# What did actually happen when Staudinger tried to synthesise diamond?

It is a famous reaction that used to be a teaching lab experiment, but is now banned in Germany, because it is too dangerous. To quote-translate quite liberally from the German www.seilnacht.com:

In a stone quarry near Zurich, Hermann Staudinger attempted to artificially produce a diamond by reacting the potassium-sodium melt with tetrachlorocarbon in a bomb tube. The attempt failed as the mixture tore the bomb tube apart.
In einem Steinbruch bei Zürich versuchte Hermann Staudinger einen Diamanten künstlich herzustellen, indem er die Kalium-Natrium-Schmelze mit Tetrachlorkohlenstoff in einem Bombenrohr reagieren ließ. Der Versuch misslang, da die Mischung das Bombenrohr zerfetzte.

I was probably one of the last students who were still able to see this experiment, and while considerably down scaling the actual set-up, it was still one of the most powerful explosions I ever witnessed.

To me it was actually surprising that I found pages, while researching this reaction, that asked whether $\ce{CCl4}$ can act as a solvent in the Wurtz Reaction, or that in the Wurtz reaction of carbon tetrachloride and sodium no product would be formed, because $\ce{CCl4}$ is too stable to react.

However, due to this I found the following passage in Inorganic Chemistry:

Tetrahaloalmethanes can be reduced by strong reducing agents, such as alkali metals. For example, the reaction of carbon tetrachloride with sodium is highly exoergic: \begin{align} \ce{CCl4 (l) + 4 Na (s) &-> 4 NaCl (s) + C (s)}& \Delta_\mathrm{r}G^\circ &=\pu{-249 kJ mol^-1} \end{align} This reaction can occur with explosive violence with $\ce{CCl4}$ and other polyhalocarbons, so alkali metals such as sodium should never be used to dry them.

Unfortunately I reached a dead end with finding more literature about the reaction. I am especially interested in the mechanism, and the final products. I would assume that the above equation only represents a theoretical model, and the products will likely be carbon dioxide and other combustion related products. I'd be interested to know if there are any practical and/ or theoretical studies to the kinetics and thermodynamics of the reaction.

If the source does not cover tetra-, but tri-, or bihalogenated methane, I assume it is fine, too, but it should go beyond the Wurtz reaction ($\ce{2 R-Cl + 2 Na -> R-R + 2 NaCl}$).

• We need a tag for this kind of question... like... reaction? – orthocresol Jun 28 '17 at 13:32
• @orthocresol I tried that, but it wouldn't let me. They really hate fun at stack exchange :( – Martin - マーチン Jun 28 '17 at 13:38
• @Martin-マーチン So how was this reaction initiated? And are you interested in the products of a controlled reaction with dilute carbon tetrachloride in an inert solvent, or in Staudingers bomb? – Karl Jun 28 '17 at 19:36
• I know very little about chemistry, so I don't know whether there's any connection, but.... en.m.wikipedia.org/wiki/Detonation_nanodiamond – WGroleau Jun 29 '17 at 2:15
• Isn't it possible that the $\ce{NaCl}$ gets incorporated into the diamond structure. In such case, the diamond wouldn't be pure though. – Pritt says Reinstate Monica Jun 30 '17 at 3:35

This is not really an answer, but more like a historical and literature review. Anyway, I hope it can help to further understand the reaction the the ideas behind.

First of all, thaditional Wurtz reaction suggests formation of 2D bonds such as $\ce{R^1 - R^2}$, whereas the idea in Staudinger's experiment is to obtain hree-dimensional network, ideally the the $\mathrm{sp^3}$ diamond hybrid state. Reaction of alkali metals with organics with high halogen content most likely will always lead to an explosion. For this reason qualitative Lassaigne's test should always be performed carefully, and one must not use fire extinguishers with tetrachloromethane for burning sodium.

According to the great review in [1, p. 8], the ﬁrst documented record of a combustion reaction between a metal and halocarbon compound refers to the ways of obtaining aluminium carbide for technical methane production. In 1907 Camille Matignon observed a very exothermic reaction between hexachlorobenzene and aluminium [2]:

$$\ce{10 Al + C6Cl6 ->[\pu{225^\circ C}] 2 Al4C3 + 2 AlCl3}$$

In 1913 H. Staudinger published his attempts to synthesize ethylenedione $\ce{O=C=C=O}$ [3]. He suggested abstracting the halogen atoms ($\ce{X}$) from either oxalyl chloride and -bromide $\ce{(COX)2}$ by a reaction with potassium or its sodium alloy ($\ce{NaK}$). This is one of the experiments performed by Staudinger (doing science was much more fun back then):

In einer starken Bombe wurde aus 5 g Kalium und 5 g Natrium die flüssige Kalium-Natrium-Legierung hergestellt, dazu ein Röhrchen mit 8 g Oxalylbromid gegeben, und die Bombe nach dem vollständigen Evakuieren zugeschmolzen. Wenige Sekunden nach dem Zertrümmern des Röhrchens trat äußerst heftige Explosion unter gewaltiger Detonation ein, die nur durch glücklichen Zufall ohne erhebliche Beschädigung des einen von uns verlief.
Liquid potassium-sodium alloy was prepared from 5 g of potassium and 5 g of sodium in a strong bomb, then a tube of 8 g of oxalyl bromide was added, and the bomb was melted after complete evacuation. A few seconds after the tube had been trimmed, and an extremely violent explosion ensued, with a great detonation, which proceeded only by chance without considerable damage to one of us.

Formation of an unknown highly reactive intermediate such as Dioxyacetylenkalium was suggested, but it was not confirmed experimentally.

