Industrial Crops and Products 33 (2011) 132–139

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Industrial Crops and Products

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Synthesis and physical properties of petroselinic based estolide estersଝ

Steven C. Cermak a,∗, Terry A. Isbell a, Roque L. Evangelista a, Burton L. Johnson b a Bio- Research, National Center for Agricultural Utilization Research, USDA, Agricultural Research Service, 1815 N. University St., Peoria, IL 61604, USA b Department of Plant Sciences, North Dakota State University, Fargo, ND 58108, USA article info abstract

Article history: A new series of petroselinic (Coriandrum sativum L.) based estolide 2-ethylhexyl (2-EH) were syn- Received 14 July 2010 thesized, as the capping material varied in length and in degrees of unsaturation, in a perchloric acid Received in revised form catalyzed one-pot process with the esterification process incorporated into an in situ second step to pro- 20 September 2010 vide the coriander estolide 2-EH . The kinematic viscosities ranged from 53 to 75 cSt at 40 ◦C and Accepted 22 September 2010 9.1 to 14.6 cSt at 100 ◦C with a viscosity index (VI) ranging from 151 to 165. The caprylic (C8) capped coriander estolide 2-EH ester had the lowest low-temperature properties (pour point = −33 ◦C and cloud point = −33 ◦C), while the coco-coriander estolide 2-EH ester produced an estolide with modest low- Keywords: − ◦ − ◦ Cloud point temperature properties (pour point = 24 C and cloud point = 25 C). The coco-coriander estolide 2-EH Coriander ester was explored for the ability to resist oxidative degradation with the use of an biodegradable additive Estolides package added in 1.5%, 3.5%, or 7.0% units based on weight. The oxidative stability increased as the amount Pour point of stability package increased (rotating pressurized vessel oxidation test (RPVOT) times 65–273 min). RPVOT Along with expected good biodegradability, these coriander estolide 2-EH esters had acceptable proper- Viscosity ties that should provide a specialty niche in the U.S. as a biobased lubricant. Published by Elsevier B.V.

1. Introduction and is used in detergent applications. With the potential of coriander becoming a biobased feedstock in the near future other Coriandrum sativum L., belonging to the family Umbelliferae industrial applications of the must be explored and/or expanded. (Apiaceae), commonly known as Chinese parsley or cilantro is Most new crops require a high value of return, and thus initially grown for its leaves (Zheljazkov et al., 2008; Kiralan et al., 2009). may be developed for high value applications such as cosmetic or Coriander is native to southern Europe and North Africa and south- specialty lubricants. Estolides have allowed new crop oils to be eas- western Asia (Ramadan and Mörsel, 2002). Coriander seeds have a ily incorporated into a variety of potential products. To date, the lemony citrus flavor when crushed, due to the presence of the ter- best performing estolides are produced from oleic (18:1) sources penes linalool and pinene. The seeds have many uses as a spice in (Cermak and Isbell, 2000, 2003, 2004; Cermak et al., 2007) such as food applications, in pickling vegetables, making sausages in Ger- sunflower, canola, or soybean. many as well as used in brewing certain styles of beer, Belgian Estolides have been used to help develop new products from wheat beers in particular (Vanderhaegen et al., 2003). industrial crops (Cermak and Isbell, 2000; Isbell et al., 2000). Coriander seeds contain oil that is rich in petroselinic acid (18:1 Estolides are formed through the formation of a carbocation at the n-12) (74%) with lesser amounts of (18:1 n-9) (7%), carbon carbon double bond position that subsequently undergoes Table 1. Petroselinic has many potential uses as an industrial raw nucleophilic addition with or without carbocation migration along base chemical with the most promising application supplying the the length of the chain. The carboxylic acid functionality of one chemical industry with adipic and lauric acids via oxidative cleav- links to the site of unsaturation of another fatty acid to age of the 6 double bond in petroselinic acid (Isbell et al., 2006). form oligomeric esters. The extent of oligomerization is reported Adipic acid is commonly used as a monomer for nylon synthesis by estolide number (EN) which is defined as the average number of fatty acids added to the base fatty acid. The estolide carboxylic acid functionality can be converted in situ under esterification con- ditions with the addition of an alcohol to yield the corresponding ଝ Names are necessary to report factually on available data; however, the USDA estolide ester (Fig. 1). neither guarantees nor warrants the standard of the product, and the use of the Estolides have been developed to overcome some of the short name by USDA implies no approval of the product to the exclusion of others that falls associated with vegetable oils which are known to have poor may also be suitable. ∗ thermal oxidative stability (Cermak and Isbell, 2003) and low tem- Corresponding author. Tel.: +1 309 681 6233; fax: +1 309 681 6524. E-mail address: [email protected] (S.C. Cermak). perature properties (Asadauskas and Erhan, 1999). Some of these

0926-6690/$ – see front matter. Published by Elsevier B.V. doi:10.1016/j.indcrop.2010.09.012 S.C. Cermak et al. / Industrial Crops and Products 33 (2011) 132–139 133

Table 1 Chemical compositions of coriander and coconut fatty acids.

FA (%)a

8:0 10:0 12:0 14:0 16:0 18:0 18:1 18:2 18:3

Coriander – 0.5 – – 3.4 0.8 81.3b 14.0 – Coconut 5.1 4.9 48.3 21.7 10.6 7.0 2.4 – –

