Part A: Dilute 2.0 mL of concentrated HCI in 50 mL of water in a 125 ml flask. Then add 2.05 g (2.0 mL) of aniline. Stir the mixture until the...
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Question

Bromination of Aniline

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Why is this approach to prepare the para bromination product not considered an example for "Green Chemistry"? (3 answer to this & I only got 1)

  • The reaction only employs non-toxic chemicals.
  • The reaction employs a lot of corrosive and toxic compounds.
  • The reaction produces a lot of hazardous waste.
  • The reaction has a low atom economy.
  • Most reactions are carried out at very low temperatures.



How many signals does the p-bromo acetanilide show in the 13C-NMR spectrum?

  • 7
  • 8
  • 5
  • 6
  • 4


In part C, in the extraction of the basic solution with dichloromethane, where is the bulk of the target compound?

  • There will be an equal quantity in the upper and lower layer
  • In the lower aqueous layer
  • In the lower organic layer
  • In the upper organic layer


Given is the following TLC plate obtained in part C. Determine the Rf-values for the two compounds in lane 2 and assign the compounds. Note that that the line on the bottom is the start line and the line on the top the solvent front.

TLC.png


Why is a sodium acetate solution added in part A?

  • To protonate the intermediate and make it less soluble.
  • To deprotonate the intermediate and make it less soluble..
  • The sodium ion directs the position of the acetyl group.
  • The acetate catalyzes the formation of the amide bond.

Why is the protection of the amine function needed in this reaction? (3 answer to this)

  • The protection increases the selectivity for the ortho substitution.
  • The protection increases the reactivity of the reactant in the bromination.
  • The protection decreases the reactivity of the reactant and highly favors the para substitution
  • Without protection, the reaction with bromine yields several products
  • The protection changes the regioselectivity of reaxtion.


Which precautions must be taken when working with bromine? (Check all that apply)

  • Work in a closed system
  • Work behind a blast shield
  • Wear a respirator
  • Wear nitrile gloves
  • Work under a well ventilated hood


In part C, why is sodium hydroxide solution added once the reaction is deemed completed. (Check all that apply)

  • To deprotonate the acetic acid
  • To deprotonate the anilinium ion.
  • To make the product more soluble in dichloromethane.
  • To cause the hydrolysis of the amide function.
  • To form the anionic form of the product.


The student observes a melting point of 110-113 oC for the acetanilide. The literature melting point is 114 oC. Which conclusion can he draw from this observations?

  • The student isolated anilinium acetate.
  • The compound has a 98 % purity.
  • The isolated compound in the target compound.
  • The sample is still wet.


In part B, the crude is dissolved in hot ethanol. Why is water is added to the hot, saturated solution? (Check all that apply)

  • To increase the solubility of the reactants.
  • To decrease the polarity of the solution.
  • To increase the volume of the solution.
  • To increase the polarity of the solution
  • To reduce the solubility of the product at low temperature.


Why is charcoal used in part A?

  • To make it easier to filter the solution.
  • To adsorb colored impurities in the solution.
  • To catalyze the reaction to form the amide.
  • To neutralize the solution.


Which of the following mobile phases is most polar?

  • ethyl acetate:hexane=1:1
  • ethyl acetate:hexane=1:4
  • hexane
  • ethyl acetate:hexane=4:1

Which of the following intermediate is initially formed in the hydrolysis of the p-bromoacetamide?

intermediate.png

  • Intermediate E (Incorrect)
  • Intermediate A
  • Intermediate B
  • Intermediate D
  • Intermediate C



Using infrared spectroscopy, how could the student determine that the reaction in part C was successful? (Check all that apply)

  • The absence of a strong peak in the range from 1650-1680 cm-1 
  • The presence of two medium sized peaks in the range from 3350-3500 cm-1
  • The presence of a strong peak in the range from 800-850 cm-1
  • The presence of two strong peaks in the range from 1450-1620 cm-1
  • The absence of peaks in the range from 2850-3000 cm-1


The reported yields for the reactions are 80 %, 85%,and 85 %, respectively. What is the overall yield based on aniline?

