Electroselective α-bromination of acetophenone using: In situ bromonium ions from ammonium bromide

Article abstract of DOI:10.1039/c6ra04541c

A greener and expeditious method for the side chain bromination of acetophenone using in situ generated bromonium ions from NH₄Br and a catalytic amount of H₂SO₄ as a supporting electrolyte in a H₂O:CH₃CN medium at ambient temperature has been developed in an undivided cell equipped with a Pt/Pt electrode. This method results in a good yield (80%) of α-bromo acetophenone with high selectivity when only 2F of electricity was passed. Optimization studies such as variation of the current density, charge passed, solvent, solvent/water ratio, acid, acid strength, bromide salt, bromide salt concentration, etc., are carried out and reported.

Full text of DOI:10.1039/c6ra04541c

RSC Advances
View Article Online
View Journal | View Issue
PAPER
Electroselective a-bromination of acetophenone
using in situ bromonium ions from ammonium
bromide†
Cite this: RSC Adv., 2016, 6, 35602
a
a
b
c
*
R. Jagatheesan, K. Joseph Santhana Raj, S. Lawrence and C. Christopher
A greener and expeditious method for the side chain bromination of acetophenone using in situ generated
bromonium ions from NH4Br and a catalytic amount of H2SO4 as a supporting electrolyte in a H2O:CH3CN
medium at ambient temperature has been developed in an undivided cell equipped with a Pt/Pt electrode.
This method results in a good yield (80%) of a-bromo acetophenone with high selectivity when only 2F of
electricity was passed. Optimization studies such as variation of the current density, charge passed, solvent,
solvent/water ratio, acid, acid strength, bromide salt, bromide salt concentration, etc., are carried out and
reported.
Received 20th February 2016
Accepted 4th April 2016
DOI: 10.1039/c6ra04541c
www.rsc.org/advances
bromination,27 solvent free condition28 and electrochemical
bromination involved HBr29 and NaBr–HBr30–32 methods have
1. Introduction
also been reported. Although NBS is easier and safer to handle
than bromine, precautions should be taken to avoid inhalation.
NBS should be stored in a refrigerator. NBS will decompose over
time giving off bromine. In general, reactions involving NBS are
exothermic. Therefore, extra precautions are required for using
in a large scale.
Selective bromination of aromatic ketones is a signicant
reaction in synthetic organic chemistry.1 The side chain
bromination of aromatic ketones has attracted much attraction,
because the resulting bromo ketones are versatile synthetic
intermediates for a variety of biologically active compounds2
and are precursors for various organic transformations.3 Espe-
cially, phenacyl bromide acts as a protecting group for acids and
phenols in peptide synthesis4 and its derivatives actively
participated in the inhibition of protein tyrosine phosphatase
such as SHP-1 and PTP1B.5
So far several attempts have been made in the eld of
conventional organic synthesis for the bromination of ketones
which includes acetyl cupric bromide,6 ammonium bromide–
V2O5,7 dioxane dibromide,8 tetra butyl ammonium tribromide,9
H2O2–HBr,10 (CH3)3SiBr–nitrate salt,11 bromo dimethyl sulfo-
nium bromide,12 NH4Br–oxone,13 pyridinium bromo chro-
mate,14 ethylene bis[N-methyl imidazolium]ditribromide,15
NaBr–oxone16 and trihaloisocyanuric acids.17
However, all these methods are still prone to several disad-
vantages such as long reaction times,13 cost and preparation of
catalyst,11 use of hazardous chemicals and complicated reaction
procedure like temperature maintaining.31 To surmount these,
a convenient electrochemical method reported for the electro-
chemical bromination of acetophenone into phenacyl bromide,
is a reliable method of preparation of a-haloketones as shown
in Scheme 1. The development of a more efficient and economic
method for bromination is still highly desirable. In green
chemistry perspective, the replacement of such harmful
reagents with non-toxic, inexpensive, commercially available,
non-polluting and more selective reagents is an important goal.
Now a days green chemistry protocols are inevitable to achieve
better result in the eld of electroorganic synthesis.33,34 In the
context of green chemistry, noncatalytic processes have
engrossed considerable attention. However, to the best of our
knowledge, an efficient a-halogenation of carbonyl compounds
without catalyst has not been reported so far.
