General acid catalysis in benzophenone ketal hydrolysis

Wolfe, R. H.; Ivanetich, Kathryn M.; Perry, Noreen F.

doi:10.1021/jo01256a015

Cited by 12 publications

(6 citation statements)

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“…Acid-catalyzed reactions that involve formation of a carbonium ion intermediate can in principle have a continuous mechanistic spectrum ranging from the A-1 mechanism typical of aliphatic acetal to the S E 2 mechanism typical of ortho ester hydrolysis. Reactions that occur by both of these mechanisms are characterized by the formation of resonance-stabilized carbonium ion intermediates . The two mechanisms differ in that for the A-1 mechanism carbonium ion formation is the rate-limiting step, while for the S E 2 mechanism substrate protonation (perhaps concerted with carbonium ion formation) is the rate-limiting step.…”

Section: Resultsmentioning

confidence: 99%

“…Reactions that occur by both of these mechanisms are characterized by the formation of resonance-stabilized carbonium ion intermediates. 47 The two mechanisms differ in that for the A-1 mechanism carbonium ion formation is the rate-limiting step, while for the S E 2 mechanism substrate protonation (perhaps concerted with carbonium ion formation) is the rate-limiting step. Dioxolanes hydrolyze 46 by a specific acid A-1 mechanism (Scheme 2) with small negative ΔS ⧧ values, as is frequently observed for acid-catalyzed hydrolysis reactions of cyclic compounds.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Cucurbituril-Mediated Catalytic Hydrolysis: A Kinetic and Computational Study with Neutral and Cationic Dioxolanes in CB7

et al. 2018

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Cucurbit[7]uril (CB7) catalyzes the acid hydrolysis of alkoxyphenyldioxolanes bearing both neutral and cationic alkoxy groups. The magnitude of the catalytic effect depends on the dioxolane structure, as reflected by both the CB7 binding constants and the catalysis rate constants. However, there is no clear relationship in such a way that increasing the binding affinity (cationic dioxolanes or large alkoxy groups) does not enhance the catalytic effect. The A-1 mechanism for dioxolane hydrolysis involves the protonation and formation of a carbocation by protonated dioxolane ring opening. Supramolecular catalysis takes place through the formation of the ternary complex dioxolane@CB7@H3O+, where the hydronium ion is stabilized by hydrogen bonding with the carbonyl groups of the CB7 portal. The ternary complex evolves to a binary complex by protonation of dioxolane and release of a water molecule. It is important to note that these structures are only stable in the presence of CB7 and not in bulk water. The carbocation is formed by opening the protonated dioxolane group in the rate-determining step. The distance between the carbonyl portal of CB7 and the dioxolane group in the ternary and binary complexes (protonated and carbocation) increases with the alkyl chain length, resulting in the loss of the CB7 stabilizing effect and decrease in catalytic efficiency. The existence of two recognition motifs with cationic dioxolanes results in the formation of both 1:1 and 2:1 complexes with different catalytic properties.

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Section: Resultsmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Cucurbituril-Mediated Catalytic Hydrolysis: A Kinetic and Computational Study with Neutral and Cationic Dioxolanes in CB7

et al. 2018

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“…value of 17.2 kcal./rnole reported by Ceder (15) for the hydrolysis of 2,2-diphenyl-1,3-dioxolane under similar conditions. The enthalpy of activation (AHf) is somewhat larger than that reported by De Wolfe et ul (16). for the hydrolysis of 2,2-diphenyl-1,3dioxolane in 30% dioxane ( A H 1 = 14.6 kcal./mole).…”

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confidence: 62%

“…De Wolfe er a/. (16) found that hydrolysis of a number of benzophenone ketals was susceptible to general acid catalysis. The catalytic constants for acids other than the hydronium ion were small but significant.…”

Section: Resultsmentioning

confidence: 99%