Isoquinolinium Dichromate and Chlorochromate as Efficient Catalysts for Oxidative Halogenation of Aromatic Compounds under Acid-Free Conditions

Article abstract of DOI:10.1080/15533174.2014.989596

Isoquinolinium dichromate and isoquinolinium chlorochromate were found as efficient catalysts to trigger oxidative bromination and iodination of aromatic hydrocarbons with KBr/KI and KHSO₄ under acid-free conditions. Reaction times reduced highly significantly under sonication, followed by corresponding mono bromo derivatives in very good yield with high regioselectivity.

Full text of DOI:10.1080/15533174.2014.989596

Synthesis and Reactivity in Inorganic, Metal-Organic, and
Nano-Metal Chemistry
ISSN: 1553-3174 (Print) 1553-3182 (Online) Journal homepage: http://www.tandfonline.com/loi/lsrt20
Isoquinolinium Dichromate and Chlorochromate
as Efficient Catalysts for Oxidative Halogenation of
Aromatic Compounds Under Acid-Free Conditions
A. Sambashiva Rao, K. C. Rajanna, K. Rajendar Reddy & Subhash Kulkarni
To cite this article: A. Sambashiva Rao, K. C. Rajanna, K. Rajendar Reddy & Subhash
Kulkarni (2016) Isoquinolinium Dichromate and Chlorochromate as Efficient Catalysts for
Oxidative Halogenation of Aromatic Compounds Under Acid-Free Conditions, Synthesis
and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry, 46:6, 832-837, DOI:
10.1080/15533174.2014.989596
To link to this article: http://dx.doi.org/10.1080/15533174.2014.989596
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Synthesis and Reactivity in Inorganic, Metal-Organic, and Nano-Metal Chemistry (2016) 46, 832–837
Copyright© Taylor and Francis Group, LLC
ISSN: 1553-3174 print / 1553-3182 online
DOI: 10.1080/15533174.2014.989596
Isoquinolinium Dichromate and Chlorochromate as Efficient
Catalysts for Oxidative Halogenation of Aromatic
Compounds Under Acid-Free Conditions
A. SAMBASHIVA RAO, K. C. RAJANNA, K. RAJENDAR REDDY, and SUBHASH KULKARNI
Department of Chemistry, Osmania University, Hyderabad, India
Received 17 January 2014; accepted 4 November 2014
Isoquinolinium dichromate and isoquinolinium chlorochromate were found as efficient catalysts to trigger oxidative bromination
and iodination of aromatic hydrocarbons with KBr/KI and KHSO4 under acid-free conditions. Reaction times reduced highly
significantly under sonication, followed by corresponding mono bromo derivatives in very good yield with high regioselectivity.
Keywords: isoquinolinium chlorochromate, isoquinolinium dichromate, KBr, KI, rate enhancements, sonication, acid-free conditions
Introduction
molecular halogen (bromine/iodine) several methods have
been tried in the past several years. Oxyhalogenation proto-
Halogenation of aromatic compounds is an area of evergreen cols were among such efforts[11,12] through which smooth
interest to chemists among electrophilic aromatic substitution halogenation could be achieved. Use of onium halo chro-
(EAS) reactions because organic halides can be converted mates and dichromates was among the few most effective oxi-
efficiently into other functional groups by simple chemical dizing and oxyhalogenation reagents.[13] This could be
transformations.[1–3] Over the years, a large number of halo- probably due to the mildness, stability, selectivity, ease of
genated aromatic compounds are employed as important handling, simple work-up, and regeneration of the reagent
building blocks for drugs and bioactive molecules synthe- used in the work. On the other hand, during the past few dec-
sis.[4–8] Several laboratories still use classical halogenation ades, enormous interest has been paid for the development of
protocols. For instance, in the bromination method, molecu- environmentally safe and economically viable methods in
