Novel Approaches for Synthesis of Polyols from Soy Oils

Transcription

1 Novel Approaches for Synthesis of Polyols from Soy Oils by Saswati Ghosh Roy A thesis submitted in conformity with the requirements for the degree of Master of Science in Forestry (M. Sc. F) Faculty of Forestry University of Toronto Copyright by Saswati Ghosh Roy 2009

2 Novel Approaches for Synthesis of Polyols from Soy Oils Abstract Saswati Ghosh Roy Master of Science in Forestry (M. Sc. F) Faculty of Forestry University of Toronto 2009 A method for synthesis of polyol from soybean oils has been developed using a two-step continuous route. The method involved epoxidation of soy oils and subsequent hydroxylation to produce polyols. The epoxidation was carried out using biphasic catalytic system (Na 2 WO 4 / H 2 WO 4 ) with 50 % hydrogen peroxide. The major advantages of this approach are that; the use of biphasic system allows easy separation of the products, does not require any chlorinated solvent (more environment-friendly), can be conducted at room temperature and requires relatively lower catalyst load. The functional groups of soy-polyol were identified using FTIR and NMR spectroscopy. This confirmed complete disappearance of the signature of the C=C double bonds, formation of the epoxy linkage following the epoxidation process, its further disappearance and incorporation of hydroxyl groups after the hydroxylation process. The hydroxyl number, hydroxyl functionality, acid value, iodine value and viscosity of the synthesized polyols were also determined. ii

3 Acknowledgments It is with great pleasure; I express my deepest gratitude to my supervisor Prof. Mohini M. Sain for his guidance, suggestions and supervision of my thesis work. I am deeply indebted to him, for patiently sharing his abundance of knowledge with me and for his active support at every step of this work. His foresight and keen scientific intuition was absolutely vital for the progress of this work. It has been a great learning opportunity for me to work under his supervision. I am particularly indebted to Prof. D. N. Roy and Prof. Sally Krigstin for critically evaluating my work and for their encouragement and advice. Their guidance and suggestions has helped shaping up of the work. I would like to thank Dr. Sanchita Bandyopadhaya Ghosh for her guidance, fruitful discussions and for participating in some of the studies presented in this thesis. I would also like to thank Dr. Sabina Di Risio for her help and support during the experiments. I wish to thank Dr. Subrata Bandhu Ghosh and Abdul for their help in various stages of my studies. I am also thankful to Dr. Min Zhu, Smith, Crystal and all other members of Centre for Biocomposites and Biomaterials Processing, Faculty of Forestry. I have been benefited one way or the other from their association and timely help. My deepest gratitude goes to my parents and my husband for their constant support, encouragement, caring and guidance over the years. They have enriched my life beyond measure with love and caring. It is their aspiration that has motivated me to think of building up a scientific career. Finally, I dedicate this thesis to our one-year-old son Soham. iii

4 Table of Contents Abstract Acknowledgements Table of Contents List of Tables List of Figures List of Appendices Organization of the Thesis ii iii iv vii viii x xi Chapter 1 Introduction Background Review of Methods for Synthesis of Polyols from Soy Oils 3 Chapter 2 Motivations and Objectives Motivations Objectives 5 Chapter 3 Experimental Procedures Materials and Methods 7 iv

5 3.2 Synthesis Process Scheme Scheme Chemistry Behind the Epoxidation 14 Process with the Biphasic Catalytic System Chapter 4 Soy Polyol Synthesis Using Scheme 1: Results and Discussion Characterization of Soy Oil Early results of Soy-polyol Synthesis using Scheme 1 17 Chapter 5 Soy Polyol Synthesis Using Scheme 1: Results and Discussion Optimization of the Reaction Process 21 and Determination of Various Properties 5.2 FTIR Spectroscopic Results NMR Spectroscopic Results 29 Chapter 6 Synthesis of Polyols from Genetically Modified Soy Oil Characterization of Genetically Modified Soy Oil Synthesis Process Early Results of Synthesis of Polyol from 39 v

6 Genetically Modified Soy Oil Chapter 7 Conclusions and Future Studies Conclusions Future Studies 43 References Appendices vi

7 List of Tables Table 1: The different methods used for characterizing the soy oil, epoxidized soy oil and the polyol. Table 2: The determined hydroxyl number, hydroxyl functionality, acid value and iodine values of the synthesized polyols (using scheme 1). The time of hydroxylation is also listed. Table 3: The epoxidation of soy oil with biphasic catalysts (Na2WO4 / H2WO4) with 50% H2O2. The concentrations of the catalysts were varied starting from 0.4 mole percentage (0.2 mole % of Na 2 WO mole % of H 2 WO 4 ). The epoxidation time (in hours) and percentage conversion (amount of double bonds converted) are listed. The amount of conversion was calculated from the 1 H NMR spectra. (* At room temperature no conversion obtained. Epoxidation performed at 60 o C). Table 4: The determined hydroxyl number, epoxide content, hydroxyl functionality and acid values of the synthesized polyols using scheme 2. Results are shown for polyols obtained with varying concentration of the catalysts used in the epoxidation process. The variations of the values for these parameters of polyols synthesized with varying time of hydroxylation are also listed (for polyols obtained with 0.6 mole % of catalysts used in epoxidation). Here, percentage epoxide content NF (not found) indicates almost complete conversion of epoxidized soy oil to polyol. Table 5: The variation of the measured viscosity of the polyols with their hydroxyl number. Table 6: The determined molecular weight, iodine value, acid value and average number of double bonds per TG molecule of genetically modified soy oil. Table 7: The determined acid values, hydroxyl number and hydroxyl functionality of the polyols synthesized from genetically modified soy oil using scheme 2. The variations of the values for these parameters of polyols synthesized with varying time of hydroxylation are also listed (for polyols obtained with 1 % of catalysts used in epoxidation). vii

