7/2/2012 - Synthesis of Geosmin

The scent of rain is a very familliar odour for most, but most of those people have no clue why rain smells and question why rain should smell at all, it's just water.  Well the smell doesn't come from the rain itself, but from the soil below it.  The molecule in this scent is Geosmin, which also makes soil smell the way it does.  It is synthesized by microbes in the ground and when the rain disturbs the soil, this molecule gets released into the air.  Now chemists have found a way for us to make this molecule without the help of our little friends in the soil.  It all begins with a simple condensation reaction with ethyl vinyl ketone, and 2-methyl-cyclohexanone in presence of sodium ethoxide (NaOEt) creating the second ring.  But now there is an extra ketone on that second ring, so a second step of a special reduction method is required.  This involves the addition of (CH₂SH)₂ with BF₃ to create a thioketal derivative, and then desulfurization with Raney Nickel.

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