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Pabpa
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| Quote: | | Btw.: the Phosphoric acid might maybe help to prevent the sublimation (or what ever) by washing the stuff down again - maybe my error is the too small
scale? i always do it in a test tube. |
The phosphoric acid (or phosphorous acid) is used as a catalyst. You can do it in a test tube, too. But you need only one drop of phosphoric acid in
this case. Have you noticed the smell of ammonia and bubbles coming out of the hot liquid?
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dr. nick
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| Quote: | | Have you noticed the smell of ammonia and bubbles coming out of the hot liquid? |
Sure, both - bubbles like beer and smells like, well, ammonia 
But the walls where almost full of crystals after some minutes
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Pabpa
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| Quote: |
But the walls where almost full of crystals after some minutes |
Are these crystals soluble in cold water? Is there carbon dioxide released when treated with an acid (acetic acid, HCl...)?
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dr. nick
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oh - got to test that, will report later!
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dr. nick
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ok then -
once again i put 2g Carbamide and 4g Benzoic Acid into a large test tube and heated it just as much as it needed to liquefy both substances. After
around 5 min. the whole test tube walls where full of fluffy, snowy white cristals that almost closed the tube.
The rest of the mixture on the bottom of the tube has (after cooling) a slighly yellow-dirty white color with maybe a 1mm thick darker, more gray top
layer that seems to be a bit more clear as the rest and evolved tiny bubbles after the rest of the mix was already compact again. Very hard to see in
such small amounts, maybe only an optical delusion.
When some of the white-fluffy-snow crystals from the vessel walls where mixed with a little cold tap water they dissolved almost completely very fast,
but when i mixed some more of that stuff with around 25% HCL the powder didn't dissolve. Not sure there was CO2 emission, but the walls of the vessel
became a bit milky. When it spoiled the fluffy-snow-HCL-mix to the drain it began to fizz after it came into contact with the waterdrops in there.
Hm. Now what does this mean?
btw: the described fluffy stuff has a smell like, i don't know, sweet, nice, almost tasty
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garage chemist
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I'm gonna do some experiments today.
Are the proportons of 1 part benzoic acid and 2 parts urea correct? If yes, then it's a large excess of urea. But maybe that is needed to keep
sublimation down and make the reaction proceed rapidly. I'll use those proportions, and add a drop of phosphoric acid.
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Pabpa
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| Quote: | | Are the proportons of 1 part benzoic acid and 2 parts urea correct? If yes, then it's a large excess of urea. |
0.25mol benzoic acid and 1mol urea. You might read this b4:
http://v3.espacenet.com/textdoc?DB=EPODOC&IDX=DE869639&a...
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dr. nick
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oh ...
i thought it was 2 part Benzoic Acid to 1 Part Urea ... ?
Hm, maybe only the excess of Benzoic Acid sublimates?
Btw: that doc is interesting - so you say in the case of Benzamid
Ammomia solution can be used to wash the Product and then it can
be recrystallised from hot water?
cool! Since i scraped the sublimed what-ever from the test tube walls
there didn't happen much more sublimation when heating again -
interesting (to me) i found that there builded a solid white core in the yellow,
hot bubbling liquid.
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garage chemist
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The patent you posted is very good: short but contains everything that is needed. BTW, are you from germany Pabpa?
Anyway, last evening I did some experiments, without having read the patent before. It was a success: I can verify that benzamide is formed in an
urea/benzoic acid melt, even without addition of phosphoric acid.
2g benzoic acid and 4g urea were ground together in a mortar to yield an intimate mix of the constituents.
This was transferred into a 50ml beaker which was covered loosely with a teflon sheet. The beaker was placed on a wire gauze (without ceramic or
asbestos) and heated directly with the bunsen burner. The mix rapidly melted, and when heated further, gas evolution and boiling was observed
(vigorous bubbling). Lots of crystals sublimed to the walls of the beaker and to the teflon, which prevented loss of product/educt via sublimation.
Ammonia was smelled in the escaping gases.
The mix was heated and kept bubbling vigorously for 2-3 minutes, the teflon sheet was tapped from time to time to make the crystals fall down into the
melt again.
It was then left to cool.
To the still warm, solidified mix there was added 30ml water and it was heated again, under stirring. As the water reached the boiling point, all
solids dissolved after some stirring to yield a clear solution.
The heat source was removed and 20% ammonia solution added with stirring until the solution aqcuired a strong smell of it (about 5ml). This keeps
benzoic acid and cyanuric acid from precipitating, because they get bound up as their soluble ammonium salts.
The solution was left to cool. After it was at room temperature, it was cooled further to 5°C. It was only after some stirring that the benzamide
started to crystallize, apparently its crystallization is slow. Lots of white flocculent crystals filled the liqid after half an hour.
The benzamide was filtered with suction and washed with ice- cold water until free from ammonia odor. It formed a white fluffy powder which was placed
in the vacuum desiccator to dry (it should be dry by now). The yield does not seem to be good, but this can be improved by longer heating time.
Today I will determine its melting point to clear all doubts on the identity of the product.
