Hexamethonium bis(tribromide) (HMBTB) a recyclable and high bromine containing reagent

Article abstract of DOI:10.1016/j.tetlet.2015.08.063

A recyclable and high bromine containing di-(tribromide) reagent, hexamethonium bis(tribromide) (HMBTB) has been synthesized and utilized for the bromination of various organic substrates. The spent reagent hexamethonium bromide (HMB) can be effectively recycled by regenerating and reusing it without significant loss of activity. The crystalline and stable bis(tribromide) is an effective storehouse of very high percentage of active bromine requiring just half an equivalent of it for complete bromination. Both the Br₃^- moieties in HMBTB are nearly linear with Br-Br-Br angle of 179.55°.

Full text of DOI:10.1016/j.tetlet.2015.08.063

Accepted Manuscript
Hexamethonium bis(tribromide) (HMBTB) a recyclable and high bromine con-
taining reagent
Bappi Paul, Bishal Bhuyan, Debraj D. Purkayastha, Siddhartha S. Dhar, Bhisma
K. Patel
PII:
S0040-4039(15)30017-4
DOI:
http://dx.doi.org/10.1016/j.tetlet.2015.08.063
TETL 46647
Reference:
Tetrahedron Letters
To appear in:
Received Date:
Revised Date:
Accepted Date:
22 July 2015
19 August 2015
22 August 2015
Please cite this article as: Paul, B., Bhuyan, B., Purkayastha, D.D., Dhar, S.S., Patel, B.K., Hexamethonium
bis(tribromide) (HMBTB) a recyclable and high bromine containing reagent, Tetrahedron Letters (2015), doi: http://
dx.doi.org/10.1016/j.tetlet.2015.08.063
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Graphical Abstract
Hexamethonium bis(tribromide) (HMBTB) a
recyclable and high bromine containing
reagent
Leave this area blank for abstract info.
Bappi Paul,a Bishal Bhuyan,a Debraj D Purkayastha,a Siddhartha S Dhar*a and Bhisma K Patel*b
UHP
KBr
-
+ Br-
Br-
-
Br3
N+
N+
+ Br3
N
N
RT/Solvent-Free
Organics
Bromoorganics

1
Tetrahedron Letters
Hexamethonium bis(tribromide) (HMBTB) a recyclable and high bromine
containing reagent
Bappi Paul,a Bishal Bhuyan,a Debraj D Purkayastha,a Siddhartha S Dhara and Bhisma K Patelb
a Department of Chemistry, National Institute of Technology, Silchar, Silchar – 788010, India
b Department of Chemistry, Indian Institute of Technology Guwahati, Guwahati – 781039, India
ARTICLE INFO
ABSTRACT
Article history:
Received
A
recyclable and high bromine containing di-(tribromide) reagent, hexamethonium
Received in revised form
Accepted
Available online
bis(tribromide) (HMBTB) has been synthesized and utilized for the bromination of various
organic substrates. The spent reagent hexamethonium bromide (HMB) can be effectively
recycled by regenerating and reusing it without significant loss of activity. The crystalline and
stable bis(tribromide) is an effective storehouse of very high percentage of active bromine
-
Keywords:
requiring just half an equivalent of it for complete bromination. Both the Br3 moieties in
Di-tribromide
Active bromine
Recyclable
Regioselective
Green
HMBTB are nearly linear with Br-Br-Br angle of 179.55.
