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Complexes of Crown Ethers with Uronium Salts: Preparation and Crystal Structure of 18-Crown-6 Uronium Nitrate (1:1) and Benzo-27-Crown-9 Uronium Perchlorate (1:1)

Wiley-VCH Verlag
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PII: S0040-4020(01)89995-6 Tetrahedron Vol 43. No 3. pp. 617 lo 624. 1987 OO4&4020!87 13 00+ 00 Prlntcd I” Grea1 kitam. Pergamon Journals Ltd. LIqUIDLIQUID PBASB TRANSFER Op DRINIIII SACL'S VIA CXMPIgxATIoN BY (DI)BENYO CRCBBI BIBBBB; x-RAYsTRacmRg CP TREBRC4W27_CIEOm-9 lJRGtmm pgA[RmRATE (1:l) CDuPLex Veronika M.L.J. Aarts,a Jan Geevers,a David N. Reinhoudt, *a Wim Lengton, b Martinus BOS ,b Jos W.H.M. Uiterwijk,' and Sybolt HarkemaC Laboratories of aOrganic Chemistry, bChemical Analysis, and 'Chemical Physics, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands (Receiced in UK 10 December 1986) Abstract - The canplexation of uronium perchlorate with crown ethers of different ringsizes (18-33 ring atcans) has been studied by using two-phase extraction experiments. Crown ethers with 27 or more ring atans are the best hosts to transfer uronium salts from an aqueous phase to an organic phase. The amount of uronium perchlorate transferred was measured by coulanetric titration of the stoichicmetric amount of ammonia produced by enzymatic degradation of urea. The crystal and molecular structure of the 1:l canplex of uronium perchlorate with benzo-27-crown-9 has been determined by X-ray crystallography. The uronium cation is encapsulated in the crown ether cavity with all its hydrogen atoms bonded to the macrocyclic host. A 1:l complex of uronium picrate with benzo-21-crown-7 was isolated and is assumed to be a perching complex. Introduction In relation to our work on the synthesis of macrocyclic receptor molecules for the selective complexation of urea we have recently reported the synthesis and X-ray structures of the complexes of urea with 18-crown-6 and with aza-18-crown-6, both with a 5:l stoichianetry.lt2 We have also shown that canplexes of crown ethers with neutraLmolecules, such as nitranethane, acetonitrile, and malononitrile, are rather weak compared with complexes with charged molecules. 3 This is also the

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