Maui3
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Phthalimide -> Anthranillic acid Reaction Not Working
Hi!
I have tried to make anthranillic acid from phthalimide too many times now. It just does not want to precipetate once I add HCl + Acetic Acid.
I have tried this at least 5 times using different methods, both using bromine water and sodium hypochlorite.
I have cooled everything to below 5 C. I have only neutralized with HCl, then made acidic with Acetic Acid.
This is procedure I am following:
40 g of finely powdered phthalimide and 80 g of sodium hydroxide are dissolved together in 280 ml of water, the solution being cooled during the
operation. The solution is agitated, and 400 g of a 5% solution of sodium hypochlorite run in. When all is added, the solution is warmed for a few
minutes at 80° C to complete the reaction; it is then cooled and neutralised exactly with hydrochloric acid (or sulphuric acid). An excess of strong
acetic acid is added to precipitate the anthranilic acid, which is filtered off and washed with water.
Sometimes it goes brown when adding HCl, sometimes yellow, sometimes it precipetates white stuff which redisolves.
I have found a lot of people on here who also say it does not want to precipetate (like mine), I have also found a lot of people who did it
succesfully.. I just really dont get it - but I geuss that is chemistry  .
I apologize I don't have any pictures of the process, I assume that would help.
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Texium
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Here’s my write-up, which was based on ChemPlayer’s video: https://texiumchem.com/2017/03/22/preparation-of-anthranilic...
Differences that I notice are that I used relatively less sodium hydroxide and significantly less water for the original solution. I also had 10%
hypochlorite solution rather than 5%. I understand that you may not be able to get 10% (I found it as pool chlorine at a hardware store) but all of
these factors contribute to you having a much more dilute solution. Most likely, your product just stays dissolved.
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Texium
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Thread Moved
7-12-2024 at 07:51 |
Keras
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I have always seen phthalamide → anthranilic acid being done using sodium hypobromide for the Hoffmann rearrangement. The advantage is that you can
directly drip bromine into the solution.
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Texium
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Yes, and I’d have no doubt that using bromine may potentially be higher yielding, but hypochlorite is much cheaper and does work. I’d rather save
my bromine for other uses.
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Maui3
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Thank you. I think my bleach might also contain impurities, since the mixture turned black. I am suprised you say that an ice-bath is unneccesary,
since other procedures say you have to keep all of the reaction under 5 C. I'll try to make my own (more conc. and pure) NaClO I think. Hope this
works.
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Texium
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Quote: Originally posted by Maui3  | | I am suprised you say that an ice-bath is unneccesary, since other procedures say you have to keep all of the reaction under 5 C.
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Since it was 7 years ago, I'm not really sure why I said that myself. My guess is that I observed there
wasn't much exotherm, and decided it would be ok to let it warm up since it was about to get heated to 75 ºC anyway. My recommendation would be to
use the ice bath for the addition of the hypochlorite, but then it can be removed and allowed to warm up.
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walruslover69
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There is also a route to anthranilic acid from Methyl Anthranilate, sold as bird repellent or grape flavor. Removing the methyl ester should be very
high yield with a simple reflux. I believe nile red has/had a video on isolating it.
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Pumukli
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A few years ago I tried this reaction and found it rather unpredictable. I made several iterations at different temperatures and pH ranges and could
not establish a foolproof, amateur friendly route with a fair chance of success for every time.
On the other hand I discovered that if I "only" aimed for isatoic acid anhydride I could get pretty acceptable yields (70%-ish), albeit never the same
hues of grey-purple-pink-ochra. :-) Never mind the hue, because from isatoic anhydride there is a very high yielding (90+%-ish) route to anthranilic
acid methylester. With that in hand you are pretty much "in town".
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Maui3
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Thank you for the tips!
Pumukli, what procedure were you following for the isatoic anhydride?