lar bromine or a brominating mixture (mixture of KBr and organic synthesis in the lines of Green Chemistry.[14] One
KBrO3) and mineral acid are essential components for the such effort is the drive for the development of ultrasonically
generation of bromonium ion. However, in iodination reac- assisted or sonicated reactions using ultrasound wave to trig-
tions activation of molecular iodine is by protons, metal ions, ger/accelerate the progress of reactions. Earlier reviews and
or a suitable solvent for the generation of active iodonium publications[15–21] in this field prove the importance of ultra-
species or to oxidize the released iodide to iodine. Generally a sonically assisted organic synthesis and also highlight that
stoichiometric amount of iodine is employed in these strate- this technique is not only simple; but also satisfies both eco-
gies to trigger iodination.[9,10] In these traditional procedures, nomical and environmental demands. Over the past one
after completion of the reaction, a large amount of acid waste decade our research group is also actively working on exploit-
is drained through the outlets of laboratories and industries. ing the use of eco-friendly materials such as metal ions, sur-
This acid waste became root cause for environmental pollu- factants, and nonconventional energy sources (e.g.,
tion. Besides, molecular bromine is hazardous, toxic, and microwave and ultrasound) to assist various organic transfor-
corrosive, and also pollutes the environment. Another disad- mations such as bromination, nitration, and Vilsmeier-Haack
vantage of classical bromination of aromatic systems arises reactions.[22,23] Present investigation is aimed at exploring the
from the wasteful use of the employed bromine as one half possibility of Isoquinolinium chlorochromate (IQCC) and
ends up as hydrogen bromide. In large-scale operations this is isoquinolinium dichromate (IQDC) as catalysts[24,25] to
an economical problem. In oxyhalogenation, hydrogen achieve oxidative bromination/iodination of certain aro-
halide (HX), generated in situ could be used as a halogen matic compounds with various functional groups phenols,
source. In order to prevent acid-waste and direct use of anilines and acetanilides under acid free conditions.
Address correspondence to K. C. Rajanna, Department of
Chemistry, Osmania University, Hyderabad-500007 India.
E-mail: kcrajannaou@yahoo.com

Halogenation Under Acid-Free Conditions
833
General Procedure for Conventional Halogenation Reactions
Experimental
A centimolar (0.01mol) organic substrate (phenols, anilines,
or acetanilides), about 0.01 mol of potassium halide (KBr or
KI), 0.001 mol hypervalent Cr (VI) reagent (IQCC or
IQDC), and solvent (DCE or ACN) were taken in a previ-
ously cleaned round-bottom flask. About 50 mg of KHSO4 is
also added to the reaction flask. The reaction mixture is
refluxed for about 4–5 h at 50–60ꢀC. Progress of the reaction
was monitored by TLC technique. After completion, the
reaction mixture is treated with 5% sodium thiosulfate solu-
tion followed by the addition of ether. The aqueous layer was
separated, dried, and evaporated under vacuum, and purified
with column chromatography using chloroform:n-hexane
(9:1) as eluent to get pure product.
Materials
All chemicals used were synthesis-grade reagents and pro-
cured from Merck, SD Fine, or Avra Chemicals.
Isoquinolinium dichromate. Isoquinoline (30 mL, 0.25 mol)
is added in small portions to the aqueous solution of chro-
mium trioxide (30.0 g or 0.30 mol 30 mL water) in a beaker
at chilled temperature in an ice bath. The reaction mixture
was stirred for about 30 min. The resultant solution was
diluted with 100 mL of acetone and cooled again to –10ꢀC.
