Introduction

First of all many thanks go to CHEM_GUY for his continuous urging of the Hive community to try Urushibara Nickel reduction on phenylnitropene. This reduction turned out to be easier than any so far encountered. This is not based on any of the excellent references pertaining to Urushibara that have been mentioned on the hive, only chem_guys postings!

Procedure

Dissolve 4.0g Nickel Chloride hydrate (light green crystals) in 75 ml 95% ethanol w/ mag stirring and warming to 50°C. After salt is dissolved remove stir bar and add 1ml water and 1ml conc. HCl.¹ While solution at 50°C slowly add 5g regular Reynolds wrap torn up into 0.25 x 1.0in strips in 1g portions with manual stirring. The aluminum will SLOWLY react with the nickel salt forming the metal Ni_(s) through metathesis as a dark grey chunky powder which settles to the bottom. A gentle effervescence of hydrogen occurs during reaction. Add aluminum at a rate that maintains a steady effervescence and keeps temperature roughly in the 50°C range. Note this may take up to two hours! At the end of Al addition all green color from nickel salt should be discharged. If any color remains add another gram of aluminum and wait for soln to clear. Precipitated Nickel powder was added to 100ml 20% NaOH soln and manually stirred at 60°C for 30 min. Excess NaOH is decanted and nickel is washed with 5 x100ml aliquots of distilled water to remove excess base. At this point Urishubara nickel catalyst is prepared and ready for reduction.

Dissolve 5g pure phenylnitropropene in 50ml Ethanol and add to Ni solution.² Now slowly add 3ml conc. HCl³ and 1 gram shredded aluminum w/ manual stirring. Aluminum will slowly dissolve with a more vigorous effervescence of hydrogen than the first step. Maintaining good stirring with a glass stirring rod is essential in beginning. Attempted magnetic stirring will result in frustration because nickel is ferromagnetic and will stick to stirbar preventing surface area exposure necessary for reduction. After aluminum is dissolved add three more milliliters HCl and one more gram Al. Repeat adding acid and Al until 10 grams Al and about 30ml HCl has been added. Aluminum reacts slowly. Expect addition to take about six hours, longer if temp falls below 50°C. Constant stirring towards end is not necessary, just give mix a good stir occasionally.

After all aluminum is added and mostly decomposed slowly pour in a soln of 30g NaOH in 100ml H₂O with careful stirring. Wear goggles and be careful! Base neutralization is highly exothermic! In 30 minutes all aluminum sludge will solvate into bottom aqueous layer and a nice orange alcohol layer reeking of amine will settle out on top. Nickel is not dissolved by the NaOH so it will remain floating around between the two layers but this does not present a major problem. After all, it’s not poisonous like mercury or anything! Now decant off the top orange organic layer and distill off alcohol down to a orange stinky syrup completely different smelling than the P2NP. Dissolve these goodies in acetone and slowly add sulfuric acid to precipitate the amine sulfate. Voila!!!!!! about 3 grams light yellow amphetamine sulfate.

Notes

1. Addition of water and acid found to be necessary to initiate rxn between NiCl₂ and Al.
2. When nitropropene was added to NiCl₂ soln before conversion to Ni powder was complete some polymerization occurred greatly reducing yield. It seems essential to add P2NP to rxn after Ni is fully precipitated.
3. Use of Sulfuric acid produced inferior results causing polymerization of P2NP to red tar.

Increasing Yield: Use overhead mechanical stirring to keep nickel catalyst better suspended during reduction. Re-extract aqueous NaOH/Al layer w/ toluene and work up in standard manner. Use larger amount of nickel catalyst and more aluminum for H₂ generation.