2015 Elsevier Ltd. All rights reserved.
———
 Corresponding author. Tel.: +91-361-2582307; fax: +91-361-2690763; e-mail: patel@iitg.ernet.in
 Corresponding author. Tel.: +91-3842-242915; fax: +91-3842-224797; e-mail: ssd_iitg@hotmail.com

2
Tetrahedron
1. Introduction
after washing thoroughly with water (2 x 10 mL). The product so
obtained was recrystallized from acetonitrile. The crystallized
product has shelf life up to six months. The role of UHP here was
Bromination is a an important synthetic process as bromo-
-
to oxidize Br- to Br3 in the presence of H2SO4. The UHP a non-
organics are often used as intermediates in the synthesis of
pharmaceuticals, agrochemicals and other speciality chemicals.1
Numerous industrially important products such as pesticides,
insecticides, herbicides and fire retardants contain bromo-
functionality.2 These bromo-organics are precursors to CC bond
CX (X= heteroatom) bond forming processes.3,4 The use of
liquid bromine in industry as well as in academia is still a
common practice, in spite of its associated hazards. Furthermore,
bromination of an aromatic substrate using bromine involving an
electrophilic substitution results in the formation of HBr as by-
product thereby reduces the atom efficiency to 50%. However,
besides liquid bromine, several other safer and user-friendly
brominating agents such as tribromide,5-11 Importantly, a few
ditribromides and ionic liquid tribromides12-16 have also made a
prominent mark as brominating agents. Most of the tribromides
mentioned above although are safe, user-
toxic solid with relatively high proportion of hydrogen peroxide
in urea adduct (36.2%). Its safe handling, smooth decomposition
into environmentally friendly substances such water and urea,
ensures its place among the top ecofriendly oxidants. The
-
hydrogen peroxide present in UHP, safely oxidizes Br- to Br3
without the need of any transition metal activator, making it an
environmentally safe metal-free process. Interestingly, UHP sets
-
free H2O2 for oxidation of Br- to Br3 leaving behind the urea. The
left behind urea upon treatment with 30% hydrogen peroxide at
60C for a few minutes regenerates urea hydrogen peroxide.
Thus choice of UHP for the preparation tribromides is favourable
from green chemistry perspective. This novel ditribromide was
1
characterized by single crystal XRD technique, H NMR, FTIR
and UV-visible spectroscopy and CHN analysis. The crystal
structure reveals that both the Br- ions of hexamethonium
-
bromide (HMB) are converted to Br3 in HMBTB, thereby
friendly, stable, easy to store and transport but preparation of
some of these reagents invariably involve direct or indirect use of
toxic liquid bromine.
confirming the formation of ditribromide (Figure 1a and 1b). The
Br3- moiety is linear with Br-Br-Br bond angle of 179.55 (Figure
1a). Other analytical data are also evidential in support of the
formation Br3- (See Supporting information).
Ditribromides are considered to be superior to quaternary
ammonium tribromides (QATBs) mainly due to higher content of
active of bromine and less phase-transfer property. Moreover,
most of the QATBs contain expensive organic ammonium cation
and use only 1/3 of its total bromine for an aromatic electrophilic
substitution type reaction and 2/3 for addition of bromine across
CC multiple bonds. Some of QATBs posses phase transfer
properties due to which organic ammonium cation become
soluble in the solvent used for the extraction of brominated
products, causing considerable difficulty in work-up and
purification process. Therefore such QATBs are not preferable as
brominating agent particularly in large scale reaction. There are
some issues regarding stability and selectivity of a few organic
ammonium tribromides such as pyridinium hydrotribromide,17 N-
methylpyrollidi-2-one hydrotribromide,18 in spite of their
versatility as reagent for other reactions. Moreover, recovery and
recyclability of QATBs have not been explored adequately. We
have already reported12 that ditribromides have the features that
can overcome most of these aforementioned drawbacks of
QATBs.
Scheme 1. Formation of HMBTB from hexamethonium bromide
(a)
(b)
Development of efficient and environmentally benign processes
with simple work-up coupled with high purity and high yield of
the products is currently receiving a lot of interest. In this context,
ditribromides with high percentage of active bromine, play an
important role for obtaining bromo-derivatives in hazard-free,
waste-free and solvent-free manner. As mentioned previously
ditribromides with high bromine content and recyclability, are
gaining popularity over monotribromides, particularly from green
chemistry perspective. In continuation our interest on synthesis
and application of organic ammonium ditribromides,12,14,19 we
wish to report herein, an environmentally favourable synthesis of a
novel ditribromide and its use as recyclable and efficient
brominating reagent.
Figure 1. (a) ORTEP view of HMBTB (b) crystal packing of
HMBTB showing formation of di(tribromide)
Inspired by our earlier success with ditribromides as
brominating reagent,12,14,19 we have endeavoured into synthesis of
this novel ditribromide, hexamethonium bis(tribromide), which
has nearly same bromine content but better efficiency and
stability. This novel reagent has variable solubility in different
polar protic and aprotic solvents but insoluble in non-polar
aprotic solvent such as dichloromethane, toluene, petroleum ether
etc. Importantly, the precursor of the reagent i.e. HMB
(hexamethonium bromide) is highly soluble in water. This
property of the reagent may help in clean and easy separation of
brominated products as well as efficient recovery of the HMB,
which may be advantageous over other ammonium tribromides.
To explore the versatility of this reagent, large variety of organic
substrates were chosen for bromination (Table 1 and 2).
