keywords: zincdust, ironfilings, old references, german references
After some experiences with reactions described in older (german) references I want to disclose some observations made by me and what I did dig up afterwards on the historical background.
This refers to references - in special german references - from the middle of the 19th century up to the beginning of the WWII, in special the period between 1885 and 1936.
The german chemical manufacturers soon discovered the need for cooperation and coordination for optimizing the production of chemicals of all kind - this led lateron to the formation of the IG-Farben in Germany (which probably would rule the world now if there wouldnt have been this stupid accident with this Schickelgruber guy). The usability of chemical inventons in industry and the use of cheap reagents was most important - science which wasnt directly useful in the production was hardly supported if at all. (so had Mr. Neumann the man who discovered the L-PAC synthesis by bakers yeast and worldwide leading in biosynthesis not enough money to buy new rubberstoppers for his experiments - rubber was expensive these days around 1920 and Germany was poor).
Ok. And wtf does this tell for some reductions with zincdust or ironfilings?
The zincdust used in these days was by no way pure zinc. No it was an disposable from zincoxide production - hard to purify, waste, toxic waste as it contained about 8% cadmium, 88% zinc and the rest was some other metals and dirt. Zinc wasnt used for its most favorable properties but for the availability and the price.
(after WWI the cadmium was mostly removed for it has gotten a metal of worth by its own, but the purity of the zincdust never exceeded 93%)
The iron filings or iron-dust used was plain milled cast-iron which was also by no way pure Fe but a mixture with predominantly iron - and some other metals, carbon, silicium and more.
I can tell by experience that if one tries to reproduce the results described in these old references it is not a good idea to use pure zinc or pure iron from the chemsupplyhouse, much better results are possible if cast iron (smash it with a hammer, mill it or file it, sand it, whatever) is used. Same can be told for zincdust, I recommend the use of zinc from casted zinc pieces, and you dont need the hazardous DUST - filings do the job quite fine just use a little more of them and the reaction time is somewhat longer - strong stirring is a "must be" in all those reactions if mentioned in the text or not.
If you are a poor scrapyard-fearing SIGMA-ALDRICH junkie
you may try to substitute the magic impurities by adding some Al, Zn, Fe, to the reaction, but of course nothing beats the real stuff (scrapyardscrap)
As a rule of thumb:
Al - kickstarts Zn and Fe catalyzed reactions
Zn - kickstarts Fe catalyzed reactions and substitutes most of them at lower temperatures
Fe - lets Zn catalyzed reactions go to completeness
And dont forget:
The actual catalyst should make 90% or more of volume. But thats no question for the scrapyardchemist. He uses what he gets and reproduces the very good yields named in the old references without hassle.