The next step will be upscaling (20g benzoic acid) and usage of phosphoric acid.
If I have a few tens of grams of benzamide, the Hofmann degradation will be performed to yield some aniline.
I have looked in Organikum and they give a procedure which uses NaOCl, made directly before the reaction by bubbling a measured amount of chlorine
through icecold NaOH solution. I will use this method.
[Edited on 9-12-2006 by garage chemist]
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dr. nick
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wow - cool!
i'm sorry-haven't found that in Organikum yet -
please, which edition of Organikum do you use?
[Edited on 9-12-2006 by dr. nick]
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garage chemist
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I have the 15th edition of Organikum. The preparation is for 3,4- Dimethoxyaniline from the corresponding benzamide, not for unsubstituted aniline,
but that doesn't matter of course.
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dr. nick
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Thank you!
If been so long after this without success that i already had given it up!
Would you mind to report if you're done with it (Hoffmann Degradation, I mean)?
Anyway, thanks again
[Edited on 9-12-2006 by dr. nick]
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garage chemist
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Yes, I will report my experimental findings here, and if the production of aniline turns out to work well, I will make detailed synthesis
instructions.
But why exactly did you give up? You didn't even try to synthesize anilin, you made no effort to isolate any product and you didn't even try to see if
the intermediate was being formed. What you have done can not be called synthesis, not even experiment.
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dr. nick
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i do not have sufficient knowledge, even not much basic knowledge, almost no talent of and for chemistry - just a lately developed interest (last 3
years maybe). Now i try to get into it the only way i can think of being of value to me - some "learning by doing" - that means i do not know what to
expect as results so i never know if i did it right.
That's why i gave up.
to me it looked like my experiments always went wrong and i wasn't able to ask the right questions and also couldn't find out myself. You can damn me
for being around here on that base, but as there's no "kindergarden forum" for my interests i'm still here
[Edited on 9-12-2006 by dr. nick]
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Pabpa
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| Quote: | | I have looked in Organikum and they give a procedure which uses NaOCl, made directly before the reaction by bubbling a measured amount of chlorine
through icecold NaOH solution. I will use this method. |
It might be easier to avoid the preparation of chlorine and use household bleach instead:
http://designer-drugs.com/pte/12.162.180.114/dcd/pdf/hofmann...
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DeAdFX
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I kinda feel stupid asking this but... I wish to do this experiment but my only source of ammonia contains sodium silicates + other filler material.
Is this source of Ammonia acceptable for the purifying stage of Benzamide or should I try and capture the ammonia gas released from the benzamide
syntheis and use that?
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garage chemist
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OK, the stuff from my described experiment IS NOT BENZAMIDE.
It doesn't melt even at 180°C, while a sample of pure benzamide from benzoyl chloride and ammonia had the correct melting point of 124°C. I am
really glad that I did the melting point determination.
I did a new experiment, this time with 5g benzoic acid and 5g urea and a few drops of 85% phosphoric acid (less than 0,1ml).
This looked much better.
I heated it in a 100ml rbf with the small flame of a bunsen burner so that it fizzed gently. Sublimated material was periodically melted back into the
reaction mix by heating the upper walls with a bunsen burner. After a few minutes, ammonia smell was present and got intense shortly afterwards. It
was left fizzing with continued heating until the melt started to partially solidify despite the heating and smell of benzonitrile started to become
noticeable (about 30- 45min, I didn't look at my watch).
After addition of 50ml water and 4ml 20% ammonia, heating dissolved nearly all solids. It was decanted from a little undissolved material and left to
cool in a beaker, and many small needles slowly appeeared which look nice and uniform. The melting point test will show if they are the desired
product.
As a preliminary conclusion, the addition of phosphoric acid seems to be essential for the reaction to occur.
[Edited on 16-12-2006 by garage chemist]
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Pabpa
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I just tried the Organikum synthesis of aniline with success. Took bleach (2.8% NaOCl solution -> DanKlorix) instead of chlorine + KOH. I'm
distilling it now.
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garage chemist
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Would you give us a report of the synthesis, e.g. the used amounts of reactants, what you have done exactly etc...? Just like I did with my report of
the benzamide synthesis above. That would be nice.
The product from my last experiment with phosphoric acid (described above) has the correct melting point and is indeed benzamide. I did an additional
test by boiling a sample with acetic anhydride- upon hydrolyzing the mixture with hot water, the almond odor of benzonitrile was evident and the
identity test thus positive.
I will do a larger batch (25g benzoic acid), either today or next week. I will also have to get some more benzoic acid, and I'll have to go to the
pharmacy for that (which is stupid because chemicals are at least twice as expensive there than from internet suppliers, but its the only way to get
it before christmas holidays).
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dr. nick
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| Quote: | | the melt started to partially solidify despite the heating |
can confirm that so far.
of course you can well i couldn\'t before
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DeAdFX
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| Quote: | Originally posted by garage chemist
Would you give us a report of the synthesis, e.g. the used amounts of reactants, what you have done exactly etc...? Just like I did with my report of
the benzamide synthesis above. That would be nice.