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Keras
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BTW, you should update your video links which still point to the deceased YouTube channel…
The process I have is this (never attempted it, I don’t have phthalamide, which I intend to make starting from naphthalene, but I’m still quite
groping with naphthalene → phthalic acid):
100 mL of 20% w/w NaOH solution is poured into a 250 mL Erlenmeyer flask and cooled to -5 °C using an ice and salt bath. 5 mL of bromine are added
dropwise slowly with stirring. 15 g of phthalamide are made into a paste with water and added to the cold hypobromite solution and stirred. After 10
minutes, the flask is removed from the ice bath and allowed to warm up to r.t. A further 20 g of NaOH is then added slowly and the flask is warmed to
80 °C for 5 to 10 min max. The liquid is filtered if necessary, transferred to a 600 mL beaker cooled in the same ice bath as before and acidified
with HCl until just neutral. Finally, 15 mL of glacial acetic acid are added. After 5 min, the crystals are filtered, washed with a little water and
recrystallised from hot water. Anthranilic acid crystallises in needles, mp. 143 °C. Yield: 12 g.
[Edited on 8-12-2024 by Keras]
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bnull
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Fieser [1] recommends one of these two ways: from chlorine gas or from calcium hypochlorite. I usually go with a modification of the second because it
is safer and it doesn't require much in terms of glassware, basically a funnel and two flasks.
The first way is "a solution of 100 g of sodium hydroxide in 500 cm3 of water is cooled in an ice bath, 400 g of crushed ice is added and,
while cooling well in the ice bath, chlorine gas is passed in from a tank until 71 g has been added." The solution is filtered if needed and diluted
to 1 liter. Lerner [2] has instructions on how to make chlorine gas from TCCA. The common 200 g block of TCCA generates about 1.3 moles of
Cl2.
The second is an adaptation of Fieser's number 2. Instead of dissolving the alkaline carbonate and adding it to a calcium hypochlorite solution, I put
a filter paper on a funnel, add an excess of solid alkaline carbonate (I use sodium but potassium works just the same), and then pass the hypochlorite
solution through it. You can dilute it to whatever degree you want. Calcium carbonate remains in the filter and acts like an in situ celite.
No gelatinous precipitate or goop, and you end up with a quite nice cone of calcium carbonate.
[1] Loius F. Fieser, Experiments in Organic Chemistry, 2nd ed. (1941), page 431.
[2] Leonid Lerner, Small-scale Synthesis of Laboratory Reagents, page 142.
Quod scripsi, scripsi.
B. N. Ull
P.S.: Did you know that we have a Library?
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Pumukli
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I don't have the lab. papers at hand right now. As I remember the main problem was that the initial phase of the reaction was very picky about the
starting temperature - starting volume (mass) of the reactants. Basically, when it was too cold the reaction rate was too slow and the exotherm was
low. The low exotherm could not heat up the mixture to the "right" temperature where the concurrent reactions would run "just right". When it was not
cold enough severe oxidation took place, producing the well-known black crap. It is a complex reaction with concurrent hydrolysis, substitution,
rearrangement, condensation, whatnot. If one finds the right starting temperature - starting mass of reactants - starting concentration of NaOH and
NaOCl, the yield can be good. But there are too many variables as one can see and so many "less fortunate" combinations of these and just a narrow
"optimum" window that I could not do it right.
If memory serves me well I used the Rao et. al, 1980 (or so) paper that can be found on the net as a basis for my trials.
When you have the raw isatoic anhydride mix it with a base (NaOH or Na2CO3?) in methanol and slowly heat it up. The anhydride will efficiently be
transformed into the methyl ester of anthranilic acid. Distill off the excess methanol. Steam distill the pure ester.
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Maui3
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Bnull, thank you for sending me the procedure  I'll probably try that.
Pumukli, thank you too! Would you recommend I do the isatoic anhydride instead of the anthranillic one?
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Pumukli
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I'd definitely do. I could (repeatedly) achieve acceptable yields of quite pure isatoic anhydride. (Purity was checked by melting point
determination.) The resulting anhydride was always fairly light coloured, light beige, tan, pink, purplish grey, mostly light grey. Isatoic anhydride
is much less reactive than say acetic anhidride towards water! It does not easily decomposed by cold water, it can be isolated from cold solutions by
filtering, then resuspending in cold water, washing with cold water on the filter and drying on a hotplate (in ceramic cups) without appreciable
decomposition. At least this was my experience with it. The melting points of such air dried powders were consistently only slightly under the
literature value.
(I do remember these details because this compound was a big, pleasant surprise for me. I thought at first "heck, I'd give it a try, after all I
failed the anthranilic acid, what could go more wrong with this one?" Then the actual preparations went unexpectedly smoothly (compared to the
anthranilic acid synths) and yielded a fairly pure product with good yields.)
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