[Intelegent]

I've faced in the practice the oxidizing properties of ascorbic acid in the water-alcohol solution. As far as I understand the ascorbic acid is oxidized to form dehydroascorbic acid that is a strong oxidizing agent. Where I can read about oxidizing activity of dehydroascorbic acid? Are there oxidating/reducing potentials described?

[Garneck]

As far as I understand the ascorbic acid is oxidized to form dehydroascorbic acid that is a strong oxidizing agent.

How can something oxidise and be an oxidiser in the same time? As far as I know, ascorbic acid is a reducing agent.

[Borek]

How can something oxidise and be an oxidiser in the same time? As far as I know, ascorbic acid is a reducing agent.

Welcome back - Summer is over?

Read original post once again - it becomes oxidizer AFTER it was oxidized.

Intelegent - have you tried Google?

[Garneck]

Welcome back - Summer is over?

Thanks Borek. Sadly it is. At least I'm back on the board to help out

Read original post once again - it becomes oxidizer AFTER it was oxidized.

My bad. I read it too quickly.

[Intelegent]

Intelegent - have you tried Google?

Yes, I had. Most of references found was from the bakery professionals, not from chemists. In a bakery ascorbic acid is mentioned as oxidizer. See, e. g., http://www.classofoods.com/page1_1.html:
"Ascorbic acid differs in one aspect from other dough conditioners. In itself is it not an oxidizer but a reducer. Its activity stems from a preceding reaction during kneading with oxygen in the air. It is than converted to dehydro-ascorbic acid and that is an oxidizer."
But I need reliable references such as organic chemistry handbooks/textbooks, journal articles etc. In the practice I see that ascorbic acid added to the water-alcohol mixture causes rapid increasing of acetaldehyde content in the solution. I thihk that in the system an oxidizer acts, probably dehydroascorbic acid.

[Borek]

In the practice I see that ascorbic acid added to the water-alcohol mixture causes rapid increasing of acetaldehyde content in the solution. I thihk that in the system an oxidizer acts, probably dehydroascorbic acid.

It may depend on the purity of ascorbic acid added.

Standard potential of dehydroascorbic acid reduction to ascorbic acid is given as -0.07 V in  Handbook of Chemical Equilibria in Analytical Chemistry, Kotrly and Sucha, Ellis Horwood Ltd. 1985.

[Intelegent]

I've found an abstract of the old article: http://www.ajevonline.org/cgi/content/abstract/25/2/119  
H. L. Wildenradt and V. L. Singleton The Production of Aldehydes as a Result of Oxidation of Polyphenolic Compounds and its Relation to Wine Aging Am. J. Enol. Vitic. 25:2:119-126 (1974)
"Evidence is presented showing that oxidation of ethanol to acetaldehyde by direct chemical reaction with air occurs at an appreciable rate in wine only by a coupled autoxidation of certain phenolic substances occurring in the wine. The oxidation of vicinal di- and tri-hydroxyphenols like caffeic acid, catechin, or myricetin in 12% ethanol model wine produced acetaldehyde. Similar reaction in aqueous 1-propanol produced propanal showing that the source of the volatile aldehyde is the wine's alcohol. A mechanism is postulated which appears to be general for autoxidation of phenols, ascorbic acid, melanoidins, reductones, enediols, and related compounds whereby the oxidation of the phenol to a quinone (or ascorbic to dehydroascorbic, etc.) coproduces a strong oxidant, probably hydrogen peroxide, which then can oxidize other substances in the wine such as ethanol."