Organic matter formed from hydrolysis of metal carbides of the iron peak of cosmic elemental abundance

Abstract

This work is a modern revisitation of an old idea of great chemists of the past such as Berthelot, Mendeleev, Cloez and Moissan: the formation of organic matter under pre-biotic conditions starting from the hydrolysis of metal carbides. This idea was originally proposed for the formation of petroleum in the Earth and was extended to other bodies of the solar system by Sokolov at the end of the 19th century. The reason for this revisitation lies in the fact that complex organic matter resembling a petroleum fraction may exist in certain protoplanetary nebulae. The present work starts with a survey of the theory of the inorganic origin of petroleum and reports on current evidence for its derivation from residues of formerly living matter, but also considers theories that admit both a biogenic and an abiogenic origin for petroleum. By considering the cosmic abundance of elements and the evidence concerning the presence of carbides in meteorites, we discuss the formation, structure and hydrolysis products derived from the metal carbides of the iron peak of cosmic elemental abundance. Chromium carbide (Cr₃C₂) has then been used as a model compound for all the key carbides of the iron peak of the cosmic abundance (Cr, Fe, Ni, V, Mn, Co) and it has been hydrolysed under different conditions and the hydrocarbons formed have been analysed using electronic spectroscopy, high-performance liquid chromatography with a diode-array detector (HPLC-DAD) and by Fourier-transform infrared (FT-IR) spectroscopy. Methane, a series of about 20 different alkenes with single and conjugated double bonds have been detected. Paraffins are formed simultaneously with the alkene series but no acetylenic hydrocarbons have been detected. This study confirms early works considering the easy hydrolysis of the carbides of Cr, Fe, Ni, Mn and Co with the formation of H₂, a series of alkanes including methane and a series of alkenes including ethylene. The peculiar behaviour of copper carbide (copper is inside the iron peak of the cosmic abundances) has been discussed as well. A survey of the hydrolytic behaviour of other carbides has been included so that all lanthanides and actinides are considered as well as carbides of the second and third groups of the periodic table of elements and highly refractory carbides such as those of Ti, Zr, Ta and W have been briefly discussed. Furthermore, the hydrolysis of mixed metal carbides and nitrides is discussed, which gives a mixture of extremely interesting molecules that are considered the raw materials for the formation of the molecules of life: guanidine, methyl hydrazine, formic acid, hydrogen cyanide, urea, cyanamide, methylamine and formaldehyde. The hydrolysis of metal carbides has also been discussed within the framework of other reactions that are well considered in the present day in an astrochemical context: the ion–molecule reaction, the Miller–Urey and the Sagan–Kaare synthesis as well as the catalytic Fischer–Tropsch synthesis and the radiation-driven Fischer–Tropsch synthesis.