many a time we encounter reaction involving aniline. How to remove this reactant when the difference between of RF between this and of the product is very small, almost they overlap each other on TLC. Is there is any way to remove without flash.
is your intended product basic? if not, you can dissolve the crude in ether or ethyl acetate and extract with diluted HCl which will take up aniline in the aqueous phase as aniline hydrochloride
If what I shall suggest doesn't react with other components, then add cautiously hydrochloric acid. HCl(aq) will react with aniline to form anilinium chloride, C6H7NH+Cl-, which is water-soluble. The anilinium salt will go to the aqueous phase.
Search for a solvent where your compound is soluble and aniline is not, or viceversa. Otherwise, the treatment with HCl to extract aniline into an aqueous phase is the most sensible idea
The simplest solution is a steam destillation according to a suggestion by Mr Jasiński. In case of small scale reaction you can try a multiple preparative TLC on plates 20cm *20cm. There is a specific method of preparative TLC like seperation by CHROMATOTRON (http://www.harrisonresearch.com/chromatotron/specs.html). Just recently we were able to separate a mixture of compounds with almost the same values of Rf using this device. The serious drawback of this mathod is the high cost of the CHROMATOTRON.
Sincerely,
AD
All the above answers are correct. In fact, the choice of method will depend on the composition of the reaction mixture and synthetic scale. In addition, I would propose to remove aniline by several evaporations on an oil pump. Its boiling point is 184oC, close to DMF. It can be useful to add a second solvent forming the azeotropic mixture - for aniline it is e.g. etghylene glycol. In this case you will be able to remove small traces of aniline (however, you will introduce the other component which may be a problem).
The method forming anilinium cholride i guess worked out for me, waiting for NMR data, to get it confirmed.
Regards
Thanks
Aniline from the reaction mixture can be removed as an hydrochloride by treating mix. with 10% HCl by shaking in separating funnel.
To remove aniline from the reaction mixture you can wash reaction mixture with 10% HCl in separating funnel Shake well for 10 minutes to remove aniline base.
Depending on the basic nature and stability of your product to acidic conditions, it may be appropriate to use liquid-liquid extraction to remove excess aniline. Using 1M or 2M aqueous HCl solution will extract the aniline out into the aqueous layer as the HCl salt form. If you product is also basic and liable to salt formation, or if it is acid sensitive, you may be able to separate the aniline out as the free base using solubility difference (i.e. dissolve your crude mixture in a small amount of a solvent such as EtOAc, then add hexanes or petroleum spirits to precipitate your product. If you crude is soluble in diethyl ether, then this may be even more effective. The aniline should remain soluble in the solvent, assuming your product is more polar, or present in higher amount).
As so many person suggeted use 15-20 % HCl, i am also using HCl for removal deffrent substituted anilines and it is working fine.
An additional method to remove unwanted amines is to wash your organic phase with 10%wt copper (II) sulphate solution. The CuSO4 solution should go from blue to slightly purple when there are amines present so wash until your aqueous phase no longer changes colour. This method works well for alot of amines and heterocycles like imidazole and pyridine. If you're lucky your compound will remain in the organic phase
Dear Ramit
It depends if your compound you want to separate it from aniline has basic properties or not?. If your compound has'nt basic properties, try to use 1N HCl to convert aniline into water soluble salt. If it has basic character, try to extract your compound by liqiud-liquid extraction using solvent like ethyl acetate or methylene chloride or diethyl ether.
Good Luck
Yours
Prof. Dr. Talaat El-Emary
I have tried using the dil HCl method, but due to the basic property of the product, in addition to anilinium chloride, product is also lost in salt form, and over all yield is really less.
I am planning to use BOC as a protecting group which will make aniline polar and easily separable from the product, do you think this method will work.?
Dear Ramit
Yes you can try using BOC as protecting group.
Good luck
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