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13 Dec 2019

Can someone please look over my short paragraph about my organic laboratory experiment for any edits on making it more detailed yet concise at the same time. For example, I'm not sure if I should include that acetonitrile and toluene should be stated that they were insoluble compared to the other three solvents just for claification?

The purpose of this second laboratory experiment was to determine a proper solvent for recrystallization of acetaminophen by using the solubility properties in five different solvents: acetonitrile, methanol, tetrahydrofuran, toluene, and acetone. Acetaminophen was insoluble in toluene at room temperature and at elevated temperatures. On the other hand, the compound was also found to be insoluble in acetonitrile at room temperature but soluble at warm temperatures. This observation led to recrystallization of acetaminophen afterwards, and thus would make acetonitrile a suitable solvent.

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Procedure: Setting Up: Add 1.0 g of p-aminobenzoic acid and 10 mL of absolute ethanol to the round-bottom flask containing a stir bar. Stir the mixture until the solid is completely dissolved. Add 1 mL of concentrated [18M] sulfuric acid dropwise to the ethanolic solution of p-aminohenzoic acid, equip the flask with a condenser, and set up the apparatus for heating under reflux using the heating mantle. Reaction: Heat the mixture under gentle reflux for 30 min, stirring all the while. If any solid remains in the flask at this time, remove the flask from the heat source and allow the mixture to cool for 2-3 min. Add an extra 3 mL of ethanol and 0.5 mL of concentrated H2SO4, to the reaction flask and resume heating under reflux. After the reaction mixture becomes homogeneous, continue heating it under gentle reflux for another 30 min. For the experiment to succeed, it is important that all of the solids dissolve during the reflux period. Work-Up and Isolation: Allow the reaction mixture to cool to room temperature and then pour it into a beaker containing 30 mL of water. Basify the mixture to a pH of about 8 by slowly adding 10% aqueous sodium carbonate with stirring. Be careful in this step as frothing occurs during the neutralization. You should calculate beforehand the approximate volume of 10% aqueous sodium carbonate that will be required to neutralize the total amount of sulfuric acid you used. Collect the crude benzocaine that precipitates by vacuum filtration. Use three 10-mL portions of cold water to rinse the solid from the beaker and wash the filter cake. Air-dry the product. Purification: Weigh the crude product and recrystallize from methanol/water pair of solvents: Place the solid in a 50 mL Erlenmeyer flask. Add the minimum amount of hot methanol to dissolve it. Keep on a steam bath. Slowly add hot water to the solution using a disposable pipette just until the solution becomes cloudy and fails to clear up when it is swirled. To the hot solution on the steam bath add hot methanol, drop wise, until the turbidity or crystals just disappear. Allow the solution to cool to room temperature and then cool it in an ice-water bath for 10-15 min to complete crystallization. Isolate the crystals by vacuum filtration, wash them with 5-10 mL of cold water, and allow them to air-dry. Weigh the crystals and calculate the percentage yield.

True or False? When analyzing the IR spectra of starting material and product, a positive indication suggesting that the product was made would be the disappearance of a strong stretch between 1690-1740 cm-1.

True

False

Why is it important that all of the solids dissolve during the reflux period for you to obtain a good yield of product?

A. Because everything needs to be in solution for the reaction to happen to the fullest extent.

B. Because the product will be impure if the intermediate doesn't dissolve completely.

C. Because the ethanol will evaporate off if it's not dissolved.

D. All of the above

What is the gas that is evolved during neutralization?

A. O2

B. CO2

C. SO2

D. CO3

Why is it necessary to neutralize the reaction mixture to work up the product?

A. Because it is dangerous to work with an acidic solution.

B. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as ammonia and must be protonated so that it becomes insoluble and collectable.

C. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as a soluble carboxylic acid and must be neutralized so that it becomes insoluble and collectable.

D. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as a soluble ammonium salt and must be neutralized so that it becomes insoluble and collectable.

If you end up adding 1.5 mL of concentrated sulfuric acid (18 M), how many mL of 10% aqueous sodium carbonate would be required to neutralize the reaction mixture?

A. 1.5 mL

B. 3 mL

C. 15 mL

D. 29 mL

What is the purpose of the sulfuric acid?

A. To catalyze the reaction.

B. To protonate the intermediate salt.

C. To protonate the ethanol.

D. To increase the pH of the reaction mixture.

What is the theoretical yield of the product?

A. 1.00 g

B. 2.98 g

C. 1.20 g

D. 10 mL

This is the description from my organic chemistry lab.

Lab Observations and Data

We obtained 1.17g of cyclohexene oxide (clear liquid) and 3 mL of water into a 50 mL flask with a stir bar. When added a single drop of sulfuric acid, the clear liquid started to change to a very, very light yellow/brownish color. We obtained an ice bath on the side in case our mixture started to boil. After the solution stirred for about 25 minutes, we added sodium hydroxide. We inserted a pH paper and it turned a dark blue, meaning basic. Added another drop of sulfuric acid to make it a little less basic. Added the mixture to a separation funnel, shook it around and ended with separated layers. We separated the layers, thinking the bottom layer was the organic layer, when it was really the aqueous layer. So we ended up mixing the wrong layers back together. After some error, we isolated our new organic layer and added some drying agent. We then put that mixture with the drying agent, NaOH, into the rotovap. Our final product was a white powder and weighed 1.51 grams. We then set up a vacuum filtration while boiling water. We boiled our dried organic layer into the hexane. Added two drops of ethyl acetate to help the boiling process go faster. After vacuum filtering it, it weighed .394 grams. The melting point is 91 to 93 degrees Celsius. Our IR spectra matches the "trans" conformation. So for our TLC plate we observed blue dots to match the trans conformation.

The question is "calculate your percent yield" Which is actual yield/theoretical yield x 100. I just dont understand how I get those numbers.

Here is the lab manual description as well.

Procedure for the Preparation of 1,2-Cyclohexanediol Place a mixture of 1.18 g (0.012 mole) of cyclohexene oxide and 3 mL water into a 50 mL Erlenmeyer flask, equipped with a magnetic stir bar. To this mixture with vigorous stirring add one drop of 6 M sulfuric acid (33% H2SO4) Caution: After a short incubation time, the reaction mixture will become quite warm. This epoxide ring opening reaction is very exothermic. (Why?) If the reaction mixture begins to boil, place the flask in a bath of ice and water. Allow the reaction mixture to stir for the next 15 minutes and let it cool to room temperature. Afterwards, add a small amount of 10% sodium hydroxide drop-wise to neutralize the stirring solution. (No more than 3 or 4 drops of 10% NaOH should be necessary.) Place a drop of the reaction mixture on pH paper to check the pH. Extract the product from the reaction mixture into ethyl acetate or diethyl ether (2 x 15 mL). Dry the combined extracts over sodium sulfate. Decant the solution and remove the solvent to yield the crude product (~1 g). The product can be purified by recrystallization from a small amount (~ 5 mL) of hot toluene or hexanes. Collection of the purified product by suction filtration yields 1,2-cyclohexanediol. The cis isomer has a melting point of 97-101 Â°C whereas the trans isomer melts at 101-103 Â°C. Determine the product(s) or products the reaction. Include a percent yield calculation in your report along with the results of your TLC analysis

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