Syn the Sizer
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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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njl
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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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Syn the Sizer
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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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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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Syn the Sizer
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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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S.C. Wack
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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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Syn the Sizer
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I was not able to find the document referenced.
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solo
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...try this....solo
https://b-ok.lat/book/2043594/414aa6
It's better to die on your feet, than live on your knees....Emiliano Zapata.
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Syn the Sizer
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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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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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Tsjerk
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http://www.sciencemadness.org/talk/viewthread.php?tid=155329
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Syn the Sizer
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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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Syn the Sizer
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Hello everyone, I am now planing my synthesis of anthranilic acid.
I guess I am out of GAA and was wondering if another organic acid such as citric acid would work in place of the GAA?
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Pumukli
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Probably. When I tried, I also was low on GAA and used citric acid in one series of trials, albeit they were only test tube sized batches. The weak
acid is required because the desired pH is around 5-6 at one point and it is hard to reach this sweet spot with strong acids. Moreover some buffering
capacity is also a welcome addition.
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Syn the Sizer
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@Pumukli Awesome, thank you. I found the small sample of phthalimide I made last spring so I am going to do some trials too before I use the product I
made a couple days ago.
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Syn the Sizer
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I now have a further question. Should I use pure citric acid crystals in the hypochlorite solution, or should I dissolve them in a little
H2O first?
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njl
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It shouldn't really matter. It's generally good practice to deal with solutions but in this case it won't make a big difference.
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Syn the Sizer
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Thanks
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