Customarily bromination of an organic substrate by tribromides
is carried out with 1:1 molar ratio of substrate to reagent. We
2. Results and discussion
The procedure for synthesis of HMBTB is rather simple.
Hexamethonium bromide (HMB) (1 equiv), potassium bromide
(4 equiv) and urea-hydrogen peroxide (UHP) (4 equiv) along
with 4N H2SO4 (4 equiv) were mixed in a beaker. After
continuous stirring for 5 min, an orange-yellow product was
obtained indicating the formation of a ditribromide (Scheme 1).
The product was separated by filtration from other components

3
have chosen acetanilide (1) as the model substrate to test
bromination efficiency of HMBTB with a substrate to reagent
ration of 1:0.5 in acetonitrile. The reaction appeared to be
complete within 30 min as observed from TLC with nearly
quantitative precipitation of solid spent reagent HMB. While the
HMB was filtered and recovered for further use, the CH3CN
solution was concentrated to obtain p-bromoacetanilide in 95%
yield. Thus bromination of p-acetanilide (1a) using HMBTB
shows that the reagent is worthy of not only a very good bromine
carrier but also able to transfer it selectively and efficiently to the
organic substrate (Table 1). This procedure was successfully
applied to number of other substrates. Even though acetonitrile is
an ecofriendly solvent but our objective was to explore
bromination in solvent-free condition. In the solvent-free version,
acetanilide was treated with HMBTB in a molar ratio of 1:0.5 of
substrate to reagent in a mortar and pestle and the mixture was
agitated form time to time for a period of 20 min. The progress of
the reaction as indicated by GC showed more than 99%
conversion to p-bromoacetanilide after 20 min. The mixture was
treated with water (5 mL) and allowed to pass through a filter
paper. The residue containing p-bromoacetanilide was further
washed with water (2 x 5 mL) to afford the product in 95% yield.
Bromination of phenol (2) and aniline (3) is important as their
bromo derivatives are known to be intermediates to a variety of
synthetic transformations. Thus realizing the importance of
bromo derivatives of these substrates, we extended the solvent-
free methodology of bromination by HMBTB for these substrates
as well. As expected, p-bromophenol (2a) and p-bromoaniline
(3a) were obtained regioselectively in very high yield (Table 1).
The reagent transfers bromine only in contact with the substrate
and with controlled stoichiometry, formation of polybrominated
products can be completely arrested. The versatility of the
reagent can also be clearly brought out with exclusive
regioselective bromination of majority of substrates (Table 1). It
can be seen for substrates 4-6 that regioselectivity of this reagent
is emphatic, when both o, p- directing groups are present in the
aromatic ring. Substrates containing various combinations of
functional groups were exclusively and selectively
monobrominated (7-8) (Table 1). Phenolic substrate containing
benzoyl group (9) withstood the described reaction conditions to
give corresponding o-bromo product (9a). The fused ring
phenolic compound α-naphthol (10) afforded the expected 2-
bromo-α-naphthol (10a). Heterocyclic compounds such as
imidazole (11) which is sensitive to usual bromination, can be
brominated by this reagent to 2,4,5-tribromoimidazole (11a) in
reasonably high yield using 1.5 equiv of the reagent (Table 1).
2,4,5-Tribromoimidazole is believed to be capable of
catalytically reactivating phosphorylated acetocholinestearase.20
In another interesting reaction bisphenol-A (12) was brominated
to tetrabromobisphenol-A (12a) by using 2 equiv of the reagent
(Table 1). It may be cited here that tetrabromobisphenol-A is well
known fire retardant.21 The reagent is equally efficient for
bromination of substrates bearing several other functionalities
such as ethylenic and acetylinic, carbonyl as well as active
methylene of 1,3-diketone and -ketoester. For example
substrates 13-15 (Table 2) were all brominated to their
corresponding trans-dibromo compounds with 0.5 equivalent of
the reagent. The methodology has also been proved to be
effective for carrying out bromination of α,-unsaturated ketones
such as 4-phenylbut-3-en-2-one (16) to its corresponding erythro-
dibromo product (16a). Bromination of cinnamaldehyde
diacylate (17) afforded corresponding erythro-dibromo product
(17a) in excellent yield without affecting the acylal functionality
under present reaction conditions (Table 2). The present reagent
is capable of chemoseletively brominate only one double bond in
a substrate containing two symmetrical double bonds as
demonstrated for dibenzylidene (18) (Table 2).
