Addition reactions of malonic nitriles with alkanethiol in aqueous solution
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In order to evidence new reactions of prebiotic synthesis in aqueous solution between the S-containing compounds, such as alkanethiols, which can be obtained in gaseous phase during the simulation of the evolution of primitive atmosphere, and the malonic nitriles which are generally considered as important intermediates in the Chemical Evolution, a kinetic study on the eventual reactions of ethanethiol with cyanoacetaldehyde and malononitrile has been carried out.
It appears that ethanethiol does not react directly in aqueous solution with cyanoacetaldehyde, but it gives an addition reaction with the double bond of the crotonic dimer of this malonic compound giving a thioether.
With malononitrile, ethanethiol reacts directly by addition reaction on the CN group of the monomer, producing an iminothioester. These two reactions are equilibrated. The specific rate constants and the apparent equilibrium constants for these two reactions have been simultaneously studied by UV spectrophotometry at room temperature as a function of pH.
The conditions for the formation of iminothioester will be discussed in terms of the respective pKa values of the thiol and of the malonic nitrile.
These two addition products, principally the iminothioesters, because of their hydrolysis in thioesters may have played an important role in the prebiochemical evolution.
KeywordsThiol Spectrophotometry Addition Reaction Chemical Evolution Malononitrile
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