Electrophilic+Aromatic+Iodination+of+Vanillin

Zach Chandler Megan Bernard

This is a really nice report. I've really got no comments--no need to nit pick! Well done.


 * Lab #5:** Electrophilic Aromatic Iodination of Vanillin


 * Objective:** The objective is to Iodinate an aromatic substance called vanillin.

The first two molecules shown below display the molecular structures of the reactant vanillin (4-hydroxy-3-methoxybenzaldehyde), and the desired product 5-iodovanillin (4-hydroxy-3-iodo-5-methoxybenzaldehyde). Then the reaction is shown below.
 * Introduction:** The purpose of this lab is to conduct a greener approach for an aromatic compound to undergo an electrophilic substitution. In order for this to be accomplished, a combination of sodium iodide and common household bleach will be used as the oxidizing agent; rather than nitric acid which is a more hazardous oxidizing agent. The slow addition of the bleach should aid in the result of a higher percent yield and easier purification. The vanillin used in the experiment, 4-hydroxy-3-methoxybenzaldehyde, is an organic compound which includes the functional groups ether, phenol, and aldehyde. The reaction shown below depicts an electrophilic substitution as opposed to an addition reaction across the double bond. The reason for this substitution reaction is based upon the stability of the aromatic ring due to resonance. The addition of an iodine atom, or iodination, is considered a much safer and greener from of halogenation than the addition of Bromine or Chlorine.


 * Structure of Vanillin**


 * Structure of 5-iodovanillin**


 * Electrophilic substitution reaction involving the iodination of vanillin.**


 * Procedure:**
 * Step 1:** In a 100 mL round bottom flask containing a magnetic stir bar, dissolve 1.0 g of vanillin in 20 mL of ethanol. Add 1.17 g of sodium iodide, and then cool to 0 degrees Celsius with ice water bath.


 * Step 2:** Use a separatory funnel to add 11 mL of aqueous sodium hypochlorite solution (5.25 % w/w) drop-wise to the stirred reaction mixture over a period of 10 minutes. The color should change from pale yellow to red-brown.


 * Step 3:** After the addition is complete, allow mixture to warm to room temperature and continue stirring another 10 minutes.


 * Step 4:** Add 10 mL of sodium thiosulfate (10% w/w), then acidify with 10% HCL. Use litmus paper to monitor acidity; generally 6 mL is typically required. At this point, the aryl iodide should precipitate out of solution.


 * Step 5:** Remove the ethanol from the suspension on a rotary evaporator. Water should still be present.


 * Step 6:** Cool the flask in an ice bath for 10 minutes, and then collect the precipitate by vacuum filtration. Wash well with ice cold water, then a small amount of cold ethanol. Continue to draw air through the crude product to help dry it for several minutes. Record the mass of the crude product.


 * Step 7:** Recrystallize your crude product using aqueous 2-propanol: place crude product in a 100 mL Erlenmeyer flask, and with heating, add enough 2-propanol to dissolve it. Then, add hot water until the mixture becomes cloudy, then add enough 2-propanol to generate a clear (though colored) solution. Allow hot solution to cool, and then place in an ice bath to ensure complete crystallization.


 * Step 8:** Collect by vacuum filtration again drawing air through the product for a few minutes to facilitate drying.


 * Step 9:** Take the mass of the product and determine its melting point (literature value = 183-185 degrees Celsius)

Helpful hint from Carol Higginbotham:
 * calculate rate addition of NaOCl in drops per second. Approximately 20 drops per mL. Calculated 1 drop every 2.7 seconds.


 * Observations/Data:** As shown below, the percent yield of 5-iodovanillin was 31.4%, since the actual yield was over three times as small as the theoretical yield. The percent yield was rather low, possible explanations given below in sources of error. Although there was a low percent yield, the final product was a pure substance. The literature value of the melting point is 183-185 degrees C and the average of two melting points obtained for the product were 179.8-182.3 degrees C. Given the range of the melting point for the final product was only 2.5 degrees C, the ending substance of 5-iodovanillin was very pure, even though the bleach was added a little faster than intended.




 * Source of Error:** At several steps in the experiment some of the potential yield was lost. A small amount of product material was left inside the rotovap flask, a few crystals escaped around the edges of the filter paper during vacuum filtration, and there appeared to be a significant loss as crystals dissolved upon rinsing the product especially during the rinse with ice cold ethanol. Crystals also stuck to the filter and the spatula used to retrieve the product from the flasks. When added together, these sources seem to represent a significant factor in low product yield. This could have also occurred because of adding the bleach to quickly. The seperatory funnel was opened too much initially and some bleach went into the flask. The procedure states that the bleach needs to be added slowly over a ten minute period in order to obtain the best results. Nonetheless, a pure product occurred in the electrophilic aromatic iodination of vanillin.


 * Conclusion:** By using an electrophilic aromatic substitution reaction, 5-iodovanillin (4-hydroxy-3-iodo-5-methoxybenzaldehyde) was produced by a greener approach of halogenation (the replacement of a hydrogen atom by one of the group VIIA elements) of vanillin (4-hydroxy-3-methoxybenzaldehyde). Since bromine is a volatile liquid, chlorine is a volatile gas, and iodine is much easier to work with, the reaction was carried out with sodium iodide and an oxidizing agent, which was household bleach. Although the percent yield was low, the melting point of 5-iodovanillin was only 3 degrees C off from the literature value melting point and had a range of only 2.5 degrees C, which proves that the substance was pure.

Atom economy is defined on Wikipedia, but essentially is the mass of the desired product divided by the mass of all reactants (don't include catalysts or solvents in the reaction).
 * Atom Economy:**



Calculation to give a percent of atom economy:

Molecular weight of desired product: 5-iodovanillin: 278.04 g/mol

Molecular weight of reactants: Vanillin: 125.15 g/mol Sodium Iodide: 149.89 g/mol Total: 302.04 g/mol

278.04 g/mol **/** 302.04 g/mol * 100 = 92.054% Atom Economy

Doxsee, K. M., & Hutchison, J. E. (2004). // Green Organic Chemistry: strategies, tools, and laboratory experiments // (1st ed., pp. 186-187). Southbank, Vic., Australia: Thomson-Brooks/Cole. (Procedure) Reaction image: Google image search (Electrophilic Aromatic Iodination of Vanillin)
 * References:**