Observation of a stable hemiortho ester anion. Acidity constant for a tetrahedral intermediate

McClelland, Robert A.; Seaman, N. Esther; Cramm, David A.

doi:10.1021/ja00328a034

Cited by 14 publications

(5 citation statements)

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“…Moreover, it is well‐indicated that the acyl migration of 1,2‐diol mono‐esters ( i.e . isomerization) can be happened through a five‐membered ring intermediate 5 ( Scheme ) . Thus, product 4 can be also produced through the acyl transfer of initially generated 3 .…”

Section: Resultsmentioning

confidence: 99%

“…isomerization) can be happened through a five-membered ring intermediate 5 ( Scheme 3). [46] [47] Thus, product 4 can be also produced through the acyl transfer of initially generated 3. However, the ring opening of epoxides with carboxylic acids was regioselectively achieved using the current catalyst in which majorly led to isomers 3 in good to excellent yields.…”

Section: Application Of Cssnh Catalyst In Ring Opening Of Epoxides VImentioning

confidence: 99%

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Chitosan‐Silica Sulfate Nano Hybrid as a Novel and Highly Proficient Heterogeneous Nano Catalyst for Regioselective Ring Opening of Epoxides via Carboxylic Acids

Behrouz

Rad

Piltan

et al. 2017

Helvetica Chimica Acta

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The synthesis and characterization of chitosan‐silica sulfate nano hybrid (CSSNH) as a novel and efficient heterogeneous nano catalyst involving acid‐base bifunctional activity is described. The catalytic potency and activity of this eco‐friendly catalyst was investigated in regioselective ring opening of epoxides with carboxylic acids to access structurally diverse 1,2‐diol mono‐esters in good to excellent yields. CSSNH catalyst was characterized using different microscopic and spectroscopic techniques encompassing scanning electron microscopy, transmission electron microscopy, X‐ray diffraction, N2 adsorption isotherm, and Fourier transform infrared spectroscopy. The green nature, cheapness, efficiency, ease of preparation, handling and reusability of this new catalyst makes this catalyst to be useful for green industrial processes.

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Section: Resultsmentioning

confidence: 99%

Section: Application Of Cssnh Catalyst In Ring Opening Of Epoxides VImentioning

confidence: 99%

Chitosan‐Silica Sulfate Nano Hybrid as a Novel and Highly Proficient Heterogeneous Nano Catalyst for Regioselective Ring Opening of Epoxides via Carboxylic Acids

Behrouz

Rad

Piltan

et al. 2017

Helvetica Chimica Acta

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“…An interesting example on the selectivity of this method is shown by the hydroxy benzoic acid derivatives ( Table 3, entries [14][15][16]. In basic media, these benzoic acid derivatives may act as ambident nucleophiles and therefore complicated products are obtained because of the contribution of phenolic OH in epoxides ring opening; however, this problem was not seen in our method.…”

Section: Methodsmentioning

confidence: 90%

“…It is important to emphasize that in particular mono-esters of 1,2-diols are known to isomerize 12 and such isomerization is very fast in acidic 15 or alkaline 16 media. This becomes a serious drawback for chemoselective preparation of mono-esters of 1,2-diols specially for 1,2-diols lacking C 2 symmetric centers.…”

Section: Methodsmentioning

confidence: 99%

An Efficient Method for the Chemoselective Preparation of Benzoylated 1,2-Diols from Epoxides

Khalafi-Nezhad¹,

Rad²,

Khoshnood³

2003

Synthesis

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A very efficient and highly regioselective ring-opening reaction of epoxides with benzoic acid and its derivatives in the presence of cat. amount of tetrabutylammonium bromide (TBAB) in anhydrous acetonitrile has been developed. This effective method is useful for the preparation of selectively protected diols as precursor for many organic syntheses such as those of acyclic nucleosides and other synthetic purposes. The advantages of this method are efficiency, selectivity, low cost, and the applicability in large-scale synthesis of β-benzoyloxyalkanols.

