Mechanisms of Acylal Hydrolysis in Sulfuric Acid Solutions

Abstract

The acid-catalyzed hydrolysis (in aqueous &So4) of acylals ArOCH20Ac is reported, and compared with that of normal acetate esters. On the basis of r plot behavior and the effects of the aromatic substituents, an A*,-2 ester hydrolysis mechanism is shown to occur in dilute acids, with a changeover to a mechanism analogous to A,,-1 ester hydrolysis (intermediate cation ArOCH2 +) in more concentrated acids, the position of the changeover being dependent on the substituent. Methylene diacetate is also investigated and shown to display the same behavior, with an A-1 mechanism involving an intermediate CH3COOCH2+ becoming important at about 75% &Sod. The relative AA1-1 reactivities for acetates ROAc, R = CH30CH,, tertbutyl, C6H50CH2, C6H5CH2, 4-N0,C6H40CH2, CH3COOCH2, isopropyl, are 6 x lo3, 5 x lo2, 1, 7 x 4 x 1.1 x 1.3 x respectively.ROBERT ALLAN MCCLELLAND. Can. J. Chem. 53,2763Chem. 53, (1975.On rapporte I'hydrolyse acido-catalyse (dans I'acide sulfurique aqueux) d'acylals du type

Acyloxymethyl as a drug protecting group. Part 5.1 Kinetics and mechanism of the hydrolysis of tertiary N-acyloxymethylsulfonamides

“…Similar ρ values (0.36 and 0.42) have been reported for the B Ac 2-type hydrolysis of compounds 5. 21,22 In contrast, the ρ value for substituents in the benzoate group is much closer to the value of ca. 2.2 reported for the alkaline hydrolysis of benzoate esters in aqueous acetone and aqueous methanol.…”

“…20 Whichever protonated species is involved we are led to conclude that the acid-catalysed hydrolysis of 2 occurs via an A Al 1 mechanism involving formation of a sulfonyliminium ion (Scheme 3). Interestingly, the acid-catalysed hydrolysis of aryloxyethyl propanoates 21 (5, R 1 = Et, R 2 = Me) and the hydrolysis of aryloxymethyl acetates (5, R 1 = Me, R 2 = H) in concentrated Scheme 3 sulfuric acid 22 yield Hammett ρ values of Ϫ2.07 and Ϫ3.06, respectively. These values also are consistent with an A Al 1 mechanism, involving the formation and subsequent decomposition of a carbonyl oxygen protonated intermediate.…”

Vinyl sulfide hydrolysis

“…Su2firr Table 3 sumnlarizes relative rates for vinyl ethers and sulfides, along with those of the acylals and thioacylals (reaction I). The latter data are based on the step-wise colnparison previously described (1); the former data are based on direct coinparison in 1 N HC1 (Table 2). the number for methyl vinyl ether being obtained by comparing its hydrolysis rate in more dilute acid (k,, = 0.76 M -' s -l (15)) with that of methyl vinyl sulfide.…”

“…A recent study (1,2) of acylal and thioacylal hydrolysis allowed a comparison of the effects of oxygen and sulfur in a reaction generating an adjacent carboniurn ion centre (reaction 1, X = 0, S: R = Me, Ar), this system showing a much closer reactivity between oxygen-and sulfur-containi~lg compounds than that anticipated on the basis of previous results, for example, on the solvolysis of chloromethyl ethers and chloromethyl sulfides (3). For further comparison, we have turned to the acid-catalyzed liydrolysis of vinyl ethers and vinyl sulfides.…”

Chemical reaction method for growing photomechanical organic microcrystals

“…Since 9-AYAA is a carboxylic acid, we chose a tert-butyl ester as our precursor molecule. Acid sensitive functional groups such as tert-butyl esters or acylals can be cleaved at low pH to yield the corresponding carboxylic acid 34 or aldehyde 35 respectively (Scheme 1a and b). For high yield product formation, the reactant has to be in a homogenous phase with the aqueous acid.…”