99618-41-4

Upstream product

• 24531-81-5 4'-methoxyflavylium ion 
• 99618-46-9 (Z)-3-(2-Hydroxy-phenyl)-1-(4-methoxy-phenyl)-propenone 

Downstream Products

• 99618-46-9 (Z)-3-(2-Hydroxy-phenyl)-1-(4-methoxy-phenyl)-propenone 
• 24531-81-5 4'-methoxyflavylium ion 

Relevant academic research and scientific papers

Hydration of the Flavylium Ion. 3. The Effect of 3-Alkyl Substitution

An investigation is reported of the transformations undergone by four flavylium salts-two 3-methyl-substituted cations, the 3-methylflavylium ion, and the 4'-methoxy-3-methylflavylium ion-and two cations where an ethylene unit bridges the 3-position and the 2'-position of the phenyl ring, the 5,6-dihydrobenzoxanthylium ion, and the 3-methoxy-5,6-dihydrobenzoxanthylium ion.Three transformations have been identified and studied-a rapid and reversible hydration of the cations to produce a pseudobase, the rapid reversible ring opening of this pseudobase to a (Z)-chalcone, and the slow irreversible cis-trans isomerization of this species to an (E)-chalcone.Rate and equilibrium constants have been obtained for these processes and compared with values previously obtained for 3-H-substituted flavylium ions, the parent flavylium ion itself, and the 4'-methoxyflavylium ion.There is little effect of the alkyl substitution on the pseudobase: (Z)-chalcone equilibration.The ethylene-bridged systems undergo cis-trans isomerization at a similar rate to the 3-H systems, while the 3-methyl systems undergo this reaction about 30 times more slowly.The most significant effect, however, is seen on the flavylium ion hydration equilibrium, the bridged cations being about 2 orders of magnitude more stable than their 3-H-substituted counterparts with these in turn 2 orders of magnitude more stable than the 3-methyl analogues.To explain this, it is proposed that there is a steric interaction involving the 3-hydrogen or 3-methyl substituent and an ortho hydrogen on the nearby phenyl ring, resulting in a twisting of this ring so that it is not coplanar with the benzopyrylium portion of the cation.

Hydration of the Flavylium Ion

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.