Preparation of Diphenylacetylene PDF

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Final paper for lab 8 in o chem 1 lab at UGA...

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Preparation of Diphenylacetylene Introduction: Today’s lab will be focused on the formation of a carbon-carbon triple bond using two reactions. These two reactions include: halogenation of the alkene and dehydrohalogenation of an alkyl halide. Alkene halogenations, for the purpose of this experiment, uses pyridinium hydrobromide perbromide to deliver bromine to the reaction flask in the first step. This allows for the bromine atom to attach itself to trans-stilbene, thus allowing for the halogenation of that alkene. In step two of this reaction, dehydrohalogenation using KOH allows the bromine atoms to detach themselves from the product, allowing for the formation of carbon-carbon triple bonds. This experiment utilizes previously explained lab techniques like reflux, suction filtration, recrystallization, and melting point determination. There are no new lab techniques used for this experiment. Balanced Equations and Reaction Mechanisms:

Table of Reagents:

Part 1:

Name

Structure

Molecular Weight 180.25 g/mol

Melting Point 122-126ºC

Density

Glacial Acetic Acid

60.05 g/mol

61.95ºC

1.0446

Pyridinium Hydrobromide

319.83 g/mol

127-133ºC

-

Sodium Bisulfite

104.061 g/mol

150ºC

-

Methanol

32.04 g/mol

-143.7ºC

0.79

Melting Point 232ºC

Density

Stilbene Dibromide

Molecular Weight 340.05 g/mol

Potassium Hydroxide Ethylene Glycol

56.1056 g/mol 62.07 g/mol

680ºC

-

8.78ºC

1.11

Trans-Stilbene

-

Part 2: Name

Structure

-

Ethanol

46.07 g/mol

-144.1ºC

-

Diphenylacetylene

178.24 g/mol

62.5ºC

-

Safety Information: -

Trans-Stilbene is toxic and causes eye irritation. It should never be inhaled or ingested. It is flammable and should only be extinguished using water spray, carbon dioxide, dry chemical, and alcohol-resistant foam

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Glacial Acetic Acid is highly flammable- extinguishable by carbon dioxide, dry chemical, water spray, and alcohol-resistant foam. It can cause severe skin burns and eye damage.

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Pyridinium Hydrobromide is toxic and can cause skin/eye irritation. Pyridinium Hydrobromide should always be handled with extreme caution and should not be inhaled or ingested. Pyridinium Hydrobromide is flammable and should be extinguished with carbon dioxide, dry chemical, dry sand, and alcohol-resistant foam.

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Sodium Bisulfite is acutely toxic and can cause skin and eye irritation. Sodium Bisulfite Is not flammable.

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Methanol is highly flammable. It can only be extinguished using dry chemicals, foam, dry sand, or carbon dioxide. It is also toxic and can cause severe skin damage.

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Stilbene Dibromide can cause severe skin and respiratory irritation. It is also flammable and can be extinguished using CO2, dry sand, dry chemical, or alcohol-resistant foam.

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Potassium Hydroxide is toxic and can cause skin corrosion and eye damage. Potassium Hydroxide is not flammable.

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Sodium Bisulfite is toxic and can cause mild skin irritation. Sodium Bisulfite is flammable but not combustible- water, dry chemical, chemical foam, carbon dioxide, and alcohol resistant foam is the acceptable extinguishing media.

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Methanol is toxic and can cause mild skin irritation. It is also highly flammable and should be extinguished using dry chemical, foam, dry sand, or carbon dioxide.

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Stilbene Dibromide is toxic to the respiratory system. It can also cause severe skin corrosion and eye damage. It is flammable, and should be extinguished using carbon dioxide, dry chemical, dry sand, and alcohol-resistant foam.

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Potassium Hydroxide is toxic and can cause severe skin and eye damage. It is also corrosive to metals. Potassium hydroxide is not flammable.

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Ethylene Glycol is toxic to the central nervous system, kidney, and liver. It is flammable and should be extinguished using water spray, alcohol-resistant foam, dry chemical, or carbon dioxide.

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Ethanol is toxic to the central nervous system, optic nerve, respiratory system, kidney, liver, spleen, and blood. It is also highly flammable, and should be extinguished using water spray, alcohol-resistant foam, dry chemical, or carbon dioxide.

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Diphenylacetylene is not considered hazardous by the 2012 OSHA hazard communication standard. Diphenylacetylene is flammable and should be extinguished using water spray, carbon dioxide, dry chemical, and alcohol-resistant foam.

Proper lab attire, gloves, safety goggles, and a mask are required at all times in the lab. Do not ingest or inhale any compounds used in the lab. Contact the TA immediately in case of fire, broken glass, or chemical spill. Procedure: Step One: 1. Add 2.0 g of trans-stilbene and 40 mL of glacial acetic acid to a 125 mL Erlenmeyer flask. 2. Gently heat this flask using a hotplate to dissolve the trans-stilbene. 3. Slowly add 4.0 g of Pyridium hydrobromide to the flask and swirl. 4. Heat the flask for five more minutes. 5. Cool the flask in an ice bath for the solution to crystalize. 6. Wash crystals with 10-12 mL of methanol and dry through a Buchner funnel. Weigh the product Step Two: 1. Weigh out 1.5 g of potassium hydroxide into a 100 mL round bottom flask. 2. Add 20 mL of ethylene glycol to the flask and place on a heating mantle. Warm and swirl the mixture. 3. After KOH dissolves, add crystals from step one into the flask with several boiling chips. 4. Reflux for 20 minutes. 5. Pour the hot, refluxed solution into a 250 mL flask and cool to room temperature. 6. Cool in an ice bath for 5 minutes.

