Pre Lab #8 - pre lab 8 PDF

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pre lab 8...

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Jessie Hays 10/25/18 Thurs 3:30

PreLab #8 Title: Let’s take a trip (le bond) Introduction: This week in lab the students will be forming carbon-carbon triple bonds. Traditionally, liquid bromine would be used but because of its extreme toxicity the students will be substituting PHPB. PHPB delivers the equivalent reaction that a Br would.

Equation: 2 mol

1 mol

Mechanism:

1 mol

Jessie Hays 10/25/18 Thurs 3:30

Reactant Trans-Stilbene

Structure

Glacial Acetic Acid

MW (g/mol) 180.25

MP (°C) 5-6

BP(°C) n/a

60.05

n/a

118.1

Pyridinium Hydrobromide Perbromide

319.82

-8

Density 1.049 g/mL n/a

Sodium Bisulfite

104.5

150

n/a

Methanol

32.04

n/a

64.7 Density 0.791 g/mL

Reactant Stilbene Dibromide

Potassium Hydroxide Ethylene Glycol

Ethanol Diphenylacetylen e

Structure

MW (g/mol) 340.06

MP (°C) 241

BP (°C) n/a

56.11

360

n/a

62.07

n/a

197.3

n/a 62.5

Density 1.113 g/mL 78.37 n/a

46.07 178.23

Jessie Hays 10/25/18 Thurs 3:30

Safety: Lab coat, gloves, and face protection needed. Use under fume hood and snorkel. Liquids are very. Do not breathe in, could cause respiratory distress. Only pour liquids in sink when explicitly told to do so, all other liquid need to go in waste container under hood. Do not heat too quickly, some materials are flammable.

Procedure: Step One 1. Add 2.0 g of trans-stilbene to 125 mL Erlenmeyer flask (use powder funnel) 2. Add 40 mL of glacial acetic acid to same flask 3. Place this flask on hotplate and start heating 4. Heat GENTLY to dissolve 5. Add SLOWLY 4.0 g pyridinium hydrobromide perbromide to flask 6. Swirl contents for mixing 7. Rinse crystals if stuck to side of flask with acetic acid if necessary 8. Heat GENTLY for five minutes 9. Crystals will form 10. Cool in ice bath to crystallize 11. Suction filtration 12. Wash crystals with 10-12 mL methanol to remove impurities 13. Dry crystals in buchner funnel for five minutes 14. Dry in watch glass for ten minutes 15. Weigh product before moving on to Step Two Step Two 1. Weigh 1.5 g potassium hydroxide (KOH) in 100 mL round bottom flask 2. Add 20 mL ethylene glycol to flask 3. Place in heating mantle 4. Warm and swirl to dissolve KOH 5. Add SLOWLY crystals from Step One 6. Add boiling hips and assemble reflux apparatus 7. Reflux for 20 minutes 8. Pour hot solution into 250 mL Erlenmeyer flask 9. Cool to room temperature 10. Product will precipitate 11. Allow to settle for ten minutes 12. Cool in ice bath for five minutes 13. Suction filtration 14. Rinse with 5-10 mL cold water 15. Put crystals in 100 mL beaker

Jessie Hays 10/25/18 Thurs 3:30

16. Dissolve in 10-12 mL warm ethanol 17. Keep warm on hotplate but do not melt 18. After dissolved, add 0.5-1.0 mL water until solution clouds 19. Allow to cool 20. Collect crystals 21. Air dry 22. Weigh 23. Determine melting point...