y0ssarian87
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4-bromo-(N,N-diethy)aniline formation?
Hi everyone,
This is my first time posting on this site. I've been a long time lurker, but I have a question about a potential synthesis.
For the sake of full disclosure, I'm asking for help with a synthesis project for my OChem class. Our assignment is to design and carry out a
synthesis of any molecule of our choosing using precursor molecules from any of our past labs.
I thought it would be fun to generate a dye molecule, because the analysis would be fun, colorful, and easy with UV/Vis spectroscopy. This was my
thought below:
bromobenzene + HNO3 ---(cat. H2SO4)---> 2-bromonitrobenzene + 4-bromonitrobenzene
Isolate 4-bromonitrobenzene by recrystallization
4-bromonitrobenzene + Na2S2O4 ---(aq. + bicarbonate + heat)---> 4-bromoaniline
Isolate the precipitate
Dissolve insolubles in organic solvent
Acidify the mixture to yield the anilinium salt
Isolate an aqueous phase
Bring up the pH
Isolate the precipitate as the 4-bromoaniline
4-bromoaniline + 2 eq bromoethane ---(organic solvent)---> 4-bromo-(N,N-diethyl)aniline + Br-
This is the step I have the most issues with. I know that alkylation of amines using alkyl halides yields a statistical mixture of amines including
the quaternary ammonium salt. But I was wondering if I might have decent luck with this since this is an aryl amine, and even better with the bromine
substitution, making my amine much less nucleophilic. I'm trying to get only 4-bromo-(N,N-diethyl)aniline, and I don't know how to separate this from
the other amines I would get from alkylation (4-bromoaniline, 4-bromo-N-ethylaniline, and 4-bromo-(N,N,N-triethyl)anilinium bromide).
Any recommendations on how to get this specific molecule using limited reagents (no diethyl oxalate)?
It's important that I can get decent purity of the tertiary product (even if I have significant loss) because I intend to use it for a Grignard, so I
can't have any acidic hydrogens.
4-bromo-(N,N-diethyl)aniline + Mg ---(Et2O)---> 4-(N,N-diethyl)aniline magnesium bromide
This last step is the easiest...
4-(N,N-diethyl)aniline magnesium bromide + 0.5 eq methyl benzoate ---(Et2O followed by HCl and H2SO4)--->
brilliant green triarylmethane dye
Any help or recommendations? Particularly with the formation of the quaternary anilinium salt and with good techniques for isolating my desired
products? I'm probably trying way too hard to make something impractical work, but I bet it can be done. Thoughts?
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Nicodem
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Please open threads without references only in the Beginnings section (see the forum guidelines for more info - link in my signature).
Anilines can easily be selectively N,N-dialkylated, because these are the thermodinamic products under proper stoichiometry (anilinium salts easily
transalkylate), but because the use of bases is detrimental (competing E2 due to the relatively poor N-nucleophilicity of anilines), the alkylation
needs to be repeated two or three times on the basified mixture for a good conversion (see the published procedures).
I'm sure you can easily find a reference for the synthesis of 4-bromo-N,N-diethylaniline, if you search the literature. There has also been some
discussion with references on this forum in regard to the N,N-diethylation of anilines and their N,N-dialkylation in general. If I remember correctly,
Magpie even posted his experience with the synthesis of N,N-dimethylaniline using methanol and sulfuric acid. This method is also applicable for the
N,N-diethylation of some anilines when using ethanol (see DOI: 10.1021/i360055a007).
…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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Nicodem
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Thread Moved
13-11-2012 at 09:07 |
y0ssarian87
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Hi Nicodem,
Thanks for moving the thread. My apologies. This morning I found a preparation published by Noyes:
Put in a small flask 30 grams of aniline and 45 grams of ethyl bromide, and heat with a reversed condenser for one or two hours, or until the mass
solidifies. Cool, add 60 cc. of a solution of sodium hydroxide (3 cc. = 1 gram), with cooling, separate the ethyl aniline, add to it 45 grams of ethyl
bromide, and heat with reversed condenser as before, till the mass solidifies. Dis solve in water, boil to expel any ethyl bromide which remains,
cool, add 60 cc. of caustic soda, and separate the diethyl aniline. Dry with powdered potassium hydroxide, and distil, collecting as much as possible
of the portion boiling at 212°-215°. (Aniline boils at 183.7°, ethyl aniline at 206°, and diethyl aniline at 213,5°.)
I think this will work pretty nicely. Thanks for your help.
Unfortunately I'm limited to only reagents and supplies that we've used in past labs, so virtually all catalysts are off the table. Also I cannot use
an autoclave or any pressurized system, so I don't think I can do alkylation with ethanol. We just have basic OChem lab equipment for distillation,
reflux, separatory funnel, etc.
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Nicodem
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Quoting without citing the reference is not tolerated here - no matter what, this is a science forum! Please edit the post accordingly.
Otherwise, yes, that is the typical procedure for the N,N-dialkylation of anilines. I found no examples of its use on 4-bromoaniline, but it might
work even without modification, except that you will have to fractionate under reduced pressure. Make sure you have an efficient distillation column
or else you will get a product too impure for the reaction with magnesium (which might not start at all). By the way, we are still waiting for the
references of the other reactions you mentioned in the first post.
…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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