JohnWW
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How Many Carbon Oxides?
Everyone knows about CO2, produced by the complete combustion of carbon or its compounds; and CO, produced by partial combustion of same (or as a
constituent of coal gas by the reaction of hot coke with water, or as the anhydride of formic acid).
What about other compounds containing only C and O? As far as I am aware, there are two others:
(1) Carbon suboxide, C3O2, an evil-smelling poisonous gas, formed in small quantities along with CO in the incomplete combustion of some materials
(and also by the high-temperature catalytic dehydration of malonic acid, similarly to the dehydration of acetic acid to produce ketene ay 700ºC with
P2O5 or AlPO4), which has a O=C=C=C=O structure, resonance-stabilized with two alternative canonical arrangements in which there are alternating
single and triple bonds and opposite charges on the O's; and
(2) Mellitic anhydride, C6(C2O3)3, which is the anhydride of mellitic acid, C6(COOH)6, which can be formed by the oxidation of graphite with nitric
acid and is also found naturally occurring in coal deposits.
Note that CO is also the high-temperature dehydration product of formic acid, HCOOH, formed in a similar manner to the dehydration of acetic acid to
ketene.
Regarding other possibilities:
In addition to C3O2, the suboxides C5O2, C7O2, etc., could exist with similar resonance-stabilized structures, although they have not, as far as I
know, been isolated.
Also, oxalic acid, HOOC-COOH, could theoretically dehydrate to form a cyclic
dimeric anhydride, C4O6, which would be also dioxane tetraketone, but as far as I know it has not been isolated because oxalic acid decomposes at the
required temperatures.
There are other theoretical structures, like trioxane triketone C3O6, naphthalene octocarboxylic acid anhydride C10(C2O3)4, etc., but I have not heard
of their being isolated. Does anyone know of any others? In addition to these ether-ketones and acid anydrides, there may be epoxides and peroxides
and ozonides containing no hydrogen.
John W.
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BromicAcid
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I remember from the book "Preparative Inorganic Chemistry" there are procedures for producing several of the suboxides of carbon by heating
graphite powder with a calculated quantity of oxygen, some of them have intense colors as I remember. At the time I last had the book in my
possession I really didn't have much interest in the topic and as a consequence I just skimmed the properties and such, but I found it
interesting that there were other oxides of carbon.
However they may not have been true stoichiometric compounds, mixed oxides most likely, but I don't remember.
I also know there are certain bucky ball oxides but I cannot recall any useful information on the subject.
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chemoleo
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I like little mindgames like that!
Damn, but JohnWW came up with nearly all! Except this theoretical polymer, which are basically fused trioxane rings :
[=C(O-CO-O)2C]n , or [C(O-CO-O)2]n
That reminds me, I have not seen many C(OR)4 compounds (or neither C(OH)4, there corresponding acid). Is that because the oxygen has a great tendency
to SP2 hybridise? In the case of C(OR)4, would this always react to form (RO)2CO and ROR?
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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sheldonwhite
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| Quote: | Originally posted by chemoleo
That reminds me, I have not seen many C(OR)4 compounds (or neither C(OH)4, there corresponding acid). Is that because the oxygen has a great tendency
to SP2 hybridise? In the case of C(OR)4, would this always react to form (RO)2CO and ROR? |
Things like ethyl orthoformate C(OEt)4 are well known, but easily hydrolysed. I'm sure it gets increasingly hard to make bulkier esters;
there's just not much room around a carbon atom!
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unionised
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Ethyl orthoformate is HC(OEt)3. You need to get the orthocarbonate to get all 4 alkoxy groups.
This site
http://gltrs.grc.nasa.gov/cgi-bin/GLTRS/browse.pl?1997/TM-11...
gives some information about graphite oxides.
[Edited on 12-8-2004 by unionised]
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JohnWW
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I have come across another carbon oxide - this time another solid one. Is is the polymer of C3O2 (Carbon suboxide); to see structure:
http://www.geocities.com/ismkarimi/xfactor/xfactor3.htm
However, polymer or polymerization of C3O2 or carbon suboxide produces less
than 10 results when searched for on Google. Its polymerization to an intensely yellow or red solid, (C3O2)n, can be induced by ionizing radiation at
25ºC, accompanied by mild pressure for best results (otherwise a substantial part decomposes to the reactive diradical C2O). The structure of C3O2,
obtained as a poisonous evil-smelling lachrymatory
gas by high-temperature catalytic dehydration of malonic acid with P4O10, and in small amounts along with CO by incomplete combustion of carbon, is
O=C=C=C=O (which is resonance-stabilized to some extent through the end Os being alternately positively and negatively charged and neutral). It forms
a "ladder" polymer, which is paramagnetic
(delocalization of unpaired electrons can account for its color), but there are other modes by which it can polymerize, with multi-inter-chain linking
and cyclopropane and epoxide rings being possible. Both the
suboxide and its polymer react with water, and are light-sensitive.
There is also a somewhat similar solid polymeric compound containing only C and N. It is called paracyanogen, (CN)n, and its structure is given at http://www.geocities.com/ismkarimi/xfactor/xfactor4.htm . There are 895 results for paracyanogen on Google.
This polymer has a condensed polycyclic structure and is made with small amount of impurity by heating cyanogen gas at 800'C. It cannot have
macroscopically long chains of conjugated double bonds, and so cannot be electrically conducting. A different source says it is obtained as a brown or
black amorphous residue by heating mercuric cyanide, and that it has the infinite-chain structure -C=N-C=N-C=N-C=N-. Because the double bonds in the
latter case are conjugated, and can be exchanged with the single bonds, which allows free migration of pi electrons over the length of the molecule,
macroscopically long molecules of it should be electrically conducting along the direction of the chains, like graphite, and like polyacetylene if it
could be made. Its brown or black color reflects its electrical conductivity. It could react with alkali metals to form infinite-chain ionic secondary
amides, but it would reduce the double bonds to single, with loss of electrical conductivity in the solid phase (although in the liquid phase the
alkali metal ions' motions would provide conductivity).
There are also solid polymeric compounds containing only C and F. There is the well-kknown polytetrafluoroethylene (CF2)n, made by polymerization of
C2F4. In addition, there is "Graphite monofluoride", CFx (x = 0.63-0.99), producing 23 results on Google, obtained by reacting graphite with
F2 at 400-500ºC. The stoichiometric form (CF)n would be theoretically obtainable if single infinite-plane sheets of graphite could be completely
reacted with F2 so as to reduce all the double bonds to single bonds, with a F attached to each C. Its electrical conductivity would be lost, with the
sp2 hybrid bonding becoming sp3. Its structure is at http://www.geocities.com/ismkarimi/xfactor/xfactor2.htm . It is
amenable to both C-13 and F-19 NMR study. Then there is fullerene fluoride, C60F60, obtained in a similar manner as a crystalline solid with m.pt.
287ºC, but differing in being spherical rather than an infinite-sheet compound; http://www.webelements.com/webelements/compounds/text/C/C60F... . A partially fluorinated form is C60F48, http://edu.ioffe.ru/conf/iwfac2001/page_254.pdf . It gives 6 results on Google. These compounds are likely to be usable as high-temperature
lubricants.
John W.
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