Sterically hindered, regenerable Schiff base complexes, solutions thereof and process using the same

An oxygen-sorbing and -desorbing solution consisting essentially of a solvent, an axial base and a metallo Schiff base complex, said solvent being selected from linear and branched chain alkyl-, alkylene-, ester- and halogen-substituted aromatic hydrocarbons, mixtures thereof, and mixtures thereof with linear and branched-chain non-aromatic hydrocarbons, halocarbons, and esters, said axial base being capable of providing a coordinating atom to said metallo Schiff base complex, and said metallo Schiff base complex being of the structural formula ##STR5## where M is a +2 valence metal selected from Co, Fe, Cu, Ni, Mn, Ru and Rh;

• R.sub.1 and R.sub.2 are selected from tertiary alkyl groups containing from 4 to 8 carbon atoms;
• R.sub.3 and R.sub.4 are selected from R.sub.1 and R.sub.2 and 1-methylcyclohexyl;
• R.sub.5 and R.sub.6 are selected from linear alkyl groups containing from 1 to 8 carbon atoms;
• and
• R.sub.7 and R.sub.8 are selected from R.sub.5, R.sub.6 and, taken together, a butylene group.

A process for the separation of oxygen comprising:

• (a) contacting an oxygen-containing feed stream with a solution consisting essentially of a solvent, an axial base and an metallo Schiff base complex, said solvent being selected from linear and branched chain alkyl-, alkylene-, ester- and halogen-substituted aromatic hydrocarbons, mixtures thereof, and mixtures thereof with linear and branched-chain non-aromatic hydrocarbons, halocarbons, and esters, said axial base being capable of providing a coordinating atom to said metallo Shiff base complex, and said metallo Schiff base complex being of the structural formula ##STR6## where M is a +2 valence metal selected from Co, Fe, Cu, Ni, Mn, Ru and Rh,
• R.sub.1 and R.sub.2 are selected from tertiary alkyl groups containing from 4 to 8 carbon atoms;
• R.sub.3 and R.sub.4 are selected from R.sub.1 and R.sub.2 and 1-methylcyclohexyl;
• R.sub.5 and R.sub.6 are selected from linear alkyl groups containing from 1 to 8 carbon atoms;
• and
• R.sub.7 and R.sub.8 are selected from R.sub.5, R.sub.6 and, taken together, a butylene group, thereby sorbing oxygen from said feed stream;
• and
• (b) desorbing oxygen from said solution to a product stream.

A method of reactivating the oxygen-sorbing and -desorbing capability of a solution consisting essentially of a solvent, an axial base and an metallo Schiff base complex, said solvent being selected from linear and branched chain alkyl-, alkylene-, ester- and halogen-substituted aromatic hydrocarbons, mixtures thereof, and mixtures thereof with linear and branched-chain non-aromatic hydrocarbons, halocarbons, and esters, said axial base being capable of providing a coordinating atom to said metallo Schiff base complex, and said metallo Schiff base complex being of the structural formula ##STR7## where M is a +2 valence metal selected from Co, Fe, Cu, Ni, Mn, Ru and Rh,

• R.sub.1 and R.sub.2 are selected from tertiary alkyl groups containing from 4 to 8 carbon atoms,
• R.sub.3 and R.sub.4 are selected from R.sub.1 and R.sub.2 and 1-methylcyclohexyl,
• R.sub.5 and R.sub.6 are selected from linear alkyl groups containing from 1 to 8 carbon atoms, and
• R.sub.7 and R.sub.8 are selected from R.sub.5, R.sub.6 and, taken together, a butylene group,
• comprising heating the deactivated form of said solution at a temperature from 30.degree. C. to 180.degree. C. in the absence of water and oxygen.

A method of reactivating the oxygen-carrying capability of a metallo Schiff base complex of the structural formula ##STR8## comprising (a) dissolving the oxygenated and axial base-coordinated form of said metallo Schiff base complex in a hydrophobic solvent to form a solution thereof,

• (b) contacting the solution formed in step (a) with an aqueous acid solution to strip M and axial base from said deactivated metallo Schiff base complex to form a solution of a ligand of the structural formula, ##STR9## (c) recovering said ligand from the solution formed in step (b), and (d) refluxing a nonaqueous solution of said ligand with a salt of M in the absence of oxygen to form the active form of an metallo Schiff base complex of said structural formula
• where
• M is a +2 valence metal selected from Co, Fe, Cu, Ni, Mn, Ru and Rh;
• R.sub.1 and R.sub.2 are selected from tertiary alkyl groups containing from 4 to 8 carbon atoms;
• R.sub.3 and R.sub.4 are selected from R.sub.1 and R.sub.2 and 1-methylcyclohexyl;
• R.sub.5 and R.sub.6 are selected from linear alkyl groups containing from 1 to 8 carbon atoms;
• and
• R.sub.7 and R.sub.8 are selected from R.sub.5, R.sub.6 and, taken together, a butylene group.

A method of reactivating the oxygen-carrying capability of a metallo Schiff base complex of the structural formula ##STR10## which has been deactivated by coordination of axial base thereto where M is a +2 valence metal selected from Co, Fe, Cu, Ni, Mn, Ru and Rh,

• R.sub.1 and R.sub.2 are selected from tertiary alkyl groups containing from 4 to 8 carbon atoms,
• R.sub.3 and R.sub.4 are selected from R.sub.1 and R.sub.2 and 1-methylcyclohexyl,
• R.sub.5 and R.sub.6 are selected from linear alkyl groups containing from 1 to 8 carbon atoms, and
• R.sub.7 and R.sub.8 are selected from R.sub.5 and R.sub.6 and, taken together, a butylene group, comprising removing coordinated axial base from the deactivated form of said metallo Schiff base complex.