Chinese Chemical Letters
Original article
Ammonium persulphate promoted synthesis of polyethylene glycol
entrapped potassium tribromide and its application in acylation and
bromination of some selective organic compounds
*
Rupa Rani Dey, Siddhartha Sankar Dhar
Department of Chemistry, National Institute of Technology, Silchar, Assam 788010, India
A R T I C L E I N F O
A B S T R A C T
Article history:
In this study, a new method of synthesis of polyethylene glycol supported potassium tribromide (PEG
KBr3) and its application in acylation and bromination reactions are reported. Ammonium persulphate
oxidizes KBr to the corresponding tribromide which is entrapped by polyethylene glycol leading to stable
PEG KBr3. The reagent is proved to be highly efficient for the acylation of variety of alcohols and
bromination of activated aromatic substrates. The method is a mild, one pot reaction and involves no use
of toxic reagents.
Received 24 April 2013
Received in revised form 16 May 2013
Accepted 22 May 2013
Available online 1 July 2013
Keywords:
ß 2013 Siddhartha Sankar Dhar. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All
rights reserved.
Potassium bromide
Polyethylene glycol (PEG)
Ammonium per sulphate
Acylation
Bromination
1. Introduction
of BrÀ to Br3À. It should be noted here that potassium tribromide
(KBr3)isanefficient, cheapandenvironmentallybenignreagent. The
The upsurge in green chemistry has inspired the fraternity
of researchers to design and develop newer environmental
friendly methods of synthesis of new or existing catalysts and/
or reagents [1,2]. In this context, it may be emphasized that the
interest in the environmental friendly synthesis of organic [3,4]
and inorganic tribromides [5,6] has increased due to their
versatile utility in organic transformations. In spite of the
availability of large numbers of methodologies, most of them
are not favorable due to the use of detrimental reagents (like
liquid Br2) for the synthesis of tribromides. However, it is better to
use environmental friendly oxidizing agents for the conversion of
bromide to tribromide to achieve the synthesis of QTBs. Examples
of such oxidants include oxone [7], persulphate [8], KMnO4 [9],
and CAN [10]. Over the last few years, our group has been involved
in the development of synthetic protocols for economical, novel
and environmentally safe reagents, such as organic ammonium
tribromides (OATBs) [11,12] and catalysts [13] for important
organic reactions. We have already reported the ammonium
persulphate mediated synthesis of OATBs [8]. Taking cue from
this, the present paper reports a new method of synthesis of PEG
KBr3 using ammonium persulphate as oxidant for the conversion
application of this reagent in organic transformation reactions has
not been very successful because KBr3 is unstable at room
temperature. It has been observed that polyethylene glycol (PEG)
acts as a good host and captures the K+ cation and thus, provides
maximum stability to the reagent. Similar host-guest chemistry can
be observed in the case of {[K 18-Crown-6]Br3} [14] which on
recrystallization form red crystals. {[K 18-Crown-6]Br3} was also
used in the bromination of activated aromatic compounds. The
advantage of [{K PEG}+Br3À] over {[K 18-Crown-6]Br3} is that PEG is
less expensive and the conversion of bromide to tribromide is not
achieved by the addition of rather harmful liquid bromine.
Moreover, the application of PEG.KBr3 has not been well explored
in organic transformations other than bromination reactions. In this
article we wish to report a new environmentally benign method of
synthesisof[{KPEG}+Br3À]anditsapplicationasreagentinacylation
and bromination reactions.
2. Experimental
All the commercial chemicals are of analytical grade and
used without further purification. The completion of the
reaction was monitored by TLC. The synthesized tribromide
was characterized with UV–vis and FT-IR spectroscopy. X-ray
diffraction (XRD) analysis was also performed with
* Corresponding author.
1001-8417/$ – see front matter ß 2013 Siddhartha Sankar Dhar. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.