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Post Lab 8 – Multi Step Synthesis of p-Bromoaniline Raina Patel TA- Md Tawabur Rahman

Introduction Background Within the Bromination reaction it is known to be an electrophilic aromatic substitution, but Bromine reacting by itself is known to not be able to react with aromatic compounds. For the reaction to occur, there needs to be a Lewis Acid present, which is able to become the electron pair acceptor, which will be combined with the bromine which will end up synthesizing out the end product as substituted (Wildergirma 2018). The mechanism through which the bromiantion of an aromatic molecule occurs is through 1st, the making of the stronger electrophile, the attack on the sigma complex by the electrophile, and then lastly the deprotonation of the product. In the need to make the stronger electrophile, the bromine itself gives up a pair of its electrons to the

FeBr3 , which ends up

making the more polar Bromine to Bromine bond, making the bond between the Bromine molecule and the

FeBr3

more reactive. The aromatic ring that was left over will then become

the nucleophile, the double bond ends up attacking the Br in the the stabilized sigma complex and the

Br 2 FeBr3 , which thus forms

FeBr 4 . The Bromine that is present within that

compound is able to act as a weak base that is able to deprotonate the product of the sigma complex. In the deprotonation of the sigma complex it helps to recreate the aromaticity which helps form the HBr, and then creating back the

FeBr3 catalyst (Wildergirma 2018).

These Aromatic molecules are substituted with other functional groups at times that helps to start up or not the aromatic compounds. These “activating groups” can be amine, amide, ester, hydroxy groups. While these “deactivating” groups are groups that help to decrease the reaction rate by taking away the electron density from the ring. These groups are carbonyl, ammonium, and haloalkyl groups. 2

In the case of having to many functional groups within a molecule can cause problems with the synthesis of the end product that was needed. But also there are these “protecting groups” that help prevent the cause of problems. These groups are used to help hide time to time given functional groups. A case where this group is used is when a carbonyl group, needs to be “hidden” from these stronger nucleophiles, oxidants, or reductants. In the case of the Grignard reagent when trying to make this group with a molecule that already has a ketone, it needs to be protected as the acetal, which is done through the use of an acid, and an alcohol. After the completion of the reaction, an acid can be used to help deprotonate the ketone (Wildergirma 2018). Another case that may use the protecting group, can be when there were acidic hydrogens with there being a carbon that is electrophilic that is in the reaction. Indicative that the amine needs to be protected, this experiment itself uses the acetyl group which ends up protecting the amino group during this experiment. This amino group is then protected by the reaction between the aniline and the acetic anhydride all with HCL, water, and CH3COONa present which aids in the production of the acetanilide. In comparison to the end of the experiment where the reaction has the Hydrogen proton, the water molecule, and Sodium Hydroxide which aid in the protection of the amino (Wildergirma 2018).

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Mechanism

Figure 1: Multi-Step Synthesis of p-Bromoaniline

Figure 2: Side Reaction

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Experimental Section: Synthesis of Acetanilide 0.3 g aniline, 1 mL of HCL were all mixed in the conical vial, this solution was then labeled as A. 0.4 g of Sodium Acetate Trihydrate and 0.9 mL of water were then mixed into another conical vial labeled as B

A was then heated over a steam bath to 50ºC. When the temperature reached 50 ºC, it was taken off the heat and then the 0.36mL acetic anhydride was added in, this was mixed in well and the B was added into the A, then placed over ice

The crystals were then yielded out and then collected from the filtration, as well as the % yield and the melting point of the crystals were taken out.

Synthesis of P-Bromoacteanilide 0.2 g Sodium Bromide, 0.25g Acetanilide, 1.5 mL 95% ethanol, magnetic stir bar, and then 1.25 mL of the acetic acid were all added into a vial, then this was placed over the stir bar in the ice bath

3 mL of bleach added slowly while being stirred, the vial was then closed and still on the ice for 2 more minutes, this was then taken out of the ice bath and then left at RT for a few minutes

1g Sodium Bisulfite was then added in and then mixed for 1 more minute, the crystals were then collected as they were first dried out and then the mass and melting point were dound

Vial was placed in the ice bath with 1g of NaOH added in, while the mixture was then added in for about 1 minute, the solution was found to be basic

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Synthesis of P-Bromoaniline 5 mL of ethanol, 0.15g of 4-bromoacetanilide as well as 1 mL of HCL 12M and then boiling stones were added into the mixture, in a flask. This was added in the water-cooled condenser refluxing for about an hour

This mixture was then cooled down, and then out into the separatory funnel. The flask was then washed down with 10 mL of water, then the separatory funnel, it was then closed to be vented and then shaken out, the layers were then separated out.

