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Nucleophilic Substitution Reactions Lab

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Experiment 2 Report Scaffold (Substitution Reactions, Purification, and Identification) Purpose/Introduction 1. A Sn2 reaction was conducted; this involved benzyl bromide, sodium hydroxide, an unknown compound and ethanol through reflux technique, mel-temp recordings, recrystallization, and analysis of TLC plates. 2. There was one unknown compound in the reaction that was later discovered after a series of techniques described above. 3. To purify and identify the product, recrystallization is used in order to purify the product, then melting point and TLC techniques are used to identify the product. Theory 4. In nucleophilic substitution reactions, there are two possibilities, either Sn1 or Sn2. In this particular experiment, an Sn2 reaction…show more content…
TLC was used to identify the actual unknown product as well as other products/reactants present in the filtered solution. The procedure was conducted by placing a TLC plate in a developing chamber that is filled with a small amount of solvent. The solvent cannot be too polar because it will cause spotted compounds on the TLC plate to rise up too fast, while a very non-polar solvent will not allow the spots to move. The polarity of the spots also determines how far it moves on the plate; non-polar spots are higher than polar ones. After spots on the TLC form, the Rf values are calculated and used to analyze the similarity of the compounds. Results 8. The obtained product was 4-tert-butylbenzyl phenol ether. This leads the unknown compound # 51 to be tert-butyl phenol. 9. Theoretical yield = (150.22g/mol)(3.5 x 10^-3 mol of nucleophile) = 0.525 g Actual yield = 0.441 g, Percent Yield = (0.441g/0.525g) x 100% = 84% 10. Percent recovery from recrystallization = (0.172g/0.441g) x 100% = 38% 11. The data table provided below obtained melting point data for crude product, pure product, and mixture of the pure and 4-tert-butylbenzyl. 12. The TLC data obtained is provided in a table below. The TLC data was conducted solely in a 9:1 hexane/ethyl acetate solvent solution as opposed to the 1:1 and pure hexane solution as well. This was due to the lack of time, but as explained in number 7, a very polar solvent (1:1 solution) or non-polar solvent (pure hexane) is not ideal when obtaining…show more content…
As mentioned in number 13, the data for the melting point makes sense because my pure product and given compound almost perfectly matched. 17. Again as explained in number 14, the TLC data made sense because my pure compound and 4-tert-butylbenzyl phenol had similar distances from the solvent origin of the plate. The presence of benzyl bromide and benzyl alcohol also explains how not all the product dissolved in the filtrate. The possible explanations and changes to make are similar to the previous questions. Conclusion and Future Experiment 18. The identity of the product and unknown were 4-tert-butylbenzyl phenol ether and tert-butyl phenol respectively. The key to making this discovery was the melting point and TLC results! The substitution reaction was successful but not fully effective. 19. If the data was inconclusive, then comparing various compounds and the unknown based on physical characteristics would be the first step, titrations would also be a good method. 20. To get a better yield, redoing the experiment would require careful attention in the recrystallization steps: amount of solvent used, how hot solvent is, if the mixture cools to room temperature before placing it in an ice
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