Dash indicates not detected. a Determined by GC (SP-2380, 30 m × 0.25 mm i.d.). b 73.5% n-12 (petroselinic), 6.9% n-9 (oleic), and 0.9% n-7 (vaccenic). deficiencies inherent to vegetable oils can be reduced with the use synthesis and physical properties of a series of petroselinic-based of additive packages, but usually at the sacrifice of biodegradability, estolide esters as well as relate estolide linkage position to the per- toxicity, and cost. formance of these new petroselinic-based estolide esters to past A number of in-depth studies on estolide structure versus phys- oleic-based estolides and commercially available materials. ical properties have been conducted over the years (Isbell et al., 2001; Cermak and Isbell, 2009). The length of the base unit was determined with the optimization of low temperature properties. 2. Materials and methods The capping fatty acids were modified to include different lengths and different levels of unsaturation into the capping of the estolide. 2.1. Materials The size or EN of the estolide was varied as the low tempera- ture properties were measured. In all cases explored thus far, the Oleic acid (90%) was purchased from Aldrich Chemical Co. (Mil- estolide structure has a direct correlation to the physical properties waukee, WI). Ethyl acetate, hexanes, acetone, perchloric acid (70%), of estolides. and 2-ethylhexyl alcohol were purchased from Fisher Scientific Co. With the ability to use fatty acids from coriander in the synthesis (Fairlawn, NJ). Potassium hydroxide was obtained from J.T. Baker of estolides, the question we would like to explore is what effect the Chemical Co. (Phillipsburg, NJ). Filter paper was obtained from position of the estolide linkage point will have on estolide physical Whatman (Clifton, NJ). Acetonitrile and (both for HPLC) properties. The simple oleic estolide, oleic-oleic estolide 2-EH ester were obtained from EM Science (Gibbstown, NJ). Ethanol was pur- (Isbell and Kleiman, 1994), has the estolide linkage at primarily chased from AAPER Alcohol and Chemical Company (Shelbyville, the (18:1 n-9) and (18:1 n-10) positions (Fig. 2). Petroselinic-based KY). The fatty acid methyl ester (FAME) standard mixtures were estolides would have the estolide linkage at primarily the (18:1 obtained from Alltech Associates, Inc. (Deerfield, IL). Solvents for n-12) and (18:1 n-13) positions which would bring the two ester chromatography and extraction were HPLC grade or an equiva- functional groups substantially closer together at the intramolecu- lent, and were used without further purification. Oxidative stability lar level. package, Lubrizol® 7652, was obtained from the Lubrizol Corpo- Strong correlations between estolide structure and physical ration (Wickliffe, OH). Soy based oil: Biosoy® was obtained from properties have allowed for the ability to develop or synthesize the University of Northern Iowa (Cedar Falls, IA). Petroleum oil: estolides that exceed the properties of commercially available Mobil® 10W-30 and synthetic oil: Penzoil Synthetic® 10W-30, and industrial products such as petroleum-based hydraulic fluids, soy- hydraulic fluid: Traveler Universal Hydraulic Fluid® were obtained based fluids, and petroleum oils thus far. In this paper we report the from local vendors.

O

OH Coriander Fatty Acid

O o 1. HClO4, 60 C, 24hr, vacuum OH 2. 2-Ethylhexanol, 60oC, 3hr, vacuum Coco-Fatty Acids 3. KOH, 30min

O EN = n + 1 O O

O O 4 n

4 O

Saturated-Capped Coriander Estolide 2-EH Ester

Fig. 1. Synthesis of saturated-capped coriander estolide 2-ethylhexyl ester. 134 S.C. Cermak et al. / Industrial Crops and Products 33 (2011) 132–139

O

Capping Group O O

Base Unit O 7

Estolide Linkage Saturated-Capped Oleic Estolide 2-EH Ester

O

Capping Group O O

Base Unit O 4

Estolide Linkage

Saturated-Capped Petroselinic Estolide 2-EH Ester

Fig. 2. Oleic versus petroselinic estolides.

2.2. Coriander Piqua, OH). The cooked and dried seed was pressed immediately using a heavy-duty laboratory screw press (Model L250, French Oil 2.2.1. Coriander seed production Mill Machinery Company, Piqua, OH). The crude oil was allowed to Agronomic procedures for field production of coriander (C. settle before it was filtered through No. 54 Whatman filter paper. sativum L.) followed standard procedures at Prosper, ND (46◦58N, The crude coriander seed oil (350 g, 559 mmol) was hydrolyzed 97◦3W; elevation 284 m) during the 2006 and 2007 growing sea- by the addition of 2.0 M KOH/EtOH (112 g of KOH in 1 L 95% ethanol) sons. A bulk seed increase of coriander was sown 2.5 cm deep at followed by heating