Carbonyl oxygen exchange of glycol monoesters. Rate and equilibrium constants for the formation of a tetrahedral intermediate

McClelland, Robert A.; Ahmad, M.; BOHONEK, J.; Gedge, Sherrin

doi:10.1139/v79-250

Cited by 15 publications

(8 citation statements)

References 9 publications

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“…Experiments have recently been reported of the direct observation of the two types of intermediates of the hydrolysis of ortho esters (1)(2)(3)(4)(5)(6)(7). These experiments obviously verify the three-stage reaction mechanism commonly accepted for this hydrolysis (8).…”

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confidence: 65%

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The tetrahedral intermediate of a lactonization reaction

McClelland¹,

Alibhai²

1981

Can. J. Chem.

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ROBERTA. M C C L E L L A N D~~~MASUMA ALIBHAI. Can. J. Chem. 59, 1169Chem. 59, (1981. 'The hydrolysis of the ortho ester 1,l-diethoxy-l,3-dihydroisobenzofuran (1) is described. This hydrolysis proceeds with initial expulsion of an exocyclic ethoxy group, producing upon hydration of the oxocarbonium ion I-hydroxy-1-ethoxy-1,3-dihydroisobenzofuran (7), the tetrahedral intermediate of the lactonization of ethyl (2-hydroxymethyl)benzoate (6) to phthalide (8). Based on the kinetic behavior of the ortho ester hydrolysis, the pH variation in the ratio of 6:8 initially formed from the ortho ester, and the kinetic behavior of the lactonization reaction, rate constants for the breakdown of the tetrahedral intermediate 7 have been determined, along with the equilibrium constant for its formation from the hydroxy ester 6. The breakdown occurs in an extremely rapid hydroxide-ion-catalyzed reaction, with the rate being at the diffusion limit. Hydronium ion catalysis is also observed; this breakdown is also rapid although considerably less so than the hydroxide ion reaction. The changeover from H+ to OH-catalysis occurs at pH 3.5. The rate of breakdown is a minimum at this point, and corresponds to a half-life for the tetrahedral intermediate of about 0.1 s. It is concluded that this allows sufficient time for conformational changes in the tetrahedral intermediate prior to breakdown; this factor must be taken into account in stereoelectronic considerations.ROBERT A. MCCLELLAND et MASUMA ALIBHAI. Can. J. Chem. 59,1169Chem. 59, (1981. On dkcrit I'hydrolyse de I'ortho ester diethoxy-1,l dihydro-1,3 isobenzofuranne (1). Cette hydrolyse se fait avec une expulsion initiale d'un groupe ethoxy exocyclique conduisant aprks hydratation a I'ion oxocarbonium hydroxy-1 Cthoxy-1 dihydro-1,3 isobenzofuranne (7), I'intermediaire tttraedrique de la lactonisation du (hydroxymethy1)-2 benzoate d'ethyle (6) en phtalide (8). On a determine la constante de vitesse de rupture de I'intermediaire tttraedrique 7 ainsi que la constante d'equilibre conduisant a sa formation a partir de I'hydroxy ester 6 en se basant sur le comportement cinktique de I'hydrolyse de I'ortho ester, sur la variation du pH dans le rapport du produits 6:8 qui se forment initialement a partir de I'ortho ester et sur le comportement cinetique de la reaction de lactonisation. La rupture se produit au cours d'une reaction extrcmement rapide catalysee par I'ion hydroxyde dont la vitesse est limitee par la diffusion. On observe egalement la catalyse par I'ion hydronium; cette rupture est egalement rapide quoique considerablement plus faible que celle de la reaction catalysee par I'ion hydroxyde. Le changement de catalyseur de H+ a OH-se produit a un pH de 3,s. La vitesse de rupture est minimale i c e point et correspond a une demie-vie de I'intermediaire tetraedrique d'environ 0,l s. On en conclut que ceci accorde suffisamment de temps a des changements conformationnels de I'intermediaire tktrakdrique avant sa rupture. On doit tenir compte de ce facteur dans les considerations ste...

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confidence: 65%

“…These experiments obviously verify the three-stage reaction mechanism commonly accepted for this hydrolysis (8). Moreover they provide a direct measure of the kinetic behavior associated with the later two stages and, in certain cases (7), are capable of furnishing the free energy of the intermediates.…”

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confidence: 99%

The tetrahedral intermediate of a lactonization reaction

McClelland¹,

Alibhai²

1981

Can. J. Chem.

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“…Studies conducted over the past few years (7,(10)(11)(12)(13)(14)(15)(16) have shown that the exocyclic alkoxy group OR is lost in the dialkoxy carbocationforming stage, with the key feature that ky is usually signifi- cantly smaller than both ky and k!, . The latter two are in fact quite close in magnitude, since they represent similar processes, loss of an exocyclic OR and OH to form the same cyclic cation.…”

Section: Kyh(0h-) Oh Kg Ky(h+)mentioning

confidence: 99%

Hydrolysis of trioxaadamantane ortho esters. II. Kinetic analysis and the nature of the rate-determining step

McClelland¹,

Lam²

1984

Can. J. Chem.

