As a youth, I read whatever chemistry books I could get hold of. One made reference to an obscure synthesis of the liquid aromatic compound benzene from coal and lye, by means of heat. This reaction would seem to be an improbable one. Can a stoichiometric equation be written for such a synthesis? The answer is, Yes. This in itself does not guarantee the reaction can actually take place.
6 NaOH + 9 C → 3 Na2O + C6H6 + 3 CO
I learned of this synthesis from an old book, possibly published in the 1800s.
Coal and Lye – What Conditions?
Such a reaction strongly suggests isolation. The reaction required considerable heat. Also, air was to be excluded, since carbon would react preferentially with the oxygen in it. And likely an excess of carbon would be used to assure reaction completion.
C + O₂ → CO₂
Plus, any benzene that would tend to form would also react with gaseous oxygen according to the reaction,
C6H6 + 6 O2 → 6 CO2 + 3 H2O
Can anyone of our readers verify this is a valid method for the synthesis of benzene? And if it is valid, can he or she hazard a guess at the mechanism involved?
Reminiscent of Acetylene
It will be recalled that acetylene gas, used in an oxy-acetylene welding, has the chemical formula H–C≡C–H. It, too, can be made in a most interesting way—by the hydration of calcium carbide. First, calcium carbide is made in an electric furnace from lime (calcium oxide, CaO) and coke (C).
CaO + 3 C → CaC2 + CO
CaC2 + 2 H2O → H–C≡C–H + Ca(OH)2
Although early preparatory methods are more often than not replaced by more modern methods in the commercial world, and even in the laboratory, it would seem prudent to retain a written record of earlier successes. Potentially helpful data should always be archived, n’est-ce pas?
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