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Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: lutesium on November 22, 2007, 11:18:49 PM

Title: NaNO2 + R-X ---> R-NO2 why not??
Post by: lutesium on November 22, 2007, 11:18:49 PM
Dear Sir/Ma'am

Why doesn't this rxn occur??? And why do we need the expensive reagent AgNO2 for this rxn to occur??? Mechanism please...

NaNO2 + R-X ---> R-NO2 + Na-X

And how can the used AgNO2 be recycled from the occuring Ag-X???

Any help would be appreciated!!!

Thank you very much!!!
Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: cetirizine on November 23, 2007, 12:25:24 AM
i think one of the product  AgCl is unsoluble,it will sink to the bottom,it help the reaction processing favored the right direction.
Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: AWK on November 23, 2007, 01:14:39 AM
This reaction can proceed  also to RONO. And this is a problem. Whwn we use AgNO3 the main product in nitrocompound, otherways - nitrite
Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: lutesium on November 23, 2007, 06:06:51 AM
I didn't understand anything... You didn't understand my question or I cannot understand you :) ... Please give me an accurate answer!!!

Thank you very much!!!
Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: AWK on November 23, 2007, 07:10:29 AM
Quote
Why doesn't this rxn occur??? And why do we need the expensive reagent AgNO2 for this rxn to occur??? Mechanism please...

NaNO2 + R-X ---> R-NO2 + Na-X

This reaction should be written:
MeNO2 + R-X ---> R-NO2 + R-ONO +Me-X

where Me is univalent metal
In the case where Me=Na or K mainly R-ONO is produced
In the case of Me=Ag both RNO2 and RONO are produced but RNO2 prevails
Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: ultrashogun on November 23, 2007, 02:41:36 PM
Quote from: cetirizine on November 23, 2007, 12:25:24 AM
i think one of the product  AgCl is unsoluble,it will sink to the bottom,it help the reaction processing favored the right direction.

Yeah on general chemistry they always have that example for the common ion effect in every book.

If you add NaCl the solubility of AgCl will diminish and should precipitate out.
Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: lutesium on November 23, 2007, 09:35:39 PM
Quote from: AWK on November 23, 2007, 07:10:29 AM

This reaction should be written:
MeNO2 + R-X ---> R-NO2 + R-ONO +Me-X

where Me is univalent metal
In the case where Me=Na or K mainly R-ONO is produced
In the case of Me=Ag both RNO2 and RONO are produced but RNO2 prevails

Why??? Can you tell me the mechanism???
Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: AWK on November 26, 2007, 01:11:25 AM
You have two possibilities SN1 or SN2
Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: puppy8800 on November 26, 2007, 04:00:12 AM
the nitrite ion is an ambident anion, as it can react either at nitrogen or at oxygen which is negatively charged
therefore the product could either be nitroalkane or nitrite depending on the conditions and the reactants
the reason of using AgNO2 is because Ag+ and X- could form precipitate AgX, which moves the equilibrium rightwards
Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: lutesium on November 29, 2007, 11:35:49 AM
As far as I know while making this rxn a polar aprotic solvent is needed. I can understand why the solvent must be polar (to dissolve the NaNO2 but I cannot understand why it must be aprotic??? Any suggestions???


Lutesium...
Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: ultrashogun on November 29, 2007, 12:17:39 PM
Quote from: lutesium on November 29, 2007, 11:35:49 AM
As far as I know while making this rxn a polar aprotic solvent is needed. I can understand why the solvent must be polar (to dissolve the NaNO2 but I cannot understand why it must be aprotic??? Any suggestions???


Lutesium...

Probably because an aprotic solvent will not solvate the NO2 anion while at the same time stabilizing a cationic intermediate.
Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: lutesium on December 02, 2007, 02:02:21 AM
Now I do understand. So we must have a stable NO2 cation to make this rxn possible and an aprotic solvent serves this!

Thank you all guys!!!

Title: Re: NaNO2 + R-X ---> R-NO2 why not??
Post by: ultrashogun on December 02, 2007, 05:18:52 AM
Quote from: lutesium on December 02, 2007, 02:02:21 AM
Now I do understand. So we must have a stable NO2 cation to make this rxn possible and an aprotic solvent serves this!

Thank you all guys!!!



From your original post I concluded that NO2 was an anion because it was there in the form of NaNO2.

In general polar aprotic solvents are used in Sn2 reqctions in which the nucleophile is and anion. That way the solvent does not lower the energy of the nucleophile by solvating it.