[Enthalpy]

More and more articles at Wiki claim:
"geminal polyamines have never been observed",
Seemingly because it's alleged in a popular book.

What is a geminal polyamine, then? Doesn't Guanidine fit the definition?
http://en.wikipedia.org/wiki/Guanidine

unprotected amines, even three on a single carbon.

And is the next one a geminal polyamine, though its nitrogens are populated with methyls?
Tetrakis(dimethylamino)ethylene or Octamethylethylenetetramine
[(CH₃)₂N]₂C=C[N(CH₃)₂]₂ cas=996-70-3



Did I get something wrongly?
Thanks!

[AndersHoveland]

Both compounds to which you refer certainly exist. Furthermore, I am aware of a very stable energetic compound (DADNE) with the structure (O2N)2C=C(NH2)2.
What was certainly meant is that (R)2C(NH2)2 does not exist, where there are two separate groups attached to the carbon. R=C(NH2)2 can exist under limited conditions, if R is an (NH group), or if there are electron withdrawing groups that lend aromaticity, then R could be a carbon. However, the structure is such a compound would be more accurately described as (-)O2N=C(NO2)--C(NH2)=NH2(+)
Of course (CH3)2C(N[CH3])2 could certainly exist (since it cannot ionize), but not (CH3)2C(NHCH3). This is because of ionization. Anhydrous liquid NH3 can ionize to NH4+ and NH2- (ammonium cation and amide anion).
In the case of guanidine HN=C(NH2)2, there is probably some small equilibrium when dissolved in a solvent, but the guanidine molecule almost completely dominates. It would be expected that guanidine molecules would slowly exchange atoms in solution, as water is also known to do.

Thus "geminal polyamines have never been observed" is a simple, yet not completely accurate, phrase which avoids the complexities of explaining under what limited conditions two amines can exist on the same atom.

[Enthalpy]

This is how Wiki's article defines geminal polyamines in http://en.wikipedia.org/wiki/Polyamine :
"As of 2004, there had been no reports of any geminal diamine, a compound with two or more unsubstituted -NH2 groups on the same carbon atom"
so at least this definition is in trouble. Urea would be an even more common example of such compound.

Well, if the assertion needs dozens of But, If and When, it gets less useful.

[AWK]

I agree
should be "with two or more -NH2 or -NHR groups on the same sp3 carbon atom"

[AMEDIO]

i think guanidine certainly is one example.

[AndersHoveland]

Urea has somewhat non-intuitive reactivity, suggesting that a more accurate structure could be represented
by [ +]H2N=C(NH2)--O[-]. For example, no reference can be found about urea easily condensing with hydrazine, with evolution of NH3, as guanidine is known to do. If there was an actual =O double bond, one would expect urea to easily hydrolyze with water.

[AWK]

Urea has somewhat non-intuitive reactivity, suggesting that a more accurate structure could be represented
by [ +]H2N=C(NH2)--O[-]. For example, no reference can be found about urea easily condensing with hydrazine, with evolution of NH3, as guanidine is known to do. If there was an actual =O double bond, one would expect urea to easily hydrolyze with water.

For reaction of urea with hydrazine search patent literature
eg United States Patent 4482738

[AndersHoveland]

There are a few patents that mention this, but there are very few mentions about this type of condensation from any reputable sources. Patents are not always accurate.

However, I found this in a reputable piece of literature:
"...semicarbazide is best made from urea and hydrazine; using excess urea."

The only reference that I could find referred to Rossel and Frank, Ber. 27, 56 (1894) but I have not actually seen this original article.

[AWK]

Patents should show a correct way of reaction, othewise they are invalid, but usually some details are missing and only an experienced chemist can repeat this reaction in lab.

[Enthalpy]

This geminal polyamine seems to exist. What do you think?

Smiles = NCCNCC(N)N
Cas = 100231-77-4
1,1,2-Ethanetriamine,N-(2-aminoethyl)-

Listed at Chemos GmbH :
http://www.chemos-group.com/details.asp?id=250257

It includes a real NC(N)C end, or if you prefer
(H₂N)₂CH-CH₂-NH- etc
with two naked amines on a tetrahedral carbon.

Well, if I get it properly (please check), this is an authentic geminal diamine, with an industrial supplier.

