Naslov
Protonation and anion complexation equilibria of aromatic urea derivatives in solution

Autori
Bregović, Nikola ; Barišić, Dajana ; Cindro, Nikola ; Juribašić Kulcsar, Marina ; Tomišić, Vladislav

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, sažetak, znanstveni

Izvornik
European Winter School of Physical Organic Chemistry / - , 2017

Skup
European Winter School of Physical Organic Chemistry

Mjesto i datum
Bressanone, Italija, 29.01.2017. - 03.02.2017

Vrsta sudjelovanja
Poster

Vrsta recenzije
Nije recenziran

Ključne riječi
urea derivatives ; protonation ; anion complexation ; thermodynamics ; stability constants

Sažetak
The anion complexes are constantly in the spotlight of supramolecular chemistry research, being utilised in most different ways: controlling molecular motion, catalysing chemical reactions, allowing qualitative and quantitative detection of specific species, etc.3 It has been recognised that systematic thermodynamic studies of complex formation reactions are of great importance in the process of developing novel anion receptors with enhanced properties, thus expanding the possibilities of their application. This includes the identification and characterisation of diverse reactions coupled with the anion binding processes, such as proton transfer, ion pairing or aggregation, which have often been disclosed, but were rarely thoroughly studied. In this work we present the synthesis of a series of aromatic diureas (Scheme 1) and a detailed thermodynamic study of their deprotonation and binding of anions (dihydrogen phosphate and acetate) in DMSO by UV-Vis and NMR titrations. In contrast to the common assumption that the dissociation of urea group is highly unfavourable (pKa (urea) = 26.9), it was found that aromatic urea derivatives can be readily deprotonated in the presence of many bases. Namely, it was determined that the pKa values of the herein studied aromatic compounds bearing urea moieties were in the range of 13.1–15.27. Significant stabilisation of the anionic forms was attributed to the electron delocalisation through the aromatic substituents. It was found that fully protonated forms of the receptors form mono- and di-anionic complexes with H2PO4– and AcO– in DMSO. Proton-transfer processes were taken into account in the analysis of the gathered titration data rendering reliable complex stability constants. The results were discussed with respect to the substituents on the pendant arms of the receptors (R = H, OCH3, CH3, NO2) and relative positions of the urea groups (ortho- and meta- derivatives).

Izvorni jezik
Engleski

Znanstvena područja
Kemija

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