INFLUENCE DE LA SOLVATATION PAR LE TERT-BUTANOL SUR LA STRUCTURE ET LA REACTIVE DE L'ENOLATE DE POTASSIUM DE L'ACETYLACETATE D'ETHYLE EN PRESENCE DE COURONNE OU DE CRYPTAND. ETUDE PAR SPECTROMETRIE INFRA-ROUGE ET CINETIQE.

Article abstract of DOI:10.1016/0040-4020(80)80058-5

The structure and the nucleophilic reactivity of crowned (18-crown-6) or crypted potassium ethyl acetoacetate enolate have been compared in tert-butanol and in DME (or THF).In the protic solvent tert-butanol, the crowned and the cryptated potassium enolate species both exist as loose ion pairs in which the enolate anion, strongly hidrogen-bonded to the solvent, is in a "transoid" (non chelating) conformation.Both species show similar reactivities towards alkylating agents but completely different reactivities are observed in aprotic weakly dissociating media (THF, DME).In contrast to what is observed in tert-bu tanol, the cryptated species and the crowned species have very different nucleophilic reactivities in THF or DME: in those solvents only the cryptated species retains a loose ion pair structure; the crowned species is a contact ion pair in which the enolate anion chelates the potassium cation.The solvatation of this crowned chelate species by tert-butanol has been demonstrated in binary mixtures of solvents (C6D6-t-BuOH, THF-t-BuOH).The oxygen basicity of the enolate anion is very different in the crowned chelated ion pair compared with the cryptand separated ion pair.