Spontaneous Ether Hydrolysis on Cryogenic Water Ice Surfaces

We report the hydrolytic cleavage of C-O bonds in aliphatic ethers at cryogenic water ice surfaces under ultrahigh vacuum conditions. Ethers are conventionally resistant to hydrolysis, requiring strong Brønsted acids and elevated temperatures for C-O bond activation; their reactivity toward neutral water ice at temperatures as low as 10-50 K is therefore unexpected. Using Cs+ reactive ion scattering and low-energy sputtering in combination with isotopic labeling (H2O vs D2O), we demonstrate that dimethyl ether (DME), tert-butyl methyl ether (tBuOMe), and diethyl ether (DEE) undergo hydrolysis to form the corresponding deuterated alcohols upon contact with amorphous and crystalline D2O ice between 10 and 150 K. Isotopic incorporation establishes D2O ice as the source of the incorporated hydrogen. CH3OD was formed even at 10 K in codeposited DME-D2O films and it persisted on crystalline ice, while tBuOMe exhibited distinct product selectivity through the appearance of a tert-butyl carbocationic fragment in low-energy sputtering. These observations reveal an unexpected chemical reactivity of cryogenic water ice toward aliphatic ethers and establish ether hydrolysis as a previously unexplored low-temperature surface reaction.