Lab5-2 - Lecture notes 5-2 PDF

Preview

Summary

Lecture reading from TA...

Description

Marlin Amy Halder 4 February 2014 Partner: Maurice Dixon TA: Wiktoria Pecak, Tues 12pm Steam Distillation of (S)-(+)-Carvone from Caraway Seeds and (R)-(-)-Carvone from Spearmint Leaves Methods and Background The goals of this experiment are to separate essential oils from caraway seeds and spearmint leaves using steam distillation, and analyze it using IR Spectroscopy, TLC and R f factor and Bayers Test. The extraction from an aqueous mixture of carvone (C10H14O) and CH2Cl2 is done using a separatory funnel. The extracts are then analyzed for the major component – carvone – using thin-layer chromatography (TLC) and infrared spectroscopy (IR). The IR spectroscopy cannot determine whether the sample of carvone is (R) or (S). This is because the spectroscopy only shows the functional groups, not where they are positioned. The extracted oils are also used in the TLC plate to see which enantiomer is present in each of the oils. Structures of Carvone Enantiomers (R)-(-)-Carvone

(S)-(+)-Carvone

There are two different types of carvone (5-isopropylene-2-methyl-2-cycloxenone) involved in this experiment: (S)-Carvone and (R)-Carvone. In relation to each other, the two molecules are entantiomers. Enantiomers are two molecules that contain the same elements in the same order, however they have different molecular shape around a chiral center; they are non-superimposable mirror images of one another. Spearmint contains (R)-(-)-carvone whereas caraway contained (S)-(+)-carvone. Due to enantiomers’ difference on being the spatial arrangement, the boiling points (231oC), density (960 kg/m³), infrared spectra, and retention factors will all be the same. The only differences would be the optical rotation and the smell of the substance. Polarimeter determining optical rotation

The optical rotation occurs in opposite directions in plane-polarized light. Caraway seed’s optical rotation is 61o and spearmint’s is -61o. The optical rotation is the ability of a chiral substance to rotate a plane of polarized light. A light source shines on an unpolarized light and then goes through a polarizing filter so that the light only oscillates in one plane. Once the polarized light oscillates into the sample tube, containing carvone, the angle of the polarized light changes. This optical rotation has to be experimentally determined and cannot be automatically linked with a certain enantiomer of a compound. Noses are also chiral environments. There are different nose receptors depending on the shape of carvone. This is what leads to the different smells, one smelling like caraway seeds and the like spearmint leaves. Steam Distillation Apparatus

In this experiment, carvone was extracted through steam distillation. Steam distillation is commercially used to separate oils from plant matter, and is a useful method to distill substances with high boiling points at less than 100OC. This is because steam distillation essentially boils a mixture of the substance (oils) and water; water has the lower boiling point so it boils first, and the steam that rises and condenses also carries molecules of the substance along with it. The substance can then by extracted from this distillate in a variety of ways; methylene chloride is used to extract the carvone from the water. The requirements in order to perform steam distillation of a substance are: immiscible and non-reactive with water, stable (cannot decompose) at 100OC, and have an equilibrium vapor pressure greater than 5 torr at 100OC. Steam distillation is used for compounds that decompose close to their boiling points. Since the distillation takes place at a temperature much lower than the boiling point of the compound (at the bp of water), it will not decompose.

The boiling point of a liquid refers to the temperature at which the liquid’s equilibrium vapor pressure is equal to total pressure (Pox = Ptotal). Compounds with lower boiling points are more volatile and have higher equilibrium vapor pressures. In simple and fractional distillation, which separate solutions of miscible liquids, as the more volatile component vaporizes, its concentration increases in the vapor phase and the concentration of the less volatile compound increases in the liquid phase, causing the mixture’s vapor pressure to decrease. Raoult’s Law describes this behavior: Px = Pox × Nx, Px = partial pressure of component X, Pox = equilibrium vapor pressure of component X, and Nx = mole fraction of component X in the mixture. Steam distillation, on the other hand, separates immiscible substances (such as carvone and water) so the partial pressure and vapor pressure of each component do not rely on the component’s mole fraction in the mixture. In fact, in steam distillation, the partial pressure of each component is equal to its vapor pressure as described by the following equation: Px = Pox. These laws are modifications of law, which quantitatively conveys the concept that, in a mixture of two or more volatile components, the total vapor pressure is identical to the sum of the partial pressures of the volatile compounds. Dalton’s law is expressed as follows: Ptotal = PX + PY + PZ + … PX, PY, PZ are individual partial pressures Infrared spectroscopy (IR) is a IR Spectra of Carbonyl and Alkene Groups spectral method that measures for any functional groups present in a given compound. The IR spectroscopy measures the bond’s dipole when it stretches, bends and vibrates. The frequency of vibration depends on the size of the compounds attached to the bonds as well as the strength of the bond. Each functional group has a specific size and shape, which results in its own distinctive peak in the IR spectra. The frequency of each vibration is measured in wavenumbers (cm-1). The application of IR in this experiment is to ensure that the carvone has been isolated. It cannot help determine which enantiomer of carvone it is. The IR spectra can only determine which groups are present, and not the connectivity. Since enantiomers have the same functional groups present but in a different shapes, the IR spectra of both the caraway seeds

