CHE201 Lab3 Report PDF

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CHE201 Lab3 Report, CHE201 Lab3 Report...

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CHE201 Difei Jiang (TA)

Wednesday 5:00 p.m. Lab 3 Introduction

The title of the experiment is Heating Under Reflux: Synthesis of Salicylic Acid from Wintergreen Oil. In this experiment, we carried out an organic synthesis which was the preparation of salicylic acid from methyl salicylate. Methyl salicylate is the limiting reactant in this synthesis; sodium hydroxide is used in excess to ensure a reasonably fast, complete reaction. The experiment is relatively green because the reactants and products (in the concentrations used) are not highly toxic. Chemical Reaction and Mechanism

Reaction

Mechanism Procedure We assembled an apparatus for heating under reflux that consisted of an air condenser and conical reaction vial. We then measured 2 mmol of methyl salicylate into the reaction vial and then added 2.5mL of 6M sodium hydroxide and a boiling chip. Next, we heated the reaction mixture for 30 minutes. When the reaction was completed, we removed the boiling chip and transferred the reaction mixture to a beaker. We then added 2.7mL of aqueous 3M sulfuric acid and made sure the pH was 2. The next step was collection of the salicylic acid by vacuum

filtration and washing it on the filter with ice cold water. We then purified the salicylic acid by recrystallization. Data Compound Methyl Salicylate Sodium Hydroxide Sulfuric Acid Salicylic Acid- crude DI Water Salicylic Acid- After recrystallization

Molecular Weight 152.1 g/mol 39.99 g/mol 98.1 g/mol 138.1 g/mol N/A 138.1 g/mol

Amount used/formed .3042 g 2.5 mL 2.7 mL .41 g 4.5 mL .34 g

Moles used/formed .002 moles .015 moles .0081 moles .0030 moles N/A 157-162 degrees melting point

Results and Discussion After the experiment the crystals that were formed were not needlelike. We heated further and finally had needlelike crystals. The values that we got for our data sheet were near perfect so there were few errors that we encountered in out experiment. One of the errors that we faced when doing our experiment is that we spilled just a little bit of our chemical when transferring it to the apparatus. Another error that could have occurred but didn’t for us is that there could have been a spill when the initial chemicals were obtained. Also the scale could have been a little off when we weighed our chemicals. Another error could have been that the flask accidently touched the hot plate. One way in which the experiment could be modified is that a more stable apparatus for filtration could have used in this experiment. Conclusion The purpose of this experiment was to synthesize salicylic acid from wintergreen oil. We did this by using an intricate apparatus that involved heating and then purification and recrystallization.. In the end our experiment was very successful. We did the experiment and we obtained values that were very similar to values obtained in other experiments. If there was one thing that I would change/improve for this experiment would be to use a better and more stable apparatus over the one we used for this experiment. Calculations Theoretical yield of salicylic acid (in grams) =

. ./

= .002 (138.1 g/mol) = .2762 grams

Post Lab Questions 1. (.26mL methyl salicylate)*(2 mol NaOH/1mol methyl salicylate) = .52 mL NaOH 2.5-.52= 1.98 excess NaOH

2. 4. Due to methanol’s lower boiling point, it was evaporated during the half hour reflux period while the sodium sulfate was separated during the first vacuum filtration....