8 List of Figures Figure 1: (a) The basic chemical structure of soy-oil. The different unsaturated Fatty Acids (FA) are also shown. (b) The general Triglyceride structure. Here, R 1, R 2 and R 3 are alkyl group. Figure 2: A schematic of the process for synthesis of polyols from soy oils using the two-step continuous route (Scheme 1). Figure 3: A schematic of the process for synthesis of polyols from soy oils using the two-step continuous route (Scheme 2). Figure 4: The MALDI-TOF mass spectra of soy oil. Figure 5: The FTIR spectra of the soy oil. The spectra are shown for the range cm -1. Figure 6: The FTIR spectra of the polyol synthesized using scheme 1. The spectra are shown for the range cm -1. The inset shows the same spectra for the range cm -1, to highlight the C=C H stretch at ~ 3010 cm -1. Figure 7 (a): The FTIR spectra of the epoxidized soy oil (using scheme 2). The spectra are shown for the range cm -1. (b): A comparison of the spectra of the soy oil and the epoxidized soy oil (scheme 2) for the range cm -1, to highlight the difference in the peak of C=C stretch at 1654 cm -1. Figure 8 (a): The FTIR spectra of the polyol (scheme 2). The spectra are shown for the range cm -1. (b): A comparison of the spectra of the epoxidized soy oil and the polyol (scheme 2) for the range cm -1, to highlight the difference in the peak of the epoxy groups (C O twin bands at 823 and 845 cm -1 ). viii

9 Figure 9 (a): The 1 H NMR spectra recorded from soy oil. The different characteristic peaks are noted inside the figure. (b): The 1 H NMR spectra recorded from polyol (scheme 2). (c) The 1 H NMR spectra recorded from deuterated polyol (scheme 2). Figure 10: A photograph of the soy-polyol synthesized using the two-step continuous route (scheme 2). Figure 11: The MALDI-TOF mass spectra of genetically modified soy oil. Figure 12: The 1 H NMR spectra recorded from genetically modified soy oil. Figure 13: The 1 H NMR spectra recorded from polyol synthesized from genetically modified soy oil (scheme 2). Figure 14: The 1 H NMR spectra recorded from soy oil. The area under the peak corresponding to oliphinic proton is noted inside the figure. Figure 15: The 1 H NMR spectra recorded from epoxidized soy oil. The area under the peak corresponding to oliphinic proton is noted inside the figure. ix

10 List of Appendices Appendix 1: Determination of Percentage Conversion of Soy Oil to Epoxidized Soy Oil x

11 Organization of the Thesis The thesis is organized as follows. In Chapter 1, an introduction to bio-polyol synthesis is provided. The need for synthesis of polyols from bio-based resources (vegetable oils) is highlighted. A brief overview of the related research carried out for bio-polyol synthesis is also presented in this chapter. Chapter 2 describes the major motivations and objectives of the thesis work. Chapter 3 describes the experimental procedures. These include the details of the synthesis process and the spectroscopic, chemical and physical methods used to characterize the synthesized polyol. A method for polyol synthesis from soybean oils has been developed using a two-step continuous route. The two-step continuous process involved epoxidation of soy oils and subsequent hydroxylation to produce polyols. Two different schemes were explored for epoxidation (scheme 1 and scheme 2). In scheme 1, epoxidation of soy oils was performed by Sodium perborate (NaBO 3. 4H 2 O) and acetic anhydride (Ac 2 O) mixture using dichloromethane (CH 2 Cl 2 ) as solvent in room temperature. In the second scheme, this was achieved using biphasic catalytic system (Na 2 WO 4 / H 2 WO 4 / phase transfer reagent / chloroacetic acid) with hydrogen peroxide (H 2 O 2 ). Synthesis processes using both these schemes are described in Chapter 3. In Chapter 4, early results of polyol synthesis (and its characterization) using scheme 1 are presented. The shortcomings of scheme 1 are also discussed in this chapter. In Chapter 5, the detailed results of polyol synthesis using scheme 2 are described. The FTIR and NMR spectroscopic results and the results of determination of the various chemical and physical properties of the polyol are presented in this chapter. Initial exploration of the developed synthetic strategy for the synthesis of polyols from genetically modified soy oils, are discussed in Chapter 6. The thesis concludes in Chapter 7, with the implication of the newly developed synthetic strategy for the production of soy-polyol and its ongoing and prospective applications in polyurethane foam formation. xi

12 1 Chapter 1 Introduction 1.1 Background The use of bio-based renewable resources for the production of useful chemicals and new materials has grown rapidly during the past few years. This is motivated by the potential advantages offered by the bio-based resources, in environment compatibility and economical feasibility, as compared to the traditional petrochemical derivatives [1-3]. Polyol, a polyhydroxy compound, is an important building block of polyurethanes and polyesters that are useful in wide range of applications such as construction, coatings agents, adhesives, sealants, elastomers, resins etc. Polyols are traditionally produced from petroleum. However, the production of polyols from petrochemicals is costly, requires a great deal of energy and also has adverse effects on the environment. Research in recent years has thus focused on alternative, non-petroleum based sources of polyols that are renewable, less costly and more ecofriendly. The bio-polyols synthesized from vegetable oils are an attractive alternative for this purpose and has therefore drawn considerable current attention [4-9]. Vegetable oils such as sunflower, canola, corn, olive, palm and soy oils are being explored for the synthesis of polyols. The vegetable oil molecules must however, be chemically transformed to introduce hydroxyl groups for formation of polyols. Among the different vegetable oils, the soy oils have been the more widely explored for polyol synthesis. In addition to being an abundant and inexpensive vegetable oil, there are few other compelling reasons to use soy-oil as the major green feedstock for bio-polyol synthesis. Soy-oil is highly unsaturated oil (high iodine value ~ ) and its number of unsaturations is higher than other vegetable oils (for example, iodine values of palm oil, corn oil, rapeseed oil, sunflower oil are ~ 64, 71, 84, and 115 respectively [10]). The basic chemical structure of soy-oil is shown in Figure 1. It is mainly composed of Triglyceride (TG) molecules (TG structure is also shown in the figure) derived from unsaturated Fatty Acids (FA) such as linoleic acid (55 %), oleic acid (22 %), and linolenic acid (7 %) [11].