to reflux for 60 min. After cooling to room tem- 22 kg/ha pure live seed near 27 May both years. Soil type at the perature, the reaction mixture was placed in a 6 L Erlenmeyer with Prosper location is a complex of Bearden/Perella silty-clay loam 1 L of hexane and cooled in an ice bath. A 1 M HCl solution (∼2.1 L) (Bearden: fine-silty, mixed, superactive, frigid Aeric Calciaquolls; was slowly added to the cooled hydrolysis mixture with overhead Perella: fine-silty, mixed, superactive, frigid Typic Endoaquolls). stirring. Addition was maintained until the solution was slightly The soil is of lacustrine origin and characterized with moderate acidic, as measured by pH paper. The mixture formed an emulsion organic matter levels, generally high cation exchange capacity, and as the transition occurred. The pH of the organic layer was adjusted high water holding capacity and plant available water. to 5.3–6.0 with the aid of a pH 5 buffer (NaH2PO4,519gin4LH2O, The previous crop both years was hard red spring wheat 2 × 100 mL). The organic layer was removed, dried over sodium sul- (Triticum aestivum L.) grown under conventional tillage consisting fate, and filtered. All reactions were concentrated in vacuo and then of fall chisel plowing and a single spring cultivation/harrow oper- kugelrohr-distilled at 160–190 ◦C at 0.013–0.067 kPa to purify the ation prior to coriander seeding. Nitrogen fertility was adjusted fatty acids. A small sample of the fatty acids was then esterified to to target a 2688 kg/ha hard red spring wheat yield. Soil phospho- the corresponding methyl ester under conditions described above rus and potassium levels were adequate for the targeted wheat to yield the coriander fatty acid profile, Table 1. yield and did not require any additional fertilizer amendments. The coriander plot was approximately 0.3 ha each year and seeded with 2.3. General coriander estolide 2-ethylhexyl ester synthesis a plot seeder with double-disk openers and two vee-packer wheels. Row spacing was 30 cm with six rows seeded per planter pass across An acid-catalyzed condensation reaction was conducted with- the plot area. out solvent in a 500 mL round bottom flask that had been Stand emergence was approximately 10 days after seeding and pre-treated with an acidic wash. Coriander fatty acids (100.0 g, ranged from 65% to 90% among years. Flowering occurred 60 days 354.6 mmol) and capping fatty acids, i.e. oleic acid (50.0 g, after seeding; plant height was 103 cm; and plant lodging was high 177.3 mmol) were combined together, heated to 60 ◦C under house at 4.3 on a scale from 0 to 5. There were few pest issues other than vacuum (7.5–10.9 kPa), and stirred with a Teflon coated stir bar. some annual grass and broadleaf weeds that occurred later in the Once the desired temperature of 60 ± 0.1 ◦C was reached, per- season when the pre-plant soil incorporated herbicide trifluralin chloric acid (26.6 mmol, 2.30 mL, 0.05 eq.) was added, vacuum began to lose effectiveness. Harvest was performed directly with restored, and stirred. After 24 h, 2-ethylhexyl alcohol (208.0 g, a plot combine at harvest maturity with seed collected in cloth 1.60 mol, 235.4 mL) was added to the vessel, vacuum was restored, sacks and aerated in a grain dryer at ambient temperatures for 7 d. and the mixture was stirred for an additional 3–4 h. The com- Seed yield was low to moderate at approximately 1000 kg/ha with pleted reactions were quenched by the addition of KOH (1.64 g, a 1000-seed weight of 9.3 g. 29.2 mmol, 1.2 eq. based on HClO4) in 90% ethanol/water (10 mL) solution. The solution was allowed to cool with stirring for 45 min 2.2.2. Coriander seed cleaning, dehulling, press, and hydrolysis followed by filtration through a Buchner funnel with Whatman The coriander seeds were cleaned by screening and aspirating #1 filter paper. The organic layer was dried over sodium sulfate and then dehulled using and impact huller (Model 15-D, Fors- and filtered through a Buchner funnel with Whatman #1 filter bergs Inc., Thief River Falls, MN). The dehulled seeds contained paper. All reactions were concentrated in vacuo then kugelrohr- 26% oil (dry basis). The dehulled seed was cooked (180–200 F) and distilled 90–110 ◦C at 6–13 kPa to remove any excess ethanol dried to around 5% moisture content using a laboratory seed con- and 2-ethylhexyl alcohol. The residue was further distilled by ditioner/cooker (Model 324 French Oil Mill Machinery Company, kugelrohr-distillation 180–200 ◦C at 6–13 kPa to remove any unre- S.C. Cermak et al. / Industrial Crops and Products 33 (2011) 132–139 135

