Experiment 10-Phase Transfer Catalysis PDF

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Phase Transfer Catalysis Introduction: The objective of this experiment was to observe the use of a phase transfer catalyst to cause an SN2 reaction in a dichloromethane solution without conducting the extraction for the product isolation. Methods used to accomplish the object include thin-layer chromatography and the isolation of allyl-2-napthyl ether. The product of the phase transfer reaction will be isolated using liquid chromatography and a small column packed with silica gel. Summary of Experiment: For this experiment, TLC is used to monitor the reaction of the reaction solution containing 2-napthol, benzyl-tri-n-butylammonium chloride (the catalyst), and allyl bromide in dichloromethane. At 0 minutes, 10 minutes, 30 minutes, and 60 minutes, samples from the bottom organic phase of the mixture are taken. The Rf values for the 1st TLC plate are shown in the table below. TLC Plate 1: Developed in Dichloromethane Time= # minutes (Sample) (S1) Time= 0 minutes (S2) Time=10 minutes (S3) Time= 30 minutes (S4) Time= 60 minutes

Rf 1 cm/3 cm= 0.333 0.8 cm/3 cm= 0.267 2.7 cm/3 cm= 0.900 2.7 cm/3 cm= 0.900

The sample taken at 30 minutes had the largest Rf value of 0.9. The Rf values were calculated using the formula: Rf=(d1/ds). This shows that S3 is the spot for allyl 2-napthyl ether, as it has the first largest Rf value and as the reaction nears completion, the spot became less visible and the intensity and Rf became constant (as seen when time=60 minutes). For the 2nd TLC plate, the bottom dichloromethane layer of the 60-minutes sample from the reaction vial was extracted with a syringe and dried with 0.501 grams of anhydrous calcium chloride. The dried solution was next transferred to a sample vial to find the total volume of dichloromethane containing product, which had a volume of 0.58 mL. For the 2nd plate, 5 spot samples were taken by running the dried dichloromethane through the minicolumn with silica gel at consistent levels and filling 5 sample vials with each trial/sample. Below is a table showing the recorded data and observations. TLC Plate 2: Developed in Dichloromethane Sample Vial # Rf Vial #1 1 cm/3.2 cm= 0.313 ; 3.0 cm/3.2 cm= 0.938 Vial #2 0.8 cm/3.2 cm= 0.250 ; 2.9 cm/3.2 cm= 0.906 Vial #3 3.0 cm/3.2 cm= 0.938 Vial #4 0.8 cm/3.2 cm= 0.250 ; 3.0 cm/3.2 cm= 0.938 Vial #5 0.9 cm/3.2 cm= 0.281 ; 3.0 cm/3.2 cm= 0.938

The TLC plate and large Rf values of 0.938 proved that sample vials 3,4, and 5 contained pure product. Sample 3 was the vial used to obtain an IR spectrum as it had the strongest TLC spot and the largest Rf value (0.938) that remained constant as the reaction continued to completion. The obtained IR spectrum showed that 2-napthol was the remaining starting material in the sample. The strong peak of 3058.41 cm-1 shows the O-H stretch of 2-napthol. Below are the calculations done to calculate the yield of product for the samples of pure product (3,4 & 5). Yield of product=

[ ( Sample product +Vial Mass )− ( Vial Mass ) ] ∗100 % 0.8 mL

Sample 3 Yield=

7.226 g−7.207 g 0.019 g = ∗100=2.375 % product yielded 0.8 mL 0.8 mL

Sample 4 Yield=

7.213 g−7.205 g 0.008 g = ∗100=1.000 % product yielded 0.8 mL 0.8 mL

Sample 5 Yield=

7.240 g−7.2 g 0.019 g = ∗100=5.125 % product yielded 0.8 mL 0.8 mL

Possible source of errors and probable solution: One possible error includes stirring the mixture too fast after the reaction mixture is added to the dichloromethane and the NaOH is added. If the mixture is stirred too fast it may look emulsified and the mixture will not separate into its proper layers. Be cautious when shaking in order to avoid this possible error. Another possible error includes letting the solvent level drop below the top of the silica gel when filling he mini-column during the isolation of allyl 2-napthyl ether. If this error occurs, air bubbles can form in the column and this could cause the samples spotted on the TLC plate and Rf values to be inaccurate and the IR spectrum for sample 3 could be skewed. Carefully watching the solvent level of the column helps avoid this possible problem. Discussion of Results: The Rf values of TLC plates 1 and 2 and the identified IR spectrum peak successfully helped determine the sample vials that still contained pure product as well as determine the starting material that remained in the sample after completion of the reaction, the drying with anhydrous calcium chloride, and the running of the samples through the silica gel. The Rf values helped determine that sample vials 3, 4, & 5 contained pure product as they had the largest and most consistent to completion Rf value of 0.938. The IR spectrum peak helped determine that the remaining material in the sample was 2-napthol. From the data and the observations, it can be concluded that experiment was successful in achieving the given objective of using a phase transfer catalyst to result in a SN2 reaction in dichloromethane and observing the results....