13 2 (a) -OOC (CH 2 ) 7 CH = CHCH 2 CH=CH(CH 2 ) 4 CH 3 -OOC (CH 2 ) 7 CH = CH (CH 2 ) 7 CH 3 Linole ic Oleic - OOC (CH 2 ) 14 CH 3 Palmitic -OOC (CH 2 ) 7 CH = CHCH 2 CH=CHCH 2 CH = CHCH 2 CH 3 Linolenic - OOC (CH 2 ) 16 CH 3 Stearic (b) Figure 1: (a) The basic chemical structure of soy-oil. The different unsaturated Fatty Acids (FA) are also shown. (b) The general Triglyceride structure. Here, R 1, R 2 and R 3 are alkyl group.

14 3 About one in three TG molecules has one saturated acid and one acid (linoleic acid) with three double bonds. The average number of double bonds per molecule is 4.6. The excellent number of unsaturations present in it makes it a good candidate for polyol synthesis. For the formation of polyol, the soy-oil molecules need to be chemically transformed so that the double bonds are converted into hydroxyls. Several studies have been conducted over the years to develop suitable methods for synthesis of polyols from soy-oils. In the following, we provide a brief overview of the related research carried out for soy-polyol synthesis. 1.2 Review of Methods for Synthesis of Polyols from Soy Oils One of the early methods used for preparing polyols from various vegetable oils was based on transesterification of the FA in TG with a polyol such as glycerin, glycerol or pentaerythritol [4]. The main disadvantage of this process was the long reaction time and the occurrence of premature degradation due to high temperature. Hydroformilation is another synthetic strategy that has been explored for the preparation of polyols [5,6]. In this approach, the double bonds of the vegetable oil are first converted to aldehydes using suitably chosen catalysts. The aldehydes are subsequently hydrogenated to alcohols. The mechanical properties of the polyurethanes prepared from these polyols were however, found to vary significantly with the choice of the hydroformilation catalyst [6]. More recently, epoxidation of soy-oil and subsequent opening of the epoxide rings either by heating or by hydroxylation with polyfunctional alcohols, have been explored for devising more efficient methods for soy-polyol synthesis [7]. Usually the processes that have been used for epoxidation involve peroxycarboxylic acids, especially the peracetic or performic acids, because of their stability at ordinary temperature and easy availability [12]. However, these processes have been found, to be time consuming, to have low selectivity and also to possess hazards associated with handling peracids [13]. Therefore, new epoxidation systems have been intensively investigated to overcome these problems [14-17]. Several approaches for ring opening of the oxirane groups from epoxidized soy oils have also been investigated simultaneously to accomplish the second stage (of polyol synthesis), that is, conversion of epoxy groups to hydroxyl groups [11].

15 4 Apart from the two most general methods discussed above, there does exist a few recent reports on exploring alternative processes for polyol synthesis. These include the catalytic ozonolysis process [8] in which the method is based on oxidizing an olefin (having a carbonyl group) with molecular oxygen, followed by hydrolysis and reduction of the acetal to alcohol [9]. It should be noted here that reactions of preparing polyols (in many of the processes discussed above) from soy-oils are time consuming and are often not very selective. Several by-products in addition to alcohol groups are created during the chemical transformations. Moreover, most of the previously explored methods do not produce polyols with desirable hydroxyl functionality and viscosity. Therefore there is a need to investigate novel routes to improve the chemistry as well as the process for more efficient synthesis of polyols from soy-oils. In this project, this issue has therefore been investigated and a two-step continuous process for synthesis of polyols from soy-oils has been developed. The details of this process and the results of characterization of the synthesized soy-polyols are described in this thesis. The thesis is organized as follows. In Chapter 1, an introduction to bio-polyol synthesis is provided. The need for synthesis of polyols from bio-based resources (vegetable oils) is highlighted. A brief overview of the related research carried out for bio-polyol synthesis is also presented in this chapter. Chapter 2 describes the major motivations and objectives of the thesis work. Chapter 3 describes the experimental procedures. These include the details of the synthesis process and the spectroscopic, chemical and physical methods used to characterize the synthesized polyol. The novel two-step continuous process developed in this work involved epoxidation of soy oils and subsequent hydroxylation to produce polyols. Synthesis processes using two different schemes for epoxidation (scheme 1 and scheme 2) are presented. In Chapter 4, early results of polyol synthesis (and its characterization) using scheme 1 are presented. The shortcomings of scheme 1 are also discussed in this chapter. In Chapter 5, the detailed results of polyol synthesis using scheme 2 are described. The FTIR and NMR spectroscopic results and the results of determination of the various chemical and physical properties of the polyol are presented in this chapter. Initial exploration of the developed synthetic strategy for the synthesis of polyols from genetically modified soy oils, are discussed in Chapter 6. The thesis concludes in Chapter 7, with the implication of the newly developed synthetic strategy for the production of soy-polyol and its prospective applications in polyurethane foam formation.

16 5 Chapter 2 Motivations and Objectives 2.1 Motivations As noted in the previous chapter, the reactions of preparing polyols (in many of the processes previously investigated) from soy oils, are often not very selective. Several by-products in addition to the desired alcohol groups are created during the chemical transformations. Furthermore, most of the methods do not produce products with desired hydroxyl functionality and viscosity. Therefore, the main objective of this project was to investigate novel routes to improve the chemistry as well as the process and to devise a more efficient method of synthesis of polyols from soy oils. Emphasis was on developing a method for making polyols having a favorable distribution of hydroxyl groups in the molecule so that when these polyols are reacted with isocyanates to form polyurethanes, cross-linking within the polyurethane is optimized. The other objective was to characterize the product composition and to measure the various chemical and physical properties, namely, hydroxyl number, hydroxyl functionality, acid value, iodine value and viscosity of the synthesized polyols. FTIR / NMR spectroscopic studies were conducted to identify the functional groups of the polyol based on their characteristic spectral signatures. In the following section, the major objectives of the project are noted down. 2.2 Objectives (i) Investigate novel routes to improve the chemistry as well as the process and to devise an efficient method of synthesis of polyols from soy oils. Emphasis on exploring ways to synthesize soy-polyol (having desirable viscosity and desired hydroxyl functionality) via a continuous route avoiding intermediate steps.

