Question

What is Barfoed’s test?

Answer 1

Barfoed’s test:

• A chemical test known as the Barfoed's test is used to identify the presence of monosaccharides and can identify reducing monosaccharides when disaccharides are present.
• Disaccharides might be used in this reaction, although it would proceed extremely slowly.
• A diluted acetic acid solution of copper acetate $\left(\mathrm{Cu}{\left({\mathrm{CH}}_3\mathrm{COO}\right)}_2\right)$ makes up the Barfoed reagent.
• Strong reducing agents such as monosaccharides react in just a few minutes because an acidic pH is not favorable to reduction.
• However, because they must first be hydrolyzed in the acidic solution before reacting with the reagent, the reducing disaccharides require a longer reaction time of roughly $7-8$ minutes.
• After the reaction occurs, thin red precipitate forms at the tube's edges and bottom.
• Thus, the difference in the precipitate's appearance time helps in distinguishing between reducing monosaccharides and reducing disaccharides.

Reaction involved

• In this reaction, aldehydic group is oxidized to carboxylic acid.
• The chemical reaction is as follows:

${\text{RCHO(l) + 2Cu}}^{2+}\text{(aq)}+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to \mathrm{RCOOH}+{\mathrm{Cu}}_2\mathrm{O}\left(\mathrm{s}\right)+4{\mathrm{H}}^{+}\left(\mathrm{aq}\right)$