The orange crystalline IQDC [(C9H7NHC)2 Cr2O72–] formed
in the beaker is filtered, washed with acetone, recrystallized
from hot water and dried in vacuum for about 2 h. The melt-
ing point of the compound (169–170ꢀC) is verified with litera-
ture reports.[24]
General Procedure for Ultrasonically Assisted Halogenation
Reactions
Isoquinolinium chlorochromate. The method of preparation
of IQCC is mostly similar to IQDC. Isoquinoline (30 ml, The general method for ultrasonically assisted bromination
0.25mol) is added in small portions to the aqueous solution reaction is almost similar to conventional reaction as men-
of chromium trioxide (30.0 g or 0.30 mol 30 mL water) and tioned above. A centimolar (0.01 mol) organic substrate (phe-
few mL of 6M HCl in a beaker in an ice bath under constant nols, anilines, or acetanilides), 0.001 mol potassium halide
stirred conditions for about 30 min. The resultant solution (KBr), about 50 mg of dilute KHSO4, and hypervalent Cr
was diluted with 100 mL of acetone and cooled again to (VI) reagent (IQCC or IQDC) were suspended in about
–10ꢀC. Dark brown crystalline isoquinolinium chlorochro- 30 mL solvent (DCE or ACN) in a previously cleaned round-
mate (IQCC) formed in the beaker is filtered, washed with bottom (R.B) flask placed in a sonicator. The reaction mix-
acetone, recrystallized from hot water, and dried in vacuum ture is sonicated at room temperature about 30–40 min. Prog-
for about 2 h. Observed melting point of the compound ress of the reaction was monitored by TLC technique. Work-
(169–170ꢀC) is by and large in the range of previous literature up procedure after completion of the reaction mixture is simi-
reports.[25]
lar to the one described previously.
Table 1. Oxidative bromination of aromatic hydrocarbons
Conventional yield (%)
Sonication yield (%)
S. N
Substrate
Product
4-bromo phenol
A
B
A
B
1
2
3
4
5
6
7
8
Phenol
65
60
69
69
68
59
65
66
69
65
65
58
64
69
61
69
59
64
66
62
67
66
61
62
69
68
67
70
68
62
64
70
64
68
66
70
68
63
64
68
66
69
69
66
66
71
69
56
66
68
61
68
52
69
69
67
62
62
68
62
62
63
66
72
72
65
67
72
69
65
62
72
o-cresol
p-cresol
m-cresol
4-chloro phenol
2-chloro phenol
4-bromo phenol
1,4 dihydroxy benzene
1-Naphthol
benzaldehyde
1-(3-OH phenyl)ethanone
4-NO2 phenol
2-OH benzaldehyde
4-OH benzaldehyde
Toluene
2-OH-benzoic acid
2-OH-aniline
4-bromo-2-methylphenol
2-bromo-4-methylphenol
4-bromo-3-methylphenol
4-chloro-2-bromo phenol
2-chloro-4-bromo phenol
4-bromo-2-bromo phenol
2-bromo benzene-1,4-diol
2-bromo-1-naphthol
9
10
11
12
13
14
15
16
17
18
3-bromobenz-aldehyde
1-(3-OH-4-bromo phenyl)ethanone
4-NO2-2-bromo phenol
5-bromo-2-OH-benz-aldehyde
3-bromo-2-OH-benz-aldehyde
2-bromo-toluene
3-bromo-6-OH-benzoic acid
3-bromo-4-OH-aniline
3-bromo-4-Cl-acetophenone
4-Cl-acetophenone
Reaction time, conventional: 4–5 hr; sonication: 30–40 min; (A) KBr/ IQCC; (B) KBr/ IQDC.

834
Rao et al.
Table 2. Oxidative iodination of aromatic hydrocarbons
Conventional yield (%)
Sonication yield (%)
S. N
Substrate
Product
4-Iodo phenol
A
B
A
B
1
2
3
4
5
6
7
8
Phenol
64
62
69
70
65
69
67
70
69
68
65
69
67
68
69
69
55
69
66
68
66
68
69
65
65
69
68
70
68
62
64
70
67
68
59
68
66
69
66
66
66
66
67
69
68
68
66
69
65
65
66
69
55
66
69
60
62
60
68
70
67
70
67
69
70
65
70
66
69
66
60
69
o-Cresol
p-Cresol
m-Cresol
4-Chloro phenol
2-Chloro phenol
4-Bromo phenol
1,4 dihydroxy benzene
1-Naphthol
Benzaldehyde
1-(3-OH phenyl)ethanone
4-NO2 phenol
2-OH benzaldehyde
4-OH benzaldehyde
Toluene
2-OH-benzoic acid
2-OH-aniline
4-Iodo-2-methylphenol
2-Iodo-4-methylphenol
4-Iodo-3-methylphenol
4-Chloro-2-iodo phenol
2-Chloro-4-iodo phenol
4-Bromo-2-iodo phenol
2-Iodo benzene-1,4-diol
2-Iodo-1-naphthol
3-Iodobenz-aldehyde
1-(3-OH-4-Iodo phenyl)ethanone
4-NO2-2-iodo phenol
5-Iodo-2-OH-benzaldehyde
3-Iodo-2-OH-benzaldehyde
2-Iodo-toluene
3-Iodo-6-OH- benzoic acid
3-Iodo-4-OH-aniline
9
10
11
12
13
14
15
16
17
18
4-Cl-acetophenone
3-Iodo-4-Cl-acetophenone
Reaction time, conventional: 4–5 hr; sonication: 30–40 min; (A) KI/ IQCC; (B) KI / IQDC.
