Methyl orthobenzoates, hydrolysis

The observation of very pronounced inhibition of the sodium dodecyl sulfate-catalyzed hydrolysis of methyl orthobenzoate by inorganic cations is also consistent with the proposed mechanism for the micelle catalyzed reaction (Romsted et al., 1967 Dunlap and Cordes, 1968). For alkali-metal cations, the inhibition was found to increase with increasing ion size, i.e. ionic radius, but for alkaline-earth cations the inhibitory effectiveness was observed to be relatively independent of the ion. For... 

In the NMR experiments carried out by Wenthe and Cordes [187] with methyl orthobenzoate and methyl orthocarbonate in CD3OD—D20 solutions, the rate coefficients for the disappearance of orthoester and those for the formation of CH3OD and of carboxylic ester have been found identical within experimental error (Table 15). This indicates that there is no exchange of methoxy groups prior to hydrolysis. The same result has been obtained from product analysis studies of the carboxylic esters formed. Consequently, the rate-determining step must be carbonium ion formation or a previous step. The findings do not support an A2 mechanism, for the following reason. As the nucleophilic reactivities of water and methanol are similar, the A2 reaction with attack of water... 

If the hydrolysis of methyl orthobenzoate in weakly acidic solution is carried out in the presence of various amounts of added nucleophiles, such as hydroxylamine or semicarbazide, a considerable fraction of the orthoester is transformed to the product of the reaction with the amine rather than to methyl benzoate, while the rate coefficient remains unchanged [183]. Similarly, the rate of hydrolysis of ethyl orthocarbonate in aqueous cacodylic acid buffer is the same in the presence of 0.04 M NaC104 and of 0.04 M Nal [192]. Thus, nucleophilic catalysis is absent even under conditions when general acid catalysis is effective. 

The effect of the chain length of sodium alkyl sulfates on the acid-catalyzed hydrolysis of methyl orthobenzoate (65) is illustrated in Fig. 6. It can be seen that up to a given concentration there seems to be... 

FlO. 6, Acid-catalyzed hydrolysis of methyl orthobenzoate in the presence of sodium alkyl sulfates as a function of the number of carbon atoms in the alkyl chain and of detergent concentration 0.008 M sodium acetate, 0.002 M aeetio acid, 6x 10" JIf methyl orthobenzoate, temperature 25°. 

In the very early phase of the kinetic studies on the effects of [micelles] on the reaction rates, it has been observed that an empirical kinetic equation similar to Equation 7.48 with replacement of [M X ] by [Smflj - CMC (where [Smflj and CMC represent total surfactant concentration and critical micelle concentration, respectively) is applicable in many micellar-mediated reactions. But the plots of kobs vs. ([Surf]j - CMC) for alkaline hydrolysis of some esters reveal maxima when surfactants are cationic in nature. - - Similar kinetic plots have also been observed in the hydrolysis of methyl orthobenzoate in the presence of anionic micelles. Bunton and Robinson suggested a semiempirical equation similar to Equation 7.49, which could explain the presence of maxima in the plots of ko s vs. ([Surflj - CMC). In Equation 7.49), J, is an empirical constant. 

Dunlap, R.B., Cordes, E.H. Secondary valence force catalysis. Vni. Catalysis of hydrolysis of methyl orthobenzoate by anionic surfactants. J. Phys. Chem. 1969, 73(2), 361-370. 

EtOH produced cleanly the cz5-la,2a-diol 5 in 81% yield. The benzoylation of the I -a-hydroxyl group in 5, which is surrounded by the two 1,3-diaxially juxtaposed methyl groups, proved to be quite difficult under the standard benzoylation conditions. However, treatment of 5 with trimethyl orthobenzoate at 100°C in the presence of a catalytic amount of benzoic acid followed by acid-catalysed hydrolysis of the resulting 1,2-cyclic orthobenzoate provided the 1-monobenzoate derivative of 5., ) Benzoylation of this monobenzoate under standard conditions afforded the desired 1,2-dibenzoate 6 ) in 95% yield. 

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