Synthesis of Epoxidized Cardanol and Its Antioxidative Properties for

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Synthesis of epoxidized cardanol and its antioxidative properties for vegetable oils and biodiesel Zengshe Liu, Jie Chen, Gerhard Knothe, Xiaoan Nie, and Jianchun Jiang ACS Sustainable Chem. Eng., Just Accepted Manuscript • DOI: 10.1021/ acssuschemeng.5b00991 • Publication Date (Web): 11 Jan 2016 Downloaded from http://pubs.acs.org on January 12, 2016

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Synthesis of epoxidized cardanol and its antioxidative properties for vegetable oils and biodiesel Zengshe Liu*a, Jie Chenb, ◊, Gerhard Knothea, Xiaoan Nieb, and Jianchun Jiangb a

USDA, ARS, National Center for Agricultural Utilization Research, Bio-Oils

Research Unit, 1815 N University St, Peoria, IL, 61604, United States b

Institute of Chemical Industry of Forestry Products, Chinese Academy of Forestry;

National Engineering Laboratory for Biomass Chemical Utilization; Key Laboratory of Biomass Energy and Material, Nanjing, Jiangsu 210042, China;

KEYWORDS: Vegetable oil, Biodiesel, Oxidative stability, Antioxidants, Epoxidized Cardanol

* Corresponding author: [email protected]

ABSTRACT: A novel antioxidant, epoxidized cardanol (ECD), derived from cardanol was synthesized and characterized by FT-IR, 1H-NMR and 13C-NMR. Oxidative stability of ECD used in vegetable oils and biodiesel were evaluated by the pressurized differential scanning calorimetry (PDSC) and Rancimat method, respectively. The results indicated that ECD exhibited antioxidative activity in

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soybean oil and increased its onset temperature (OT) by nearly 10 °C with 0.7 wt.% ECD. It was also observed that other vegetables oils showed significantly improved oxidative stability with the addition of 0.7 wt.% ECD. Oliver oil showed the highest increased OT by 19.5 °C. Furthermore, the ECD has superior antioxidant activity compared to the synthetic antioxidant butylated hydroxytoluene (BHT), and thus could be used as an optimized primary antioxidant for biodiesel. Thermogravimetric analysis (TGA) indicated that ECD shows better thermal stability than cardanol. The data presented in this study indicate that ECD could be a new bio-based antioxidant with better thermal stability.

INTRODUCTION Natural antioxidants present in fruits and vegetables have attracted considerable attention in recent years because they are able to directly scavenge peroxy radicals formed during oxidative degradation, thus breaking the auto-oxidation chain reaction.1,2 Cardanol (alkyl phenol structure shown in Scheme 1), a constituent of cashew nut shell liquid (CNSL) and its derivatives are examples of such compounds. They possess significant antioxidant characteristics, being applied as additive for food, lubricants, polymers and rubber industries. 3-9 CNSL is an important agricultural by-product of cashew nut production. The potential annual production of this material, which accounts for about 32% of the shell, is enormous. Food and Agricultural Organization (FAO) reported that the cashew nuts global production was more than 3 million metric tons in 2008.10 The use of an abundant and low cost natural compound

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is in accordance with the concept of green chemistry, also known as environmentally benign chemistry or sustainable chemistry. In comparison to mineral diesel, biodiesel presented advantages of the renewability and biodegradability, however its decomposition property confers to itself lower oxidative stability.11-14 The fatty acid profile of biodiesel is virtually identical to that of the parent oil.14 Factors relevant to fatty acid degradation are mainly contain the unsaturation composition, exposure to air, high temperatures and the presence of metals. 15-18 The oxidation products (ketones, aldehydes, alcohols, peroxides, etc.) corrode the engine chamber or obstruct the injection filters of vehicles.19, 20 Those oxidation products have many other effects including sludge / sediment formation, poorer combustion properties, etc. Also, polymers can be formed. In order to control oxidation, many antioxidants can be used to improve oxidative stability of biodiesel. Recent research on the low cost antioxidants derived from renewable sources has been reported.1, 21 Cardanol and its derivatives are examples of such compounds present significant antioxidant characteristics. Because of unsaturated alkyl of cardanol, hydrogenated cardanol has been reported 21 as antioxidant additive for cotton biodiesel in order to confer higher thermo-oxidative stability. Due to the harsh conditions, such as higher temperature, higher pressure, expensive catalysts and flammable hydrogen gas, hydrogenation reactions have been concerned. As well as the unsaturated alkyl chain of cardanol might weaken the oxidative stability. The present work reports the synthesis of epoxidized cardanol (ECD) (Scheme 1) and its anti-oxidative properties as additive for vegetable oil and biodiesel. ECD was

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characterized by FT-IR, 1H-NMR and 13C-NMR. The oxidative stability of vegetable oils and biodiesels with ECD as additive is evaluated by the pressurized differential scanning calorimetry (PDSC) and the Rancimat method. The antioxidant activity of ECD was comparable to that of 2,6-di-tert-butyl-4-methylphenol (BHT), a synthetic antioxidant.

