I,I-Dimorpholinethane is shown to be the principal product of the reaction between acetaldehyde and morpholine, in the presence of a dehydrator. In the liquid state I,I-dimorpholinethane is in a dissociation equilibrium with morpholine and N-vinylmorpholine, whose extent increases with temperature and becomes relevant above 70°-80°C. The two dissociation products have a similar volatility and can be distilled jointly; after condensation, however, they recombine with heat development. By collecting them at very low temperature, one can prevent recombination and have a metastable equimolar mixture of morpholine and N-vinylmorpholine. In any case the enamine can undergo any reaction wich is not sensitive to the presence of morpholine; in particular it can be polymerized in the presence of acids and give low molecular weight polymers.