and the spearmint leaves should be exactly the same. It is expected to see a carbonyl group and an alkene group in both IR spectra. TLC Developing Chamber

Chromatography is a technique that separates organic mixtures on the basis of their varying affinities for a stationary phase and a mobile phase as determined by the polarities of the solvents, adsorbents, and the original mixtures’ components. The amount of time that it takes for the solute to flow through the stationary phase is called its retention time. The greater the polarity of the solute, the longer its retention time due to its higher affinity for the stationary phase. Because the individual polarity of each component in a mixture causes it to move through the stationary phase at a unique speed, different components are forced to separate from one another. The specific method used in this experiment was TLC. The TLC plate was dotted with mixture and placed inside a chamber that contains a small amount of the mobile phase solvent. As the solvent travels up the TLC plate, the mixture’s components separate at different locations, according to their individual polarities. More polar substances bind to the stationary phase more strongly and travel less than do less polar substances. As a result, the more polar substances would have a lower retention factor. The retention factor was equal to the distance the substance travelled divided by the total distance travelled by the solvent. Since the more polar substances would spend more time bound to the stationary phase the distance travelled up the TLC plate would be lower than that of a non-polar substance. In conclusion, the TLC test provided with information that the oil extracted has mainly one component, the IR spectroscopy showed that both carvones has similar functional groups. But the smell, which acted as a chiral environment differentiated the two oils as the S(+) carvone smelled like caraway seeds and R(-) carvone had a minty fragrance. Experimental Procedure(s) Obtain a sample of 5g of dry spare mint leaves, weigh it and place it in a round-bottom flask (500mL). Boil 150mL of water and add it to the spare mint leaves. The flask is then attached to the steam distillation apparatus, pictured right

which consists of a Claison adaptor, separatory funnel, stillhead, thermometer, thermometer adapter, West Condensor and vacuum adaptor. Heat the flask until there is a constant rate of distillate flowing into the awaiting graduated Steam distillation apparatus – used to extract oil

cylinder. Once the distillate begins to drip into the graduated cylinder open the separatory funnel containing the hot water and adjust the flow rate in order to maintain a constant volume inside the flask. The temperature is recorded every 10mL until 75mL of water and oil mixture is collected. At this point, turn off the heating mantle so that the distillate would stop flowing. In a closed separatory funnel, pour the distillate and add 7mL of methylene chloride. Cover the funnel with a stopper and shake the mixture from side to side. Take off the stopper to release the gas build up inside the funnel and filter out the clear bottom layer into an Erlenmeyer flask. Repeat it two more times and collect all the ethylene chloride in a flask. Mix in Na2SO4 so that the excess water was removed. Them, the salt is then removed from the mixture using gravity. The extract was then used for TLC plating in order to make it less concentrated. TLC is performed with three different spots; one with the authentic carvone, the other and co-spot with caraway oil and the last one with just the sample carvone. Perform the Bayers test by staining the plate with KMnO4 and dried using the hair gun. Before the IR spectroscopy was done, the mixture is heated to reduce it to its essential oils. Use an ATR to scan essential oils. IR Spectroscopy: Clean the IR spectrometer’s crystal with a q-tip and acetone and a background scan was run prior to placing two drops of the carvone extract on the crystal. An IR spectrum of the extract was obtained. Repeat the experiment for the other mixture. TLC: A developing chamber is prepared by adding a 1:9 mixture of ethyl acetate and hexanes to a beaker to create a liquid layer that was 0.5 cm deep. A TLC plate is obtained and a line is marked about 1 cm above the bottom of the plate. The TLC plate is placed in the developing chamber, which is then covered with a watchglass. The plate is observed until the solvent travels close to the top. The plate is taken out of the chamber and the solvent’s travelled distance was marked and measured. The plate is placed in an ultraviolet light chamber and the distances that each spot travels are marked. The TA then stains the plate with KMnO4 and each spot’s travel distance is measured. Data Acquisition These temperature and volumes were noted from the steam distillation apparatus and observing how much distillate came out and what the temperatures were. Temperature vs. Volume of Distillate for Caraway Seed and Spearmint Leaves Distillation Caraway Seed Distillation

