TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The reducing environment comprises metal and aqueous carboxylic acid (preferably zinc or magnesium and aqueous acetic acid, more preferably zinc and 80-90% acetic acid). The phenethyl halide used is chloride, bromide or iodide, preferably bromide. The halogenated hydrocarbons employed are chloroform, dichloromethane, dichloroethane, tetrachloroethane, preferably dichloroethane. The solvent employed for solvent extraction is halogenated hydrocarbons, preferably dichloromethane.    TECHNOLOGY FOCUS - PHARMACEUTICALS - In the reaction, step (A) is initially conducted at room temperature for 15-35 (preferably 20-30) hours followed by at an elevated temperature of 50-90 (preferably at 65-80) degrees C for 15-35 (preferably for 20-30) hours. In the step (A), NPP and aniline is used in 1:1 ratio. In the step (A), the reaction is quenched with water preferably ice cold water and 4-ANPP is isolated by filtration followed by alkali neutralization. In the step (B), the highly alkaline medium has a pH around 14 and is provided by alkali metal hydroxide preferably sodium hydroxide. The step (b) is proceeded optionally purifying 4-ANPP. The reaction employs and adds 4-anilino-N-phenethylpiperidine in step (C), 4-5 times propionyl chloride with respect to 4-anilino-N-phenethylpiperidme. ACTIVITY - Analgesic. No biological data given.    MECHANISM OF ACTION - m-Opioid receptor agonist.    EXAMPLE - In a three neck round bottom flask equipped with mechanical stirrer and water condenser, 4-piperidone hydrochloride monohydrate (15.36 gm) and aniline (20.95 gm) was added. To this mixture, zinc (26.14 gm) and 90% acetic acid (120 gm) were added. The reaction mixture was stirred at room temperature for 12 hours and at 50-70 degrees C for 12 hours. Water was then added to the reaction mixture and filtered. Crushed ice was added to the filtrate and was neutralized with excess of aqueous sodium hydroxide solution. The crude 4-anilinopiperidine was obtained by filtration. In two neck round bottom flask equipped with condenser, 4-anilinopiperidine (17.6 gm), and 100% sodium hydroxide (50 ml) was added. The reaction mixture was heated up to 120 degrees C and 2-phenethyl bromide (37 gm) was then added. The reaction mixture was stirred for 2 hours. After the completion of the reaction, the reaction mixture was poured in the ice cooled water. The crude product was obtained by filtration and recrystallized from petroleum ether (60-80 degrees C) to give colorless crystals of 4-anilino-N-phenethyl piperidipure fentanyl N-(1-phenethyl-4-piperidyl)propionanilide). In two neck round bottom flask equipped with condenser pressure equalizing funnel and calcium chloride guard tube, a solution of 4-anilino-N-phenethyl piperidine (0.10 moles), in dichloroethane (55 ml) was taken. To this solution, propionyl chloride (9.25 gm) was added drop wise through pressure equalizing funnel with continuous stirring. After the completion of the addition, the mixture was further stirred for 5 hours. After the completion of the reaction, the reaction mixture was washed with 20% sodium hydroxide solution. After work up, colorless crystals of pure fentanyl having melting point of 82-83 degrees C, was obtained.