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Rhodium (Chief Bee) 05-21-02 22:28 No 312072 |
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Vanillin demethylation improvement (Rated as: excellent) |
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This variation on an old theme uses much less pyridine than earlier methods, and may also give higher yields. Synthetic Communications Volume 32, Issue 4, Pages 641-649 (2002) A simple, economical, selective and high-yielding procedure for the rapid demethylation of nitro-catechol methyl ethers has been developed using reagents and solvents suitable for production of medicinal products. This procedure is superior to other demethylation methodologies especially for larger-scale operations. The method should prove generally useful for the rapid demethylation of ortho-hydroxy arylmethyl ethers. 1-(3,4-Dihydroxy-5-nitrophenyl)-2-phenyl To a stirred yellow suspension of 1-(4-hydroxy-3-methoxy-5-nitrophenyl)-2- 3,4-Dihydroxy-5-nitrobenzaldehyde (Entry 5) Yellow-orange crystals, m.p. 142–143°C (lit12 m.p. 145–146°C). |
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foxy2 (Distinctive Doe) 05-22-02 03:30 No 312249 |
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but | Bookmark | |||||
"The method should prove generally useful for the rapid demethylation of ortho-hydroxy arylmethyl ethers." Should prove or has PROVEN? Is it as effective without that nitro group? I don't think it is because the strong electron withdrawing effect of the nitro group stabilizes the phenolate ion. Those who give up essential liberties for temporary safety deserve neither liberty nor safety |
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terbium (Old P2P Cook) 05-25-02 19:41 No 314066 |
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Eugenol demethylation via alkali fusion. | Bookmark | |||||
Here is a high yield demethylation of vanillin. It would be very nice if this could be adapted to eugenol. Since the eugenol does have a free phenol it would seem that it might also be miscible with the fused alkali. Note the use of sulfur dioxide (a bisulfite could also be used) to prevent formation of black crap during acidification. http://www.orgsyn.org/orgsyn/prep.asp?pr It was Post 313045 (paracelsus: "Protocatechuic Acid from Turmeric", Chemicals & Equipment) by paracelsus that led me on the search where i found the above. |
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PrimoPyro (Hive Prodigy) 05-26-02 00:56 No 314171 |
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Isomerization | Bookmark | |||||
Wouldn't the alkalai also isomerize the allyl group to a propenyl group, like in the standard alkalai isomerization? Upon methylenation, this yields isosafrole, not safrole. ![]() But the propenyl group would be more sensitive to oxidative cleavage to benzoic acid would it not? PrimoPyro |
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terbium (Old P2P Cook) 05-26-02 03:38 No 314246 |
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Yes. | Bookmark | |||||
Wouldn't the alkalai also isomerize the allyl group to a propenyl group, like in the standard alkalai isomerization? Most likely. Upon methylenation, this yields isosafrole, not safrole. Yep, you are really sharp today. But the propenyl group would be more sensitive to oxidative cleavage to benzoic acid would it not? Why would you want to produce the benzoic acid? |
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PrimoPyro (Hive Prodigy) 05-26-02 03:41 No 314248 |
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Re: Yep, you are really sharp today. | Bookmark | |||||
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kid_trippin (Newbee) 05-27-02 03:29 No 314602 |
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easy vanillin demethylation | Bookmark | |||||
Terbium: Wow, that looks incredibly simple. That link only synths protocatechuic acid . How hard is it to get from protocatechuic acid -> isosafrole. How's it done? I can't find any posts ![]() Resistance to government is so valuable on certain occasions that I wish it to be always kept alive. |
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terbium (Old P2P Cook) 05-27-02 08:25 No 314668 |
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3,4-dihydroxypropenylbenzene. | Bookmark | |||||
Or are you saying that could be tried on eugenol to get the allylpyrocatechol? Almost, the isosafrole equivalent. |
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starlight (Stranger) 05-27-02 12:48 No 314716 |
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workup | Bookmark | |||||
do you think the workup would have to be changed? |
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terbium (Old P2P Cook) 05-27-02 19:17 No 314822 |
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Same workup. | Bookmark | |||||
I would think that the workup would be pretty much the same. I have no information about the physical properties of the ally and propenyl 3,4-dihydroxybenzene but would guess that they are solids at room temp. I especially like the innovation of using sulfur dioxide to prevent oxidation of the phenolics in acidic conditions. As for the reaction conditions, I would expect that they could also be very much the same and with the same molar ratios. The one change I would make is that I would try to maintain an inert atmosphere in the reaction vessel out of concern that at the 240-245°C reaction temperature the alkene side chain would air oxidize. The experimenters seem quite specific as to the temperature required for the demethylation; anyone who does this should have a thermocouple (or RTD) probe to monitor the temperature. |
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starlight (Stranger) 05-27-02 22:03 No 314873 |
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The melting point of allyl 3,4-dihydroxybenzene .. | Bookmark | |||||
The melting point of allyl 3,4-dihydroxybenzene is around 46-48.5°C (solid at room temp). I don't know what the m.p. of propenyl 3,4-dihydroxybenzene is. Is it likely to be a bit lower? (m.p. of isosafrole is 4-4.5°C lower than that of safrole) That would make them both solids at room temperature. The solubility of the allylpyrocatechol in water is 25 g/l at 26°C. I don't know what the solubility of the propenylpyrocatechol is. The workup described ends up with 3l of water in the reaction mixture. 3l of water would be enough to solvate 75g of allyl pyrocatechol (and an unknown amount of pyrocatechol) at 26°C. Of course they cool down the reaction mixture in order to crystallise their product, and in addition the reaction mixture is acidic. Anyone got an idea of the solubility of the propenyl pyrocatechol in acidic solution at 0°C? Or in ether? ./ |
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terbium (Old P2P Cook) 05-27-02 23:11 No 314900 |
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Concentrate perhaps. | Bookmark | |||||
Sounds like it would be advantageous to concentrate the solution some. The concentrated salt in the solution should also help drive out the dihydroxypropenylbenzene. |
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