The First Inexpensive, Simplified and Large Scale Synthesis of p-tert-butylcalix[7] and [9]arenes

The nuclear industry and the rare earth elements mining need methods in order to separate lanthanides and actinides. Large organic macrocycles have demonstrated their contribution to this domain. Due to the lack of an efficient and reproducible method of synthesis, the chemistry of large p-tert-butylcalix[n] arenes (with 6 < n < 10) has been much less explored than the one of their inferior homologs. Excepted for the p-tert-butylcalix[8]arene which is obtained in good yields, the procedures described in the literature for the preparation of p-tert-butylcalix[7] and [9]arenes involve many steps of purification and lead to, in the very best case, a couple of grams of product, after one month of labor. In this work, a set of experiments with varying parameters has demonstrateed the crucial role of the solvent and of the amount of catalyst in the macrocyclization reaction. Then, a scale-up study was done, the procedure being adapted and realized on a semi industrial scale reactor. Finally, an original purification pathway avoiding the numerous silica-gel chromatographies and recrystallizations was set up and optimized. This simplified procedure opens gateways for the preparation of a few dozen grams of pure p-tertbutylcalix[7] and [9]arenes and should lead to the preparation of new selective complexants.