Thompson synthesis of p-bromoaniline PDF

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Karla Thompson Synthesis of p-bromoaniline INTRODUCTION Electrophilic aromatic substitution reactions are examples of halogenation. In a halogenation reaction the benzene is attacked by the electrophile (a halogen with a Lewis acid catalyst) provoking the substitution of hydrogen. Bromination is one of the most widely used types of halogenation. As the name states, Bromine is transformed into an electrophile when reacted with a Lewis acid catalyst. The catalyst allowing Bromine to react with benzene. For this experiment, aniline is brominated to form p-bromoaniline. This reaction consists of more than just an electrophilic attack of bromine on the aniline. One problem that can be encountered in the synthesis of compounds is the formation of undesired side products. The formation of any unwanted side products can be prevented through protection and deprotection within aromatic synthesis reactions. An example in this experiment would be the aniline containing an amine group, which is a very strong activator and is an ortho, para-directing group. To form an amide, an aryl amine such as aniline can be protected by reacting with acetic anhydride. The amide, acting as the protecting group, will direct the Bromine to attack the new ring (acetanilide) at the para position. This process creates p-bromoacetanilide. The amide on the ring can be deprotected through acid or base hydrolysis. The removal of the blocking group will convert pbromoacetanilide back into an aniline. Resulting in the desired product: p-bromoaniline.

MECHANISM:

EXPERIMENTAL SECTION: PART A: 1. Start by preparing two vials, Vial A and Vial B. 2. Add in 300 mg of aniline to vial A. (about 30 drops) 3. Add 1mL of 1M HCl. 4. Cap and shake. 5. Place this vial over a water bath and heat at 50o centigrade 6. While Vial A is heating, prepare Vial B. 7. In Vial B and 480 mg of sodium acetate. 8. Add in 0.9mL of water, and cap. 9. Once Vial A reaches the desired temperature, Add 0.360 mL of acetic anhydride.

10. Slowly add the contents of Vial B to Vial A 11. Cap the vial loosely and allow it to cool to room temperature. 12. Once the vial has cooled to room temperature, place it in an ice bath for about 5 minutes to cool it to 5o centigrade. 13. Vacuum filtrate to obtain final product of first part. 14. Obtain mass and melting point. BROMONATION: 1. Add 0.25g acetylaniline (product of first part) to a round bottom flask and make sure there is a stir rod in place. 2. Add in 0.2g sodium bromide. 3. Add 1 and ½ ml ethanol 4. Add 1.25 ml of glacial acetic acid 5. Cap and place above the stir plate. Assure it is fully mixed before moving on. 6. Once fully mixed, cool in an ice bath 7. Add 3ml of sodium hypochlorite, or 6% bleach dropwise. 8. Allow to react for two minutes in the ice and then an additional 15 minutes at room temperature. 9. Add 1g of sodium hydroxide in small batches, leaving about a minute between additions 10. Use a glass stirring rod and litmus paper to check the solutions acidity level and make sure it’s a basic solution

11. Once the solution is confirmed basic, add in 1g of sodium disulfate and allow to react for about a minute 12. Vacuum filtrate to collect the solids. 13. Obtain mass and melting point of product. PART B: 1. Using the product from last week (4-bromoacetanilide) 0.15g and place into flask 2. Add a boiling stone. 3. Add 5ml od acid solvent to dissolve the product. 4. Add 1mL of hydrochloride (12M) . 5. Place into sand bath set up before starting and begin heating. 6. Allow an hour to reflux. 7. Transfer all product into separate funnel rinse with 10ml water to make sure everything is transferred 8. Add 10mL of Dichloromethane into the separate funnel 9. Cap, shake and complete the extraction. Make sure to vent it between shaking it. 10. Place the first layer into the organic waste container. 11. Pour the top layer into a new beaker. 12. Treat the solution with sodium hydroxide to neutralize it to a pH of 7. 13. Once the solution is at the desired pH, Pour it back into the separate funnel. 14. Extract again by shaking and venting.