The product from my last experiment with phosphoric acid (described above) has the correct melting point and is indeed benzamide. I did an additional
test by boiling a sample with acetic anhydride- upon hydrolyzing the mixture with hot water, the almond odor of benzonitrile was evident and the
identity test thus positive.
I will do a larger batch (25g benzoic acid), either today or next week. I will also have to get some more benzoic acid, and I'll have to go to the
pharmacy for that (which is stupid because chemicals are at least twice as expensive there than from internet suppliers, but its the only way to get
it before christmas holidays). |
I would but I cannot purify the benzamide yet(no ammonia water). I am waiting on some rubber tubing so I can synthesis some from urea. But here is
what I have done so far.
Anywho I heated up Urea and Benzoic acid in a filter flask with a saran wrap cap and a tygon tube in some water. The reactants where in a 4mol:1mol
ratio scaled down to ~13.5(urea)grams 7(benzoic)grams(to lazy to convert to mols). The mixture was heat for 1 hour with the temperature maintained
between 160-180C. About 45 minutes into the reaction the temperature dropped 20c to 150C and continued to drop some more (10C) until I turned the
heat up so more. I am wondering if this 45 min mark indicates completition or if I wasn't paying attention.
The flask began to fog up as benzoic acid crystals formed on the sides. The reaction smelt strongly of Ammonia and benzoic acid. The crystals were
difficult to knock back into the reaction mixture because of the shape of the filter flask. I think a beaker with some saran wrap would work better.
I don't expect a very high yeild(10-35%) unless those crystals on the side happen to be benzamide.
The reason for using the filter flask was because I was hoping to capture the ammonia from the reaction so I could recycle it. I only got a couple
bubbles before the nipple side got clogged.
[Edited on 17-12-2006 by DeAdFX]
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Nicodem
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| Quote: | Originally posted by garage chemist
2g benzoic acid and 4g urea were ground together in a mortar to yield an intimate mix of the constituents.
This was transferred into a 50ml beaker which was covered loosely with a teflon sheet. The beaker was placed on a wire gauze (without ceramic or
asbestos) and heated directly with the bunsen burner. |
I'm afraid you will only get a bunch of a biuret, cynuric acid and other similar crap if you do things with such negligence. You should use an oil
bath and maintain it for 3h at 170-180°C instead of using brute force aka Bunsen burner. Use 4 equivalents of urea and 15mol% of boric or metaboric
acid rather than phosphoric acid. At least that is how I used to prepare amides out of carboxylic acids with excellent yields (though I never tested
the method on any benzoic acid).
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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garage chemist
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I certainly will not heat up an oil bath for such small test runs. The small pilot flame of my burner has very often done a good job at keeping things
hot throughout a reaction. The conditions are not "brute force", as the flame is really small.
For actual synthesis of useable amounts of product it will be a different story. I will use an oil bath then.
Where did you get the procedure with boric acid as catalyst? Is that also from a patent? I'd like to read that procedure.
BTW, I got 3g Benzamide from 5g benzoic acid with the synthesis above, using equal weights of urea and benz and with H3PO4 as catalyst and with 45min
heating with bunsen burner.
Biuret, cyanuric acid and the like don't bother me as they will stay in solution due to the added ammonia.
EDIT: Check out this patent: US5550286
They use stochiometric amounts of urea and phosphorous acid (which is H3PO3, NOT H3PO4) in an inert high- boiling hydrocarbon solvent and get yields
of 70- 90% with benzamides (substituted and unsubstituted).
With H3PO4 instead of H3PO3 they get 60% yield for benzamide, which isnt that great, but the unreacted benzoic acid can be recycled by acidifying the
filtrate from the amide precipitation.
[Edited on 17-12-2006 by garage chemist]
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Nicodem
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| Quote: | Originally posted by garage chemist
I certainly will not heat up an oil bath for such small test runs. |
Well, the temperature control is of huge importance in organic synthesis, hence the oil bath. But if you manage to control the heat with a flame,
never mind.
| Quote: | | Where did you get the procedure with boric acid as catalyst? Is that also from a patent? I'd like to read that procedure. |
I know from this work that the carboxylic acids get activated by complexing with the boric acid which itself gets activated by its equilibrium with metaboric
acid at elevated temperatures. It is similar like the phosphoric acid<>pyrophosphoric acid thing, but more effective at the given temperature.
But anyway, I never compared the yields with the uncatalyzed reaction so the addition of the boric acid might just as well be obsolete.
…there is a human touch of the cultist “believer” in every theorist that he must struggle against as being
unworthy of the scientist. Some of the greatest men of science have publicly repudiated a theory which earlier they hotly defended. In this lies their
scientific temper, not in the scientific defense of the theory. - Weston La Barre (Ghost Dance, 1972)
Read the The ScienceMadness Guidelines!
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garage chemist
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Hmm, the orgsyn prep looks interesting- but the use of an organic solvent makes the procedure more time- consuming and more expensive. I think I'll
stay with the urea melt method. I might try adding boric acid instead of phosphoric acid though, and I will first ensure temperature control (oil
bath).
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