garage chemist
chemical wizard
Posts: 1803
Registered: 16-8-2004
Location: Germany
Member Is Offline
Mood: No Mood
|
|
Methyl benzoate synthesis
I just started a batch of methyl benzoate, with the intructions from this synthesis.
The mixture has been refluxed for 2h 30min so far and will be refluxed for an extra 1h 30min tomorrow (its too late now).
It already strongly smells like methyl benzoate (similar to methyl salicylate, the structures are quite similar too).
However, I don't like the way the ester is isolated.
The crude ester (obtained by distilling away the methanol) is poured into water and the solution is extracted two times with ether.
However, I read that methyl benzoate is very insoluble in water (100ml of water dissolves only 0,1g of the ester at RT).
Wouldn't it also work to pour the crude ester into water and just separate the lower layer (methyl benzoate is more dense than water) and then
wash and purify the ester?
This should give an almost equal yield as the ether extraction and wouldn't require expensive ether.
I'm going to try this and report yield and bp of the ester.
I'll also use only 100ml of water instead of 250 to pour in the crude ester, because my sep. funnel holds only 250ml.
The methyl benzoate will be used to make benzamide and I will try out the Hofmann degradation to aniline. If it works, I'll write a synthesis!
|
|
|
runlabrun
Hazard to Others
Posts: 172
Registered: 4-12-2004
Member Is Offline
Mood: No Mood
|
|
Water wash would work to remove the unreacted components but just remember to use a bicarb wash to bring the solution back to neutral, water wash a
few mroe times and then dry the ester with MgSO4.
If you skip the bicarb, this will leave small conc of acid in the ester which upon heating (eg distillation) will cause the reverse reaction
destroying the ester.
-rlr
Spelling mistakes.... Whoops.
[Edited on 7-2-2005 by runlabrun]
|
|
|
Polverone
Now celebrating 21 years of madness
Posts: 3186
Registered: 19-5-2002
Location: The Sunny Pacific Northwest
Member Is Offline
Mood: Waiting for spring
|
|
I have made methyl benzoate (or was it ethyl benzoate? memory escapes me) before. I too was interested in making benzamide and then aniline. The ester
had an odd (kind of nice) characteristic odor.
I tried making benzamide by mixing the ester with 30% aqueous ammonia. It didn't react very rapidly at all. I saw no change after 12 hours. This
is in sharp contrast with (for example) methyl oxalate, which nearly immediately yields oxamide even in household-strength aqueous ammonia. I
didn't have any suitable apparatus to heat the ammonia/ester mixture in without expelling a lot of ammonia, so I just left it alone. A week or
more later, I looked again. The blob of ester that had been sitting at the bottom of the container had vanished, and in its place was a mass of fairly
large, clearish rectangular crystals.
I didn't immediately think of any way to verify the composition of this mass, so I went directly to hypochlorite oxidation. The oxidation gave
me an orange-brownish mixture with an unfamiliar and unpleasant smell. I've not experienced aniline before so I don't know if this was its
smell. Obviously pure aniline is not orange-brown, so whatever was created was not pure aniline. I tried a few variations on the hypochlorite
oxidation, but all gave essentially the same results until I'd consumed my small mass of crystals. I have not made benzoic acid esters since,
mostly because I have to make the benzoic acid myself.
PGP Key and corresponding e-mail address
|
|
|
Synopsis
Harmless
Posts: 27
Registered: 28-1-2005
Member Is Offline
Mood: Freely Radical
|
|
In theory, yes the isolation you propose certainly would work. However, ugly emulsions might form if you simply wash the crude ester. The drying part
also might be probletic, as you will lose much ester over MgSO4 and a dessicator would take quite an amount of time to afford a dry product.
I would rather pour the crude ester into a basic solution and then extract it with a cheaper solvent like petroleum ether or toluene. But well, if
your way do work, it seem simpler than actually doing the extractions.
Your theory is crazy, but it\'s not crazy enough to be true. - Niels Bohr
|
|
|
garage chemist
chemical wizard
Posts: 1803
Registered: 16-8-2004
Location: Germany
Member Is Offline
Mood: No Mood
|
|
Yes, I will make sure that the ester isn't acidic anymore. Washing will be done as in the synthesis, just with the crude ester instead of the
ethereal solution.
@ Polverone: You may find this helpful:
Benzamide synthesis with methanol/water as solvent
In the Organikum, there are instructions for the hofmann degradation and the isolation of high- boiling amines (such as aniline) and low- boiling
amines (such as methylamine).
High- boiling amines are isolated from the reaction mix (hypohalogenite + amide, heated just under below its bp for some time) by extracting the mix
several times with... benzene.
Maybe xylene can be used. I will try this out.
Methylamine (from acetamide) is isolated by basifying the reaction mixture and heating and leading the escaping gases/vapors into dilute HCl.
On evaporating the HCl, pure methylamine hydrochloride is obtained. No further purification is required.
The methyl benzoate batch is again refluxing at the moment. I also like the
smell.
In about one hour I will isolate and purify the ester.
I will use CaCl2 for the drying, because I have no MgSO4.
