Barfoed's test

Barfoed's test is a chemical test used for detecting the presence of monosaccharides. It is based on the reduction of copper(II) acetate to copper(I) oxide (Cu₂O), which forms a brick-red precipitate.<ref name="barfoed">Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>

RCHO + 2Cu²⁺ + 2H₂O → RCOOH + Cu₂O↓ + 4H⁺

(Disaccharides may also react, but the reaction is much slower.) The aldehyde group of the monosaccharide which normally forms a cyclic hemiacetal is oxidized to the carboxylate. A number of other substances, including sodium chloride,<ref>Template:Cite journal</ref> may interfere.

Its author is the Danish chemist Christen Thomsen Barfoed<ref name="barfoed" /> and it is primarily used in botany.Template:Citation needed

The test is similar to the reaction of Fehling's solution to aldehydes.

Composition

Barfoed's reagent consists of a 0.33 molar solution of copper (II) acetate in 1% acetic acid solution.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The reagent does not keep well and it is therefore advisable to make it up when it is actually required.<ref>Template:Cite book</ref>

Procedure

1 drops of Barfoed's reagent is added to 2 mL of given sample in a test tube and boiled for 3 minutes and then allowed to cool. If a red precipitate occurs, a monosaccharide is present.