Lab 10 Wittig Reaction PDF

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Wittig Reaction Introduction: This week’s lab focuses on the Wittig reaction, which forms a double bond between a nucleophilic phosphorus ylide and a carbonyl-containing electrophilic species, extending the original carbon skeleton. A phosphorus ylide is neutral, but a dipolar molecule with a positive and negative charge on adjacent atoms. Sodium hydroxide is used to deprotonate and form the ylide and that reagent is then reacted with the aldehyde. The solvent system used is multi-phase, and the solution of the phosphorus ylide and the aldehyde must constantly be stirring for them to interact with each other, as the ylide is hydrophilic but the aldehyde is hydrophobic. The simple distillation is used to separate the methylene chloride from the product, and suction filtrations are used to isolate the product. IR spectroscopy will be used to identify if the reaction went through. Other techniques that will be used are liquid/liquid extraction, simple distillation, melting point, and recrystallization. Balanced equations and Mechanisms

Table of Reagents: Compound Name

Benzyltriphenylphosphonium chloride

Structure

Molecular Weight (g/mol) 388.875

Melting Boiling Density Safety Point Point (g/cm^3) Information (°C) (°C) 337 Toxic if swallowed or in contact with skin Hazardous in skin contact

(irritant), eye contact (irritant), indigestion. Do not breathe in fumes 1-propanol

60.096

9-Anthraldehyde

206.244

405.7

Trans-9-(2phenylethenyl)anthracene

280.37

130-133

Methylene chloride

84.927

39.75

Cl

Cl

97.2

.805

Hazardous in skin contact (irritant), eye contact (irritant), and ingestion. Keep away from heat, do not breathe fumes. Hazardous in skin contact (irritant), eye contact (irritant), and ingestion. Hazardous in skin contact (irritant), eye contact (irritant), and ingestion. Keep dry, do not breathe in dust.

1.325

Positive and 2B carcinogen; toxic to lungs, nervous system, liver, mucous membranes, CNS; target organ damage Hazardous in skin contact (irritant), eye contact

Sodium hydroxide

Na+ OH-

Calcium Chloride

Ca2+ -

Cl

Water

39.997

323

110.978

772-782

-

Cl

18.02

100.0

1.00

(irritant), and ingestion. Keep away from heat, do not breathe fumes. Mutagenic for mammalian somatic cells; toxic to mucous membranes, upper respiratory tract, skin eyes; target organ damage Hazardous in skin contact (irritant), eye contact (irritant), and ingestion. Keep dry, do not breathe dust Toxic to lungs, nervous system, mucous membranes; toxic to heart, cardiovascular system; target organ damage Hazardous in skin contact (irritant), eye contact (irritant), and ingestion. Keep away from heat, do not breathe fumes. ---

Safety Information: General: Safety Glasses and lab gloves must always be worn. Make sure the snorkels are positioned properly, turned on, and are functioning properly before dispensing liquids. Avoid breathing fumes or

allowing liquid to meet skin. Any vapor or liquid exposure should be reported to the TA immediately. Dispose of all liquid and solid waste in the appropriately labeled bottle in the lab hood.

Experimental Procedure: Add 1.0 g of the benzyltriphenylphosphonium chloride, 0.590 g of the 9-anthraldehyde, and spin vane to a clean, 10 mL round bottom flask and dissolve with 3.5 mL of methylene chloride Slowly stir the mixture over the span of three minutes, slowly add 1.3 mL of 50% sodium hydroxide to the reaction mixture Allow the flask to stir at room temperatre for 30 minutes, making sure the stirring is even Remove the spin vane and pour the contents of the flask into a separatory funnel Rinse the round bottom flask with 5 mL of fresh methylene chloride and once with 5 mL of deionized water Pour each rinsing into the separatory funnel and drain the organic layer into a clean 25 mL Erlenmeyer flask Extract the remaining aqueous with 10 mL of methylene chloride and drain the methylene chloride extract in the same flask Add calcium chloride pellets to the organic extract Once dry, decant into a 50 mL round bottom flask Construct a simple distillation and use it to separate the methylene chloride from the crude product, being careful not to distill the solution to dryness Allow the mixture to cool to room temperature once the product forms a thick, yellow slurry Recrystallize the crude product using 1-propanol, using an ice water bath to aid in the recrystallization Collect the purified trans-9-(2-phenylethenyl)anthracene via suction filtration Weigh and record the final mass and obtain an IR spectrum Post Lab Data Initial weight of benzyltriphenylphosphonium chloride used: 1.008 g Intial weight of 9-anthraldehyde used: 0.587g Volume of methylene chloride used to dissolve the starting materials: 3.5 mL Volume of aqueous sodium hydroxide used: 1.3 mL Volume of methylene chloride used to rinse the reaction flask: 5 mL Volume of water used to rinse the reaction flask: 5 mL Volume of methylene chloride used to extract the reaction mixture: 10 mL Approximate amount of calcium chloride used to dry the organic extract: 0.25 g Volume of 1-propanol used to recrystallize the crude product: 20 mL The final weight of the purified product: 0.343 g

Melting point range of the purified product: 124-128 Deg Celsius Miscellaneous Experimental Observations: 9-anthraldhyde: bright yellow powder; Benzyl triphenyl phosphonium chloride: white powder; reaction mixture: dark yellow/brown; Impure product: muddy yellow solid; pure product: bright yellow powder Limiting Reagent Calculations: 1mol 280.37 g 1 mol trans−9−( 2− phenylethenyl ) anthracene 1.005 g benzylPh3P x x x 388.875 g 1 mol 1 mol benzylPh3 P = 0.725 g 1 mol 1 mol trans−9− ( 2− phenylethenyl ) anthracene x x 0.592 g 9-anthraldehyde x 206.244 g 1 mol 9−anthraldehyde 280.37 g = 0.805 g 1 mol Percent Yield Calculations: 0.343 g x 100% = 47.3% 0.725 g Discussion and Conclusion: The percent yield obtained was 51.34 %. This is relatively low yield. The rovotap could have also evaporated too much of the product. The melting point range was 124-128 C, whereas the literature value of trans-9-(2-phenylethenyl)anthracene is 130-133 C. This melting point range is not too far off from the literature value; however, the discrepancy between the two ranges indicate that there are impurities in the product obtained to account for the depression and broadening of the melting point. The solvent system in this experiment is unique, because the aldehyde used is hydrophobic, whereas the benzyltriphenylphosphonium chloride is hydrophilic. To make sure they come into contact, the solution was stirred continuously and evenly. That is why methylene chloride, or DCM, was used. The aldehyde was more soluble in DCM, but because of that, simple distillation was used to extract the methylene chloride out of the solution, taking advantage of the difference in boiling points, where DCM has a lower melting point. FTIR Spectrum Analysis: From the IR spectrum, it indicates that the reaction progressed to completion. There are smaller stretches around 3000 cm-1 that indicate the presence of sp2 hybridized carbons. At ~1700-2000 cm-1, there is an indication of small peaks, indicating aromatic undertones. At around ~1600-1500 cm-1, there are two sharp peaks there, indicating the presence of benzene rings. The spectrum for 9-anthraldehyde is very similar to trans-9-(2phenylethenyl)anthracene. However, at around 1644 cm-1, on the 9-Anthraldehyde, there is a big, sharp peak there, indicating the presence of a carbonyl bond. There is no such peak in our final product, indicating the Wittig reaction did indeed go through, and all there’s left in our product spectrum is the presence of an alkene bond. Thus the final product is trans-9-(2-phenylethenyl)anthracene.

Postlab Questions 1.

2. 3.

No E/Z...