Amide acetal hydrolysis. 2-Aryl-2-(N,N-dimethylamino)-1,3-dioxolanes. Rapid and reversible ring opening in neutral and basic solutions. Rate-determining decomposition of hydrogen ortho esters in acidic solutions

McClelland, Robert A.; Ahmad, Mahmood

doi:10.1021/jo01325a024

Cited by 14 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).…”

supporting

confidence: 65%

“…[6]. The : variation in this ratio, however, has little effect on the shape of the rate-pH profile and in particular causes no "break" of the type observed with the coumarinic acid systems (14).…”

Section: Discussionmentioning

confidence: 93%

“…As seen in Table 2 large values of koH are not unexpected. The hydrogen ortho ester 2-phenyl-2-hydroxy-l,3-dioxolane also reacts with hydroxide ion at a rate near the diffusion limit, and the number in this case is actually measured when this intermediate is generated from a highly reactive precursor amide acetal (6). Rates of breakdown (and formation) of a hemiacetal analog of 7 have also been measured (27), and koH is again large, although not up to the diffusion limit.…”

Section: Discussionmentioning

confidence: 93%

“…Equations [6]- [9] are derived from the general scheme of eq. [4] with the assumption being made that the decomposition of 7 occurs only by H+ catalyzed and OH-catalyzed reactions or, in other words, that the pH independent reactions kH$ and kHZO4 are never important.…”

Section: Discussionmentioning

confidence: 99%

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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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supporting

confidence: 65%

Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

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The tetrahedral intermediate of a lactonization reaction

McClelland¹,

Alibhai²

1981

Can. J. Chem.

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“…6 for the acid hydrolysis of N-(trifluoroacetyl)indole in DlSO4 can also be calculated by using the limited number of data points (Table I) 6 for the acid hydrolysis of N-(trifluoroacetyl)indole in DlSO4 can also be calculated by using the limited number of data points (Table I) …”

Section: Discussionmentioning

confidence: 99%

Acid-catalyzed hydrolyses of acylpyrroles and acylindoles. Noninvolvement of protonated substrates

Cipiciani¹,

Linda²,

Savelli³

et al. 1981

J. Am. Chem. Soc.

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contain several minor impurities not easily removed by fractional distillation; it was purified by partial neutralization with HC1, removal of volatile material at reduced pressure, and recovery after basification much as described elsewhere3 for the purification of piperidine; the distilled purified amine was shown by GLC to be of high purity. Butylmethylammonium chloride, mp 174-175 OC, was prepared by addition of 0.56 mol of HCl (as concentrated solution in water) to 0.64 mol of the amine, with stirring below 5 "C, cooling to -78 "C, collecting the crystalline salt, and recrystallizing from acetone. Anal. Calcd for C5H14C1N: C1, 28.68. Found (by potentiometric titration): C1, 28.64. 1 -(Butylmethylamino)-2,4-dinitronaphthalene (IC) was prepared by the reaction of l-chloro-2,4-dinitronaphthalene with a twofold excess of butylmethylamine in Me2S0, and crystallized from ethanol; mp 69.5-70.5 OC. Anal. Calcd for CI5Hl7O4N3: C, 59.40; H, 5.64; N, 13.85. Found: C, 59.60; H, 5.72; N, 13.91.Spectral Characteristics and Changes. IC in Me,SO shows a single broad absorption band with A,, 425 nm, e 7.80 X lo3 M-' cm-l. Upon addition of butylmethylamine (0.875 M), the spectrum changes to one of two bands with X , 391 and 522 nm and e respectively 1.45 X lo4 and 2.41 X lo4 M-' cm-I. The latter spectrum, attributed to 3c, was essentially fully developed after 5 h at ambient temperature.la in Me2S0 shows a single absorption band with A,, 439 nm, e 1.90 X lo4 M-' cm-I. Upon addition of pyrrolidine, the spectrum changes to one of two bands with A, , , 400 and 523 nm. When this spectrum due to 3a is fully developed, e at 523 nm is 1.85 X 10' M-' cm-' in the absence. of pyrrolidinium chloride and 2.16 X lo4 M-' cm-' in the presence of this salt (0.0104 M). lb in MezSO shows a single broad absorption band with X , 422 nm, e 7.8 X lo3 M-' cm-I. Upon addition of piperidine, the spectrum slowly changes to one with two bands, A , , 392 and 524 nm, attributed to 3b, but the data were not suitable for definitive evaluation of e for 3b.Kinetic Procedure. Reaction rates were determined by photometric observation of the absorbance at ca. 523 nm of reacting solutions. Determinations were made with use of a Gilford 2000 automated kinetics spectrophotometer with thermostated cell compartment. Good first-order behavior was observed in all cases. Rate constants were reckoned by the Guggenheim method. All kinetic runs were performed in duplicate; the rate constants reported are means of concordant values. The pseudofirst-order rate constant is symbolized k+ in Tables I and 11. Acknowledgment.Abstract: The labilization of a coordinated formyl group in a platinum(I1) chelate by nucleophilic ligands has been examined structurally. The chelating ligand is the deprotonated dimeric Schiff base condensate of o-aminobenzaldehyde, The aldehyde was trapped in its uncoordinated form by adding a 1:l molar ratio of triphenylphosphine to the complex in acetonitrile. The resulting adduct crystallizes in the space group C2/c with unit cell dimensions a = 32.75...

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ChemInform Abstract: AMIDE ACETAL HYDROLYSIS. 2‐ARYL‐2‐(N,N‐DIMETHYLAMINO)‐1,3‐DIOXOLANES. RAPID AND REVERSIBLE RING OPENING IN NEUTRAL AND BASIC SOLUTIONS. RATE‐DETERMINING DECOMPOSITION OF HYDROGEN ORTHO ESTERS IN ACIDIC SOLUTIONS

McClelland¹,

Ahmad²

1979

Chemischer Informationsdienst

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Amide acetal hydrolysis. 2-Aryl-2-(N,N-dimethylamino)-1,3-dioxolanes. Rapid and reversible ring opening in neutral and basic solutions. Rate-determining decomposition of hydrogen ortho esters in acidic solutions

Abstract: References and Notes(1) Portions of this work were presented at the 9th International Symposium on the Chemistry of Natural Products, Ottawa, June 1974. (2) (a) J. Romo and P.

Cited by 14 publications

References 2 publications

The tetrahedral intermediate of a lactonization reaction

The tetrahedral intermediate of a lactonization reaction

Acid-catalyzed hydrolyses of acylpyrroles and acylindoles. Noninvolvement of protonated substrates

ChemInform Abstract: AMIDE ACETAL HYDROLYSIS. 2‐ARYL‐2‐(N,N‐DIMETHYLAMINO)‐1,3‐DIOXOLANES. RAPID AND REVERSIBLE RING OPENING IN NEUTRAL AND BASIC SOLUTIONS. RATE‐DETERMINING DECOMPOSITION OF HYDROGEN ORTHO ESTERS IN ACIDIC SOLUTIONS

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