Scheme 1. The compounds used in this study and the conversion of cardanol into ECD.

EXPERIMENTAL SECTION Materials. Cardanol was supplied by Shanghai Meidong Biological Materials Co., Ltd. (Shanghai, China) and was purified by distillation using a Pascal 2105 SD vacuum pump (Asslar, Germany) at 220-230 °C under 3-5 Torr. The product obtained was pale yellow in color and contained 3.6% triene, 62.1% diene, 25.7% monoene, and 3.1% saturated compounds. Toluene (99%), p-toluenesulfonic acid (98%), formic acid (88%) and hydrogen peroxide (30%) were purchased from Sigma-Aldrich Co. (St.

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Louis, MO, USA). 2,6-di-tert-butyl-4-methylphenol (BHT) was purchased from Sigma-Aldrich Co. (St. Louis, MO, USA). Soybean oil (SO-5) was purchased from Purdue Farms Inc., Refined Oil Division (Salisbury, MD, USA). Olive oil, Sunflower oil, Peanut oil, Canola oil, Corn oil, Sesame oil, Cotton seed oil obtained from commercial sources (Liberty Vegetable Oil Co., Santa Fe Springs, CA, USA). Methyl oleate and methyl linoleate, ˃99% were purchased from Nu- Chek Prep Inc. (Elysian, MN, USA). Synthesis of ECD. To a 250 ml flask equipped with a magnetic stirrer, reflux condenser and thermometer, cardanol (5.00 g, 17 mmol), formic acid (0.78 g, 15 mmol), p-toluenesulfonic acid (0.1 g, 0.58 mmol), and toluene (5.00 g, 54 mmol) were charged. The mixture was slowly heated to 50 °C and 30% hydrogen peroxide (5.78 g, 51 mmol) was added dropwise. The reaction was allowed to continue at 65 °C for 3 h. After the reaction was complete, the crude product was filtered and washed with a 5 wt% sodium bicarbonate and distilled water, respectively. Then the organic phase was dried with anhydrous sodium sulfate. Finally, toluene was removed by distillation under vacuum at 65 °C for 3 h and 4.60 g yellowish liquid was obtained (yield: 82% relative to cardanol). The ECD product has an epoxy value of 4.67%, an acid value of 0.62 mg/g, I2 value of 12 g/100g and the number of hydroxyl group with 151 mg KOH/g, respectively. Characterizations. Fourier transform infrared (FTIR) analysis was conducted using a Thermo Nicolet Nexus 470 spectrometer (Thermo Scientific, Madison, WI, USA). The samples were scanned from 4000 to 500 cm−1. 1H and 13C NMR spectra of

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the compounds in deuterated chloroform (CDCl3) were recorded with a Bruker 400 MHz spectrometer (Bruker, Rheinstetten, Germany) at room temperature. Pressurized DSC (PDSC) experiments were carried out using a DSC 2910 thermal analyzer from TA Instruments (New Castle, DE, USA). Typically, a 2 µl samples was placed in an aluminum pan hermetically sealed with a pinhole lid and oxidized in the presence of reactant gas (dry air). Dry air (Gateway Airgas, St. Louis, MO, USA) was used to pressurize the module at a constant pressure of 1379 kPa(200 psi). A heating rate of 10 °C/min from room temperature to 300 °C was used during the experiments. The oxidation onset temperature (OT) was calculated from the exotherm in each case. The oxidative stability of biodiesel with and without antioxidants was determined using a model 873 Rancimat equipment (Metrohm, Herisau, Switzerland) at 110 °C according to the standard EN 14112.22 Generally, 3 g of the samples were used in the experiments. Induction Period (IP) was determined from the inflexion point of the conductivity curve. RESULTS AND DISCUSSION The Characterizations of ECD. FT-IR technique was employed first to study the structures of cardanol and ECD. The FI-IR spectra of cardanol and ECD are depicted in Figure 1. In the spectrum of cardanol, there are several typical peaks: the phenolic hydroxyl group (3336 and 1347 cm-1 ), C-H stretching of the inner unsaturated moiety (3008 cm−1), methyl, methylene and methine groups (2925, 2851 and 1453cm−1), C=C on aromatic ring (1595 cm−1), symmetric and asymmetric stretching of C=C (1261 cm−1, 1149 cm−1), vibration of the four hydrogen atoms adjacent to the benzene