Pertinent to the availability, N-bromosuccinimide (NBS) has
been extensively used as brominating agent with various cata-
lysts such as Mg(ClO4)2,18 NH4OAc,19 Amberlyst-15,20 silica-
supported NaHSO4,21 silica supported NaHCO3,22 sulfonic acid
functionalized silica,23 FeCl3.24 In addition to that, for instance,
ionic liquids,25 photochemical bromination,26 sonochemical
aDepartment of Chemistry, St. Joseph's College, Tiruchirappalli-620 002, India
bDepartment of Chemistry, Govt. Thirumagal Mills College, Gudiyattam-632 602,
India
cDepartment of Chemistry, St. Xavier's College, Thirunelveli-627 002, India. E-mail:
chrischemo@gmail.com
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c6ra04541c
Scheme 1 Electrochemical selective bromination of acetophenone.
35602 | RSC Adv., 2016, 6, 35602–35608
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
The most fascinating features of this procedure are: (a) characterized by 1H NMR, 13C NMR and Fourier transform-
bromination without the use of molecular bromine (or) HBr (b) infrared (FT-IR) spectra.
selective bromination at the a-position of aromatic ketones at
ambient temperature (c) simple technique (d) straight forward
choice of an appropriate halide salt such as NH4Br (e) a regio- 3. Result and discussion
selective mono halogenating procedure, resulting in high yield
Generally elemental bromine was generated in situ by simple
of a-brominated products and (f) catalytic free conversion. This
constant current electrolysis of reaction mixture acetonitrile
method is expected to be of great synthetic utility because of its
solution and ammonium bromide in the presence of
a substrate. The bromination of arylalkyl ketones lead to a side
high selectivity for the a-monobrominated product.
chain a-bromination as well as ring bromination based on the
conditions employed.13,29 The most favourable conditions for
the electrochemical side chain bromination of acetophenone
and the results are given in detail. Moreover optimization of the
electrolysis condition was monitored periodically in relative of
2. Experimental
2.1 Electroselective bromination of acetophenone
Ammonium bromide (80 mL of 60% solution) and sulphuric
acid (3 mL) were added to the solution of acetophenone (10
mmol) in acetonitrile (20 mL) and the resulting solution was
taken in an undivided cell. Sulphuric acid was added to main-
the increase in the yield of the product and current efficiency.
tain the acidic medium as well as for conductivity purpose. Two
platinum electrodes (each of 15 cm2 area) were introduced at
a distance of 2 cm2 into the homogeneous solution. 2F of
electricity was passed galvanostatically at a current density of
100 mA cmꢀ2 at the ambient temperature and the whole solu-
tion was stirred constantly throughout the reaction (Fig. 1).
Aer passing required charge per mole of acetophenone the
current ow was stopped and the reaction mixture alone was
stirred another 5 hours to allow the in situ generated hypobro-
mous acid to react with the acetophenone completely. Aer this
additional stirring, the reaction mixture was extracted with
ethyl acetate (3 ꢁ 25 mL). Finally the combined organic layer
was washed with water (20 mL) and dried over anhydrous
sodium sulfate. The product a-bromo acetophenone was ob-
tained aer evaporation of the solvent at reduced pressure and
crystallized from a mixture of methanol and hexane.
The electrochemical reaction was monitored by Shimadzu
HPLC with LC-8A column (250 mm ꢁ 4.6 mm) as stationary
phase. The eluent consisted of acetonitrile/water (60 : 40) at
a ow rate of 1 mL minꢀ1. Samples were analyzed at a wave-
length of 254 nm with a UV detector coupled to a printer.
Authentic samples were used to calculate the peak areas of the
respective experimental products for yield calculation.
3.1 Effect of temperature and UV-light
The electrochemical side chain bromination of acetophenone
was tried in three different temperatures and also in the pres-
ence of UV-light as mentioned in Table 1 and the report sug-
gested that the rate of formation of phenacyl bromide varies at
different reaction temperature.
3.2 Effect on stirring time
The effect of stirring time of reaction mixture was studied at
various intervals like 0, 3, 5 and 24 hours aer the completion of
actual theoretical electricity was passed (2F). It was observed
that the conversion is effectively proceeding with increase of
agitation time. The results are presented in Table 2.
One of the most remarkable features of the electroorganic
reaction is that it is generally achievable at room temperature.
