For environmental reasons, a new class of environmentally acceptable and renewable biolubricant based on vegetable oils is available. In this study, oxirane ring opening reaction of monoepoxide linoleic acid (MEOA) was done by nucleophilic addition of oleic acid (OA) with using
The use of renewable biolubricant derivatives from vegetable oils and its fatty acids, to obtain industrial products, is of increasing importance [
Vegetable-oils-based materials have inferior oxidation stability and low-temperature operability when compared to petroleum products. Chemical modification of the unsaturation fatty acids can provide products with improved oxidation stability and low-temperature properties. Examples from the studies, though certainly not exhaustive, include acylation, metathesis, hydroxylation, oxidative cleavage, carboxylation, and epoxidation [
A variety of chemical modifications of vegetable oils and fatty acids are possible, and one of the most commonly used is the oxirane ring opening reaction [
In this study, report the oxirane ring opening reaction of monoepoxide linoleic acid (MEOA) by the nucleophilic addition of oleic acid (OA) in the presence of solid acid catalyst such as
The oxirane ring opening reaction was carried out using oleic acid (OA) and
Independent variables and their levels for D-optimal design of the oxirane ring opening reaction.
Independent variables | Variable levels | |||
---|---|---|---|---|
−1 | 0 | +1 | ||
(1) OA/MEOA (w/w) | 0.30 | 0.45 | 0.60 | |
(2) PTSA/MEOA (w/w) | 0.2 | 0.35 | 0.5 | |
(3) Temperature (°C) | 90 | 100 | 110 | |
(4) Time (h) | 3 | 4.5 | 6 |
To explore the effect of the operation variables on the response in the region of investigation, a D-optimal design was performed. Ratio of OA/MEOA (g/g,
FTIR spectra were recorded neat on a Thermo Nicolet Nexus 470 FTIR system (Madison, Wis) with a Smart ARK accessory containing a 45 Ze Se trough in a scanning range of 650–4000 cm−1 for 32 scans at a spectral resolution of 4 cm−1 [
13C and 1H NMR spectra were recorded using a JEOL JNM-ECP 400 spectrometer operating at a frequency of 400.13 and 100.77 MHz, respectively, using a 5-mm broadband inverse Z-gradient probe in DMSO-d6 (Cambridge Isotope Laboratories, Andover, Mass) as solvent. Each spectrum was Fourier-transformed, phase-corrected, and integrated using MestRe-C 2.3a (Magnetic Resonance Companion, Santiago de Compostela, Spain) software [
Pour point (PP) value was measured according to the ASTM D5949 method [
Flash point (FP) determination was run according to the American National Standard Method using a Tag Closed Tester (ASTM D 56-79) [
Viscosity index (VI) is an arbitrary measure for the change of kinematic viscosity with temperature. Automated multirange viscometer tubes HV M472 obtained from Walter Herzog (Germany) were used to measure viscosity. Measurements were run in a Temp-Trol (Precision Scientific, Chicago, Ill, USA) viscometer bath set at 40.0 and 100.0°C. The viscosity and viscosity index were calculated using ASTM method ASTM D 2270-93 [
Pressurized DSC (PDSC) experiments were accomplished using a DSC 2910 thermal analyzer from TA Instruments (Newcastle, Del) [
Many nucleophilic reagents are known to add to an oxirane ring, resulting in ring opening [
The nucleophilic attack by fatty acid molecules such as oleic acid (OA) on the oxirane ring of MEOA in the presence of PTSA resulted in the ring-opened products 9,12-hydroxy-10,13-oleioxy-12-octadecanoic acid (HYOOA), as shown in Figure
Mechanism for the MEOA ring opening to afford ring opening product, 10 or 13-hydroxy (a); 9 or 12-hydroxy (b).
Optimisation study of the oxirane ring-opening-based esterification reaction using D-optimal design took place in the presence of OA with using PTSA as a catalyst. The design is used to obtain 25 design points within the whole range of four factors for experiments. The designs and the response OOC% (
D-optimal design arrangement and OOC% response of HYOOA.
