Synthesis and application of poly(diallyldimethylammonium tribromide) as a novel polymeric brominating agent

Article abstract of DOI:10.1002/cjoc.201090367

In this study, the synthesis and applications of a new supported tribromide reagent based on poly(diallyldimethylammonium chloride) is reported. This supported tribromide is used in α-bromoacetalization of ketones, bromination of alkenes and regioselective bromination of activated aromatic compounds. This method is mild and no Br₂ and HBr were used. Other advantages of this reagent are stability, high efficiency, simple filtera- bility and reusability. In this study, the synthesis and applications of a new supported tribromide reagent based on poly(diallyldimethylammonium chloride) is reported. This supported tribromide is used in α-bromoacetalization of ketones, bromination of alkenes and regioselective bromination of activated aromatic compounds. This method is mild and no Br₂ and HBr were used. Other advantages of this reagent are stability, high efficiency, simple filterability and reusability. Copyright

Full text of DOI:10.1002/cjoc.201090367

FULL PAPER
Synthesis and Application of Poly(diallyldimethylammonium
tribromide) as a Novel Polymeric Brominating Agent
Hossein, Mahdavi*
Zahra, Kachoei
School of Chemistry, University College of Science, University of Tehran, Tehran, Iran
In this study, the synthesis and applications of
a new supported tribromide reagent based on
poly(diallyldimethylammonium chloride) is reported. This supported tribromide is used in α-bromoacetalization of
ketones, bromination of alkenes and regioselective bromination of activated aromatic compounds. This method is
mild and no Br2 and HBr were used. Other advantages of this reagent are stability, high efficiency, simple filtera-
bility and reusability.
Keywords poly(diallyldimethylammonium tribromide), brominating agent, α-bromoacetalization
Introduction
ganic products during work up. Recovery and recycling
of expensive organic ammonium cations is also poor
after the reaction.
α-Bromoacetals are useful synthetic precursors in
organic synthesis such as in preparation of
α,β-unsaturated ketones,13 and enol-ethers.14 One of the
effective methods for preparation of α-bromoacetals is
one-pot α-bromoacetalization of carbonyl compound
with tribromide reagents.15
Here, to overcome the problems of high cost, recov-
ery and recycling of the spent tribromide reagents, we
wish to report the synthesis and application of the
poly(diallyldimethylammonium tribromide) (PDAD-
MATB), as a novel polymeric brominating agent.
Since the first report on the solid-phase peptide syn-
thesis by Merrifield,1 the utilization of insoluble poly-
mers as supports in the organic synthesis has received
considerable attention.2
The practical significance of poly(diallyldimethyl-
ammonium chloride) has increased rapidly since thirty
years ago. This development is caused by a great num-
ber of its industrial applications such as processing aids,
flocculants, dewatering agents and emulsifiers in pro-
cesses of water purifications, paper making, mining and
petrol industry, as well as the application as additives.3
Recently, this polymer was introduced as a new and
efficient phase transfer catalyst.4,5
Generally, bromination is carried out by elemental
bromine, but organic ammonium tribromides (OATB)
are preferable owing to hazards associated with bromine.
The other advantages of organic ammonium tribromides
are involving their solid form, high stability, ease of
storage, ease of transport, maintenance of desired
stoichiometry and mild reaction condition.6 Hitherto, in
the literature several tribromides species have been re-
Experimental
Materials and techniques
All of the reagents and solvents were purchased
from Fluka and Merck and used without further purifi-
cations. TGA was recorded on a TA, TGA-Q50.
UV-Vis analysis was recorded on Perkin Elmer Lambda
850, UV-Vis spectrometer. IR-spectra were run on a
Bruker-Equiuox 55, FTIR Spectrophotometer. NMR
spectra were recorded on a Bruker Avance DPX instru-
ment (250 MHZ).
