Electrophilic+Aromatic+Iodination+of+Vanillin

= Electrophilic Aromatic Iodination = = = = of Vanillin = =

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Introduction:
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An electrophilic substitution reaction is when an electrophile replaces a group within a compound. During an electrophilic aromatic substitution reaction, an important way of introducing a functional group into a benzene ring, an affixed atom to the ring will be replaced by the electrophile. A type of this substitution reaction is an electrophilic aromatic halogenation. Halogenation is a reaction in which a halogen atom, such as bromine, iodine, chlorine, or fluorine, is incorporated into a molecule.

This lab uses the halogen iodine, in the form of sodium iodine iodide, to perform an electrophilic aromatic iodination of vanillin. Bleach is used as a catalyst it's not a catalyst, it's an oxidizer and ethanol is used as an aqueous solvent. This type of reaction occurs in a two-step addition and elimination mechanism. The reaction takes place when a electrophilic atom, Iodine for the purpose of this lab, attaches to the benzene ring by attacking the pi-electrons. This causes a cationic intermediate to form, eliminating the leaving group forming a substituted product.



Procedure:
Green Organic Chemistry: Strategies, Tools, and Laboratory Experiments by Doxsee, Kenneth M. Experiment B, Iodination of vanillin to 5-iodovanillin I need a more complete citation.

Data:
1.04 g of actual Vanillin sig figs 1.172 g sodium iodide 20 mL ehtanol 11 mL sodium hypochlorite - aqueous (bleach): Last drop of bleach: 9 minutes, 13 seconds 10 mL sodium thiosulfate solution 10% HCl: 20 drops (1 mL) added to acidify solution pH of solution~ 6 pKa of substance ~ 10 you didn't measure this, so it's not actually data. Mass of crude product: .431 g 2-propanol (aqueous): 5 mL to dissolve with heat 2-propanol (aqueous): 8 mL to generate clear but colored substance Final product mass: .114 g

Melting Point of 5-iodovanilliin product: 173.2 - 179.1 degrees Celsius (sweating - melting)

Observations:
Went from clear to pale yellow after the ethanol, vanillin and sodium iodide was combined:

Sodium iodide solution was pale yellow then went to dark brown at the beginning of bleach addition.

Became light brown after the bleach addition was complete.

When warming to room temp and stirring for an additional 10 minutes it looked like raw apple cider. *Mass of crude product was .431 g pale yellow precipitate

Added 8 mL of 2-propanol to generate the clear (but slightly colored) substance. There was brown chunks of precipitate in the clear but colored liquid. Possibly paper from scrapping product off filter paper after aspiration. Now that's an interesting comment. I wonder if the filter paper actually WAS the source of those crumblies?

Vanillin:
Chemical formula: C8H8O3 Molecular mass: 152.15 g/mol

5-iodovanillin: Chemical formula: C8H7IO3 Molecular mass: 278.04 g/mol



sig figs again here.

Error Analysis:

 * 1) Bleach began dripping before the 100 mL flask solution, containing 1.04 g vanillin, 20 mL ethanol, and 1.172 g of sodium iodide, was at an acceptable temperature. The stopcock on the separating funnel was loose, causing bleach to be slowly released.
 * 2) The bleach was added when the 100 mL flask solution reached 2.8 degrees Celsius instead of 0.0 degrees Celsius. This was seen as acceptable because 0.0 degrees Celsius would be very difficult to reach.
 * 3) When the 100 mL flask solution was at an acceptable temperature for bleach to be added, it took a moment to get the rate correct. Bleach was added at an inconsistent rate until the correct drip rate was attained.
 * 4) When removing the product from the filter paper, small pieces of paper were lifted along with the product. This could account for the brown specks in the final product.
 * 5) When removing the product with aspiration, there was a large amount of product remaining in the collection flask. Not all the product was captured on the filter paper. This went unnoticed until the end of the procedure.

Conclusion:
The purpose of this lab was to complete an electrophilic aromatic substitution by the iodination of vanillin. There was a poor percent yield of only 6%. This low yield can be explained from the excess of product left over in the collection flask during aspiration. During the reaction, the amount of precipitate observed before the aspiration should have yielded a higher percent. Also, as indicated the bleach was initially added to quickly, this can lead to the production of diiodo hindering recrystallization of product. The melting temperatures recorded, also indicate an impurity in the substance. The final product collected had many small brown pieces within. These impurities can cause the melting temperature range to decrease to 173.2 - 179.1 degrees Celsius compared to the literature value of 183-185 degrees Celsius.

I think sodium hypochlorite solution should also be included in the post-lab calculation. This report earned the following scores for: format (2/2) style (1.5/2) data (3/3) quality of result (1/1) quality of reported data (0.5/1) conclusion (2/2) error (1/1) post-lab Q (1/2) for a total of 12/14.