17 6 (ii) Develop a method for making soy oil-based polyols having a favorable distribution of hydroxyl groups for polyurathane formation. (iii) Characterize the synthesized product via spectroscopic techniques (FTIR spectroscopy) and measure various physical and chemical properties. In order to achieve the above-mentioned objectives, polyols were synthesized from soy-oils using a two-step continuous process. The two-step continuous process involves epoxidation of soy oils and subsequent hydroxylation to produce polyols. Two different schemes for epoxidation (scheme 1 and scheme 2) were explored. The details of the synthesis process using these two schemes, and the spectroscopic, chemical and physical methods used to characterize the synthesized polyol are presented in the following chapter (Chapter 3).

18 7 Chapter 3 Experimental Procedures In order to achieve the objectives noted in the previous chapter, polyols were synthesized from soy-oils using a two-step continuous process. The two-step continuous process involved epoxidation of soy oils and subsequent hydroxylation to produce polyols. Two different schemes for epoxidation (scheme 1 and scheme 2) were explored. (i) Epoxidation of soy oils by Sodium perborate (NaBO 3. 4H 2 O) and acetic anhydride (Ac 2 O) mixture using dichloromethane (CH 2 Cl 2 ) as solvent in room temperature. (ii) Epoxidation of soy oil using biphasic catalytic system (Na 2 WO 4 / H 2 WO 4 / phase transfer reagent / chloroacetic acid) with hydrogen peroxide (H 2 O 2 ). In this chapter, the experimental materials and methods are described. The details of the synthesis process using both the schemes are presented. The spectroscopic, chemical and physical methods used to characterize the synthesized polyol are also discussed in this chapter. 3.1 Materials and Methods Refined Soy oil was supplied by BUNGE (Oakville, ON, Canada) and was used without any additional purification. The H 2 O 2 (50 %) was procured from Sigma-Aldrich (Oakville, Ontario, Canada). Sodium perborate (NaBO 3. 4H 2 O), acetic anhydride (Ac 2 O), dichloromethane (CH2Cl2), sodium tungstate (Na2WO4), tungstic acid (H2WO4), chloroacetic acid (CH2ClCOOH), phase transfer reagent Aliquat 336 (methyltri-n-octylammonium chloride), and conc. H 2 SO 4 were procured from Caledon Labs. (Georgetown, ON, Canada). Prior to using for polyol synthesis, the soy oils were characterized. The molecular weight of soy oil was determined using NMR ( 1 H) spectroscopy [10]. The molecular weight distributions of the different components of soy oil were determined using Matrix-assisted laser desorption and ionization-time of flight (MALDI-TOF) mass spectroscopy [18]. The acid values and iodine values were determined using AOCS standard methods (AOCS Ca 3a 63 for acid value and

19 8 AOCS Cd 1 25 for iodine value) [19]. The functional groups were characterized using FTIR and NMR ( 1 H) spectroscopy. The functional groups of the epoxidized soy oils and the polyols were also characterized using FTIR and NMR ( 1 H) spectroscopy. The hydroxyl number of polyols was determined by ASTM test method D [20]. The corresponding hydroxyl functionality was derived from the determined hydroxyl number. The acid value (AOCS Ca 3a - 63), iodine values (AOCS Cd 1-25) and epoxide content (AOCS Cd 9-57) of the polyols were also determined [19]. Viscosity of polyols was measured at 25 o C with a Brookfield viscometer (model RVT). In Table 1, the different methods used for characterizing the soy oil, epoxidized soy oil and the polyol, are summarized. The details of these methods are described below. Material Test methods Molecular weight distribution (MALDI- TOF) Molecular weight [NMR ( 1 H) spectroscopy] Iodine value (AOCS standard method Cd 1 25) Acid value (AOCS standard method AOCS Ca 3a 63) Hydroxy l number (ASTM test method D ) Epoxide content (AOCS standard method Cd 9 57) Functional groups (FTIR and 1 H NMR spectroscopy) Soy oil Epoxidized soy oil Polyol Table 1: Methods used for characterizing the soy oil, epoxidized soy oil and the polyol. Molecular Weight Distribution: The MALDI-TOF mass spectroscopy is a powerful tool for determining the molecular weight distribution of the various components of any high molecular weight compound. The MALDI- TOF (4800 MALDI TOF/TOF Analyzer, Applied Biosystems) mass spectra of the soy oils were

20 9 recorded to identify the unsaturated fatty acids components present in it. For recording the mass spectra, the soy oil was methylated with methyl alcohol and sodium hydroxide [18]. Briefly, in a 100 ml round bottomed flask (equipped with a magnetic stirring bar), 2.5 gm of soy oil was mixed with 25 ml of methanol and 1.25 gm of sodium hydroxide. The flask was then fitted with a water condenser, and the mixture was heated to reflux for 30 minutes. The mixture was then slowly added to ice water and the resulting semi-solid was separated by vacuum filtering and subsequently air-dried. 100 mg of this off-white solid was dissolved in 5 ml of methanol / water (4:1, v/v) and stored at 4 o C. The matrix, 2,5-dihydroxybenzoic acid (DHB) solution was prepared by dissolving 20 mg of DHB in 2 ml of acetone and was also stored at 4 o C. The 5 µl of the sample and 5 µl of matrix solution were mixed and were used for MALDI-TOF analysis. Iodine value determination: It is a measure of the unsaturations of fats and oils and is expressed in terms of the number of centigrams of iodine absorbed per gram of sample. This was determined using AOCS standard method AOCS Cd Briefly, the sample was dissolved in cyclohexane and Wij s solution was added to this. The sample was then allowed to absorb iodine from the mixture. The excess iodine was titrated with sodium thiosulphate solution in presence of starch indicator. The number of centigrams of iodine absorbed per gram of the sample is then determined. Acid value determination: It is defined as the mass of potassium hydroxide in milligrams that is required to neutralize one gram of the sample. This was determined following AOCS standard method, AOCS Ca 3a 63. Briefly, certain amount of the sample was dissolved in hot ethyl alcohol and titrated with KOH solution using phenolphthalein as indicator. The required amount of KOH (mg) per gram of the sample, is the acid value of the sample. Hydroxyl number determination: It is expressed as the milligrams of potassium hydroxide (KOH) equivalent to the hydroxyl group of one gram of oil. In order to determine the hydroxyl number ASTM test method D was followed. Briefly, the OH group of polyol was acetylated with acetic anhydride in presence of pyridine and the excess acetic anhydride was hydrolysed with water to produce acetic acid.