10mL of the DCM were added into the funnel again, which allowed to further separate the layers again, bottom layer was collected again the same flask. To dry out the solution the anhydrous sodium sulfate was added in, after which the solution was placed into the vacuum filtration set up

The layer at the bottom were then taken out into a beaker as it was unnecessary. The 3M NaOH was then added into the separatory funnel, while the solution became basic. To further allow the layers to separate 10 mL of DCM were added. The layers separated again, the bottom layer was collected into a flask

DCM evaporated out through the evaporation of the vacuum, the solid was then collected out from the flask. The weight, melting point, and HNMR spectra were gathered.

Table of Chemicals

Common Name

Aniline

Acetic Anhydride

Hydrogen Chloride

Sodium Acetate

Molar Mass

93.13 g/mol

102.09 g/mol

36.46 g/mol

82.03g/mol

Melting Point

-6.3 ºC.

-73 ºC

-114.2 ºC.

324 ºC.

Boiling Point

184.1 ºC.

139.8 ºC.

-85.05 ºC.

8811.4 ºC.

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Hazards

Eye, and skin irritant, Flammable

Corrosive to skin, Flammable

Skin and eye irritant

Eye and skin irritant, flammable

Chemical Structure

Table 1: Table of Chemicals first part

Acetanilide

Sodium Bromide

Sodium Hypochlorite

Acetic Acid

p-Bromo acetanilide

p-Bromoaniline

135.17 g/mol

74.44 g/mol

60.05 g/mol

214.062 g/mol

172.05 g/mol

114.3 ºC.

102.894 g/mol 747 ºC.

18 ºC.

17 ºC.

166 ºC.

64 ºC.

304 ºC.

1396 ºC.

101 ºC.

118.1 ºC.

353.4 ºC

225.9 ºC.

Combustible at high temps, skin and eye irritant

Skin and eye irritant

Skin and eye irritant

Eye and Skin irritant, flammable

Skin eye irritant, combustible at high temperatures

Skin and eye irritant, combustible at high temperatures

Table 2: Table of Chemicals second part 7

Results Product 1,

Product 2,

Acetanilide p-Bromoacetanilide Mass .288 g .425 g Melting Point 114 ºC 152 ºC Percent Yield 66.16% 107.35% Table 3: Data collected from the experiments end products

Figure 3: H-NMR Spectrum for p-Bromoaniline

Calculations Reaction 1 8

Product 3, p-Bromoaniline 0.098 g 62-64 ºC 81.26%

0.3g aniline x (1 mol aniline/93.13 g/mol aniline) = 0.003221 mol aniline 0.36 g acetic anhydride x (1 mol acetic anhydride/102.09 g/mol) = 0.003526 mol acetic anhydride Aniline limiting reagent 0.003221 mol aniline x (135.17 g/mol acetanilide/ 1 mol acetanilide) = 0.4353 g acetanilide % yield = actual/theoretical x 100 = .288 g acetanilide / .4353 g acetanilide x 100 = 66.16%

Reaction 2 0.25 g acetanilide x (1mol acetanilide/ 135.17 g/mol acetanilide) = 0.001849 mol acetanilide 0.2 g sodium bromide x (1mol sodium bromide/ 102.849 g/mol sodium bromide) = 0.001944 mol Sodium Bromide Acetanilide is the limiting reagent 0.001849 mol acetanilide x (214.06 g/mol p-bromoacetanilide/ 1 mol p-bromoacetanilide) = 0.3959 g p-bromoacetanilide % yield = (.425 g p-bromoacetanilide/ .3959 g p-bromoacetanilide) x 100 = 107.35%

Reaction 3 0.15 g p-bromoacetanilide x (1 mol p-bromoacetanilide/ 214.06 g/mol p-bromoacetanilide) = 0.0007007 mol p-bromoacetanilide 3.945 g ethanol x (1 mol ethanol/ 46.07 g/mol ethanol) = 0.08563 mol Ethanol p-Bromoacetanilide is the limiting reagent 0.0007007 mol p-bromo acetanilide x 172.05 g/mol p-bromoaniline/ 1 mol p-bromoaniline = 0.1206 g p-bromoaniline

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% yield = (0.098 g p-bromoaniline/ 0.1206 g p- bromoaniline) x 100 = 81.26%

