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A sample of crude Pendimethalin containing 18 weight percent of N-nitroso-pendimethalin was synthesized according to the procedure described in U.S. Pat. 4,621,157. Primary denitrosation was achieved by treating the crude, molten sample with a 5 molar excess of 37% HCl (based on contained N-nitroso-pendimethalin) at 105° C. After 1.5 hours, the concentration of N-nitroso-pendimethalin had decreased to <1.0 weight percent. The molten product was neutralized with dilute caustic and washed with hot water and cooled to room temperature. A 120 mg sample of the resulting solid was heated to 170° C. under 20 mm Hg vacuum for 15 minutes. The recovery of Pendimethalin was essentially quantitative and the concentration of N-nitroso-pendimethalin had decreased to 0.8 ppm.

1. additionwith dilute caustic
2. washwashed with hot water
3. temperatureA 120 mg sample of the resulting solid was heated to 170° C. under 20 mm Hg vacuum for 15 minutes