HYDROGEN-BONDING .45. THERMODYNAMIC AND IR STUDY OF THE HYDRATES OF N-METHYLMORPHOLINE OXIDE AND QUINUCLIDINE OXIDE - EFFECT OF HYDRATE STOICHIOMETRY ON STRENGTH OF H-O-H...O-N HYDROGEN-BONDS - IMPLICATIONS FOR THE DISSOLUTION OF CELLULOSE IN AMINE OXIDE SOLVENTS

N-Methylmorpholine oxide forms two hydrates containing 2.5 and 1 mole H2O respectively. Equilibrium dissociation vapor pressure measurements show that the strength of H-O-H...O-N hydrogen bonds in the higher hydrate (15.83 kcal mol-1) is greater than in the monohydrate (12.01 kcal mol-1). The failure of cellulose to dissolve in N-methylmorpholine oxide when the H2O content is greater than 2 moles H2O per mole of amine oxide may arise because H2O is more tightly bound to the N-O group at higher H2O content, rather than because the amine oxide oxygen is "saturated" with two or more hydrogen bonds. Quinuclidine oxide forms a crystalline monohydrate; no other stable hydrates are observed at 25-degrees-C. The similarity of the IR spectra for bound H2O in N-methylmorpholine oxide monohydrate and quinuclidine oxide monohydrate and the similarity of thermodynamic parameters for the dissociations of these two hydrates suggests that they have the same ribbon-type hydrate structure.