ChemRaver
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What exactly is the mechanism by which catechols are methylenated? Why does the methylenedioxy group rotate?
I've been studying this and have seem to run into some conflicting information.
I have attached a paper below which I will use as reference.
I've noticed when some molecules are methylenated, the methylenedioxy group seems to rotate around the benzene ring, while in other molecules, the
methylenedioxy group forms exactly where the OH OH bonds were.
Rotates according to the paper:
2,3-dihydroxybenzaldehyde -> Piperonal
http://www.chemspider.com/Chemical-Structure.81781.html?rid=... > http://www.chemspider.com/Chemical-Structure.13859497.html?r...
I assumed piperonal would come from methylenation of http://www.sigmaaldrich.com/catalog/product/aldrich/284548?l...
4-methylcatechol -> 4-methyl-1,3-benzodioxole.
http://www.chemspider.com/Chemical-Structure.9564.html?rid=5... > http://www.chemspider.com/Chemical-Structure.79904.html?rid=...
With the above molecule I figured 4-methylcatechol would turn into 3,4-methylenedioxytoluene:
http://www.sigmaaldrich.com/catalog/product/aldrich/284548?l...
Does not Rotate:
Catechol -> Benzo-1,3-dioxle
http://www.chemspider.com/Chemical-Structure.13837760.html?r... > http://www.chemspider.com/Chemical-Structure.13881169.html?r...
2,3-hydroxynapthalene -> Naphtho(2,3-d)-1,3-dioxole
http://www.chemspider.com/Chemical-Structure.6824.html?rid=1... > http://www.chemspider.com/Chemical-Structure.88076.html
Looking at the paper attached below, there is a drawing of the mechanism of the methylenation. It makes sense in theory, yet, it does not explain or
account for the rotation that occurs in two of the products. How is it meant to be determined whether the methelendioxy group will rotate around the
molecule when it occurs?
Attachment: 3489-3490.pdf (110kB)
This file has been downloaded 788 times
[Edited on 20-12-2013 by ChemRaver]
[Edited on 20-12-2013 by ChemRaver]
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Crowfjord
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You must be mistaken about this "rotation." This would be a rearrangement, and in these circumstances, it doesn't happen. For instance, methylenation
of 2,3-dihydroxy benzaldehyde would simply give 2,3-methylenedioxybenzaldehyde. Piperonal can be synthesized by methylenating
3,4-dihydroxybenzaldehyde (catechualdehyde).
The mechanism is just a regular SN2 reaction at each phenol oxygen.
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solo
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.....this might shed some light,....solo
High Selectivity in the Oxidation of Mandelic Acid Derivatives and in
O-Methylation of Protocatechualdehyde: New Processes for Synthesis of
Vanillin, iso-Vanillin, and Heliotropin
Hans-Rene´ Bjørsvik,,Lucia Liguori,
Organic Process Research & Development
2000, 4, 534-543
Abstract:
New synthetic procedures for vanillin, iso-vanillin, heliotropin,
and protocatechualdehyde starting from catechol are described.
The utilisation of statistical experimental design and multivariate
modelling and the mechanistic interpretation of the acid
and base catalysis in the condensation of catechol derivatives
with glyoxylic acid and in the regiocontrolled methylation of
protocatechualdehyde and of the Cu(II) salt catalysis in the
oxidative decarboxylation of mandelic acid derivatives have
allowed the development of new highly selective process.
Attachment: Synthesis.Vanillin.Isovanillin.Heliotropin.pdf (183kB)
This file has been downloaded 954 times
[Edited on 20-12-2013 by solo]
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ChemRaver
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Quote: Originally posted by Crowfjord  | You must be mistaken about this "rotation." This would be a rearrangement, and in these circumstances, it doesn't happen. For instance, methylenation
of 2,3-dihydroxy benzaldehyde would simply give 2,3-methylenedioxybenzaldehyde. Piperonal can be synthesized by methylenating
3,4-dihydroxybenzaldehyde (catechualdehyde).
The mechanism is just a regular SN2 reaction at each phenol oxygen. |
So is that paper incorrect saying piperonal was recovered via the methylenation of 2,3-dihydroxybenaldehyde?
I was also under the impression that 4-methylcatechol would methylenate to form 3,4-methylenedioxytoluene -> http://www.sigmaaldrich.com/catalog/product/aldrich/284548?l...
Yet the paper says it 'rearranges' into something else (http://www.chemspider.com/Chemical-Structure.79904.html?rid=...)?
---
Thanks Solo, I'll have a look at that
edit:
I don't see how that has to do with what I was asking Solo. Seems like basic reaction preceding there from Catechol -> various derivatives.
[Edited on 20-12-2013 by ChemRaver]
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solo
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| Quote: |
I don't see how that has to do with what I was asking Solo. Seems like basic reaction preceding there from Catechol -> various derivatives.
