Student Comments 2008: Vanillin Synthesis from 4-Hydroxybenzaldehyde

This was a tricky experiment. I followed the instructions to the letter and still obtained a product that hardly smelled of vanilla (GC analysis will confirm whether the reaction worked, I suppose). It seems that many in the lab obtained a pink-tinged product---probably from the bromine. Be forewarned that you should wait the full 30 seconds for the first reaction to take place. Also be sure to have your reactants ready before actually starting the first part of the experiment.

-Peter Nani

All I can really say about this lab is that it takes a lot of patience! There are many steps and no matter how you cut it, this lab will take the full period (if you are lucky) if you want it to be successful. Perform each technique exactly how the instructions say and allow for the full amount of time each step asks for. I honestly took my time with this one because I was forewarned, and it helped. --Patrick Hughes

Be careful not to misread the directions under the "Preparation of Vanillin." Don't accidentally add only 11.5mL of the sodium methoxide solution since the directions say to add 11.5 TIMES the grams of 3-bromo-4-hydroxybenzaldehyde. You could miss this by moving too fast so like Pat said, patience! --Megan Wasz

When it comes time to heat the solution be patient but also be watchful; don't walk away. It is important not to let the solution stand on the heat or it could burn. This happened to a student in my lab period and he unfortunately had to go back and perform some steps over. --Allison Kolman

In this experiment, be careful to collect the organic layer into seperate beakers and pour the aqueous layer back into the funnel. This was tricky because we are used to keeping the top organic layer in the funnel. In this experiment, you drain out the top layer and add the bottom layer back.--Marie-France Likanje

Make sure you have all the necessary materials at hand before you begin!!! In this lab you need to quench the reaction after 30 seconds with sodium bisulfite, and if you have to run to the stock hood, you will take onger than 30 seconds. Also be mindfull that you are saving the correct layer! -Andrea Prosperi

In this experiment be sure to read the directions carefully when you have to pour the aqueous layer back into the separatory funnel and keep the organic layer in a separate beaker. This experiment requires each step to be done with patience and make sure to complete each step according to what the directions say. Also be precise in measuring the solutions that need to be added! Tamara Pike

If you are a lab assistant or professor, take care when preparing the MeOH/Cu solution. It MUST be prepared fresh or stored in a refrigerator. Its container must also be air tight. Do not let it sit out of a refrigerator for more than a couple hours. If it is not fresh, it has most likely been oxidized and the rest of the experiment will not work. This was a very challenging lab. It is best done in two lab periods.

-Laura Volpe

The reason you must add the Sodium Bisulfate after 30 seconds is due to Kinetics. Ill explain, when  4-hydroxybenzaldehyde and the cooled Bromine in methanol solutions are combined, they begin to form an intermediate. The initial concentration of the intermiate is 0 mol/L, as the bromine and the

4-hydroxybenzaldehyde combine, the concentration of the intermediate increases to a maximum and then begins to fall as the reaction proceeds to completion or equillibrium. Through some previous experimental design, the value of time t in seconds where the intermediate reaches maximum concentration is determined to be  30 seconds. This intermediate is essential for the synthesis of vanillin, so it would be ideal to have the most intermediate present to continue the reaction. So it is important to quench the reaction with sodium bisulfate at 30 seconds. This is why 30 seconds is important. ( PChem Rocks)

-Ricardo Rodriguez

Ricky is completely right (though not about P chem "rocking" ;)  ) timing is completely important.  That is why you have to make sure that you do not add the 4-hydrobenzaldehyde directly to the flask when measuring but rather weigh it in the plastic weighing boats and take it back to your lab hood to add it.  Adding it directly messes with the timing and you are gonna have to start over (take my word for it Lol)--K.S.