FX 90Q. IR spectra were recorded on a Shimadzu 435 IR spectrophotometer.
General electrolysis procedure
A solution (ca. 20 mL) of sodium bromide and 1,3-indandione (1 mmol) in water/acetic acid or
methanol/acetic acid (see Table 1) was electrolyzed in an undivided cell equipped with C-anode (an
assembly of four rods, 4 mm diameter and 12 mm length) and Fe-cathode (10 mm width and 20
mm length) at 25°C under constant current density 50 mA Cm-2 until the quantity of the electricity
indicated in Table 1 was passed. At the end of electrolysis, the reaction mixture was diluted with a
ca. two-fold volume of water and placed in a cold water bath. The precipitated solid was filtrated,
washed, dried and recrystallized from methanol/water mixture (80% V/V). The recrystallized
products gave satisfactory IR, 1H-NMR, 13C-NMR spectra and analyses of bromine content.
Characterization of the products
2-Bromo-1,3-indandione (2); m.p. 118-20°C (dec.) (Lit.[15]: 117-19°C). IR(KBr): νmax = 585 (C-
Br), 1615, 1721 (C=O). 1H-NMR, δ ppm (CDCl3): 4.14 (H, s, -CHBr-), 7.61-8.08 (4H, m, -CH-).
13C-NMR, δ ppm (CDCl3): 31.06(-CHBr-) 123.12, 125.63, 137.84 (aromatic carbons), 204.1
(C=O).
2,2-Dibromo-1,3-indandione (3); m.p. 181-182°C (dec). (Lit.[18]: 182-182.5°C). IR(KBr): νmax
=
1
13
590 (C-Br), 1701, 1736 (C=O). H-NMR, δ ppm (CDCl3): 8.04 (4H, m, aromatic protons), C-
NMR, δ ppm (CDCl): 51.26(-CBrBr-) 125.71, 135.49, 137.97 (aromatic carbons), 209.22 (C=O)

Molecules 2001, 6
645
Determination of bromine content [21]
The sample (about 15 mg) was dissolved in THF and/or chloroform (ca. 10 mL) to which
aqueous 0.3 M potassium iodide (5 mL) and aqueous 1 M hydrochloric acid (5 mL) were added and
the liberated iodine (Scheme 3) was titrated with aqueous 0.01 M sodium thiosulphate.
O
O
H+
Br
+
Br +
+
I
+
I2
O
O
1
2
Scheme 3
Table 1. Electroanalytical and preparative data.
Electricity
Product
Electrolysis
Solvent
Bromine Content (%)
Found Required
NaBr
Passed
(F mol-1)
Conversion
mmol
Yield%
methanol/acetic acid
(3% V/V)
1
1
2
3
1
3.1
6.4
34.94
51.69
35.37
52.26
83
→
→
water/acetic acid
(40% V/V)
2
73
Table 2. Effect of current density on product yield1.
Product Yield %
Current
Density
mA/cm2
5
2-bromo-1,3-
2,2-dibromo-1,3-
indandione2
indandione3
14
24
56
83
81
12
21
48
73
69
15
25
50
75
1
General conditions for electrolysis are similar to those mentioned in Table 1.
Conditions for synthesis of 2-bromo-1,3-indandione are: solvent:
methanol/acetic acid 3% V/V, NaBr 1 mmol, 1,3-indandione 1mmol, current
consumption: 299.1 C or 3.1 Fmol-1.
2

Molecules 2001, 6
646
3
Conditions for synthesis of 2,2-dibromo-1,3-indandione are: solvent:
water/acetic acid 40% V/V, NaBr 2 mmol, 1,3-indandione 1mmol, current
consumption: 617.6 C or 6.4 Fmol-1.
References and Notes
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4. Golabi, S. M.; Nematollahi, D. J. Electroanal. Chem., 1997, 420, 127.
5. Golabi, S. M.; Nematollahi, D. J. Electroanal. Chem., 1997, 430, 141.
6. Nematollahi, D.; Golabi, S. M. Bull. Electrochem., 1998, 14, 97.
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8. Nematollahi, D.; Golabi, S. M. Electroanalysis, accepted for publication.
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37.
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Marcel Dekker: New York, 1973; p 720.
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