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TAMU CHEM 237 - Phase Transfer Catalyst

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1Maureen Jariwala!Christopher Komatsu!Phase Transfer Catalyst!237-501-104!April 11, 2021!Phase Transfer Catalyst!Objective:!To observe the use of phase transfer catalyst to result in a Sn2 reaction in a DCM solution.!Data:!Preweighed Vial -Fraction 3 (g)Preweighed Vial -Fraction 4 (g)Vial and Product - Fraction 3 (g)Vial and Product - Fraction 4 (g)11.39311.40311.39511.415TCL SampleRf value (bottom)Rf value (top)At 0 min0.3At 5 min 0.30.64At 15 min0.30.61At 30 min0.30.58TCL SampleRf value Vial 10.00Vial 20.00Vial 30.86Vial 40.87Vial 50.262Percentage yield (Fraction 3): Actual mass of the Product: 11.395 -11.393 = 0.002!Theoretical yield: 0.029g!Percentage Yield: 0.002/0.026 * 100 = 7.69% Vial 3 and 4 had the highest Rf value which means that they contained most of the product ( allyl 2-naphthyl ether), in the IR spectrum of the product there’s a C-O stretch (ether) at 1119 cm^-1 and a C=C stretch (alkene) at about 1628 cm^-1, after examining both the IR spectrums, I determined the vial that contained the pure product was Vial 3 because the IR spectrum for Vial 4 had an extra peak at 3381 cm^-1, which indicates an O-H stretch. The stretch is due to the presence of 2-naphthol. Hence, the calculated percentage yield was"7.69% Understanding of the Scientific concepts!A phase transfer catalyst facilities the movement of a reactant between different phases, in this experiment the two phases are organic and aqueous. PTC is used to manufacture chemicals and also used in pollution prevention by removing impurities from industrial waste streams. Compounds are rarely soluble in both phases, examples of these rare compounds include soaps and detergents. This lab aimed to use PTC to effect an Sn2 substitution. Sn2 substitution is a nucleophilic reaction where one bond is formed and 1 bond is broken in a single step. In this lab, the two reactants have dif-ferent solubility, 2- naphthol is soluble in the aqueous phase whereas allyl bromide is insoluble in the aqueous phase but is soluble in the organic phase. Hence for the reac-3tion to take place, a phase transfer catalyst is required, the PTC used in this experi-ment is benzyl tri-n-butylammonium chloride, this catalyst is an ionic compound and is capable of transferring anions into the organic phase. benzyl tri-n-butylammonium chloride is soluble in DCM and the organic solvents. The reason for this is because of the hydrocarbon chains. The reaction occurs after the PTC takes the naphtholate salt to the organic phase so that the reac-tion can occur and produce the product, allyl 2-naph-thyl ether. !The TLC beaker is prepared by using filter paper and the solvent ( DCM ). The filter paper helps the beaker to become saturated with the solvent vapor, this helps the solvent from evaporating as it rises the plate. The TLC plate is coated with a stationary phase, silica, that is very polar due to the -OH groups attached to the Si atoms. Therefore nonpolar molecules move up the plate faster than polar molecules. The Rf value is inversely promotional to the polarity. All the spots had the same Rf values at the bottom and roughly the same Rf values at the top except the spot at time 0. There was no spot at the top for a spot at time 0 because that was be-fore sodium hydroxide was added. The top spots were due to sodium hydroxide. In addition to that, the spots got darker, this might be because as the reaction progresses the concentration of the product increases.!The other type of chromatography that we use in this experiment is column chromatog-raphy. The main difference is that instead of the silica gel being on a sheet of glass it's4in a glass column. column chromatography is used to separate organic mixture, the separation is not as good as in TLC but it's a lot faster and a lot more of the sample can be separated. In this experiment we use it to isolate the product, in the second TLC plate for the fractions, Vial 1 & 2 had an Rf value of 0 which indicates that those Vials had no product in them. Vial 5 did have an Rf value but it was smaller compared to ones of vial 3 & 4. To further determine which vial had the pure compound an IR spectroscopy is conducted. From the results, we can determine that vial 3 had the pure product. !Unexpected events or problems!While performing TLC one of the most common sources of error is “tailing” this could occur if the compound is too heavy or if the spot was spotted too big. The best way to avoid this to make sure only a small amount is added at first and you can add a little more on top of the spots too tiny. Another error can occur if the TLC plate is dam-aged while handling this could change the direction of the movement of the spots therefore a lot of care should be taken while handling the plates. Using unsuitable sol-vents can also Abe considered a source of error, for my case the hexane solvent was not suitable because it was too non-polar and was incapable of moving all the spots. It is also possible that the spots sometimes might not be visible the reasons for this could be that the spots were too volatile and they evaporated or if the solvent is above the line, this prevents the spots from traveling upwards but rather into the solvent. Hence, it is essential to make sure that the solvent does not touch the line. During the microscope extraction, if the mixture is stirred too fast the layers won’t be able to sepa-5rate properly and cause emulsion. There’s also a possibility of contamination which can result in a wrong conclusion. Lastly, DCM is highly flammable and sodium hydroxide can cause eye irritation and severe skin damage.!Conclusion:!The objective of observing the use of phase transfer catalyst to result in an Sn2 reac-tion in a DCM solution was met. The separation of layers and extraction were per-formed successfully. Thin-layer chromatography was also conducted without any er-rors and the Rf values and IR spectrums were used to properly isolate the product and calculate the percentage yield.


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