Separation of Ethyl Acetate and Butyl Acetate by Simple Distillation and Analysis of Fractions by Gas PDF

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Separation of Ethyl Acetate and Butyl Acetate by Simple Distillation and Analysis of Fractions by Gas-Liquid Chromatography

O H3 C

O O

CH 3

Ethyl acetate (C4H8O2) B.P. 77°C, 88.11 g/mol

H3C

O

CH 3

Butyl acetate (C6H12O2) B.P. 126.3°C, 116.16 g/mol

Methods and Background The objective of this lab is to set up a simple distillation apparatus in order to separate a 1:1 mixture of ethyl acetate and butyl acetate. The goal was to analyze the fractions collected in simple distillation through gas chromatography to determine the % composition of ethyl acetate and butyl acetate in each fraction. And finally the last one was to create a graph of volume vs. temperature from the simple distillation. 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. More volatile liquids can readily vaporize at very low temperatures and they have low boiling points. Relatively, volatile liquids have higher equilibrium vapor pressure at low temperatures. In this lab, two compounds will be examined. Their structures contain an ester group but due to more number of carbon chains in butyl acetate than ethyl acetate, they differ in their boiling points and equilibrium vapor pressures. The boiling point of ethyl acetate and butyl acetate is 77ºC and 126ºC respectively. Ethyl acetate is more volatile than butyl acetate.

The simple distillation apparatus has several parts that are still head, thermometer adapter, thermometer, still pot(round bottom flask), west condenser , vacuum adapter. Keck clips, rubber tubing, graduated cylinder, and beakers. They are all connected together which is shown in figure 1. Simple distillation is used to separate volatile liquid from non-volatile solute or separate two volatile liquids when their boiling points difference is less than 50 °C. In simple distillation, the distillates are separated from less volatile substances that remain as pot residues after the completion of distillation. Since ethyl acetate has lower boiling point, it will be evaporated first in simple distillation. This process follows Raoult's law which says partial pressure is calculated by multiplying the mole fraction and equilibrium vapor pressure. During this process, three fractions will be collected depending upon the temperatures. The first fraction remains close to the boiling point of ethyl acetate. The second fraction temperature

begins to increase and the third fraction stabilizes at or near the boiling point of butyl acetate.. These fractions are then used for gas chromatography.

Figure 1. Simple Distillation Apparatus Gas chromatography is used to separate a mixture of two volatile liquids. Gas chromatography separates the components of a mixture between two immiscible phases: mobile phase and stationary phase. The mobile phase in gas chromatography is a gas which is called a “carrier gas”; gases that include nitrogen and helium A stationary phase is a very high boiling, carbowax. In gas chromatography, the components that get adsorbed to the mobile phase move through the column more quickly, whereas those that show high affinity to the stationary phase migrate more slowly. More volatile substances such as ethyl acetate in this lab would elute out from the column faster and have lower retention time than less volatile substances such as butyl acetate which have higher retention time. The time required for the compound to pass from the point of injection to the detector is called as the retention time of the component. The retention time of a component is not affected by the presence or absence of other mixture components. However, experimental factors affect the retention time of a compound are nature of the stationary phase, length of the column, temperature of the column, and flow rate of the carrier gas. Thus, for a particular column, the retention time will be the same for a specific compound. In gas chromatography, the column’s efficiency increases with increasing length and decreasing diameter. Increasing the length of the column increases the difference in retention time between bands, whereas decreasing the diameter results in narrower bands. Fractions inserted into the gas chromatography instrument are analyzed by observing the peaks on the graph. The first peak observed in the graph is of a less polar compound, which has a short retention time. The second peak observed in the graph is of a more polar compound, which has a larger retention time. Area under peak is also calculated which is proportional to the moles of the compound eluted in the column. For this lab, the ideal % composition is calculated to figure out the % composition of each compound in each fraction. However, the thermal conductivity of substances is slightly different. So, a correction factor must be used in order to figure out the corrected % composition of substances in a given fraction

Experimental Procedures For The simple distillation, the apparatus was set up according to Figure 1. Attach a 100 mL still pot equipped with a still head, west condenser (thick column), bend vacuum adapter, thermometer, and thermometer adapter in a vertical position. Then, to ensure the stability, the apparatus was clipped with Keck clips to prevent any leakage of vapor. A thermometer was placed into the still head with the support of thermometer adapter. The thermometer was kept below the entrance of the condenser to ensure the correct temperature of the vapors. Then, two water rubber tubes were connected with west condenser, one allowing the water to enter in the condenser and other one to drain the water out of the condenser. Graduated cylinder was by the open end of bent vacuum adapter to collect three fractions. After everything was set up, the hot plate was placed underneath the still pot, while 30 mL of 1:1 mixture of ethyl acetate and butyl acetate was added to the still pot. The temperature was set to 45ºC. The vapors were collecting more than 1 drop/ sec so the temperature was lowered to 0 ºC . Three fractions were transferred in a beaker with a watch glass containing 10 mL, 10 mL, and 8 mL for fractions 1,2 and 3 respectively. The temperature was recorded for every 1 ml of liquid distilled. All of the fractions were taken to run and analyzed by the gas chromatography instrument. The graph indicating peaks and area of each fractions was printed out to further analyze. Data Acquisition/Calculations: I. Equations  Boiling Point (mixture) B.P= Ptot= Patm o Ptot- Total pressure above the liquid o Patm- Atmospheric pressure