21 10 This acetic acid was back-titrated with ethanolic KOH, the amount of the KOH (in mg) required for this titration is the hydroxyl number of the sample. Hydroxyl functionality determination: It is defined as the average number of hydroxyl groups per mole of TG molecule. This can be calculated from the hydroxyl number, the molecular weight of the soy oil and the equivalent weight of KOH in mg (= 56100) as Hydroxyl functionality = (Molecular weight Hydroxyl number)/ Epoxide content determination: This was determined following AOCS standard method, AOCS Cd Briefly, the sample was dissolved in glacial acetic acid and titrated with HBr solution using crystal violet as indicator. The epoxide content is calculated from the ml of HBr consumed by the sample and the mass of the sample. FTIR spectroscopy The FTIR spectra from soy oils, epoxidized soy oils and polyols were recorded on KBr discs using a Brucker FTIR spectrometer Tensor 27. A regular scanning range of cm -1 was used at a spectral resolution of 4 cm -1. For each spectrum, 32 scans were recorded for signal averaging. Multiple measurements were carried out to verify IR observations. NMR spectroscopy: NMR ( 1 H) spectra were obtained on a Varian Mercury 300 instrument. Approximately 360 mg of the sample was dissolved in 1.8 ml of deuterated chloroform (CDCl3) containing 0.05 % TMS. 750 µl of this solution was kept in a 5 mm diameter NMR tube to record the 1 H NMR spectra at room temperature. The spectra were recorded with 7.5 degree pulse angle, 2.5 sec. relaxation delay, 3 sec. acquisition time and 32 scans. 3.2 Synthesis Process

22 11 The synthesis of polyols from soy oils was carried out using a two-step continuous route. In the first step, soy oils were epoxidized using suitably chosen reagents. The epoxidized soy oils were subsequently hydroxylated (with 8 % H 2 SO 4 ) to produce polyols. As noted previously, we have explored two different schemes for epoxidation. The details of both these schemes are described below Scheme 1 Soy oil + NaBO 3. 4H 2 O + Ac 2 O + CH 2 Cl 2 Vigorous stirring Epoxidized soy oil Solvent removed by evaporation. Acetic acid produced from Ac 2 O was also removed by washing with water Hydroxylation with 8 % H 2 SO 4 (at o C) Polyol Figure 2: A schematic of the process for synthesis of polyols from soy oils using the two-step continuous route (Scheme 1). This approach is comprised of epoxidation of soy oil by Sodium perborate (NaBO 3. 4H 2 O) and acetic anhydride (Ac 2O) mixture using dichloromethane (CH2Cl2) as solvent in room

23 12 temperature. The idea was to optimize the epoxidation process by suitably adjusting the molar proportions of the reagents. For this purpose, the molar proportions (per double bond present in soy oils) of both the reagents (Sodium perborate and acetic anhydride) were varied. Following this optimization process, the epoxidized soy oils were subsequently hydroxylated (with 8 % H 2 SO 4 ) to produce polyols. A schematic of this process is shown in Figure Scheme 2 Soy oil + 50% H (Na 2 WO 4 and H 2 WO 4 ) Vigorous stirring Phase transfer reagent Aliquat 336 / Chloroacetic acid Epoxidized soy oil Hydroxylation with 8 % H 2 SO 4 (at o C) Polyol Figure 3: A schematic of the process for synthesis of polyols from soy oils using the two-step continuous route (Scheme 2).

24 13 In this scheme, soy oil was epoxidized using biphasic catalytic system (Na2WO4 / H2WO4 / phase transfer reagent Aliquat 336 / chloroacetic acid CH 2 ClCOOH) with H 2 O 2. Epoxidation of various alkenes using this biphasic catalytic system has recently been explored by Maheswari et al [14]. A similar approach has been followed here. The reaction conditions and the catalytic system have been optimized for obtaining optimal epoxidation of soy oils. The chemistry behind the epoxidation process with this biphasic catalytic system is briefly described at the end of this subsection. Initially, 30 % H 2 O 2 was chosen for the epoxidation process. However, with 30 % H2O2, complete conversion could not be achieved. In contrast, complete conversion was achieved with 50 % H 2 O 2. This concentration of H 2 O 2 was therefore chosen for all the subsequent studies using this approach. The epoxidized soy oils were subsequently hydroxylated (with 8 % H 2 SO 4 ) to produce polyols. A schematic of this process is shown in Figure 3. The biphasic catalysts Na 2 WO 4 and H 2 WO 4 were dissolved in 5 ml of distilled water and were stirred for 10 minutes. 81 gms (the amount was calculated as 1.5 equivalents per double bond of the soy oils used) of 50 % H 2 O 2 was added to the catalytic system followed by 1.6 mol % of chloroacetic acid. The amount of Na 2 WO 4 and H 2 WO 4 in the mixture was varied to optimize the catalytic system for obtaining complete epoxidation (conversion of double bonds to epoxy rings). This mixture was stirred for another 10 minutes followed by the addition of 150 gms of soybean oil. The phase transfer reagent Aliquat 336 was finally added to this mixture and was stirred vigorously until the epoxidation process was complete. In order to remove excess H 2 O 2, sodium bisulfite solution (10 % wt. / vol.) was added to the mixture and was stirred for another 2 hours. The organic phase of the mixture was separated using separating funnel and were collected in a beaker. Thus obtained epoxidized soy oils were subsequently hydroxylated (with 8 % H 2 SO 4 ) at o C to produce polyols. The organic phase was once again separated using separating funnel and was further washed with sodium carbonate solutions (10 % wt. / vol.) until it became neutral (ph 7).