All products were characterized by comparison of
their IR and NMR spectra and physical data with those
of the authentic samples. All yields refer to the isolated
products.
ported
i.e,
tetramethylammonium
tribromide
(TMATB),7 phenyltrimethylammonium tribromide
(PTATB),8
cetyltrimethylammonium
tetrabutylammonium
tribromide
tribromide
(CetTMATB),9
(TBATB),10 1,8-diazobicyclo[5,4,0]-tetrabutylammo-
nium tribromide (DBUHBr3)11 and pyridinehydrobro-
mide perbromide (PyHBr3).12 However, their prepara-
tions involve elemental bromine and in some cases HBr
as well. This again causes an environmental concern. In
addition, the problems associated with these reagents
are the use of expensive organic ammonium cations and
in some cases a substantial amount of the organic am-
monium tribromides get extracted along with the or-
Preparation of poly(diallyldimethylammonium tri-
bromide)
An aqueous solution of diallyldimethylammonium
chloride (2 g, 60 wt%) was purged with nitrogen for 1 h
prior to polymerization. The mixture was placed in an
*
E-mail: hmahdavi@khayam.ut.ac.ir; Tel./Fax: 0098-021-66495291
Received January 24, 2010; revised May 14, 2010; accepted June 3, 2010.
Chin. J. Chem. 2010, 28, 2221— 2225
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Hosssein & Zahra
FULL PAPER
oil bath (65 ℃). Then aqueous solution of ammonium
persulfate (0.2 g, 4 wt%) was added in 1.5 h to the
monomer solution with vigorous stirring. After 24 h, the
mixture was poured in DMSO as non-solvent (40 mL).
The polymer was filtered and the resultant solid
(PDADMAC) (1.85 g) was added to an aqueous solu-
product. The product was characterized by IR and
NMR.
Recycling procedure of the recovered polymers
The recovered polymers (5 g) were added to an
－
1
aqueous solution of KBr (6 mL, 1 mol•L ) and stirred
for 1 h. Then, the mixture was added to DMSO as a
non-solvent (80 mL) and the precipitated polymer was
filtered. The resultant solid (PDADMABr) was again
－
1
tion of KBr (2.25 mL, 1 mol•L ) and stirred for 1 h.
The mixture was added to DMSO as a non-solvent (40
mL). Then the polymer was filtered and the resultant
solid (PDADMABr) was again added to an aqueous
－
1
added to an aqueous solution of KBr (5 mL, 1 mol•L ),
and an aqueous solution of oxone (3 g, 60 wt%) was
added to the mixture over a period of 10 min. The solu-
tion became yellow with concurrent precipitation of
orange poly(diallyldimethylammonium chloride) sup-
ported tribromide (PDADMATB). The product was fil-
tered and washed with water 2 or 3 times and dried in
air or by pressing between the folds of a filter paper.
－
1
solution of KBr (2.25 mL, 1 mol•L ), and an aqueous
solution of oxone (1.23 g, 60 wt%) was added to the
mixture over a period of 10 min. The reaction took
place readily and the solution became yellow with con-
current
precipitation
of
orange
poly(diallyldimethylammonium chloride) supported
tribromide (PDADMATB). The product was filtered
and washed with water 2 or 3 times and dried in air or
by pressing between the folds of a filter paper. The iso-
lated yield was 60%.
Results and discussion
Organic ammonium tribromides are more stable than
the liquid bromine because of their crystalline nature,
and hence their storage, transport and maintenance of
desired stoichiometry are easy. However, general pro-
cedure for preparation of these reagents involves reac-
tion of organic ammonium bromide and molecular bro-
mine. Thus an indirect use of toxic molecular bromine,
recovery and recycling of expensive organic ammonium
cations is very interesting.
α-Bromoacetalization of ketones: PDADMATB (3.6
g, 10 mmol) was added to a stirred solution of the ke-
tone (10 mmol) in dry THF (12 mL) and ethyleneglycol
(12 ml). The reaction mixture was stirred at room tem-
perature for 20 hours and then the mixture poured into a
cold solution of 10% sodium hydrogen carbonate (250
ml) and 5% sodium thiosulfate (25 mL) and extracted
with ether (100 mL×2). The combined organic extract
is washed with water (100 mL×3) and brine (100 mL)
and dried with anhydrous sodium sulfate. The solvent
was removed under reduced pressure to yield the corre-
sponding α-bromoacetal which was further purified by
column chromatography on alumina [V(petroleum
ether)/V(diethyl ether)=20/1], and characterized by IR
and NMR.
