Synthesis, characterization and evaluation of antioxidant activity of tyrosol derivatives from olive mill wastewater

Article abstract of DOI:10.1007/s11696-018-0591-7

The use of biophenols to synthesize antioxidants has greatly developed due to their capability of solving environmental problems, economical reasons and renewability. In the present work, the tyrosol derived from olive mill wastewater (OMWW) was alkylated

Full text of DOI:10.1007/s11696-018-0591-7

Chemical Papers
https://doi.org/10.1007/s11696-018-0591-7
ORIGINAL PAPER
Synthesis, characterization and evaluation of antioxidant activity
of tyrosol derivatives from olive mill wastewater
Zeinab Namazifar1 · Fariba Saadati1 · Ali Akbar Miranbeigi2
Received: 21 March 2018 / Accepted: 11 September 2018
© Institute of Chemistry, Slovak Academy of Sciences 2018
Abstract
The use of biophenols to synthesize antioxidants has greatly developed due to their capability of solving environmental prob-
lems, economical reasons and renewability. In the present work, the tyrosol derived from olive mill wastewater (OMWW) was
alkylated to improve its utilization. The synthesized antioxidants were characterized by nuclear magnetic resonance (NMR)
and CHN analyses. To study their thermal behavior, thermogravimetry analysis (TGA) and derivative thermogravimetry
(DTG) techniques were employed. Antioxidant action of these compounds in gasoline sample was investigated by accelerated
oxidation and induction period tests. Induction period results show the best stability time (188 min) at 10 ppm concentration
of synthesized antioxidant in a gasoline sample. Reduction of carbonyl and peroxide band areas indicates the good antioxidant
activity of these compounds (1.0% concentration) in the gasoline. Considering what was mentioned above, easy synthesis
method and using bio-based material provide a highly efcient antioxidant to inhibit the oxidative process of gasoline.
Keywords Antioxidant · Olive mill wastewater · Phenol · Tyrosol · Gasoline
Introduction
From among the wide range of reported antioxidants,
bio-based compounds have received a lot of attention. Their
most signifcant advantages are sustainability, low cost, low
toxicity and availability (Salimon et al. 2010). In such class
of materials, biophenolic compounds exist in nature as
intrinsic antioxidants that are capable of directly scaveng-
ing peroxy radicals, donating hydrogen atoms or electrons
to radical species or removing metal cations through forma-
tion of chelate during oxidative degradation (Amarowicz
et al. 2004). This potential can be widely considered for
inhibiting the oxidation process of petrochemical products
like gasoline. There are several types of biophenolic antioxi-
dants such as cardanol (Maia et al. 2015; Voirin et al. 2014),
chitosan Schif base (Guo et al. 2005; Demetgül and Beyazit
2018), rosemary extract (Yang et al. 2016), and green tea
(Donlao and Ogawa 2018). In addition, some biophenolic
compounds with antioxidant activity have been identifed
in several agricultural by-products, such as buckwheat hulls
(Watanabe et al. 1997), rice hulls (Ramarathnam et al. 1989),
almond hulls (Sfahlan et al. 2009) and olive mill wastewater
(OMWW) (De Marco et al. 2007; Aissa et al. 2017).
Additives in oil industry are the most important chemical
compounds to improve specifc qualities and solve degra-
dation problem of petrochemical products (Facanha et al.
2007). In recent years, due to the destructive consequences
of by-product formation in oxidation reaction in food, phar-
maceutical and oil industries, antioxidant additives have
been considered remarkably (Bhatnagar and Vergnaud
1983). Antioxidant additives are able to decelerate the
oxidation of other compounds and prevent gum formation
(Ohkatsu and Nishiyama 2000). Consequently, researchers
are interested to use this kind of additives in petrochemical
and industrial products (Feng et al. 2017; Gülçin 2012).
Electronic supplementary material The online version of this
article (https://doi.org/10.1007/s11696-018-0591-7) contains
supplementary material, which is available to authorized users.
* Fariba Saadati
saadati@znu.ac.ir
Olive fruit has the most abundant phenolic compounds.
