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Synthesis, Characterization and Evaluation of Castor oilbased Acylated Derivatives as Potential Lubricant Base Stocks Geethanjali Gorla, Korlipara Venkata Padmaja, and Rachapudi Badari Narayana Prasad Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b01550 • Publication Date (Web): 12 Aug 2016 Downloaded from http://pubs.acs.org on August 14, 2016

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Industrial & Engineering Chemistry Research

Synthesis, Characterization and Evaluation of Castor oil-based Acylated Derivatives as Potential Lubricant Base Stocks

Gorla Geethanjali, Korlipara V. Padmaja, Rachapudi B. N. Prasad*

Centre for Lipid Research, CSIR-Indian Institute of Chemical Technology, Hyderabad 500 007, Andhra Pradesh, India.

Correspondence to: E-mail address: [email protected] (R.B.N. Prasad). Tel.: +91 040 27193179; fax: +91 040 27193370.

1 ACS Paragon Plus Environment


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ABSTRACT: Synthesis, characterization, and evaluation of a series of novel acylated derivatives of castor oil as biolubricant base stocks are described. The acylated derivatives of castor oil, castor oil fatty acid methyl and 2-ethylhexyl esters were synthesized using different anhydrides (C1-C6) in about 90-95% yield. All the products were structurally characterized using NMR and IR spectral data. The acylated products were evaluated for their physico-chemical and lubricant properties. Although these products belong to group V, based on viscosity index (130-156), acylated derivatives of castor fatty acid alkyl esters belong to group III, category of base fluids as per API classification. The acylated products exhibited excellent pour point (-21 to -39 °C) and flash point (174-280 °C). The hexanoylated and butanoylated ester of castor oil exhibited excellent flash points of 280 and 272 °C respectively. The air release value was found to be excellent in the range of 0.38-0.99 min, and NOACK volatilities in the range of 3.25-3.92 %. The other lubrication properties such as load carrying capacity, emulsion stability were found to be good. Therefore, these derivatives will have utility in hydraulic and metal working fluids and other industrial fluids with their wide range of properties.

Key words: Castor oil, Fatty acids, Acylation, Acylated castor oil, biolubricants


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1. INTRODUCTION Lubricants and functional ﬂuids derived from vegetable oils and their derivatives are attractive alternatives to petroleum-derived products due to their biodegradability and renewability. A steady increase in utilization of eco-friendly user products such as lubricants has occurred due to strict government regulations and increased awareness for a pollution-free environment.1-3 Castor oil (Ricinus communis), is a very valuable renewable feed stock, a native of tropical Asia and Africa4, 5. India is the world’s largest producer of castor beans as reported by the Food and Agriculture Organization of the United Nations (FAO). It is also exporter of castor oil, with a share of 70 % of the total exports. Since 1845, it was proved that heating of castor oil at high temperature produces interesting products and broadens the application possibilities and the value of castor has ever since increased greatly.6 Castor oil has already been used in carts and Persian wheels as a lubricant.7 Castor oil as a lubricant, posses unusual properties compared to other vegetable oils and used for equipment operating under extreme conditions.8, 9 Among vegetable oils, castor oil has received much attention as a building block to prepare functional materials. It exhibits high lubricity, high viscosity, and high solubility in alcohols and insolubility in aliphatic solvents. Castor oil has been exploited in the manufacture of several products and also used in many applications such as functional fluids, process oils, base oil formulations for lubricants, feedstock for fuels and oleo chemicals and also reactive components for paints, inks and coatings, polymers and foams.9, 10, 11



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Different types of reactions such as hydrogenation, dehydration, epoxidation, and sulfation of castor oil, are reported to prepare a variety of high value products.6, 12 Castor oil-based biodiesel is projected as an alternative to petroleum derived diesel as fuel and as green energy option.13 Castor oil is a promising renewable raw material for the chemical and polymer industries.14,

