Wittig Rxn - Lab Report - Experiment: Synthesis Of (Z)- And (E)- Stilbenes PDF

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03/7/2018 Experiment: Synthesis of (Z)- and (E)- Stilbenes by a Wittig Reaction The purpose of this lab experiment is to form E and Z conformations of Stilbene through a Wittig reaction. Mechanism Formation of ylide

Compound

Boiling point

Melting Point

Amount

weight (g/mol) (g/mL)

°C

°C

used

Benzyltriphenylphosphonium chloride NaOH

388.86

NA

NA

345-347

0.76 g

40

2.13

1388

318

1.0 mL

Benzaldehyde

106.13

1.04

179

-26

0.2 mL

DCM

84.92

1.33

40

-97

2 mL

Sodium bisulfate

104.06

1.48

104

6

2.5 mL

Sodium sulfate

142.06

2.66

1100

888

NA

Bromine

159.81

3.10

58.78

-7.25

NA

Potassium permanganate

158.03

2.47

NA

240

NA

(E)-Stilbene

180.25

0.97

305

122-125

NA

(Z)-Stilbene

180.25

1.01

307

5-6

NA

Structures

Molecular

Density

1. DCM

2. Benzyltriphenylphosphoniumchloride

3. Benzaldehyde

4. (E)-Stilbene

5. (Z)-Stilbene

MSDS 1. Benzyltriphenylphosphoniumchloride: irritant of skin and eyes 2. Benzaldehyde: irritant of skin and eyes, permeator, combustible. 3. DCM: irritant of skin and eye, corrosive, may cause severe burns, permeator. 4. NaOH: irritant of skin and eye, corrosive, permeator, may cause severe burns 5. Sodium bisulfite: irritant of skin and eyes 6. Sodium sulfate: irritant of skin, eyes, ingestion and inhalation. 7. Bromine: irritant of skin and eyes, corrosive, may cause burns 8. Potassium permanganate: irritant of skin and eyes, corrosive and may cause inflammation. 9. (E) and (Z)-Stilbene: irritant of skin and eyes. Procedure 1. In a 5 mL conical vial add 0.76 g of benzyltriphenylphosphonium chloride, 0.2 mL of benzaldehyde, and 2 mL of dichloromethane.

2. Set up the apparatus for reflux . (Figure 1) 3. Once the reaction mixture has begun reflux, slowly add 1.0 mL 50% NaOH solution through the top of the condensed dropwise. 4. Continue refluxing for an additional 30 min. 5. Cool reaction to room temp 6. Transfer to a test tube 7. Add 0.5 mL of dichloromethane and transfer the organic layer to another test tube 8. Wash the organic layer with 1.5 mL of water and then 2.5 mL of a saturated sodium bisulfite solution a. separate the layers after each wash 9. Wash an addition two times with 1.5 mL of water 10. Dry the organic layer with sodium sulfate 11. Evaporate off the organic solvent 12. Collect the mass of your crude product 13. Redissolve a small amount of your crude produce dichloromethane and perform a saturation test with a bromine and potassium permanganate solution 14. Obtain a 1HNMR & Calculate percent yield for each isomer Set Up

Calculations Mass of petri dish:

96.9067g

Mass of petri dish and product: 97.7734 g Mass of product: 0.8667 g 1 mol ∏ ¿=0.356 g ∏ ¿ × 180.25 g 1 mol ¿ 1 mol BTP 1 mol BTP 0.7684 g BTP × ×¿ 388.86 g 1 mol ∏ ¿=0.353 g 180.25 g ∏¿ × 1mol ¿ 1 mol Benzaldehyde 1.04 g benzaldehyde ׿ 0.2 mL benzaldehyde × 1 mL Benzaldehyde

Z product: 0.8667 g ×

0.3886 g 1 = ×100=110.1 % ' 2.23 H s 0.353 g

E product: 0.8667 g ×

0.68 0.264 g = ×100=74.8 % ' 2.23 H s 0.353 g

Percent yield 0.8667 g ×100=245.5 % 0.353 g

Conclusion/ Discussion During this lab experiment, E and Z conformations of stilbene were synthesized by a Wittig reaction. Z product had a percent yield of 110.1% and the E product 74.8%. The percent yield for the overall reaction was 245.5% and this is due to excess DCM, failed to evaporate all the DCM in the product. Z conformation has a lower energy if activation according to Hammond’s postulate so, it’s the major product. In addition, aromatic rings on the alkene are bulky, it forces the product into the Z conformation.

NMR was taken for this product, and there is a mix of E and Z conformations. Around 7.10 ppm there is a singlet indicating Hc and HD which are the hydrogen for E conformation. Around 6.58 ppm there is a singlet indicating HA and HB which are the hydrogens for the Z conformations. Around 5.8 ppm there is a singlet indicating excess DCM....