mnick12
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Oxidation of eugenol to vanillin
Hello everyone,
I was looking through my medicine cabinet and stumbled upon a small bottle of eugenol which my brother used for his teeth after he got his wisdom
teeth pulled. I started thinking about its possible uses and decided I would try and synthesize vanillin from it.
After doing some research I did not find a whole lot of information on eugenol oxidation, but I did find a few papers on the oxidation of anethole to
anisaldehyde using dichromate and sulfuric acid. So I thought this synthesis could be adapted to eugenol, but one thing bothers me the yields are
absolutely terrible. One article mentions 9gr of anisaldhyde from 20gr of anethole.
So my question is what would be an effective way to oxidize eugenol to vanillin? Would a peroxyacid give the aldehyde?
Also I do realize vanillin is pretty cheap, but I am more interested in synthesizing it. And if I can find an effective procedure for the oxidation of
eugenol I will post pics.
Thanks,
mnick12.
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Satan
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Oxidation of eugenol was once commercial route to vanillin so it must be covered in literature completely. First you must isomerize eugenol to
isoeugenol with base, then proceed with oxidation.
SYNTHETIC COMMUNICATIONS, 27(24), 4335-4340 (1997) describes quick isomerization using KOH, glicerol and MW heating(98% yield for isoeugenol) .
[Edited on 30-6-2010 by Satan]
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mnick12
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Thanks for that paper, I looked it up on google but I can not view the whole thing without paying 37.00 dollars. However I did find a similair paper
here http://www.drugs-forum.com/chemistry/chemistry/eugenol.isome... , now rhodium chloride does not seem like the catalyst I am going to use but they
have a part mentioning isomerization using KOH and glycerol just like you mentioned.
The article you provided Satan mentioned isomerization taking place in a microwave assisted reaction, is plausible to do this in a home setting I mean
with a standard kitchen microwave?
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Satan
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They used modified microwave (so its possible to reflux), but in case of eugenol+grycerol+4eq KOH reaction is finished in 3min, so ordinary microwave
oven should be enough.
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JohnWW
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What is vanillin used for in Hell, Satan?
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Nicodem
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Quote: Originally posted by mnick12  | | The article you provided Satan mentioned isomerization taking place in a microwave assisted reaction, is plausible to do this in a home setting I mean
with a standard kitchen microwave? |
It is more plausible to use just normal heating. You seem to have very little experience in practical chemistry so don't go putting in your kitchen
microwave things that don't belong there. Just use KOH in glycerol at 180-200°C like any normal person would.
Postpone risky situations for when you will have enough experience to know how to handle them.
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mnick12
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Yes you are correct I do not have very much experience in practical chemistry. Though I dont think my idea was as dangerous as it sounds. In the
article Satan provided it said their microwave was a kitchen microwave modified with a hole in the top to allow a reflux to be setup. But you are
right, and I will do the KOH in glycerin method.
Thanks.
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peach
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I have considerable experience with eugenol and I'm curious to know which oxidizer you're talking about. If I know Rhodium, it'll be palladium
chloride, which should produce a ketone. However, it doesn't work. I haven't tried it, but I've read that peracids don't work either. But it may be
possible to double chlorinate the tail bond and then work it up with KOH to a ketone. I may give both a go to see if either works.
There are a number of sources on google if you search 'vanillin from eugenol'.
Here's one showing the mechanism.
I'm in the middle of extracting some caffine and sorting the pictures out for a post, but I have a bunch of eugenol handy and might have a go at
making some vanillin with you. I'll check back when I have some more time, maybe later tonight, and see if I can be more helpful - I'm trying to do an
experiment a day at the moment 
You need to be incredibly careful microwaving things like KOH. I've done that. When a drop of it spilled on the platter, it created a superheated
spot. The glass is reinforced to prevent accidents, so it stores up energy rather than breaking. When I opened the microwave door and the cool air
touched the platter, it literally exploded as if someone had put a huge firework in there, sending finger sized shards of glass everywhere, with me
stood directly in front of it.
The bang was loud enough to temporarily deafen me in one ear and I actually took my shirt off and checked my skin in the mirror, thinking a shard may
have gone into me without me noticing. That was enough to stop me touching chemistry for around six months.
Long story short, no... it's not safe. I've seen the results of what happens when it goes a tiny bit wrong first hand, and I'm not talking them up.
[Edited on 10-7-2010 by peach]
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mnick12
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Thanks for the tip, I now realize how dangerous microwave reactions can be and have chosen to do a simple reflux. The link I posted uses KOH and a
higher alcohol for the isomerization, but in a few of the reactions they use rhodium chloride which is a little out of reach for most people. I only
have about 8-10gr of eugenol left from a different project, and I wont be able to do any experimenting for at least a week. But I would llike to try
the reaction once I get some more time. Also I am curious how do you plan on oxidizing the is isoeugenol to eugenol? I dont think dichromate works
well which is a bummer since I have a rather large amount of it.
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peach
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Here's what I've deduced from the mechanism thus far.
You need to isomerise it first.
Then treat it with acetic anhydride, oxidize, then acetic in water.
I don't know the reaction conditions. E.g. temperatures for the acid stages or how they're oxidizing it.
I'll have to look into them tomorrow.
