Cannizarro

Thus, formaldehyde is not an efficient reductant in electroless Cu solutions, not that this is an issue, given its continuous depletion by the parasitic homogeneous Cannizarro reaction. 

It undergoes a parasitic Cannizarro reaction as readily as H2CO, yielding glycolate and oxalate as products ... 

Benzaldehydes are not subject to base catalyzed aldol condensations, and under the reaction conditions Cannizarro reactions are not important. 

Only in 1859 did the modern definition come into being, when the Italian scientist Stanislao Cannizarro (1826-1910) defined a molecule as the smallest fundamental unit comprising a group of atoms of a chemical compound . This statement arose while Cannizarro publicized the earlier work of his compatriot, the chemist and physicist Amedeo Avogadro (1776-1856). 

This definition of a molecule soon gained popularity. Before modern theories of bonding were developed, Tyndall had clearly assimilated Cannizarro s definition of a molecule when he described the way atoms assemble, when he said, A molecule is a group of atoms drawn and held together by what chemists term affinity . 

Reduction of ethyl 1-dibenzothiophenecarboxylate with LAH affords 1-hydroxymethyldibenzothiophene (96%), which is smoothly converted into the chloromethyl derivative with thionyl chloride (70%). Both the Cannizarro reaction and LAH reduction of 2-dibenzothiophenecarboxaldehyde yield the 2-hydroxymethyl derivative in good yields. 3-Hydroxymethyl-4-methyldibenzothiophene has been prepared via Cannizarro reaction of the corresponding 3-aldehyde however, 3-hydroxymethyldibenzothiophene itself has not been recorded, although the necessary precursors are available. Considerable interest has centered around 4-hydroxymethyldibenzothiophene, which... 

The usual range of reactions has been recorded for the aldehydes of dibenzothiophene. Oxidation yields the corresponding acid, - reduction with LAH the corresponding alcohol, reduction under Huang-Minlon conditions the corresponding methyl compound, and two examples of the Cannizarro reaction have been described. ... 

Fragmentation and recombination reactions predominate in nearneutral, alkaline solutions. Fragments from the cleavage of the carbohydrate, and from its dehydration products, undergo further dehydration, condensation, and intermolecular, Cannizarro-type reactions. The benzilic acid rearrangement, an intramolecular Cannizarro reaction, seems to be inoperative. 

Hayami and his coworkers have studied the mechanism of formation of acetol and pyruvic acid from D-glucose- -14C, -6-14C, and -3,4-14C2, reacting in a concentrated, phosphate buffer solution.148-151 Their data supported the supposition that the products are formed from pyruvaldehyde by way of a Cannizarro reaction. As in the formation of lactic acid, the pyruvaldehyde can be formed either from the reducing or the nonreducing end of the D-glucose molecule, and the distribution of radioactivity in the pyruvic acid and acetol... 

In the Cannizarro reaction, benzaldehyde is both oxidized and reduced to form benzoic acid (as the benzoate salt) and benzyl alcohol. 

Hydroxymethylation of 1 to 9 in the first reactor is very fast at 40 °C. In principle, a strongly basic ion exchange resin may be used as a solid catalyst, but as expected the catalyst failed in test runs due to inactivation by formic acid produced by Cannizarro reaction. 

Effective molarity measurements for intramolecular hydride transfers are scarce, and a conclusion that high effective molarities are a feature of hydride shifts would be premature. Only two other measurements are available, a low value of 13 for the Cannizarro reaction of phthalaldehyde (McDonald and Sibley, 1981), discussed below, and a larger value, 200, for... 

To account for the vanom oxygenated products observed in catalytic CO reductions, a Cannizarro-iype reaction should also be considered. Maiilis reports the disproportionation of aldehydes to acids and alcohols using complexes of rhodium and ruthenium 7l),... 

The aldol reaction appears to have taken place but there has been reduction of the ketone product. The only possible reducing agent is more formaldehyde and reduction is by the Car" reaction (p. 1081). The aldol can be successful if a weaker base (Na2C03 will do) is used Cannizarro reaction requires a dianion. 

Treatment of tributyltin hydride with a Grignard reagent enables preparation of the corresponding organotin anion, which undergoes the Cannizarro reaction with pentanal providing an acyl stannane (Scheme 12.130) [233]. 

A more complex oligomer is obtained by treatment of butanal with KOH or NaOH in aqueous ethanol. This reaction has been shown to produce the tetramers (3)-(5) and trimer (6 equation 14), some in respectable yield, depending on the exact reaction conditions. Compound (3) is produced as a mixture of four diastereomers and probably arises from dimerization of the initial aldol condensation product, 2-ethylhexenal. Diol (4), also obtained as a mixture of four stereoisomers, appears to be a Cannizarro reduction product of (3). Lactones (5) and (6) can reasonably arise by mechanisms involving hydride transfer from a cyclic hemiacetal. 

One obvious candidate for a reactive non-enolisable carbonyl compound is formaldehyde, CH2O. The trouble with this compound is that it is rather too reactive, adding repeatedly and transforming the product by Cannizarro reactions to give such compounds as (40). 

Condensation of (31) to (32) requires formaldehyde and base. Reduction to (33) occurs under these conditions by the Cannizarro reaction so the synthesis is shorter than seemed likely. The reverse Diels-Alder reaction to (30) goes at high temperature. 

The undesired diol (-)-32 was recycled by first oxidizing to the dialdehyde with Dess-Martin s reagent (Scheme 15). After heating the dialdehyde in acid to racemize the material, ( )-29 was subjected to the Cannizarro/DCC conditions providing racemic lactone ( )-28 in a 60% yield. Performing this kinetic resolution/recycling process provided (+)-28 in an overall yield of 61% (98% ee). 

Note that the modern use of the word molecule was not introduced until Cannizarro publicised the work of Avogadro in 1859. 

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