  • 85 %
  • 72 %
  • 83 %
  • 68 %
  • 58 %

Image transcriptions

Part A: Dilute 2.0 mL of concentrated HCI in 50 mL of water in a 125 ml flask. Then add 2.05 g (2.0 mL) of aniline. Stir the mixture until the aniline completely dissolves (HCI and aniline react forming anilinium chloride). Add 2.77 g (2.56 mL) of acetic anhydride, stir until it is dissolved. Then, immediately pour a solution of 3.3 g of sodium acetate in 10 mL of water into the flask. After complete addition, stir vigorously for 5 minutes, then cool in an ice-bath to cause crystallization. When no more crystals seem to form (-10 minutes), isolate the acetanilide by vacuum filtration using a small Buchner funnel, wash the crystals with small volumes of ice-cold water, and air dry for 5 minutes. Recrystallize the obtained acetanilide from a minimum of hot water. Use 10 mL of water to start and increase the amount of water depending on the amount of acetanilide. If the initial crystals were not white, add 0.5 g of decolorizing charcoal to the product in water and then heat to gently boiling. Remove the charcoal by hot gravity filtration using two pieces of fluted filter paper. To avoid contaminating the filtrate with charcoal, do not overflow the filter funnel. After recrystallization, wash the crystals again with small volumes of cold water. Dry the product, obtain the mass, an infrared spectrum, and the melting point. The pure acetanilide is usually obtained as white flakes. The typical yield for this reaction is 80 %. Part B: Add 1.0 g of acetanilide and 4.0 mL of acetic acid to a 50 mL Erlenmeyer flask. Swirl the mixture until the solids dissolve. Place a magnetic stirring bar in the flask and place the flask on a hot plate and clamp. In the hood, obtain 2.5 mL of 4.1 M bromine/acetic acid (1:4). In the hood, add the bromine dropwise using a disposable Pasteur pipet over 5 minutes. Cover the flask with a small beaker and stir the reaction mixture for another 15 minutes to complete the reaction.

In the meantime, clean the used pipet and graduated cylinder with 2 mL of aqueous NaHSO; (sodium bisulfite). The excess bromine will be quenched with NalSO; until its color will change from red to colorless. After the reaction is completed, pour the reaction mixture into a 150 mL beaker containing 30 mL of water in the hood. Rinse the reaction flask with an additional 10 mL of water. A precipitate should form. Stir the precipitate with a glass rod to break up any chunks. If the solution still has an orange color from excess bromine, add aq. NaHSO; (sodium bisulfite) dropwise until the color disappeared. Collect the crude product by vacuum filtration and wash the solid four times with 10 mL of cold water (mix equal parts of ice and water). Transfer the crude solid into a 125 mL Erlenmeyer flask. Recrystallize the major product from a minimum amount of hot ethanol. It is recommended to try to dissolve the solid in approximately 5 mL ofhot ethanol. Add more hot ethanol if necessary . Keep track of the amount of solvent used. While heating the reaction mixture, add 1 ml of water for every 2 mL of ethanol used ( or half the volume). Allow the solution to cool down at room temperature. When crystals start appearing, place the flask in the ice bath for 15 minutes. Then isolate the solids by vacuum filtration. Rinse the product with cold water. Allow the crystals to dry overnight. Determine the mass, obtain an infrared spectrum, the mass spectrum and a melting point of the product. The typical yield for this reaction is 85 %. Part C: Transfer 1.0 g of p-bromoacetanilide into a 100 mL round-bottomed flask. Add 10 mL of water into the flask. Place the reaction mixture in an ice bath Chill the mixture and carefully add 10 mL of concentrated sulfuric acid carefully and slowly. Heat the mixture to reflux for 60 minutes. Initially, the p-bromoacetanilide will be insoluble but as the reaction progresses it will completely dissolve. Stop the reaction and wait 10 minutes for the mixture to cool off. Analyze the crude reaction mixture by TLC by using 10 mL of hexane/ethyl acetate (8:2) as mobile phase. Dissolve a small amount of the samples from the reaction mixture for the TLC in EtOAc (ethyl acetate). Spot the p-bromoacetanilide, the crude mixture, and a co-spot. Allow the mobile phase to migrate until 1 cm from the top. Visualize the TLC using the UV lamp. Estimate the extent of the reaction. (The product should stay at the origin. Is there any starting material left? Is the reaction complete?) If the reaction is not complete, continue the reflux for another 30 minutes to an hour. Upon completion, cool the reaction flask and pour the contents into 20 mL of ice-cold water. Neutralize the acidic solution with 10 M NaOH slowly. Theoretically, it should require 18 mL of 10 M NaOH to neutralize the sulfuric acid present. Add the aqueous NaOH solution portion-wise with the help of a Pasteur pipette. When half of the calculated theoretical volume has been added to check the PH. Add enough NaOH to bring the pl to 8. If a different concentration of NaOH is used, the required theoretical volume should be calculated. Transfer the neutralized solution to a separatory funnel and extract the free amine three times with 10 mL of dichloromethane. Back extract the combined organic layer with 20 mL of water and 20 mL of saturated sodium chloride solution. The combined organic layer is dried over anhydrous sodium sulfate (NazSO4). Remove the drying agent by gravity filtration and evaporate the dichloromethane in the hood over low heat. Remove the solvent, as the oily residue begins to crystallize. Allow the crystals to dry overnight. Obtain the mass of the product, the infrared spectrum, and the melting point. The typical yield for this reaction is 85 %.

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