Steam Distillation of Ethyl Acetate and Butyl Acetate PDF

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Steam Distillation of (S)-(+)-Carvone from Caraway Seeds and (R)-(-)-Carvone from Spearmint Leaves Riyushi Mahadik

Introduction Structures

(R)-(-)-Carvone (S)-(+)-Carvone B.P 231 ºC 231 ºC Smell Spearmint Caraway Optical rotation -61° +61° Density 0.96 0.96 IR spectrum same same Rt The objective of this lab is to isolate carvone by steam distillation, to extract carvone from an aqueous mixture with CH2Cl2 using a separatory funnel, to operate IR spectrometer to print out IR peaks, to verify isolation of carvone by thin-layer chromatography comparison with authentic samples and to confirm identity of functional groups by Baeyer test. The Rf values of the distillate will be compared with the Rf values of an authentic sample of R-(-)-carvone and also to examine the relationship between enantiomers of carvones using IR spectroscopy with carbonyl and alkene groups present in the structures. The boiling point of a substance is the temperature at which equilibrium vapor pressure of a liquid equals to the atmospheric pressure. Boiling point is an important physical property of each compound which determines the purity and identity of each compound. It is process when liquid bubbles and there is a spontaneous vaporization. Compounds with higher equilibrium vapor pressure have lower boiling points whereas compounds with lower equilibrium vapor pressure have higher boiling points. The importance of boiling points is crucial in steam distillation to separating the components of a mixture. The liquid boiling in a closed system increases the number of gas molecules until the rate of the molecules entering the gas phase and liquid phase equal out. And reach the dynamic equilibrium. This process of molecules in gas phase in a rapid motion collides against the walls of the vessel exerting pressure. The pressure is called equilibrium vapor pressure which is dependent on the temperature. As the temperature increases, the vapor pressure above the boiling liquid increases. Whereas when a liquid is boiled in an open system, the vapor above the liquid is mixed with air and the total pressure. This process is denoted by Dalton’s Law of partial pressures, Ptotal = Psample + Pair. So, the total pressure above the

liquid is calculated by adding the partial pressure of each component. The partial pressure of the sample is equal to its equilibrium vapor pressure at a given temperature. In this lab, steam distillation will be used to separate carvone from caraway seeds and spearmint leaves. Steam distillation can isolate liquids with high boiling points and are unstable at the boiling temperature. This method can be applicable to substances that are immiscible with water, are non-reactive with water, and are stable at 100 °C and also for a vapor pressure greater than 5 torr at the 100 °C. It is used to isolate the essential oils from caraway seeds and spearmint leaves. For the apparatus of steam distillation, the organic compounds with water to be distilled are placed in a round bottom flask connected with a Claisen adapter, a steelhead and a watercooled condenser as shown in Figure 1. To avoid splashing the mixture into the condenser during the process of the distillation, a small amount of water is added from the separatory funnel directly to the distillation flask with the organic compounds to be separated. A heating mantel is controlled along the process while the thermometer reads the temperature of the vapor and distillate is collected in graduated cylinder.

Figure1: Steam Distillation Apparatus The theory behind the steam distillation is based on the partial pressure Pi of each component i of a mixture of immiscible, volatile substances at a given temperature is equal to the vapor pressure Pio of the pure compound at the same temperature. Thus, this equation-- Pi = Pio summarizes the above sentences. So, this theory does not depend on the mole fraction of the compound in the mixture and each component of the mixture vaporizes independently of the other components or the Roaults Law. Steam distillation also follows the Dalton’s law of partial pressure which says the total pressure above the liquid is calculated by adding the partial pressure of each component. The partial pressure of the sample is equal to its equilibrium vapor pressure at a given temperature. The total vapor pressure is always higher than the most volatiles component. Similarly, the boiling point of the mixture is always lower hat the lowest boiling component. Infrared (IR) Spectroscopy doesn’t provide with chemical composition or quantitative data rather it provides the peaks at certain wavenumber indicating the carbon to carbon double/triple bonds, aromatic rings, carbonyl groups, or hydroxyl groups. IR uses the wavenumber in cm-1 which provides direct relationship between energy and wavenumber and also proves the Hooke’s law. IR measures the light transmitted by the sample than absorption. The lower % transmittance, the

