Chemical Forums
Chemistry Forums for Students => Organic Chemistry Forum => Topic started by: Enthalpy on January 26, 2011, 03:13:24 PM
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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
(http://upload.wikimedia.org/wikipedia/commons/thumb/e/e5/Guanidine-2D-skeletal.png/200px-Guanidine-2D-skeletal.png)
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
(http://upload.wikimedia.org/wikipedia/commons/thumb/8/88/Tetrakis%28dimethylamino%29ethylene.png/100px-Tetrakis%28dimethylamino%29ethylene.png)
Did I get something wrongly?
Thanks!
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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.
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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.
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I agree
should be "with two or more -NH2 or -NHR groups on the same sp3 carbon atom"
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i think guanidine certainly is one example.
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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?
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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.
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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!
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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.
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Since they are a Chinese chemical company it is very likely they made a mistake ;D
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.
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I've made pictures of compounds known to exist, grouped as (A) unsaturated (B) saturated linear and cycles (c) saturated polycycles.
Incidentally, some would be interesting as rock... oh, you guessed ::) :
- Guanidine recomposes without soot, well-known
- Bis(dimethylamino)metane (Sigma-Aldrich, Cole-Parmer. Measured heat of formation? Longer chain?), azetidine and C6H8N4 as energetic fuels
- Tetrakis(dimethylamino)ethene as pyrophoric igniter with liquid oxygen? At RT it reacts with air.
- C6H8N4 as hypergol with N2O4?
Hexamine and C6H8N4 result from formaldehyde reacting with ammonia or ethylene diamine ("Ethyleneamines" by Huntsmann p32, what amount?), something miraculous to me.
http://www.huntsman.com/performance_products/Media%20Library/a_MC348531CFA3EA9A2E040EBCD2B6B7B06/Products_MC348531D0B9FA9A2E040EBCD2B6B7B06/Amines_MC348531D0BECA9A2E040EBCD2B6B7B06/Ethyleneamines_MC348531D0CD3A9A2E040EBCD2B6B7B06/files/ethyleneamines_brochure_huntsman_ethyleneamines.pdf
As Anders already suggested, the amines are tertiary, or the carbon that carries them has multiple bonds. Apart from the suggested stability reasons, could it be that splitting into ammonia and an imine during the synthesis hinders geminal polyamines? That would be consistent with existing compounds, and would suggest to synthesize unsaturated compounds as an intermediary step.
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Urea-Formaldehyde http://en.wikipedia.org/wiki/Urea-formaldehyde
is an other example where the geminal amines bind easily enough to create a polycondensate.
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Geminal positions of tertiary amines stabilize the molecule (sketch appended). If my data is correct and unless I botched something:
- The heat of formation of 2,4-dimethylpentane is known.
- I hand-estimate the monoaza from trimethylamine and triethylamine (-27.3kJ/mol per added -CH2-) to get -73kJ/mol for ethyldimethylamine, then add -25.4kJ/mol for each -CH2- and -4.9 for the but-last methyl isomerization.
- The diaza comes from the Crc Handbook of Chemistry and Physics.
- The first aza adds +106kJ/mol, the second +78kJ/mol, indicating a stabilizing interaction of -28kJ/mol.
In a double-check attempt, I deduce the heat of formation of the tetramethyldiaminomethane from its heat of synthesis
http://webbook.nist.gov/cgi/cbook.cgi?ID=C51809&Mask=8#Thermo-React
H2CO + 2NH(CH3)2 -> (CH3)2N-CH2-N(CH3)2 + H2O releasing 191kJ/mol (92% yield!)
Interpreting "gas phase" as "all species gaseous", the heats of formation are
-108.6kJ -18.8kJ*2 -241.8kJ per mole
giving -95.4kJ/mol of gaseous tetramethyldiaminomethane, and by misusing at 298K the 32.3kJ/mol vaporization heat, -127.7kJ/mol of liquid tetramethyldiaminomethane. That's quite different from the previous -51kJ/mol, not very credible, and would indicate an even stronger stabilizing interaction. But probably, some reactants or products are liquid.
So while geminal tertiary amines are infrequent, interaction energy wouldn't explain that.
Welcome to double-checkers...
If you have better experimental thermo data about the cited molecules, please tell!
Or credible thermo data about adamantane and hexamethylene tetramine, or about trimethyl-triazinane for instance.
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On message #15, I suggested that geminal polyamines are uncommon because they split to an imine and ammonia. It may be already known, and is inspired by geminal alcohols that are uncommon because they split to a ketone or aldehyde and water. This explanation is consistent with the easy synthesis of geminal tertiary amines while primary ones are scarce.
It is also consistent with the stability of urea, guanidine and the like. As the sketch illustrates, if the diaminated carbon has already a double bond, the expulsion of ammonia would create cumulated double bonds, which is energetically unfavourable. A polymer would be unfavourable too as it would contain hydrazines.
I wish I had credible heats of formation for imines and geminal polyamines.
Pushing the similarity with geminal alcohols, where cyclopropanone reacts with water to make the diol because a carbon unfavourably cumulates a small ring ans a double bond, the hypothetical stability of gem-diaminocyclopopane would be a test for this explanation. As on the other sketch, just react dihalocyclopropane with excess ammonia, for instance as warm gases.
Exaggerating further, the hypothetical hexaaminocyclopropane might be interesting for rockets. With H=4×C, it would need little additional hydrogen (mix with a guanidine) to decompose without soot and produce heat, and may also burn efficiently in oxygen.
Marc Schaefer, aka Enthalpy
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More heats of formation for zero, one or two amines at the same carbon: acetone, acetamide and urea. All gaseous at +298°C at least in figures.
This time primary amines replace primary carbons, and the common carbon makes a carbonyl. The replacement releases heat here, the second one less so.
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Nist has narrowed the range of heat of formation for adamantane and hexamine
http://webbook.nist.gov/cgi/inchi?ID=C281232&Mask=2#Thermo-Condensed
http://webbook.nist.gov/cgi/inchi?ID=C100970&Mask=2#Thermo-Condensed
from that, geminal tertiary N replacing CH add +79kJ/mol each.
The effect of one single tertiary N replacing CH is +97kJ/mol with data from the CRC Hdbk of Chem & Phys.
The heat of fusion and vaporization is nearly the same for an alkane and the homologue tertiary amine, so comparing liquid and solid pairs is legitimate.
Like in Replay #17, geminal positions reduce the heat of formation of ("stabilize" if you wish) tertiary amines.
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Tris(dimethylamino)methane HC(N(CH3)2)3 or CN(C)C(N(C)C)N(C)C has three (tertiary) amines on one carbon, hence is a geminal triamine
http://www.sigmaaldrich.com/catalog/product/aldrich/221058
https://en.wikipedia.org/wiki/Tris(dimethylamino)methane
Despite being saturated, it decomposes already at +150°C into an alkene and the unfavourable dimethylamine. Would someone see its heat of formation? This compound might be a decent rocket fuel - or a similar one, possibly with a methyl at the central carbon. Thanks!
Marc Schaefer, aka Enthalpy
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And the tetrakis has been known since 1966:
Preparation http://pubs.acs.org/doi/abs/10.1021/ja00964a071
Pyrolysis http://pubs.acs.org/doi/abs/10.1021/jo01286a107
plus 1000 hits at google with "Tetrakis(dimethylamino)methane", including Houben-Weyl.
It too decomposes around +150°C to dimethylamine and a tar, so it may have a good heat of formation as a rocket fuel. Dissolve some in (methylated?) tri(dimethylamino)methane to raise the flash point and depress the melting point?
Marc Schaefer, aka Enthalpy