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“…For PhC(OMe)20H itself, an alternative relationship of Fox and Jencks (23), with a simple alcohol as a starting point, provides a pK, value of 10.90. Moreover there is a measured value of 10.4 for the more stable derivative 2-hydroxy-2-(4-nitropheny1)-4,4,5,5-tetramethyl-l,3-dioxolane (24).…”

Section: K2mentioning

confidence: 99%

Flash photolysis production of the tetrahedral intermediate of the methanolysis of methyl benzoate. Direct measurement of the rate of breakdown of the conjugate base form

McClelland¹,

Kanagasabapathy²,

Steenken³

1990

Can. J. Chem.

Self Cite

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. Can. J. Chem. 68, 375 (1990). Laser flash photolysis in aqueous basic solutions of the ortho acid derivatives 1-(phenyldimethoxymethyl)benzimidazole 2 and 4-bromo-1-(phenyldimethoxymethyl)imidazole 3 results in production of the phenyldimethoxymethyl cation, which has A, , at 260 nm. The cation decays in reactions with water (k = 9.9 X lo4 s-I) and hydroxide ion (2.5 X 10' M-' s-' )to finally yield methyl benzoate, whose formation was monitored at 234 nm. In solutions with pH 10-12, rate constants measured at this wavelength are the same as those,obtained at 260 nm, but with pH >13 and pH <9, rate constants at 234 nm are smaller. With pH 9-10 and pH 12-13, single exponential kinetics are not observed at 234 nm. This behavior is interpreted in terms of a scheme where at each pH there are two consecutive first-order reactions, cation -+ phenyldimethoxyhydroxymethane (5) + ester, and the pH dependencies of the rate constants are such that they cross twice over the pH range of this study. The intermediate 5 is the tetrahedral intermediate formed in the methanolysis of methyl benzoate, and the 234-nm buildup at pH > 13 and pH <9 directly measures its breakdown. At pH > 13 the rate constant is independent of pH with k = 9 X lo6 s-'. This represents the rapid expulsion of methoxide from the conjugate base of 5. At pH <9 the rate constants are proportional to hydroxide ion concentration, with koH-= 7.5 X 109M-I s-l. In these solutions the neutral intermediate predominates and the dependence on [OH-] of its rate of conversion to ester is interpreted in terms of breakdown of the anion and protonation of this species by water occurring at comparable rates. Thus, koH-represents a situation where there is partial rate-limiting deprotonation of the neutral intermediate by hydroxide. The intermediate of this study bears a close resemblance to the tetrahedral intermediate of the hydrolysis of methyl benzoate. The observation that the anionic forms of such intermediates undergo breakdown at rates similar to those associated with the establishment of proton transfer equilibrium explains why the ester undergoes carbonyl oxygen exchange in base at a rate slower than hydrolysis. , conduit a la formation du cation phCnyldimCthoxymCthyle qui prCsente un A, , , a260 nm. Le cation se dCcompose par rCaction avec l'eau (k = 9,9 x lo4 s-I) et l'ion hydroxyde (2,5 X 10' M-I s-I) pour donner finalement du benzoate de mCthyle dont on determine la formation en suivant la progression de la bande a 234 nm. Dans des solutions dont le pH varie de 10 a 12, les constantes de vitesse telles que mesurCes a cette longueur d'onde sont identiques celles que l'on obtient a 260 nm; toutefois, a des pH >13 ou <9, les constantes de vitesse CvaluCes h 234 nm sont plus faibles. A 234 nm et a des pH de 9 a 10 ou de 12 B 13, on n'observe pas de cinCtiques exponentielles uniques.On interprkte ce comportement en fonction d'un schCma selon lequel il existe, pour chaque pH, deux rCactions consCcutives du premier ordre : cation -+ phCnyldimCthoxyhydroxymCthane (5) ...

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Observation of a stable hemiortho ester anion. Acidity constant for a tetrahedral intermediate

Cited by 14 publications

References 1 publication

Chitosan‐Silica Sulfate Nano Hybrid as a Novel and Highly Proficient Heterogeneous Nano Catalyst for Regioselective Ring Opening of Epoxides via Carboxylic Acids

Chitosan‐Silica Sulfate Nano Hybrid as a Novel and Highly Proficient Heterogeneous Nano Catalyst for Regioselective Ring Opening of Epoxides via Carboxylic Acids

An Efficient Method for the Chemoselective Preparation of Benzoylated 1,2-Diols from Epoxides

Flash photolysis production of the tetrahedral intermediate of the methanolysis of methyl benzoate. Direct measurement of the rate of breakdown of the conjugate base form

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