15

Use of partially dehydrated castor oil as lubricants is reported.16

Hydrogenated castor oil has been used in the development of high temperature lubricating grease compositions.17 Volkhard Scholz and co workers have reviewed the prospects and risks of the use of castor oil as fuel. The high viscosity and high water content complicates the use of straight castor oil as a fuel for internal combustion engines18 or as lubricant base stocks, and due to this reason, several researchers are modifying castor oil for variety of applications including lubricant base stocks. The chemical modification of castor oil and its fatty acids would serve as good raw materials for the production of biolubricant base stocks. Estolide esters of castor oil fatty acids and their acetates were reported as potential lubricant base stocks.19 Esters of castor oil and hydrogenated castor oil using C6, C12, C16 and C18 fatty acids, were prepared. The physical properties of the prepared esters such as viscosity, specific gravity, refractive index and melting point were evaluated by M. G. Kulkarni et al.20 Chemical modification of ricinoleic acid was carried out to synthesize biolubricant base stocks such as esters of ricinoleic acid and evaluated for their low temperature properties.21 Improved pour point and flash points were obtained using modified epoxy ricinoleic acid.22,

23

Ricinoleic acid based-tetra esters and their evaluation for physico-

chemical and tribological properties was discussed by Nadia Salih et al.24 Amit Suhane


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et al have conducted experimental observations and suggested that castor has immense potential as base fluid for lubricant formulation for automotive gear applications.25 Lesquerella and castor oil-based triglyceride estolides were prepared by T.A. Isbell et al. Fully capped and mono capped estolides were evaluated for their physical properties such as kinematic viscosity, pour point and oxidative stability. However they didn’t evaluate lubricant properties in detail.26 Although reports on utilization of castor oil exist, detailed study on the preparation of acylated derivatives of castor oil alkyl esters and their detailed evaluation as lubricant base stocks was not carried out. Further, in view of developing new eco-friendly biolubricant base stocks, we report the synthesis and characterization and evaluation of novel acylated derivatives of castor oil. The acylated products of castor oil such as acylated derivatives of castor oil, castor oil fatty acid methyl and 2-ethylhexyl esters were prepared using different anhydrides (C1-C6). A systematic study was carried out on the physico-chemical and lubricant properties of the synthesized acylated products.

2. MATERIALS AND METHODS 2.1.

Materials

Methanol, 2-ethylhexanol, p-toluene sulfonic acid (p-TSA), sodium hydroxide, sodium sulphate, xylene were purchased from M/s SD Fine Chem Ltd., Mumbai, India. Sulfuric acid (H2SO4), hydrochloric acid (HCl), dimethylaminopyridine (DMAP), acetic anhydride, and sodium bicarbonate were purchased from M/s Rankhem, New Delhi, India. Acetic, propionic, butyric, and hexanoic anhydrides were procured from M/s Sigma–Aldrich (St.



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Louis, USA). Ethyl acetate and hexane were purchased from M/s Spectrochem Pvt. Ltd, Mumbai, India. Castor oil having acid value 2.2 procured from local company (Hyderabad, India) was used as such. All the reagents were of analytical grade and were used without further purification. 2.2. Methods. The analytical determinations of the acylated derivatives of castor oil were determined using the American Oil Chemists’ Society (AOCS) official methods. Acid value (AOCS Cd 3d-63) and hydroxyl value (H.V) (AOCS Cd 13-60) standard methods. Proton nuclear magnetic resonance (1H NMR) spectra were recorded on Bruker (Wissenbourg, France) AR X 400 spectrometer (400 MHz) with CDCl3 solvent and TMS as an internal standard. A Fourier transform-infrared (FT-IR) spectrum was carried out on a 1600 FT-IR Perkin Elmer spectrophotometer (Norwalk, CT, USA) with a liquid film between NaCl disks. The fatty acid composition was analyzed using GC and GC-MS analysis using Agilent 6890 N series gas chromatograph equipped with a flame ionization detector (FID) on a split injector using HP-1 column (30 m × 0.25 mm × 0.5 µm) employed in GC analysis. Nitrogen was used as carrier gas at a flow rate of 1.5 mL/min. The flame ionization detector and injector were kept at 300 °C. The oven temperature was programmed at 150 °C for 2 min and then increased to 300 °C at a rate of 10 °C/min and nitrogen was used as carrier gas at a flow rate of 1.5 mL/min. The GC-MS analysis was carried out using Agilent 5973 (Palo Alto, USA) with HP-1 MS capillary column (30 m × 0.25 mm × 0.5 µm) connected to mass spectrophotometer at 70 eV (m/z 50-600; source at 230 °C and quadruple at 150 °C) in the EI mode. The oven temperature was