Spearmint Leaves Distillation

Volume (mL)

Temperature (°C)

Temperature (°C)

10

100

99.5

20

102

100.1

30

102

100.2

40

102

100.5

50

102

100.5

60

102

100.5

70

102

100.5

75

102

100.7

Thin-Layer Chromatography For the TLC plates, about 1mL 1:9 mixture of ethyl acetate and hexane was poured into a beaker and the plate contained three spots with a co-spot in the middle, authentic oil and extracted oil on the sides. Three spots were looked under the UV-light and measurements were taken down and calculated below. Afterwards, the Bayers test was performed and it showed an orange color indicating there was a double bond (alkane) or triple bond (alkene) present. Spearmint Leaves

Caraway Seeds Spearmint Leaves: (R)-Carvone: Rf = 2.6 / 6.5 = .40 Co – Spot: Rf = 3.1 / 6.5 = .48 Pure: Rf = 2.5 / 6.5 = .38 Caraway Seeds: (S)-Carvone: Rf = 2 / 4.1 = .49 Co – Spot: Rf = 2 / 4.1 = .49

Pure: Rf = 2 / 4.1 = .49 Distance of Solvent (cm) Spearmint Leaves 6.5 6.5 6.5 Caraway Seeds 4.1 4.1 4.1

Distance (cm)

Retention Time (Rf )

(R)- Carvone Co – Spot Pure

2.6 3.1 2.5

.40 .48 .38

(S)- Carvone Co – Spot Pure

2 2 2

.49 .49 .49

Smell and Bayers Test When the caraway extract was smelled, it gave off a strong caraway odor, and when the spare mint leave extract was sniffed, it smelled very strongly of mint. This proves that they are enantiomers with different properties when put in a chiral environment (our nose). The Bayers test concluded that there is an alkane present as the brown turned into purple when put into KMnO4.

Infrared Spectroscopy The IR spectra are obtained following the previously described process. The wavelengths that were most helpful are listed below with the functional groups. The actual IR Spectroscopy graphs are attached with the lab report in the back. Wavenumber of Characteristic Peak (cm-1)

Functional Group

R-carvone

S-carvone

1669

1668

C = C (sp2 Carbons)

1712

1670

C=O

Conclusion The goals of this lab were to use the technique of steam distillation to isolate carvone enantiomers in the form of essential oils from caraway seeds and dried spearmint leaves and to use the analytical methods of infrared spectroscopy (IR) and thin-layer chromatography (TLC) to confirm that the isolation was successful. Steam distillation did, in fact, prove to be effective in separating carvone from the two extracts, as was proven by the IR spectra and TLC results. The head temperatures of each mixture during steam remained fairly constant with a range of 99°C – 102°C. Thus, the boiling point of the mixture was close to the boiling point of the lowest-boiling component in the mixture (water), though it was not always lower because water has a boiling point of 100oC. The goal of this experiment was to isolate the essential oil and analyze and verify the mixture of products by infrared spectroscopy and thin-layer chromatography. Steam distillation was used because the essential oil extracted was immiscible with water and it had a relatively high boiling point (230°C); steam distillation allowed the distillate to be collected at a much lower temperature (103°C). From the IR spectrum, the presence of a C=C functional group was detected at 1668cm-1, and 1669 cm-1. The presence of a C=O group was detected at 1670 cm-1 and 1712 cm-1. Based off the TLC, the essential oil can said to be composed of carvone only for both R and S carvone because, as the Rf value (0.38 and 0.49) of the essential oil similar to that of pure carvone (0.40 and 0.49). Bayers test also revealed that the compound contained double bonds. The only difference between enantiomers is its characteristics when presented in a chiral environment and that is noticed by the smell observations. References Gilbert, J.C., Experimental Organic Chemistry. Austin: Thompson Brooks/Cole, 2006. 4th Ed. 145-147, 223-226, 251, 869...