1
Each reaction is repeated at least half a dozen times and 7.2-Bromo-4-methylphenol: H NMR d 2.30 (s, 3H), 5.30 (s,
the reaction times are reproducible with an accuracy of §
5 min. The yields of the products have been compiled in
Tables 1 and 2.
1H, -OH), 6.79 (d, 1H, Ar-H), 7.01 (d, 1H, Ar-H), 7.25 (d,
1H, Ar-H); m/z D 187
1
8.4-Bromoaniline: H NMR d 3.70 (brs, 2H, -NH2), 6.54 (d,
2H, Ar-H), 7.24 (d, 2H, Ar-H); m/z D 172
1
9.2-Bromo-4-chloro phenol: H NMR d7.43 (d, 1H, Ar-H),
7.16 (dd, 1H, Ar-H), 6.94 (d, 1H, Ar-H), 5.49 (s, 1H,
Spectral Data of Certain Compounds
-OH); m/z D 207
1
1
10.1-Bromo 2-napthol: H NMR d5.10 (s, 1H, -OH), 6.6–8
1.4-Bromophenol: H NMR d 5.3 (s, 1H, -OH), 6.72(d, 2H,
(m, 6H, Ar-H); m/z D 223
Ar-H), 7.33 (d, 2H, Ar-H); m/z D 173
11.4-Iodo phenol : 1H NMR d D 7.48 (d, J D 7.98 Hz, Ar, 2H),
6.42 (d, J D 7.98 Hz,Ar,2H), 5.45 (br, s, -OH, 1H). (m/z D
220)
2.2-Bromo-4-nitrophenol: 1H NMR d6.16 (s, 1H, -OH), 7.8 (d,
1H, Ar-H), 8.07 (dd, 1H, Ar-H), 8.42 (d, 1H, Ar-H); m/z
D 218
1
3.2-Bromo-4-aminophenol: 1H NMR d 5.7 (s, 1H, -OH), 4.13
12.2-Iodo-1-naphthol: H NMR d 7.93 (d, 1H, 8-H), 7.69 (d,
)
2H, 4-H and 5-H), 7.46 (t, 1H, 7-H), 7.26 (t, 1H, 6-H),
7.15 (d, 1H, 3-H) 5.24 (s, 1H, OH); m/z:270
(s, 2H, -NH2 , 6.42–6.53 (m, 3H, Ar-H); m/z D 188
1
4.4-Bromoanisole: H NMR d 3.78 (s, 3H, -OCH3), 7.33 (d,
13.4-Iodo-anisole: 1H NMR d3.79 (s, 3H, -OMe), 6.66 (d, 2H,
Ar-H), 7.53 (d, 2H, Ar-H); m/z D 234
2H, Ar-H), 6.79 (d, 2H, Ar-H); m/z D 187
1
5.2-Bromo-4-methylanisole: H NMR d 2.27 (s, 3H, CH3),
14.4-Iodo toluene: 1H NMR d 2.3 (s, 3H, -Me), 6.9 (d, 2H, Ar-
H), 7.55 (d, 2H, Ar-H); m/z D 218
3.83 (s, 3H, -OCH3), 6.79 (d, 1H, Ar-H), 7.02 (dd, 1H, Ar-
H), 7.34 (d, 1H, Ar-H). m/z D 201
15.4-Iodo-3-methylphenol: 1H NMR d D 7.46 (d, J D 8.08 Hz,
Ar, 1H), 6.7 (s, Ar,1H), 6.38 (dd, J D 2.9,2.9 Hz, Ar, 1H),
2.35 (s, -CH3, 3H) 5.45 (br, s, -OH, 1H).). (m/z D 234
6.5-Bromo-2-hydroxy benzaldehyde: 1H NMR d 10.80 (s, 1H,
-OH), 9.83 (s, 1H, -CHO), 7.66 (d, 1H, Ar-H), 7.51 (dd,
1H, Ar-H), 6.64 (d, 1H, Ar-H); m/z D 201
Sch. 1. Where Y D OH, NH2 and NHCOCH3; X = electron donating or withdrawing group.