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programmed at 150 °C for 2 min, 10 °C/min to 300 °C and 20 min at 300 °C and helium was used as carrier gas at a flow rate of 1.0 mL/min. 2.2.1. Kinematic Viscosity: Kinematic viscosity of the synthesized products was determined by following the ASTM D 445 - 01 and ASTM D 2270 methods. Kinematic viscosity measurements were made at 40 and 100 °C using calibrated Cannon Fenske viscometer tubes in a Cannon constant temperature viscosity bath (Cannon Instrument Co., State College, PA, U.S.A.). All viscosity measurements were run in duplicate and the average value was reported [ASTM method (D 445 – 01) information is given in Supporting Information].

2.2.2. Pour Point: Pour points of the synthesized products were measured as described by the ASTM D 97 method with an accuracy of +3 °C using pour point test apparatus manufactured by Dott. Gianni Scavini & Co., Italy. Pour point of a lubricant can be defined as the minimum temperature of a liquid lubricant below which the liquid ceases to flow and which is a significant factor in cold-weather start-up. Pour points of the products were measured in 3 °C increments at the top of the product until it stopped pouring and all the runs were carried out in duplicate and the average value was reported. 2.2.3. Flash Point. Flash points of the test samples were evaluated by following the ASTM D 93 using a Koehler Inc. apparatus. The flash point test method is a dynamic test method, and is defined as the lowest temperature at which application of the test flame causes the vapor above the surface of the liquid to ignite at ambient barometric pressure. Duplicate measurements were made, and the average values were reported.



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2.2.4. Copper Strip Corrosion Test. The corrosiveness of the synthesized products was determined using a Koehler Inc. apparatus; U.S.A. as per ASTM D 130 method. A polished Cu strip was immersed in 30 mL of the sample being tested at 100 °C for 3 hr. Then after the Cu strip was removed, washed. The color and tarnish level of the test specimen of the Cu strip were correlated using the ASTM copper strip corrosion standard. 2.2.5. Rotating Pressurized Vessel Oxidation Test (RPVOT). Oxidative stability of the products was determined as per the ASTM method D 2272. RPVOTs for the synthesized products were carried out using a sample size of 50 g, reagent grade water of 5.0 mL and copper catalyst at 150 °C; and the vessel was sealed and charged with oxygen to 90 psi pressure. The test was completed at which the pressure of the bomb has dropped by 25 psi. 2.2.6. Air Release Value. Air release value of the synthesized products was determined using the ASTM method D 3427 using a Koehler Inc. apparatus. The test requires a sample size of 180 mL, and the measurement of the time required for the air entrained in the oil is reduced back to a value of 0.2 %, and the value is reported in min as the air release time; the test method was described in detail elsewhere.27 2.2.7. NOACK Volatility. NOACK Volatility of a test sample in percentage by weight lost was determined as evaporative loss as determined by ASTM method D 5800 using Koehler inc. apparatus as described in detail elsewhere.27 Experiments were conducted on a non woods metal Noack evaporative tester using a sample size of 65.0 ±0.1 g to a precision of 0.01 g. The test was about the determination of weight loss of a sample