[Edited on 8-2-2005 by garage chemist]
|
|
|
frogfot
Hazard to Others
Posts: 212
Registered: 30-11-2002
Location: Sweden
Member Is Offline
Mood: happy
|
|
My local paint related stores carry gasoline (heptane type) with bp of 92-96*C. This should be a widely available and cheap solvent for extraction.
Another solution to prevent emulsion could be to saturate aqueous layer with NaCl.
To be economical it would be probably better to do the way you've suggested. Then, after drying and decanting the ester, one could wash the
drying agent with ether.. this way less solvent is needed.
Btw, for benzamide synth the methyl benzoate doesn't have to be dry..
|
|
|
garage chemist
chemical wizard
Posts: 1803
Registered: 16-8-2004
Location: Germany
Member Is Offline
Mood: No Mood
|
|
I just worked up the reaction mix.
I first distilled away the methanol/reaction water at 65- 72°C.
Then, after about 60- 70ml of Methanol had distilled, the mix in the flask suddenly became cloudy!
I stopped the distillation at this point. Maybe some benzoic acid crystallized out at this point?
Anyway, I added about 120ml water.
The ester separated as a heavy cloudy phase and looked exactly like nitroglycerine, only slightly more viscous.
It was washed with strong aqueous NaHCO3. No emulsion formed.
The ester was separated from the aqueous phase and a few pieces of CaCl2 were added.
It will be left to dry overnight (I won't distill it- the product seems pure enough, because the NaHCO3 wash should have removed residual benzoic
acid (is this true?).
I haven't measured my yield yet, but it seems bad, I have no more than about 20ml of liquid.
Perhaps I should extract the washing liquids with gasoline? But this won't be worth the extra 10g of product.
The next time when I do this synthesis, I'll use gasoline for the extraction- I also have the ~80- 100°C bp heptane stuff.
[Edited on 8-2-2005 by garage chemist]
|
|
|
frogfot
Hazard to Others
Posts: 212
Registered: 30-11-2002
Location: Sweden
Member Is Offline
Mood: happy
|
|
Multiple extractions shouldn't increase yield much, as you've mentioned, because of products low solubility.
Main problem could be at which temp the methanol is distilled off.. In original text (Vogel) they're using vacuum (forgot to add this  ), but this way all precious methanol is lost (unless one has liquid nitrogen cooled
condencer  )
I did this experiment with 40 g benzoic acid and got 83% yield (vacuum was used to distill off the methanol).
|
|
|
Synopsis
Harmless
Posts: 27
Registered: 28-1-2005
Member Is Offline
Mood: Freely Radical
|
|
Why distill the methanol? I don't get the point as this pushes the equilibrium in favor of the reactant within theses acidic conditions (you add
excess alcohol, then remove the excess..? weird?). The cloudy precipitate you observed probably was benzoic acid, as a as a result of the hydrolysis
of your ester. At lower temperature I guess the hydrolysis is slow enough to let you distill the excess methanol under vacuum.
I would either first neutralize the reacting mixture (somewhere near pH 8) and then distill the excess methanol so to stop the reaction from
equilibrating or use more water to pour it in and extract a few times with petroleum ether (or any other cheap solvent). This should increase your
yield. Fisher esterification like this generally give >95% yield when under excess alcohol conditions.
Yes it is true that sodium bicarbonate washes will get you rid of residual benzoic acid as the sodium benzoate formed is water-soluble.
Your theory is crazy, but it\'s not crazy enough to be true. - Niels Bohr
|
|
|
Random
International Hazard
Posts: 1120
Registered: 7-5-2010
Location: In ur closet
Member Is Offline
Mood: Energetic
|
|
Quote: Originally posted by Polverone  | I have made methyl benzoate (or was it ethyl benzoate? memory escapes me) before. I too was interested in making benzamide and then aniline. The ester
had an odd (kind of nice) characteristic odor.
I tried making benzamide by mixing the ester with 30% aqueous ammonia. It didn't react very rapidly at all. I saw no change after 12 hours. This is in
sharp contrast with (for example) methyl oxalate, which nearly immediately yields oxamide even in household-strength aqueous ammonia. I didn't have
any suitable apparatus to heat the ammonia/ester mixture in without expelling a lot of ammonia, so I just left it alone. A week or more later, I
looked again. The blob of ester that had been sitting at the bottom of the container had vanished, and in its place was a mass of fairly large,
clearish rectangular crystals.
I didn't immediately think of any way to verify the composition of this mass, so I went directly to hypochlorite oxidation. The oxidation gave me an
orange-brownish mixture with an unfamiliar and unpleasant smell. I've not experienced aniline before so I don't know if this was its smell. Obviously
pure aniline is not orange-brown, so whatever was created was not pure aniline. I tried a few variations on the hypochlorite oxidation, but all gave
essentially the same results until I'd consumed my small mass of crystals. I have not made benzoic acid esters since, mostly because I have to make
the benzoic acid myself. |
Is this working? This orange brown stuff should be aniline that can be salted out with nacl like in benzoic acid --> benzamide --> aniline
thread
|
|
|
![[*]](images/xpblue/default_icon.gif){kind=icon}
