SynopsisThe reactions of model molecules were considered to study the kinetics and the mechanism of the esterification and the alcoholysis reactions catalyzed by various metal compounds (Li, Na, K, Zn, Co, Mn, Ti). Ti was found to be the most active catalyst for both reactions and to be acting via a different mechanism (concerted). The possible structure of the active titanium intermediate was investigated by means of 'Hand 13C-NMR spectroscopy, FT-IR spectroscopy, and electroconductivity.

SynopsisMonofunctional compounds (benzoic acid, heptyl alcohol, and 2-butoxy-ethanol) were used to investigate the kinetics of the esterification and the alcoholysis reactions. Carboxylic acids (benzoic acid) are the only catalysts present in the reaction medium. The factors which influence the kinetics of the esterification reaction were studid: the nature of the carboxylic acid (substituents on the benzene ring), the nature of the alcohol, the composition of the reaction medium (alcohol alone or with another solvent, ester, or water). The results point out for an acyl type (AAC2) mechanism. The alcoholysis reaction needs the presence of carboxylic acid as a catalyst to occur significantly. A similar mechanism is pro@ for both reactions: nucleophilic attack by the oxygen atom of the alcohol at the ion pair formed by protonation of the acid (esterification reaction) or by protonation of the ester (alcoholysis).

SynopsisWith a reaction conducted on model molecules with low amounts of catalysts and at low temperatures (170-225"C), it was shown that esterification is mainly catalyzed by the carboxylic acid groups and by the titanium derivatives; the activity of the other metals can only be seen when the concentration in carboxylic acid groups is low. In the alcoholysis reaction, the activity of Zn, Mn, and (much less) Ti, decreases when the percentage of ester in the reaction medium decreases, whereas it is the opposite with Sb. Moreover, Zn, Mn, and Co are sensitive to trace amounts of carboxylic groups (their activity decreases), whereas Ti is much less affected.

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The esterfication of ethylene glycol (EG) with benzoic acid (BA) is an acid‐catalyzed reaction which leads, as a first intermediate, to ethylene glycol monobenzoate (EGMB). This compound has an OH group which is more active towards carboxylic groups than the first OH group of EG. Moreover, it is a key intermediate in the formation of sideproducts containing diethylene glycol (DEG) moieties. The condensation reaction of EGMB was particularly studied in the presence of carboxylic acids or metal derivatives as catalysts. Titanium is the most active. Sb, which is widely used in the industrial synthesis of PET, needs to be present at a high level of concentration to show an activity. The presence of carboxylic groups in the reaction medium does not affect its activity, but it is necessary to remove the ethylene glycol as soon as it is formed in order to keep it active during the condensation reaction.