Wittig Reaction PDF

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Ochem 2 Wittig Reaction Lab Report...

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Wittig Reaction: Making of Alkenes Introduction The purpose of this lab is to create an alkene using the Wittig reaction which makes a double bond between the nucleophilic phosphorus ylide and a ketone or aldehyde. In this experiment, benzyltriphenylphosphonium chloride is the nucleophile and 9-anthraldehyde is the electrophile. Sodium hydroxide is used to deprotonate benzyltriphenylphosphonium chloride to form the ylide. The solvent system in this experiment is multi-phase in nature. The aldehyde is hydrophobic, while the benzyltriphenylphosphonium chloride used to form the ylide is very hydrophilic. Thus, the salt will dissolve in the water layer, but not in the organic nonpolar solvent. However, the two starting materials are still able to interact with one another at the phase barrier between the organic and aqueous layer. Due to this reason, the solution must be stirred constantly to increase contact surface area between them. Methylene chloride is used to dissolve the starting materials. In the reaction, water is used to rinse the reaction flask after rinsing it with the methylene chloride. 1-propanol is used to recrystallize the crude product after it becomes a slurry of a sort. Calcium chloride is used to remove any remaining water in the organic layer. There will be seven techniques used in this week’s lab including: Liquid/Liquid Extraction, Decanting, Simple Distillation, Recrystallization, Suction Filtration, Melting Point determination, and IR Spectroscopy. Liquid/ liquid Extraction is a technique that is used to separate two immiscible liquids, typically an organic and aqueous layer. Solvent decanting is a technique that is used to separate mixtures by allowing the mixtures to settle and be separated by gravity. Solvent removal by snorkel is a technique that removes the solvent by using the snorkels to extract the solvent fumes. Simple distillation is a technique where two liquids with different boiling points can be separated. Recrystallization is a technique used to purify crystals. Suction filtration is a technique where a pressure gradient is introduced in order to allow a greater rate of filtration to happen via suctioning. Melting Point determination is a technique that helps identify compounds based on their relative melting points while also determining the purity of the compound based on how big or small the melting point range is. IR spectroscopy is a technique used to find the functional groups in a molecule. General Reaction Scheme

Reaction Mechanism

Table of Reagents

Name

Structure

Benzyltriphenylphosphonium Chloride

MW (g/mol)

388.875

Melting/Boiling Point (°C)

Safety

MP = 337

FATAL IF SWALLOWED/ INHALED, skin irritant, eye damage, respiratory irritant Can cause irritation, slightly flammable

9-Anthraldehyde

206.244

Trans-9-(2-phenylehtenyl) anthracene

280.37

Methylene chloride

84.927

Water

H-O-H

1-propanol

Sodium Hydroxide Calcium Chloride

18.015

60.096

NA+ ------OH

Cl -

Ca2+ Cl

39.997 117.855

MP = 104

Combustible at high temperature, MP = 130-133 flammable, dangerous to eyes, skin Flammable, skin BP = 39.75 corrosive, eye Density= 1.322 irritant, serious eye g/cm3 damage can occur None BP = 100 Density = 1 g/cm3 Highly flammable, BP = 97.2 risk of damage to Density = 0.803 eyes, drowsiness, g/cm3 dizziness Leads to severe MP = 323 burns if comes in contact to skin Irritant to all routes MP = 772 of exposure, nausea,

headaches, shortness of breath Safety        

Avoid sparks, flames, and hot surfaces. Avoid breathing any fumes as the chemicals are toxic. Use snorkels while working with boiling liquids. Make sure not to heat a sealed vessel. Report any vapor or liquid exposure to TA immediately. Dispose all organic solvent waste in appropriate labeled bottle in lab hood. Wear safety glasses, gloves, and lab coat at all times. Never seal a reflux apparatus airtight.

Procedure                

1.0 g of benzyltriphenylphosphonium chloride, 0.590 g of 9-anthraldehyde, and a spin vane were added to a clean 10 mL round bottom flask. The starting materials were dissolved in 3.5 mL of methylene chloride and the reaction mixture was stirred slowly using a spin vane. Over the course of 3 minutes, 1.3 mL of 50% sodium hydroxide solution was slowly added to the reaction flask in a dropwise fashion. Once the hydroxide solution was added in its entirety, the flask was allowed to stir at room temperature for an additional 30 minutes. The flask was monitored constantly to ensure that the spin vane continued to stir the reaction mixture for the entire 30-minute period. If the stirring were to be interrupted or was uneven, the reaction would not be successful. Next, the spin vane was removed, and the contents of the flask were poured carefully into a separatory funnel. The organic and aqueous layer should be noticed. The round bottom flask was rinsed with 5 mL of fresh methylene chloride and 5 mL of deionized water. Each rinsing was poured into the separatory funnel and allowed to separate once again. The two layers were identified based on the density values. The organic layer was drained in to a clean, dry 25 mL Erlenmeyer flask and the remaining aqueous layer was extracted with a fresh 10 mL portion of methylene chloride. Methylene chloride extract was drained and collected in a 25 mL Erlenmeyer flask. The aqueous solution was drained out of the separatory funnel and saved until the end of experiment. An appropriate amount of calcium chloride pellets was added to the organic extract in order to remove any residual water. The exact amount of calcium chloride needed was based on volume of water present in the flask. Once the solution was dry, it was decanted into a clean, dry 50 mL round bottom flask.