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experiences through volatization and the test results were reported in percentage by weight lost. 2.2.8. Extreme Pressure Test. The extreme pressure tests of the synthesized products were determined using a precision scientific four-ball extreme pressure tester, as per IP 239 method. Experiments were run at 1,475 rpm, for 1 min, without application of external heat, or until the load at which balls welded, whichever occurred first. The weld load points reported are reproducible to within one loading increment (± 10 kg for 10 kg loading increments). 2.2.9. Emulsion Characteristics. Emulsion stability of the prepared products were determined by ASTMD 1401 using Dott.Gianni Scavini apparatus equipped with tachometer and speed variator and thermo stated heater. The acylated products of each 40 mL sample size and distilled water are kept at 54 °C and stirred for duration of 5 min. The time lapsed for the separation of the formed emulsion is thus determined.

2.3. Synthesis of Acylated Derivatives of Castor Oil and its Alkyl Esters 2.3.1. A typical procedure for the synthesis of acylated derivatives of castor oil. Castor oil (0.09 mol), alkanoic anhydride (C1-C6) (0.36 mol), dimethyl amino pyridine (DMAP) (1 wt % of castor oil) and xylene (150 mL) were taken into a three necked round bottom flask. The contents of the flask were magnetically stirred at 140150 ºC for duration of 7-9 h. The progress of the reaction was monitored by TLC and IR. The reaction product was distilled at 140-160 °C and 3-5 mm Hg to eliminate excess alkanoic anhydride and xylene. The distilled product was extracted using ethyl acetate and washed with water until acid free, and passed through the anhydrous sodium



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sulfate. The crude product was concentrated by removing the solvent and dried under reduced pressure. The acylated products such as acetylated, propionoylated, butanoylated and hexanoylated cator oil were analyzed for hydroxyl value and acid value. It was further purified by eluting through basic alumina column to obtain the final product with an acid value less than 0.1. The formation of acylated product was further confirmed by IR and 1H NMR. Acetylated Castor Oil: (335 g, 95% yield, H.V=0.9 mg KOH/g) 1

H NMR (200 MHz, CDCl3): 0.8 (t, -CH3); 1.2-1.6 (m, -(CH2)n-CH3); 2.2-2.4 (t, -CH2-

C=O); 4.0-4.4 (m, sn-1, sn-3); 5.2 (m, sn -2);4.8-5.4 (m, -CH-O-CO-R) IR (neat, cm-1): 2926 (C-H), 1742(C=O), 1178 ( C-C(=O)-O). Propionoylated Castor Oil: (338 g, 95% yield, H.V=0.5 mg KOH/g) 1

H NMR (CDCl3, ppm): 0.8 (t, -CH3); 1.2-1.6 (m, -(CH2)n-CH3); 2.2-2.4 (t, -CH2-C=O);

4.0-4.4 (m, sn-1, sn-3); 5.2 (m, sn -2);4.8-5.4 (m, -CH-O-CO-R) IR (neat, cm-1): 2926 (C-H), 1742(C=O), 1178 ( C-C(=O)-O). Butanoylated Castor Oil: (350 g, 94.5 % yield, H.V=2.7mg KOH/g) 1


4.0-4.4 (m, sn-1, sn-3); 5.2 (m, sn -2);4.8-5.4 (m, -CH-O-CO-R) IR (neat, cm-1): 2926 (C-H), 1742(C=O), 1178 ( C-C(=O)-O). Hexanoylated Castor oil: (375 g, 95.3 % yield, H.V=1.9 mg KOH/g) 1


4.0-4.4 (m, sn-1, sn-3); 5.2 (m, sn -2);4.8-5.4 (m, -CH-O-CO-R) IR (neat, cm-1): 2926 (C-H), 1742(C=O), 1178 ( C-C(=O)-O).


