|It is one of these classic Organic Syntheses preps: para-t-butyl-8-calixarene (DOI). Just take para-tert-butylphenol, paraformaldehyde, sodium hydroxide and xylene, stir and reflux and out comes the wonderfully vase shaped molecule. In a recent JOC contribution Cornelius Haase has been re-investigating this reaction and claims to have found the industrial scale recipe with top yields and more importantly top purities (DOI). To be fair the 1990 Gutsche prep is pretty basic involving no purification whatsoever. The authors note that the melting point is not consistent and the product riddled with impurities. What is Haase doing differently? Less excess of formaldehyde, xylene solvent replaced by diethylether / xylene (bringing down the boiling point, xylene sticking around for azeotropic water removal), tetraethylammonium hydroxide catalyst added, concentration increased (as long as the mixture can stir) and reaction time considerably increased. The Gutsche prep has 4 reflux hours and the new prep has 12 hours of reflux and then another 10 hours of distillation. According to Haase the first phase grows all the linears and the second phase the cycles. And the results: 81.2% yield with 98% HPLC purity versus 62-65% and unknown purity.
Note: a 100 gram scale is hardly industrial, expecting 1000 Kg follow-up in Organic Process Research & Development. |