25 Chemistry Behind the Epoxidation Process with the Biphasic Catalytic System It is important to understand the chemistry behind the epoxidation process using the biphasic catalysts and H 2 O 2. Here, this aspect is briefly discussed. It is well known that usually H 2 O 2 decomposes to form water and atomic oxygen. Thus H2O2 can in principle, act as a oxygen donor in epoxidation process. However, since oil and H 2 O 2 are immiscible, H 2 O 2 cannot directly perform epoxidation of oil. The biphasic catalytic system (Na 2 WO 4 / H 2 WO 4 / phase transfer reagent Aliquat 336 / chloroacetic acid) is therefore used to enhance the epoxidation process in presence of H 2 O 2. Here, the reagent chloroacetic acid (pk a value = 2.7) is used to maintain the ph of the reaction, so that the biphasic catalysts act at its maximum efficiency. A plausible explanation for this process is that, in this reaction, Na 2 WO 4, H 2 WO 4, CH 2 ClCOOH and H 2 O 2 forms a dinuclearperoxo-tungsten [W2(ClCH2COO)2(O2)4(O)3] species and a mononuclearperoxo-tungsten [W (ClCH 2 COO) 2 (O 2 ) 4 (O) 3 ] species. It is these tungsten species that act as oxygen donor for the epoxidation process [14]. Note that the tungsten species are formed in aqueous phase. The phase transfer reagent Aliquat 336 carries these tungsten species from aqueous to organic phase such that it can donate oxygen to the oil for epoxidation. Another plausible explanation is that, in presence of the biphasic catalysts (Na 2 WO 4 / H 2 WO 4 ) and H 2 O 2, the chloroacetic acid forms perchloroacetic acid [CH 2 ClCOOOH], which can act as a direct oxygen donor.

26 15 Chapter 4 Soy Polyol Synthesis Using Scheme 1: Results and Discussion Synthesis of polyols from soy oils was initially explored using scheme 1. In this chapter, early results of these studies are described. Note that soy-polyols could not be produced with desirable reproducibility and efficiency using scheme 1. In this chapter, the early results of this approach are therefore briefly presented. The shortcomings of this approach and plausible alternative approaches are also discussed. Before going into these details, in the following section, the results of characterization of the soy oils used for polyol synthesis, are presented. 4.1 Characterization of Soy Oil Prior to using for polyol synthesis, the soy oils were characterized. The Triglyceride fatty acid components were identified by recording MALDI-TOF mass spectra. The spectra were recorded following the process described in the previous Chapter. In Figure 4, the MALDI-TOF mass spectra recorded from soy oil is shown. The peaks corresponding to the major fatty acid components are noted inside the figure. These are, palmitic acid (m/z 301), linolenic acid (m/z 323), linoleic acid (m/z 325), oleic acid (m/z 327), stearic acid (m/z 329) [18]. Among these, the linolenic acid, linoleic acid and oleic acids are unsaturated components.

27 16 m/z = m/z = 301 m/z = Mass (m / z) Figure 4: The MALDI-TOF mass spectra of soy oil. The functional groups of the soy oils were also characterized by FTIR and NMR spectroscopy (detailed results are presented in Section 2 and Section 3 of Chapter 5). The acid value and iodine values were determined following the process described in the previous chapter. These values were determined to be 0.4 and 138 respectively. The average number of double bonds per TG molecules of soy oil was calculated (using the iodine value and molecular weight of 865 g/mol) to be 4.6.

28 Early results of Soy-polyol Synthesis using Scheme 1 As discussed previously, in scheme 1, the epoxidation of soy oil was performed using sodium perborate (NaBO 3. 4H 2 O) and acetic anhydride (Ac 2 O) mixture with dichloromethane (CH 2 Cl 2 ) as solvent at room temperature. Attempts were made to vary the molar proportions of the reagents for obtaining optimal epoxidation using this approach. The molar proportions of both the reagents (sodium perborate and acetic anhydride) were varied from mole per double bond of oil. However, for molar proportions of 0.5, 1.5 and 2 mole per double bond of oil, conversion of soy oil to epoxidized soy oil could not be achieved. Epoxidation was achieved for molar proportions of one mole of Sodium perborate and acetic anhydride per double bond of oil only. The epoxidized soy oil was subsequently hydroxylated (with 8 % H 2 SO 4 ) to produce polyols. Time of hydroxylation Hydroxyl number Hydroxyl functionality Acid value Iodine value (h) Table 2: The determined hydroxyl number, hydroxyl functionality, acid value and iodine values of the synthesized polyols (using scheme 1). The time of hydroxylation is also listed. The hydroxyl number, hydroxyl functionality, acid value, iodine value of the synthesized polyols were determined following the methods described in Chapter 3. These values are listed in Table 2. The functional groups of the soy oil and the synthesized polyols were characterized using FTIR spectroscopy. In Figure 5, typical FTIR spectra recorded from soy oil is displayed. As can be noted, the soy oil spectra shows prominent signature of the double bonds, C=C H stretch at ~ 3010 cm -1 and C=C stretch at ~1654 cm -1 [8].

29 18 Soy Oil Absorbance C=C-H stretch (3010 cm -1 ) C=C stretch (1654 cm -1 ) Wavenumber (cm -1 ) Figure 5: The FTIR spectra of the soy oil. The spectra are shown for the range cm -1.

30 19 Absorbance OH stretch (3440 cm -1 ) Polyol Absorbance C=C-H stretch (3010 cm -1 ) C=C-H stretch (3010 cm -1 ) Wavenumber (cm -1 ) Polyol Wavenumber (cm -1 ) Figure 6: The FTIR spectra of the polyol synthesized using scheme 1. The spectra are shown for the range cm -1. The inset shows the same spectra for the range cm -1, to highlight the C=C H stretch at ~ 3010 cm -1. In Figure 6, the FTIR spectra recorded from polyol synthesized using the process, is shown. The spectra of polyol show prominent signature of the broad hydroxyl-stretching peak at around 3440 cm -1, confirming the incorporation of the hydroxyl groups. However, careful examination reveals that the signature of double bond, the C=C H stretch at ~ 3010 cm -1, is still present in the spectra of polyol (this is highlighted separately in the inset of the figure). The spectra of

31 20 epoxidized soy oil also showed similar signature of double bonds (not shown here). Thus even for the optimized molar proportions of the reagents, complete conversion of the double bonds could not be achieved during epoxidation of soy oils using this approach. Another major problem of this approach was that the polyols synthesized using this approach was also not reproducible. In fact, the process was repeated six times and polyol could be successfully synthesized twice only among these six attempts. To summarize this chapter, the results presented here shows that soy-polyols could not be produced with desirable reproducibility and efficiency using scheme 1. It is therefore important to develop alternative approach for soy-polyol synthesis using the two-step continuous route. As an alternative approach, the use of biphasic catalytic system was therefore explored for epoxidation process (the first step for polyol synthesis). The detailed results are presented in the next chapter.

