Chem 2211 Preparation of Diphenylacetylene Lab PDF

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Lance Fountain UGA MyID: lcf19888 Preparation of Diphenylacetylene Intoduction: In this experiment, we will be studying the formation of an alkyne (carbon-carbon triple bond) using two reactions. These reactions are halogenation of an alkene and the dehydrohalogenation of an alkyl halide. However, for the halogenation part of the experiment we will be using PHPB instead of Br2. PHPB is a much safer alternative than Br2 due to the toxic and corrosive nature of liquid bromine. The double dehydrohalogenation will be using KOH. Previously administered laboratory techniques that will be use in this experiment include reflux and recrystallization to isolate and form the crystalline products for both of the reactions. Also, melting point determination will be used to determine the melting point range and purity of the final product, diphenylacetylene crystals.

Balanced Equation:

Reaction Mechanism:

Table of Reagents: Compound

Melting Point (oC)

Boiling Point (oC)

Molecular

Density (g/mL)

Trans-Stilbene

125

305-307

Weight (g/mol) 180.24

Acetic Acid

16.5

118.1

60.05

1.049

Pyridinium Hydrobromide Perbromide

--

205

319.86

--

--

Structure

2.742

64.7

120.06 (anhydrous) and 138.07 (monohydrat e) 32.04

238

--

340.07

--

360

1320

56.105

2.044

−12.9

197.3

62.068

1.1132

−114.3

78.4

46.06844

0.789

0–97

178.22

0.990

Sodium Bisulfate

58.5 (monohydrat e) and 315 (anhydrous)

--

Methanol

-97

Stilbene Dibromide Potassium Hydroxide Ethylene Glycol Ethanol

Diphenylacetylen 61 e

0.792

--

Safety: 

Glasses and gloves need to be worn at all times.



Snorkels must be turned on and working properly. Acetic Acid has a pungent smell



Avoid breathing in fumes.



Dispose of waste in the proper container.

Procedure: Step 1 1. Add 2.0 g trans-stilbene and 40 mL glacial acetic acid to 125 mL Erlenmeyer flask. 2. Place flask on hotplate and gently heat to dissolve. a. Use powder funnel for solids to avoid spillage. 3. Add 4.0 g of PHPB to flask once trans-stilbene has dissolved. Swirl contents of flask. a. Use swirling to mix any crystals that adhere to flask wall above the solvent line. You may use a small amount of acetic acid to rinse crystals if needed.

4. Continue to gently heat reaction flask for 5 more minutes. Notice product crystals forming in solution as reaction progresses. 5. Once heating is done cool flask in ice-water bath. 6. Collect solid product via suction filtration. Wash solid with 10 – 12 mL of methanol to help remove soluble impurities. 7. Dry crystals by drawing air through Buchner funnel for 5 minutes. 8. Dry crystals on watch glass for 10 minutes. Proceed to set up step 2. a. allow crystals to dry completely before using in step 2. b. add sodium bisulfite to aqueous filtrate to remove orange color before showing it to your TA before discarding in lab sink. 9. Weigh product before using in step 2. Step 2 10. Weigh out 1.5 g of KOH in 100 mL round bottom flask. 11. Add 20 mL ethylene glycol to flask and place in heating mantle. 12. Gently warm and swirl mixture until all KOH has dissolved in solution. 13. Slowly add dibromo stilbene crystals to flask. 14. Add several boiling chips and attach a reflux condenser to apparatus. Reflux for 20 minutes. 15. After reflux, detach condenser and pour hot solution into 250 mL erlenmeyer flask. Allow solution to cool to room temperature. 16. Impure product will begin to precipitate as cooling progresses. Allow product to settle for 10 minutes. 17. Cool in ice-water bath for 5 minutes. 18. Collect impure product via suction filtration.

19. Use 5-10 mL cold water to rinse out Erlenmeyer flask and wash collected crystals. Aqueous filtrate may be discarded in sink. 20. Transfer product to 100 mL beaker and dissolve in 10-12 mL warm ethanol. Keep solution warm using hotplate. Keep in mind temperature. Don't let it get too hot, where you can't hold it. 21. After products are dissolved, add 0.5-1.0 mL water to beaker drop-wise until solution is cloudy. 22. Allow solution to cool and observe formation of crystals. Collect solid crystals via suction filtration. Air dry product. 23. Weigh product and determine melting point.

Figure 1: Reflux Apparatus

Figure 3: Melting Point Determination Apparatus

Results:

Figure 2: Suction Filtration Apparatus

Figure 4: Recrystallization Apparatus

Step One 

Starting weight of trans-stilbene: 2.017 g



Starting weight of Pyridinium Hydrobromide Perbromide: 4.001 g



Starting volume of glacial acetic acid: 40 mL



Volume of methanol used to wash crude product: 13 mL



Weight recovered product (stilbene dibromide): 3.341 g

Limiting Reagent:



Trans-Stilbene is limiting reagent for step one

Theoretical Yield of Stilbene Dibromide:

Percent Yield:

Step Two 

Starting weight of stilbene dibromide: 3.341 g



Starting weight of potassium hydroxide: 1.5 g



Starting volume of ethylene glycol: 20 mL



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



Volume of ethanol used to recrystallize crude product: 12 mL



Weight of purified product (Diphenylacetylene): 0.835 g



Melting point range of the purified product: 60-61°C

Limiting Reagent:



Stilbene Dibromide is the limiting reagent for step two.

Theoretical Yield Diphenylacetylene:

Percent Yield:

Discussion/Conclusion:

The yield achieved for the experiment was reasonable, but there were many potential factors that could have led to error and loss of product. First, there was loss of stilbene dibromide when attempting to transfer the product onto a watch glass. Next, some product was lost in the beaker when trying to transfer it to the Buchner funnel. Throughout the experiment, the product was repeatedly shown to be lost onto the counter of the lab, so it can be assumed that product was being loss during each transfer due to how fine its grains were. The final product, Diphenylacetylene, was a fine, white, crystalline solid. After obtaining the final product, it was confirmed that this was pure Diphenylacetylene due to its melting point range being almost to its exact literature value....