Alder carbon-hydrogen activation

These reactions do not occur at lower temperatures because of activation energy barriers and because H2 becomes the dominant form of hydrogen. Aromatic species are produced initially from acetylene via Diels-Alder type processes, in which a two-carbon and a four-carbon hydrocarbon condense into an aromatic species. Once PAHs are synthesized, they may continue to grow to form carbonaceous small grains. 

Alder, J.F., Fielden, P.R., and Smith, S.J. (1988). The adsorption of hydrogen cyanide by impregnated activated carbon cloth. Part I studies on cobalt and nickel acetatates as impregnants for hydrogen cyanide removal. Carbon, 25, 701-11. 

In the first step, the oxaloacetic acid is decarboxylated.Thereby, the enolate form of the pyruvic acid is stabilised with a magnesium ion in the macro-phomate-synthase. This then undergoes the DIels-Alder reaction with the pyrone favourably positioned for the cycloaddition, while the enzyme is activated by hydrogen bonding. The anf/ -elimlnation of water and carbon dioxide leads ultimately to macrophomic acid. 

Tetracyclo[3.3.0.0. 0 ]oct-7-ene gives various dihydropentalenes upon pyrolysis with an estimated activation energy of 38 kcal/mol apparently by a retro Diels-Alder reaction followed by hydrogen and carbon shifts (Scheme 9.21)." ... 

Anstice, P.J.C., and Alder, J.F., The effect of sulphur dioxide exposure under controlled environmental conditions on the challenge performance of copper- and chromate-impregnated active carbon against hydrogen cyanide, Adsorpt. Sci. Technol., 15(7), 531-540 (1997). 

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