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2.3.2. Preparation of castor fatty acid methyl esters. Castor oil (100 g, 0.11 mol), methanol (27.8 mL, 0.66 mol) and sulfuric acid (1.1 mL, 2 wt % of castor oil) were stirred under refluxing at 65 ºC for 6 h. The progress of reaction was monitored by thin layer chromatography (TLC) using solvent system hexane/ethyl acetate (80:20). After complete conversion of the reaction as shown by TLC, methanol was distilled and the product was extracted with ethyl acetate followed by water washing to make it neutral and passed through sodium sulphate, then concentrated. The weight of the product was 95 g (97% yield). The product was analyzed by GC (Table 1) and further characterized by FT-IR and 1H NMR. 1

H NMR (CDCl3, δ ppm): 0.88 (t, -CH2-CH3); 1.26-1.42 (m, -CH2-CH3); 1.56-1.63 (m,

CH2-CH2-CO-); 2.05 (m, =CH-CH2-CH2), 2.20 (t, -CH-CH2-CH=CH-),

2.30 (t, -CH2-

C=O), 3.6 (m, -CH-OH-): 3.65 (s, CH3-O-C=O), 5.42-5.54 (m, -CH=CH-). IR (Neat, cm-1): 3504 (-OH), 3010 (-C=C-H), 2929 (-C-H), 1732 (C=O).

2.3.3. A typical procedure for the preparation of castor fatty acids. Castor oil (1000 g, mol) and sodium hydroxide solution (145 g in 1200 mL water) were taken in a three necked round bottom flask and stirred mechanically for 3 h at 80-85 °C. The reaction mixture was cooled to 50 °C, neutralized with dilute aqueous hydrochloric acid solution (6 N) to completely decompose fatty acid soap at pH less than 4. The total contents were extracted with ethyl acetate followed by drying over anhydrous sodium sulphate.

The sample was concentrated using rotary evaporator and dried under

reduced pressure (3-5 mm Hg) to get castor oil fatty acids 920 g (96% yield) with an acid value of 195.



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2.3.4. Preparation of castor fatty acid 2-ethylhexyl esters. Castor fatty acids (CFA) (500 g, 2.74 mol), 2-ethylhexanol (223 g, 4.19 mol), p-TSA (1 wt % of CFA), and 100 mL of xylene were stirred at reflux under nitrogen atmosphere using a Dean and Stark apparatus until a theoretical amount of water was collected. The crude product was distilled at 60−150 °C and 5 mm Hg to remove excess alcohol and xylene. The resultant product was extracted using ethyl acetate, washed with NaHCO3 solution, filtered through anhydrous Na2SO4, concentrated and dried under vacuum to obtain castor fatty acid 2-ethylhexyl esters of 740g (92% yield). The product was analyzed by GC and further characterized by FT-IR and 1H NMR. 1

HNMR (CDCl3, δ ppm). 0.89 (t, -CH2-CH3); 1.25-1.4 (m, -(CH2)n); 1.52-1.67 (m, -CH2-

CH2-CH2-CO-); 1.97-2.05 (m, -CH-CH2-CO-, -CH=CH-CH2-); 2.42 (m,

2.3 (t, -CH2-CH2-CO-);

-CH2-CH=CH-CH2-CH=CH-); 3.6 (m, -CH-OH-); 4.0 (d, -CH-CH2-O-CO-);

5.32-5.36 (m, -CH2-CH=CH-CH2-). IR (neat, cm-1). 3509 (-OH), 2926 (C-H), 3010 (-C=C-H), 1736(C=O); 1181.26 (C-O). 2.3.5. A typical procedure for the acylation of castor fatty acid alkyl esters. Castor fatty acid alkyl esters (0.3 mol), alkanoic anhydride (C3, C4 and C6) (0.3 mol) were taken in to a three necked round bottom flask. DMAP (1 wt % of castor fatty acid alkyl ester) and xylene (150 mL) was added and stirred at 140-150 ºC for a period of 7-9 h. The progress of the reaction mixture was monitored with TLC and IR. After ensuring the maximum conversion, the reaction mixture was distilled at 140-160 °C and 3-5 mm Hg to eliminate xylene. Using ethyl acetate the distilled product was extracted and washed with water until it was acid free, and passed through the anhydrous sodium sulfate. The crude product was concentrated and dried under reduced pressure. The obtained acylated