In the oiling process, the total phenolic content of the olive
fruit is separated into three parts: only 2% remains in the oil
phase, approximately 53% is lost in the OMWW and 45%
1
Department of Chemistry, Faculty of Science, University
of Zanjan, P.O. Box 45371-38791, Zanjan, Iran
2
Oil Refnery Research Division, Research Institute
of Petroleum Industry, Tehran, Iran
Vol.:(0123456789)
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remains in the pomace (Rodis et al. 2002). OMWW, as a
major by-product of oiling process, is a source of phenolic
compounds such as hydroxytyrosol, tyrosol, oleuropein, and
a variety of hydroxycinnamic acids (Obied et al. 2005). The
phenolic fraction in OMWW causes environmental prob-
lems, antimicrobial activities and biological degradation
(Bisignano et al. 1999). In this pursuit, extraction of phe-
nolic compounds from olive oil wastewater can solve the
environmental problems; meanwhile, these compounds can
be used as inexpensive and afordable natural raw materials
for antioxidant production.
ambient temperature to 900 °C. The measurements were car-
ried out in N2 atmosphere (120 mL min−1) from 25 to 200 °C
and O2 atmosphere (120 mL min−1) from 200 to 900 °C.
Accelerated oxidation tests
Accelerated oxidation test was carried out in a bench-scale
oxidation apparatus in laboratory using two samples simulta-
neously according to modifed ASTM D-2440 method (Koh
and Butt 1995). The antioxidant capability was investigated
for two gasoline samples: one of them without antioxidant
and the other one containing 1% antioxidant in the presence
of the copper wire spiral. The samples were placed in two
10-mL round-bottom fasks and were kept at constant tem-
perature (60 °C) under a fow of oxygen. Each sample was
collected after 72 h and analyzed by FT-IR spectroscopy.
Among the phenolic content of OMWW, the tyrosol com-
pound has been utilized as a basis for the synthesis of efec-
tive antioxidants (Wen et al. 2013; Storozhok et al. 2004).
Tyrosol with two hydroxyl groups (phenolic and alcoholic)
could be an excellent antioxidant but it is crucial to be modi-
fed (Gülçin 2007; Storozhok et al. 2012).
This study intends to describe the synthesis and charac-
terization of novel and highly efcient agents with excellent
antioxidant properties. In this process, tyrosol is alkylated
with tert-butyl group in the presence of silica gel as catalyst
to improve its thermal stability, solubility and volatility. The
synthesized compounds were assessed by thermal-oxidative
stability and antioxidant activity in gasoline for more accu-
rate identifcation.
Induction period test for oxidative stability
Specifc concentrations of synthesized substances were pre-
pared (5 mL) to accelerate the assays of oxidative stability,
induction period test (ASTM D 525) (Petroxy from Petrotest,
Germany) until the observation of pressure drop.
Methods
Experimental
Procedure for the alkylation of tyrosol
Materials
Tyrosol (1 mmol, 0.138 g), tert-butyl bromide (6 mmol,
0.67 mL), sodium carbonate (12 mmol, 1.272 g) in the
presence of silica gel (1 g) in carbon tetrachloride (5 mL)
were stirred at 65°C for 24 h. The reaction progress was
monitored by TLC. The reaction mixture was washed thor-
oughly with diethyl ether and fltered of. Following that,
the product was concentrated under reduced pressure and
purifed by column chromatography on silica gel 60, eluting
with n-hexane/ethyl acetate (70:30). 2,6-di-tert-butyl-4-(2-
hydroxyethyl)phenol (di-tert-butylated tyrosol) was obtained
as a white solid compound (225.3 mg, 90%).
The chemicals and solvents were purchased from commer-
cial suppliers and used without further purifcation. Gasoline
was supplied by Bouali Sina Petrochemical Co. with no fur-
ther distillation procedure (Mahshahr, Iran).
Thin-layer chromatography (TLC), Merck silica gel 60
F254 plates, was used to follow-up the reaction progress.
Purifcation was done by column chromatography on silica
gel 60, Merck (n-hexane/ethyl acetate as eluent).
Apparatus and instruments
Employing the same procedure, but using a lower amount
of tert-butyl bromide (2 mmol, 0.22 mL) led to preparing
mono-tert-butylated tyrosol. 2-tert-butyl-4-(2-hydroxyethyl)
phenol (mono-tert-butylated tyrosol) product was obtained
as an oily compound (185.00 mg, 95%). All products were
characterized by 1H NMR, 13C NMR, and CHN analysis.