greater is the absorption of light. The device used in this experiment is Attenuated Total Reflectance (ATR) FT-IR accessory that creates graphs with peaks indicating specific functional groups in unknown. Increasing adsorption on polar stationary phases RCO2H > ROH > RHN2 > RR’C=O > RCO2R’ > ROR’ > C=C > R-X Figure 2: Elutropic series for polar stationary phases. In chromatography there are two phases that helps the mixture to separate in to components. Mobile phase is the phase with a liquid or a gas that is passes through the stationary phase. The mobile phase in this lab will be the solvents. The stationary phase is the fixed solid or liquid phase. In this lab, the polar stationary phase is the silica gel. The components bind with of theses phase in order to create the separation of pigments. The polarity also comes in the play when the stationary phase is polar and the mobile phase in non-polar, the polar components of the mixture bind to the stationary phase and the non-polar components would move down the mobile phase. This hence proves the idea of “like dissolves like”. Based on the Figure 2 above that describes the elutropic series, the functional groups that are more polar are the ones that have greater affinity for the polar stationary phases. In this experiment, silica gel was used which is a polar stationary phase and dissolves the polar components of the dyes to the stationary phase better. Thus, the indication of the results would be that more polar substances in thin-layer chromatography will stay at stationary phase longer period of time. In order to calculate the time the component of the mixture spends in a particular phase, the concept of retention time can be applied. Retention time is the time corresponds to the time spent in the stationary phase. The more time the component spent in the stationary phase, the less time spent in the mobile phase and thus, the retention time of that component is more. Retention factor is the calculation of a distance travelled by the substance over the distance traveled by the solvent. This predicts that the higher Rf values are for the non-polar substances because they would travel the most in polar stationary phases. A mobile phase used in the experiment is the solvent system containing ethyl acetate and hexane. The definition of Eluting power is that the ability of a mobile phase to move a substance through a stationary phase. So, if the stationary phase is polar like Silica gel, the nonpolar mobile phases will have less eluting power to move a polar substance. Carvone from both spearmint leaves- (S)-(+)-Carvone and caraway seeds (R)-(-)-Carvone are monoterpenes which means they have ten carbons in terepenes and two isoprene units in terpenes. They have an asymmetric carbon or chiral center and enantiomers. Stereoisomers are molecules that have the same molecular formula and constitution, but different orientations of the atoms. One of the categories of stereoisomers are Enantiomers which are mirror images isomers, and non-superimposable. Enantiomers have same physical properties -- same boiling point, melting point, densities, color, viscosity, infrared spectra, indices of refraction, and thin layer and gas chromatography, but different polarimetry and odor. They have different optical activity because of the chiral center and the directions in which they rotate polarized light are opposite but equal magnitude. R-(-)-Carvone smells like spearmint and is the principle component of spearmint oil and S-(+)-Carvone has an earthy smell and is the major component

of caraway seeds. The nose, being chiral, contains hundreds to thousands of olfactory receptors can identify different molecules by sending signals to the nervous system. The optical density and physical properties are shown in the beginning of the introduction. The R/S configuration of the molecules does not correlate to the (+)/ (-) sings of rotation of molecule. R / S configuration is a naming system for denoting enantiomers. It labels each chiral center R or S according to a system by which its substituents are each assigned a priority, based on atomic number. R means the priority of the remaining three substituents decreases in clockwise direction whereas S stands for the priority of the remaining three substituents decreases in counterclockwise direction. An enantiomer can also be named by the optical activity. So, if enantiomer rotates the light clockwise then it is labeled (+) and if enantiomer rotates the light counterclockwise then it is labeled (−). The thin-layer chromatography is used to analyze the separation of Spearmint leaves pigments according to their polarities. This will help to analyze the extracted compounds-carvone from the steam distillation matches the pure oil carvone. If the dots of oils are happened to travel the same distance then all of the liquids contain carvone. This will conclude that the steam distillation was effective in extracting out the carvone from the spearmint leaves. The retention factors of the carvone will be based on the affinity of polar components of the mixture to the polar stationary phase. TLC follows the capillary action that moves components upward depending on affinities for the mobile phase. Baeyer test uses the reagent which is potassium permanganate. The process goes through a redox reaction in which the KMNO4 reacts with double or triple bonds (-C=C- or -C≡C-) in an organic material (carvone) and displays the color from purplish-pink to brown. The infrared spectroscopy graph of the carvone extract from caraway seeds and spearmint leaves must be the same because enantiomers have identical IR data. Both the R and S configurations of carvone have an alkene and a carbonyl group which will be identified through the IR graphs. Alkenes have a frequency between 1610-1680 cm-1 and carbonyl groups is around 1675-1760 cm-1 with strong intensity. However, the alkene peak is not seen clearly in the graph for both of the samples. The data collected also shows that the steam distillation was efficient in extracting out the carvone oils from the leaves and seeds because the Rf values of all the spots were similar Experimental Procedures Steam distillation Procedures First, the sample—spearmint leaves were weighed upto 5.01 grams and then they were transferred to a round bottom flask. The apparatus was setup for steam distillation which included the organic compounds with water to be distilled are placed in a round bottom flask connected with a Claisen adapter, a steelhead and a water-cooled condenser as shown in Figure 1. To avoid splashing the mixture into the condenser during the process of the distillation, a small amount of water is added from the separatory funnel directly to the distillation flask with the organic compounds to be separated. A heating mantel is controlled along the process while the

