Valeraldehyde, 8-hydroxy

Degradative oxidation of a-hydroxy carboxylic acids furnishes aldehydes or ketones. Glycolic acid, lactic acid, and mandelic acid are converted into formaldehyde, acetaldehyde, and benzaldehyde, respectively, in 50% yields on refluxing with A -bromosuccinimide in water [745]. Periodates, with phase-transfer reagents, convert a-hydroxyhexanoic acid and mandelic acid into valeraldehyde and benzaldehyde in respective yields of 90 and 88% (equation 478) [776, 778]. 

In a fourth procedure dihydropyrane is hydrolyzed by brief heating with 0.2 N nitric acid on the steam bath to 6-hydroxy valeraldehyde, and the solution is added in about 3 hrs. to coned, nitric acid, with stirring and cooling at 10 or below. The aqueous liquor is removed by distillation and the residue crystallized from ether-benzene. Crude glutaric acid, m.p. 90°, is obtained in yield of 70-75%. 

Good yields of aldehydes from esters as well as hydroxyaldehydes from lactones can be obtained by reduction with NaAlH4 at low temp.— E NaAlH4 in tetra-hydrofuran added gradually at —45 to —60° to a soln. of methyl hydro-cinnamate in the same solvent, and the product isolated after 3 hrs. stirring -> hydrocinnamaldehyde. Y 80%.—Similarly d-Valerolactone 8-hydroxy-valeraldehyde. Y 75%. F. e. s. L. I. Zakharkin et al., Tetrah. Let. 1963, 2087. 

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