Sciencemadness Discussion Board

Hydroquinone

giacobinozeta - 13-1-2005 at 07:16

Some time ago someone posted a compekte writeup to the Hive about a complete synthesys form Hydroquinone to DMB with sodium methoxyde or with Nameso4 . I think the title was Kitchen methylation or Hydroquinone part II.Anyway have some one a copy of it?

[Edited on 13-1-2005 by giacobinozeta]

?

UpNatom - 13-1-2005 at 13:47

Do you mean the P-MeO-phenol from hydroquinone: part II thread?

If so yes, but I don't know how to add this post.

hydroquinone

giacobinozeta - 14-1-2005 at 04:00

Yes I mean this post of antoncho where he mixed H2so4, MeoH and Naoh with Hydroquinone. I think it was Part II.
Have you the thread?

[Edited on 14-1-2005 by giacobinozeta]

This will have to do

UpNatom - 14-1-2005 at 13:28

...for now I'm afraid because I can't find the thread. I definitely have it though.

From the patent GB1557237:

10mls of H2SO4 are added to 50mls of MeOH and returned to room temp. Then 9g hydroquinone and 1g benzoquinone are added and everything is stirred at room temp. overnight (16hrs). The mixture is either neutralised with sufficient NaOH and vacuum distilled or the product is solvent extracted. Yield of HQ monomethyl ether is 80% of theoretical.

This is a paraphrased sum up of the reaction of course.(but it is actually pretty much as simple as that)

From memory, the resulting product was a very dirty looking oil which was very hard to purify. As I remember it various suggestions were made for recrystalisation but how successful those attempts were I don't remember. Reimer-Tiemann formylation of the crude p-MeO-phenol, while successfully carried out by Antoncho, was not easily repeatable with most bees failing to get anything but an unworkable mess. Vacuum distillation of the crude p-MeO-phenol before the RT is essential unless any of the bees here know of an effective solvent method.

wait wait

giacobinozeta - 14-1-2005 at 14:07

In the post I mean he ended with dimetoxybenzene , and the goal was to obatain 2,5 DMB for the 2c series.
In the Rhodium site was a link to a page with 1000´s such reaction and with patent reference but I can´t find this link in the mirror and fucked christ I did not save the post of Antoncho.

Betaine Maybe???

enima - 14-1-2005 at 18:30

If you are trying to synthesize dimethoxybenzene, I'd recommend you take a look at the methylation of phenol using betaine, CaO, and a base.
FYI the betaine anhydrous (which is what you need) is also called trimethylglycine.

You should be able to find it at any updated rhodium mirror.

Keep in mind that if you want to make the benzaldehyde, you have a glyoxylic acid option, or you can go with a chloromethylation/bromomethylation and a react that with DMSO.

The other ways (using POCl3) don't seem so friendly, and I assume since you are unable to obtain dimethoxybenzene you definitely would not be able to obtain the POCl3 (which actually can be used with methanol to produce trimethyl phosphate, a nice methylating agent which ain't so bad). (TMP is watched as it is used to make sarin gas.)

Good luck with your synthesis.

un0me2 - 21-7-2010 at 21:22

You could do worse than read this paper using Quaternary ammonium salts to methylate phenols... In one variant they use a strong base NaOH in dry Ethylene Glycol (which would form the sodium glycolate, which in glycol is a STRONG BASE - pKa of a 3M solution of Glycoxide/Ethylene Glycol is ~17.2).

Makes me wonder about betaine/trimethylglycine which has been reported to work in the presence of a strong base.

IIRC the same author has written a similar article (whcih I suppose I now have to go request) where they use tetramethylammonium salts in the MW to methylate phenols (if you read the attached article you'll see the methylation & isomerization of eugenol in one pot, giving methyl isoeugenol as the product in fucking good yield):o.

Attachment: Maras.Polanc.Kocevar.Synthesis.of.Aryl.Alkyl.Ethers.by.Alkylation.of.Phenols.with.Quaternary.Ammonium.Salts.pdf (145kB)
This file has been downloaded 1133 times

Nicodem - 25-7-2010 at 12:30

Quote: Originally posted by un0me2  
You could do worse than read this paper using Quaternary ammonium salts to methylate phenols... In one variant they use a strong base NaOH in dry Ethylene Glycol (which would form the sodium glycolate, which in glycol is a STRONG BASE - pKa of a 3M solution of Glycoxide/Ethylene Glycol is ~17.2).

I found nothing on using ethylene glycol. They used either diglyme or polyethylene glycol (PEG) as solvents with classical heating. Maybe you confused ethylene glycol with PEG? In the Tetrahedron paper they try out several solvents and it turns out water and alcohols perform worst while aprotic non-polar solvent are better. This means that using ethylene glycol is a bad idea. They also tried out several bases and it appears to me that it is not all about the pKa, but about other factors as well (solvation effects, like the authors propose, is way more likely). Phenoxides are about hundred thousand times less basic than the hydroxide anyway. Already carbonates are basic enough to deprotonate phenols, and they used K2CO3 in most cases. (Besides a pKa measured in ethylene glycol says little unless you measure also the pKa of the substrate in the same solvent - pKa values are solvent dependent!)

Quote:
Makes me wonder about betaine/trimethylglycine which has been reported to work in the presence of a strong base.

With betaine you have two competing reactions, the formation of the methyl aryl ether (anisols) and the formation of aryloxyacetate salt (or its acid after acidification). In the Monatshefte für Chemie paper where this is published, they got the anisols as the main products (usually in a 3:1 ratio), but it was done solventless and under rather extreme conditions. If using betaine in diglyme or PEG then this ratio might be quite different and not necessarily in favor of the anisols. Only an experiment could tell and even if it gives mainly the aryloxyacetic acids, it is still a nice reaction for an amateur setting. But tetramethylammonium chloride is just as cheap, uncontrolled and available at chemical supliers, so...

Quote:
(if you read the attached article you'll see the methylation & isomerization of eugenol in one pot, giving methyl isoeugenol as the product in fucking good yield):o.

If you read thoroughly, you will notice the yield is for the "sum of products", which I assume is the (E/Z) mixture of the methyl isoeugenols plus the remains of the nonisomerized methyl eugenol. Though they report that only little remains nonisomerized, they also say they were unable to separate the mixture.

peach - 25-7-2010 at 16:43

And if you visit my thread, downgraded to the beginner's forum, then scroll to the bottom, you'll see the demethylated catechol. :P