Dalton's Law: Ptot = Px + Py + Pz..., where: o Ptot = sum of all the partial pressure of the components in a mixture



Mole Fraction: Nx=nx/(nx+ny) o Nx – Mole fraction o nx – Moles of one compound in a compound o nx+ny – Total moles of compound



Ideal % Composition Mol % (of compound A) =



Area of compound A x 100 [(Area of compound A) + (Area of compound B)]

Correction % Composition Mol % (of compound A) = Area of compound A x Mf (A) x 100 [ [(Area of compound A x Mf) +(Area of compound B x Mf)]

Part I: Simple Distillation In Part I, three fractions were collected: 10mL of fraction one was collected between the temperature range of 86.8-99° C, 10mL of second fraction was collected between 100-104° C

and 8mL of third fraction was collected between 118-129°C. The table below illustrates the data observed for the three fractions.

1. Ethyl Acetate: Mole fraction = 0.89 Molecular Weight = 88 g/mol Boiling Point = 77° C

2. Butyl Acetate: Mole Fraction = 0.74 Molecular Weight = 116 g/mol Boiling Point = 126° C Fraction One: Volume (mL) 1 mL 2 mL 3 mL 4 mL 5 mL 6 mL 7 mL 8 mL 9 mL 10 mL

Temperature ºC 86.8 88 90 91 93 94 95 98 98 99

Fraction Two: Volume (mL) 11 mL 12 mL 13 mL 14 mL 15 mL 16 mL 17 mL 18 mL

Temperature ºC 100 101 103 103 104.5 106 108 110.5

19 mL 20 mL

113 114

Fraction Three: Volume (mL) 21 mL 22 mL 23 mL 24 mL 25 mL 26 mL 27 mL 28 mL 29 mL 30 mL

Temperature ºC 118 120 122 124 126 127 128 129 -

Graph 1: Volume vs. Temperature for the simple distillation results:

V o lu m e(m l)

Temperature (°C) at Each Volume in Simple Distillation of 1:1 mixture of EtOAc/BuOAc (1 drop /sec) 130 125 120 115 110 105 100 95 90 85 80 0

5

10

15

20

25

30

35

Temperature (°C)

The Volume vs. Temperature graph shows that in fraction one, the temperature is relatively constant between 86.8-99° C. In fraction two, between 11-20mL, there is a sudden rise in temperature. And in Fraction three between 21-28mL, the temperature again remained constant around 120ºC. Part II: Analysis of Distillation Fractions by GC

The peaks from the GC in the graph were analyzed and Mole percentages of the compound were calculated. See attached copies of the three fractions from gas chromatography. Ideal % Composition Mol % (of compound A) =

Area of compound A

x 100

[(Area of compound A) + (Area of compound B)]

Correction % Composition Mol % (of compound A) =

Area of compound A x Mf (A)

x 100

[(Area of compound A x Mf) + (Area of compound B x Mf)]

Table 1: Analyzing Fractions from Simple Distillation and Gas Chromatography Fractions Peaks Area (s*mV) Retention Time (s)

Fraction 1 Peak 1 Peak 2 3484 329.2 14 8 Ethyl Butyl Acetate Acetate 91.3 8.63

Identity Ideal % Composition Corrected % Composition 92.7 7.28 II. Calculation for Mole percent ideal:

Fraction 2 Peak 1 Peak 2 2337 1154 14 11 Ethyl Butyl Acetate Acetate 66.9 32.9 70.9

29.1

Fraction 3 Peak 1 Peak 2 240.7 3227 9 13 Ethyl Butyl Acetate Acetate 6.9 93 8.23

Fraction one: Peak one: Mol % = {(3484 s*mV)/ [(3484 s*mV) + (329.2 s*mV)]} x 100 = 91.3% Peak two: Mol % = {(329.2 s*mV)/ [(3484 s*mV) + (329.2 s*mV)]} x 100 = 8.63 % Fraction two: Peak one: Mol % = {(2337 s*mV)/ [(2337 s*mV) + (1154 s*mV)]} x 100= 66.9% Peak two: Mol % = {(1154 s*mV)/ [(2337 s*mV) + (1154 s*mV)]} x 100 = 32.9 % Fraction three: Peak one: Mol % = {(240.7 s*mV)/ [(240.7 s*mV) + (3227 s*mV)]} x 100 = 6.9% Peak two: Mol % = {(3227 s*mV)/ [(240.7 s*mV) + (3227 s*mV)]} x 100 = 93%

