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Lab 7: Nitration of Salicylic Acid Name: Teaching Assistant: Patrick Avery Lab Partner: Date Collected: August 5, 2014 CHE202 – Organic Chemistry 2

Abstract This experiment was a nitration of salicylic acid, which is a type of electrophilic aromatic substitution. The experiment was successful, a percent yield of 83.3% was obtained and the melting point of 200 oC was observed and compared to a literature value of 229 oC. This shows a successful reaction and purification.

Introduction There are a lot of acids in this reaction, which means that each one acid must act as the “base.” Sulfuric acid is the stronger acid, so it gets to act as the “acid” and therefore, nitric acid will acid as the “base” because it is the weaker of the two acids. The nitration reaction has a rate determining step that is the attack of the electrophile. A new method of recrystallization was introduced in this experiment. This method uses a Craig tube and a centrifuge tube along with a small amount of the crude product, absolute ethanol for purification, and cold DI water to make the product precipitate out. This method is a very fast way to recrystallize because the liquid is centrifuged out and the purified product is left alone to be tested. This can be done with any reagents. The objective of this experiment was to do a nitration reaction with salicylic acid and recrystallize the product using the Craig tube method. The following is the relevant mechanism for this experiment:

Safety Long sleeves, long pants, closed toe shoes, Monogoggles, and gloves were worn to protect the skin and eyes from chemicals in the laboratory. All chemicals were kept in the fume hood. Sulfuric and Nitric acids were handled were great care because they are highly acidic, very reactive with water, and highly toxic. Nitric acid and nitrogen dioxide can also produce toxic fumes. Nitro salicylic acid can irritate skin, it was handled with care.

Experimental The procedure for this experiment is listed in the handout on UBLearns on slides 11-12 [1]. In step #4, when the cold mixed acid was added to the cold salicylic acid, a glass stir rod was used to keep the temperature low as well as to keep the mixture from clumping. The round bottom flask was kept in the ice bath during this process. In step #6, there was some difficulty to get all of the mixture into the beaker with the ice, so the ice water was poured back into the round bottom flask and the flask was swirled for about 5 seconds, then the contents were poured back into the original 50 mL beaker and the procedure continued as planned. This was done to get as much of the contents of the round bottom flask into the 50 mL beaker with the ice. Some possible errors that may occur in this experiment include: not letting the reagents cool in the ice baths long enough at the start of the experiment, not adding the salicylic acid slowly enough and allowing the solution to stay cool, not cooling the solution or warming the solution for the proper amount of time at any point during the experiment, not obtaining all of the solution out of the round bottom flask (or leaving a large amount behind), not decanting the proper layer or using the proper layer for filtration. In this experiment, just about any of the steps could be done wrong and the results could be effected in some way.

Results Reactant/Product

Mol. Wt. (g/mol) Sulfuric acid/Nitric X acid Salicylic acid 138.121 Ethanol X Nitro salicylic acid 183.12

Theoretical Yield Actual Yield - crude Actual Yield - recrystallized

Melting Pt. (oC) X

Boiling Pt. (oC) X

Density Amounts (g/ml) X 1.0 mL

158.6 X Lit: 229 oC Exp: 200 oC

211 78.37 X

1.443 0.789 X

Color X Red-Brown Light Pink

Weights (mass) 0.7955 g 0.633 g 0.016 g

0.609 g 0.5 mL Crude: 0.663 g Pure: 0.016 g

Moles (mmoles) 4.344 mmol 3.6 mmol 0.087 mmol

The following are the appropriate calculations for this experiment:

Discussion Something that is very important to consider in this experiment is what type of product will be made, a meta, para, or ortho product? The way to determine this is by looking at the hydroxyl and carboxylic acid substituents on the benzene ring, and see what sort of a directing effect they will have on the nitro group that comes from the nitric acid. On salicylic acid, as well as the nitrated product, the hydroxyl group and the carboxylic acid group are in ortho positions to each other. The nitro group will attach at the para position to the hydroxyl group as seen above in the Introduction section. This is due the directing effects of all three substituents and the steric hindrances that may occur if the nitro group attached at any other carbon. There are a lot of different options that could have been the final product, but the product that was made was the only product that was expected. The percent yield, using the crude product to calculate, was 83.3%, which is a good amount of yield. The recrystallized product cannot be used to calculate percent yield, since only a fraction of the total yield was recrystallized.

Conclusion This experiment is meant to teach the concepts of the electrophilic aromatic substitution reaction called nitration. Most of the characteristics of this reaction are true in most of the other reactions in this category. The main characteristic that is common within this category is the regiochemistry is greatly varied among all of the reactants. Changing one electron in one reagent could change the regiochemistry of the products entirely.

References: [1] Ahsan, Khalid. "Lab 7: Nitration of Salicylic Acid." CHE202: Organic Chemistry 2. University at Buffalo. NSC 337, Buffalo, NY. 31 July 2014. Class lecture....