need help of a reaction's mechanism

It‘ s about aminofurazan's diazotization(with HNO2--mix of NaNO2/HOAc). when the reaction occurs, a-Hydroximinoacetonitriles were common products.
The problem is how can a C+ becomes a C- . My point is by oxizdation of HNO2, but it seems to be weired. At least, I ve never seen a reaction like that before. My friend thought that it may form a structure like C-N=N-O- and lose N2O to form a C-, but from my point of view, it's wrong again, 'cause usually, a C-N=N-O- is obtained in strong base like conc.KOH.
Does any body know the answer? Thank you!

This reaction is not known in the literature, or at least not the way you've drawn it. I would not recommend you invoke anions under acidic conditions, this is a fairly universal rule. So, I disagree with your friend as well.

As you pointed out, the starting material is in a higher oxidation state than the product, and thus must undergo a reduction. A good idea when drawing mechanisms is to consider the oxidation state of starting materials and products to determine whether or not it is a redox reaction (see scheme A).
- rings = +1
- heteroatoms = +1
- pi bonds = +1



So others know what you're talking about, nitrous acid is formed, and dissociates into the nitrosonium cation (scheme B). This would lead to diazotization by a mechanism such as shown in C, but cannot proceed to product due to lack of a reducing agent. According to literature precedent, this diazonium salt leads to a nitrofurazan in the presence of sodium nitrite. Obviously it could add any nucleophile present.

If any one of these intermediates were reduced, monosubsitututed 1,2,5-oxadiazoles decompose spontaneously, or under acid/basic conditions to give alpha-oximinonitriles by cycloreversion - you know this it seems.

Other options might include radical fragmentation or intramolecular hydride delivery, but I'm not sure exactly how.


[Edited on 7-1-2012 by Arrhenius]

Quote: Originally posted by Arrhenius

This reaction is not known in the literature, or at least not the way you've drawn it. I would not recommend you invoke anions under acidic conditions, this is a fairly universal rule. So, I disagree with your friend as well. As you pointed out, the starting material is in a higher oxidation state than the product, and thus must undergo a reduction. A good idea when drawing mechanisms is to consider the oxidation state of starting materials and products to determine whether or not it is a redox reaction (see scheme A). - rings = +1 - heteroatoms = +1 - pi bonds = +1 So others know what you're talking about, nitrous acid is formed, and dissociates into the nitrosonium cation (scheme B). This would lead to diazotization by a mechanism such as shown in C, but cannot proceed to product due to lack of a reducing agent. According to literature precedent, this diazonium salt leads to a nitrofurazan in the presence of sodium nitrite. Obviously it could add any nucleophile present. If any one of these intermediates were reduced, monosubsitututed 1,2,5-oxadiazoles decompose spontaneously, or under acid/basic conditions to give alpha-oximinonitriles by cycloreversion - you know this it seems. Other options might include radical fragmentation or intramolecular hydride delivery, but I'm not sure exactly how. [Edited on 7-1-2012 by Arrhenius]

Okay, thanks. I found it, but I can only get a few of the papers cited - most are foreign journals, and I don't read Russian anyway. Of the one I do get, and ran into before I posted, they claim to obtain the oximinonitrile byproduct when attempting a Sandmeyer reaction. They used 1eq of copper 1 or 0, and got poor yield of methyl oximinonpropionitrile. Copper is serving as the reducing agent. They draw both the radical (as I've shown) and a cation, which is bloody confusing, because I thought they meant radical cation for a moment, but it could be the cation as well, which ultimately must undergo one electron reduction and hydrogen abstraction (e.g. from solvent) or a second one electron reduction and a proton abstraction. Maybe you could get a good yield with the proper stoichiometry of copper - i.e. >2eq.


Rakitin, O.A. et al, Russian Chem. Bull., (1993) 42(11) 1865.

Oy. Here's another idea from a paper that yields a similar product (also cited in the book). Not sure I buy this one, but you decide. I don't even know what to call NO2+ .


Churakov, A.M. et al, Chem Heterocycl Comp. (1988)24, 1378.

[Edited on 7-1-2012 by Arrhenius]

Quote: Originally posted by Arrhenius

Okay, thanks. I found it, but I can only get a few of the papers cited - most are foreign journals, and I don't read Russian anyway. Of the one I do get, and ran into before I posted, they claim to obtain the oximinonitrile byproduct when attempting a Sandmeyer reaction. They used 1eq of copper 1 or 0, and got poor yield of methyl oximinonpropionitrile. Copper is serving as the reducing agent. They draw both the radical (as I've shown) and a cation, which is bloody confusing, because I thought they meant radical cation for a moment, but it could be the cation as well, which ultimately must undergo one electron reduction and hydrogen abstraction (e.g. from solvent) or a second one electron reduction and a proton abstraction. Maybe you could get a good yield with the proper stoichiometry of copper - i.e. >2eq. Rakitin, O.A. et al, Russian Chem. Bull., (1993) 42(11) 1865. Oy. Here's another idea from a paper that yields a similar product (also cited in the book). Not sure I buy this one, but you decide. I don't even know what to call NO2+ . Churakov, A.M. et al, Chem Heterocycl Comp. (1988)24, 1378. [Edited on 7-1-2012 by Arrhenius]