Table 2 Characterization of a series of coriander estolide 2-ethylhexyl esters.

Estolide Capping fatty acid Fatty acid # (EN)a (IV)b Cappedc (%) Acid value (mg/g)

A None None 1.64 31.5 8.8 1.85 B Caproic 6:0 1.87 23.0 28.3 3.78 C Caprylic 8:0 1.88 17.6 44.4 5.42 D Capric 10:0 1.59 19.3 45.4 4.22 E Lauric 12:0 1.46 18.7 49.6 1.69 F Myristic 14:0 1.64 13.1 61.9 0.92 G Palmitic 16:0 1.33 18.3 53.4 3.85 H Stearic 18:0 1.11 18.7 57.1 4.82 I Oleic 18:1 1.91 28.0 10.0 1.15 J Coco –d 1.40 21.0 45.6 1.66

a Estolide number—see Fig. 1. b Iodine value. c Percent of estolide saturated-capped. d Mainly C12:0—see Table 1. acted saturated and unsaturated fatty acids and by-products, such acetone) was used to follow the reaction which provided informa- as lactones (Cermak and Isbell, 2001) and 2-EH esters (monomers). tion on the overall reaction progress. The ELSD drift tube was set ◦ The percent yield of the estolide 2-EH esters reported in Table 2 at 55 C with the nebulizer set at 20 psi (138 kPa) N2, providing a were modest at 65–76% and similar to past synthesized estolides flow rate of 2.0 standard liters per minute (SLPM). Retention times (Cermak and Isbell, 2001, 2004). Estolides for example when for eluted peaks: estolides, 10.3–13.9 min and starting fatty acids, defined as an lauric capped oleic estolide, means that the estolides 5.4–5.9 min. are capped with an lauric, oleic, and also some are capped with Thermo Separations Spectra System AS1000 autosam- the saturates found in the oleic material as well as any fatty acid pler/injector (Fremont, CA) with a P2000 binary gradient pump contaminates in the lauric material. This same purity issues are from Thermo Separation Products (Fremont, CA) coupled to an applicable to coriander. Alltech ELSD MKIII evaporative light scattering detector (Alltech Associates, Deerfield, IL) was used for normal phase-HPLC analysis 2.4. Equipment and procedures of the esterification step. A silica normal phase analysis was carried out with a Dynamax column (250 mm × 4.6 mm, 8 ␮m) 2.4.1. Characterization from Rainin Instrument Co. (Woburn, MA). Components were 2.4.1.1. Gas chromatography (GC). Hewlett-Packard 6890N Series eluted isocratically from the column with a 4:1 (hexanes:acetone) gas chromatograph (Palo Alto, CA) equipped with a flame- mixture at a flow rate of 1 mL/min, with the ELSD drift tube set at ◦ ionization detector and an autosampler/injector was used for GC 55 C with the nebulizer set at 20 psi (138 kPa) N2, providing a flow analysis. Analyses were conducted on a SP-2380 30 m × 0.25 mm rate of 2.0 standard liters per minute (SLPM). Retention times for i.d. column (Supelco, Bellefonte, PA). Saturated C8–C30 FAMEs pro- eluted peaks: estolide-2-ethylhexyl esters, 2.8–2.9 min; and free vided standards for making fatty acid and by-product assignments. acid estolide, 3.8–3.9 min. Parameters for SP-2380 analysis were: column flow 1.4 mL/min with a helium head pressure of 136 kPa; split ratio 50:1; pro- 2.4.1.4. Iodine values (IVs) and estolide numbers (ENs). Iodine values grammed ramp 120–135 ◦Cat10◦C/min, 135–175 ◦Cat3◦C/min, (IVs) were determined from the GC results using AOCS Method Cd 175–265 ◦Cat10◦C/min, hold 5 min at 265 ◦C; injector and detector 1c-85 (Firestone, 1994). Estolide numbers (ENs) were determined ◦ temperatures set at 250 C. Saturated C8–C30 FAME provided stan- by GC from the SP-2380 column analysis as described previously dards for calculating ECL values, which were used to make FAME (Isbell and Kleiman, 1994). assignments. 2.4.1.5. GC analysis of hydroxy fatty acids. Analytical estolide sam- 2.4.1.2. GC–mass spectrometry (GC–MS). Hewlett-Packard 5890A ples for GC were prepared using procedures described by Cermak GC with a 30 m × 0.20 mm i.d. SPB-1 column (Supelco, Bellefonte, and Isbell (2001). PA) and a Hewlett-Packard 5970 mass selective detector was used for GC–MS analysis. GC conditions were helium head pressure 2.4.1.6. TMS derivatization of hydroxy fatty esters. Analytical 15 psi (103 kPa) at 170 ◦C set for constant flow with varying pres- estolide samples for GC were prepared using procedures described sure; split ratio 50:1; injector temperature set at 250 ◦C; transfer by Cermak and Isbell (2001). line temperature set at 250 ◦C; programmed ramp from 170 to ◦ ◦ 270 Cat3 C/min. MS conditions: mass range 50–550 amu; elec- 2.4.1.7. Nuclear magnetic resonance (NMR). 1H and 13C NMR spec- tron multiplier 200 V relative. tra were collected on a Bruker Avance 500 (Billerica, MA) spectrometer with a 5 mm BBI probe. All spectra were acquired at 2.4.1.3. High-performance liquid chromatography (HPLC). Thermo 300.0 K using CDCl3 as a solvent in all experiments. Chemical shifts Separations Spectra System AS1000 autosampler/injector (Fre- are reported as parts per million from tetramethylsilane with an mont, CA) with a P2000 binary gradient pump from Thermo absolute frequency 500.11 MHz. The assignments of protons were Separation Products (Fremont, CA) coupled to a Alltech ELSD 500 not to the whole number. The representative NMR sample con- evaporative light scattering detector (Alltech Associates, Deerfield, tained a compound that had an average estolide number of 1.40 for IL) was used for reverse phase-HPLC analysis. A C-8 reverse phase the estolide ester (J, Table 2) which made whole number assign- analysis used to separate reaction mixtures was carried out with ment impossible. The data reported for the number of protons in a Dynamax column (250 mm × 4.5 mm, 8 ␮m particle size) from the NMR reflect the actual numbers present in the reaction product. Rainin Instrument Co. (Woburn, MA). 1H and 13C NMR of coco-coriander estolide 2-ethylhexyl A 16 min run time (1 mL/min; 0–4 min 80% acetonitrile 20% ester J (Table 2). 1HNMR:ı 5.40–5.32 (m, 1.04 H, –CH CH–), acetone; 6–10 min 100% acetone; 11–16 min 80% acetonitrile 20% 4.89–4.82 (m, 1.22 H, –CH–O–(C O)–CH2–), 4.02–3.94 136 S.C. Cermak et al. / Industrial Crops and Products 33 (2011) 132–139

