Isopropyl benzoate

A nucleophilic acyl substitution reaction involves the substitution of a nucleophile for a leaving group in a carboxylic acid derivative. Identify the leaving group (Cl- in the case of an acid chloride) and the nucleophile (an alcohol in this case), and replace one by the other. The product is isopropyl benzoate. 

The intermediates 74 and 76 can now lose OR to give the acid (not shown in the equations given), or they can lose OH to regenerate the carboxylic ester. If 74 goes back to ester, the ester will still be labeled, but if 76 reverts to ester, the 0 will be lost. A test of the two possible mechanisms is to stop the reaction before completion and to analyze the recovered ester for 0. This is just what was done by Bender, who found that in alkaline hydrolysis of methyl, ethyl, and isopropyl benzoates, the esters had lost 0. A similar experiment carried out for acid-Catalyzed hydrolysis of ethyl benzoate showed that here too the ester lost However, alkaline hydrolysis of substimted benzyl benzoates showed no loss. This result does not necessarily mean that no tetrahedral intermediate is involved in this case. If 74 and 76 do not revert to ester, but go entirely to acid, no loss will be found even with a tetrahedral intermediate. In the case of benzyl benzoates this may very well be happening, because formation of the acid relieves steric strain. Another possibility is that 74 loses OR before it can become protonated to 75. Even the experiments that do show loss do not prove the existence of the tetrahedral intermediate, since it is possible that is lost by some independent process not leading to ester hydrolysis. To deal with this possibility. Bender and Heck measured the rate of loss in the hydrolysis of ethyl trifluorothioloacetate- 0 ... 

The following liquids may be used (boiling points are given in parentheses) — chlorobenzene (132-3°) bromobenzene (155°) p-cymene (176°) o-dichloro-benzene (180°) aniline (184°) methyl benzoate (200°) tetralin (207°) ethyl benzoate (212°) 1 2 4-trichlorobenzene (213°) isopropyl benzoate (218°) methyl salicylate (223°) n-propyl benzoate (231°) diethyleneglycol (244°) -butyl benzoate (250°) diphenyl (255°) diphenyl ether (259°) dimethyl phthalate (282°) diethyl phthalate (296°) diphenylamine (302°) benzophenone (305)° benzyl benzoate (316°). 

Furthermore, the injection of organic aromatic solvents and soaking is a feasible method to remove the precipitates [924]. The precipitation of asphalt from crude oil can be reduced by adding an N,N-dialkylamide of a fatty acid [1525,1527]. When asphaltenes are precipitated out, they can be removed from the walls of a well, pipeline, and so forth by washing with a hydrocarbon solvent. However, it has been shown that isopropyl benzoate is exceptionally useful as a solvent for asphaltene removal [1583]. 

A good correlation was obtained in 20-80% acetonitrile-water mixtures. The standard non-ionic compounds used to evaluate the columns were 2-hydroxy-acetophenone, coumarin, acetophenone, indole, propiophenone, butyro-phenone, isopropyl benzoate, butyl benzoate, and isopentyl benzoate. The plotted lines for the linear relationship measured in five different proportions... 

Fig. 6.29. El spectmm of isopropyl benzoate. Used by permission of NIST. NIST 2002.

Leisten6 found that the introduction of a p-nitro group into ethyl benzoate causes a 60-fold decrease in the rate of hydrolysis in 100% sulphuric acid at 65°C, while in the case of isopropyl benzoate it causes a 200-fold rate increase. 

This suggests that the hydrolysis of the ethyl ester involves the Aac1 mechanism, but that protonated isopropyl benzoate cleaves by alkyl-oxygen cleavage. A change in mechanism at this point would explain the order of reactivity towards hydrolysis of the various alkyl benzoates, observed by Kuhn18. 

Voltammetric data for ester reductions are available for several aromatic esters [51-54], and in particular cyclic voltammetry shows clearly that in the absence of proton donors reversible formation of anion radical occurs [51]. In dimethylfonnamide (DMF) solution the peak potential for reduction of methyl benzoate is —2.29 V (versus SCE) for comparison dimethyl terephthalate reduces at —1.68 V and phthalic anhydride at —1.25 V [4]. Half-wave potentials for reduction of aromatic carboxylate esters in an unbuffered solution of pH 7.2 are linearly correlated with cr values [51] electron-withdrawing substituents in the ring or alkoxy group shift Ei/o toward less negative potentials. Generally, esters seem to be more easily reducible than the parent carboxylic acids. Anion radicals of methyl, ethyl, and isopropyl benzoate have been detected by electron paramagnetic resonance (epr) spectroscopy upon cathodic reduction of these esters in acetonitrile-tetrapro-pylammonium perchlorate [52]. The anion radicals of several anhydrides, including phthalic anhydride, have similarly been studied [55]. 

Similarly, acetic acid and ethanol react to produce ethyl acetate, and the product of the reaction between benzoic acid and isopropyl alcohol is isopropyl benzoate. 

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