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A detailed kinetic study of the hydrolysis of a series of 3-aryl-2,4, LO-trioxaadamantanes is reported. These ortho esters equilibrate with the ring-opened dialkoxycarbocation, in a very rapid process which could be studied using temperature-jump spectroscopy for aryl = 2,4-dimethylphenyl. Relaxation rate constants are of the order of lo4 s-'; these could be analyzed to provide the rate constants for both the ring opening and the ring closing. Product formation from this equilibrating mixture is much slower. In acid solutions (0.01 M H+ -50% HzS04). first-order rate constants for product formation initially increase with increasing acidity, but a maximum is reached at 2 0~3 5 % H2S04 and the rate then falls. This behavior is explained by a counterbalancing of two factors. Increasing acidity increases the amount of the dialkoxycarbocation in the initial equilibrium, but, outside the pH region, it decreases the rate of hydrolysis of this cation through a medium effect. Rate constants over a range of pH have been measured for two trioxaadamantanes and for the cation DEt+ derived by treatment of the ortho ester with triethyloxonium tetraafluoroborate. The latter models the cation formed in the ortho ester hydrolysis but it cannot ring close. Rate-pH profiles obtained in these systems are more complex than expected on the basis of rate-determining cation hydration. An interpretation is proposed with a change in rate-determining step between high pH and low pH. Cation hydration is rate determining at high pH but at low pH hemiorthoester decomposition becomes rate determining. Under these conditions the hemiorthoester equilibrates with both the dialkoxycarbocation and with the trioxaadamantane. The change in ratedetermining step occurs because acid-catalyzed reversion of the hemiorthoester to dialkoxycarbocation is a faster process than acid-catalyzed hemiorthoester decomposition. This makes the latter rate-determining in acid solutions. Additional pathways available to the decomposition, however, make it the faster process at higher pH. A kinetic analysis furnishes all of the rate and equilibrium constants for the system, and provides support for the mechanistic interpretation. A comparison of these numbers with those obtained for the three stages in the hydrolysis of a simple monocyclic ortho ester underlines the novelty of the trioxaadamantane system. la spectroscopie de saut de T lorsque I'unitC aryle = dimethyl-2,4 phtnyle. Les constantes de vitesse de relaxation sont de I'ordre de lo4 S-I; on peut les analyser pour obtenir les constantes de vitesse d'ouverture et de fermeture de cycle. La formation des produits a partir du mtlange ii I'Cquilibre est beaucoup plus lente. Dans des solutions acides (0,Ol M H+ -50% H2S04), la constante de vitesse d'ordre un de la formation du produit augmente au depart avec l'aciditt mais elle atteint un maximum ti 20-35% de H,SO,; ensuite, la vitesse diminue. On explique ce comportement par I'effet oppost de deux facteurs. L'augmentation de l'aciditt augmente la quantitC de dialkoxy...

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“…For cyclic systems k −3 becomes more dominant in the pH range of about 4–6 [ 23 ], however stage 1 remains rate limiting [ 26 ]. The overall rate of reaction can therefore be established by measuring the consumption of the geminal ether [ 27 ]. We present here kinetic data measured for a range of acyclic orthoformates, orthoacetates, 1,3-dioxolane orthoesters, oxanes, and 1,3-dioxanes ( Fig.…”

Section: Introductionmentioning

confidence: 99%

The hydrolysis of geminal ethers: a kinetic appraisal of orthoesters and ketals

Repetto¹,

Costello²,

Lam³

et al. 2016

Beilstein J. Org. Chem.

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SummaryA novel approach to protecting jet fuel against the effects of water contamination is predicated upon the coupling of the rapid hydrolysis reactions of lipophilic cyclic geminal ethers, with the concomitant production of a hydrophilic acyclic hydroxyester with de-icing properties (Fuel Dehydrating Icing Inhibitors - FDII). To this end, a kinetic appraisal of the hydrolysis reactions of representative geminal ethers was undertaken using a convenient surrogate for the fuel–water interface (D2O/CD3CN 1:4). We present here a library of acyclic and five/six-membered cyclic geminal ethers arranged according to their hydroxonium catalytic coefficients for hydrolysis, providing for the first time a framework for the development of FDII. A combination of 1H NMR, labelling and computational studies was used to assess the effects that may govern the observed relative rates of hydrolyses.

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Carbonyl oxygen exchange of glycol monoesters. Rate and equilibrium constants for the formation of a tetrahedral intermediate

Cited by 15 publications

References 9 publications

The tetrahedral intermediate of a lactonization reaction

The tetrahedral intermediate of a lactonization reaction

Hydrolysis of trioxaadamantane ortho esters. II. Kinetic analysis and the nature of the rate-determining step

The hydrolysis of geminal ethers: a kinetic appraisal of orthoesters and ketals

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