Reactions of Glycol

Ethylene glycol (ethane-1,2-diol) carries two primary -OH groups and shows the general reactions of alcohols, doubled. With metallic sodium it forms mono- then disodium glycolate. Its -OH groups convert to halides with a halogen acid (or PCl3/PCl5/SOCl2); with HI or P/I2 it first gives 1,2-diiodoethane, which then loses I2 to form ethene. On heating with concentrated HNO3/conc. H2SO4 it forms the explosive dinitroglycol (ethylene glycol dinitrate). Under DEHYDRATION conditions glycol gives different products depending on conditions: at 773 K it forms the three-membered cyclic ether oxirane (1,2-epoxyethane, losing H2O); with dilute H2SO4 or anhydrous ZnCl2 under pressure in a sealed tube it forms acetaldehyde (via vinyl alcohol, which tautomerises to ethanal); and on distillation with concentrated H2SO4 it forms the six-membered cyclic diether 1,4-dioxane (losing two moles of H2O). On OXIDATION, depending on the oxidant, glycol can give glycolaldehyde, glycolic acid, glyoxal, glyoxalic acid or oxalic acid (with nitric acid or alkaline KMnO4); with PERIODI …