Run | Coded independent variable levels | Response | |||
Number | OAa/MEOAb (w/w, | PTSAc/MEOA (w/w, | Temperature (°C, | Time | OOCd |
1 | 0.60 | 0.20 | 110 | 4.5 | 2.60 |
2 | 0.60 | 0.50 | 110 | 6 | 0.90 |
3 | 0.30 | 0.20 | 90 | 4.5 | 3.80 |
4 | 0.30 | 0.50 | 90 | 6 | 3.20 |
5 | 0.30 | 0.20 | 110 | 3 | 3.40 |
6 | 0.30 | 0.50 | 90 | 3 | 3.10 |
7 | 0.45 | 0.50 | 100 | 4.5 | 2.70 |
8 | 0.60 | 0.50 | 90 | 4.5 | 2.40 |
9 | 0.30 | 0.35 | 100 | 4.5 | 2.10 |
10 | 0.30 | 0.50 | 100 | 3 | 1.80 |
11 | 0.30 | 0.20 | 100 | 6 | 1.50 |
12 | 0.30 | 0.50 | 90 | 4.5 | 2.90 |
13 | 0.45 | 0.20 | 100 | 4.5 | 3.05 |
14 | 0.30 | 0.20 | 90 | 3 | 3.50 |
15 | 0.30 | 0.35 | 110 | 6 | 0.60 |
16 | 0.60 | 0.50 | 110 | 3 | 0.80 |
17 | 0.45 | 0.20 | 110 | 6 | 0.40 |
18 | 0.60 | 0.50 | 110 | 3 | 0.30 |
19 | 0.60 | 0.20 | 90 | 3 | 2.95 |
20 | 0.45 | 0.35 | 100 | 3 | 1.40 |
21 | 0.45 | 0.35 | 100 | 5.25 | 0.20 |
22 | 0.60 | 0.20 | 100 | 6 | 0.90 |
23 | 0.60 | 0.20 | 90 | 6 | 0.70 |
24 | 0.30 | 0.50 | 110 | 4.5 | 0.05 |
25 | 0.60 | 0.35 | 100 | 4.5 | 0.60 |
Notes: oleic acid (a); 9(12)-10(13)-monoepoxy 12(9)-octadecanoic acid (b);
Table
The quadratic regression coefficients obtained by employing a least squares method technique to predict quadratic polynomial models for the OOC% (
Regression coefficients of the predicted quadratic polynomial model for response variables of the OOC% of HYOOA.
Variables | Coefficients ( | Notability | ||
---|---|---|---|---|
Intercept | 1.63 | 5.19 | 0.0064 | *** |
Linear | ||||
| −0.31 | 1.76 | 0.2143 | |
| −0.55 | 5.73 | 0.0378 | ** |
| −0.11 | 0.23 | 0.6395 | |
| −0.064 | 0.9325 | ||
Quadratic | ||||
| 0.16 | 0.19 | 0.6699 | |
| 1.18 | 8.1 | 0.0172 | ** |
| −0.078 | 0.65 | 0.4377 | |
| −1.01 | 1.47 | 0.2537 | |
Interaction | ||||
| 0.13 | 0.51 | 0.4912 | |
| 0.14 | 2.05 | 0.1830 | |
| −0.22 | 0.40 | 0.5423 | |
| −0.23 | 5.99 | 0.0344 | |
| 1.02 | 8.22 | 0.0168 | |
| −0.017 | 0.9289 | ||
| 0.87 |
Notes:
The lack of fit
Analysis of variance, showing the effect of the variables as linear, square and interactions on the response OOC% of HYOOA (
Source | Sum of squares | Mean square | |||
---|---|---|---|---|---|
Mean | 1 | 85.75 | 85.75 | ||
Linear | 4 | 19.89 | 4.97 | 5.76 | 0.0030 |
2FI | 6 | 8.48 | 1.41 | 2.25 | 0.0987 |
Quadratic | 4 | 4.28 | 1.07 | 2.38 | 0.1214 |
Lack-of-fit | 10 | 4.50 | 0.45 | ||
Pure error | 25 | 122.90 | 4.92 |
From the experimental design in Table
Significant interaction variables in the fitted models (Table
Figure
Response surface (a) and contour plots (b) for the effect of the OA/MEOA ratio (
Optimum conditions of the experiment to obtain high yield% of HYOOA and lowest OOC% were predicted at ratio of OA/MEOA of 0.30 : 1 (w/w), ratio of PTSA/MEOA of 0.50 : 1 (w/w), reaction temperature 110°C, and 4.5 h of reaction time. At this condition, the OOC of HYOOA was 0.05%, yield was 84.61%, and IV was 134.82 mg/g. The observed value was reasonably close to the predicted value as shown in Figure
Predicated versus actual plot of
The spectrum from the FTIR analysis displays several absorption peaks as shown in Figure
The main wavelengths in the FTIR functional groups of MEOA and HYOOA.
Wavelength of MEOAa | Wavelength of HYOOAb | Functional group |
---|---|---|
— | 3003 | OH stretching (alcohol) |
3009 | 3003 | C=C bending vibration (aliphatic) |
2927, 2856 | 2925, 2855 | C–H stretching vibration (aliphatic) |
— | 1737 | C=O stretching vibration (ester) |
1711 | 1711 | C=O stretching vibration (carboxylic acid) |
— | 1461 | C–H scissoring and bending for methylene group |
— | 1176, 1117 | C–O stretching vibration (ester) |
1279, 1262 | 1279 | C–O stretching asymmetric (carboxylic acid) |
934 | 934 | C–O bending vibration (carboxylic acid) |
967 | 967 | C–H bending vibration (alkene) |
820 | — | C–O–C oxirane ring |
723 | 723 | C–H group vibration (aliphatic) |
Notes: Monoepoxide linoleic acid (a); 9,12-Hydroxy-10,13-oleioxy-12,9-octadecanoic acid (b).