Accordingly the ambient temperature (30–35 ꢂC) was elected as
suitable reaction condition with 5 hours stirring.
3.3 Effect of current density
Electrochemical a-bromination of acetophenone was carried
out in homogeneous medium and the current density was
varied from 30 to 100 mA cmꢀ2. The lower current density did
not favour much for the formation of desired product. But when
moved from lower to higher current density maximum yield and
current efficiency was obtained only at 100 mA cmꢀ2. Moreover
it takes very minimum time to carry out the electrolysis
(Table 3). So this current density was chosen as an optimum
current density for further studies.
HPLC analysis of the crude indicates the presence of 80% a-
bromo acetophenone. The product was analyzed and
3.4 Effect of charge passed
The selective bromination of acetophenone was carried out at
different charges ranging from 2F to 5F in an undivided cell.
The yield at 2F was 80% and rose to 87% at 5F. From the Table 4,
it is observed that the maximum yield with high current effi-
ciency was achieved only at 2F. Hence this lesser 2F of charge
per mole is chosen as optimal charge.
Fig. 1 Electrochemical reaction cell set up.
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 35602–35608 | 35603

View Article Online
RSC Advances
Paper
Table 1 Effect of temperature and UV-light on bromination at side chain of acetophenonea
S. No
Temperature (ꢂC)
Phenacyl bromide yieldb (%)
Current efficiency (%)
1
2
3
4
10–15
30–35
66
54
73
73
66
54
73
73
55–60
UV-lightc
a
Reaction mixture: 60% NH4Br + 0.33 M H2SO4 + 10 mmol acetophenone + water 80%–acetonitrile 20%. Electrolysis conditions: amount of
electricity, 2F; current density, 100 mA cmꢀ2; electrodes, platinum/platinum. Stirring time: 0 hour aer electrolysis. The electrochemical
b
c
reaction was carried out in the presence of a Philips HPL-N (250 W, lmax ¼ 200–600 nm) lamp at ambient temperature.
Table
2 Effect of stirring time on selective bromination of
Table
4 Effect of charge passed on selective a-bromination of
acetophenonea
acetophenonea
Phenacyl bromide yield (%) at
Charge passed
Phenacyl bromide
yield (%)
Current efficiency
(%)
S. No Timeb (hours) 10–15 ꢂ
C
30–35 ꢂ
C
55–60 ꢂ
C
UV-lightc
S. No
(F molꢀ1
)
1
2
3
4
2.0
3.0
4.0
5.0
80
78
78
87
80
52
39
35
1
2
3
4
0
3
5
66
69
73
76
54
62
80
82
73
71
43
38
73
76
72
65
24
a
a
Reaction mixture: 60% NH4Br
+ 0.33 M H2SO4 + 10 mmol
Reaction mixture: 60% NH4Br
+
0.33
M
H2SO4
+
10 mmol
acetophenone + water 80%–acetonitrile 20%. Electrolysis conditions:
acetophenone + water 80%–acetonitrile 20%. Electrolysis conditions:
current density, 100 mA cmꢀ2
; electrodes, platinum/platinum;
amount of electricity, 2F; current density, 100 mA cmꢀ2; electrodes,
temperature, 30 to 35 ꢂC; stirring time, 5 h.
b
platinum/platinum. To obtain the best yields of the products the
agitation aer electrolysis (aer passing 2F charge per mole) was
c
extended. The yield at 2F (zero hours stirring aer electrolysis) was
73% and rose to 76% at 3 hours of stirring and there was no
remarkable increase in the yield aer 3 hours of stirring.
Table
3 Effect of current density on selective bromination of
acetophenonea
Current density
Phenacyl bromide
yield (%)
Current efficiency
(%)
S. No
(mA cmꢀ2
)
1
2
3
4
30
50
70
47
80
65
80
47
80
65
80
100
a
Reaction mixture: 60% NH4Br
+ 0.33 M H2SO4 + 10 mmol
acetophenone + water 80%–acetonitrile 20%. Electrolysis conditions:
amount of electricity, 2F; electrodes, platinum/platinum; temperature,
30 to 35 ꢂC; stirring time, 5 h.
Fig. 2 Graphical representation of effect of bromide salts.