91.8

Calculation for Mole percent corrected: Fraction one: Peak one: Mol % = {(3484 s*mV x 0.89)/ [(3484 s*mV x 0.89) + (329.2 s*mV x 0.74)]} x 100 = 92.7 % Peak two: Mol % = {(329.2 s*mV x 0.74)/ [(3484 s*mV x 0.89) + (329.2 s*mV x 0.74)]} x 100 = 7.28 % Fraction two: Peak one: Mol % = {(2337 s*mV x 0.89)/ [(2337 s*mV x 0.89) + (1154 s*mV x 0.74)]} x 100 = 70.9% Peak two: Mol % = {(1154 s*mV x 0.74)/ [(2337 s*mV x 0.89) + (1154 s*mV x 0.74)]} x 100 = 29.1 % Fraction three: Peak one: Mol % = {(240.7 s*mV x 0.89)/ [(240.7 s*mV x 0.89) + (3227 s*mV x 0.74)]} x 100 = 8.23% Peak two: Mol % = {(3227 s*mV x 0.74)/ [(240.7 s*mV x 0.89) + (3227 s*mV x 0.74)]} x 100 = 91.8% Conclusion The objective of this lab was to separate a 1:1 mixture of ethyl acetate and butyl acetate using simple distillation and then analyzing it by gas chromatography. For the first fraction, the temperature it was collected was 86.8-99°C which is close to the boiling point of ethyl acetate (77°C). This means the first fraction had higher moles of ethyl acetate than butyl acetate. This is true because the results from gas chromatography graph of fraction on showed that the first peak is ethyl acetate with shorter retention time and the second peak is butyl acetate with larger retention time. In the first fraction, the mole percent of ethyl acetate was 92.7% which was much larger than the mole percent of butyl acetate which was 7.28%. The second fraction was collected at constant temperature of 100-114° C which indicates it contained about equal proportions of both ethyl acetate and butyl acetate. From the peaks by GC, for fraction two, the mole percent of ethyl acetate and butyl acetate were 70.9% and 29.1% respectively. The results from gas chromatography graph of fraction two showed that the first peak is ethyl acetate with shorter retention time and the second peak is butyl acetate with larger retention time. For the third fraction, the temperature it was collected was 118-129°C which is close to the boiling point of butyl acetate (126.3°C). This means the first fraction had larger portion of butyl acetate than ethyl acetate. This is true because the results from gas chromatography graph of fraction on showed that the first peak is ethyl acetate with shorter retention time and smaller area and the

second peak is butyl acetate with larger retention time and larger area. In the third fraction, the mole percent of ethyl acetate was 8.23% which was much smaller than the mole percent of butyl acetate which was 91.8%. Comparing the corrected data with the ideal data for the first fraction, the simple distillation is efficient because there was no significant difference between the ideal composition and the corrected composition. Since butyl acetate has higher boiling point and is less volatile, it eluted out from the column last and had a larger retention time. Comparing the corrected data percent composition with the ideal data for the all of the fractions, the simple distillation is efficient because there was no significant difference between the ideal composition and the corrected composition. There have few of the challenges associated with this lab First most, setting up the distillation apparatus was challenging because it wouldn’t stand still at place until it was clipped. It was hard to determine how to divide up the fractions after looking at the temperatures. The last part of analyzing of the GC graphs was difficult because it was hard to understand how to use area and what identity it stands for until after reading the text again, it was much clear. But finally, the results obtained from this lab are very significant in determining successful separation of ethyl acetate and butyl acetate. Ethyl acetate is more volatile and has a lower boiling point would elute out first, whereas butyl acetate is less volatile and has a higher boiling point would elute out last.

Post lab Questions Carbowax will be the most appropriate for separating a mixture of ethyl acetate and butyl acetate because it is a polar stationary phase. Butyl acetate would elute out first because it is less polar than ethyl acetate. If the polarity of stationary phase increased, th retention time will increase. Absorption is a process in which substance are dissolved. In adsorption, the substance adheres to adsorbent. In Gas Chromatography, the mobile phase passes in an oven. If the rate of distillation would be increased, the temperature at each ml will be harder to measure. Due to fast boiling rate, both compounds would get mixed together and difficult to create fractions. Reference Gilbert, John C., and Stephen F. Martin. Experimental Organic Chemistry. Cengage Learning, Massachusetts, 2011, 5th Ed, pp. 55-58, 127-132, 196-206....