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A simple distillation apparatus was constructed and used to separate the methylene chloride from the crude product. Caution was taken to not distill the solution to dryness. The heating mantle was removed, and the apparatus was allowed to cool to room temperature once the product formed a thick yellow slurry in the bottom of the flask. The crude product was recrystallized using a minimal amount of 1-propanol. Ice-water bath was used to aid in final precipitation of crystals. The purified trans-9-(2-phenylethenyl)anthracene was collected via suction filtration for 5 minutes after the crystals were collected. The final product was transferred onto a watch glass and the crystals were placed in a drying oven for approximately five minutes before weighing. The final mass of the product was determined, and melting point range was obtained. Finally, the IR spectrum was obtained of the final product.

Wittig Reaction: Making of Alkenes Results 

Initial weight of benzyltriphenylphosphonium chloride used: 1.0 g

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Initial weight of 9-anthraldehyde used: 0.588 g 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: 2 scoops Volume of 1-propanol used to recrystallize the crude product: 3 mL Final weight of the purified product: 0.081 g Melting point range of the purified product: 124-128 °C

Calculations Limiting Reagent 1.0 g benzyltriphenylphosphonium chloride x (1 mol benzyltriphenylphosphonium chloride / 388.875 g benzyltriphenylphosphonium chloride) x (1 mol Trans-9-(2-phenylehtenyl) anthracene / 1 mol benzyltriphenylphosphonium chloride) x (280.37 g Trans-9-(2-phenylehtenyl) anthracene / 1 mol Trans-9-(2-phenylehtenyl) anthracene) = 0.721 g Trans-9-(2-phenylehtenyl) anthracene 0.588 g 9-anthraldehyde x (1 mol 9-anthraldehyde / 206.244 g 9-anthraldehyde) x (1mol Trans9-(2-phenylehtenyl) anthracene / 1 mol 9-anthraldehyde) x (280.37 g Trans-9-(2-phenylehtenyl) anthracene / 1 mol Trans-9-(2-phenylehtenyl) anthracene) = 0.799 g Trans-9-(2-phenylehtenyl) anthracene 3.5 mL methylene chloride x (1.32 g methylene chloride / 1 mL methylene chloride) x (1 mol methylene chloride / 84.927 g methylene chloride) x (1 mol Trans-9-(2-phenylehtenyl) anthracene / 1 mol methylene chloride) x (280.37 g Trans-9-(2-phenylehtenyl) anthracene / 1 mol Trans-9-(2-phenylehtenyl) anthracene) = 15.25 g Trans-9-(2-phenylehtenyl) anthracene Percent Yield 0.081 g x 100 = 11.23 % 0.721 g Benzyltriphenylphosphonium chloride is the limiting reagent. IR Spectrum

Discussion The experimental melting point of trans-9-(2-phenylehtenyl) anthracene was 124-128 °C while the literature melting point was 130-133 °C. Our melting was very close to the literature value, but presence of some impurities might have lowered the value by a bit. The limiting reagent calculations determined benzyltriphenylphosphonium chloride was the limiting reagent. The percent of this reaction was 11.23% which is very low. This was because the reaction mixture was spilled while pouring it in the separatory funnel resulting in a loss of product. The solvent system used for this reaction was multi-phase (non-homogenous) in nature. The aldehyde is hydrophobic, while the benzyltriphenylphosphonium chloride used to form the ylide is very hydrophilic. Thus, the salt dissolved in the water layer, but not in the organic nonpolar solvent. However, the two starting materials were still able to interact with one another at the phase barrier between the organic and aqueous layer. The IR spectrum of trans-9-(2phenylehtenyl) anthracene shows the presence of C=C stretch at 1621 cm-1 and the absence of C=O bend around 1660 cm-1 and the OH bend around 3500 cm-1. This shows that the Wittig reaction took place and went to completion....