The purpose of this lab is to separate a 1:1 mixture of ethyl acetate and butyl acetate by simple distillation, which is then analyzed by gas chromatography. The chromatography test will then assure us if the distillation gave us a good separation of ethyl acetate and butyl acetate (Figure 1). Both compounds have almost similar structures due to the presence of an ester group. This is the only similarity shared between these compounds, however they differ in their boiling point, dipoles, attractive forces, number of atoms, number of electrons and equilibrium vapor pressure.
These differences then help in determining the relation between compound and two immiscible phases. The separation of mixture is obtained based on different boiling points of both compounds where ethyl acetate has a boiling point of 77° C and butyl acetate has a boiling point of 126° C. As the mixture is heated, the first compound to vapor will be ethyl acetate due to its lower boiling point and as the temperature increases, there will be less ethyl acetate in the mixture.
At around 77° C – 80° C, the vapor that being condensed should contain both compounds and an increase in the temperature will be observed. Then, after the temperature becomes steady around 122° C – 130° C, vapor is being condensed at this point will be butyl acetate. When performing simple distillation, three fractions are collected. First is when the temperature remains close 77° C; second, when a rapid increase in temperature is observed and third, when the temperature remains close to 126° C. These fractions are then used for gas chromatography.
Ethyl Acetate Butyl Acetate
Figure 1: Structures of Ethyl Acetate and Butyl Acetate
Distillation is a laboratory method to separate and purify a mixture of compounds. There are many kinds of distillation techniques such that simple distillation and fractional distillation. However, this lab is based on simple distillation following Gas – Liquid Chromatography (GLC). Gas chromatography is based upon the same principles of chromatography as column and TLC, but GLC is used for separating a mixture of compounds that can vaporize without dissolution.
Similar to column and TLC, gas chromatography is a process of separating a mixture of two or more compounds based on their relative affinity with two immiscible phases, stationary, and mobile phases. In gas chromatography, the stationary phase is the high boiling liquid and the mobile phase is not reactive gas, such as nitrogen and helium. In this lab, the mobile phase is termed as “carrier gas” as its responsible for carrying the mixture through the column, which is supported by a very reactive high boiling liquid. The high boiling liquid in this case is the stationary phase and can be obtained by performing simple distillation as mentioned above.
Gas chromatography is performed to check correct distillation of mixture by observing the peaks on the graph. The first peak observed in the graph is a result of less polar compound, which has short retention time, measured in seconds and second peak results in more polar compound, which has larger retention time. Moreover, area under peak is also calculated and is proportional to the moles of compound eluted. Overall, chromatography test determines many characteristics of mixture.
The simple distillation apparatus was constructed accordingly to the diagram seen in the textbook, page 56. The 100 mL round bottom flask was equipped with a stillhead, west condenser (thick column), bend vacuum adapter, thermometer, and thermometer adapter. The equipments were tightly clipped to prevent vapor from escaping apparatus. A thermometer was placed into stillhead with the support of thermometer adapter. The thermometer was suppose to be kept below the entrance of condenser to endure that the mercury bulb of thermometer is immersed thoroughly in vapors. Then, two water tubing were obtained and were hooked with west condenser. One of the water tubing allowed the water into condenser and the other was there to drain it. Also, a cylinder was placed by the open end of bent vacuum to collect three fractions.
See figure 2. 30 mL of the 1:1 mixture of EtOAc/ BuOAc was obtained and added to the round bottom flask. The thermowell was initially set to 60 in order to heat the apparatus, and then lowered to 40 in order to maintain a 1 drop per second rate. The temperature was recorded for every ml of liquid distilled. The first fraction was collected until the temperature began spiking (temperature close to 77° C). The second fraction was collected until the temperature again reached a plateau. The last fraction was collected until the initial volume was completely distilled (temperature around 126° C). Each fraction was covered with a watch glass to minimize evaporation.