Fourier transform infrared (FT-IR) spectra were obtained
using FT-IR Bruker-Vector 22 spectrophotometer in KBr/
Nujol mull in the range of 400–4000 cm−1 under ambient
conditions. 1H NMR and 13C NMR spectra were recorded
by BRUKER spectrometer, at the frequency of 250 and
62.5 MHz, respectively, in CDCl3.
2‑tert‑Butyl‑4‑(2‑hydroxyethyl)phenol
(mono‑tert‑butylated tyrosol)(2a)
Elemental CHN analyser (Germany) was used for the
CHN analysis of all products.
Thermogravimetry (TG/DTG) measurements were car-
ried out by a PerkinElmer thermogravimetric analyzer
using ceramic pan at an increasing rate of 10 °C min−1 from
Oily compound; 1H NMR (250 MHz, CDCl3, δ/ppm): 7.15
(1H, s), 6.97 (1H, d, J=8.00 Hz), 6.65 (1H, d, J=8.00 Hz),
5.11 (1H, s), 3.57 (3H, t, J = 8.00 Hz), 3.13 (3H, t,
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J = 8.00 Hz), 1.47 (9H, s); 13C NMR (62.9 MHz, CDCl3,
δ/ppm): 153.16, 136.30, 130.83, 127.54, 126.94, 116.60,
39.10, 33.48, 30.31, 29.55.
di-alkylated products. In the presence of the excess amount
of t-BuBr (6 mmol) and less amount of t-BuBr (2 mmol),
di-tert-butylated and mono-tert-butylated compounds are the
major products, respectively.
Anal. Calcd. for C12H18O2: C, 74.19, H, 9.34 and O,
16.47. Found: C, 72.20, H, 9.30 and O, 18.50.
The NMR spectroscopy and CHN analysis were
employed to characterize the obtained products. For mono-
tert-butylated tyrosol in 1HNMR, three peaks in 6.65, 6.97
and 7.15 ppm were referred to the aromatic hydrogen atoms.
For proton of phenolic group, one singlet peak was observed
at 5.11 ppm. Aliphatic hydrogen atoms appeared in 3.13 and
3.57 ppm as two triplet peaks. The nine protons of the CH3
groups of t-Bu were observable at 1.47 ppm as a singlet
peak (Fig. 1a).
2,6‑Di‑tert‑butyl‑4‑(2‑hydroxyethyl)phenol
(di‑tert‑butylated tyrosol)(2b)
White solid; m.p.: 75–78 °C; 1H NMR (250 MHz, CDCl3,
δ/ppm): 7.04 (2H, s), 5.19 (1H, s), 3.56 (3H, t, J=8.00 Hz),
3.11 (3H, t, J = 8.00 Hz), 1.48 (18H, s); 13C NMR
(62.9 MHz, CDCl3, δ/ppm): 152.69, 136.04, 129.71, 125.24,
39.75, 33.43, 30.26, 29.69.
For di-tert-butylated tyrosol a singlet peak in 7.04 ppm
verifed the existence of two aromatic hydrogen atoms. The
proton of phenolic group appeared at 5.19. Two triplet peaks
at 3.56 and 3.11 ppm were attributed to methylene groups
of the aliphatic chain. The peak that appeared at 1.48 ppm
with 18 integral corresponded to the presence of two t-Bu
groups (Fig. 1b).
Anal. Calcd. for C16H26O2: C, 76.75, H, 10.47 and O,
12.78. Found: C, 74.70, H, 10.40 and O, 14.90.
Results and discussion
Synthesis and characterization of tert‑butylated
tyrosol derivatives
The 13CNMR of mono-tert-butylated tyrosol showed
six peaks at 153.16, 136.30, 130.83, 127.54, 126.94 and
116.60 ppm for six carbons of aromatic ring. The peaks
at 39.10 and 33.48 ppm were attributed to the aliphatic
chain (ethyl alcohol). In addition, the carbons of t-Bu group
appeared at 30.31 and 29.55 ppm which belong to tertiary
and primary carbons, respectively. The 13CNMR for di-tert-
butylated tyrosol exhibited four peaks at 152.69, 136.04,
129.71 and 125.24 ppm which verify the symmetry of
aromatic ring. The carbons of aliphatic groups (tert-butyl
and ethyl alcohol) appeared at 39.75, 33.43, 30.26 and
29.69 ppm (supplemental material).