Table 1. Brominationa of organic substrates with HMBTB
under solvent-free condition
Substrate
Product
Time (min) Yieldb,c
aReactions were monitored by TLC. bIsolated yields. cProducts were
characterized by comparison of their spectral data with those of authentic
samples (please see ESI)
Acetylinic substrates (19) and (20) could also be brominated with
this reagent in very good yields Successful α-bromination of
ketones such as cyclohexanone (21) and acetophenone (22) has
been achieved as well (Table 2). Finally we have also studied
monobromination of active methylene compounds. Whereas such
bromination with conventional reagents is difficult22 the reaction
could be achieved in good yield with present regent. Bromination
of 1,3-diketone such as 1,3-diphenylpropane-1,3-dione (23) as
well as ethyl-3-oxo-3-phenylpropionate (24) gave exclusively α-
monobrominated product (23a and 24a) with 0.5 equiv of the
reagent (Table 2).

4
Tetrahedron
Table 2. Brominationa of organic substrates with HMBTB
under solvent-free condition
1.2 equiv of KBr and 1.1 equiv of UHP under mild acidic
condition to regenerate the reagent in quantitative yield. For
reactions involving addition of bromine across a double bond, 2
equiv of KBr and 2 equiv of UHP are required. The recovered
reagent shows same efficiency as that of the parent reagent.
Substrate
Product
Time(min) Yieldb,c
Figure 2. Various ditribromide reagents
Table 3. Comparison of HMBTB with other ditribromides in
regioselective bromination of phenol (2), aniline (3),
acetanilide (1), and p-methoxyphenol (4)
% of product (isolated yields/ GC yields)
Reagent
p-
Phenol
(2)
Aniline
(3)
Acetanili
de (1)
Methoxy
phenol
(4)
HMBTB (I ) 85/90
DPTBE (I I ) 85/89
85/91
85/90
95/99
95/99
95/99
90/96
82/88
85/90
EPDBT (I I I ) 81/85
80/86
81/86
88/95
88/96
EBMIDTB
80/85
(I V)
A comparative study on recoverability and recyclability of
HMBTB has been carried out with aforementioned ditribromides.
The spent reagents recoverability for HMBTB (I), DPTBE (II),
EPDBT (III) and EBMIDTB (IV) are respectively, 97%, 93%,
95% and 91%. While the overall recoverability of their
corresponding tribromides are 92%, 88%, 85% and 85%
respectively. These results suggest HMBTB (I) can be overall
recovered better compared to other ditribromides.
aReactions were monitored by TLC. bIsolated yields. cProducts were
characterized by comparison of their spectral data with those of authentic
samples (please see ESI)
To conclude, an ecofriendly synthesis of novel ditribromide
viz., hexamethonium bis(tribromide) from hexamethonium
bromide is reported. Urea-hydrogen peroxide was used to oxidize
bromide to tribromide. The reagent contains nearly 47% active
bromine per molecule which is one of the highest among reported
organic ammonium tribromides. The reagent makes nearly 100%
efficient delivery of bromine to organic substrate making the
bromination reaction highly atom economic. The other features
of bromination reactions involving the present reagent that are
important from Green chemistry perspective are solvent-free
conditions, high yield and high selectivity of products and ability
to react towards wide range of substrates. These advantages
coupled with ease of recovery and reuse of the HMBTB, make it
a reagent of choice for bromination reactions. All in all, the
reagent is believed to complement other green ditribromides,
particularly DPTBE, in bromination of organic substrates.
A comparative study of this reagent with three other reported
ditribromides (Figure 2), viz., 1,2-dipyridiniumditribromide-
ethane (DPTBE) (II), 1,10-(ethane-1,2-diyl)phenanthrolinediium
bistribromide (EPDBT) (III), ethylenebis(N-methylimidazolium)
ditribromide (EBMIDTB) (IV) has been made by carrying out
bromination of phenol, aniline, acetanilide and p-methoxyphenol
for amount of time mentioned in Table 1. The results are
summarized in Table 3. The results clearly indicate that although
active bromine (47%) content of HMBTB (I) is comparable to
these ditribromides, DPTBE (II), (48%), EPDBT (III), (46.5%)
and EBMIDTB (IV), (47.6%) but it certainly proves to be
superior in terms of yield and reaction times under similar
reaction conditions (Table 3).
