Sciencemadness Discussion Board

How to decompose precipitated alkaloids in Wagner's Reagent?

beerwiz - 12-11-2015 at 16:52

Wagner's reagent is an alkaloid precipitant and constists of 2g Iodine and 6g Potassium iodide in 100ml water.

So I precipitated some alkaloids using this reagent. Does anybody know how to decompose the iodide to get the free alkaloids?

If picric acid was used to precipitate the alkaloids (1g picric acid in 100ml water), then simple ammonia or NaOH frees them up. But what about alkaloids precipitated with Wagner's Reagent?

[Edited on 13-11-2015 by beerwiz]

careysub - 12-11-2015 at 18:54

Quote: Originally posted by beerwiz  
Wagner's reagent is an alkaloid precipitant and constists of 2g Iodine and 6g Potassium iodide in 100ml water.

So I precipitated some alkaloids using this reagent. Does anybody know how to decompose the iodide to get the free alkaloids?

If picric acid was used to precipitate the alkaloids (1g picric acid in 100ml water), then simple ammonia or NaOH frees them up. But what about alkaloids precipitated with Wagner's Reagent?

[Edited on 13-11-2015 by beerwiz]


From an olde book:
"The alkaloids may be recovered from their polyiodides by treating the precipitate with sulphurous acid, a sulphite and dilute sulfuric acid, or sodium thiosulphate and then adding an alkali and shaking with a suitable immiscible solvent. Treatment with sodium thiosulphate ("hyposulphite"), avoiding excess, is a convenient means of purifying the polyiodides of coprecipitated foreign matter. The reduced solution is filtered and again treated with Wagner's reagent, when the polyiodid is obtained in a condition of purity. "

https://books.google.com/books?id=p77nAAAAMAAJ&pg=PA138&...

[Edited on 13-11-2015 by careysub]

AvBaeyer - 12-11-2015 at 18:55

Perhaps simple reduction of the iodine with sodium thiosulfate might work. That's what I would try.

AvB

AvBaeyer - 12-11-2015 at 18:57

Wow- simultaneous post with Careysub! At least we gave the same answer.

AvB

Syntropymancer - 14-12-2015 at 18:29

sodium metabisulphite works too, we use it regularly to clean up I2.

[Edited on 15-12-2015 by Syntropymancer]

beerwiz - 22-12-2015 at 22:05

Thanks to all who responded on this thread, very useful info.

Does anyone know if when Wagner's reagent is added to a neutral or acidic aqueous solution and there's zinc acetate in the solution, will the zinc precipitate along with the alkaloids? Or will the zinc acetate remain in solution?

[Edited on 23-12-2015 by beerwiz]

[Edited on 23-12-2015 by beerwiz]

beerwiz - 25-12-2015 at 01:41

Tested it, the zinc acetate remains in solution and does not precipitate.