I'm using the protocol of Tianqi et al. (dimerisation of mandelic acid by 3 days of reaction in mixed xylenes while removing water byproduct by means of a Dean-Stark trap), but for some reason, on average, I keep obtaining an excess of racemic mandelide instead of the 50% meso-mandelide that was mentioned in the article. Additionally, even after three recrystallisations the meso-fraction still contains a lot of rac. mandelide which is detrimental for the polymerisation.
Any tips and hints in this regard are most welcome.
Article Synthesis of Polymandelide: A Degradable Polylactide Derivat...
Meso-mandelide is the R,S-dimer.
R,R and S,S mandelide form a racemic mixture, which is less suitable for polymerisations.
I did my doctoral work on the kinetics of mandelic acid esterification. The RR and SS cyclic dimers precipitate during esterification in benzene, which you probably know. I regret that I do not know how to isolate the RS cyclic dimer.
sorry
john
Dear John,
I guess the precipitation of RR and SS mandelide from benzene is indeed quite similar to the synthesis of mandelide in mixed xylenes, so I'm interested in your work on the kinetics, since I'm trying to further optimise the synthesis. Have your results been published?
The RS compound is somewhat more soluble in xylenes, so after filtration of the racemic mandelide and subsequent removal of the solvent under vacuüm, you obtain crude meso-mandelide, but this fraction still contains a lot of the RR and SS isomers.
But anyway: many thanks for your reply.
Kind regards,
Geert-Jan
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