Discussion There was 3 different products that were synthesized out, as well as the melting point. In the case of the Acetanilide, the melting point was found as the 114 ºC, which is exactly the same as the literature value. Which indicates that the synthesized out product was pure, and that there were no impurities that affected the synthesized out product. The percent yield was 66.16% which is indicative of the fact that a lot of the product was synthesized out and lost, in the case of the evaporation, also lost through the transferring of the product from vial to vial. In the second reaction of the p-bromoacetanilide the melting point was found to be 152 ºC, in comparison to the literature values of being 166 ºC. The difference in the melting point was pretty drastic indicative of the fact that the end product was very impure. This was very apparent when the p-bromoacetanilide was analyzed, with the HNMR. When looking at the percent yield of 107.35% , it is indicative that there must be have been error when drying out the final product as the final product weighed heavier then the literature experiment value, in having the final product not dried out completely can be the sign of having the percent yield over 100%. In the third reaction for the p-bromoaniline, the melting point was given at a range of 6264 ºC, while the literature value was 64 ºC. In seeing that the final product was almost the same except of having the range of 2 higher, can be through small contaminants but rarely anything else as the end product was relatively pure. This was supported when looking at the H NMR spectra for the p-bromoaniline was looked at. In looking at the percent yield of 81.26% it shows that there was a significant amount of end product that was synthesized out. But in the percent yield not being 100% can be signs of having the final product contaminated with other

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substances or water. When looking at the peaks in the HNMR spectra given the peak at around the 7.3ppm mark indicates the existence of the aromatic parts that are close to the bromine substituent. While the peak around the 6.5ppm mark indicates the existence of the aromatic protons that are close to the amine sub parts. While the third peak that is very lightly seen at the 5.3ppm is to show the amine group that is close to the amine group. This group is not that heavily seen as the spectrum is sort of shifted onto the side, as the end products were somewhat contaminated with water, indicative the p-bromoaniline was synthesized out but that it was contaminated with water.

Part 2 1. It was not directly brominated, as the aromatic amines are very reactive, they can become over brominated very easily making the substitution of the bromine in 2 positions at the O, and then P 2. This was not the method used to produce the acetanilide due to the high temperatures of the reflux could have caused to create side products, as water is easily able to attack the acetic anhydride, which ends up making end products 3. In using the Sodium hydroxide, it is a strong base so in using that it will therefore oxidize the aniline relatively quick, which allows for the Nitrogen on the aniline to attack another anilines Nitrogen creating an azobenzene. 4. The spectra given is indicative of the acetanilide product. There are to be the peak at the 2ppm mark which shows that there are the protons in the methyl group of the carbonyl group, the one peak that is over the 7ppm mark shows the 3 protons that are the most far from the substituent groups. The other peak that is under the 7.5 ppm mark shows the 2

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groups that are the most close to the substituents, while the last peal that is under the 8ppm mark shows the group attached to the Nitrogen. The H NMR of the pbromoacetanilide is to have 3 peaks, one at 2 ppm(protons in methyl group on carbonyl), one at 7.5ppm (aromatic groups), and then the peak around the 10ppm indicative of the proton that is attached to the Nitrogen. Lastly the spectrum for the p-bromoaniline is also going to have 3 more peaks one at around 3ppm, showing protons attached to the Nitrogen group. Another peak around the 6.5ppm showing the most close aromatic protons to the amino group, as well as the last group at the 7ppm which shows the aromatic group that is closest to the bromine.

Conclusion The aim of the experiment was through the multi-step synthesis of aniline to help produce the p-bromoaniline. Through the end of the experiment it was shown that the end product was truly the p-bromoaniline. As looking the H NMR spectrum it is able to be told that even though the spectrum is shifted off. When looking at the melting points it is also told the same thing as the melting point that was gained through the experiment of the p-bromoaniline was a range of 62-64 ºC, in comparison to the literature value of 64 ºC. Both of which these values are exactly the same, indicative that the final product was not contaminated with water. Through the percent yield gathered was 81.26% depicts the fact that a good amount of the product must have been lost through the transference of the solutions. Skills learned through this experiment are very important as they are used in the Real Life Applications such as in the fire department, as they used these bromiantion reactions to help make better the quality of rubber, as well in the storage of energy. In completing the experiment

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it is thus concluded that the experiment was a success as a multi-step synthesis of aniline aided in creating the pure end product of p-bromoaniline.

References

Libretexts. “18.15: Multistep Synthesis.” Chemistry LibreTexts, Libretexts, 14 July 2020, chem.libretexts.org/Bookshelves/Organic_Chemistry/Map %3A_Organic_Chemistry_(Smith)/Chapter_18%3A_Electrophilic_Aromatic_Substitution/ 18.15%3A_Multistep_Synthesis.

Wildergirma, S. Experimental Organic Chemistry Lab Manual; University of South Florida: Tampa, FL, 2018; P. 106-108

Wildegirma, S. Experimental Organic Chemistry Lab Manual; University of South Florida: Tampa, FL, 2016; P. 92-95 13

Wildegirma, S. Experimental Organic Chemistry Lab Manual; University of South Florida: Tampa, FL, 2016; P. 92-95

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