6272-41-9Relevant articles and documents
Photoreactions of 3-(2-hydroxyphenyl)-1-(substituted phenyl)-2-propen-1-ones (substituted 2-hydroxychalcones) in organic solvents in the presence and absence of acid
Matsushima,Murakami
, p. 2215 - 2219 (2000)
Absorption spectra and photochemical reactivities of a dozen 3-(2-hydroxyphenyl)-1-(substituted phenyl)-2-propen-1-ones (substituted 2-hydroxychalcones) have been investigated in organic solvents in the presence and absence of added acid. Upon UV irradiation in the presence of 5 mM perchloric acid, flavylium ions were formed in high quantum yields around 0.34, regardless of the nature of the substituents. Upon irradiation in neutral solution, on the other hand, amino-substituted chalcones gave photo-Z-isomers as thermostable products, while the majority of other chalcones gave cyclic hemiacetals (2-hydroxy-2-phenyl-2H-1-benzopyranes). The quantum yields for the photochemical E/Z isomerization in the neutral solution were comparable to those in the acid solution, except for the amino-substituted chalcones which revealed lower quantum yields. Remarkable hypsochromic shifts were observed for the absorption spectra of the amino-substituted chalcones upon addition of acid, reflecting protonation on the amino group.
Hydrolysis of Benzopyrylium Dyes - An Application of the Concept of Chemical Hardness
Lietz, Heike,Haucke, Guenter,Czerney, Peter,John, Birgit
, p. 725 - 730 (2007/10/03)
A systematic study on the relationship between the substitution pattern, the pKa values, and spectral properties of flavylium cations and the respective-(CH2)2-bridged analoga (5,6-dihydrobenzo[c]xanthylium cations) is given in order to find rules concerning their spectral behaviour and their chemical reactivity. Our results show that the concept of chemical hardness can explain the different reactivity of 4′- and 7-substituted flavylium ions against HO-. The pKa values of these species, which can act as a measure of reactivity with respect to a nucleophile, correlate linearly with the absolute hardness calculated from half the energy gap between the frontier orbitals. Since the longest-wavelength UV/VIS absorption maximum is mainly determined by the HOMO-LUMO transition, an analogous linear correlation is obtained between the spectral 0-0 transition and the pKa value. Deviations from these correlations are assumed to be due to steric effects.
Hydration of the Flavylium Ion
McClelland, Robert A.,Gedge, Sherrin
, p. 5838 - 5848 (2007/10/02)
A spectral and kinetic investigation has been carried out of the transformations undergone in aqueous solution by the parent flavylium ion and its 4'-methyl and 4'-methoxy derivatives.Evidence is reported for the existence at some time under some condition of seven species, the flavylium ion (F+), two pseudobases, a 2-hydroxy adduct (B2) and 4-hydroxy adduct (B4), the cis-2-hydroxychalcone and its ionized form (cC and cC-), and the trans-2-hydroxychalcone and its ionized form (tC and tC-).At pH 6.5-8.5, F+ is relatively rapidly hydrated producing a mixture of B4, B2, and cC.The latter two are in equilibrium, their equilibration proceeding far more rapidly than F+ is hydrated.B4 is a kinetic product of the hydration only; over a short period of time it rearranges via F+ to the equilibrium mixture of B2 and cC.In base solution the behavior is similar, but the B2 cC equilibrium is displaced toward the chalcone since it ionizes.Thus, at pH 12, F+ reacts very rapidly with OH- producing a mixture of B4 and cC-, the latter coming from B2 initially formed.This is followed by the rearrangement of B4, the kinetic product, to cC-.In acid solutions, pH 2-6, an acid-base type equilibrium is relatively rapidly established between the cationic F+ and the neutral species B2 and cC.In all of these solutions, with the exception of strong acids, a slow further reaction occurs resulting eventually in complete transformation to tC or, in base, tC-.The upper limit on the relative amount of cis-chalcone or pseudobase present in equilibrium with the trans-chalcone after complete reaction is 0.02percent.For a scheme B4F+B2cC(cC-)-->tC(tC-), rate constants and equilibrium constants for each reaction stage have been obtained by a kinetic and spectral analysis.