SteveZissou
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5-iodovanillin alternate synthesis
Okay, so the textbook standard route to synthesizing 5-iodovanillin is via aromatic substitution with a triiodide ion formed by Na! and I2, I have two
questions:
1. Due to it's better availability does anyone see any issue with substituting KI for NaI to form the triiodide ion?
2. Could you use a far easier route with sodium bicarbonate and iodine as in:
http://pubs.acs.org/doi/pdf/10.1021/ed084p1799
to produce the target compound?
I know I could go through the hassle of making my own NaI from tinctures but that'd be impractically expensive and time-consuming. Thanks ahead of
time, folks.
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Mailinmypocket
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More Fun with Vanillin
Having a pretty good outcome with the synthesis of bromovanillin without elemental bromine, I figured I would have a go at the iodination of vanillin
without the usual triiodide method and share it here.
I found this synthesis which is from the book "Green Organic Chemistry: strategies, tools and laboratory experiments" by Doxsee, K.M., & Hutchison, J.E.
(2004).
The use of sodium iodide is preferred due to its higher solubility in the reaction medium, ethanol.
The procedure was followed verbatim, minus removing the ethanol via rotary evaporator in step 5, because:
a) I don't have a rotovap
b) I was too lazy and didn't feel like setting up a distillation apparatus for 20ml of ethanol. I couldn't really see a benefit in doing it anyways,
there was a precipitate that was easily filtered from the ethanol anyways after cooling.
The required reagents:
HCl - 10%,
Sodium thiosulfate - 10%
Vanillin
Sodium iodide
Ethanol
Sodium hypochlorite (household bleach, ~5.25%)
In a 100ml RBF, 1g of vanillin was dissolved in 20ml ethanol with the help of a magnetic stirrer. Then 1.17g sodium iodide was added, this dissolved
rather quickly in the alcohol. This was cooled, per directions, to 0c.
Once the proper temperature was reached, a separatory funnel containing 11ml of sodium hypochlorite was put in place. Dropping was commenced at a very
slow rate over the course of 15 minutes, supposed to be 10 minutes but my sep funnel is picky. Anyways - As soon as the first drop of hypochlorite hit
the reaction mixture the color instantly went brown. The addition was quite uneventful, no exotherm noted.
 
The ice bath was removed when the addition was complete, and allowed to warm to room temperature with stirring. The reaction was poured into a 100ml
beaker to allow for easier pH testing in the next step. Once in the beaker, 10ml's of 10% sodium thiosulfate was added resulting in the destruction of
the dark iodine and a pale tan solution.
 
Next, dilute HCl (~15%) was added dropwise until the mixture was acidified. A heavy precipitate materialized. The alcoholic suspension was filtered
without removing the ethanol, and washed with ice cold dH2O and cold ethanol. Then allowed to dry. The crude yield was 1.26g
 
This was recrystallized using an isopropanol/dH2O pair. This is where I think a screw up may have happened. The procedure says to add hot isopropanol
to the crude material until it dissolves, then add hot distilled water until a cloudy solution appears, then add more isopropanol to re-clarify the
solution, cool slowly and finally place in an ice bath for complete crystallization.
Well, I was using a heated hotplate and magnetic stirring, I kept adding isopropanol but I was never getting a complete dissolution (or so I thought)
It just looked like a suspension of the material... so... 60ml's of isopropanol later I turned off the stirring to see how much material settled. once
the liquid stopped moving it turned out that what I thought was the product ended up being extremely fine bubbles. The solution became clear and light
tan. Water was added, then more isopropanol, and allowed to cool slowly and then placed in the refrigerator. Very fine needle-like crystals grew
(sorry for the bad picture) and filtered. Once filtered they no longer resembled crystals but more of a waxy material that can be broken up into a
powder easily. Final yield of this was only 0.61g though, a melting point will be taken when I have access to a mel-temp.
 
This is definitely more of a pain compared to the bromovanillin synthesis. I plan on trying again, paying closer attention to the recrystallization
process and titrating my sodium hypochlorite - It is quite old and most likely is less than 5.25% in concentration.
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Haber
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Isn't there an risk that you would develop chlorine gas when you add the acid, in case there is some leftover NaClO in the flask?
Or is virtually all OCl 'consumed' by the NaI?
And don't you need to know the molarity of the bleach to safely conduct this experiment?
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Mailinmypocket
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Sodium thiosulfate is added at the end before acidification to destroy any remaining hypochlorite, assuming it is fresh and not older like mine was.
In my case I really should have titrated the bleach and adjusted accordingly but I didn't, oh well. It was a quick experiment. There likely was as
excess of thiosulfate.
During acidification there was no chlorine generated as far as my nose could tell. This is an experiment I would like to try again, having recently
bought a gallon of "fresh" bleach.
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