7. Collect the product using suction filtration. Rinse the flask with cold water. 8. Place the crystals in a 100 mL beaker and dissolve in 10 mL of warm ethanol. 9. Add 1 mL of water to the beaker in drops until the solution is cloudy. Cool the solution to room temperature 10. Collect, weigh, and determine the melting point of the crystals. 11. Dispose of all used chemicals into the waste receptacle and clean the lab station. Data and Observations: Step One: -

Starting weight of trans-stilbene: 1.98 grams

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Starting weight of Pyridium hydrobromide perbromide: 4.10 grams

-

Starting volume of glacial acetic acid: 40 mL

-

Volume of methanol used to wash crude product: 11 mL

-

Approximate weight of sodium bisulfate used to neutralize the filtrate: around 1.0 grams

-

Weight of recovered product (stilbene dibromide): 3.29 grams

Step Two: -

Starting weight of stilbene dibromide: 3.29 grams

-

Starting weight of potassium hydroxide: 1.51 grams

-

Starting volume of ethylene glycol: 20 mL

-

Volume of water (ice cold) used to wash the crude product: 10 mL

-

Volume of ethanol used to recrystalize the crude product: 12 mL

-

Weight of the purified product: 1.59 grams

-

Melting point of the purified product (range): 60.0-61.5 degrees Celsius

When combined and heated, the trans-stilbene and glacial acetic acid solution visually looks transpartent and water-like. When initially weighed out, the pyridium hydrobromide perbromide was a powdery, red color. When the pyridium hydrobromide perbromide was combined with the glacial acetic acid and trans-stilbene solution, the solution turned a reddish brown color. Once allowed to react, the solution seems to separate into a yellow solid at the bottom of the flask and a reddish/orange liquid at the top of the flask (the solid and liquid separated). After impurities are filtered out through suction filtration, the crystals turned into a white, powdery color rather than a yellow color. After reflux in the second step, the translucent, the yellow liquid turned into a more opaque orange liquid as the solid began to form. The final, crystal product is again a white, powdery solid. Results: Limiting Reagent for Step 1: -

(1.98 grams trans-stilbene) x (1 mol trans-stilbene)/ (180.25 grams trans-stilbene) x (1 mol stilbene dibromide)/(1 mol trans-stilbene) = 0.01098 mol stilbene dibromide

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(4.10 grams Pyridium hydrobromide perbromide) x (1 mol Pyridium hydrobromide perbromide)/ (319.82 grams Pyridium hydrobromide perbromide) x (1 mol stilbene dibromide)/ (1 mol Pyridium hydrobromide perbromide) = 0.0128 mols stilbene dibromide

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(0.0128 moles stilbene dibromode) x (340.05 grams stilbene dibromide) / (1 mol stilbene dibromide) = 4.35 grams stilbene dibromide

Limiting Reagent for step 2:

-

(3.29 grams stilbene dibromide) x (1 mol stilbene dibromide)/ (340.05 grams stilbene dibromide) x ( 1 mol diphenylactetylene) / (1 mol stilbene dibromide) x (178.24 grams diphenylactetylene) / (1 mol diphenylactetylene) = 1.72 grams diphenylactetylene

-

(1.51 grams KOH) x (1 mol KOH) / (56.11 grams KOH) x (1 mol diphenylactetylene) / (1 mol KOH) x (178.24 grams diphenylactetylene) / (1 mol diphenylactetylene) = 4.80 grams diphenylactetylene

Precent Yield Calculation for step 1: -

(3.29 grams stilbene dibromide) / (4.35 grams stilbene dibromide) x 100% = 75.6%

Percent Yield Caclulation for step 2: -

(1.59 grams diphenylactetylene) / (1.72 grams diphenylactetylene) x 100% = 92.4%

Discussion and Conclusion: This lab utilized the halogenation and dehalogenation of an alkene to synthesize diphenylactetylene using multiple steps. Part of the experiment used trans-stilbene and pyridium hydrobromide perbromide, and the trans-stilbene was found to be the limiting reagent in this step. Diphenylactetylene was then synthesized, and a melting point range was taken from this sample. The experimental melting point range was found to be 60.0-61.5 degrees Celsius. This is a bit lower than the literature value of 62.5 degrees Celsius. This could be due to impurities within the final product. The most probable impurity that contaminated the final sample was the ethanol used to dissolve the crystals. The ethanol was probably not completely filtered out and dried, causing not only the melting point of the final product to be incorrect, but also the final mass. In the future, it is necessary to make sure that the crystals are completely dry and no contaminants are left within the final product. This can be achieved through filtering the crystals with suction filtration for an extended period of time.

The percent yield for the stilbene dibromide was slightly low. This could be due to multiple factors. The most probable factor was that some of the crystals are extremely hard to collect, as they stick to the beaker in which they formed, thus making the percent yield lower. This can be addressed in the future by making sure that any product that is stuck to the glass within the beaker is rinsed before proceeding with the experiment. The percent yield for the diphenylactetylene was extremely high, and therefore it is concluded that this specific portion of the experiment was performed with little to no errors. Post Lab Questions:

1.

2. (1R,2S)-1,2-dibromo-1,2-dicyclopentylethane (5R,6R)-5,6-dibromo-3,8-diethyldecane 3. a.

b.

c....