(m, 2.0 H, –O–CH2–CH(CH2–)CH2–), 2.34–2.19 (m, 5.08 H, estolide esters during the titration. All acid values were run in dupli- –CH2–(C O)–O–CH2–, –CH2(C O)–O–CH–), 2.08–1.24 (m, 72.02 H, cate and average values were reported. 13 –CH2–), and 0.91–0.86 ppm (m, 13.50 H, –CH3). CNMR:ı 173.9 (s, C O), 173.7 (s, C O), 173.6 (s, C O), 173.6 (s, C O), 130.9–130.0 2.4.2.6. Rotating pressurized vessel oxidation test. Test determina- (d,–CH CH–, very small signals, only a small amount of alkene tions were conducted on a rotating pressurized vessel oxidation present), 73.8 (d,–CH–O–C O), 73.8 (d,–CH–O–C O), 66.7 (t, test (RPVOT) apparatus manufactured by Koehler (Bohemia, NY) –O–CH2–CH–), 66.6 (t, –O–CH2–CH–), 66.6 (t, –O–CH2–CH–), 38.8 using the ASTM Method D 2272-98. Estolides and commercial prod- ◦ (d, –CH2–CH(CH2–)–CH2–), 33.8 (t), 34.0 (t), 34.1 (t), 34.1 (t), 34.2 ucts were run at 150 C. Samples were measured to 50.0 ± 0.5 g with (t), 34.3 (t), 34.3 (t), 34.4 (t), 34.4 (t), 32.6 (t), 32.4 (t), 32.2 (t), 31.9 5.0 mL of reagent water added to the sample. The copper catalyst (t), 30.4 (t), 29.7 (t), 29.6 (t), 29.6 (t), 29.5 (t), 29.5 (t), 29.4 (t), 29.3 was measured to 3 m and sanded with 220 grit silicone carbide sand (t), 29.3 (t), 29.2 (t), 29.1 (t), 29.1 (t), 29.0 (t), 28.9 (t), 25.3 (t), 25.2 paper produced by Abrasive Leaders and Innovators (Fairborn, OH) (t), 25.1 (t), 25.1 (t), 25.0 (t), 24.9 (t), 23.8 (t), 23.0 (t), 22.7 (t), 14.1 and was used immediately. The wire was wound to have an outside (q,–CH3), 14.0 (q,–CH3), and 11.0 ppm (q,–CH3). diameter of 44–48 mm and a weight of 55.6 ± 0.3 g and to a height of 40–42 mm. The bomb was assembled and slowly purged with oxygen twice. The bomb was charged with 90.0 ± 0.5 psi (620 kPa) 2.4.2. Properties of oxygen then tested for leaks by immersing in water. The test 2.4.2.1. Gardner color. Lovibond 3-Field Comparator from Tin- was complete after the pressure dropped more than 175 kPa below tometer Ltd. (Salisbury, England) using AOCS Method Td 1a-64 the maximum pressure. All samples were run in duplicate and the (Firestone, 1994) was used for Gardner color measurements. average time was reported. Gardner color, of both the residue and distillate materials, was mea- sured. The “+” and “−” notation was employed to designate samples 2.4.3. Statistical analysis that did not match one particular color. Standard curves were developed for the GC to determine the response factors for the different fatty acid chain lengths. Standard 2.4.2.2. Viscosity and viscosity index. Calibrated Cannon-Fenske vis- deviations for all the GC data were less than ±0.05. ORIGIN 7.0 was cometer tubes obtained from Cannon Instrument Co. (State College, used to make bar graphs. PA) were used to measure kinematic viscosity. Measurements were run in a Temp-Trol (Precision Scientific, Chicago, IL) viscometer 3. Results and discussion bath set at 40.0 and 100.0 ◦C. Viscosity and viscosity index were calculated using ASTM methods D 445-97 and ASTM D 2270-93, Estolides are formed from the cationic homo-oligomerization of respectively. Duplicate measurements were made and the average unsaturated fatty acids resulting from the addition of a fatty acid values were reported. carboxyl moiety across the olefin (Isbell et al., 1994). This conden- sation can continue, resulting in oligomeric compounds where the 2.4.2.3. Pour point. ASTM Method D97-96a was used to measure average extent of oligomerization is defined as the estolide num- pour points to an accuracy of ±3 ◦C. The pour points were deter- ber (EN = n +1, Fig. 1)(Isbell and Kleiman, 1994). When saturated mined by placing a test jar with 50 mL of the sample into a cylinder fatty acids are added to the reaction mixture, the oligomerization submerged in a cooling medium. The sample temperature was mea- terminates upon addition of the saturated fatty acid to the olefin sured in 3 ◦C increments at the top of the sample until the test since the saturate provides no additional reaction site to further material stopped pouring. This point is determined when the mate- the oligomerization. Consequently, the estolide is stopped at this rial in the test jar did not flow when held in a horizontal position for point from further rapid growth, thus we term the estolide as being 5 s. The temperature of the cooling medium was chosen based on “capped” (Cermak and Isbell, 2001). As the estolides increase in size, the expected pour point of the material. Samples with pour points the ability for individual polyestolides to link to each other becomes that ranged from (+9 to −6, −6to−24, and −24 to −42 ◦C) were less likely based on stearic interactions, therefore estolides do not placed in baths at different temperatures (−18, −33, and −51 ◦C), have rapid growth from the carboxylic acid site of the estolides. respectively. The pour point was defined as the coldest tempera- Coriander seeds were pressed for oil which was hydrolyzed fol- ture at which the sample still poured. All pour points were run in lowed by distillation to yield the corresponding petroselinic fatty duplicate and average values were reported. acids, shown in Table 1. Table 2 outlines a series of reactions (Fig. 1) that explored the formation of a new series of petroselinic (coriander) based estolide 2-EH esters. The type of capping mate- 2.4.2.4. Cloud point. ASTM Method D 2500-99 was used to mea- rial was varied (chain length) to include examples of both saturated sure cloud points to an accuracy of ±1 ◦C. The cloud points were and unsaturated capping materials as all other reaction param- determined by placing a test jar with 50 mL of the test sample into eters were held constant. The acid catalyzed process converted a cylinder submerged into a cooling medium. The sample tempera- ◦ the fatty acids to the free acid estolides under vacuum at 60 C ture was measured in 1 ◦C increments at the bottom of the sample followed by an in situ esterification under similar conditions to until any cloudiness was observed at the bottom of the test jar. yield the estolide 2-EH esters in modest yields. The final products The temperature of the cooling medium was chosen based on the underwent vacuum distillation to remove any excess 2-ethylhexyl expected cloud point of the material. Samples with cloud points alcohol, fatty acids, fatty esters, and other by-products, providing that ranged from (room temperature to 10, 9 to −6, and −6to−24, estolide 2-EH ester samples. The EN, iodine value (IV), percent of −24 to −42 ◦C) were placed in baths of temperature (0, −18, −33, estolide saturated-capped, and the acid value for the petroselinic and −51 ◦C), respectively. The cloud point was defined as the cold- estolides are reported in Table 2. These new coriander based est temperature at which the sample remained opaque. All cloud estolide 2-EH esters have a petroselinic acid backbone with a ter- points were run in duplicate and average values were reported. minal saturated capping group. Fig. 2 shows one such example of a saturated-capped petroselinic estolide 2-EH ester where the ter- 2.4.2.5. Acid value. 751 GPD Titrino from Metrohm Ltd. (Herisau, minal saturated capping group, saturated (C12:0) lauric (Table 2, Switzerland) was used for measurements. Acid values were deter- Estolide E). mined by the official AOCS Method Te 2a-64 (Firestone, 1994) with The saturated-capped % values in Table 2 were obtained from ethanol substituted for to increase the of the GC analysis of the estolide 2-EH esters which were saponified and S.C. Cermak et al. / Industrial Crops and Products 33 (2011) 132–139 137

Table 3 Physical properties of coriander estolide 2-ethylhexyl esters with various capping fatty acids.

Estolide Capping fatty acid Fatty acid # Pour point (◦C) Cloud point (◦C) Vis. @ 40 ◦C (cSt) Vis. @ 100 ◦C (cSt) Vis. index Gardner color

