Orgo 2 Lab 3 - Lab report 3 PDF

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Lab report 3...

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Experiment 28: Halogenation: Synthesis of 4-Bromoacetanilide by Electrophilic Aromatic Substitution, Part 2 Objective The purpose of this experiment is to become experienced with the technique of recrystallization for purification of a crude product. We will be recrystallizing and purifying the crude product of last week's electrophilic aromatic substitution between bromine and acetanilide, 4-Bromoacetanilide. Additionally, we will analyze the product by obtaining both a melting point and IR spectra, as we become familiar with the FT-IR instrument. Procedure Experiment 28 was performed according to the procedure in Mayo, pages 368-371, with the modifications listed in the Canvas document. Modifications include: ● Recrystallize the crude product from 1:1 ethanol:water instead of 95% ethanol ● Reweigh crude product from last week prior to purification ● Determine melting point and IR spectra of purified product ● Omit chemical tests and TLC analysis Reaction Scheme

Acetanilide

Bromine

Data and Results Amount of Acetanilide used in Part 1: 101mg 0.75mmols Theoretical Yield of Product

4-Bromoacetanilide

Limiting Reactant - 0.75 mmols Acetanilide 0.75 mmols ×

1 𝑚𝑜𝑙 𝐴𝑐𝑒𝑡𝑎𝑛𝑖𝑙𝑖𝑑𝑒 1000 𝑚𝑚𝑜𝑙

×

1 𝑚𝑜𝑙 4−𝐵𝑟𝑜𝑚𝑜 1 𝑚𝑜𝑙 𝐴𝑐𝑒𝑡𝑎𝑛𝑖𝑙𝑖𝑑𝑒

×

214.06 𝑔 1 𝑚𝑜𝑙 4−𝐵𝑟𝑜𝑚𝑜

= 0.1605 g of

4-bromoacetanilide ---- 161 mg Observations ● The crude product was an off white crumbly solid ● Upon completely dissolving the solid in hot solvent, a clear brownish liquid was left ● The precipitate formed in the solution was a white solid ● Filtering the product left behind small white/clear crystals ● The melting point of the purified product was 169.3 ℃ (Range 167.8 ℃ - 170.4 ℃) Calculations Yield of crude 4-bromoacetanilide after drying for one week 0.107 g of crude product Yield of recrystallized 4-bromoacetanilide 0.075 g of purified product % Yield of 4-bromoacetanilide for purification step (Recrystallization mass)/(crude mass) x 100 = 0.075 𝑔𝑟𝑎𝑚𝑠 0.107 𝑔𝑟𝑎𝑚𝑠

× 100 = 70.09 = 70.1% yield

% Yield of bromination reaction (Recrystallization yield)/(theoretical yield) x 100 = 0.075 𝑔𝑟𝑎𝑚𝑠 0.161 𝑔𝑟𝑎𝑚𝑠

× 100 =46.58 = 46.6% yield

Questions 1) A. Ethyl Acetate and Hexane - This solvent pair would work as the two solvents are miscible with each other, due to their similar polarities. B. Water and Diethyl Ether - This solvent pair would not work as water and diethyl ether are not miscible with each other, water is a highly polar solvent and diethyl ether is nonpolar. C. Methanol and Methylene Chloride - This solvent pair would work as the two solvents are miscible with each other, due to their similar polarities. 2) Toluene would not be a good solvent for the recrystallization of the product in this experiment. 4-Bromoacetanilide is a polar molecule, as shown by the polar solvents used

in part 2 (EtOH:H2O) and by the unequal sharing of electrons within the molecule itself (ex/ the carbon oxygen double bond on the amide). Toluene is a nonpolar solvent, therefore the crude product and solvent would simply create an immiscible mixture, effectively halting the entire process. A polar solvent would be necessary for the experiment. 3) A. Aromatic C-H Stretch --- 3122 cm -1 B. Amide N-H Stretch --- 3300 cm -1 C. Amide C=O Stretch --- 1668 cm -1

See attached IR Spectra at end of report

4) A. From the IR spectrum alone, one can only tell the functional groups that a given sample contains, not necessarily their location within a molecule, rendering it inefficient at differentiating between isomers. Therefore, given that the starting material for this experiment contains the same functional groups of the product, the IR spectrum cannot confirm that the product of the reaction was indeed the desired product as the functional group can be in different positions (like in the ortho position). B. The experimental melting point range can help confirm that the product was indeed 4-Bromoacetanilide. The literature melting point for the product was around 168 ℃. The melting point obtained from the product in this trial was between 167-170 ℃ with a singularity at 169.3 ℃. C. This data is consistent with expectations as the theoretical and experimental melting points are only within a degree off. The small difference in temperature provides evidence that the product isolated was, in fact, 4-Bromoacetanilide. 5) A. The spectrum provides unambiguous evidence that the molecule is indeed the para product because of the number of unique hydrogen signals. The para product should produce four separate signals, as the spectrum shows, while the ortho product would produce six separate signals: four from the aromatic ring and two from the amide substituent. The para configuration creates two equal hydrogen environments on the four empty carbons of the ring, leading to the unique four signal spectrum. B. Signal A - 3 Hs on the methyl group next to carbonyl Signal B - 4 Hs, two on each carbon of aromatic ring Signal C - 4 Hs, two on each carbon of aromatic ring Signal D - H attached to Nitrogen of amide

Works Cited Mayo, D. W.; Pike, R. M.; Forbes, D. C. Microscale Organic Laboratory with Multistep and Multiscale Syntheses, 5th ed.; John Wiley & Sons, Inc., 2011; pp 368-371. Melting Point of 4-Bromoacetanilide, www.sigmaaldrich.com. Modifications for Experiment 28: Electrophilic Aromatic Substitution Part 1, Canvas document....