32 21 Chapter 5 Soy Polyol Synthesis Using Scheme 1: Results and Discussion In this chapter, the use of biphasic catalytic system for epoxidation process (the first step for polyol synthesis) was explored. The epoxidized soy oil was subsequently hydroxylated to produce polyol. Here, the detailed results of polyol synthesis using this approach (scheme 2) are discussed. The results of the optimization studies, determination of the various chemical and physical properties of the polyol and the FTIR and NMR spectroscopic results are presented in detail. 5.1 Optimization of Reaction Process and Determination of Various Properties As noted previously, the soy polyols were synthesized in two steps. In the first step, soy oils were epoxidized with biphasic catalysts (Na 2 WO 4 / H 2 WO 4 ) in presence of 50 % H 2 O 2 (1.5 equivalents per double bond of the soy oils used). In order to optimize the reaction conditions of the epoxidation process, the catalysts concentrations were varied starting from 0.4 mole percentage (0.2 mole % of Na 2 WO mole % of H 2 WO 4 ). For each concentration of the catalysts, the percentage conversion (amount of double bonds converted) was determined. The conversion rate was determined from the 1 H NMR spectra. This was calculated by the area decrease of the double bond hydrogen signals (oliphinic proton -H - C=C-H- ) between ppm region of the spectra (an example, illustrating the determination of conversion rate is presented in Appendix 1). The results are summarized in Table 3, where the epoxidation times are also listed. As can be seen, almost complete conversion of double bonds to epoxy rings was obtained for catalysts concentration of 0.6 mole % (0.3 mole % of Na2WO mole % of H2WO4) and

33 22 beyond. Although complete conversion was obtained at catalysts concentration of 0.6 mole %, the time of epoxidation was significantly higher (~ 10 hours). In contrast, for catalysts concentration of 1 mole % (0.5 mole % of Na 2 WO mole % of H 2 WO 4 ), the epoxidation time was considerably reduced (~ 1 hour). This concentration of the catalysts was therefore chosen as optimal for polyol synthesis. Reaction Na 2 WO 4 + H 2 WO 4 (mole %) Time (hours) Percentage Conversion (%) ~ 4 * ~ ~ 1 92 Table 3: The epoxidation of soy oil with biphasic catalysts (Na 2 WO 4 / H 2 WO 4 ) with 50% H 2 O 2. The concentrations of the catalysts were varied starting from 0.4 mole percentage (0.2 mole % of Na2WO mole % of H2WO4). The epoxidation time (in hours) and percentage conversion (amount of double bonds converted) are listed. The amount of conversion was calculated from the 1 H NMR spectra. The values for percentage conversion is the mean of three independent measurements. The relative error was ~ 3 %. (* At room temperature no conversion obtained. Epoxidation performed at 60 o C) In the second step, the epoxidized soy oil was hydroxylated with 8 % H 2 SO 4 at o C. For this purpose, the amount (by weight) of 8 % H 2 SO 4 was chosen to be four times higher than the amount of epoxidized soy oil. The hydroxyl number, epoxide content, hydroxyl functionality, acid value, iodine value and viscosity of the synthesized polyols were determined following the methods described previously. These parameters were determined for the polyols synthesized with varying concentrations of the catalysts used in the epoxidation process and the corresponding values are listed in Table 4. Although complete epoxidation was obtained for

34 23 catalysts concentration of 0.6 mole % or beyond, results are also displayed for polyol synthesized with 0.4 mole % of catalysts used in the epoxidation process. All the tests were repeated three times and the values for the parameters listed in Table 4, are the mean values of three independent measurements. The results also showed good reproducibility with relative error ~ 5 %. Note that the time of hydroxylation also significantly influences the properties (specifically the hydroxyl number) of the synthesized polyol. Therefore, the effect of hydroxylation time on the hydroxyl number of the polyol was also investigated. A typical variation for this is shown in Table 4 (for polyol synthesized with 0.6 mole % of catalysts). As can be noted, the hydroxyl number increases with increasing hydroxylation time between 1 h to 4h and attains a maximum value of ~ 197. Beyond the hydroxylation time of 4 h, the value was however, found to remain almost constant. This observed variation of hydroxyl number with increasing hydroxylation time therefore offers a control on the hydroxyl number of polyols synthesized using this two-step process. (Na 2 WO 4 / H2WO4) catalysts (mole %) Time of hydroxylation (h) Hydroxyl number Epoxide content (%) Hydroxyl functionality Acid value ± 3 NF ± 2 60 ± ± 2 45 ± ± 4 10 ± ± 3 NF Table 4: The determined hydroxyl number, epoxide content, hydroxyl functionality and acid values of the synthesized polyols using scheme 2. Results are shown for polyols obtained with

35 24 varying concentration of the catalysts used in the epoxidation process. The variations of the values for these parameters of polyols synthesized with varying time of hydroxylation are also listed (for polyols obtained with 0.6 mole % of catalysts used in epoxidation). Here, percentage epoxide content NF (not found) indicates almost complete conversion of epoxidized soy oil to polyol. The values for the listed parameters are mean of three independent measurements (the standard deviations are also listed). Note that the viscosity of the polyols was also measured. In general, the viscosity was found to increase with increasing hydroxyl number of the polyol. Typical variation of the measured viscosity of polyol with its hydroxyl number is shown in Table 5. The values of viscosity listed here are also mean of three measurements. The standard deviations are also listed. Hydroxyl number Viscosity (cps) ± ± ± ± 125 Table 5: The variation of the measured viscosity of the polyols with their hydroxyl number. As can be seen, the values for viscosity of polyols varied between 8000 cps to cps for increasing hydroxyl number of 109 to 199. This possibly arises because, with increasing hydroxyl groups, the polar interaction increases leading to increased viscosity. 5.2 FTIR Spectroscopic Results FTIR spectra were recorded from soy oil, epoxidized soy oil and the soy polyol prepared using scheme 2. The spectra of soy oil were previously presented in Chapter 4. Here, the spectra for the