thermometer reads the temperature of the vapor and distillate is collected in graduated cylinder at 1 drop per second. 150 ml of hot water and leaves are added to the round bottom flask. Attach two tubes on the condenser to water in and out. Then, using the heating mantel the apparatus was heated upto 45 °C until approximately 75ml of distillate is collected. Throughout the process, the water was replaced in the round bottom flask from the separatory funnel. After each 10 ml of distillate collected, the temperature was recorded. Extraction Procedures

Figure 3: Extraction of Carvone oils in Separatory Funnel. In a sepratory funnel, 7 ml methylene chloride was added to the extract distillate. Then, the funnel with a stopper was inverted approximately 10 times to get the clear separation of layers. The top layer was the aqueous layer while the bottom layer is an oil layer. This process is done three times and the bottom layer of oil was collected three times in a 50 ml Erlenmeyer flask. Then, approximately 1.5 grams of anhydrous sodium sulfate was added to the extract to remove water. Then, the drying agent is removed while the top liquid was decanted into another 50 ml Erlenmeyer flask. This solution was heated under the hood on the heating mantel until 0.5 ml of solution was left for the last procedure. Characterization For the IR of the unknowns, the surface of the apparatus was cleaned with Q-tip and acetone. Particularly, the silver disc and knob was cleaned properly. The background scan was taken and was compared to the spectrum of the standard. After matching the standard, the liquid sample up to five drops was added to the black disc, and the black top was covered. The commands were followed on the computer in order to find the peaks on the graph which was printed. Again, the disc and the knob were cleaned with Q-tip, and acetone and the black disc was placed on the middle of apparatus. Then, TLC plate was prepared with three dots 1 cm from bottom. Left spot was for isolated extract oil, the middle dot for co-spot (both isolated extract oil and authentic oil of (R)-carvone, and the right dot just for authentic oil of (R)-carvone as shown in Figure 5 in results. The 10 ml solvent system of 1:9 ethyl acetate and hexane was poured in a beaker with the TLC plate and covered with watch glass until the solution travelled through the top of the plate. After the test, the plate was seen in UV light which shows the bands of the components in the mixture as shown in Figure 4 in results. Then, the TLC plate was kept in KMnO4 solution for Baeyer Test exposing

the dots and bands from clear to light brown spots. The plate was dried with a heat gun. The middle of the spots was marked for calculating the retention factor values. Data Acquisition Equations: Dalton's Law: Ptot = Px + Py + Pz..., where: Ptot = sum of all the partial pressure of the components in a mixture. Retention Factor: Rf = (distance traveled by substance)/ (distance traveled by solvent) Boiling Point (mixture) B.P= Ptot= Patm Ptot- Total pressure above the liquid Patm- Atmospheric pressure Raoult’s Law: Pi = NiPio P i = Pi o Steam Distillation Distillate Observations: Caraway Seeds (5 grams)

Spearmint leaves (5 grams)

Color: Brown

Color: Green

Smell: Strongly earthy

Smell: Minty

Sample: Somewhat clear

Sample: Somewhat cloudy

More than one phase: Yes

More than one phase: Yes

Our group performed steam distillation of spearmint leaves. During steam distillation, temperature and volume at 10 mL intervals was recorded and is listed in the table below. About 80 mL of the total distillate was collected. Table 1: Temperature at each 10 mL of Distillate Collected in Steam Distillation Volume of Distillate (mL) 10 20 30 40 50