Synthesis and characterization of the polymer
Linear poly(diallyldimethylammonium chloride) was
prepared by free radical cyclo-polymerization.3-5 Poly-
(diallyldimethylammonium chloride) was changed to
bromide form via exchange reaction with aqueous solu-
tion of KBr. For preparation of poly(diallyldimethy-
lammonium tribromide) (PDADMATB), the poly(di-
allyldimethylammonium bromide) was again treated
with KBr (2 equiv.) and then followed by oxidation of
bromide to bromine with aqueous solution of oxone (1
equiv.) (Scheme 1, Figure 1).
Aromatic bromination of active aromatics
PDADMATB (3.6 g, 10 mmol) was added to aro-
matic substrate (10 mmol) in a mortar and was grinded
for the desired reaction time, and the progress of the
reaction was monitored by TLC (n-hexane/ethyl acetate:
10/1). After this, the reaction mixture was poured to
ethyl acetate (20 mL) and then filtered. The filtrate was
washed with distilled water (5 ml×5) and the organic
phase was extracted and dried with anhydrous sodium
sulfate and evaporated in vacuum to obtain the pure
p-brominated product. The product was characterized
by IR and NMR spectra.
Scheme 1
Bromination of alkenes
PDADMATB (3.6 g, 10 mmol) and alkene (10
mmol) were grinded for the specified period of time,
and the progress of the reaction was monitored by TLC
[V(petroleum ether)/V(diethyl ether)=20/1]. After com-
pletion of the reaction which was evidenced from the
changing color of the PDADMATB to white, the reac-
tion mixture was diluted with diethyl ether (10 mL) and
then was filtered. The filtrate was distilled to give pure
The capacity of the polymeric reagent (PDAD-
MATB) was determined idometrically, to be 0.36
mmole per gram of resin. The structure of PDADMATB
was confirmed by UV-spectroscopy and FT-IR tech-
niques. The UV spectrum of PDADMATB shows an
intense absorption band centered at 268 nm which is the
typical λmax for tribromide anion ( Br－ )16(Figure 2).
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Chin. J. Chem. 2010, 28, 2221— 2225

Synthesis and Application of Poly(diallyldimethylammonium tribromide)
Figure 1 Poly(diallyldimethylammonium chloride) supported
tribromide.
Figure 4 TGA thermogram of poly(diallyldimethylammonium
tribromide).
The PDADMATB was insoluble in most organic
solvents and thus facilitating its efficient recovery.
Applications
α-Bromoacetalization of ketones The synthetic
utility of the PDADMATB as a polymeric reagent was
studied at first by examining the transformation of ke-
tones to the corresponding α-bromoacetal derivatives.
PDADMATB gives α-bromoacetals from ketones when
used in the presence of ethylene glycol (Scheme 1).
Scheme 1 α-Bromoacetalization of ketones in the presence of
PDADMATB
Figure 2 UV spectrum of poly(diallyldimethylammonium tri-
bromide).
The IR spectrum of PDADMATB exhibits charac-
teristic ( Br－ ) IR bands at 170 (ν ) and 191 (ν ) cm－
1
1
3
3
(Figure 3).17
In-situ generation of HBr from the reaction of
PDADMATB with ethylene glycol caused further ac-
celeration of reaction. It is reasonable to assume that
PDADMATB can be dissociated by water as it is shown
in the following reaction:
PDADMATB H O→PDADMABr HOBr HBr
＋
＋
＋
2
The effects of solvent and amount of the polymeric
reagent (g) to substrate (mmol) on the rate of reaction
were investigated. The reactions were carried out in
different solvents such as THF, acetonitrile, ethylacetate,
dichloromethane, chloroform, and hexane. THF was
found to be the best solvent for this purpose. The opti-
mum amount (g) of the polymeric reagent to substrate
(mmol) was found to be 0.36∶1.
Figure 3 IR spectrum of poly(diallyldimethylammonium tri-
bromide).
Thermal stability study of the PDADMATB was
performed via thermo-gravimetric analysis (TGA) (Fig-
ure 4). It was also observed that the polymer initiated to
lose Br2 near 70 ℃ and continued to 200 ℃ in an open
cell. Clearly this observation is fully adapted with first
part of TGA curve.
Under these conditions, α-bromoacetalization of
various ketones was performed in excellent yields. The
results were summarized in Table 1.
Moreover, interestingly the PDADMATB was fully
stable for several months (at least 8 months) at room
temperature and in open vessel without any loss of its
activity.
