Electrophilic Aromatic Iodination Of Vanillin

Electrophilic Aromatic Iodination of Vanillin

Purpose:

The purpose of this laboratory experiment is for an aromatic compound to undergo an electrophilic substitution reaction. To carry this out, our method combines sodium iodide and common bleach as the oxidizing agent in aqueous alcohol as the solvent.

Balanced Chemical Equations:

Physical Properties:

Name of Chemical Chemical Structure Molar Mass (g/mol) BP/MP (Ð'Ñ"C) Density (g/mL) Mass/Vol. Used Purpose

3-methoxy-4-hydroxybenzaldehye C8H8O3 152.1494 MP=81-83, BP=285 NA 0.1g Solute

Ethanol CH3CH2OH 46.0688 MP=-114.1, BP=78.3 0.789 2.0mL Solvent

Sodium Iodide NaI 149.8943 MP=661, BP=1300 3.667 0.117g Catalyst

Bleach NaOCl 74.4422 MP=NA, BP=40dec 1.209 1.1mL Oxidizing Agent

Sodium Thiosulfate Na2O3S2 158.0977 NA 1.667 1.0mL Extraction

Hydrochloric Acid HCl 36.4609 MP=-114.2, BP=-85.1 0.909 0.6mL Acid Agent

Limiting Reagent and Theoretical Yield:

(0.1g Vanillin/152g/mol) = 6.58 x 10^-4 mol Vanillin  Limiting Reagent

(0.117g NaI/150g/mol) = 7.8 x 10^-4 mol NaI

Theoretical Yield:

(6.58 x 10^-4 mol Vanillin/1)(279g/mol)  0.18g product

Procedure:

In an Erlenmeyer flask (or beaker), dissolve ~ 0.1 g of 3-methoxy-4-hydroxybenzaldehyde in 2.0 mL of ethanol. Cool the flask in an ice bath for a few minutes. To the ice-cold solution, add 0.117 g of sodium iodide. Over a

period of 10 minutes, add 1.1 mL of Bleach (5.25% w/w NaOCl) dropwise to the cooled flask. The solution should turn a yellow color. Once the addition is complete, let the solution warm to room temperature and stir for about 10 minutes.

Stir the solution gently, and then add ~ 1 mL of sodium thiosulfate (10% w/w). The solution will turn a cloudy, grayish yellow. Acidify the solution with 3.2 M HCl, using pH paper to check the acidity of the solution (it will take approximately 0.6 mL of added HCl). Gently evaporate any excess ethanol. (Apply gentle heat only if necessary). Cool in an ice bath for about 10 minutes, and then collect the precipitate by vacuum filtration. Wash the crystals well with ice-cold water. Recrystallize the crude aryl iodide from isopropanol. Place in an ice bath and collect the crystals by vacuum filtration.

Determine the weight of your crystals, determine the melting point, and take an IR spectrum. As always, analyze your data by comparing your values to literature values.

Cleaning Up: Place all waste in the appropriate waste container.

Results:

After the addition of hydrochloric acid, the solution solidified slightly to a thick, white, slushy material. This material was then cooled in an ice bath for approximately ten minutes, and then the crystals were collected via vacuum filtration. Once the crystals were collected, the product was recrystallized from isopropanol. This process required the heating of the crystals with isopropanol as the solvent, cooling to room temperature, sit in an ice bath for a few minutes, and collect the final crystals through vacuum filtration once again. This final product is the wanted iodovanillin.

Wt. of Vanillin Wt. of Sodium Iodide Wt. of Iodovanillin crystals MP of Iodovanillin pH after HCl addition

0.1035g 0.1171g 0.061g 183.8Ð'Ñ"C 0

Calculations:

Theoretical Yield: (See above for limiting reagent info.)

(6.58