Electrophilic aromatic substitution

The introduction, experimental methods, findings, discussion, and conclusion are the different sections of this study.
The purpose of the introduction is to introduce the reader to and familiarize them with the fundamentals of electrophilic substitution.
The experimental process outlines the precise actions that were done throughout the experiment to obtain the obtained results.
The discussion section serves to defend the findings.
Additionally, this section provides answers to the queries posed in the reporting manual.
The conclusion section, which comes last, serves as a wrap-up for the report and informs the reader of what was done.
This is an organic reaction where an atom attached to the aromatic compound, which is usually hydrogen, get replaced by an electrophile. The typical examples of electrophilic substitution include aromatic nitration, aromatic sulfonation, aromatic halogenation, alkylating craft reactions. This report will focus intensely on aromatic nitration.

Aromatic nitration

Typical nitration reactions involve a “mixed-acid” scenario. In this case, a mixture of concentrated sulfuric acid and nitric acid are used. This acid mixture produces a nitronium ion (NO+) which is an active species in the aromatic nitration. The active ingredient affects the nitration process even where there is no acid mixture. In the mixed condition, the sulfuric acid does not take part in the reaction but serves as a catalyst and water-absorbent agent. To nitrate a benzene compound, the process has to be conducted at about 50°C temperature. The reaction is a typical example of electrophilic aromatic substitution where the electron-rich benzene is attacked. the equation demonstrates the reaction explained in this passage.



In the reaction above, the leading end product is nitrobenzene.

Apparatus and Reagents used

Weighing boat

250ml conical flask

Pasteur pipette

Water bath

Filter paper, Buchner funnel, and flask

TLC tank

TLC funnel

Measuring cylinder

Sample jars

Hair drier

Retort clamp and stand

Aluminum foil

Thermometer

Pencil

2, 150ml conical flasks

Phenol

Toluene at 60-80oC in the ratio50:50 (v/v)

Concentrated nitric acid

o-nitrophenol

p-nitrophenol

2,4-dinitrophenol

Experimental procedures

4.7g of 0.05mol phenol was weighed out using a weighing boat and carefully transferred into the 250ml conical flask. 15ml of toluene was added to the flask, and the solution was cooled in an ice bath to slightly below 10oC. 4ml of concentrated nitric acid was then added to the mixture dropwise. Meanwhile, the temperature of the content of the flask was kept constant below 10oC. The mixture in the flask was swirled thoroughly to ensure proper mixing of flask contents. After all the reagents had been added, the conical flask was kept in the ice bath for approximately 5 minutes. Thereafter, the flask was placed to stand at room temperature for about 20 minutes. Meanwhile, periodic shaking of the flask was being done. The flask was then taken to the ice bath once again for chilling, and the solution was cooled to approximately 0oC. Precipitation process of the crystal started forming out. Using the flask and the Buchner funnel, the solid precipitate was then collected using suction filtration. A little amount of cold toluene was then used to clean the precipitate. The washed precipitate and the filtrate were kept to be used for carrying out TLC analysis. The product was transferred into a sample container with a predetermined weight in readiness for drying. Once drying was complete, the product yielded was recorded. Thin layer chromatographic (TLC) analysis

2mg with a spatula of the recrystallized product, para-nitrophenol, ortho-nitrophenol, 2,4-dinitrophenol, and a few drops of the filtrate were added sequentially into separate test tubes. 0.2ml of toluene at 60-80oC in the ratio50:50 (v/v) was added to each sample tube. Each sample was then placed on the baseline of the TLC plate. Each spot was placed at equidistant from each other and the bottom of the plate at 1.5cm. the TLC plate was then placed in the TLC tank and covered with aluminum foil. The plate was given time until the solvent front was well developed in a magnitude of about 1cm. the plate was then removed from the tank and pencil marks were made where the solvent front reached. The spots were then observed. The spectra were then compared and optimum time needed for the reaction was evaluated.

Results

Table 1: Experimental Results

Item

Mass in grams

Container

7.23

Container + product

7.91

Product

0.68

The yield is calculated as:

Yield = x100% = =68%



Figure 1: illustration of the solvent fronts of the five samples displayed after chromatography process

Discussion

The results of the experiment are obtained quickly since the TLC plates are formed while the reaction is going on. The presence of UV light makes it possible to visualize the spots. It is possible to confirm the ending point of the reaction with the disappearance of phenol. When the reaction is complete, a precipitate of the product is formed, and recrystallization also takes place. The process is carried using toluene, and it is important since it is a less volatile for performing recrystallization process. The yield of the product is often between 60-70%. In our case, the yield was 68%. Therefore, the product was fairly pure with exceptions of some levels of impurities.

Response to questions

Chief products of mononitration of the following compounds:



Compound a is benzaldehyde. Mononitration equation of this substance is given below.



Therefore, the principal product obtained when benzaldehyde undergo a mononitration process is referred to as m-Nitro benzaldehyde.

The second compound shown below is bromobenzene. When this substance is taken through mononitration reaction, a mixture of two compounds may be formed. The first one is Bromo nitrobenzene. In case nitric acid is available in excess, Bromo dinitrobenzene is formed. These are the chief products created in this reaction. The equation below illustrates the equation of the result.



How the following compounds are formed from phenol:



The above-shown compound is known as 4-aminophenol. It is produced through the process of phenol nitration and reducing the product using iron. The chemical equation leading to the formation of this product is given below.

C6H5NO2 + 2 H2 → C6H5NHOH + H2O

Formation of water in this process is inevitable. The chart below gives an illustration of the process that takes place in the formation of the product.



Therefore, apart from the formation of 4-aminophenol, other products such as paracetamol is also formed. The products can be separated by applying fractional distillation since they all have different boiling points.

Conclusion

In conclusion, this experiment was conducted successfully. It was possible to verify the development of solvent fronts with the use of TLC. It was possible to characterize the products with the use of their melting points and the TLC results. The concept of recrystallization was also employed in this experiment. Other theories of regarding the chemical reactions of phenol with other compounds were also learned in the course of the report.

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