Sciencemadness Discussion Board
Not logged in [Login - Register]
Go To Bottom

Printable Version  
Author: Subject: Schiffs base / imine with an amine salt?
DIBALL
Harmless
*




Posts: 5
Registered: 4-1-2017
Member Is Offline


[*] posted on 2-1-2018 at 10:12
Schiffs base / imine with an amine salt?


Right now I´m trying to make a Schiffs base from a ketone with methylamine. And I wanted to know, if I can use methylamine HCl for the reaction with the ketone or if it could cause problems with the salt form?

I dissolved the ketone with toluene and anhyd. ethanol together with the methylamine HCl, put some magnesium sulfate in it and let it stand for a couple of days. Then I boiled the ethanol off and it looks like everything reacted, since no methylamine HCl precipitate out of the solution.
And now I want to do a Grignard reaction.

Does the amine salt group interfere with the reaction? Or is the Schiffs base even possible to make with an amine salt?
View user's profile View All Posts By User
zed
International Hazard
*****




Posts: 1427
Registered: 6-9-2008
Location: Great State of Jefferson, City of Portland
Member Is Offline

Mood: Semi-repentant Sith Lord

[*] posted on 3-1-2018 at 14:32


Free base is traditional.
View user's profile View All Posts By User
Reboot
Harmless
*




Posts: 38
Registered: 8-8-2017
Member Is Offline


[*] posted on 3-1-2018 at 18:25


The reaction of an amine with a ketone is driven by the attraction between the electron poor carbon (with the oxygen double-bonded to it) in the ketone and the electron rich nitrogen atom of the amine. If the amine is protonated (as it is in acid salt form) the nitrogen is no longer electron rich. I wouldn't expect a reaction at all with an amine salt.

Grignards do not play nice with acidic hydrogens floating around, so if there's residual amine salts in the mix, that could completely screw up the reaction (as those acidic hydrogens react with the electron rich carbon ion formed during the Grignard.)

You'll have to free that amine from the salt I expect. On the small scale it could be as simple as a bit of hydroxide, molecular sieves to remove the water, and patience.
View user's profile View All Posts By User
AvBaeyer
National Hazard
****




Posts: 372
Registered: 25-2-2014
Location: CA
Member Is Offline


[*] posted on 4-1-2018 at 20:40


The best practical way to efficiently form a Schiff base from ketones is to react the carbonyl compound with a weak acid salt of the amine such as an acetate. This can be accomplished by dissolving the amine hydrochloride and the ketone in ethanol or methanol and adding an equimolar amount of anhydrous sodium acetate. Because the formation of Schiff bases from ketones is relatively slow, an excess of either the ketone or the amine salt is typically used. Usually the amine salt is used in excess. Aldehydes are usually so reactive that equimolar amounts of aldehyde and amine free base can be mixed with immediate product formation.

AvB
View user's profile View All Posts By User
zed
International Hazard
*****




Posts: 1427
Registered: 6-9-2008
Location: Great State of Jefferson, City of Portland
Member Is Offline

Mood: Semi-repentant Sith Lord

[*] posted on 7-1-2018 at 13:05


Yup. Amine salts of strong acids, are usually neutralized before attempting to react with ketones or aldehydes.

Same goes for oximes (and phenylhydazones?). These may drop out of solution, upon formation. And, some analytical procedures, utilize this property. Been a while, since I ruminated on this. I should upgrade my mindware.

Hydroxylamine HCl, is neutralized via Sodium Acetate, to form NaCl plus Hydroxyamine Acetate. This acetate reacts readily. And, shazaam..... A crystalline derivative.



[Edited on 7-1-2018 by zed]

[Edited on 7-1-2018 by zed]
View user's profile View All Posts By User

  Go To Top