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ring (778 cm−1, 691 cm−1).23, 24 In the spectrum of ECD, there are also some characteristic peaks: the phenolic hydroxyl group (3358 and 1347 cm-1 ), methyl and methylene (2925 and 2851 cm-1), epoxy group (823- 917cm−1). And two obvious changes are observed in the spectrum of ECD. First, the peak of C-H in the inner unsaturated moiety at 3008 cm−1 is absent because of the conversion to epoxide.23 Second, the characteristic features of the epoxy group are found at 823, 871 and 917cm−1. Furthermore, the typical peak of phenolic hydroxyl group still exists. These indicate that cardanol had been converted into ECD.

Figure 1. FT-IR spectra of cardanol and ECD.

Figure 2 and Figure 3 display the 1H NMR and 13C NMR spectra of cardanol and ECD, respectively. The characteristic peaks at 6.6-7.3 ppm correspond to the protons on the benzene ring. Compared to the spectra of cardanol (Figure 2(a) and ECD (Figure 2(b), the peaks at 5.4 ppm, corresponding to the proton of -CH=CH- in Figure 2 (a), have almost disappeared in Figure 2 (b). This indicates that the unsaturated

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double bonds on the alkyl chain have been converted into epoxy groups during the epoxidation. The phenolic hydroxyl group at 5.2 ppm is still observed. Additionally, the new peaks at 2.9-3.2 ppm indicate epoxy groups in ECD. Furthermore, the changed chemical shift of the peaks at 1.3-1.8 ppm also supports the formation of epoxidized groups. The 13C NMR peaks at 114.7-137.1 ppm are present in Figure 3(a) assigned to carbons 11, 13 and 14 in Fig, 3(a) have disappeared in Figure 3(b). Likewise, the epoxy groups distinguish between cardanol and ECD with the new peaks at 54.5 - 54.7 ppm corresponding to the carbons in the epoxy group.25

Figure 2. 1H NMR spectra of (a) cardanol and (b) ECD.

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Figure 3. 13C NMR spectra of (a) cardanol and (b) ECD.

Antioxidant capacity of ECD in vegetable oils. The oxidation data of the vegetable oils with and without antioxidant were studied using PDSC. Figure 4 shows the thermograms of soybean oil with ECD contents at 0%, 0.2%, 0.5%, 0.7% and 1.0% by weight. The onset temperature profiles of oxidation (OT) for these samples are shown in Table 1. During the temperature ramping sequence an exothermic release of heat was observed, indicating the occurrence of oxidation. With increasing content of ECD, the OT increased from 141.7 °C to 142.9 °C, 148.0 °C, 151.3 °C and 158.9 °C with ECD concentration at 0.0, 0.2, 0.5, 0.7 and 1.0 by weight percent, respectively. The antioxidant additive of ECD responded very well to soybean oil and increased its OT by nearly 10 °C with 0.7 wt.% ECD.

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Figure 4. PDSC profile of oxidative stability of soybean oil with different ECD contents.

Table 1. Effect of the ECD content on oxidation stability of soybean oil.

Sample

OT-0 ad (°C)a

OT-0.2 ad (°C) a

OT-0.5 ad (°C) a

OT-0.7 ad (°C) a

OT-1.0 ad (°C) a

Soybean oil

141.7

142.9

148.0

151.3

158.9

a

OT-0 ad means no ECD added, OT-0.2 ad means 0.2% (w/w) ECD added, OT-0.5 ad means 0.5%

(w/w) ECD added, OT-0.7 ad means 0.7% (w/w) ECD added, OT-1.0 ad means 1.0% (w/w) ECD added.

Figure 5 and Table 2 show the OT results obtained from PDSC programmed temperature experiments for vegetables oils with 0.7 wt.% antioxidant ECD. The vegetable oils show different oxidation stabilities because of their fatty acid profiles. It was also observed that the vegetables oil samples show significantly higher oxidative stability with the addition of ECD. For example the OT of oxidation for olive oil without antioxidant additives was found to be 165.1 °C compared to the

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OT of it with ECD at 184.6 °C, with a difference of 19.5 °C. The OT for Cotton seed oil without antioxidant additives shows at 173.2 °C compared to OT of the sample with ECD at 182.0 °C, the difference is only 8.9 °C. The reason for these differences is the varying content of unsaturated, especially polyunsaturated fatty acids, in the fatty acid profiles of these oils.

