1: With nitrogen; water; oxygen; multimetal oxide catalyst according to Example 1,3/multimetal oxide material II of DE-(753)A19817 T=350°C; P=1350.14 - 1500.15 Torr; Gas phase; 2: With nitrogen; oxygen; multimetal oxide catalyst according to Example b,S1 of DE-(423)A4446 T=270°C; P=1275.13 - 1350.14 Torr;