Temperature (°C) Spearmint leaves 101 101.5 101 101 101

Temperature (°C) Caraway seeds 100 100 100 100 100

60 70 80

101 101 101

100 100 100

T e m p er atu r e(°C )

Graph 1: Temperature at each 10 mL of Distillate Collected in Steam Distillation of Spearmint Leaves 101.6 101.5 101.4 101.3 101.2 101.1 101 100.9 0 10 20 30 40 50 60 70 80 90 Volume of Distillate (mL)

T e m p era tu re(°C )

Graph 2: Temperature at each 10 mL of Distillate Collected in Steam Distillation of Caraway seeds 120 100 80 60 40 20 0 0

10 20 30 40 50 60 70 80 90 Volume of Distillate (mL)

The graph of temperature vs. volume for spearmint leaves is constant around 101 °C and caraway seeds is constant around 100°C. There is no application of Raoult’s law for steam distillation because the total vapor pressure is independent of the mole fraction of each component of the mixture. However, Dalton's law is applicable for steam distillation which states that the total vapor pressure of the mixture is equal to the sum of individual vapor pressures of its components. Therefore, the total vapor pressure is always higher than most volatile component and boiling point of mixture is always lower than the lowest boiling component (water in steam distillation). Because of the presence of water another component of mixture boils below its normal boiling point. According to our results, the temperature of distillation is around the boiling point of water (100°C). Even though the temperature was higher than the boiling point of water, these differences are the results of impurities in the sample or any other errors during the distillation process. Infrared Spectroscopy

The IR spectrums for caraway seeds and spearmint leaves are attached to this report. There was a little peak of Alkenes C=C which was not indicated with an intensity on both of the graphs. Overall, the IR data for both caraway seeds and spearmint leaves are the same. Spearmint leaves: 1671.55 cm-1 → Ketones C=O strong stretch Caraway seeds: 1668.34 cm-1 → Ketones C=O strong stretch Thin-Layer Chromatography and Baeyer’s Test

Figure 4: TLC plate of Spearmint Leaves in UV light

Figure 5: TLC plate of Spearmint Leaves after Baeyer’s Test

Figure 6: TLC plate of Caraway Seeds after Baeyer’s Test

Figure 5 and 6 shows the three spots corresponding to different mixture. In Figure 5, spot A corresponds to spearmint extract, spot B is a co-spot both isolated oil and authentic oil, and spot C is of authentic oil R-(-)-Carvone. In Figure 6, spot A corresponds to caraway seeds extract, spot B is a co-spot both isolated oil and authentic oil, and spot C is of authentic oil R-(-)Carvone. After the spots were observed on the TLC plate, their retention factors were calculated. Also, the solvent was prepared by using 1:9 concentrations of ethyl acetate and hexane, respectively. The data in the table below shows that R and S carvones have almost the same Rf values. Table 2: Calculations of Retention Factors of Each Spot in Both Samples Plate Numbe r

Sample

Pigments Observed

Distance Traveled by Substance (cm)-dx

Distance Traveled by Solvent (cm)ds

Rf Value (dx/ds)

1

Spearmint Leaves

Extract sample

4.1

5.1

4.1 cm/5.1 cm= 0.804

Co-spot (Extract and authentic oil)

4

5.1

4 cm/5.1 cm= 0.784

Authentic Oil

3.9

5.1

3.9 cm/5.1 cm= 0.765

Extract sample, Co-spot (Extract and authentic oil), Authentic Oil

4

7

4 cm/7 cm= 0.57

2

Caraway Seeds

Conclusion The objective of this lab was to isolate (S)-(+)-Carvone from caraway seeds and (R)-(-)-Carvone from spearmint leaves using steam distillation and examine the properties of the enantiomers of carvone. Since, they have similar physical and chemical properties, these characteristics of the enantiomers of carvones were analyzed through the peaks of infrared spectroscopy data, Rf values obtained from thin-layer chromatography, and the Baeyer test. The extract of spearmint leaves obtained from steam distillation had minty smell, whereas caraway seeds had a earthy odor. These differences in smell indicates that the there is a difference in stereochemistry of these compounds. During the...