CLAIMS
1. A method of producing s-caprolactam, comprising: the step 1 of mixing at least one selected from the group consisting of 3-oxoadipic acid and salts thereof with a catalyst and a solvent in the presence of hydrogen to produce 3-hydroxyadipic acid; and the step 2 of reacting the 3-hydroxyadipic acid which is a product of the step 1, a salt or carboxylic acid derivative thereof, or a mixture of these with hydrogen and ammonia.
2. The method according to claim 1, wherein the solvent is an aqueous solvent or an organic solvent having a polarity value of 0 to 0.3.
3. The method according to claim 1 or 2, wherein the solvent is an organic solvent that mainly contains at least one selected from the group consisting of ether solvents and ester solvents.
4. The method according to any one of claims 1 to 3, wherein the solvent is an organic solvent that mainly contains at least one selected from tetrahydrofuran, dioxane, 1,2-dimethoxyethane, diglyme, and ethyl acetate.
5. The method according to any one of claims 1 to 4, wherein the step 1 is carried out under the condition of the following (i) or (ii):
(i) in an aqueous solvent at a reaction temperature of 0°C to 50°C; (ii) in an organic solvent having a polarity value of 0 to 0.3 at a reaction temperature of not lower than 0°C and lower than 75°C.
6. The method according to any one of claims 1 to 5, wherein the step 2 is carried out in the presence of a catalyst.
7. The method according to any one of claims 1 to 6, wherein the catalyst used in the step 1 and/or the step 2 comprises one or more metals selected from the group consisting of palladium, platinum, ruthenium, rhodium, rhenium, nickel, iridium, osmium, copper, and chromium.

8. The method according to claim 7, wherein the metal is supported on at least one support selected from the group consisting of alumina, carbon, silica, titania, zirconia, tantalum oxide, niobium oxide, and zeolite.
9. The method according to any one of claims 1 to 8, wherein the partial pressure of hydrogen in the step 1 and the step 2 is 0.1 MPa to 10 MPa at ordinary temperature in terms of gauge pressure.
10. The method according to any one of claims 1 to 9, wherein the reaction temperature in the step 2 is 150°C to 280°C.
11. A method of producing 3-hydroxyadipic acid, comprising mixing at least one selected from the group consisting of 3-oxoadipic acid and salts thereof with a catalyst in the presence of hydrogen under the condition of the following (i) or (ii):
(i) in an aqueous solvent at a reaction temperature of 0°C to 50°C; (ii) in an organic solvent having a polarity value of 0 to 0.3 at a reaction temperature of not lower than 0°C and lower than 75 °C.