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.....not really sure what direction you're going with your line of questions.....solo
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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ChemRaver
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| Quote: Originally posted by solo |
| Quote: |
I don't see how that has to do with what I was asking Solo. Seems like basic reaction preceding there from Catechol -> various derivatives.
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.....not really sure what direction you're going with your line of questions.....solo
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Look at the links in the first post. Those are the molecules claiming were gained via methylenation as per the linked paper. I don't see why the
methylenedioxy group ends up shifting which carbons its on half of those molecules, but not on the others?
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Crowfjord
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I am a little confused. All I see in those links are structures and properties. Where does it say, for example in your first link, that piperonal is
synthesized from 2,3-dihydroxybenzaldehyde? Maybe you are confused about the naming/numbering? They can either be called methylenedioxybenzenes or
benzodioxoles, but numbering is different depending on which name is being used.
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ChemRaver
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There is a PDF attached at the bottom of the OP that I said in the OP that I would be using for reference >.>. In that attached paper all of
those molecules I have linked are claimed to have been methylenated and their subsequent products listed.
Am I confused? Would methylenation of 4-methylcatechol not yield 3,4-methylenedioxytoluene? The paper claims otherwise, yet, the diagram for how the
reaction precedes contradicts its finds which seem to imply a rearrangement/rotation of where the methylenedioxy group lies.
4-methylcatechol
http://www.chemspider.com/Chemical-Structure.9564.html?rid=5... >
3,4-methylenedioxytoluene:
http://www.sigmaaldrich.com/catalog/product/aldrich/284548?l...
[Edited on 20-12-2013 by ChemRaver]
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Crowfjord
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Oh, I see now. Didn't see that PDF the first time around. That is odd. I'm pretty sure the authors just made a typo. The reactant that gives piperonal
should be 3,4-dihydroxybenzaldehyde, not 2,3-dihydroxybenzaldehyde. This is consistent with the mechanism. Everything else in the table looks correct.
You are correct; methylenation of 4-methylcatechol (3,4-dihydroxy toluene) would give 3,4-methylenedioxytoluene.
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ChemRaver
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That is what I was thinking, though, if what you are saying is right about the Authors making a typo, then they also made the typo in saying
4-methyl-benzo-1,3-dioxole (4-methyl-1,3-benzodioxole and not 4-methylenedioxytoluene) is the resultant of methylenation of 4-methylcatechol. My
question is how could they make 2 major mistakes like that, in terms of reporting the one of the reactants used, as well as one of the products?
Did they simply mix up both of those molecules? IIRC this is not the first incidence that I have seen these indirect claims. The claims that products
with a rotated methylendioxy group were yielded from a methylenation, though I do not immediately have any of those sources on hand.
[Edited on 20-12-2013 by ChemRaver]
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Crowfjord
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4-methyl-benzo-1,3-dioxole, 4-methyl-1,3-benzodioxole and 3,4-methylenedioxytoluene are all names for the same molecule. It's just funny (and
confusing at first) nomenclature. So those are not mixed up in the paper (though the nomenclature is inconsistent and therefore confusing), and there
is still no rearrangement.
If you can find the other sources that cite rearrangement during a methylenation, I would like to see them. As far as my understanding of organic
chemistry goes, such a rearrangement is not possible under such mild conditions. The benzene ring is just far too stable. If it actually does happen
in some cases, I would be quite eager to learn something new.
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ChemRaver
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I'm glad to hear you say that. I was beginning to doubt my sanity, haha. I didn't think those carbon bonds could just shift like that.
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Nicodem
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| Quote: Originally posted by Crowfjord | | 4-methyl-benzo-1,3-dioxole, 4-methyl-1,3-benzodioxole and 3,4-methylenedioxytoluene are all names for the same molecule. |
No, they are not all the same. 3,4-Methylenedioxytoluene is regioisomeric to 4-methyl-benzo-1,3-dioxole (4-methyl-1,3-benzodioxole). There are two
nomencature errors in the table.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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Crowfjord
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Hey there Nicodem, I was hoping you would peek in. Looks like I still have some confusion on the nomenclature (as did the author of that Tetrahedron
paper, apparently).
Okay, I think I get it now, after looking up 4-methyl-1,3-benzodioxole. I forgot that in the fused ring naming, the numbering is like in any
heterocyclic. So 3,4-methylenedioxytoluene would be 5-methyl-1,3-benzodioxole. For some reason, I was thinking that the 4 referred to the position on
the phenyl ring, but the 1 and 3 still referring to the dioxole ring. It seems the authors of that paper made the same mistake.
Thanks for helping to clear that up, Nicodem.
[Edited on 20-12-2013 by Crowfjord]
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