3.5 Effect of bromide salt
Considering the possibility of achieving the selective bromina-
tion of acetophenone by different reaction routes, the effect of
changing the bromide salt was investigated. A 60% of bromide
salts such as KBr, NaBr and NH4Br solution were used inde-
pendently and they gave yields 73%, 74% and 80% respectively
(Fig. 2). Thus NH4Br was preferred due to its excellent
performance.
electrochemical cell at ambient temperature. The formation of
phenacyl bromide varies with the concentration of bromide salt
as shown in Table 5.
Since commercially available HOBr is unstable and easily
decomposed at room temperature, its reactivity is not as good as
the in situ formed acid. Hence the excess amount of ammonium
bromide was used to produce sufficient HOBr.
3.6 Effect of ammonium bromide concentration
3.7 Effect of acetophenone concentration
Ammonium bromide was used as bromonium ion source for In order to standardize the substrate concentration for the
the a-bromination of acetophenone in an undivided present electrochemical cell set up, acetophenone quantity was
35604 | RSC Adv., 2016, 6, 35602–35608
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
Table 5 Effect of ammonium bromide concentration variation on Table
8
Effect of acid variation on selective bromination of
selective bromination of acetophenonea
acetophenonea
Amount of NH4Br
(%)
Phenacyl bromide
yield (%)
Current efficiency
(%)
Phenacyl bromide
yield (%)
Current efficiency
(%)
S. No
S. No
Acid
1
2
3
4
5
05
10
15
30
60
35
58
60
62
80
35
58
60
62
80
1
2
3
4
HNO3
38
49
72
80
38
49
72
80
HClO4
p-TsOH
H2SO4
a
Reaction mixture: 60% NH4Br + 0.33 M various acids such as HNO3,
HClO4, p-TsOH and H2SO4 + 10 mmol acetophenone + water 80%–
acetonitrile 20%. Electrolysis conditions: amount of electricity, 2F;
a
Reaction mixture: various concentrations of NH4Br + 0.33 M H2SO4 +
10 mmol acetophenone + water 80%–acetonitrile 20%. Electrolysis
current density, 100 mA cmꢀ-2
; electrodes, platinum/platinum;
conditions: amount of electricity, 2F; current density, 100 mA cmꢀ2
;
temperature, 30 to 35 ꢂC; stirring time, 5 h.
electrodes, platinum/platinum; temperature, 30 to 35 ꢂC; stirring
time, 5 h.
the acidic medium was recommended for this reaction
condition.
Table
6 Effect of substrate concentration variation on selective
bromination of acetophenonea
Acid-catalyzed a-bromination leads to the exchange of only
one a-hydrogen for a halogen even if the a-carbon carries
additional hydrogens. Under acidic conditions, the enol is
continually supplied through keto–enol tautomerism and the
reaction rate of a second bromination is much lower than that
of the rst halogenation. Therefore, halogenation of carbonyl
compounds under acidic conditions yields monohalogenated a-
halocarbonyl compounds, whereas in neutral and basic
medium undesired product also formed.
Acetophenone
(mmol)
Phenacyl bromide
yield (%)
Current efficiency
(%)
S. No
1
2
3
4
05
10
15
20
74
80
55
54
74
80
55
54
a
Reaction mixture: 60% NH4Br + 0.33 M H2SO4 + different mmol of
water 80%–acetonitrile 20%.
acetophenone as given in table
+
Electrolysis conditions: amount of electricity, 2F; current density, 100
mA cmꢀ2; electrodes, platinum/platinum; temperature, 30 to 35 ꢂC;
stirring time, 5 h.
3.9 Effect of acid
Acid plays a key role in the conduction of ionic current between
the electrodes as supporting electrolyte. The reaction was
examined by using various supporting electrolytes like HNO3,
HClO4, p-TsOH (p-toluenesulfonic acid) and H2SO4 (Table 8).
Among these acids H2SO4 performed well due to its higher
conductivity (<2 V). Moreover it is cheaper and readily available
one. Henceforth H2SO4 was selected as good supporting elec-
trolyte for the side chain bromination of acetophenone
reaction.
varied from 5–20 mmol. From that 10 mmol of acetophenone
was chosen as suitable quantity for the formation of desired
product (Table 6).
3.8 Effect of medium
On the side of increasing the yield of phenacyl bromide at room
temperature, this electrochemical side chain bromination
reaction was conducted in the subsequent (Table 7) medium.
