Esterification relative reactivity

Sulfonate Esters. Sucrose sulfonates are valuable intermediates for the synthesis of epoxides and derivatives containing halogens, nitrogen, and sulfur. In addition, the sulfonation reaction has been used to determine the relative reactivity of the hydroxyl groups in sucrose. The general order of reactivity in sucrose toward the esterification reaction is OH-6 OH-6 > OH-1 > HO-2. 

Explain in detail how steric hindrance would lead you to expect that the relative reactivity of these two hydroxyl groups in esterification is C3 > C11 and in chromic acid oxidation is C11 > C3. 

A review of the relative reactivities of the hydroxy-groups of carbohydrates has dealt with esterification, etherification, acetalation, halogenation, and oxidation, and with the migration of substituents. Shallenberger s rationale is considered to explain satisfactorily the relative sweetness of sucrose, xylitol, arabinitol, ribitol, D-galacto-sucTOSG, and methylated derivatives of sucrose. ... 

Process Applications The production of esters from alcohols and carboxylic acids illustrates many of the principles of reactive distillation as applied to equilibrium-limited systems. The equilibrium constants for esterification reactions are usually relatively close to unity. Large excesses of alcohols must be used to obtain acceptable yields with large recycles. In a reactive-distiUation scheme, the reac-... 

Fiery1 252-254) studied only the last stage of the reactions, i.e. when the concentration of reactive end groups has been greatly decreased and when the dielectric properties of the medium (ester or polyester) no longer change with conversion. Under these conditions, he showed that the overall reaction order relative to various model esterifications and polyesterifications is 3. As a general rule, it is accepted that the order with respect to acid is two which means that the add behaves both as reactant and as catalyst. However, the only way to determine experimentally reaction orders with respect to add and alcohol would be to carry out kinetic studies on non-stoichiometric systems. 

Especially for large-scale work, esters, may be more safely and efficiently prepared by reaction of carboxylate salts with alkyl halides or tosylates. Carboxylate anions are not very reactive nucleophiles so the best results are obtained in polar aprotic solvents54 or with crown ether catalysts.55 The reactivity for the salts is Na+ < K+ < Rb+ < Cs+. Cesium carboxylates are especially useful in polar aprotic solvents. The enhanced reactivity of the cesium salts is due both to high solubility and to the absence of ion pairing with the anion.56 Acetone has been found to be a good solvent for reaction of carboxylate anions with alkyl iodides.57 Cesium fluoride in DMF is another useful combination.58 Carboxylate alkylation procedures have been particularly advantageous for preparation of hindered esters that can be relatively difficult to prepare by the acid-catalyzed esterification method (Fischer esterification) which will be discussed in Section... 

The most important examples of reactive separation processes (RSPs) are reactive distillation (RD), reactive absorption (RA), and reactive extraction (RE). In RD, reaction and distillation take place within the same zone of a distillation column. Reactants are converted to products, with simultaneous separation of the products and recycling of unused reactants. The RD process can be efficient in both size and cost of capital equipment and in energy used to achieve a complete conversion of reactants. Since reactor costs are often less than 10% of the capital investment, the combination of a relatively cheap reactor with a distillation column offers great potential for overall savings. Among suitable RD processes are etherifications, nitrations, esterifications, transesterifications, condensations, and alcylations (2). 

The advantage of bidimensional representation is evident if four reactive components are involved, as in the class of reversible reactions A + B <-> C + D. This situation covers an important number of industrial applications, as the esterification of acids with alcohols. Selecting C as the reference, the transformed variables are XA = xA + xc, XB = xB + xc and XD = xD- xc since v, = 0. The transformed variables sums to one, but only two are used as co-ordinates. Accordingly, the pure components may be placed in the corner of a square diagram, reactants or products on the same diagonal. Figure A. 5 displays the reactive distillation map traced as before for the relative volatilities 4/2/6/1 and the equilibrium constant K t = 5. 

The acylium ion is understandably more reactive than a covalent acyl species, and is able to acylate even relatively unreactive secondary and tertiary steroid alcohols. In some situations, however, the acidic reagent causes elimination reactions, with or without rearrangement, so that esterification is inefficient or impossible (p. 105 and 271). 

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