Carbonylation gets a phase lift: The usual liquid-phase, high-pressure processes for carbonylating formaldehydes are avoided in a novel vapor-phase reaction. Using an acid zeolite (Faujasite) at near-atmospheric pressure dimethoxymethane (DMM; the dimethyl acetal of formaldehyde; see scheme) is carbonylated to produce methyl methoxyacetate (MMAc). This approach provides a new route to ethylene glycol under mild conditions.