A None None −27 −27 74.5 12.2 162 11− B Caproic 6:0 −30 −33 58.0 10.2 165 15 C Caprylic 8:0 −33 −33 60.9 10.3 158 11− D Capric 10:0 −30 −33 54.4 9.6 162 9+ E Lauric 12:0 −27 −23 53.4 9.1 151 10+ F Myristic 14:0 −21 −14 62.9 10.8 163 10+ G Palmitic 16:0 −15 −9 58.1 10.1 162 9+ H Stearic 18:0 −12 −3 53.7 9.6 165 9+ I Oleic 18:1 −30 −32 92.8 14.6 164 7+ J Coco –a −24 −25 55.9 9.8 162 12−

a Mainly C12:0—see Table 1. esterified. The components of the GC were classified as one of the Additionally, the coco-oleic estolides synthesized in the past by following: unsaturated, saturated, and hydroxy fatty acids. The per- Cermak and Isbell (2001) had outstanding low temperature proper- cent saturated-capped was calculated from Eq. (1): ties as well as outstanding oxidative stabilities. The coco-coriander   estolide 2-EH esters (Estolide J, Table 3)hadaPPof−24 ◦C as com- molar % saturated fatty acids pared to −33 ◦C for the corresponding coco-oleic based-estolide × 100 = % saturated-capped 100 − molar % hydroxy fatty acids 2-EH ester. If the results from Table 3 are plotted against the oleic (1) based-estolide 2-EH ester PP data reported by Cermak and Isbell (2002) the advantage of one over the other is obvious (Fig. 3). In As the chain length increased, the percent of saturated-capped almost all cases the oleic based estolide 2-EH esters had superior estolide also increased. Caproic, C6:0, exhibited the least amount of or equal PP as compared to the coriander based estolide 2-EH esters. saturated capped material with only 28.3% while myristic, C14:0, The position of the estolide linkage must play an active role in the had 61.9% of the estolides capped with saturated materials while determination of the low temperature properties of these estolide the palmitic, C16:0, and stearic, C18:0, percentages decreased. The esters. saturated fatty acids were added to the reaction in a 2:1 excess as Table 3 shows no general trend of the Gardner color of the compared to the coriander base material. This trend suggests that estolides produced from coriander. Previous work reported by during estolide formation, the fatty acids added preferred to be of Cermak and Isbell (2009) showed that the same general results similar chain length regardless of the degrees of saturation due to were observed, with the caproic, C-6, producing the darkest capped either steric effects or solubility issues. estolide. In all cases the estolide 2-EH esters produced were from The IVs have shown to play a critical role on the physical prop- coriander fatty acids that came from oil that was not refined. The erties of the estolide. The IVs reported provide information on the extra color bodies could have come from the underfined oil or impu- amount of unsaturation located in the molecule. A number of fac- rities carried over in distillation. Generally, the Gardner colors of the tors influence the IVs of the estolide samples with the two greatest estolides could be improved by a double distillation of the corian- influences are from the amount of unsaturation and the EN of the der fatty acids prior to estolide formation. Color improvements estolide 2-EH ester. As the amount of saturation and/or estolide have been accomplished via an additional costly distillation step number increases the IV decreases; as unsaturation or possible for estolides previously synthesized. Estolides 2-EH esters where unsaturation is removed from the reaction sample. Past demonstra- improved from a Gardner color in the 10–11 range to a −6(Cermak tions have proven that lowering the iodine values of the estolides et al., 2007). dramatically improves the oxidative stability of the estolide 2-EH Not only are low temperature properties important for a esters as reported by Cermak and Isbell (2003). biobased material to be considered a lubricant, they must also Table 3 outlines the physical properties, viscosity, color, pour (PP) and cloud points (CP) of these new coriander based estolides. As the chain length of the saturated capping material decreased, the PP and CP were also decreased. With coriander as the base unit Coriander of the estolide, the lowest PP material was capped with caprylic, Coco C8:0, fatty acid (Estolide C, Table 3). The caprylic-capped coriander ◦ ◦ estolide 2-EH ester had a PP of −33 C and CP of −33 C. As the chain C18:1

length increased the low temperature properties for the coriander Capping Fatty Acid based estolides became less desirable (Estolide H, stearic capped Coriander Based Estolide C18:0 estolide, PP −12 ◦C and CP −3 ◦C). Oleic Based Estolide C16:0 Cermak and Isbell (2001, 2004) showed that complex oleic based estolides had the best low temperature properties when capped C14:0 with short chain, saturated fatty acids such as those present in cuphea and coconut. Previously, caprylic (C8:0) or capric (C10:0) C12:0 capped oleic estolide 2-EH esters had the best cold temperature C10:0 properties, with a PP of −39 ◦C. The coriander based estolide 2-EH esters did not follow the same general trend as the cuphea-capped C8:0 oleic estolide 2-EH esters synthesized in the past in terms of what saturated capping material maximized the cold temperature prop- C6:0 erties (Cermak and Isbell, 2004). Thus, the position on the base unit -40 -35 -30 -25 -20 -15 -10 -5 0 where the estolide linkage (Fig. 2) is located has some degree of ºC influence on the low temperature properties of these coriander based estolide 2-EH esters. Fig. 3. Effect of fatty acid capping group on pour point. 138 S.C. Cermak et al. / Industrial Crops and Products 33 (2011) 132–139

Table 4 Coriander based estolides and commercial lubricants—physical property comparison.

Lubricant Pour point (◦C) Cloud point (◦C) Vis. @ 40 ◦C (cSt) Vis. index RPVOT (min)

Commercial petroleum oila −27 2 65.0 155 208 Commercial synthetic oila −45 <−45 60.2 156 161 Commercial soy based oila −18 1 49.6 220 28 Commercial hydraulic fluida −33 1 56.6 146 464 Estolide Jb −24b −25b 55.9b 162b 16b Estolide Jc –– – –65c Estolide Jd – – – – 212d Estolide Je –– –b – 273e

