TLC Lab report Organic chem PDF

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TLC lab report...

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Tiffany Nguyen Potla Sandesh Chem 302Lab Mar 31st, 2020 Thin layer Chromatography Result and Discussion Results Solvent

Compound

Rf

Toluene

trans-stilbene acetophenone benzoic acid

0.86 0.22 0.1

1,2-dichloroethane

trans-stilbene acetophenone benzoic acid

0.84 0.43 0.16

trans-stilbene 0.8 acetophenone 0.76 benzoic acid 0.63 Thin layer chromatography revealed the polarity relative for solvent as mobile phases, the

acetone

compound as a sample, and its binding affinity to polar absorbent/stationary phase SiO2. The retention factor (Rf) is a quantitive value of TLC. It based on how far the compound can go over the distance of carrying solvent (MAHSH, 2014).

Rf=

distanceof compound has traveled distance of solvent has traveled

In the experiment part I, three different solvents was used to develop the samples, trans-stilbene, acetophenone, and benzoic acid.

Table 1. TLC retention time for developing solvents toluene, 1,2-dichloroethane, acetone with different compounds trans-stilbene, acetophenone, and benzoic acid. In part two of this experiment, the developing solvent was a mixture of ethyl acetate and hexane in ration 80:20, 20:80, and 50:50. The development is similar to part one.

Solvent

Compound Rf trans-stilbene 0.80 80/20 acetophenone 0.73 benzoic acid 0.68 trans-stilbene 0.66 acetophenone 0.43 20/80 benzoic acid 0.21 trans-stilbene 0.84 50/50 acetophenone 0.69 benzoic acid 0.45 Table 2. TLC retention time for three developing solvents trans-stilbene, acetophenone, benzoic acid with three mixtures in different ratios of ethyl acetate to hexane.

Discussion Thin layer chromatography is a type of chromatography to identify solvents and compound and polarity identity. It is also efficient and affordable to perform in the mass industry (MAHSH,2014). Its mechanism depends on two phases, mobile and stationary. The TLC plate is coated with a thin layer of silica gel (SiO2), which also called the absorbent and stationary phase of TLC ( Lab manual, 2018). In the stationary phase, the plate is constructed by a structure of SiO2 bonded together. Each composition is polar. Therefore the whole thin layer is a big network of Si, O2, and -OH group on the outside surface. It increases its polarity and strong

intermolecular bonds of hydrogen. For unlike characteristics such as non-polar substances, it has only Van der Waals force to support (MAHSH,2014). The mobile phase is the developing solvents; in this experiment, it would be toluene, 1,2-dichloroethane, acetone and the mixture of ethyl acetate and hexane in part II. The developing solvent, or eluent, traveled from the bottom of the TLC plate to the top brought the sample along the way. The solvent molecules rise by capillary action. The polarity of TLC, developing solvent, and sample will decide how far it would go. If the solvent and the sample are polar related. The solvent and eluent will compete for absorbent. More polarity needs a longer time to react, so it goes slower and shorter distances. And vice versa. In the experiment part I, three different solvents was used to develop the samples, transstilbene, acetophenone, and benzoic acid. Among those three, trans-stilbene is non-polar because it has a structure of symmetry by the double bond C=C; it does not have any difference of electronegative value. Benzoic acid and acetophenone are more polar since benzoic has a carboxyl group attaches to benzene. Acetophenone is moderative polar compared to benzoic acid because the hydroxyl group creates a ketone. However, a carboxyl acid group has higher polarity. It is analyzing the TLC plates in trans-stilbene with three solvents: toluene, 1,2dichloroethane, and acetone (Table 1). Toluene has a higher Rf value then 1,2-dichloroethane then acetone. It means acetone has more polar than 1,2-dichloroethane than toluene. Since the trans-stilbene is a non-polar solvent, but the stationary phase is polar will interact with acetone the most, keeping it placed at the lowest point, relatively to second to most polar, 1,2dichloroethane and toluene. Trans-stilbene is a non-polar compound, so when it in interaction toluene, another non-polar compound, the eluent binds to compound tightly and carries to the highest point.

In the acetophenone TLC plate, the mobile phase had changed into a more polar solution. In reverse to trans-stilbene data, toluene is the lowest point (0.22) then increases to 1,2dichloroethane (0.43) and last acetone (0.76). The developing solution with acetophenone has more polarity than the previous trans-stilbene. It interreacts most with the highest polarity compound, acetone, then brings it to the highest point. The solvent has eluted the compound in the mobile phase since acetophenone shows more similar polar properties with acetone; it secures the bond by dipole-dipole forces. Then it follows the lower order of polarity, 1,2dichloroethane, and toluene. Benzoic acid is the most polar compound. Therefore, its results were the lowest Rf values compares to others. Similar to acetophenone, the highest point on TLC was marked for acetone, then 1,2-dichloroethane and toluene. It follows what is most polar to the least. Benzoic acid has bonded to acetone most than the least polar toluene. In the second part of the experiment, ethyl acetate and hexane were mixed in different ratios. Hexane is non-polar with its symmetrical structure. Ethyl acetate is polar because it has carbonyl bonds, and dipole moment does not cancel each. The different rates created a difference of polarity between mixtures. In mixture 80:20, there was more ethyl acetate than hexane; therefore, the polarity of the solvent. Trans-stilbene was used to develop with 80:20, and it had the highest value over the other two (Table 2). It shows the highest polar solvent does not have a lot of interaction with this particular least polar compound. Acetophenone has lower Rf, and benzoic acid is most moderate since it has the highest polarity. In the mixture of 20:80 ratio, the polarity of ethyl acetate is decreased and replaced by non-polar hexane. It predicts the most polar substance would lowest Rf and least polar is the highest Rf. Since the most polar compound will look for a similar mixture, the stationary phase SiO2 is polar like it. So, it instead to create a

dipole bond when it is possible to be stable. While the least polar compound seeks for non-polar solvent, which is hexane in the mixture, developing solvent would bring it to the highest point on TLC. The increasing distance of compound travel will increase the Rf value. It confirmed with the result in 20:80 mixture, trans-stilbene had most top Rf then decreased to 1,2-dichloroethane and then benzoic acid. In a 50:50 mixture, an equal amount of hexane and ethyl acetate were mixed. Benzoic acid had the lowest Rf value, then increased to 1,2-dichloroethane, toluene perceptively. Since polar and non-polar will not mix as in water and oil don't mix. Benzoic acid can bind to the most polar solvent it could found, ethyl acetate. Similar to the previous polar solvent-polar compound, benzoic acid induced a bond with ethyl acetate to adsorb the plate then absorb with the stationary phase. 1,2-dichloroethane was still relatively less polar. It could follow ethyl acetate in the mobile phase and absorbed over a thin layer of SiO2. However, toluene is the least polar, and hexane is non-polar. It ran farthest comparing to other samples using the same developing solvent and in different solvents. Therefore, it did not form a secure connection with polar material like silica gel but travel through with the mobile phase, hexane.

References CSUF Department of Chemistry (2018). Chem 302 Laboratory Manual. Hayden-Mcneil.

Mohrig, J. R., Hammond, C. N., & Schatz, P. F. (2014). Techniques in organic chemistry miniscale, standard taper microscale, and Williamson microscale. New York, NY: Freeman....