3- Hydroxyl propionaldehyde

In ethyl alcohol, only the hydroxyl hydrogen is acidic in propionaldehyde, two hydrogens on the carbon adjacent to the C=0 group are very slightly acidic. In phenol, the situation is more complicated not only is the hydroxyl hydrogen acidic, but so also are three of the five ring hydrogens in the positions shown. 

On the basis of the metabolic products identified and their relative amounts formed during incubation, a degradative pathway involving hydroxylation and sulfoxidation mechanisms is proposed (Figure 7). EPTC is first hydroxylated at the a-propyl carbon to form a-hydroxy-propyl EPTC. This compound is unstable and breaks down to form N-depropyl EPTC and propionaldehyde. The N-depropyl EPTC is further metabolized to s-ethyl formic acid and propylamine. The s-ethylcarboxylic acid is then demethylated to s-methyl formic acid. This product is hypothesized to degrade to form C02 and methyl mercaptan. 

The most interesting method of polyether polyol odour elimination is based on the acidic hydrolysis of the purified polyether [90]. Thus a polyether polyol is treated with 10% water in the presence of an acid (H2S04 or HC1) at 90-100 °C, for one to two hours. The propenyl ether is hydrolysed to propionaldehyde and, instead of a double bond, a hydroxyl group is generated (reaction 4.23). At the same time the cyclic compound in Figure 4.35, formed during the purification step, is hydrolysed with the formation of propionaldehyde and dipropyleneglycol ... 

In anticipation of the final carbon-carbon bond construction that is required to prepare the intact seco acid of erythronolide B using a directed aldol reaction to form the C(10)-C(l 1) bond, it was first necessary to prepare the requisite chiral aldehyde 80. Although the synthesis of 80 had been previously reported, we elected to devise an alternative route to access this material that commenced with the addition of the chiral boron enolate 37 0 to propionaldehyde to furnish 81 (Scheme 12). The sequential protection of the secondary hydroxyl group and removal of the chiral auxiliary gave 82, which was then converted to 80 by over-reduction followed by reoxidation under Swem conditions. 

Vandenberk, S., and J. Peelers (2003), The reaction of acetaldehyde and propionaldehyde with hydroxyl radicals Experimental determination of the primary H2O yield at room temperature, J. Photochem. Photobiol. A, 157, 269-21 A. 

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