a Commercial, fully formulated material from local vendors. b Unformulated. c Formulated with 1.5% Lubrizol® 7652 additive. d Formulated with 3.5% Lubrizol® 7652 additive. e Formulated with 7.0% Lubrizol® 7652 additive. have some degree of thermal stability towards oxidation (Isbell Estolide J, Tables 2 and 3, was picked for the commercial compar- et al., 1999). The RPVOT times were determined for the coco- ison due to the fact that it was one of best performing estolides coriander estolide 2-EH ester (Tables 2 and 3, Estolide J), with in the past when oleic was used as the base material as well its varying amounts of an oxidative stability package, Lubrizol® 7652, estimated low production costs. The coco-coriander estolide 2-EH at 150 ◦C(Table 4, Estolide Jb,Jc,Jd, and Je). The unformulated ester (Estolide Jb) was completely unformulated, unlike the com- coco-oleic estolide 2-EH ester, Estolide Jb, showed the expected mercial products, which can contain up to 40% additives designed to low RPVOT time of 16 min (Table 4) as is typical for most unfor- improve cold temperature properties. All the commercial products mulated vegetable oils (Cermak and Isbell, 2003). The oxidative in Table 4 have cold temperature-functional PPs and CPs depending stability package, Lubrizol® 7652, was added in 1.5%, 3.5%, or 7.0% on the application. The coco-coriander estolide 2-EH ester (Estolide units based on weight. As 1.5% of the oxidative stability package Jb) competed well with all the commercial fluids except for the syn- was added, there was four times the improvement in the RPVOT thetic fluid based on the cold temperature properties, PP. Another value to 65 min (Table 4, Estolide Jc). Addition of a 3.5% oxida- common cold temperature problem is an oil having too high of a CP, tive stability package produced an RPVOT value of 212 min for the thus potentially leading to filter plugging and poor pumpability in coco-coriander estolide 2-EH ester (Table 4, Estolide Jd), which cold weather applications. The coco-coriander estolide 2-EH ester was comparable with petroleum and synthetic crankcase fluids (Estolide Jb) exceeded all except the synthetic material which again (Table 4). This was an improvement of more than 13 times over the was superior. The low CP is one of the estolides’ strongest selling original stability time. Addition of a 7.0% oxidative stability pack- points as a cold weather lubricant. age produced an RPVOT value of 273 min for the coco-coriander The proton NMR for the estolide 2-EH esters in Tables 2 and 3, estolide 2-EH ester (Table 4, Estolide Je), which exceeded the per- specifically coco-coriander estolide 2-EH ester J, showed the key formance of commercial petroleum and synthetic crankcase fluids features of typical estolide 2-EH esters. The ester methine sig- (Table 4). This was an improvement of more than 17 times over nal at 4.89–4.82 ppm is indicative of an estolide linkage. Another the original stability time. Due to a limited supply of coriander oil, distinctive feature is the multiplet ␣-methylene proton shift RPVOT sample destruction and RPVOT method required a sam- (2.34–2.19 ppm) adjacent to the two esters. The NMR indicates the ple size that we did not have available. The oxidative stability presence of alkene in the estolide by the appearance of an alkene package was not added in increments of 1% weight units as in signal at 5.40–5.32 ppm. The alkene signal indicated that some of previous studies (Cermak and Isbell, 2003) to determine the opti- the estolide was capped with unsaturated material, i.e. oleic acid. mum concentration in terms of min of oxidative stability. Previous The alkene signal in the proton NMR supports the IV determined data have shown that estolide 2-EH esters reached this maximum by GC, as the intensity of the NMR signals is comparable to the RPVOT range after 3% and any additional oxidative stability pack- reported IV. age greater than 10.0% showed a destructive effect on the overall The carbon NMR spectrum contained the expected estolide 2-EH RPVOT values (Cermak and Isbell, 2003). ester signals. There were three different carbonyl signals present in In general the coco-coriander estolide 2-EH esters had RPVOT the 173 ppm region (estolide esters, estolide 2-EH ester and 2-EH values that were highly comparable to commercial products, but ester). The lack of the shift in the 179 ppm region (Cermak and Isbell, did not perform to similar high levels exhibited by the saturated 2001) indicated the estolides had been converted to the 2-EH ester and unsaturated estolides (coco-oleic estolide 2-EH esters) previ- which supported the AV number in Table 2. The other distinctive ously reported by Cermak and Isbell (2003). The oxidative stability signal was the methine carbon at 73.8 ppm, which is common to difference in the coco-coriander versus coco-oleic systems may estolide 2-EH esters. These major peaks in the carbon NMR are also be caused by some residual higher unsaturates in the coriander confirmed by a distortionless enhancement by polarization transfer (Table 1) since it is a mixture and the oleic was presumably a (DEPT) experiment. pure starting material. Oxidative stability is known to be readily Estolide 2-EH ester A (from Tables 2 and 3) was saponified in dependent on the amount of unsaturation in a molecule (Isbell et 0.5 M KOH/MeOH then esterified with 1 M H2SO4/MeOH to give al., 1999). The coco-coriander 2-EH estolide esters had an IV of 21 the corresponding hydroxy and non-hydroxylated fatty esters. The while the simple oleic 2-EH estolide esters, oleic-oleic estolide 2- isolated mixture of fatty acid esters was then silylated and ana- EH ester (Isbell and Kleiman, 1994), had an IV of 42 (Cermak et al., lyzed by GC–MS (Erhan and Kleiman, 1992). The main mass spectral 2007). Contrary to our predictions the reverse was found in terms of features were m/e 371 (M+ −15, 8.97%), 73 (TMS+, 100%), and a oxidative stability. Thus, the position of the estolide linkage must Gaussian fragment representing cleavage at the C–C bond adja- influence to some degree the amount of thermal and hydrolytic cent to the silyloxy positions (masses 187–315). The fragments and stability this new class of compounds possesses. abundances for the saturated capped materials were very similar to The physical properties of various commercial materials ver- previously reported complex saturated estolide data (Cermak and sus a coco-coriander estolide 2-EH ester were compared (Table 4). Isbell, 2004; Cermak et al., 2007). The estolide position (Table 5)was S.C. Cermak et al. / Industrial Crops and Products 33 (2011) 132–139 139

