Ratio of moles of formaldehyde obtained in the reaction (1) and reaction (2).

Ratio of Formaldehyde Formed in Reactions

Periodic Acid (HIO₄) Oxidation of Sugars

• Reaction 1

Starting sugar: glucose (aldose, 6 carbons, both ends are CH₂OH groups).

Number of formaldehyde molecules produced: 2

(One from each terminal CH₂OH group.)

• Reaction 2

Starting sugar: arabinose (aldopentose, 5 carbons, one end CHO and one end CH₂OH).

Number of formaldehyde molecules produced: 1

(Only from the CH₂OH group at the terminal.)

Ratio

Ratio of formaldehyde from Reaction 1 to Reaction 2: 2 : 1

Periodic acid oxidation cleaves vicinal diols, and each terminal CH₂OH yields one mole of formaldehyde, so hexoses like glucose yield two moles while pentoses like arabinose yield one.