15. Once the two layers separate completely, remove the cap and dispense the bottom layer into a flask and continue with the second extraction. 16. Add another 10ml of DCM and complete the second extraction. 17. Drain out the bottom layer and combine with the first flask, dispose of the organic waste in the funnel properly. 18. Treat this with 1g of sodium sulfate to dry. (Until the solution is clear) 19. Transfer the solution into a vacuum flask, dry the product completely with the vacuum. 20. Collect the product (4-bromoaniline). 21. Obtain the mass and melting point of the product. TABLE OF CHEMICALS Chemical

Molecular Formula

M.P. / B.P.

Molar Mass

aniline

C6H7N

-6o C / 184oC

93.13 g/mol

Acetic anhydride

C4H6O3

-73oC / 138-140oC

102.09 g/mol

acetanilide

C8H9ON

115oC / 304oC

135.16 g/mol

p-Bromoacetanilide

C8H8ONBr

165-169oC M.P.

214.06 g/mol

Acetic acid

C2H4O2

16.2oC / 117-118oC

60.06 g/mol

p-Bromoaniline

C6H8NBrAceta

56-62oC M.P.

172.02 g/mol

RESULTS Acetanilide Mass : 0.288 g Acetylanilide Melting point : 114oC P-bromoacetanilide Mass: 0.425 g

P-bromoanetanilide Melting point : 152oC P-bromoaniline Mass : 0.098 g P-bromoaniline Melting point : 62-64oC %Yield: Aniline: 0.3g aniline/ 93.13mol=0.0032213mol 0.288g analide / 135.16 mol = 0.0021308mol (0.0021308mol/0.0032213mol)*100%= 66.14% P-bromoacetanilide: 0.25g P /135.16mol= 0.00184966mol 0.425g/ 214.06mol= 0.00198542mol (0.00198542mol/0.00184966mol)*100%= 107.34% (possibly not complexly dry or misweighed) P-bromoaniline: 0.15 g P * (1mol/214.06g)= 0.000700738 mol P 0.000700738 mol P * (172.02g/mol P/1mol)=0.1205g P (0.098/0.1205)*100%= 81.33% Reaction as a whole % yield: 0.3g aniline/ 93.13mol=0.0032213 mol aniline 0.098g P/ 172.02mol= 0.005697mol

(0.0005697/0.0032213)=0.1768 *100% so 17.7% yield p-bromoaniline

DISCUSSION The melting point of the first product was very close to the known value however the second steps product was more than ten degrees below the know, this could have been due to the product not being fully dried. The melting point of the final product was very close to the literature value, confirming the product is what was intended. Aniline had a percent yield of 66.14% which isn’t the best but better than the final product. The second steps product, p-bromoacetanilide, had a percent yield of 107.34% which could have been due to incomplete drying or possibly a pre-weighing issue. The final product, pbromoaniline, had a laughable percent yield of only 17.7%. This could have been due to the same problem that caused step two to obtain too much product or another weighing issue. The NMR spectrum consisted of two doublets around 7 to 8 which are located on the aromatic field. The two protons indicated in each of these doublets are located on the benzene ring in the final product. There was also a broad peak indicating the presence of an amino group.

CONCLUSION The synthesis of p-bromoaniline was a successful electrophilic aromatic substitution reaction that displayed the use of bromination. The information from the data revealed that the desired product was indeed obtained. The information and techniques in this lab can be used in other situations

that are seeking bromination or anything similar. The lab did accomplish what it set out to do.

REFRENCES University of South Florida Online Education, Experimental 6 videos

Kamillej11. (n.d.). Lab 8 - Experiment 8 Multi-step Synthesis of p-bromoaniline Introduction/Background An example of electrophilic aromatic substitution is halogenation In: Course Hero. Retrieved October 13, 2020, from https://www.coursehero.com/file/16302163/lab-8/

Klein, D. R. (n.d.). Organic chemistry. Wiley.

MilliporeSigma: United States. (n.d.). Retrieved October 18, 2020, from https://www.sigmaaldrich.com/united-states.html...