Figure 5. PDSC profile of oxidation stability of vegetable oils with and without ECD. Table 2. Effect of the ECD on oxidation stability of vegetable oils

Samples

OT (°C)

OT-0.7 ad (°C) a

∆OT (°C) b

Olive oil

165.1

184.6

19.5

Sunflower oil

172.9

189.3

16.4

Peanut oil

179.6

194.0

14.4

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Canola oil

148.5

161.8

13.3

Corn oil

166.9

177.0

10.1

Soybean oil

141.7

151.3

9.6

Sesame oil

165.2

174.5

9.4

Cotton seed oil

173.2

182.0

8.9

a

OT-0.7 ad means 0.7% (w/w) ECD added. b means the difference between the OT of vegetable

oils with and without ECD.

Antioxidative capacity of ECD in biodiesels. Figure 6 shows the effect of ECD on the oxidative stability of biodiesel and compared with BHT. The antioxidant concentration was at 1000 ppm. According to the results of induction period (IP) by the Rancimat method, the addition of the ECD significantly increased the IP value of methyl oleate, with an oxidative stability higher than 50 minutes. In comparison, the antioxidant BHT increased the oxidative stability close to 40 minutes. ECD improved resistance to oxidation of biodiesel by the donation of phenolic hydrogen to the free radical formed early in the oxidative process as seen in Figure 7.26-29 The long alkyl chain of ECD could also improve the miscibility with biodiesel. In order to develop the better understanding of structural effect of the cardanol based antioxidants on their antioxidant properties, in the future research, the alkylated cardanol with ter- butyl groups has been selected as a comparative compound to investigate its antioxidant capacity.

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Figure 6. Induction periods obtained by the Rancimat method of the biodiesels with and without

antioxidants.

Figure 7. The mechanism of radical scavenging for ECD.

Thermal stability of ECD. Figure 8 shows the TGA curves of cardanol and ECD heated in nitrogen at the rate of 10 °C/min. The decomposition temperatures of the samples were obtained from TGA curves and are reported in Table 3. It can be observed that 10% weight loss (T10) and 50% weight loss (T50) of cardanol happened at 218.7 and 259.5 °C, and the temperature is greatly enhanced to 263.6 and 426.1 °C

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for the ECD as a comparison. Moreover, the decomposition rate of cardanol is apparently faster than that of ECD. Since a higher decomposition temperature suggests a higher thermal stability of the sample, 30 the ECD shows significant higher thermal stability than cardanol. Carbon residue rate of cardanol and ECD are 0.71% and 3.20%, illustrating more localized carbonization was formed on the surface of ECD, which makes it more thermally stable. These results indicate the ECD is more suitable for application at higher temperature, which is in good agreement with the oxidative stability results mentioned above.

Figure 8. TGA curves of Cardanol and ECD at nitrogen atmosphere.

Table 3. TGA thermal stability data on Cardanol and ECD samples

Samples

T10 (°C)

T50 (°C)

Carbon residue rate at 600 ℃ (%)

Cardanol

218.7

259.5

0.7

ECD

263.6

426.1

3.2

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CONCLUSIONS In this study, cardanol-derived antioxidant ECD was synthesized and characterized by FT-IR, 1H-NMR and 13C-NMR. The antioxidant activity of ECD was investigated by PDSC and Rancimat methods. By using antioxidant additives, the soybean oil samples responded very well and increased their OT by nearly 10 °C with 0.7 wt.% ECD. The results also showed that adding 0.7% (w/w) ECD significantly enhanced oxidative stability of the other vegetable oils. Furthermore, the ECD is superior to the synthetic oxidant BHT, and thus could be used as an optimized antioxidant for biodiesel. In addition, TGA indicated that ECD shows significantly higher thermal stability than cardanol. Due to the long alkyl chain and epoxy group that endow the ECD with good solubility and good thermal stability, as well as its anti-oxidation potential, the ECD could be used as bio-based antioxidant.

AUTHOR INFORMATION Corresponding Author * Zengshe Liu, Bio-Oils Research Unit, National Center for Agricultural Utilization Research, Agricultural Research Service, U.S. Department of Agriculture, 1815 North University Street, Peoria, Illinois 61604, United States. E-mail: [email protected]; Tel.:+1 309 681 6104; Fax: +1 309 681 6524.

