Ethanium

In chemistry, ethanium or protonated ethane is a highly reactive positive ion with formula C
2H+
7. It can be described as a molecule of ethane (C
2H
6) with one extra proton (hydrogen nucleus), that gives it a +1 electric charge.

Ethanium is one of the simplest carbonium ions (after methanium CH+
5). It was first detected as a rarefied gas in 1960 by S. Wexler and N. Jesse. It easily dissociates into ethenium C
2H+
5 and molecular hydrogen H
2.

Production

Ethanium was first detected by infrared spectroscopy among the ions produced by electrical discharges in rarefied methane or ethane gas.

Ethanium can also be produced by irradiating methane containing traces of ethane with an electron beam at low pressure (about 2 mmHg). The electron beam first creates methanium and methenium ions. The former rapidly transfer their proton to ethane:

The latter reaction is also observed when CH+
5, N
2OH+
or HCO+
ions are injected into ethane at somewhat lower pressure.

Stability and reactions

At about 1 mmHg and 30 C, ethanium dissociates very slowly to ethenium and H
2, across an energy barrier of about 10 kcal/mol; the decomposition is considerably faster at 92 C. The decomposition has been claimed to be nearly athermal but with 8 kcal/mol of free energy due to increase of entropy.