A. Kankaanpera et al., Ureas and amides as dipolar aprotic solvents in highly basic media. The dependence of kinetic basicity on solvent composition, J CHEM S P2, (2), 1999, pp. 169-174
Citations number
25
Categorie Soggetti
Physical Chemistry/Chemical Physics
Journal title
JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2
The basicity of dipolar aprotic solvent-water-HO- systems with amides and u
reas as the organic component has been studied kinetically because previous
information is not available, excluding some H- values measured for aqueou
s dimethylformamide (DMF) and tetramethylurea (TMU). It was found that the
increase in basicity with the mole fi action of organic component is at lea
st of the same magnitude as in aqueous dimethyl sulfoxide (DMSO). For insta
nce, in the detritiation of chloroform-t the slopes of the plots log(k(2)/m
ol(-1) dm(3) s(-1)) vs x(urea) varied between 11.4-14.6 (as compared to 11.
0 in aqueous DMSO) when TMU and cyclic ureas, 1,3-dimethylimidazolidin-2-on
e (DMI) and 1,3-dimethyl-3,3,5,6-tetrahydropyrimidin-2(1H)-one (DMPU), were
used as the organic component in solvent mixture. In aqueous TMU acidity f
unctions H- were extrapolated from kinetic results using linear free energy
correlations. Agreement with literature values was evident. This method wa
s also used to extrapolate the H- values in aqueous DMPU. On the basis of p
resent work aqueous ureas can be recommended as solvents in highly basic me
dia. The utility of amides, dimethylformamide and dimethylacetamide, is lim
ited by their instability in basic water solutions.