According to the results, acidic medium was acted well. Thus
3.10 Effect of acid strength
Concerning the effect of acid strength to increase the yield,
different attempts made with a choice of acid strength such as
0.11 M, 0.33 M and 0.55 M. But there was no signicant increase
in the yield of a-bromoacetophenone. Thereby moderate acid
strength (0.33 M) was suggested for this condition.
Table 7 Effect of reaction medium on the side chain bromination of
acetophenonea
Nature of
solution
Phenacyl bromide
yield (%)
Current efficiency
(%)
3.11 Effect of solvent
S. No
To study the effect of solvent on the a-bromination of aceto-
phenone, various solvents like polyethylene glycol, CH3COOH,
DMSO, CH3OH and CH3CN were used at ambient temperature.
Two-phase electrolysis and emulsion electrolysis was also tried
using CHCl3, but it gave low yield and required mediator to
1
2
3
Basic
Neutral
Acidic
53
43
80
57b
92b
80
a
Reaction mixture: 60% NH4Br + 0.33 M NaOH or 0.33 M KCl or 0.33 M
10 mmol acetophenone water 80%–acetonitrile 20%.
H2SO4
+
+
Electrolysis conditions: amount of electricity, 2F; current density, 100 carry in situ generated bromonium ion from aqueous phase to
mA cmꢀ2; electrodes, platinum/platinum; temperature, 30 to 35 ꢂC;
stirring time, 5 h. Electricity utilized for the formation of phenacyl
bromide and undesired product.
organic phase. Among these solvents CH3CN performed well
and was preferred as a suitable solvent for the present study
b
(Table 9).
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 35602–35608 | 35605

View Article Online
RSC Advances
Paper
Table
9 Effect of solvent variation on selective bromination of
3.13 Effect of reusability of spent aqueous bromide salt
solution
acetophenonec
The brominated and unreacted acetophenone was isolated
aer the electrolysis reaction with ethyl acetate and the
remaining bromide salt aqueous solution was available for
further use (reuse 1 to 3). From the Table 11 it illustrates that
the amount of yield was decreased from 80% to 43%, since the
bromide salt had been consumed on consecutive
experiments.
Solvent (20 mL) +
H2O (80 mL)
Phenacyl bromide
yield (%)
Current
efficiency (%)
S. No
1
2
3
4
5
6
7
Polyethylene glycol
CH3COOH
38
42
52
57
55
67
80
38
42
52
57
55
67
80
a
CHCl3
CHCl3
b
DMSO
CH3OH
CH3CN
When the oxidation potential of the halogen is lower than
that of the aromatic compound, halogenation is initiated by
a
b
c
Two-phase electrolysis. Emulsion electrolysis. Reaction mixture:
60% NH4Br + 0.33 M H2SO4 + 10 mmol acetophenone is dissolved in
various solvents mentioned in table. Electrolysis conditions: current
density, 100 mA cmꢀ2; amount of electricity, 2F; electrodes, platinum/
platinum; temperature, 30 to 35 ꢂC; stirring time, 5 h.
Table 10 Effect of water/solvent ratio variation on selective bromi-
nation of acetophenonea
H2O : CH3CN
(mL)
Phenacyl bromide
yield (%)
Current efficiency
(%)
S. No
1
2
3
4
80 : 20
85 : 15
90 : 10
95 : 05
80
76
71
00
80
76
71
00
a
Reaction mixture: 60% NH4Br
+ 0.33 M H2SO4 + 10 mmol
acetophenone is dissolved in different water/solvent ratios.
Electrolysis conditions: amount of electricity, 2F; current density, 100
mA cmꢀ2; electrodes, platinum/platinum; temperature, 30 to 35 ꢂC;
stirring time, 5 h.
Scheme 2 Plausible mechanism for the electro catalytic selective a-
bromination of acetophenone.31
3.12 Effect of water/acetonitrile ratio
The various water/acetonitrile ratios were studied as given in
the Table 10. For the a-bromination of acetophenone electro-
lytic reaction, the quantity of water/acetonitrile required for
better yield was 80 : 20 mL. The greener solvent water occupies
maximum percentage in this study.
When the percentage of water increased, the solubility of
substrate was diminished and also the bromination reaction
was stopped even aer 5 hours stirring.