[Edited on 10-7-2010 by peach]
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peach
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I found a google book that mentions how it's done by isomerizing the eugenol and then oxidizing with chromic acid;
Flavours and Fragrances: chemistry, bioprocessing and sustainability
| Quote: | Experimental--Oxidation of isoeugenol to vanillin
The best results were obtained by using the optimum conditions of the previous oxidation, viz., sodium dichromate (10% excess) with sulphanilic acid
as dispersing agent. Yield, 67%. With alkaline potassium permanganate, only a 21% yield of vanillin was obtained. |
And someone mentions it on Erowid.
Although I can easily buy the chromates, I don't have any aniline to hand to make sulphanic acid.
The first thing to do would be to isomerize some eugenol and actually get the isomer out of the workup, as I've heard from someone who tried that that
it's quite messy. But I don't remember how he was doing it either.
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mnick12
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Thats interesting, 67% is not great but it is better than I expected for chromic acid. As for aniline it can be made from benzoic acid via the amide
and hoffman degredation, I will be doing this next weekend. Though I dont know about sulfonation of aniline I would expect a mixture of the p and o
isomers. But I may not be able to isomerize any eugenol for a while since as it turns out my other brother is going to get all 4 of his wisdom teeth
removed very soon and needs the clove oil for his teeth. If I am lucky I may be to convince him to use the hydrocodone instead and let me keep the
clove oil .
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peach
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I just found a cleaning company selling sulphamic acid in small, cheapo bags, but they're out of stock at the moment. £4 for 50g, with VAT and
delivery. Cool, since I'm only going to be doing a little.
The dental packs I've seen for emergency fillings have sesame seed oil mixed with the eugenol I think, and the eugenol is fairly expensive given the
amount you get.
If you're setup for distillation, buy some clove oil and distill the eugenol out of that. Holland and Barrett (among numerous others) sell it in the
UK off the shelf, so I can pick some up whenever for not a great deal - there'll be similar hippy / herbal / organic stores around you.
I wouldn't recommend A/B extracting it. I did that and it looked like this;
Whilst pure, pharmacopoeia grade eugenol looks like this;
[Edited on 12-7-2010 by peach]
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Satan
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If you give details of your purification method it would be much easier to point out why your product is colored. How did you determined that its
actually eugenol?
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peach
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I used the now infamous lab guide that is actually hosted here on SM;
Extraction of eugenol from cloves
Rather than steam distill, I started with pre-extracted clove oil. The quantities of solvents and such used in that guide are larger than they need to
be, I believe to make it easier for the students to handle the small volumes.
If those are scaled up (based on the amount of oil in that quantity of dry cloves), you'll end up using hundreds of mls of DCM, or liters, for very
small amounts of eugenol. Instead, I redid the guide by adding the additional material in small aliquots until I found something closer to the extract
amounts required.
I needed 6ml of 5% KOH per ml of crude oil, which I found was the maximum before the extractions no longer took on any colour or change in opacity
when added to the crude oil; the oil it's self was no longer changing with regards to either of these factors.
This was then washed with 1-3ml of DCM per ml of crude oil. Again, around all that's necessary to clear any scum from the aqueous KOH extract. As I
approached 3ml of DCM per 1ml of crude oil, the DCM stopped taking on any colour or opacity change, indicating that more would likely be excessive.
I then acidified with vigorous stirring, slowly, using a dropping funnel and pH meter until the pH was stable at 0.999; I did this over about 45
minutes.
The oil drops back out of the aqueous phase. Again, it takes between 2-3ml of DCM per ml of crude oil to remove the suspect product. The oil
disappears from the aqueous phase very rapidly. Using much more DCM per ml of crude oil is somewhat excessive.
As I say, those are the numbers I found necessary. The ranges are also not guesses, the lower number is the value needed to roughly clear a stage and
the upper value is to be sure. They're quite a few times less than the quantities used in the guide, so it's unlikely I've pulled over contaminants.
I didn't test the oil. Coming from crude clove oil, I know it's going to be a majority of eugenol to begin with, and this is a lab guide specifically
for extracting eugenol from the crude oil.
I could test it with iron chloride, but I know what the result will be. I can tell just by the smell what it is. Distilled eugenol also has an aroma
that is quite a lot less complex and 'spicy' than crude clove oil, whereas this A/B still had quite a bit of 'clovyness' to it, along with the crude
colour.
First KOH extraction. The basic aqueous is the baby puke yellow on top, the crude oil is below. Note that you'll get an emulsion if you do any serious
swirling or shaking at this stage, and you don't need to
Another. KOH top, crude oil below
And another, there's no real change occurring now. KOH top, crude oil below
Extracting rubbish from the aqueous phase with DCM. This is the first wash. I did three in all. By the third, there was essentially no change
occurring upon addition. If you leave the KOH extractions to stand, they may tend to 'waxy up' into a kind of waxy slushy. The DCM washes will cure
that. Freebase oil in aqueous layer at the top, DCM wash on the bottom
The acidified aqueous phase is on top and the DCM is extracting the oil below
Another DCM wash, note the lack of change, the oil has been extracted. Acidified aqueous layer on top, DCM below
The product, after removing the DCM. Yield is around 50%. Not bad considering the crude leaf oil is usually around 70% eugenol. But that's no where
near clean
A/B SIMPLIFICATION;
Extract with 6ml 5% KOH per ml crude oil - keep aqueous
Wash aqueous with 1-3ml DCM per ml crude oil - keep aqueous
Acidify to pH 1, stable
Extract with 2-3ml DCM per ml crude oil - keep organic
Remove solvent
A BETTER IDEA;
Vacuum distillation through a vigreux
[Edited on 12-7-2010 by peach]
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