Bromination of alkenes Bromination of alkenes
has previously been achieved by use of tetrabutylam-
monium tribromide in solution.18 This is suggested the
possibility of utilizing PDADMATB as a solid reagent
Chin. J. Chem. 2010, 28, 2221— 2225
© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.cjc.wiley-vch.de
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Hosssein & Zahra
FULL PAPER
Table 1 α-Bromoacetalization of ketones
Ketone
Α-Bromoacetal Yielda/% Timeb/h
useful transformations. In an aromatic electrophilic sub-
stitution reaction para-orientation is favored over or-
tho-orientation due to stereoelectronic effects. Exclusive
regioselective bromination of phenol and anisole has
been achieved with supported reagents,19 in solid-phase
reaction,20 under controlled in situ generation of elec-
trophilic bromonium ion21,10a and by using special re-
agents and conditions.22
Bromination of various electron-rich aromatic com-
pounds was performed with PDADMATB at 25 ℃ to
give monobrominated products with high regioselectiv-
ity. The results are summarized in Table 3.
Entry
1
78
76
68
82
20
20
20
20
2
3
4
Table 3 Bromination of active aromatic compounds
Timeb/
Entry
Substrate
Phenol
Product
Yielda/%
min
10
5
1
2
3
4
5
6
7
8
p-Bromophenol
80
86
92
88
93
92
—
—
Hydroquinone Bromohydroquinone
o-Cresol
m-Cresol
1-Naphthol
Anisole
4-Bromo-2-methylphenol
4-Bromo-3-methylphenol
2-Bromo-1-naphthol
4-Bromo-anisole
—
5
5
5
5
90
20
5
Toluene
—
—
a
b
Isolated yields are reported, Reactions were monitored by
t-Butylbenzene —
TLC.
a Isolated yields. b Reactions were monitored by TLC.
for convenient 1,2-dibromination of alkenes.
Successful bromination of alkenes was performed
using PDADMATB under solvent free condition. The
results are summarized in the Table 2.
Interestingly, p-bromophenol and p-bromoanisole
was obtained as sole product from the reaction of phe-
nol and anisole (Table 3, Entries 1 and 6) respectively,
which is otherwise difficult to achieve with other re-
agents. Also in the case of α-naphtol as expected
2-bromo-α-naphtol was the only product (Entry 5).
However, less activated aromatic compounds such as
toluene or cumene did not give brominated products
under this reaction condition (Table 2, Entries 7—8).
Then superiority of this reagent with respect to other
organic ammonium tribromides is its highly efficient
and regioselective bromination of phenol, anisol,
o-cresol, and m-cresol. Moreover, due to use of the re-
agent in a stoichiometric amount (1 equiv.), no poly-
bromination occurred with PDADMATB.
Table 2 1,2-dibromination of alkenes
Entry
1
Alkene
Product
Yielda/%Timeb/min
92
30
2
3
87
80
20
50
Finally, in all of these applications workup of the
reaction was easy and the polymer removed from the
reaction mixture via simple filtration. Interestingly, as
stated in experimental part the recovered polymers were
recycled and converted to their tribromide form in very
high yield (90%). It was also observed that these recy-
cled PDADMATB after several times recycling (at least
8 times) could be used without any loss in their effi-
ciency.
4
95
10
a Isolated yields. b Reactions were monitored by TLC.
Considering of green chemistry aspects, this solid
phase method is superior as no organic solvent is used
in the reaction. The good yield of di-bromo products
demonstrates that this is a powerful new synthetic
method for the organic synthesis.
Regioselective aromatic bromination Regiose-
lective bromination of phenol and anisole is an impor-
tant protocol in organic synthesis because of their versa-
tile synthetic intermediates for a considerable number of
Conclusion
In conclusion we have demonstrated that
poly(diallyldimethylammonium tribromide) is an useful
novel polymeric brominating reagent. It shows that this
reagent is useful in α-bromoacetalization of ketones,
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© 2010 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Chin. J. Chem. 2010, 28, 2221— 2225

Synthesis and Application of Poly(diallyldimethylammonium tribromide)
bromination of alkenes and regioselective bromination
of activated aromatic compounds.
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and reusability. Due to the filterability and no consume
of bromine, this reagent is more financially suit to be
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Acknowledgment
We are thankful to the Research Council of the Uni-
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