Table 12 Electrochemical a-bromination of aromatic ketones in
homogeneous phasea
Current
Yield efficiency
Entry Substrate
1
Product
(%)
(%)
80
80
Table 11 Effect of reusability of spent aqueous bromide salt solutiona
2
65
43
66
51
Phenacyl bromide
yield (%)
Current efficiency
(%)
S. No
Amount of NH4Br
1
2
3
4
Fresh solution*
Reuse 1
Reuse 2
80
69
58
43
80
69
58
43
3
Reuse 3
a
a
Reaction mixture: *60% NH4Br
+
0.33
M
H2SO4
+
10 mmol
Reaction mixture: 60% NH4Br + 0.33 M H2SO4 + 10 mmol substrate +
acetophenone + water 80%–acetonitrile 20%. Electrolysis conditions: water 80%–acetonitrile 20%. Electrolysis conditions: amount of
amount of electricity, 2F; current density, 100 mA cmꢀ2; electrodes, electricity, 2F; current density, 100 mA cmꢀ2; electrodes, platinum/
platinum/platinum; temperature, 30 to 35 ꢂC; stirring time, 5 h.
platinum; temperature, 30 to 35 ꢂC; stirring time, 5 h.
35606 | RSC Adv., 2016, 6, 35602–35608
This journal is © The Royal Society of Chemistry 2016

View Article Online
Paper
RSC Advances
the oxidation of halogen.35 The electrochemically generated
bromine combines with water, giving one molecule of hypo-
bromous acid (HOBr) and one molecule of HBr.31 The hypo-
bromous acid is unstable due to its pronounced ionic nature
and thus can react with the enol form of the ketone to form
a-bromo derivative as shown in Scheme 2. To make this
methodology broaden, the optimized conditions was applied
for further investigation on a-bromination of aromatic
6 L. C. King and G. K. Ostrum, J. Org. Chem., 1964, 29, 3459–
3461.
7 A. T. Khan, P. Goswami and L. H. Choudhury, Tetrahedron
Lett., 2006, 47, 2751–2754.
8 S. J. Pasaribu and L. K. Williams, Aust. J. Chem., 1973, 26,
1327–1331.
9 S. Kajigaeshi, T. Kakinami, T. Okamoto and S. Fujisaki, Bull.
Chem. Soc. Jpn., 1987, 60, 1159–1160.
ketones and the results are given below. In our subsisting 10 A. Podgorsek, S. Stavber, M. Zupan and J. Iskara, Green
methodology, we brought to selective bromination at side
chain.
Chem., 2007, 9, 1212–1218.
11 G. K. Surya Prakash, R. Ismail and T. Mathew, Tetrahedron
Lett., 2011, 52, 1217–1221.
Acetophenone containing electron-donating group has
higher reactivity than one containing electron-withdrawing 12 A. T. Khan, M. A. Ali, P. Goswami and L. H. Choudhury, J.
group under similar reaction conditions (entry 2 and 3). Org. Chem., 2006, 71, 8961–8963.
Unsubstituted acetophenone gave corresponding a-bromi- 13 M. Arun Kumar, C. N. Rohitha, M. Mahender Reddy,
nated product in high yield than the substituted acetophe-
nones (Table 12).13,29 Generally methoxy group present on the
P. Swamy and N. Narender, Tetrahedron Lett., 2012, 53,
191–195.
aromatic ring direct the ring bromination, whereas in 14 Y. Sarra, M. Sadatshahabi and K. Alimohammadi, Chin.
this case side chain bromination achieved in good yield. Chem. Lett., 2009, 20, 393–396.
This is due to the electron withdrawing nature of carbonyl 15 R. Hosseinzadeh, M. Tajbakhsh, M. Mohadjerani and
group.
Z. Lasemi, Monatsh. Chem., 2009, 140, 57–60.
16 E.-H. Kim, B.-S. Koo, C.-E. Song and K.-J. Lee, Synth.
Commun., 2001, 31(23), 3627–3632.
17 G. F. Mendonca, H. C. Sindra, L. S. de Almeida, P. M. Esteves
and M. C. S. de Mattos, Tetrahedron Lett., 2009, 50, 473–475.
18 D. Yang, Y. Yan and B. Lui, J. Org. Chem., 2002, 67, 7429–
7431.