According to antioxidant ability of biophenolic compounds
and improvement of the solubility and stability properties
by alkylation, in this work, two antioxidants were designed
and synthesized based on tyrosol. This biophenol is the rep-
resentative of natural compound with two functional groups.
To synthesize the efficient antioxidants, tyrosol was
alkylated in the presence of silica gel as a Lewis acid cata-
lyst (Scheme 1) (Kamitori et al. 1984). The reaction was
performed in CCl4 at 65 °C for 24 h.
2-tert-Butyl-4-(2-hydroxyethyl)phenol (mono-tert-but-
ylated tyrosol) (2a) and 2,6-di-tert-butyl-4-(2-hydroxye-
thyl)phenol (di-tert-butylated tyrosol) (2b) products were
obtained in excellent yield. It is worth mentioning that dif-
ferent t-BuBr amounts lead to diferent ratios of mono and
Thermal studies
Thermogravimetric analysis (TGA) and diferential ther-
moanalysis (DTA) were applied to determine the thermal
stability of the di-tert-butylated tyrosol. Essentially, two
weight losses were observed from 25 to 900 °C. The frst
weight loss at around 110 °C was attributed to the release
of the organic solvents. The major and sharp weight loss
between 152 and 195 °C corresponded to carbon skeleton
decomposition (Fig. 2.). The result indicated the thermal
stability of the prepared antioxidant.
OH
OH
R1
R2
Silica
t-BuBr
Na2CO3
CCl4
OH
OH
65° C
Study of the antioxidative capacity of the products
2
1
24 h
a) R1 = t-Bu , R2 = H (95%) (t-BuBr, 2 mmol)
b) R1 = R2 = t-Bu
(90%) (t-BuBr, 6 mmol)
Due to the novelty of the synthesized compounds for use in
oil industry, and to study the antioxidant capacity of these
products, accelerated oxidation test and induction period test
were performed.
Scheme 1 General procedure for alkylation of tyrosol in the presence
of silica gel
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Fig. 1 1H NMR of mono-tert-butylated tyrosol (a) and di-tert-butylated tyrosol (b)
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(a)
100
80
60
40
20
0
ROOH
C=O
Gasoline without antioxidant
after 72 h
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
(b)
100
80
60
40
20
0
ROOH
C=O
Fig. 2 Thermogravimetric diagram of di-tert-butylated tyrosol
Accelerated oxidation test of di‑tert‑butylated
tyrosol (2b)
Gasoline with 1.0% w/v antioxidant (2b)
after 72 h
For accelerated oxidation test two samples were
employed: gasoline with 1.00% w/v antioxidant (2b)
and gasoline without antioxidant (blank). Different com-
pounds such as ketones, acids, aldehydes and peroxides
were formed due to the oxidation reaction and degrada-
tion in the sample. The formation of these compounds
with C=O and OH functional group leads to the appear-
ance of vibrational peaks for carbonyl (C=O) and perox-
ides (ROOH) at 1706 and 3429 cm−1, respectively (Bow-
man and Stachowiak 1996).
4000
3500
3000
2500
2000
1500
1000
500
Wavenumber (cm-1)
Fig. 3 Infrared spectra of gasoline samples: a gasoline without anti-
oxidant (72 h) and b gasoline with 1.0% antioxidant (72 h)
Induction period test
Induction period test (ASTM D 525) was performed to study
the oxygen stability of gasoline. Auto-oxidation in gasoline
during the storage because of the presence of atmospheric
oxygen leads to the formation of mono- and di-olefns which
causes problems on the stability of the gasoline. In this test,
to optimize the concentration of antioxidant, six samples
of antioxidant (2b) at diferent concentrations (0, 5, 10, 20,
30 and 200 ppm) were used (Table 2). According to the
obtained results, increasing the concentration of antioxidant
in gasoline leads to increasing the stability time in induction
period test signifcantly.