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products were analyzed for acid value and hydroxyl value. The final product with an acid value less than 0.1 was obtained by eluting through basic alumina column. The formation of acylated castor fatty acid alkyl esters was further confirmed by FT-IR and 1H NMR. Propionylated esters of castor fatty acid methyl esters (PrECFAME): (705.9 g, 94% yield, H.V=nil) 1

H NMR (200 MHz, CDCl3): 0.8-0.95 (t, -CH3); 1.16-1.7 (t, -CO-CH2-CH3)1.24-1.4 (m, -

(CH2)n-CH3); 2.2-2.4 (t, -CH2-C=O); 3.64 (s, O-CH3); 4.8-4.9 (m, -CH-O-CO-R); 5.255.5 (m, -CH=CH-). IR (neat, cm-1): 2926 (C-H), 1742(C=O), 1178 ( C-C(=O)-O). Butanoylated castor fatty acid methyl esters (BuECFAME): (708.3 g, 95% yield, H.V=0.7mg KOH/g) 1

H NMR (400 MHz, CDCl3): 0.8-0.95 (t, -CH3); 1.16-1.7 (t, -CO-(CH2)2-CH3)1.24-1.4 (m,

-(CH2)n-CH3); 2.2-2.35 (t, -CH2-C=O); 3.64 (s, O-CH3); 4.8-4.9 (m, -CH-O-CO-R); 5.255.5 (m, -CH=CH-). IR (neat, cm-1): 2926 (C-H), 1742(C=O), 1178 ( C-C(=O)-O). Hexanoylated castor fatty acid methyl esters (HxECFAME): (730.3 g, 93% yield, H.V=0.9 mg KOH/g) 1

H NMR (400 MHz, CDCl3): 0.8-0.95 (t, -CH3); 1.1-1.2 (t, -CO-(CH2)4-CH3)1.24-1.4 (m, -

(CH2)n-CH3); 2.2-2.35 (t, -CH2-C=O); 3.64 (s, O-CH3); 4.8-4.9 (m, -CH-O-CO-R); 5.255.5 (m, -CH=CH-). IR (neat, cm-1): 2927 (C-H), 1739(C=O), 1170 ( C-C(=O)-O). Propionoylated esters of castor fatty acid 2-ethylhexyl esters (PrECFA2EtHE): (707.9 g, 93% yield, H.V=0.7mg KOH/g)



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1

H NMR (200 MHz, CDCl3): 0.85-0.95 (t, -CH3); 1.14-1.9 (t, -CO-CH2-CH3)1.24-1.4 (m, -

(CH2)n-CH3); 2.2-2.3 (t, -CH2-C=O); 3.9-4.0 (d, O-CH2-CH); 4.8-4.9 (m, -CH-O-CO-R); 5.25-5.5 (m, -CH=CH-). IR (neat, cm-1): 2926 (C-H), 1742(C=O), 1178 ( C-C(=O)-O). Butanoylated castor fatty acid 2-ethylhexyl esters (BuECFA2-EtHE): (770 g, 95% yield, H.V=nil) 1


(CH2)n-CH3); 2.2-2.35 (t, -CH2-C=O); 3.9-4.0 (O-CH3); 4.8-4.9 (m, -CH-O-CO-R); 5.255.5 (m, -CH=CH-). IR (neat, cm-1): 2926 (C-H), 1742(C=O), 1178 ( C-C(=O)-O). Hexanoylated castor fatty acid 2-ethylhexyl esters (HxECFA2-EtHE): (820 g, 92% yield, H.V=nil) 1


(CH2)n-CH3); 2.2-2.35 (t, -CH2-C=O); 3.9-4.0 (d, O-CH2-CH-); 4.8-4.9 (m, -CH-O-CO-R); 5.25-5.5 (m, -CH=CH-). IR (neat, cm-1): 2927 (C-H), 1739(C=O), 1170 ( C-C(=O)-O).

