EXPT 10 Report Perez

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Date: 2/12/2023 Name: Keren Perez Section E2 LAB REPORT FOR EXPERIMENT 10 “ The Grignard Reaction: Synth of Benzoic Acid ” PRE-LAB: Aim/Objective: To prepare phenyl magnesium bromide from magnesium and bromobenzene to create a Grignard reagent and then add this reagent to carbon dioxide and obtain, after hydrolysis, benzoic acid. Material Safety and Physical Constants: Compound MW (g/mol) MP (Celsius) BP (Celsius) Safety Magnesium 24.31 650 1091 may cause “metal fume fever.” This is a flu - like illness with symptoms of metallic taste in the mouth, headache, fever and chills, aches, chest tightness and cough Anhydrous diethyl ether 74.12 -116 35 can cause drowsiness, excitement, dizziness, vomiting, irregular breathing, and increased saliva bromobenzene 157.01 -30.72 156 Contact can irritate the skin and eyes. Exposure can irritate the nose and throat. Exposure can cause headache, dizziness and passing out Acetone 58.08 -95 56 exposure can cause drying and cracking of the skin with redness. Exposure can irritate the eyes, nose, and throat 6M HCl 36.46 -74 53 Causes severe skin burns and eye damage Benzoic acid 122.12 122.3 149.2 Exposure to Benzoic Acid in high concentrations, particularly in susceptible individuals, may cause a skin allergy NaOH 39.997 318 1388 Contact with very high concentrations of sodium hydroxide can cause severe burns to the eyes, skin, digestive system or lungs, resulting in permanent damage or death Procedure: 1. Weigh 5g of dry ice. Crush and transfer it to a small beaker. Transfer was very quick 2. Add the Grignard reagent. 3. Rinse the reaction flask with 2 mL of ether and add the rinse to the beaker. 4. Cover with a watch glass. Until excess dry ice was sublimated. 5. Add 10 mL of 6 M HCl with stirring. Produces benzoic acid, reacts with the remaining magnesium metal.

6. Transfer the solution to a centrifuge tube to separate. Two distinct liquid layers with no solid residue left. 7. Remove the lower aqueous layer keeping the ether layer in the centrifuge tube. Discard it. 8. Extract the ether layer 3 times with 4 mL of 5% NaOH solution to recover benzoic acid. 9. Save the lower aqueous layer in the same beaker. 10. Heat the combined aqueous extracts with stirring on a hot plate to a gentle boil for 5 minutes to remove ether. 11. Cool the aqueous solution to room temperature. 12. Precipitate the benzoic acid by adding 5 mL of 6 M HCl with stirring. 13. Cool the mixture on ice bath and collect the solid by vacuum filtration in a Hirsch funnel. 14. Use small portions of ice-cold deionized water to transfer and wash the benzoic acid solid. 15. Purification: Crystallize the benzoic acid using hot water in Erlenmeyer flask. Added hot water in small portions until the solid dissolved. 16. Cool to room temperature, place in an ice bath. 17. Collect using a Hirsch funnel. 18. Dry the product in a desiccator or in the oven at 90 degrees Celsius. Balanced Chemical Reactions: IN-LAB Reaction Mechanism:

Calculations: 0.149 g of Magnesium Plate without crystallized benzoic acid: 2.199 g Plate with crystallized benzoic acid: 2.487 g Weight of crystallized benzoic acid: 2.487 g - 2.199 g = 0.288 g Density of benzoic acid: 1.27 g/mL Volume = mass / density Volume of benzoic acid = (0.288 g) / (1.27 g/mL) = 0.23 mL Observation: Some observations were noted from experiment 10 “ The Grignard Reaction: Synth of Benzoic Acid ”. First, when forming the Grimard reagent, the reaction would not start. As a result, we initially decided to crush some of the magnesium in order for it to begin. However, despite our efforts, the reaction still did not start, as a result, we decided to add iodine to the reaction. Once we added the iodine, the solution turned orange or red looking and it finally started to synthesize. Additionally, it must be stated that we shared some of our solution with two of our lab peers in order to help their reaction start. Therefore, some of our percent yield was lost. After the formation of our Grignard reagent, we added dry ice, and unexpectedly our solution condensed and formed a solid layer that looked yellow. The following lab, we contibued our experiment by adding 4 mL of 5% NaOH, however, the extraction was not done properly, and it did not get crystallized benzoic acid. As a result, we lost a lot of percent yield of benzoic acid. Nonetheless, we were able to still add NaOH to our organic solution and extract a small yield of benzoic acid from it. This allowed us to proceed with the experiment and generate 0.288 g of benzoic acid. Data and Results: Mass of benzoic acid: 0.288 grams Melting Point of benzoic acid: 116 – 117.9 degrees Celsius Literature melting point: 121 – 123 degrees Celsius % Yield Calculation (0.288 / 0.753) x 100 = 38.25%

