75056-97-2Relevant articles and documents
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Rabe,Spence
, p. 349 (1905)
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Reactivity in the Para Oxo Ketene Route of Ester Hydrolysis. The Effect of Internal Nucleophilicity and the Irrelevance of B Strain
Thea, Sergio,Cevasco, Giorgio,Guanti, Giuseppe,Kashefi-Naini, Nasrin,Willams, Andrew
, p. 1867 - 1872 (2007/10/02)
The hydrolysis of 2,4-dinitrophenyl (DNP) esters of substituted 4-hydroxybenzoic acids obeys the equation kobsd = (ka + kb->)/(1 + +>/Ka) and involves a para oxo ketene intermediate.The ka term fits a Broensted equation against the pK of the 4-hydroxybenzoate (log ka = 1.15pKa - 11.71) provided the 2,6-positions of the benzoate are free.The ka term for the 2,6-dimethyl-4-hydroxybenzoate ester is 1015-fold larger than that for the parent 4-hydroxybenzoate ester.An electronic effect due to different hydroxyl pKa's may be calculated from the above linear free energy relationship to contribute 1.6percent of the discrepancy.The other component of the discrepancy is ascribed to a preferred alignment of the ester in the 2,6-dimethyl case perpendicular to the plane of the aromatic ring. The fused ketene in the microscopic reverse reaction has a LUMO acceptor orbital perpendicular to the plane of the ring, in agreement with our conclusions.Force-field calculations of nonbonding interactions indicate no strain release in the elimination mechanism giving rise to ka.The dramatic (107-fold) enhancement of the apparent second-order rate constant for alkaline hydrolysis of the 2,6-dimethyl ester compared with that of the corresponding 2',4'-dinitrophenyl 4-methoxy-2,6-dimethylbenzoate is due mostly to the steric strain imposed in the tetrahedral transition state for the latter reaction.This strain is not sufficient, however, to cause the normal BAc2 mechanism in the alkaline hydrolysis of mesitoates to change to a "square planar" concerted process.
Syntheses of 4-Hydroxy-2,6-dimethylbenzoic Acid and Its Higher Homologues
Bhattacharya, Kalyan K.,Pal, Panchanan,Ghosh, Kalpana,Sen, P. K.
, p. 191 - 194 (2007/10/02)
Syntheses of 4-hydroxy-2,6-dimethylbenzoic acid (2a) and its higher homologues, viz 4-hydroxy-2,6-dimethylphenylacetic acid (2b), 3-(4-hydroxy-2,6-dimethylphenyl)propanoic acid (2c) and 4-(4-hydroxy-2,6-dimethylphenyl)butanoic acid (2d) are described.