Chemical Papers
activated aromatics. In this report, we studied the possibility
to extend this in situ bromination method to non-activated
and deactivated aromatics and optimised the reaction condi-
tions to obtain the best outcome of the reaction.
Bromination reactions without solvents
Liquid substrate (benzene or bromobenzene) was added to a
50-mL round bottom fask. In diferent experiments, the vol-
ume of substrate was 5 mL, 2.5 mL or 1 mL. Then, diferent
amounts of oxidising agent KNO3 (1.5 mmol, 2.5 mmol or
5 mmol) and anhydrous AlBr3 as catalyst and bromine source
(3.75 mmol, 7.5 mmol or 15 mmol) were added to the fask.
The reaction mixture was stirred briefy. Then, the timing was
started. Two minutes before stopping the reaction, the reac-
tion mixture was stirred again. There was no constant stirring,
because, as discussed in our previous work (Rahu et al. 2018),
it has a perturbing efect to the bromine formation.
Experimental
Starting materials and equipment
The starting materials NaBr, AlBr3, KNO3, acetanilide and
bromobenzene were purchased from Reahim and benzene
(Batch no.: PP/2011/00025) from Lach:ner. The purities of
all substrates were verifed by gas chromatography–mass
spectrometry (GC–MS). The solvents hexane (Lot No.
8321S) and diethyl ether (Lot Nos.: STBG6864) were pur-
chased from Sigma-Aldrich.
Reactions were stopped at diferent timepoints (15, 30, 60,
120 or 240 min) by adding 25 mL of saturated NaHCO3 solu-
tion to remove unreacted AlBr3 and neutralise the solution
and 10 mL of Na2S2O3 solution to be sure there is no exces-
sive bromine in the reaction mixture. Then, 10 mL of diethyl
ether was added, and the reaction mixture was stirred properly.
Afterwards the organic layer was analysed by GC–MS. In pre-
liminary experiments, where benzene was used as a substrate,
an extra purifcation step was performed to separate main
products (bromobenzene and nitrobenzene) to analyse them
with NMR (see Supplementary data for spectrums).
The scope of bromination reactions was assayed by ana-
lysing the reaction mixture using Agilent Technologies
7890A gas chromatograph with quadrupole mass spectrom-
eter as the detector. In this study, nonpolar DB-5ms Ultra
Inert column (phenyl arylene polymer virtually equivalent to
5% phenyl-methylpolysiloxane) with the radius of 250 μm,
flm thickness of 0.25 μm, and length of 30 m was used. The
other gas chromatograph parameters were as follows: inlet
split 20:1, 0.5 μL; carrier gas helium 6.0, fow rate 2 mL/
min, and pressure 25.548 psi. Detector ionisation energy
was 70 eV, a transfer line and ion source temperatures were
280 °C and 230 °C, respectively. The scan rate of the used
detector was 2 scans/s, the scanning range was 30–400 amu,
the threshold was 20,000, and the reiteration number was
3. The GC–MS system was previously calibrated for acet-
anilide and its bromination product, and all respective data
were corrected. To analyse the benzene bromination reac-
tion, where three diferent dibrominated products formed,
the standard substances (1,2-dibromobenzene, 1,3-dibro-
mobenzene and 1,4-dibromobenzene) were used to distin-
guish between the isomers using their diferent retention
times.
Bromination reactions in solvent
1.5 mmol of substrate (acetanilide or benzene), 1.5 mmol of
KNO3 and 5 mL of hexane as a solvent were added to a 50-mL
round bottom fask. Then, diferent volumes of water, as men-
tioned in the following discussion, were added as well. The
reaction mixture was stirred thoroughly and then 7.5 mmol
AlBr3 was added and then the timing was started. The reac-
tions were stopped as discussed earlier, but instead of 10 mL
diethyl ether only 5 mL of diethyl ether was used. The organic
layer was analysed by GC–MS. In the experiments, where
acetanilide was used, the resultant bromination product was
purifed and analysed by NMR (see Supplementary data for
spectrum).
Two diferent temperature programs were used to assay
the bromination reactions. The following temperature pro-
gram was used to analyse the reaction mixture, when ben-
zene or bromobenzene was used as substrate: 50 °C held
for 4 min, followed by a temperature ramp of 10 °C/min to
200 °C, followed by 200 °C held for 5 min, giving a total
program length of 24 min. When acetanilide was used as
substrate, the temperature program was as follows: 140 °C
held for 4 min, followed by a temperature ramp of 10 °C/min
to 240 °C, giving a total program length of 14 min.
Data analysis
When acetanilide was used as a substrate, all results are cal-
culated and expressed as conversion values using peak areas
from chromatograph:
Sproduct
Conversion(%) =
⋅ 100%,
(1)
Sproduct + Ssubstrate
NMR spectra were recorded on a Bruker Avance III HD
where Sproduct is the peak area of p-bromoacetanilide, which
was the only product detected in this system and Ssubstrate
showing the peak area of unreacted acetanilide.
1
(operating at 700.1 MHz for H spectra and 176.0 MHz
for 13C spectra) at 25 °C in CDCl3 (Lot No.: B15097,
Sigma-Aldrich).
1 3