Table 5 tive package added in 1.5%, 3.5%, or 7.0% units based on weight. Estolide position as determined by gas chromatography–mass spectrometry The oxidative stability increased as the amount of stability package (GC–MS) of trimethylsilyl ether of alkali-hydrolyzed estolide. increased (RPVOT times 65–273 min). Along with expected good Estolide Hydroxy position MS fraction Total abundance biodegradability, these coriander estolide 2-EH esters had accept- Carbonyl Alkyl able properties that should provide a specialty niche in the U.S. as a bio-based lubricant. A 2 161 327 0.1 Table 2 3 175 313 0.2 4 189 299 0.4 Acknowledgments 5 203 285 3.2 6 217 271 26.9 Billy D. Deadmond and Jeffery A. Forrester assisted in the clean- 7 231 257 41.6 8 245 243 12.4 ing and processing of the coriander seeds. Amber L. Durham and 9 259 229 7.8 Rebecca Epping assisted in the synthesis and physical property 10 273 215 5.8 measurements of the coriander estolides. Authors are grateful to 11 287 201 1.6 Karl E. Vermillion for performing all the NMR experiments. 12 301 187 <0.5 13 315 173 0 E 2 161 327 0 References Table 2 3 175 313 0 4 189 299 0.5 Asadauskas, S., Erhan, S.Z., 1999. Depression of pour points of vegetable oils by blend- 5 203 285 2.4 ing with diluents used for biodegradable lubricants. J. Am. Oil Chem. Soc. 76, 6 217 271 34.1 313–316. 7 231 257 39.4 Cermak, S.C., Isbell, T.A., 2000. Biodegradable oleic estolide ester having satu- rated fatty acid end group useful as lubricant base stock. US Patent 6,316, 8 245 243 7.2 649. 9 259 229 6.1 Cermak, S.C., Isbell, T.A., 2001. Synthesis of estolides from oleic and saturated fatty 10 273 215 5.5 acids. J. Am. Oil Chem. Soc. 78, 557–565. 11 287 201 1.7 Cermak, S.C., Isbell, T.A., 2002. Physical properties of saturated estolides and their 12 301 187 2.9 2-ethylhexyl esters. Ind. Crops Prod. 16, 119–127. 13 315 173 0 Cermak, S.C., Isbell, T.A., 2003. Improved oxidative stability of estolide esters. Ind. Crops Prod. 18, 223–230. Cermak, S.C., Isbell, T.A., 2004. Synthesis and physical properties of cuphea-oleic distributed from positions 2–12 with the original 6 and 7 posi- estolides and esters. J. Am. Chem. Soc. 81, 297–303. tions having the largest abundances in the mass spectrum, which Cermak, S.C., Isbell, T.A., 2009. Synthesis and physical properties of mono-estolides with varying chain lengths. Ind. Crops Prod. 29, 205–213. also followed the very similar trend displayed with oleic based Cermak, S.C., Skender, A.L., Deppe, A.B., Isbell, T.A., 2007. Synthesis and physical material in the complex estolide data (Cermak and Isbell, 2001). properties of tallow-oleic estolide 2-ethylhexyl esters. J. Am. Oil Chem. Soc. 84, This method demonstrated that during the estolide reaction there 449–456. Erhan, S.M., Kleiman, R., 1992. Meadowfoam and rapeseed oil as accelerators in was migration of the double bond and the estolides were indeed factice production. INFORM 3, 482. complex molecules. Firestone, D. (Ed.), 1994. Official and Tentative Methods of the American Oil Chemists’ Society, fourth ed. AOCS, Champaign, IL. Isbell, T.A., Kleiman, R., 1994. Characterization of estolides produced from the acid- 4. Conclusions catalyzed condensation of oleic acid. J. Am. Oil Chem. Soc. 71, 379–383. Isbell, T.A., Kleiman, K., Plattner, B.A., 1994. Acid-catalyzed condensation of oleic A new series of petroselinic (coriander) based estolide 2-EH acid into estolides and polyestolides. J. Am. Oil Chem. Soc. 71, 169–174. Isbell, T.A., Abbott, T.P., Carlson, K.D., 1999. Oxidative stability index of vegetable esters were synthesized, as the capping material varied from oils in binary mixtures with meadowform oil. Ind. Crops Prod. 9, 115–123. caproic (C6) to stearic (C18) chain lengths and degrees of unsatura- Isbell, T.A., Abbott,T.P., Asadauskas, S. Lohr, J.E. 2000. Biodegradable oleic estolide tion, in a perchloric acid catalyzed one-pot process. Thus, followed ester base stocks and lubricants. US Patent 6,018,063. Isbell, T.A., Edgcomb, M.R., Lowery, B.A., 2001. Physical properties of estolides and by an in situ esterification second step to provide the coriander their ester derivatives. Ind. Crops Prod. 13, 11–20. estolide 2-EH esters. In general, the low temperature proper- Isbell, T.A., Green, L.A., Dekeyser, S.S., Manthey, L.K., Kenar, J.A., Cermak, S.C., 2006. ties of the synthesized estolide 2-EH esters were comparable to Improvement in the gas chromatographic resolution of petroselinate from other synthesized oleic based estolide 2-EH esters. The C8 or oleate. J. Am. Oil Chem. Soc. 83, 429–434. Kiralan, M., Calikoglu, E., Ipek, A., Bayrak, A., Gurbuz, B., 2009. Fatty acid and volatile caprylic-coriander estolide 2-EH ester had lowest low-temperature oil composition of different coriander (Coriandrum sativum) registered varieties properties (pour point = −33 ◦C and cloud point = −33 ◦C), while cultivated in turkey. Chem. Nat. Comp. 45, 100–102. the coco-coriander estolide 2-EH ester produced an estolide that Ramadan, M.F., Mörsel, J.-T., 2002. Oil composition of coriander (Coriandrum sativum − ◦ L.) fruit-seeds. Eur. Food Res. Technol. 215, 204–209. had modest low-temperature properties (pour point = 24 C and Vanderhaegen, B., Neven, H., Coghe, S., Verstrepen, K.J., Derdelinckx, G., Verachtert, ◦ cloud point = −25 C). Of all the estolides reports to date, the oleic H., 2003. Bioflavoring and beer refermentation. Appl. Microbiol. Biotechnol. 62, based materials produced the best low temperature “estolide” 140–150. Zheljazkov, V.D., Pickett, K.M., Caldwell, C.D., Pincock, J.A., Roberts, J.C., Mapplebeck, material which was the decanoic-oleic estolide 2-EH esters. The L., 2008. Cultivar and sowing date effects on seed yield and oil composition of coco-coriander estolide 2-EH ester was explored for the ability to coriander in Atlantic Canada. Ind. Crops Prod. 28, 88–94. maintain oxidative stability with the use of an biodegradable addi-