Epoxide consumption, rate

Figure 7.24 Dependencies of propylene consumption rate on propylene concentration in the epoxidation reaction at different temperatures (1 453 K 2 473 K 3 493 K and 4 513 K).

This first step had been proposed earher by Narracot. The necessity of the second step was deduced fi om the effect of isopropyl alcohol concentration on the rate of epoxide consumption. The reaction rate was found to depend sharply on the alcohol concentration no reaction occurred when there was no alcohol present, and a more rapid reaction occurred as the alcohol concentration was increased. Shechter believed these results indicate that the quatemaiy base formed in Rxn. 3 is not a catalyst, since the proximity of the base s positive and negative charges may diminish its catalytic abfiity. 

The existence of reaction (77) has been confirmed by a higher consumption rate of epoxides as compared to phenols.About 60% of the epoxide present has been shown to be consumed in epoxide-phenol reactions and the other 40% is consumed according to reaction (77). Alcohol has been found to be absent at the beginning of the reaction and forms only when phenol reacts with epoxides. The epoxides prefer to react with the so-formed alcohols, in the presence of the catalyzing influence of phenols, rather than with phenols. 

Base-catalyzed reactions are very specific and take place readily at 100 °C. In the presence of about 0.2 mol % potassium hydroxide, the consumption rate of phenols exactly corresponds to the disappearance of epoxides. This suggests that, in this case, the epoxide-alcohol reaction according to reaction (77) is absent. A reaction mechanism according to Scheme 26 has been proposed to explain this behaviour. 

Carbonylative kinetic resolution of a racemic mixture of trans-2,3-epoxybutane was also investigated by using the enantiomerically pure cobalt complex [(J ,J )-salcy]Al(thf)2 [Co(CO)4] (4) [28]. The carbonylation of the substrate at 30 °C for 4h (49% conversion) gave the corresponding cis-/3-lactone in 44% enantiomeric excess, and the relative ratio (kre ) of the rate constants for the consumption of the two enantiomers was estimated to be 3.8, whereas at 0 °C, kte = 4.1 (Scheme 6). This successful kinetic resolution reaction supports the proposed mechanism where cationic chiral Lewis acid coordinates and activates an epoxide. 

Epoxides. Epoxy compounds react with the carboxyl groups of CTPB to form polyesters. The reaction rates and extent of reaction of a number of epoxides have been determined with the model compound hexanoic acid (6). It was found that most epoxides undergo side reactions (as evidenced by the more rapid consumption of epoxide species) but that at least one difunctional epoxide, DER-332 (Dow Chemical Co.) (Table IV), exhibits a clean reaction with carboxylic acids, even in the presence of ammonium perchlorate. 

The results of model compound studies with three different types of epoxides, obtained in the presence and absence of ammonium perchlorate are shown in Figures 4, 5, and 6. The epoxide DER-332 shows a uniform rate of disappearance for the acid and epoxide species in this reaction. In the presence of ammonium perchlorate, the rate is increased, and a minimum of side reactions occur. Similar data but faster reaction rates are obtained with Epon X-801, but the consumption of epoxide species by side reactions is increased, particularly in the presence of ammonium perchlorate. On the other hand, the epoxide ERLA-0510 (Table IV), which contains a basic nitrogen, shows a reaction rate which is an order of magnitude greater than that for DER-332, accompanied by a substantial increase in side reactions. In the presence of ammonium perchlorate, the side reactions of ERLA-0510 predominate. In all probability, the side reactions of the multifunctional epoxides studied are homopolymerization. 

A kinetic model which includes both amine-epoxide and hydroxyl-epoxide addition reactions, with hydroxyl autocatalysis has been proposed by Zukas 103,104). The starting point was an expression for the rate of consumption of epoxide by reaction with primary or secondary amine and hydroxyl groups... 

By repeating these reactions, either a linear polyester is obtained or crosslinking takes place. These reactions were confirmed by the fact that the amounts of mono-and diester produced are stoichiometrically equivalent to the amount of anhydride consumed and that the initial rate of production of monoesters is equal to the rate of consumption of anhydride and considerably higher than the rate of diester formation. An alternative is the reaction of free acid with epoxide ... 

In contrast to the non-catalyzed reaction, the base-initiated copolymerization was found to be a specific reaction 35,36,39 -45) and the consumption of both monomers, epoxide and anhydride, is the same. The initiator not only affects the rate of copolymerization but also suppresses the undesirable homopolymerization of the epoxide. At equimolar ratio, epoxide and anhydride are strictly bifunctional. 

Hydrogen can of course also be lost if it is oxidised to water instead of the hydrogen peroxide that is needed for epoxidation. Its consumption can be lowered by 90% and selectivity raised to 97% at 1.7% conversion by admixing Au/Ti-MCM-41 with caesium chloride,23 but it is unclear how it acts. Water has however been found to decrease the rate of deactivation of Au/Ti02.24 25... 

Recycling Rate Consumption from Cl Ions % (our results) Liberated Epoxidized Oil Consumption (%)... 

The kinetics of heterogeneous-catalytic epoxidation of cycloh cene (CH) by tert-butyl hydroperoxide (TBHP) was investigated [202]. Catalysts were prepared by impregnating the ion-exchange resin, Amberlite IRS-84 in H-form, with the acidic solution of ammonium molybdate. The concentration of Mo was 0.35 mmole/g resin. The reaction kinetics were studied in the absence of solvent and at high molecular ratios of CH and TBHP. The reaction proceeded by pseudo-zero-order in respect of CH. Reaction selectivity was 90- 95 7o U. the initial rate could be determined from the rate of TBHP consumption. It was found that the reaction order was 1.8 for TBHP and 1 for the catalyst. Analysis of EPR spectra of catalysts before and after the reaction showed partial oxidation of Mo to Mo. The authors supposed a stepwise reaction mechanism in which the interaction between CH and a complex of Mo and TBHP is considered to be the slow and irreversible step. In this complex. Mo was present in the oxidized state. 

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