The electrochemical hydrodimerization of formaldehyde has been investigated by potential-dependent and time-dependent in situ Fourier transform IR spectrometry. The formation of ethylene glycol as the major product along with propane-1,2 diol and propane-1,3 diol was observed spectroscopically for both type of experiments. The spectra were complex over the region 1000-1700 cm(-1) due to equilibrium products formed in the base electrolyte. In the time-dependent experiments, interfacial loss of paraformaldehyde was observed along with an increase in formaldehyde concentration at the interface. This has been attributed to the unzipping of paraformaldehyde. A mechanism for the unzipping reaction is presented.