[AndersHoveland]

Doing a quick search, the only thing I was able to find was a hydrochloride of this compound.
Hydrochlorides of geminal diamines are known to exist, although somewhat chemically unstable.
Such compounds typically condense/disproportionate into a complex gunky mess. Thus this is, in a way, yet another exceptional case were geminal amines can exist. However, the compound in question
seems to have the structure (NH2)2C=NCN, where the carbon with the two amines on it is also double bonded to a nitrogen atom. This is very similar to guanidine, and so there should be little surprise.

When we are saying that "geminal polyamines do not exist", we are specifically refering to to
compounds with structures like (NH2)2C(CH3)2 or (NH2)2CHCH3, where the carbon that connects to the two amines is not double bonded to an electron withdrawing atom or group, and where the amines are "plain" without an other groups on them.

To understand why they do not exist, and what exceptions to this generalization exist, one should consider the ionization and resonance states of the compounds. Basically, if neither amine has a positive charge on it, and if there is at least one hydrogen atom on each amine, the geminal amine will not be stable.

[Enthalpy]

Thanks!

But what about the product listed at Chemos?
http://www.chemos-group.com/details.asp?id=250257

They give a product reference in their catalogue, a Cas number...
Would that happen if the molecule doesn't exist?
Or did I read something wrongly? The formula there is C₄H₁₄N₄ simply.

-----

I've also seen some hints to 1,1,2,2-tetraaminoethane but couldn't read the full articles:

http://journals.tubitak.gov.tr/chem/issues/kim-06-30-5/kim-30-5-1-0506-14.pdf
The synthesis of tetra aminoethane was accomplished employing a 3-step procedure as described in the literature (10)
with ref 10 :
I. Özdemir, B. Yigit, B. Çetinkaya, D. Ülkü, M.N. Tahir and C. Arici, J. Organomet. Chem. 633, 27-32 (2001)

http://onlinelibrary.wiley.com/doi/10.1002/anie.196807661/pdf
leads to the tetraaminoethane (5) and the diaminoethane

http://airex.tksc.jaxa.jp/pl/dr/20020011709
To prepare 1,1,2,2-tetraaminoethane (or a derivative thereof), FOX-7 has been reduced under conditions which normally reduce double bonds and nitro groups.
[FOX-7 is the secondary explosive (H₂N)₂C=C(NO₂)₂]

Did I read properly, or is that wishful interpretation of incomplete descriptions?

[AndersHoveland]

I looked over your links, and there does not seem to be anything that suggests that there are any more geminal diamines that exist. Tetraaminoethane has derivitives that exist (meaning fully substituted), but the free compound does not.

A quote from your last link:
"To prepare 1,1,2,2-tetraaminoethane (or a derivative thereof), FOX-7 has been reduced under conditions which normally reduce double bonds and nitro groups. The reactions that took place indicate that the double bond and the nitro groups were reduced. The products that have been identified are derivatives of ammonia like acetamide and ammonium salts. This indicates that the structure is broken down during the reaction and means that a saturated carbon atom carrying two free amino groups isn't stable. "

In other words, the researchers attempted to make 1,1,2,2-tetraaminoethane, but were unsuccessful.

[Enthalpy]

Oops, I could have read it properly by myself, about the failed attempt towards 1,1,2,2-tetraaminoethane. It was clear enough. Thank you!

-----

And the catalogue product at Chemos?
http://www.chemos-group.com/details.asp?id=250257
N2-(2-aminoethyl)ethane-1,1,2-triamine
Cas No. 100231-77-4
C₄H₁₄N₄
Structure there http://www.lookchem.com/cas-100/100231-77-4.html

This one is named (and drawn elsewhere) like two naked amines on the tetrahedral carbon, isn't it?

Better, its neighbour carbon also carries a (secondary) amine, giving me some hope that the similar 1,1,2-triaminoethane could be made. A mix with diaminoethane would be just fine.

[AndersHoveland]

Since they are a Chinese chemical company it is very likely they made a mistake 

However, it is also quite possible that they are refering to an aldehyde-ammonia condensate which is soluble in a solution of ammonium hydroxide, or possibly soluble in plain water. Since the condensate does not have an exact (or researched) molecular structure, it may have been easier to describe it with two amine groups on the same carbon. These types of molecular structures, which are not technically correct, and fairly commonly encounted in industrial organic chemistry. It would be a waste of time trying to draw out a more accurate structure, since condensates of this type are often a gunky mess, frequently with uncertain exact structure

Geminal amines do exist in equilibrium in water (and especially ammonia) solutions of aldehyde-ammonia condensates, but they cannot be isolated as a pure solid compound.