Halogenation Under Acid-Free Conditions
835
Sch. 2. IQDC triggered halogenation mechanism.
16.4-Iodo-2-nitrophenol: 1H NMR d D 5.42 (s, -OH, 1H), 8.40 substrates under the present reaction conditions as shown in
(s, Ar, 1H), 7.8 (dd, J D 2.2, 2.4 Hz Ar,1H), 6.74 (d, J D Scheme 1.
8.8 Hz, Ar, 1H). m/z D 265
The reactions afforded fairly good product yields. The
1
1
17.2-Chloro-4-iodophenol: Isolated yield D 87%; H NMR d products were characterized by IR, H-NMR, mass spectra,
(300 MHz, CDCl3): d D 7.6 (d, J D 1.47Hz,Ar,1H), 7.45 and physical data with authentic samples and found to be sat-
(dd, J D 2.2, 1.5 Hz Ar,1H), 6.78 (d, J D 8.08 Hz, Ar,1H), isfactory. The yields of major products are compiled in
5.5 (s, -OH, 1H).
Tables 1 and 2. It is observed that the halogenation of aro-
1
18.2-Iodo-4-nitrophenol: Isolated yield D 64%; H NMR d matic compounds is moderately slow under conventional
(300 MHz, CDCl3): d D 8.61 (d, J D 1.8Hz Ar, 1H), 8.22 conditions with three to four hours of reaction time for com-
(dd,J D 2.26, 3.12 Hz Ar, 1H), 7.11 (d, J D 9.06 Hz pletion. But under sonication the reaction times are drasti-
Ar,1H).
cally reduced to about 30–40 min followed by marginal yield
enhancements.
Because the reactions are conducted in presence of aque-
ous KHSO4 medium, it is more likely that the bisulfate ion
dissociates to give (HC), which in turn facilitates the forma-
tion of active [(IQH)C(HCrO4)–] (IQ bound chromic acid)
species due the protonation of IQDC.[26] Active species thus
formed may further react with halide ion to afford
[(IQH)C(H2CrO3X)–] species, since the reactions are con-
ducted in either KBr or KI. Finally, aromatic substrates
undergo mono halogenation through the formation of cyclic
intermediate with aromatic compound as shown in Scheme 2.
A similar type of mechanism is more likely in IQCC trig-
gered reactions through the formation of protonated IQCC
Results and Discussion
The halogenation reactions of aromatic compounds were
conducted using IQDC/KBr, IQCC/KBr, IQDC/KI, and
IQCC/KI combinations in aqueous KHSO4 under acid-free
conditions. The chemical components of the reaction are sus-
pended in a reaction vessel (R.B flask) and continuously
stirred under acid-free conditions, until the reaction is com-
pleted. To check the generality of the reaction an array of
substituted phenols, anilines, and acetanilides are used as

836
Rao et al.
Sch. 3. IQCC triggered halogenation mechanism.
([(IQH)C(HOCrO2Cl)–]) due the protonation of IQCC
([(IQH)C(CrO3Cl)–]), supplemented by the dissociation of
bisulfate ion in the dissociation step, as shown in Scheme 3.
It is also of interest that there is not much difference in the
rates of bromination and iodination as could be seen from
the data presented in Tables 1 and 2. The observed rate accel-
erations in ultrasonically assisted reactions could be
explained due to cavitation, a physical process that creates,
enlarges, and implodes gaseous and vaporous cavities in an
ultrasonically assisted (irradiated) liquid. Cavitation induces
very high local temperatures in the reaction mixture and
enhances mass transfer.[15–20]
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