Self-catalysis

For a consideration of more strictly kinetic aspects of polyesterification by direct esterification, it is convenient to discuss separately the cases of self-catalysis and catalysed esterification. 

Hinshelwood et al. [47] first showed that esterification of monobasic acids with alcohols was second order with respect to acid in the absence of 

Flory [3, 48] found that the esterification reactions between model compounds on the one hand and polyfunctional reactants on the other are substantially identical. Thus the reaction of two monofunctional compounds (lauric acid, lauryl alcohol), of a bifunctional compound with a monofunctional one (adipic acid, lauryl alcohol) and two bifunctional compounds (adipic acid, decamethylene glycol) followed essentially third-order kinetics. In the absence of added strong-acid catalyst a second molecule of the carboxylic acid functions as catalyst. Thus when the concentrations (C) of the reacting groups are identical, the rate is given by  

If the reactions are third order from the outset the constant of integration is I/Cq where Cq is the starting concentration. Ignoring the small volume change caused by loss of water during esterification, the concentration at time t may be replaced by Co(l—p) where p is the extent of reaction, and 

Flory s data are plotted in Fig. 4. The model reactions (monofunctional reactants) are somewhat slower, but the differences are due primarily to 

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Du Vail S, McCreery RL (2000) Self-catalysis by catechols and quinones during heterogeneous electron transfer at carbon electrodes. J Am Chem Soc 122 6759-6764. 

The Beckmann rearrangement of cyclohexanone oxime has been modelled kinetically, focusing on simulation of industrial conditions, and taking into account self-catalysis and the role of polymorphs.86... 

An identical mathematical description of the kinetics of curing of reactants different in chemical nature and that obtained on the basis of fundamentally different experimental methods allows us to assume that this apparent selfacceleration course of some rheokinetic parameters is common to the processes of formation of materials with a crosslinked structure. It should be emphasized once more that the self-acceleration" effect must not be identified with the self-catalysis of the reaction of interaction between epoxy monomers and diamines which is studied in detail on model compounds [116, 117]. For each particular curing process the self-acceleration effect is influenced by the mechanism of network formatic, namely, chemical self catalysis [118], the appearance of local inhomogeneities [120], the manifestation of gel eff t [78], parallel course of catalytic and noncatalytic reactions [68]. It is probably true that the phenomena listed above may in one form or another show up in specific processes and make their contribution into self-acceleration of a curing reaction. 

In commercial practice today reactions of the second type frequently utilize an excess of glycol, increasing the rate of esterification. Later stages of such polycondensations, as in the preparation of polyethylene terephthalate, take place by a transesterification mechanism with liberation of glycol. The direct esterification reaction may be catalysed by a second molecule of the carboxylic acid (self-catalysis) or by an independent acidic catalyst (catalysed esterification). 

There are several hydrogen-bonding configurations that may be drawn that also involve another molecule of amine, so the system may exhibit self-catalysis. A detailed study of the... 

In order to generate terminal hydroxyl groups an excess of glycol is currently used. The reaction takes place in uncatalysed reaction conditions (self catalysis by the acidic carboxyl groups) but the best perfomances (low reaction time, low final acidity) are obtained in the presence of specific catalysts, such as p-toluene sulfonic acid, tin compounds (stannous octoate), antimony, titanium (tetrabutyltitanate), zinc (zinc acetate), manganese (manganese acetate) or lead compounds and more recently enzymic catalysts (lipases) [1, 25]. 

The DETA-based aminic polyols are synthesised by first adding 4 mols of PO and, in the second step, adding several units of EO without any other catalyst (self catalysis). The addition of EO to the hydroxyl groups formed, being catalysed by the tertiary aminic nitrogen from the aminic polyol structure resulting from propoxylation (reactions 14.6) [11, 12]. 

It is possible to add 2-3 mols of PO/mol of Mannich base in the self catalysis of the tertiary amino nitrogen of the Mannich base, but 4-6 mols of PO/Mannich base needs a catalyst, such as a low hindered tertiary amine (for example dimethylaminoethanol, dimethy lcyclohexy lamine). 

The alkoxylation of these structures, having carboxyl groups and hydroxyl groups, is a self catalysis process, catalysed by the acidic -COOH groups. Two simultaneous reactions take place the esterification of carboxyl groups with PO (reaction 16.14) and the etherification of hydroxyl groups (reaction 16.15) [34]. 

Liu L, Chen LX et al (2006) Self-catalysis of phthaloylchitosan for graft copolymerization of epsilon-caprolactone with chitosan. Macromol Rapid Commun 27 1988-1994... 

We have computed the potentials of mean force for the decarboxylation of N-methyl orotate (NMO) ion in water, which was used by Wolfenden as the reference reaction, and OMP substrate in ODCase using a combined QM/ MM method in Monte Carlo and molecular dynamics simulations (Fig. 2) [16]. A separate calculation has been performed for the reaction of OMP in the gas phase, which yielded a reaction profile similar to that of NMO in the gas phase, indicating that there is no self-catalysis by the auxiliary phospho-... 

L. Liu, L. Chen, Y.E. Fang, Self-catalysis of phthaloylchito-san for graft copolymerization of e-caprolactone with chitosan. Macromol. Rapid Commun. 27 (2006) 1988-1994, doi 10.1002/ marc.200600508. 

The second one deals exactly with the temporal dependencies of the concentrations of the species relying on their characteristics that may, in certain cases as the ones of self-catalysis of biochemical reactions conduce to, intricate paths with a certain periodicity and that may even be conducive to chaotic situations. 

Bazsa, Gy. Beck, M. (1971). Autocatalysis, autoinhibition, self-catalysis—selfinhibition.—Specific kinetic effects of reaction products and reactants. Kem. Kozlem., 36, 167—(in Hungarian). 

A typical electroless plating solution is composed of a cation provider such as nickel sulfate, a reducing agent such as ammonium hypophosphite, and additional additives tiiat help prevent the bath from decomposition, i.e., plating spontaneously. When an activated substrate is immersed in the plating bath at a temperature of 80 C and a pH around 6, nickel cation in the bath are reduced by hypophosphorous acid, and the nucleation of nickel deposition starts at the activated locations. Because nickel readily plates to itself (self-catalysis), the deposition continues and eventually fills the via locations in the dielectric with nickel metal. The reduction reaction can be expressed by the following equations ... 

The Amadori rearrangement with amino acids as the basic component can be performed under self catalysis of the carboxylic acidic part of the molecule, but for better yields various additional acidic catalysts have also been used, depending on the starting materials. 

A reaction, speeded up by one of its products, is called self-catalyzed. Classic example of self-catalysis is a reaction of acetone iodination in acid medium, described by total scheme... 

Self-catalysis by the amines themselves is observed at the onset of the polymerization. 

An extremely large variety of resins exist which allows the fine-tuning of the processing and/or the characteristics of the final material. For instance, N,N -tetraglycidyl-4,4 diamino-diphenylmethane that carries tertiary amino groups ensures the self-catalysis of the cross-linking process. 

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