Another intriguing feature of this reagent is its easy
recoverability and reusability. The regeneration of this reagent is
simple as its precursor spent reagent HMB is highly water
soluble. For reactions that involve transfer of one bromine atom
to the substrate such as monobromination of aromatic ring, 1,3-
diketones etc., the aqueous solution containing the precursor
(HMB) and 2 equiv of leftover bromide, needs to be treated with
3. Experimental
Preparation
of
hexamethonium
bis(tribromide)
(HMBTB): Hexamethonium bromide (HMB) (100 mmol, 36.2g)
and KBr (400 mmol, 48.0g), were dissolved to 100 mL of 4N

5
sulfuric acid. To this solution was added urea-hydrogen peroxide
(UHP) (400 mmol, 37.0g) over a period of 10 min at room
temperature. The solution was stirred magnetically for ca. 15 min
to afford an orange yellow product. The stirring was continued
for another 15 min to ensure complete conversion of HMB to
HMBTB. The orange-yellow precipitate was filtered, dried in
vacuum desiccator and recrystallized from CH3CN to yield 66.5g
(96%) of hexamethonium bis(tribromide). Mp 118-120 C. UV
(CH3CN) 267 nm. FT-IR (KBr, cm-1): 650,491, 448, 262, 243,
References and notes
1.
(a) Larock, R. C. Comprehensive Organic Transformations, Wiley-
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(a) Butler, A.; Walker, J. V. Chem. Rev. 1993, 93, 1937-1944; (b)
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Counsell, R. E. Chem. Rev. 1982, 82, 575-590.
(a) Stille, J. K. Pure Appl. Chem. 1985, 57, 1771-1780; (b) Miyaura, N.;
Suzuki, A. Chem. Rev. 1995, 95, 2457-2483; (c) Zhao, D.; Fei, Z.;
Geldbach, T. J.; Scopelliti R.; Dyson, P. J. J. Am. Chem. Soc. 2004, 126,
15876-15882; (d) Choudary, B. M.; Chowdari, M. S.; Naidu, S.;
Kantam M. L.; Sreedhar, B. J. J. Am. Chem. Soc. 2002, 124, 14127-
14136; (e) Braese S.; Meijere, A. De. Metal-Catalyzed Cross-Coupling
Reactions, ed. A. de Meijere and F. Diederich, Wiley-VCH, Weinheim,
Germany 2004, pp. 217-315.
(a) Hartwig, J. F. Angew. Chem. Int. Ed. 1998, 37, 2046-2067; (b)
Wolfe, J. P.; Wagen, S.; Marcoux J. F.; Buchwald, S. L. Acc. Chem.
Res. 1998, 31, 805-818.
Chaudhuri,. M. K.; Khan, A. T.; Patel, B. K.; Dey, D.; Kharmawphlang,
W.; Lakshmiprabha, T. R.; Mandal, G. C. Tetrahedron Lett. 1998, 39,
8163-8166.
Chaudhuri, M. K.; Bora, U.; Dehury, S. K.; Dey, D.; Dhar, S. S.;
Kharmawphlang, W.; Choudary, B.M.; Mennepalli, L. K. Patent, US
7,005, 548, 2006.
2.
3.
1
132 121. H NMR (d6-DMSO) δ: 3.7 (m, 18H), 3.1 (m, 4H), 2.6
(m, 4H), 2.1 (m, 4H). Elemental Anal. Calcd for C12H30N2Br6
(Mol Wt. 682.19): C 21.15, H 4.34, N 4.11, Br 70.31. Found C
21.17, H 4.37, N 4.13, Br 70.33.
Bromination of phenol (2) to p-bromophenol (2a): Phenol
(440 L, 5 mmol) and hexamethonium bis(tribromide) (1.7 g, 2.5
mmol) were mixed in a mortar by grinding at room temperature.
The grinding continued for required time (Table 1) till the
completion of the reaction (monitored by TLC). The reaction
mixture was then transferred to a separating funnel, admixed with
ethyl acetate (10 mL) and washed with water (2 x 5 mL). The
organic layer was dried over anhydrous Na2SO4 and then
concentrated in rotary evaporator to obtain the reasonably pure p-
bromophenol. However, for the purpose of analysis, the
compound was further purified by passing it over a short column
of silica gel and using a mixture hexane: ethyl acetate (9:1) as
eluent to afford the product (2a) in 91% (790 mg) yield. The
procedure was used all substrates giving liquid product.
4.
5.
6.
7.
8.
9.
