Acetylide or Carbide salts are the reason why you should never work acetylene gas with Silver, Copper or Ag/Cu plated utensils: These unstable crystalline explosive compounds form with relative ease by the ionic exchange between acetylene gas and silver or copper salts (reaction outlined below). Silver Nitrate was chosen as the silver donor for the first synthesis as it is both readily soluble in water (1 gram per 0,4ml at 25C) and is easily available at reasonable prices, much like Acetylene gas. Both are perfectly legal and unrestricted substances.
Below, FOR INFORMATIONAL PURPOSES ONLY, the manufacture of a small batch of each is outlined. The entire synthesis takes less than an hour if done properly. Do not try to scale up the procedure, as these are very sensitive compounds which are capable of causing great damage in large enough quantities… It should be noted that although the possession of the compounds required for this synthesis does not constitute in the infringement of any law, the synthesis of any explosive compound consists in a serious criminal offence.
Once again I discourage anyone to attempt these procedures, and if you choose to do so you are doing it at your own risk.
Silver Acetylide Synthesis:
1g Silver Nitrate (AgNO3(s)) (d. 4.35g/cc)
100mL Vacuum Filtering Erlenmeyer flask.
10g Calcium Carbide (CaC2(s)) (d. 2.22g/cc) (unnecessary if acetylene gas is available, as from a welding torch)
250mL Vacuum Filtering Erlenmeyer flask
|100mL Distilled Water ((H2O)(l)) (d.1g/cc)
||60mL Buchner Funnel.
|50mL Ethanol ((C2H5OH (l)) (d. 0.8g/cc)
||Glass tubing, 6mm diameter.
Rubber corks, rubber tubing.
The reaction in this lab was carried out in a specially constructed apparatus, which splits up the reaction in two steps, which are carried out simultaneously in two reactor vessels. The two reactions are:
Vessel one, the gas generator (first step), produces Acetylene Gas from the reaction of Calcium Carbide in water (this is, of course, unnecessary if acetylene is available from a welding gas tank):
CaC2(s) + H2O(l) => C2H2(g) + CaO(s) (300cc of Acetylene gas are produced per gram of Calcium Carbide)
Than Acetylene Gas reacts with Silver Nitrate in solution to produce the insoluble Silver Acetylide crystals:
C2H2(g) + AgNO3(aq) => Ag2C2(s) + HNO3(aq)
Silver (Ag+) cation has +1 charge, Acetylide(-C2) anion has -2 charge, simply exchanging charges gives: Ag2C2, Silver (I) Acetylide.
A note on proportions: Acetylene dissolves 1cc per gram of water at 25C
The apparatus is set up as outlined above with 10 grams CaC2 in the 250mL Erlenmeyer, 50mL water in the buchner funnel and 1 gram of AgNO3 solution in 20mL water on the 100mL Erlenmeyer. The valve on the buchner funnel is opened so as to provide a steady trickle of water into the calcium carbide. As the Calcium Carbide reacts with water it produces Acetylene Gas (300 litres per kilogram) and leaves an insoluble Lime (Calcium Oxide, CaO). Calcium Hydroxide forms if excess water is used (CaO(s) + H2O(l) => Ca(OH)2(s)). The acetylene gas travels along the rubber tube and bubbles through the silver nitrate solution out of the glass tube that goes through the cork.
As the two reactions proceed simultaneously, more calcium carbide is converted into Calcium Oxide on the left flask, and the brown/black silver fulminate precipitate forms in the other flask. A brown gas is emitted out of the second flask. This gas must be properly vented as it consists mainly of Hydrogen and Acetylene, and is explosively flammable. The reaction takes about 10 minutes to complete, after which the silver acetylide is removed from the flask, filtered, washed with 100mL of distilled water and 50mL of ethanol, and allowed to dry.
Detonation velocity: 3460 m/s.
Trauzl test: 145cmï¿½ (181).
Shock-sensitivty: 2 kg – 3.4 cm.
Explosion.Temp.: 217ï¿½ C.
There are 2 other ways of producing Silver Acetylide:
1. Precipitation of SA out of ammoniacial solution
2. Precipitation out of Nitric acid solution
The apparatus and procedures used as exactly the same as outlined above, except ammonia or Nitric Acid are used instead of distilled water on the small flask.
Silver nitrate is solubilized in water and so much Ammonia (-Solution.) is added until the brownish Silver oxide-precipitate disappears and goes into solution. Then Acetylene is bubbled into this solution. One can first see a yellow, then brown, and finally a grey-white precipitate. 5.0 g Silver nitrate yields exactly 3.498 g between 3.521 g SA – according to the formula is of a secondary silver carbide(Ag2C2).
Silver nitrate is in solubilized in water, Nitric acid being added. It appears just like with the neutral SA a white, flaky precipitate that also is light-sensitive. Presumed Formula: Ag2C2*AgNO3 or Ag3C2NO3. It is not light sensitive, unlike the acetylide formed by the method outlined above.
The precipitation of SA in neutral and nitric acid solution goes faster and cleaner than in ammonicial solution.
Explosive Properties for the ammonia-precipitated silver acetylide are as follows:
Deflagration with release of soot (C) , dull explosion(report). More shock-sensitive than Mercury fulminate. Detonation velocity: 1880 m/s, Trauzl test: 132 cmï¿½. Shock-sensitivity: 0,5 kg 15 cm. Explosion. Temp.: 177ï¿½ C
For the nitric acid precipitated Ag2C2 the properties are the same as the water precipitated acetylide (properties above.) C.
Decompositon Reaction.: Ag2C2*AgNO3 –> 3 Ag + CO2 + CO + 0,5 N2 + 185 cal.
* Stettbacher/Escales, Initialexplosivstoffe
* Federoff, Encyclopedia of Explosives Vol.1
Acetylide explosives are unique in that unlike almost every other explosive known their detonation results in the formation of absolutely no gases (Ag2C2(s) => Ag2(s) + C(s)). The heat liberated is not sufficient to gasify the products and the explosive effect is entirely due to the rapidity of liberation of heat and its expansive effect on the adjacent air (this is akin to what occurs in an atomic bomb, where all the energy output is radiative and the blast results from the expansion of the surrounding air as it absorbs the energy and heats up).
Silver Acetylide is very sensitive to shock, friction and heat, exploding violently when ground hard between two solid surfaces or when struck by a solid blow between two hard surfaces. Upon burning, even single crystals detonate with a very loud report and substantial shock. Surfaces around the explosive are stained by metallic silver. The picture to the right shows one gram of the low power Ammonia precipitated Silver Acetylide detonating over a 10cm diameter glass dish. Despite the lower velocity of detonation and gas displacement, the shock was still enough to crush the dish. Click on the picture to watch a short (208k) video of the detonation.
Acetylide Heat test (206k): Two small amounts of silver acetylide are dropped on a hot plate first set to 200C, than to 250C. The first one is a very small amount and detonates in steps. The second amount is larger and detonates instantly. The sound on the video is poor because it overwhelms the microphone.
Similar in properties to Silver Acetylide, except that like Calcium Carbide it is easily decomposed in water. The synthesis has to be performed very rapidly and the product must be washed thoroughly in anhydrous ethanol and vacuum desiccated if any reasonable yield is to be had. This particularly procedure employed a solution of Copper Chloride in dilute ammonia. The result is a rust colored powder which detonates with a bright orange (due to carbon) fireball. The detonation is more energetic than for the Acetylide (47% TNT, as compared to 33% TNT for Ag2C2), but less violent when unconfined.
Click on the pictures to watch the Copper Carbide detonation video: (696k)