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Author: Subject: Questions about the Hofmann Rearrangement.
Syn the Sizer
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[*] posted on 29-7-2020 at 07:34
Questions about the Hofmann Rearrangement.


Hello members,

I am looking to synthesize anthranilic acid via the Hofmann Rearrangement. I realize there are videos on the topic but I currently do not have internet at my new place and my data is now throttled due to excessive use so videos are out of the question.

My first question is, is bleach a suitable source of hypochlorite or should I synthesize fresh stuff with Cl2 and NaOH?

My 2nd question is what is, and it is kind of a stupid one. Is the molar ratio of hypohalide and amide 1:1 with a little excess of hypohalide? I have read through the chapter in Organic Reactions Vol. 3 from the SM library and that is what I understand to be correct, but I want to make sure.

This is one of my steps in making methyl red.
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[*] posted on 29-7-2020 at 08:54


1. Yes, bleach is ok but the workup can be a mess. If you're using bleach try to use some with no soap/detergents. Another thing about bleach is that the hypochlorite concentration is often lower than what's on the label due to decomposition so you'll either have to titrate your bleach or use a large excess.

2. An excess is good because it isn't acting catalytically, so any left over after all of your phalimide is reacted will just sit there.
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[*] posted on 29-7-2020 at 09:11


Awesome, thank you.

I may just make fresh hypochlorite using the method in the Organic Reactions Vol.3 p.281-282 to ensure it is detergent free.

Also in the table on p.294 of the same book, it says if reacted in Ethanol it will produce methyl anthranilate. I may also try this to see how easy it is. Sounds fun and saves Fischer Esterification after the Hofmann Rearrangement.

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Pumukli
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[*] posted on 29-7-2020 at 10:25


In ethanol it won't. :-)

But this is a very real and nice reaction, I mean, the direct synth of methyl-anthranilate from isatoic anhydride. Because this is what you'd do if reacted in methanol. Unfortunately the anthranilic acid synthesis is not as straightforward as it seems, at least it wasn't in my hands. Try it a few times and you'll probably learn what I already learnt. :-)

On the other hand, preparing and isolating isatoic anhydride (instead of anthranilic acid) AND reacting it with methanol (with a bit of base as a catalyst I think) is a nice, fairly clean and high-yielding reaction. Last year I reported my findings somewhere here in SM, try searching for "isatoic" and you'll probably find my report. I think it is worth reading for everyone who want to play with these compounds.
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[*] posted on 29-7-2020 at 14:00


Awesome, thanks. I was wondering about that because everything else in the table used methanol to add a methyl group. I just wasn't sure if the rearrangement also affected the alcohol.

But according to the book you get a 70% yield of methyl anthranilate when doing the reaction in alcohol instead of water.

http://library.sciencemadness.org/library/books/organic_reac...

p.294 3rd formula down on the table, phthalimide, 3rd reaction with hypochlorite and ethanol.
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[*] posted on 29-7-2020 at 16:08


This is why one looks up references; predictably the word methyl doesn't appear in it. The book is imperfect.

[Edited on 30-7-2020 by S.C. Wack]




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[*] posted on 29-7-2020 at 18:38


I was not able to find the document referenced.
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[*] posted on 29-7-2020 at 19:51


...try this....solo

https://b-ok.lat/book/2043594/414aa6




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[*] posted on 29-7-2020 at 21:55


Thank you.

I found the main book but it was reference 102 in the section on Hofmann Rearrangement I could not find the document for. It is the reference for supposed methyl anthranilate from phthalimide using ethanol as a solvent in Hofmann Rearrangement.

[Edited on 30-7-2020 by Syn the Sizer]
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Pumukli
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[*] posted on 30-7-2020 at 01:31


70 % is not bad for an amateur I think.

But I wouldn't mess mixing in another unknown (ethanol) into the already messy Hoffmann rearrangement reaction of phthalimide. This is why I wrote that I'd aim for nice, clean isatoic anhydride from the rearrangement. (It is a useful compound in itself.) Then, in a second step I'd have the anhydride react with the methanol (or ethanol). This step is really high-yielding and clean, yield is reportedly around 90% with MeOH, somewhat lower with EtOH - if my memory is right.
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[*] posted on 30-7-2020 at 02:12


http://www.sciencemadness.org/talk/viewthread.php?tid=155329
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[*] posted on 30-7-2020 at 07:00


Thank Pumukli, ultimately am just looking to synthesize anthranilic acid as a step in the synthesis of methyl red, I just saw the field in the table and it made me curious. Though, I am interested in anthranilate esters, and more so esters with alcohols chains larger than ethanol, I am curious of their scents.

Thank you Tsjerk, I even did a forum search thinking there would be a thread already but oddly nothing popped up. I wonder if it has something to do with my super slow connection. I will read through this post.
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