Therefore, in the study of accelerated oxidation test-
specific spectral bands, areas from 1644 to 1763 cm−1
and 3144 to 3598 cm−1 were calculated (Fig. 3). The com-
parison was made between fresh gasoline (supplemental
material), degraded blank gasoline after 72 h (Fig. 3a) and
gasoline with 1% antioxidant after 72 h (Fig. 3b). Follow-
ing the degradation, due to oxidation reaction in blank
gasoline, sharp vibrational peaks regarding C=O and OH
at 1701 and 3370 cm−1 appeared which show the forma-
tion of a great variety of oxidation products. As shown in
Fig. 3b, the intensity of functional group peaks, arising
from oxidation reaction, is negligible for gasoline with
1% antioxidant sample. For comparison, these results are
represented as the ratio between the areas which were
obtained for the carbonyl and peroxide bands for the gaso-
line sample with antioxidants (Awith) and without antioxi-
dant (Awithout). Accelerated oxidation test proved excel-
lent efficiency of antioxidant (2b) in preventing oxidation
reaction and forming gum product (Table 1).
For comparison, induction period test for mono-tert-
butylated tyrosol (2a) antioxidants was carried out. The
Table 1 Results of the accelerated oxidation test for gasoline samples
after 72 h of degradation
C=O
ROOH
Sample
(Asample/Awithout
)
(Asample/Awithout
1
)
Gasoline without anti-
1
oxidant (72 h)
Gasoline with 1.0%
antioxidant (72 h)
0.1
0.1
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Table 2 Results of the induction
period test of di-tert-butylated
tyrosol antioxidant (2b) at
diferent concentrations
Comparison with other reported phenolic
Entry Concen-
tration
Induction
antioxidants
period (min)
(ppm)
The antioxidant action of 2,6-di-tert-butyl-4-(2-hydrox-
yethyl)phenol (2b) was compared with that of a number
of previously reported phenolic antioxidants in diferent
sources of gasoline samples (Table 4).
1
2
3
4
5
6
0
5
10
20
30
200
40
166
188
195
205
246
In comparison with other antioxidants, the synthesized
bio-antioxidant could highly improve induction period
time at very low concentration.
obtained result was good because it shows the efciency
of mono-tert-butylated tyrosol too (Table 3, entry 2). Fur-
thermore, all the results were compared with the famous
commercial antioxidant (BHT) at 10 ppm concentration
(Table 3, entry 4). The marked point is that adding very
low concentrations of antioxidant leads to very good
results and increases the stability time.
Conclusion
An efcient antioxidant based on a biophenol was prepared
under a simple protocol and completely characterized. The
developed material appears to be an excellent antioxidant
for gasoline. Most importantly, the synthesized antioxidant
could highly improve induction period time at very low
Table 3 Comparison of the
induction period result of all
synthesized antioxidants and
BHT at 10 ppm concentration
Entry
Additive
OH
Induction period (min)
Insoluble in gasoline
1
(1)
OH
OH
2
3
(2a)
178
OH
OH
(2b)
188
152
OH
OH
BHT
4
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Table 4 A comparison of the
developed antioxidant with
those reported in the literature
Entry Antioxidant Concentra- Induction period Induction period References
tion (ppm) of blank (min)
of sample (min)
1
50
135
680
Jones et al. (1952)
OH
HN
2
3
50
10
135
–
275
310
Jones et al. (1952)
Pedersen (1949)
OH
OH
HN
4
5
250
–
–
1110
1315
Thompson and Chenicek (1955)
Thompson and Chenicek (1955)
OH
HO
250
OH
OH
6
7
200
OH
160
160
890
575
Scheumann and Haslam (1942)
Scheumann and Haslam (1942)
OH
OH
HO
200
HO
OH
8
10
40
188
This work
OH
OH
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Chemical Papers
Table 4 (continued)
Entry Antioxidant Concentra- Induction period Induction period References
tion (ppm) of blank (min)
10 40
of sample (min)
152
9
This work
OH
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synthesis, renewability, excellent performance and good
thermal behavior led to the formation of efcient antioxi-
dants which were used to break oxidation chain and pre-
vent degradation. Such signifcant antioxidant efciency
could be attributed to the two steric tert-butyl groups in
phenolic ring and an alcoholic hydroxyl group in aliphatic
chain.
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Acknowledgements The authors acknowledge the fnancial support of
the Research Council of University of Zanjan.
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