On the reaction of furan with bromine in aqueous solution. Observation of the slow hydration of malealdehyde

Abstract

Thc rate of rcaction of furan with brominc in aqueous solution has bcen measurcd and thc ratc constant obtaincd by Williamson and Collcr is confirmed. Howcvcr. it is now found that thc rcaction of brominc with furan in watcr has two distinct stages: attack of brominc leading to the formation of malealdehyde 3 and hydration of 3 to a 2: 1 mixture of thc geometrical isomers of its cyclic hydrate 4. This second, slower process is observable by stopped-flow uv spectrophoton~etry occurring aftcr the consumption of bromine. The observed kinetics are vcry similar to thosc rcccntly found for thc analogous hydration of phthalaldchydc by McDonald and Martin.OSWALD S. TEE et B. E. SWEDLUND. Can. J. Chem. 61, 2171Chem. 61, (1983.On a mesuri la vitesse de la rCaction du furanne avec Ic brome en solution aqueusc et on a confirm6 la constantc de vitesse obtenue par Williamson et Coller. Cependant on trouve maintenant que la rCaction du brome avec le furanne dans I'cau a deux Ctapes distinctes: I'attaque du brome qui conduit B la formation du malCaldChyde 3 et I'hydratation du composC 3 qui conduit ? I un mClange 2: 1 des isomkres gComCtriques de son hydrate cyclique 4. Cc sccond processus. le plus lent, peut Ctre obscrvd par la spectrophotomdtrie uv a flux stoppd que I'on utilise apres la disparition du brome. Les cindtiqucs observees sont scmblables h cclles trouvCes rCcemment pour I'hydratation analogue du phthalaldehyde par McDonald ct Martin.[Traduit par le journal]The halogenation of furans is complex with the nature of products varying widely with the substrate, reagent, solvent, and reaction conditions (1 -4). However, two broad classes of reaction may be recognized, viz. addition and substitution, with the former often leading to ring-opening (1 -4).Bromination of furan in CCI, gives a mixture of 2-bromoand 2,5-dibromofuran (5). Using ' Hmr spectroscopy, Baciocchi et nl. (6) observed the formation of 1,4-and 1,2-dibromo adducts from furan and bromine in the nonnucleophilic solvent carbon disulphide, at low temperature. With time, and on warming, the adducts underwent elimination to 2-bromofuran (6). In hydroxylic solvents the reaction of furan (1) follows a different course. With bromine (or chlorine) in an alcohol solvent at low temperatures, reaction leads to the formation of a that bromination of methyl furoate in 50% aqueous acetic acid gives the substitution product, eq. [3], the same product as can be obtained under other reaction conditions (12).We have begun to study the bromination of furans systematically to try to ascertain why some derivatives undergo addition, whereas others show substitution. Our initial approach to this problem was to study the effect of substituents and solvents upon the rate of br~mination.',~ To anchor a correlation of results for aqueous solution a reliable value for furan was required.' During measurement of this value we found that another, slower process is observable, which is the subject of the present paper. Results Kinetic studies 1 2We first measured the second-order rate c...

Identification of cis-2-Butene-1,4-dial as a Microsomal Metabolite of Furan

“…The NMR spectrum revealed loss of the aldehydic and vinylic proton signals and appearance of new signals at 6.16, 6.15, 6.14, and 5.86 ppm. These singlets were assigned to the cisand irans-isomers 3 (19). Isomerization to trans-2butene-1,4-dial (5) was minimal in 24 h at room temperature.…”

“…Isomerization to trans-2butene-1,4-dial (5) was minimal in 24 h at room temperature. Therefore, 4 exists as hydrates 3 under physiological conditions (19).…”

“…The acetone solution was added to 20 mM deuterated phosphate buffer (pD 7.4). The acetone was removed under reduced pressure (5-10 min), and NMR spectra were obtained at various time points between 0 and 24 h. Only a 1:1 ratio of the cis-and trans-isomers of the cyclic cis-2-butene-1,4-dial hydrate (3) was observed (a 2:1 ratio of cis-to iroras-hydrate has been reported (19)): 1H NMR (D20) <5 6.16, 6.15, 6.14 (s, cis-and frarcs-vinylic and trans-methine protons), 5.86 (s, cis-methine proton).…”