A decade later, in 1922, Staudinger reported explosive reactions of alkali and alkaline earth metals with partially and perhalogenated solvents ($\ce{CH2Cl2}$, $\ce{CCl4}$). He again assumed the formation of different very instable species on contact that would be very sensitive to mechanical impact and thus trigger an explosive reaction. [4, part "5. Explosion mit Alkalimetallen"].

At the same time he also proposed usage of reaction between various alkali and alkaline earth metals ($\ce{Na, K, Ba}$) with halogenated organics with short $\ce{R}$ ("Rest des Moleküls") ($\ce{CH2Cl2}$, $\ce{CHCl3}$, $\ce{CCl4}$, $\ce{CH2Cl-CH2Cl}$, $\ce{CHCl2-CHCl2}$, $\ce{CHCl2-CCl3}$, $\ce{C2Cl6}$, $\ce{CHCl=CHCl}$, $\ce{CHCl=CCl2}$, $\ce{CCl2=CCl2}$, also corresponding $\ce{Br, I}$-derivatives) as an ammo detonating charges:

• DE Patent 396,209 1922 "Verfahren zur Darstellung von Sprengmitteln" (DPMA Publikationsnummer CH 100 199 A);
• DE Patent 391,346 1922 "Verfahren zur Initialzündung von Sprengstoffen" (DPMA Publikationsnummer CH 100 200 A).

He also underlined that the more halogenated the molecule is and the less other groups are present, the more vigorous the explosion will be. In addition, potassium shows better overall performance due to electropositivity ("Ver­gleicht man die Reaktionsfähigkeit der ver­ schiedenen Alkalimetalle, so ist das elektropositivste, das Kalium, das reaktionsfähigste, Lithium das reaktionsträgste"), but various amalgams or alkali metal mixtures will outperform potassium (flux).

Based on this, later its been proposed that the explosive reaction between sodium and tetrachloromethane to make diamond. His idea was implemented in late 1980s for obtaining diamonds in TNT/RDX detonation soot [5].

Finally, an autoclave synthesis based on original Staudinger work (funny enough, they didn't cite it) implementing sodium and tetrachloromethane [4] resulted in successful nanodiamond synthesis (in a 2% yield), and, subsequently, a well-recieved report in Nature in 1998 [6]:

$$\ce{CCl4 + 4Na ->[\pu{700^\circ C, 48 h}; Ni-Co (cat)] C(diamond) + 4 NaCl}$$

We call it the reduction-pyrolysis-catalysis (RPC) route. According to the free energy calculations $\Delta G^\circ (\text{diamond}) = \pu{-416.7 kcal mol^{-1}}$ and $\Delta G^\circ (\text{graphite}) = \pu{-417.4 kcal mol^{-1}}$, $$\ce{CCl4 + 4 Na -> C(diamond) + 4 NaCl}$$ and $$\ce{CCl4 + 4 Na -> C(graphite) + 4 NaCl}$$ are thermodynamically spontaneous. Formation of graphite (amorphous carbon) and diamond is possible, and the yield of graphite (amorphous carbon) and diamond may be determined by kinetics.

The role of $\ce{Ni-Co}$ catalyst is not clear yet, and athors suggested than experimentation with other transition metals can potentially improve the process.

Review [1] points out that idea of diamond synthesing is mentioned in Staudinger's monography [7], though I failed to find this book, so unfortunately I cannot provide any substantial details from there.

### Bibliography

1. Koch, E.-C. Metal-fluorocarbon based energetic materials; Wiley-VCH: Weinheim, 2012. ISBN 978-3-527-32920-5.
2. Matignon, C. Comptes rendus hebdomadaires des séances de l’Académie des sciences 1907, 145, 676–679.
3. Staudinger, H.; Anthes, E. Ber. Dtsch. Chem. Ges. 1913, 46 (2), 1426–1437. DOI 10.1002/cber.19130460222.
4. Staudinger, H. Angewandte Chemie 1922, 35 (93), 657–659. DOI 10.1002/ange.19220359302.
5. Greiner, N. R.; Phillips, D. S.; Johnson, J. D.; Volk, F. Nature 1988, 333 (6172), 440–442. DOI 10.1038/333440a0.
6. Li, Y.; Qian, Y.; Liao, H.; Ding, Y.; Yang, L.; Xu, C.; Li, F.; Zhou, G. Science 1998, 281 (5374), 246–247. DOI 10.1126/science.281.5374.246.
7. Staudinger, H. Arbeitserinnerungen; Hüthig Verlag, 1961.
• Thanks for the extensive review, it's a good read, and much more thorough than mine. I assume you also couldn't find any mentions of the kinetics or proposed reaction mechanisms? I also was looking for [7] without any luck, maybe somewhere in Germany there still is a physical copy... – Martin - マーチン Jul 25 '17 at 5:51
• It looks like UB Gießen, UB Frankfurt, ULB Darmstadt, UB Mainz, Stadtbibliothek Worms, and, what's more relevant for you, UB Marburg (Signatur = O 61/11) have physical copies. But again, it looks like an interesting reading, but I don't think there is anything mechanism-related (see the book's TOC) – andselisk Jul 25 '17 at 7:28
• Indeed, it is unlikely there is any of that in there. But most certainly it will be an interesting read. I mean the scales they were operating with at the time, incredible... – Martin - マーチン Jul 25 '17 at 8:23
• A great answer, but I'd like to add that explosive reactions like this don't go to equilibrium. The full reaction products would include everything from unreacted alkali metal to unreacted carbon tet, and a wide range of bizarre (and not necessarily stable) carbon-chlorine compounds with a Cl:C ratio less than 4. These will be very hot, and nearly all gases, so they will also burn when they hit the air, further complicating things. But the mixture will be dominated by the energetically favoured materials you mention. – Securiger Aug 21 '18 at 11:23