09-21-01 20:45
No 216002
The synthesis was done as described on Rhodium's page, 140 g 5-bromovanilline was obtained in 96 % yield by bromination of Vanillin in 95% EtOH and than hydrolysed by refluxing solution of KOH with Cu powder. All went as described on Rh page, first white precipitate, than dark green solution. After 27 hours of reflux, the solution was cooled to approx. 60°C and neutralised to pH 1 by HCl.
During the acidification no precipitate formed, the solution turned dark yellow with a violet tint and after a while dark brown.
The solution was extracted 3 times with boiling toluene (total approx. 900 ml) ant the toluene cooled to O°C. But, only approx. 5 g of off-white-brown xtals (unreacted 5-BrV?) precipitated from the cold toluene and evaporation of the toluene (mother liquore) did not yield anything but 7 g of light brown xtals, mp=70-75°C.
The 3 litters of acidified water from the toluene extract have been kept for further experimenting.
Part of the solution was basified with KOH to pH=5,5 and a very fine precipitate formed (completely unfiltrable....). Another portion of Toluene was added, but it created an unbreakable emulsion..... after acidification to pH 1-2 the emulsion dissapeared, but nothing was extractet do the toluene layer.
Can someone please suggest what to do? Where is the 5-OHvanilline?
(Distinctive Doe)
09-21-01 22:31
No 216027
5-hydroxyvanillic acid???
Do Your Part To Win The War
(Hive Bee)
09-22-01 21:01
No 216199
Where's your inert atmosphere during the reflux?
(Hive Bee)
09-22-01 23:39
No 216220
Ditto: how about aldehyde protection? /me believes that those reactions will proceed *way* better if you add a nice protective group; even with N2 or Ar atmosphere, these compounds oxidize a bit to quickly for my taste.
(Hive Bee)
09-23-01 00:49
No 216244
i wondered about the inert atomoshpere as well, it really is necessary then, huh?
7.10.01
(Hive Bee)
09-23-01 02:24
No 216261
Seems iodovanillin is easier to hydrolysize than the bromovanillin, and it doesn't require the inert atmosphere. Maybe you should look into that instead. You can even recover the iodide salt when your done, so you don't waste valuable precursors. Also, Rhodium's page gives a lot more examples of this method so it's, how should one say, "more proven/tested" than the hydrolysis of bromovanillin. Iodovanillin is probably even better if you try to go around using those alkoxides too, because it doesn't require as vigourous conditions, and therefore there'll be less of a chance that you might damage a substituted alkyl group. Anyone care to comment on that?
Yellium, would you like to elaborate on such protective groups? Swic is intrigued
(Chief Bee)
09-23-01 03:26
No 216266
A suitable protecting group could be the dimethyl acetal (reflux with trimethyl orthoformate, aka trimethoxymethane).
Ref: ../rhodium /345labr
(Hive Bee)
09-25-01 19:04
No 217076
Iff you want to use KOH in methanol, you need the Iodovaniline.
An alternative routhe is the bromination and then the substitution with Natriummethanolate in http://methanol../rhodium/ch
(Hive Bee)
09-25-01 20:14
No 217092
Iff you want to use KOH in methanol, you need the Iodovaniline.
Why? What's the difference? Just use equimolar quantities.
(Stranger)
09-27-01 19:23
No 217783
Thanks to all for inputs.
However I wonder, why is the inert atmosphere so necessary and why should the aldehyde be oxidised to vanillinic acid.
Similar reaction condition as during this hydrolysis are used in the alkaline oxidation of lignin (or sulfit waste liquors) by O2, in NaOH solution with the catalysis of CuO or Cu salts and this reaction leads to vanillin (not vanillinic acid) even with high pressure of O2 and high temperature.
(Newbee)
09-27-01 19:57
No 217798
would Helium work perhaps, w/ a big baloon over the outlet of the condesor? or would the change in volume be too much for any reasonably sized ballon to handle?
(Hive Bee)
09-27-01 20:05
No 217802
How would putting a ballon on top of the condensor get the O2 out? You've got to flush it out, not just stick a ballon on top of it. Use an adapter, or make one with a stopper. Remember, there has to be an inlet and an outlet!
PChem, that's a good question. Swic doesn't know enough to give a dignified response.
(Newbee)
09-27-01 20:08
No 217804
You miss understand me, I meant flush w/ helium, then use the ballon to keep it all from floating away, while being able to accomodate the increased volume of the hot helium and vapo[u]rs.
(Hive Bee)
09-27-01 20:20
No 217810
Ok, makes a lot more sense. Swic wouldn't keep the ballon on it, instead have a hose leading from the top of your condensor into a cup of oil (a bubbler) to keep the atmosphere from coming into your system. Of course you'd want to do this AFTER flushing with He.
If swic were doing it, he'd keep a constant stream of He during the reflux, very slow though.
(Newbee)
09-27-01 20:23
No 217814
sweet, that makes a lot of sense. just remember to take the hose out of the oil b4 cooling down!
but the slow stream of He would fix that.
(Hive Bee)
09-27-01 20:26
No 217815
Right, otherwise you might get suction. What a catastrophe that would be!
(Hive Addict)
09-27-01 22:54
No 217873
all of what is being discussed here is basic lab technique- but one thing you are forgetting is that you shouldn't ever have to worry about suction/suck-back whatever you want to call it. the reason for no worry? simple- use a trap between the rxn apparatus and the container the hose will eventually lead to.
(Stoni's sexual toy)
10-04-01 17:37
No 220254
Iīve worked with vanillin and other benzaldehydes before, getting strange results when testing identity/purity via NMR afterwards. A bunch of real chemists couldnīt explain what happened when they tried to assign the peaks to the intended target molecules. Reason: oxidation of the aldehyde group. Not one of them thought of that possibility before.
Always use an inert gas when working with benzaldehydes.