DrDevice
Hazard to Self
Posts: 74
Registered: 19-3-2012
Member Is Offline
Mood: Incompatible with carbon based lifeforms
|
|
Synthesis of 3,4,5-trihydroxybenzamide"gallamide"
I have recently attempted the synthesis of 3,4,5-trihydroxybenzamide, otherwise know as "gallamide", using a process based on that in "The Fundamental
Processes of Dye Chemistry", Fierz-David, 1921.
There have been a couple of references to this elsewhere in SM, but I could find no experimental results.
My results have been encouraging; yield is pretty much what was reported in the procedure in that publication. My procedure is below - I've commented
where it has deviated from that in Fierz-David.
The "correct" tannic acid is critical. I used winemaking tannic acid first, and all I got was gloopy mess. Later reading here showed this is probably
"cutch", and entirely useless for this procedure. The tannic acid from gall nut is required.
---
Place 44.5g of tannic acid in a 500ml flask.
Dissolve 20g potassium metabisulfite in 120ml of water.
Original procedure uses sodium bisulfite. The quantity of metabisulfite should result in the same amount of SO2.
Add 64ml of 25% ammonia solution to the metabisulfite solution, and add all liquid to the tannic acid. The solution quickly changes color to a dark
brown.
Close the flask with a rubber stopper. Use magnetic stirring and heat at 50C for 24 hrs.
12 hrs is probably sufficient - I just didn't get the chance to come back to it any earlier. It's wise to release the pressure once the
solution gets to temperature, or the stopper may pop out like it did to me 
Allow to cool, and filter the cold liquid for any undissolved/unreacted solids from the original tannic acid.
Once cool, add sufficient conc. HCl to bring the solution to a pH of 6.2. I used about 20ml of acid to achieve this.
Original text was "just acidic to litmus". I didn't experiment with higher or lower pH.
A precipitate begins to form almost immediately. I refrigerated the liquid for 12 hours. When I came back to it, a mass of crystals had formed.
Room temperature is probably OK for the ppt.
The crystals were well washed in cold water (they are practicably insoluble in cold), vacuum filtered, and then recrystalized from hot water - it took
about 200ml of water at 70C to dissolve it all.
After cooling the solution, re-filtering to obtain the solid, and drying, 16.1g of pale, sand colored crystals were recovered. MP 235 - 240C, (lit.
240C).
Yield (by mass) = 36%, cf ~ 30% in the original procedure.
I made no attempt to extract the gallic acid which should be present in the remaining solution.
I did try a second recrystalization to see if the colour was an impurity, but the second result was about the same color, and some loss of product
occurred. There did seem to be a second substance present after the second recrystalization - much less dense, which washed out with decanting. I am
looking at this now to try and work out what it is.
Recrystalization from other solvents may also work. The gallamide is soluble in warm methanol and ethanol also.
I do want to try to o-methylate this to end up with 3,4,5-trimethoxy benzamide, but want to avoid nasties like dimethyl sulphate. I have a few
references based around dimethyl carbonate and various catalyst / higher pressure etc. Any suggestions?
|
|
|
Boffis
International Hazard
Posts: 1836
Registered: 1-5-2011
Member Is Offline
Mood: No Mood
|
|
Well done! I have been meaning to try this for some time but have gotten around to it yet. I am glad to hear that it worked successfully. Nice write
up too.
I am not sure about alternative methylating agents, probably iodomethane is the best easily accessible one. Have you thought about trying the
trimethylsulphonium compound Nicodem has described? I am not sure how much less toxic it is though.
|
|
|
clearly_not_atara
International Hazard
Posts: 2696
Registered: 3-11-2013
Member Is Offline
Mood: Big
|
|
Dimethyl dicarbonate can be used at much higher temperatures (172 ºC vs 90 ºC) than dimethyl carbonate and might be an interesting option if the
latter isn't effective at reflux. It isn't cheap but isn't *that* expensive.
N,N-dimethylformamide dimethyl acetal is another option.
http://www.arkat-usa.org/get-file/29478/
Apparently "thiazynes" are the new thing.
|
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