FTIR spectrum of the MEOA (a) and HYOOA (b).
The FTIR spectroscopy analysis of MEOA and HYOOA indicated the presence of peak at 3003–3008 cm−1 which belongs to the double bond C=C (stretching aliphatic) while at 3413 cm−1 belong to OH stretching of HYOOA. The peaks at 1176 and 1117 cm−1 of HYOOA are referred to as (C–O) stretching ester. FTIR spectrum also showed absorption bands at 723 cm−1 for (C–H) group vibration. A similar observation has been reported for the FTIR spectrum of oxirane ring opening of epoxide oleic acid [
Figures
The signals at 127.90 to 130.57 ppm refer to the unsaturated carbon atoms (olefin carbons) for both MEOA and HYOOA. Figure
The main signals present in 13C NMR functional groups of MEOA and HYOOA.
Assignment | ||
---|---|---|
22.69–34.15 | 25.76–34.38 | Aliphatic carbons |
54.59–57.29 | — | ( |
— | 64.41 | –OH alcohol |
124.02–132.89 | 127.90–130.57 | –CH=CH– olefinic carbons |
— | 174.01 | C=O ester |
179.32 | 178.11 | C=O carboxylic acid |
Notes: monoepoxide linoleic acid (a); 9,12-Hydroxy-10,13-oleioxy-12,9-octadecanoic acid (b).
13C NMR spectrum of MEOA (a) and HYOOA (b).
1H NMR spectroscopy shows the main signals assignments of MEOA and HYOOA as shown in Table
The signals at 0.82–0.84 ppm referred to the methylene group (–CH3) of HYOOA which also appear in MEOA next to the terminal methyl (–CH2) at 1.23–2.06 ppm of HYOOA. The other distinctive signals were methine at about 2.26–2.33 ppm, which are common for these types of compounds [
The main signals present in 1H NMR functional groups of MEOA and HYOOA.
Assignment | ||
---|---|---|
0.86–0.88 | 0.82–0.84 | –CH3 |
1.29–2.03 | 1.23–2.06 | –CH2 |
2.29–2.33 | 2.26–2.33 | –CH |
2.92–3.12 | — | –CH–O–CH– |
— | 3.62 | –CHOH |
— | 4.06 | –CHOCOR |
5.38–5.49 | 5.31–5.40 | –CH=CH– |
Notes: monoepoxide linoleic acid (a); 9,12-Hydroxy-10,13-oleioxy-12,9-octadecanoic acid (b).
1H NMR spectrum of MEOA (a) and HYOOA (b).
Physicochemical properties of HYOOA compound are summarized in Table
Physicochemical properties of MEOA and HYOOA.
Properties | MEOAa | HYOOAb | HYBODAc |
---|---|---|---|
Pour point (°C) | −41 | −51 | −43 |
Flash point (°C) | 128 | 251 | 232 |
Viscosity index | 130.8 | 153 | 123 |
Oxidative stability, OT (°C) | 168 | 180.94 | 65 |
Notes: Monoepoxide linoleic acid (a); 9(12)-hydroxy-10(13)-oleioxy-12(9)-octadecanoic acid (b); 9-hydroxy-10-behenoxyoctadecanoic acid [
This step of reaction is used to improve the low-temperature behavior (PP) of fatty acids by opening the oxirane ring by using OA. Oxirane ring opening of HYOOA improves the PP at −51°C significantly comparing with MEOA at −41°C and HYBODA at −43°C [
The best oils (with the highest VI) will not vary much in viscosity over such a temperature range and therefore will perform well throughout. In oxirane ring opening, increased viscosity index (VI) up to 153 of HYOOA larger than MEOA at 130.8 and HYBODA at 123 (Table
The OT is the temperature at which a rapid increase in the rate of oxidation is observed at a constant, high pressure (200 psi). A high OT would suggest high oxidation stability of the material. OT was calculated from a plot of heat flow (W/g) versus temperature that was generated by the sample upon degradation and by definition. In this study, using OA for oxirane ring opening of HYOOA significantly improves the oxidation stability of OT for HYOOA at 180.94°C (Figure
Differential scanning calorimetry oxidation stability curve of HYOOA.
The oxirane ring opening of monoepoxide linoleic acid was done by nucleophilic addition of OA. PTSA shows a high catalytic reactivity that promotes the ring opening reaction and yields a minimum oxirane oxygen content (OOC%). Overall, physical properties of HYOOA have shown potential in formulation of industrial fluids for different temperature applications.
The authors thank UKM and the Ministry of Science and Technology for research Grant UKM-GUP-NBT-08-27-113 and UKM-OUP-NBT-29-150/2011.