36 25 epoxidized soy oil and the prepared soy polyol are shown in Figures 7 (a and b) and 8 (a and b) respectively. The results are presented here for the polyols prepared using 1 mole % (0.5 mole % of Na 2 WO mole % H 2 WO 4 ) of the biphasic catalysts system. As can be noted, the signature of the double bonds, C=C H stretch at ~ 3010 cm -1 and C=C stretch at ~1654 cm -1 (that were present in the soy oil spectra, Figure 5 of Chapter 4), completely disappear in the spectra of epoxidized soy oil and polyol (Figure 7a and 8a). The peak of C=C stretch at 1654 cm - 1 for the soy oil and its disappearance in the epoxidized soy oil is highlighted in Figure 7b, where the spectra for the range cm -1 are shown separately Epoxidized Soy Oil Absorbance C-O twin bands Wavenumber (cm -1 ) Figure 7a: The FTIR spectra of the epoxidized soy oil (using scheme 2). The spectra are shown for the range cm -1.

37 26 C=C stretch (1654 cm -1 ) Soy Oil Epoxidized Soy Oil Absorbance Wavenumber (cm -1 ) Figure 7b: A comparison of the spectra of the soy oil and the epoxidized soy oil (scheme 2) for the range cm -1, to highlight the difference in the peak of C=C stretch at 1654 cm -1. The spectra of epoxidized soy oil (Figure 7a) further shows clear signature of the epoxy groups, oxirane C O twin bands at ~ 823 and 845 cm -1. The other peaks are: 724 (methylene in-phase rocking), 960, 1020, 1102 (ether, antisymmetric stretch), 1161, 1240 (ester antisymmetric stretch), 1380 (methyl symmetric deformation), 1464 (methyl antisymmetric deformation) and 1746 (esters, aliphatic C=O stretch) cm -1 [10, 19]. In comparison to the spectra of epoxidized soy oil (Figure 7a), the epoxy groups (C O twin bands at 823 and 845 cm -1 ) disappears in the spectra of polyol (Figure 8a), confirming the

38 27 oxirane opening. This is highlighted in Figure 9b, where the spectra are shown separately for the range cm -1. Most importantly, the spectra of polyol (Figure 8a) show very prominent signature of the broad hydroxyl-stretching peak at around 3440 cm -1, confirming the incorporation of the hydroxyl groups Polyol Absorbance OH stretch (3440 cm -1 ) Wavenumber (cm -1 ) Figure 8a: The FTIR spectra of the polyol (scheme 2). The spectra are shown for the range cm -1.

39 Epoxidized Soy oil Polyol Absorbance C-O twin bands (823, 845 cm -1 ) Wavenumber (cm -1 ) Figure 8b: A comparison of the spectra of the epoxidized soy oil and the polyol (scheme 2) for the range cm -1, to highlight the difference in the peak of the epoxy groups (C O twin bands at 823 and 845 cm -1 ).

40 NMR Spectroscopic Results The functional groups of the synthesized polyols were further confirmed from the 1 H NMR spectra. The 1 H NMR spectra recorded from soy oil and polyol are shown in Figure 9a and 9b respectively. The different peaks are marked as A to H in the spectra. Importantly, the spectra shows clear signature of the double bond hydrogen (oliphinic proton -H - C=C-H- ) between ppm (marked as A in the figure). The other significant peaks are; methylene proton in the glyceryl group (4 4.5 ppm, B), divinyl methylene protons (2.5 3 ppm, C), α -methylene protons adjacent carbonyl group (2 2.5 ppm, D), allyl methylene proton (~ 2 ppm, E), β- methylene protons from carbonyl group (~ 1.6 ppm, F), methylene protons on saturated carbon atom (1 1.5 ppm, G) and the terminal methyl group (H). The signature of the double bond, the oliphinic proton peak at ppm, is observed to almost disappear in the spectra of polyol (Figure 9b). Further, the spectra of polyol shows appearance of new peaks between ppm, which correspond to the signature of the methylinic proton (H-C-OH) and the proton associated with the OH groups. This confirms the incorporation of hydroxyl groups. This was further supported by recording 1 H NMR spectra from deuterated polyol. The spectra is shown in Figure 9c. As for the case of the spectra of polyol (Figure 9b), the oliphinic proton peak at ppm appears to be absent here. Additionally, the peak corresponding to the proton associated with the OH groups (at ~ 3.5 ppm) also disappears in the spectra, confirming the proton exchange (replaced by the deuterium).

41 30 G F O liphinic - H - C=C - H - proton A B C D E H ppm Figure 9a: The 1 H NMR spectra recorded from soy oil. The different characteristic peaks are noted inside the figure.

42 ppm OH and H - C - OH ppm Figure 9b: The 1 H NMR spectra recorded from polyol (scheme 2).

43 ppm Figure 9c: The 1 H NMR spectra recorded from deuterated polyol (scheme 2).

44 33 The FTIR and NMR spectroscopic results presented above successfully characterized the soy-polyol synthesized using the two-step continuous route (scheme 2). These confirmed complete disappearance of the signature of the double bonds, formation of the epoxy linkage following the epoxidation process, its further disappearance and incorporation of hydroxyl groups after the hydroxylation process. The iodine value, acid value, hydroxyl number, hydroxyl functionality and viscosity of the synthesized polyols were also successfully determined (listed in Table 3 and 4). The yield of polyol synthesized using this approach was determined to be ~ 90 %. Finally, Figure 10 shows a photograph of the soy-polyol synthesized using this approach.

45 34 Figure 10: A photograph of the soy-polyol synthesized using the two-step continuous route (scheme 2).