Carbon suboxide, decomposition

Reactions. Heating an aqueous solution of malonic acid above 70°C results in its decomposition to acetic acid and carbon dioxide. Malonic acid is a useful tool for synthesizing a-unsaturated carboxyUc acids because of its abiUty to undergo decarboxylation and condensation with aldehydes or ketones at the methylene group. Cinnamic acids are formed from the reaction of malonic acid and benzaldehyde derivatives (1). If aUphatic aldehydes are used acryhc acids result (2). Similarly this facile decarboxylation combined with the condensation with an activated double bond yields a-substituted acetic acid derivatives. For example, 4-thiazohdine acetic acids (2) are readily prepared from 2,5-dihydro-l,3-thiazoles (3). A further feature of malonic acid is that it does not form an anhydride when heated with phosphorous pentoxide [1314-56-3] but rather carbon suboxide [504-64-3] [0=C=C=0], a toxic gas that reacts with water to reform malonic acid. 

The decompositions of C302, CO, C02, CS2, COS, CSe2 and COSe are dealt with in this section. Apart from carbon suboxide, this is a group of stable, un-reactive compounds. Considerable emphasis has been placed on the investigation of the photolytic decompositions of some of these compounds which are thought to provide useful sources of atoms (C, O, S and Se) and free radicals (C20). The photochemistry of carbon dioxide has particular relevance to the chemistry of planetary atmospheres, although to date the mechanism of C02 photolysis remains obscure. 

Carbonic Acid.—Berthelot1 observed the decomposition into carbon monoxide and oxygen. The reaction is reversible, an equilibrium occurs, in which, however, the partially ozonized oxygen converts carbon monoxide into carbonic acid and a solid carbon suboxide, C4O3, which Brodie 2 had already formerly observed. Carbon dioxide, under a pressure of 3-10 mm. mercury, splits up very rapidly and up to 70 per cent, into carbon monoxide and oxygen (Norman Collie 3). 

Using an apparatus constructed on the same principles, Ott and Schmidt99 prepared carbon suboxide C302 by thermal decomposition of diacetyltartaric anhydride on a feebly glowing platinum catalyst — the nature of chemical reaction is obscure. 

M. Shao et al. [59] have synthesized CNTs in a new way using an iron catalyst at the extremely low temperature of 180 °C. In this process, carbon suboxide was used as carbon source, which changed to freshly formed free carbon clusters through disproportionation. The carbon clusters grow into nanotubes in the presenee of Fe eatalyst, whieh was obtained by the decomposition in iron carbonyl at 250 °C under a nitrogen atmosphere. 

---