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Discussion: After performing experiment 10, we collected 0.288 grams of cyclohexene, this account for a percent yield of 38.25%. This percent yield is way lower than we initially anticipated because we lost some of our product when we first shared our solution with our lab partners in order to help their reaction start. Additionally, we lost most of our percent yield by not extracting benzoic

acid from the solution correctly. Because our benzoic acid was impure, we had to use leftover of the organic layer in order to finish our experiment. This means that we lost at least 70% of our percent yield because of this mistake. In order to avoid losing so much of our product in the future, we need to be more careful during our experiments. It is important to ensure we follow the instructions precisely and pay closer attention to the products we get throughout our experiment. This mistake can be avoided if we read and analyze the instructions on the lab manual carefully and ask our TA for help when we are uncertain about the mechanism and procedures of a reaction. On the other side, to the 100% pure IR spectrum of benzoic acid, our IR spectrum showed signs of not being dried enough. For instance, the first “fall” shows that the benzoic acid was a bit when still. This, as a result, affected the melting point of the benzoic acid. Because there was still aqueous solution in the final product, the melting point of our product was lower than the anticipated melting point of 100% pure benzoic acid. Nonetheless, other than that, our final product’s IR spectrum was very similar to 100% pure benzoic acid’s I R spectrum. The one we obtained had a large benzoic acid peak and similar drops or falls. From these observations, it can be concluded that our final benzoic acid product was very pure but not dried enough. Conclusion: In conclusion, all our findings from experiment 10 support the claim that our team managed to prepare phenyl magnesium bromide from magnesium and bromobenzene to create a Grignard reagent and then add this reagent to carbon dioxide and obtain, after hydrolysis, benzoic acid. Nonetheless, the percent yield of our product was greatly affected by the errors performed during the synthesis of benzoic acid. Such errors can be avoided by carefully performing the experiment. For instance, we should have shaken harder NaOH with the Grignard reagent in order to extract pure benzoic acid. Additionally, it is necessary to carefully read the lab manual and ask questions when we have doubts regarding the mechanism. On the other side, because we performed the IR spectrum and calculated the melting point of our product, we realized that the benzoic acid was not dried enough. This reflected on the lower melting point and small initial peak on the IR spectrum. Other possible errors introduced in the experiment could have been not properly protecting the Grignard reagent from moisture and air when we added the Iodine and shared some of our solution with our lab partners. Such mistakes can also be avoided by carefully performing the experiment and always paying attention to the reactions occurring in the lab.

POST – LAB 1. The Grignard reagent would reactant with water to form benzene a. The benzene is separated from the product when we extract the layer of the solution, and the benzene is left behind 2. Column chromatography separates compounds based on their polarities. The 3 products that result it this experiment from Grignard reagents are benzoic acid, biphenyl, and phenyl. The first compound that is removed is phenyl because it is the least polar. Then biphenyl because of its wander wall’s attraction and then benzoic acid. However, extraction could be used over column chromatography because it is faster. 3. The formation of benzoic acid by Grignard reaction, benzene is formed as the byproduct. We separate this from the desired compound. Benzoic acid is separated after dissolving it in aqueous solution of NaOH 5.No, the Grignard reagent can act as a nucleophile or a base, it will react as a base instead due to the presence of acidic protons in the carboxyl acid 6. Reaction of Grignard reagent formed from bromobenzene with benzophenone would give triphenylmethanol 7. B

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