Sciencemadness Discussion Board

Reduction with preciptated nickel/water

Bronstein - 20-8-2012 at 23:33

I was reading up on urushibara nickel the other day in the book New hydrogenating catalysts (1971). Usually to prepare urushibara nickel you precipitate nickel metal from nickel chloride with zinc, and then react it with either acid or base.

But in the back of this book there is a chapter where they found out you can reduce things just by refluxing the substance with preciptated nickel and water, no need for any hydrogen at all. They reduce among other things styrene to etylbenzene, nitrobenzene to aniline and benzonitrile to benzylamine. Apparently they did some experiments with heavy water to prove that the hydrogen to reduce is taken from the water.

Has anyone here ever tried such a reaction? It seems almost to easy to be true.
One of the references they give is this one, so you can have an idea of what it's about :

Dr.Bob - 21-8-2012 at 05:16

Looking at the paper, it sounds like the zinc impurities (or their alloy with the nickel) might be reacting with the water to produce small amounts of hydrogen in situ which act as the reductant. So nothing too fancy. Whether it is practical compared to other simple reductions seems doubtful to me.

There are many cases where reacts have occurred catalyzed only by the impurities in the reagents, examples are the "palladium free couplings" which turned out to be catalyzed by traces of palladium in the K2CO3 used, and the "arsenic dependent" bacteria, which turned out to survive on the traces of phosphorus (not arsenic) in the media that were low levels, but not zero. So it is just showing that you can generate hydrogen from zinc and water. If you want to reduce something, you can always just use Raney (or ppt) nickel and many other hydrogen forming reductants like formic acid, cyclohexadiene, hydrazine, or zinc and acid.

Bronstein - 24-8-2012 at 00:23

Yeah, the authors themselves mention that preciptated nickel by this method always contains Ni, Zn, ZnO, Zn(OH)Cl and Zn(OH)2. And they also did X-ray diffraction studies that showed that Zn after the reduction is transformed to ZnO (among others). But that the nickel has something to do with it as zinc alone reacts very slowly with water.

It seems to me that this is a pretty easy way for the amateur to reduce isolated double bonds for example.