Notes §

Mention of trade names or commercial products in this publication is solely for the

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purpose of providing specific information and does not imply recommendation or endorsement by the U.S. Department of Agriculture. USDA is an equal opportunity provider and employer. ◊

Jie Chen is a visiting scholar at U.S. Department of Agriculture and contributes to

this paper same as the first author. ACKNOWLEDGMENTS Jie Chen is grateful to the financial support from National “Twelfth Five-Year” Plan for Science & Technology Support (grant number: 2015BAD15B08) and Basic research funding earmarked for the national commonweal research institutes, CAF (grant number: CAFINT2014C12). The authors also gratefully acknowledge Mr. Daniel Knetzer for help in PDSC analysis and Mr. Kevin Steidley for help in Rancimat test. REFERENCES (1) Kumar, P.P.; Paramashivappa, R.; Vithayathil, P.J.; Rao, P.V.S.; Rao, A.S.. Process for Isolation of Cardanol from Technical Cashew ( Anacardium occidentale L.) Nut Shell Liquid. J.agric.food Chem. 2002, 16, 4705-4708. (2) Castro, D. T. N; Dantas, M. S. G.; Dantas, N. A.. Novel antioxidants from cashew nut shell liquid applied to gasoline stabilization. Fuel 2003, 12, 1465-469. (3) Cornelius J. A. Cashew nut shell liquid and related materials. Trop. Sci.. 1966, 8, 79-84. (4) Tagliatesta, P.; Crestini, C.; Saladino, R.; Neri, V.; Filipone, P.; Fiorucci, C.; Attanasi O. A.. Manganese and iron tetraphenylporphyrin-catalyzed oxidation of a cardanol derivative (hydrogenated tert-butylcardanol). J. Porphyrins. Phthalocyanines. 2002, 6, 12-16. (5) Attanasi, O. A.; Filippone, P.; Balducc, S.. Effect of metal ions in organic synthesis. XXXV: simple and convenient aromatic alkylation of some alkenylphenol derivatives with tert-alkyl methyl ethers in the presence of tin (IV) chloride. Gazz. Chim. Ital. 1991, 121, 487-489. (6) Attanasi, O. A.; Filippone, P.; Grossi M.. Synthesis of some phosphorus derivatives of cardanol. Phosphorus. Sulfur Silicon Relat. Elem. 1988, 35, 63-65. (7) Pillai, R.; Antony, C. K. S.; Scariah, K. J.. GPC studies on the cationic

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epoxy, benzoxazine monomer system from cardanol: Thermal and viscoelastic properties. Eur. Polym. J. 2013, 8, 2365-2376. (24) Souza J. F.G.; Pinto, J.C.; Oliveira, G.E.; Soares, B.G.. Evaluation of electrical properties of SBS/Pani blends plasticized with DOP and CNSL using an empirical statistical model. Polym. test 2007, 6, 720-728. (25) Semsarzadeh, M.A.; Mehrabzadeh, M.; Arabshahi, S.S.. Dynamic mechanical behavior of the dioctyl phthalate plasticized polyvinyl chloride-epoxidized soya bean oil. Eur. Polym. J. 2002, 2, 351-358. (26) Du, L.; Yu, P.; Rossnagel, B.G.;Christensen, D.A.; Mckinnon, J.J. Physicochemical characteristics, hydroxycinnamic acids (ferulic acid, P-coumaric acid) and their ratio, and in situ biodegradability: comparison of genotypic differences among six barley varieties. J.agric.food Chem. 2009, 11, 4777-4783. (27) Roche, M.; Dufour, C.; Mora, N.; Dangles, O.. Antioxidant activity of olive phenols: mechanistic investigation and characterization of oxidation products by mass spectrometry. Org.biomol.chem. 2005, 3, 423-430. (28) Ramalho, V.C.; Jorge, N.. Antioxidantes utilizados em óleos, gorduras e alimentos gordurosos. Química Nova 2006, 4, 755-760. (29) Robbins, R.J.. Phenolic Acids in Foods: An Overview of Analytical Methodology. J. Agr. Food Chem. 2003, 10, 2866-2887. (30) Wu, Y.; Li, W.; Zhang, M.; Wang, X.. Improvement of oxidative stability of trimethylolpropane trioleate lubricant. Thermochim. Acta 2013, 40, 112-118.

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ACS Sustainable Chemistry & Engineering

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Synthesis of epoxidized cardanol and its antioxidative properties for vegetable oils and biodiesel

Zengshe Liu*a, Jie Chenb, ◊, Gerhard Knothea, Xiaoan Nieb, and Jianchun Jiangb

Synopsis: A novel cardanol derivative, epoxidized cardanol, was successfully prepared and applied as an antioxdant for vegetable oils and biodiesel. Because the cardanol is from renewable resource, this research relates to sustainability.

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