Methyl mesitoate

In a comparable solution of benzoic acid the freezing point is depressed only twice the predicted amount, indicating only a normal acid-base reaction. Further, a sulfuric acid solution of methyl mesitoate when poured into water gave mesitoic... 

In macrobicyclic cryptate complexes where the cation is more efficiently encapsulated by the organic ligand these ion pair interactions are diminished and the reactivity of the anion is enhanced. This effect is seen in the higher dissociation constant, by a factor of 104, of Bu OK in Bu OH when K+ is complexed by [2.2.2]cryptand (12) compared to dibenzo[18]crown-6 (2). The enhanced anion reactivity is illustrated by the reaction of the hindered ester methyl mesitoate with powdered potassium hydroxide suspended in benzene. 

In a comparable solution of benzoic acid the freezing point is depressed only twice the predicted amount, indicating only a normal acid-base reaction. Further, a sulfuric acid solution of methyl mesitoate when poured into water gave mesitoic acid, while a similar solution of methyl benzoate similarly treated did not.534 The AacI mechanism is also found when acetates of phenols or of primary alcohols are hydrolyzed in concentrated (more than 90%) H2SO4 (the mechanism under the more usual dilute acid conditions is the normal Aac2).535... 

Fig. 2. Zucker-Hammett plot for the hydrolyses of methyl mesitoate and -gIycervI benzoate, at...

Since the hydrolysis of methyl mesitoate conforms with the Zucker-Hammett hypothesis, it is not unexpected that the parameters calculated from the same data should meet Bunnett s more recent mechanistic criteria The value of Bunnett s w for the reaction in sulphuric acid is calculated as —1.1. and in perchloric acid as — 2.55W, both values falling in the region (w belween—2.5 and 0) characteristic of reactions not involving a molecule of solvent in the transition state. Bunnett s is also negative, as expected, values of —0.25 and —0.425 being found for the same two sets of data at 90°C4 . 

Fig. 3. The activity coefficient of methyl mesitoate as a function of acid concentration, in aqueous solutions of three strong acids. Data from ref. 56.

As has been clearly demonstrated by X-ray studies (Section III,B), complexation of a salt by a cryptand results in cation-anion separation or dissociation. This enhances anionic reactivity and may effect solubilization of the salt in organic solvents. For example the highly hindered ester methyl mesitoate, 13, may be smoothly hydrolyzed by powdered potassium hydroxide in dry benzene in the presence of [2.2.2] (98). Indeed cryptands have proved particularly useful in phase-trans-... 

Heating of methyl esters (e.g., 216) with 10 mol equiv. of DBU in o-xylene resulted in O-methyl cleavage to give the corresponding acids (e.g., 217) in exellent yields (73JOC1223). This method could also be applied to hindered esters (e.g., methyl mesitoate or methyl triisopropylacetate) and esters containing hydrolytically sensitive functional groups. 

Methylmagnesium bromide, 63, 334 Methyl mesitoate, 118,120, 247 Methyl methacrylate, 79, 86 Methyl 3-methyl-fnms-2,4-pentadienoate, 220... 

Cleavage of methyl esters.1 The reagent (in HMPT) is very effective for cleavage of methyl esters under mild conditions. Thus the very hindered methyl mesitoate is cleaved to the acid in quantitative yield at 25° (1.25 hours). Methyl O-methylpodocarpate (1) is readily cleaved to O-methylpodocarpic acid in quantitative yield at 25° (1.5 hours). This reaction had been effected previously with potassium /-butoxide in DMSO, but required 2 hours at 52°.2 Bartlett and Johnson also examined the selective ester cleavage of methyl 3/3-acetoxy-A5-etienate (2). 

It should be noted that the acid-catalysed hydrolysis of methyl mesitoate is also an A-l reaction (Chmiel and Long, 1956). 

Hydrolysis of amides and esters, Potassium r-butoxide in combination with water (2 1 equiv.) as a slurry in ether is an excellent reagent for hydrolysis of tertiary amides at room temperature (65-1007o yield). One drawback is that primary and secondary amides are resistant to these conditions. The reagent is essentially finely divided anhydrous potassium hydroxide. It is also useful for hydrolysis of esters at room temperature (70-1007o yield). Simple esters are hydrolyzed in 1-2 hours, but longer reaction periods are required for hindered esters. Even methyl mesitoate can be saponified in 75 7 yield at room temperature in the course of 5-6 days. ... 

For example, acid-catalyzed hydrolysis of methyl mesitoate (8) labeled with in the carbonyl oxygen (equation 7.66) led to mesitoic acid (9) with no loss of 0 label, even in solutions as low as 3.09 M in H2SO4. Had the reaction occurred by the Aac2 pathway, proton exchange and loss of water from the tetrahedral intermediate would likely have resulted in loss of 0 label from starting material and, therefore, from the product. ... 

PRACTICE PROBLEM 17.12 Base-promoted hydrolysis of methyl mesitoate occurs through an attack on the alcohol... 

Pedersen reported in 1967 that the dicyclohexyl-18-crown-6 complex of potassium hydroxide was soluble in toluene and in this medium could readily hydrolyze the very sterically hindered ester methyl mesitoate [33]. He later reported that this complex could also hydrolyze the tertiary-butyl ester [34]. Similarly, Lehn found that the [2.2.2]-cryptate complex of potassium hydroxide was even more effective in this saponification reaction under directly comparable conditions [35]. The hydrolysis reaction is formulated in equation 9.15. This method has recently been applied in the hydrolysis of C-labelled methyl tetradecanoate [36]. Starks found that tetra-decanoate anion acted as a catalyst poison and impeded further hydrolysis [7]. This is therefore one of the few examples where crown ether catalysis is clearly superior to quaternary ammonium ion catalysis. 

With lithium iodide in 2,4,6-collidine under reflux the ester (28) gives a 90% yield of the acetoxy acid (29) after 8 hr. Lithium n-propylmercaptide is similarly very effective and efficient, and in 15 min at 25° methyl mesitoate gives the acid in 100% yield [93]. 

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