Dey, M.; Dhar, S. S. Green Chem. Lett. Rev. 2012, 5, 639-642.
Muathen, H. A. J. Org. Chem. 1992, 57, 2740-2741.
Feiser, L. F.; Feiser, M. Reagents for Organic Synthesis Wiley, 1967, p.
967.
10. Herari, M. H.; Derikvand, F.; Gassemzedah M.; Nuemuller, B.
Tetrahedron Lett. 2005, 46, 6243-6245.
11. Herari, M. M.; Abdolhosseini N.; Oskooie, H. A. Tetrahedron Lett.
2005, 46, 8959-8963.
12. (a) Kabala, V.; Naik S.; Patel, B. K. J. Org. Chem. 2005, 70, 4267. (b)
Kabala, V.; Naik S.; Patel, B. K. J. Org. Chem. 2005, 70, 6556.
13. Hossenzedah, R.; Tajbakhsh, M.; Mohadjerani, M.; Lasemi, Z. Montash
Chem. 2009, 140, 57-60.
14. Dey, R. R.; Paul, B.; Dhar, S. S. Syn. Commun. 2015, 45, 714-726.
15. Veisi,H.; Sedrpoushan, A.; Mohammadi, P.; Faraji, A. R; Sajjadifar, S.
RSC Adv. 2014, 4, 25898-25903.
16. Bao, W.; Wang, Z. Green Chem. 2006, 8, 1028-1033.
17. Paquet, L.A. Ed. Encyclopedia of Reagents for Organic Synthesis;
Wiley, New York, 1995, vol. 6, pp-4738-4370.
Bromination acetanilide (1) to p-bromoacetanilide (1a): A
mixture of acetanilide (1) (0.675 g, 5 mmol) and HMBTB (1.7 g,
2.5 mmol) was ground in a mortar by a pestle at room
temperature. After disappearance of the starting material
(monitored by TLC by taking a small amount of the mixture and
dissolving it in ethyl acetate), the reaction mixture was
transferred into a G3 sintered funnel and washed with water (2 x
5 mL), and the solid was dried to yield 1.02 g (95%) of p-
bromoacetanilide (1a). This procedure is applicable to all
substrates giving product as a solid.
18. Beakart, A.; Provot, O.; Rasolojaona, M.; Alami, M.; Brion, J.D.
Tetrahedron Lett. 2005, 46, 4187-4191.
Regeneration of HMBTB (from reactions involving
monobromination of substrates): The aqueous layer left after
bromination reaction containing 1 equiv of hexamethonium
bromide and 2 equiv of bromide (unused in the reaction) was
concentrated to 5 mL. The concentrated aqueous layer was
washed with ethyl acetate (2 x 5 mL) in a separating funnel to
remove organic impurities (if any). The solution was then treated
with KBr (2 equiv) and UHP (2 equiv) in 10 mL 4N H2SO4. The
mixture on stirring for 30 min afforded 95% of hexamethonium
bis(tribromide).
19. Dey, R. R.; Paul, B.; Dhar, S. S.; Bhattacharjee, S. Chem. Lett. 2014,
43, 1545-1547.
20. Nath, J.; Chaudhuri, M. K.; Green Chem. Lett. Rev. 2008, 1, 223-230.
21. Kantam, M. L.; Jeevaratnam, K. B.; Choudary, B. M.; Reddy, C. R.V.;
Raghavan, K. V.; Shivaji, L. V.; Someshwar, T. US Patent 6,245,950,
2001.
22. Meshram, H. M.; Reddy, P. N.; Sadashiv, K.; Yadav, J. S. Tetrahedron
Lett. 2005, 46, 623 and references cited therein.
Supplementary Material
Regeneration of HMBTB (from the reaction of addition to C-
C multiple bonds). Identical to the above, except 2 equiv of
additional KBr and proportionately higher amount of the oxidant
UHP were used.
Supplementary material that may be helpful in the review
process should be prepared and provided as a separate electronic
file. That file can then be transformed into PDF format and
submitted along with the manuscript and graphic files to the
appropriate editorial office.
Acknowledgement: S.S.D is grateful to Dr. T. K. Paine and
Mr. Sridhar Banerjee, Inorganic Chemistry Division, Indian
Association for Cultivation of Science, Kolkata for single-crystal
XRD analysis of HMBTB. CIF IIT Guwahati and SAIF IIT
Madras are acknowledged for NMR spectra. B.P. thanks NIT
Silchar for funding.
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