Paper
NJC
gasoline. 4-(4-Hydroxyphenyl)butan-2-one, bearing an electron- 2.3. Methods
rich aromatic ring, and hydroxyl and carbonyl groups, was alky-
2.3.1. Procedure for the alkylation of 4-(4-hydroxyphenyl)-
butan-2-one. 4-(4-Hydroxyphenyl)butan-2-one (1 mmol, 0.164 g),
2-bromo-2-methylpropane (6 mmol, 0.67 mL), sodium carbo-
nate (12 mmol, 1.272 g), and silica gel (1 g) were added to
carbon tetrachloride (5 mL) in a round-bottomed flask. The
mixture was stirred at 60 1C for 24 h. The silica gel was filtered
off and rinsed thoroughly with diethyl ether. Removal of the
solvent at reduced pressure yielded a solid which was subse-
quently purified via column chromatography on silica gel 60
with n-hexane/ethyl acetate (70 : 30) as the mobile phase. 4-(3,5-
Di-t-butyl-4-hydroxyphenyl)butan-2-one was obtained as an oily
compound (0.221 g, 80%).
lated with t-butyl groups in the presence of silica as a catalyst.
Five-membered cyclic ketals, as the main products, were formed
by the reaction between glycerol and carbonyl groups in order to
prepare multifunctional hindered phenolic derivatives. The per-
formance evaluation of the synthesized compounds was further
done by using accelerated oxidation and induction period tests.
2. Experimental
2.1. Materials
4-[(3-t-Butyl-4-hydroxyphenyl)butan-2-one] was similarly pre-
pared using a smaller amount of 2-bromo-2-methylpropane
(2 mmol, 0.22 mL) in order to compare the results with the
findings of similar studies with respect to the performance of
dialkylated compounds. The desired product was obtained as a
yellow solid compound (0.187 g, 85%).
4-(4-Hydroxyphenyl)butan-2-one was purchased from Exir Chemical
Company (Austria). 2-Bromo-2-methylpropane, silica gel, carbon
tetrachloride, sodium carbonate, glycerol, and mono hydrated
p-toluenesulfonic acid were procured from Sigma-Aldrich and
Merck. Gasoline was supplied by Bouali Sina Petrochemical Co.
(Mahshahr, Iran) with no further distillation. Thin-layer chro-
matography (TLC), drawing upon Merck silica gel 60 F254 plates,
was employed to follow up the reaction progress. The desired
products were purified through column chromatography on
silica gel using n-hexane/ethyl acetate as the eluent.
All products were characterized through 1H NMR, 13C NMR,
and elemental analyses.
2.3.2. General preparation of glycerol ketal derivatives.
Ketone (1 mmol) was added to a stirred mixture of glycerol
(1.1 mmol, 0.08 mL), monohydrated p-toluenesulfonic acid (PTAÁ
H2O) (0.02 mmol, 0.003 g), and n-hexane (4 mL) in a vessel
equipped with a thermometer, a reflux condenser, and the
Dean–Stark apparatus. The mixture was stirred at 60 1C for
40 h. Upon completion of the reaction, the mixture was treated
with sodium carbonate (0.04 mmol, 0.004 g) and it was stirred at
90 1C for 30 min. The resulting mixture was filtered, and the
solvent was evaporated at reduced pressure. The corresponding
product was obtained via column chromatography on silica gel
60 with n-hexane/ethyl acetate (70 : 30) as the eluent in good
yield. All products were characterized using 1H NMR, 13C NMR,
DEPT 1351, and elemental analysis.
2.2. Instruments
Fourier-transform infrared (FTIR) spectra were obtained using
a FTIR Bruker Vector 22 spectrophotometer in KBr/Nujol mull
in the range of 400–4000 cmÀ1 under ambient conditions.
1H NMR, 13C NMR, and DEPT 1351 spectra were recorded using
a Bruker spectrometer at a frequency of 250 MHz and 62.5 MHz,
respectively, in CDCl3.
The elemental analysis of all products was performed through
the use of an elemental analyzer (Elementar, Germany).
Thermogravimetric analysis (TG) and derivative thermogra-
vimetry (DTG) were carried out on a PerkinElmer thermogravi-
metric analyzer (PerkinElmer, USA) using a ceramic pan by
raising the ambient temperature to 900 1C in two stages: from
25 to 200 1C in incremÀen1 ts of 10 1C minÀ1 under an N2
atmosphere (120 mL min ) and from 200 to 900 1C under an
O2 atmosphere (120 mL minÀ1).
3. Results and discussion
3.1. Synthesis and characterization of new antioxidants
2.2.1. Accelerated oxidation test. For accelerated oxidation The development of a simple and general route for the synth-
tests, two samples were used concurrently to examine the esis of novel multifunctional antioxidants from readily avail-
antioxidant capability: one as the blank without antioxidant, able reagents is the major challenge in the present work.
and the other with 1% antioxidant. The prepared samples were
put in two 10 mL round-bottomed flasks and were kept at a hydroxyphenyl)butan-2-one and the alkylating agent in the presence
constant temperature of 60 1C under a flow of oxygen (1.0 L hÀ1
of silica gel as a catalyst to afford the corresponding product in
Initially, the reaction took place in a mixture of 4-(4-
)
in the presence of a copper wire spiral as a catalyst following the carbon tetrachloride (Scheme 1).
modified ASTM D-2440 method.32 After 72 h, each sample was
It has to be noted that silica gel is an effective catalyst and
analyzed via FTIR spectroscopy. Fresh gasoline was employed as Lewis acid in the alkylation of phenolic compounds.34 The
the reference sample.
reaction results in both 4-[(3-t-butyl-4-hydroxyphenyl)butan-2-one]
2.2.2. Induction period test for oxidation stability. Pre- (mono-t-butylated, 2a) and 4-(3,5-di-tert-butyl-4-hydroxyphenyl)-
defined concentrations of synthesized antioxidants were prepared butan-2-one (di-t-butylated, 2b). It was found that the ratio of
(5 mL). To determine the oxidation stability of the samples, the products depends on the amount of 2-bromo-2-methylpropane.
induction period test was undertaken until the oxygen pressure The reaction occurring in an excess amount of 2-bromo-2-
tapered off (ASTM D 525) (Petroxy from Petrotest, Germany).33
methylpropane (6 mmol) led to di-t-butylated product 2b, but
New J. Chem.
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