Decomposition of esters

Shape selective catalysis as typically demonstrated by zeolites is of great interest from scientific as well as industrial viewpoint [17], However, the application of zeolites to organic reactions in a liquid-solid system is very limited, because of insufficient acid strength and slow diffusion of reactant molecules in small pores. We reported preliminarily that the microporous Cs salts of H3PW12O40 exhibit shape selectivity in a liquid-solid system [18]. Here we studied in more detail the acidity, micropore structure and catal3rtic activity of the Cs salts and wish to report that the acidic Cs salts exhibit efficient shape selective catalysis toward decomposition of esters, dehydration of alcohol, and alkylation of aromatic compound in liquid-solid system. The results were discussed in relation to the shape selective adsorption and the acidic properties. 

A third category of syn eliminations involves pyrolytic decomposition of esters with elimination of a carboxylic acid. The pyrolysis of acetate esters normally requires temperatures above 400° C and is usually a vapor phase reaction. In the laboratory this is done by using a glass tube in the heating zone of a small furnace. The vapors of the reactant are swept through the hot chamber by an inert gas and into a cold trap. Similar reactions occur with esters derived from long-chain acids. If the boiling point of the ester is above the decomposition temperature, the reaction can be carried out in the liquid phase, with distillation of the pyrolysis product. 

Another probable reaction of homolytic decomposition of ester hydroperoxide is the intramolecular interaction of the hydroperoxide group with the carbonyl group of ester with the formation of labile hydroxyperoxide succeeded the splitting of the weak O—O bond (see decomposition of hydroperoxides in oxidized ketones in Chapter 8). 

Problem 1.15 Hydrolysis of ester, in presence of NaOH, was followed keeping their concentration same at 0.02 mol dnr3. The specific rate constant at 35°C was found to be 5.55 mor1dm3min 1. What proportion of ester will be hydrolysed in 30 min Also calculate the time for 30% decomposition of ester. 

A third category of syn eliminations involves pyrolytic decomposition of esters with elimination of a carboxylic acid. The pyrolysis of acetate esters normally requires temperatures above 400° C. The pyrolysis is usually a vapor-phase reaction. In the... 

The decomposition of esters at elevated temperatures is of exceptional practical importance, since it has often been responsible for accidents. Investigations of the decomposition of esters at elevated temperatures by laboratory tests serve as a rapid method of estimating their stability. 

The reaction typically gives 60% to 70% of the maximum yield. The reaction is a reversible process. An ester reacting with water, giving the carboxylic acid and alcohol, is called hydrolysis it is acid catalyzed. The base-promoted decomposition of esters yields an alcohol and a salt of the carboxylic acid this process is called saponification. 

Due to the high temperatures that are usually required to obtain measurable rates of decomposition of esters, most of the data refer to the gas phase. An exception to this is found in the thermal decomposition of dibenzhydryl oxalates . Difficulties in reproducibility did not allow for a precise evaluation of the activation parameters. However, for benzhydryl oxalate the values are AH = 30+3 kcal.mole and AS = —14+5 cal.deg . mole . A ff " correlation was made... 

Saponification.—As we shall see later, this is the kind of reaction which takes place when soap is made from fats and on that account it is termed an action of saponifikation. In this way the acids are obtained as salts from the naturally occurring fats, oils and waxes in which they are present in the form of esters. The hydrolysis of esters or ethereal salts is then the general reaction by which, with the taking up of the elements of water, an ester is reconverted into the two compounds from which it was formed, viz., into an acid and an alcohol. Esterification and hydrolysis or saponification are, therefore, complementary names applying to the reversible reaction effecting the synthesis and decomposition of esters. The reversible character of the reactions of esterification and... 

Alkenes are formed by the thermal decomposition of esters, xanthates, amine oxides, sulfoxides, and selenoxides that contain at least one (3-hydrogen atom. These elimination reactions require a cw-configuration of the eliminated group and hydrogen and proceed by a concerted process. If more than one (3-hydrogen is present, mixtures of alkenes are generally formed. Since these reactions proceed via cyclic transition states, conformational effects play an important role in determining the composition of the alkene product. 

Inversion of Sucrose. Many hydrolytic reactions, including the decomposition of esters, are reversible but others such as sucrose inversion and protein hydrolysis, though not necessarily complete, have not been reversed. The heat effects of these reactions, however, are important. The inversion of sucrose, for example, is an exothermic reaction with AH at 25°C approximately —3.6 kg-cal per mole. ... 

For carbonium-ion processes, unless configuration is maintained by ion association, it is unsound to assume stereochemistry of elimination from product analysis, unless it is independently shown that racemisation at the carbon bonded to the hydroxy group is slower than olefin formation. Decompositions of ester intermediates should show a preference for anti stereospecificity if they are base-induced and syn-clinal stereospecificity when they occur under thermal conditions. Typical results on the dehydration of two stereoisomers in the rigid steroid series support the above generalisations... 

Figure 2.1. " Acid produced from onium salt decomposes t-BOCPHS. A proton is reproduced during the decomposition of ester. This is called chemical amplified resist because of its high efficiency by proton cycling.

The reaction of saponification has already been discussed in the chapter on esters. This reaction is the basic procedure for decomposition of ester lipids. 

Interestingly, the same kind of carboxyl radical can be generated from the thermal decomposition of esters (usually the t-butyl ester as its reactivity is more easily controlled) of peroxycarboxylic acids. In this case, the peroxyester is not formed by oxidation of the corresponding ester but rather (Equation 9.85) by the reaction between the acid chloride of the carboxylic acid and the corresponding alkyl peroxide (often generated by direct oxygenation of the appropriate alkane. Chapter 5). 

The photolysis of unsaturated polyesters shows the disappearance of double bonds and partial decomposition of ester carbonyl groups to carbon monoxide and carbon dioxide molecules. This type of polyester contains a distinct conjugated system of double bonds and carbonyl groups (4.49), which absorbs UV radiation and exists in the triplet state (Tj) as a resonance form (4.50) ... 

Studies on the mechanism of formation of the main gaseous products of the thermal degradation of PC (CO, CO ) have established [3] that CO forms exclusively via the oxidation of CHj groups, whereas CO2 arises from the decomposition of ester groups and the oxidation of CH3 groups. 

It is most likely that the decomposition of esters in the gas phase proceeds through the six-membered transition state, as follows ... 

Shafer, J.A., Morawetz, H. Participation of a neighboring amide group in the decomposition of esters and amides of substituted phthalamic acids. J. Org. Chem. 1963, 28(7), 1899 1901. 

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