[kwev]

http://pubs.acs.org/doi/pdf/10.1021/ja9710013

It's the first reaction on the left with the ethane going to a ethylene.
I'm not sure how the the reaction mechanism works out for this one. I was thinking about the bond on the iodine going to the carbon and making a carbocation but I don't know where to go from there.

[Archer]

Hi,

Not everyone using this forum has journal access, please could you include your reaction scheme in a SMILES or picture format so that when you receive help it makes sense for other forum users.

Thanks

[kwev]

[Archer]

Probably the resultant iodide (which leaves forming a carbocation) removes I⁺ to form I₂ the electrons from this C-I bond form the double bond.

I am sorry I can't draw this at the moment but I am on a mobile device, I will upload a mechanism when I am at a PC.

This paper explains a similar elimination of vicinal dihalides to olefins.

 http://pubs.acs.org/doi/abs/10.1021/ja01607a037

[orgopete]

Probably the resultant iodide (which leaves forming a carbocation) removes I⁺ to form I₂ the electrons from this C-I bond form the double bond.

I presume you meant carbanion.

I am not surprised by separate timing for what is seemingly a second order reaction. One can make a logical argument that no reaction can be concerted in the sense that chemist draw them with all electrons moving at the same time. It makes more sense that a collision should affect the nearest electrons and upon contact, the impact will be transferred to neighboring electrons much like the coupling of train cars. The impact of the coupling is transferred from car to car after the first car couples. The electrons should behave similarly and not move in anticipation of a collision.

This reaction seems particularly susceptible for a greater timing difference as the fluorine atoms should help stabilize the intermediate. Perhaps not as extreme as showing the kinetics of an E1cb elimination, but also allowing for small timing differences. A similar reaction was reported by Stevens and Valicenti, JACS, 87, 838 (1965).

[Archer]

Probably the resultant iodide (which leaves forming a carbocation)

I presume you meant carbanion.

No, when iodide (I^-) leaves a molecule it forms a carbocation.

I apologise, the wording of my response could have been better, I was hoping to upload a mechanism but I have been too busy today.

[kwev]

Probably the resultant iodide (which leaves forming a carbocation)

I presume you meant carbanion.

No, when iodide (I^-) leaves a molecule it forms a carbocation.

I apologise, the wording of my response could have been better, I was hoping to upload a mechanism but I have been too busy today.

Would it look something like this?

[Archer]

That would be my prediction for the mechanism.

Perhaps this is a little simplified and more complex interactions occur but I am not familiar with the exact kinetics of this.

[orgopete]

Re mechanism

Probably the resultant iodide (which leaves forming a carbocation) removes I⁺ to form I₂ the electrons from this C-I bond form the double bond.

I had interpreted an addition of I(-) to give I2 to be the equivalent of forming I(+), which I agree with. That forms an anion on the carbon, stabilized by two fluorine atoms. What I don't know is the actual reaction being performed. Was it catalyzed in any way? Was it simply heated or heated in a solvent? I am familiar with I(-) used to remove an alkyl iodo group. This presumably forms a carbanion intermediate. The Stevens and Valicenti paper I referred to used iodide to induce dehalogenation. Again, attack on the halogen by iodide. They report zinc gives a similar reaction.

I think formation of a cation is a difficult reaction, not impossible, but difficult. I think a catalyst of some type would be required.

[spirochete]

I have not completely read and understood the information on the first page of the paper but the carbocation people have drawn in that mechanism would be tremendously unstable. The resonance donation of fluorine would not be near enough to be stabilizing considering how inductively withdrawing it is. And then there are other fluorines also inductively withdrawing.

The intermediate C₂F₂I⁺ must be a three membered ring, not a strict carbocation as it is drawn. I do not have time show the full mechanism but I have drawn a reasonable one on paper that includes the three membered iodonium ring, using Iodide to form I₂ and the product.

Note: If my mechanism is inconsistent with the experimental data in anyway I'd appreciate someone letting me know. It doesn't seem like it is, however.