The aqueous photolysis of ethylene glycol adsorbed on geothite
Suspensions of goethite (α-FeOOH) were photolyzed in aerated ethylene glycol-water solutions at pH 6.5, with ultraviolet light in the wavelength range300–400 nm. Under these conditions, formaldehyde and glycolaldehyde were detected as photoproducts. Quantum yields of formaldehyde production ranged from 1.9 7times; 10 -5 to 2.9 × 10 -4 over the ethylene glycol concentration range of 0.002-2.0 mol/ℓ, and gave evidence that the reaction occurred at the goethite surface. Quantum yields of glycolaldehyde were 20% less than those of formaldehyde, and displayed a concentration-dependent relationship with ethylene glycol similar to that of formaldehyde. Immediately after photolysis, Fe 2+ was measured to be 4.6 × 10 -7 mol/ℓ in an aerated suspension containing 1.3 mol/ℓ ethylene glycol, and 8.5 × 10 -6 mol/ℓ in the corresponding deoxygenated suspension. Glycolaldehyde was not generated in the deoxygenated suspensions. These results are consistent with a mechanism involving the transfer of an electron from an adsorbed ethylene glycol molecule to an excited state of Fe 3+ (Iron[III]) in the goethite lattice, to produce Fe 2+ and an organic cation. In a series of reactions involving O 2 , FeOOH, and Fe 2+ , the organic cation decomposes to form formaldehyde and the intermediate radicals “OH and” CH 2 OH. OH reacts further with ethylene glycol in the presence of O 2 to yield glycolaldehyde. Aqueous photolysis of ethylene glycol sorbed onto goethite is typical of reactions that can occur in the aquatic environment.