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Industrial scale calixarenes

05 January 2020 - Orgo

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.

2D ice growth revealed

04 January 2020 - Physical chemistry

klik hier voor de afbeelding op ware grootteEver wondered how a two-dimensional nanosheet of ice grows on the edges? With a good sense of public relations (submitted to Nature in May but published online January 1 2020, first research article in a new decade) Runze Ma et al. (DOI) have tried to find out. They grew a 2D hexagonal bilayer of ice at 120 Kelvin on a layer of gold inside an STM. Nothing new thus far but with improved resolution of the STM setup it was possible for the first time to visualize the edges.

They were found to exist as equal parts zigzag and armchair. For comparison carbon nanotubes are also hexagonal and can also be of an armchair or a zigzag type. At 120 Kelvin the edges continue to grow but by further freezing to 5K it was possible to observe the dynamics of edge growth. Zigzag edges grow by adding pentagons which then mature into new hexagons. Armchair edges first morph into pentagon-heptagon-pentagon-hexagon structures. They also have more kinks and defects. The authors also speculate on expansion of the results to 3D ice but warn that imaging 3D ice growth this way would be exceedingly difficult.