Molar mass 117.15 g/mol | Formula C5H11NO2 | |
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N-Methylmorpholine N-oxide (more correctly 4-methylmorpholine 4-oxide), NMO or NMMO is an organic compound. This heterocyclic amine oxide and morpholine derivative is used in organic chemistry as a co-oxidant and sacrificial catalyst in oxidation reactions for instance in osmium tetroxide oxidations and the Sharpless asymmetric dihydroxylation or oxidations with TPAP. NMO is commercially supplied both as a monohydrate C5H11NO2·H2O and as the anhydrous compound. The monohydrate is used as a solvent for cellulose in the Lyocell process to produce cellulose fibers.
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Solvent of cellulose
NMMO monohydrate is used as a solvent in the Lyocell process to produce Tencel fiber. It dissolves cellulose to form a solution called dope, and the cellulose is reprecipitated in a water bath to produce a fiber. The process is similar but not analogous to the viscose process. In the viscose process, cellulose is made soluble by conversion to its xanthate derivatives. With NMMO, cellulose is not derivatized but dissolves to give a homogeneous polymer solution. The resulting fiber is similar to viscose; this was observed, for example, for Valonia cellulose microfibrils. Dilution with water causes the cellulose to reprecipitate, i.e. the solvation of cellulose with NMMO is a water sensitive process.
Cellulose remains insoluble to most solvents since it has a strong and highly structured intermolecular hydrogen bonding network, which resists common solvents. NMMO is able to break the hydrogen bonding network that keeps cellulose insoluble to water and other solvents. Similar solubility has been obtained in a few solvents, particularly a mix of lithium chloride in dimethyl acetamide and some hydrophilic ionic liquids.
Dissolution of scleroproteins
Another use of NMO is in the dissolution of scleroprotein (found in animal tissue). This dissolution occurs in the crystal areas which are more homogeneous and contain glycine and alanine residues with a small number of other residues. How NMO dissolves these proteins is scarcely studied. Other studies, however, have been done in similar amide systems (i.e. hexapeptide). The hydrogen bonds of the amides can be broken by NMO.
Oxidant
NMO, as an N-oxide, is an oxidant. It is used as a stoichiometric oxidant to regenerate the main catalyst after the main catalyst has been reduced by the substrate. For example, the toxic and volatile osmium tetroxide needs to be added in stoichiometric amounts to effect dihydroxylation, but if continuously regenerated with NMO, the amount can be reduced to catalytic quantities.