Reaction Cannizaro

The activated Ba(OH)2 was used as a basic catalyst for the Claisen-Schmidt (CS) condensation of a variety of ketones and aromatic aldehydes (288). The reactions were performed in ethanol as solvent at reflux temperature. Excellent yields of the condensation products were obtained (80-100%) within 1 h in a batch reactor. Reaction rates and yields were generally higher than those reported for alkali metal hydroxides as catalysts. Neither the Cannizaro reaction nor self-aldol condensation of the ketone was observed, a result that was attributed to the catalyst s being more nucleophilic than basic. Thus, better selectivity to the condensation product was observed than in homogeneous catalysis under similar conditions. It was found that the reaction takes place on the catalyst surface, and when the reactants were small ketones, the rate-determining step was found to be the surface reaction, whereas with sterically hindered ketones the adsorption process was rate determining. 

Because the strongly basic media is often hostile to the carbonyl compound produced in these transformations, it has not been characterized in all of our studies. The fate of the carbonyl compound, however, is not unimportant to the nature of the transformation. The fragmentation of Vc produces benzaldehyde which subsequently disproportionates by the Cannizaro reaction to give benzyl alcohol and benzoate (4). This process consumes base and requires the nitrosamine cleavage reaction to be run with a near-stoichiometric quantity of base. The study of the carbonyl compounds produced in the fragmentation of Vb demonstrated that the initially produced butanal entered into several expected and unex-... 

It was, therefore, predicted (26) that this reaction should be much faster in polymeric acid solutions than in solutions of monobasic acids at the same pH. Experiments confirmed this expectation with rates more than 100 times faster in 0.01 N poly(styrenesulfonic acid) than in benzenesulfonic acid solutions of a similar concentration (27). In an analogous fashion, the Cannizaro reaction of glyoxal, which involves two hydroxyl ions,... 

As an example, phenols react with long-chain bromoalkanes under harsh conditions (refluxing DMF). In the case of p-hydroxybenzaldehyde, under liquid-liquid PTC, only a Cannizaro reaction occurred after one week. On the other hand, solvent-free PTC resulted in a quantitative yield in long chain ether within 5 h [Eq. (46)] [80]. 

The progress of the reactions was monitored by the absence of starting material by TLC. No significant change in + meso ratio was observed when the molar ratio of ARCOR TeiKOH was increased to 1 3 9. No alcohol or carboxylic acid (due to competing Cannizaro reaction) was observed to have been formed in these reactions our results are shown in Table-1. 

The trihydroxy analog 407 was prepared by acetylation of acyclovir to give 402, which monomethoxytritylated to 403 and then deacetylated to 404. Moffatt oxidation of 404 gave 405, which upon a crossed aldol-Cannizaro reaction gave 406, whose deprotection gave 407 (86JMC1384). 

The basic sites of AI2O3 have also been proposed to catalyze the Cannizaro reaction of benzaldehyde to benzoic add and benzyl alcohol [94]. The formation of this strongly adsorbed benzoate spedes plays a crucial role in catalyst deactivation, and would not have been possible to detect without in situ ATR-IR spectroscopy. When O2 was introduced into the system, signals corresponding to benzaldehyde and benzoate increased substantially, as shown in spectrum b in Figure 12.9. 

The polymerization of formaldehyde has been studied using various catalysts and complexing co-catalysts. When a bed of NaX-zeolite spheres was used, aqueous formaldehyde at 95 °C gave an initial conversion to formose sugars of 50% at pH 5—7. Rapid irreversible catalyst deactivation then occurred due to the presence of formic acid produced in the undesired Cannizaro reaction. The problem was overcome by incorporation of 0.86 cm sodium hydroxide per cm formaldehyde into the combined feed to the reactor... 

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