The formaldehyde condenses with the two active hydrogens to give a dimethylol-aldehyde. the aldehyde group may then be reduced in situ by another mole of formaldehyde, which is itself oxidized to formic acid. Alternatively, the dimethylol-aldehyde may be isolated and reduce catalytically. The same chemistry, the so-called Tollens reaction, is used to synthesize pentaerythritol and trimethylolpropane. Trimethylolethane s used for alkyd resins and urethanes