3. RESULTS AND DISCUSSION Castor oil is one of the most attractive renewable raw materials in the area of biolubricants.28,

29

Lubricants based on vegetable oils display excellent tribological

properties, high viscosity indices, and flash points. In the present study, the acylation of the hydroxy group of ricinoleic acid present in castor oil was explored to synthesize several biolubricant base stocks.


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Castor oil was converted in to its fatty acid methyl esters in 97% yields and its composition is given in Table 1. Castor oil contains ricinoleic acid (12-hydroxy, 9, 10octadecenoic acid) which is a hydroxyl fatty acid in 89.6% quantities along with other fatty acids in minor quantities. Saponification of castor oil using alkali was carried out to obtain corresponding fatty acids. 2-Ethylhexyl esters of castor fatty acids were prepared by reacting castor fatty acids with 2-ethylhexanol (1:1.5 mol/mol) in 95 % yields. Sulphuric acid (H2SO4) was used as catalyst for methyl esters and p-TSA for 2ethyhexyl esters preparation. The castor oil and its fatty acid alkyl esters were acylated using different anhydrides (C1-C6) in order to synthesize corresponding acylated products in good yields (90-96 %).

Table 1: Fatty acid Composition (wt %) of Castor Oil Fatty Acid

Composition (Wt %)

Palmitic

1.7

Stearic

1.9

Oleic

3.2

Linoleic

3.6

Ricinoleic

89.6

Acylated derivatives of castor oil was prepared by reacting castor oil with different anhydrides (C1, C3, C4 and C6) in 1: 4 mole ratio using DMAP as catalyst (1 wt



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% of castor oil) at 140-150 ºC as shown in the Scheme 1, to obtain acylated derivatives of castor oil (90- 95.4 % yield). O

OH

OH O

5

O 5

O 5

OH

O

O

Castor Oil O

DMAP

O

n O n Where, n=0,1,2,4 O

OR

OR O

5

O O

OR

5

5 O

O

Acylated Castor Oil

Where, R= -CO-CH3, -CO-CH2-CH3, -CO-CH2-CH2-CH3, -CO-CH2-CH2-CH2-CH2-CH3

Scheme 1: Synthesis of Acylated Derivatives of Castor Oil In a similar manner acylated derivatives of castor fatty acid esters were also prepared using different anhydrides (C3, C4 and C6) in 1:1 mole ratio as shown in the Scheme 2. The course of the reaction was monitored by FT-IR by withdrawing the aliquots of the reaction mixture during the course of reaction. All the products were purified by eluting through basic alumina column to obtain acylated derivatives of castor oil with an acid value less than 0.1 mg KOH/g. The hydroxyl value of acylated products of castor oil, castor FAME and castor 2EtHeE was found to be in the range of 0.5- 2.7; nil to 0.7 and nil to 0.7 mg KOH/g respectively. The acylated products were characterized by spectral


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methods like FT-IR and 1H NMR. The products were further evaluated for their physicochemical and lubricant properties. O OH

5

OH

12-hydroxy octadecenoic acid

O

O O

5

OH

O

R +

n O

n

Acid anhydride

Alkyl- 12-hydroxy octadecenoate

DMAP

O R

Where, n=1, 2, 4 R= Methyl; 2-ethyl hexyl

5

O

O

n O

Alkyl- 12-acyloxy octadecenoate Scheme 2: Synthesis of Alkyl 12-Acyloxy Octadecenoate-Rich Fatty Acid Esters from Castor Fatty Acids

The FTIR spectra of the acylated products did not exhibit O-H stretching vibration frequency at 3500-3100 cm−1 (Figure 1). The characteristic absorptions of ester group around 1737 cm−1 and the relative intensities of 1459:1367 were observed. This was also further confirmed by the low hydroxyl value (

Synthesis, Characterization, and Evaluation of ... - ACS Publications

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