Electrophilic Attack on the Furan Ring. Acid-Catalysed Protodedeuteriation, Protodetritiation, Deuteriodeprotonation, and Deuteriodetritiation at the alpha-Position. Hydrolytic Cleavage of the Ring.

On the Brønsted Acid‐Catalyzed Homogeneous Hydrolysis of Furans

“…[1] Thus, the selectivity and general applicability of the process with furans other than DMF depends on how susceptible furans are to hydrolysis or polymerization. [4][5][6][7][8][9] The hypothesis that, unlike other vinyl ethers, the hydrolysis of furans follows specific acid catalysis has been refuted. [3] Because of its importance, the hydrolysis of furans has been debated quite vigorously, but many aspects of the mechanism remain uncertain.…”

“…[4][5][6][7][8][9] The hypothesis that, unlike other vinyl ethers, the hydrolysis of furans follows specific acid catalysis has been refuted. [4,8] We are not aware of any insights into the mechanism of the reaction obtained by quantum-chemical calculations. By following the hydrolysis of 2-methylfuran by NMR spectroscopy in isotopic water, general acid catalysis via a-carbon protonation was also excluded on the grounds that the rate of ring opening is two orders of magnitude slower than the furan's rate of deuterium uptake at the C5 carbon.…”

“…The calculations were performed in Gaussian 09 (Rev. [4] The fact that protonation at the a-carbon is faster than at b-carbon, and that the acarbon-protonated species (II a ) is a stable intermediate, implies that formation of II a should precede the ring opening. [11] Calculation details and Cartesian coordinates of all ground and transition states can be found in the Supporting Information.…”

On the oligomerization mechanism of Brønsted acid-catalyzed conversion of furans to diesel-range fuels

“…On the other hand, 2,5-DMF may only undergo hydrolysis to 2,5-hexanedione [11], since the methyl substituents on the ␣-carbons of the ring inhibit electrophilic substitution on account of not being good leaving groups (Fig. S3).…”

“…It has been suggested that during oligomerization, one furan molecule first undergoes hydrolytic ring opening and then reacts with two closed-ring furan molecules, one at a time [2,10]. It is, however, not clear why certain furans, e.g., MF, form oligomers and polymers while others like 2,5-dimethylfuran (2,5-DMF) do not [11]. The rate-determining step is also unknown.…”