19 K. Tanemura, T. Suzuki, Y. Nishida, K. Satsumabayashi and
T. Horaguchi, Chem. Commun., 2004, 470–471.
20 H. M. Meshram, P. N. Reddy, K. Sadashiv and J. S. Yadav,
Tetrahedron Lett., 2005, 46, 623–626.
21 B. Das, K. Venkateswarlu, G. Mahender and I. Mahender,
Tetrahedron Lett., 2005, 46, 3041–3044.
4. Conclusions
In this study a simple and efficient method for the side chain
bromination of acetophenone with ammonium bromide in the
homogeneous medium was reported. The special features of the
present work is that the reaction takes place at the ambient
temperature, simple electrochemical cell set up, short reaction
time, environmental friendly bromide salt and at high current
density and also increases the selectivity of a-bromination in
aromatic ketones. The reaction does not require harmful
chemicals like HBr, pyridinium bromochromate and avoiding
the use of conventional reagent NBS with catalysts for this
transformation.
22 A. Rahman and S. B. Jonnalagadda, Synth. Commun., 2012,
42, 1091–1100.
23 B. Das, K. Venkateswarlu, H. Holla and M. Krishnaiah, J.
Mol. Catal., 2006, 253, 107–111.
Acknowledgements
24 H. Jin, Z. D. Huang, C. X. Kuang and X. K. Wang, Chin. Chem.
Lett., 2011, 22, 310–313.
Authors wish to show their gratitude to Dr K. Kulangiappar,
Electro Organic Division, Central Electrochemical Research
Institute, Karaikudi-630006, India and Dr P. Shanmugavelan,
School of Sciences, Tamilnadu Open University, Chennai – 600
015, India, for their aspiring guidance, invaluably constructive
criticism and friendly advice during this work.
25 H. M. Meshram, P. N. Reddy, K. Vishnu, K. Sadashiv and
J. S. Yadav, Tetrahedron Lett., 2006, 47, 991–995.
26 S. S. Arbuj, S. B. Waghmode and A. V. Ramaswamy,
Tetrahedron Lett., 2007, 48, 1411–1415.
27 M. V. Adhikari and S. D. Samant, Ultrason. Sonochem., 2002,
9, 107–111.
28 I. Pravst, M. Zupan and S. Stavber, Tetrahedron, 2008, 64,
5191–5199.
References
29 R. Senthil Kumar, K. Kulangiappar and M. Anbu
Kulandainathan, Synth. Commun., 2010, 40, 1736–1742.
30 T. Raju, K. Kulangiappar, M. Anbukulandainathan and
A. Muthukumaran, Tetrahedron Lett., 2005, 46, 7047–7050.
31 T. Raju, K. Kulangiappar, M. Anbu Kulandainathan, U. Uma,
R. Malini and A. Muthukumaran, Tetrahedron Lett., 2006, 47,
4581–4584.
1 A. M. Erian, S. M. Sherif and H. M. Gaber, Molecules, 2003, 8,
793.
2 J. Talegaonkar, S. Mukhija and K. S. Boparai, Talanta, 1982,
29, 327.
3 N. D. Kimpe and R. Verhe, The Chemistry of a-Haloketones, a-
Haloadehydes and a-Haloimines, Wiley, New York, 1988.
4 P. M. Fischer, Tetrahedron Lett., 1992, 33, 7605.
5 G. Arabaci, X. C. Guo, K. D. Beebe, K. M. Coggeshall and
D. Pei, J. Am. Chem. Soc., 1999, 121, 5085–5086.
´
32 T. Raju, G. Kalpana and K. Kulangiappar, Electrochim. Acta,
2006, 51, 4596–4600.
This journal is © The Royal Society of Chemistry 2016
RSC Adv., 2016, 6, 35602–35608 | 35607

View Article Online
RSC Advances
Paper
33 C. Christopher, S. Lawrence, A. John Bosco, N. Xavier and 35 T. Shono, Electroorganic chemistry as a new tool in organic
S. Raja, Catal. Sci. Technol., 2012, 2, 824.
34 M. Balaganesh, S. Lawrence, C. Christopher, A. John Bosco,
K. Kulangiappar and K. Joseph santhanara Raj, Electrochim.
Acta, 2013, 111, 384–389.
synthesis. Reactivity and structure: concepts in organic
chemistry, 1984, vol. 20, p. 98.
35608 | RSC Adv., 2016, 6, 35602–35608
This journal is © The Royal Society of Chemistry 2016