A rat that can sniff land mines was recognized last month for saving lives, NPR reported. The African giant pouched rat learned to smell explosives and to alert its human handlers in exchange for a banana. The standard explosive of land mines is TNT.
According to NPR, one rodent has been pulling more than his own weight in making Cambodia a safer country. “Magawa is a Tanzanian-born African giant pouched rat who has been trained by the nonprofit APOPO to sniff out explosives,” the article said. “With careful training, he and his rat colleagues learn to identify land mines and alert their human handlers so the mines can be safely removed.
“Even among his skilled cohorts working in Cambodia, Magawa is a standout sniffer: In four years, he has helped to clear more than 1.5 million square feet of land—an area about the size of 20 soccer fields.” In this time, the article said, Magawa has found 39 land mines and another 28 pieces of unexploded ordnance. Thankfully, he weighs too little to detonate the mines he finds.
Since after the First World War, TNT has been the standard explosive used in land mines. It’s chemically similar to picric acid.
Just a Step from Nitroglycerin
Picric acid is an explosive that was discovered around the same time as nitroglycerin and serves as a good introduction to TNT.
“Picric acid is a compound synthesized by reacting a compound called phenol, easily extracted from coal tar, with nitric and sulfuric acids,” said Dr. Ron B. Davis, Jr., Associate Teaching Professor of Chemistry at Georgetown University. “The product of this reaction is picric acid, an extremely powerful and very shock-sensitive reagent. We see some very similar-looking functional groups on [nitroglycerin and picric acid] molecules.”
Dr. Davis said that compared to nitroglycerin, picric acid is a larger molecule and exists as a solid at room temperature. Like nitroglycerin, it explodes at the slightest shock when kept dry. Picric acid, he said, was the explosive of choice during World War I.
After World War I, though, the world moved on to a close chemical cousin of picric acid—trinitrotoluene, or TNT, which Germany had already adopted.
It’s No Picric
Oddly enough, TNT didn’t start its life as an explosive.
“It was first synthesized in the 1860s, and TNT was used primarily then as a dye because of its attractive yellow color,” Dr. Davis said. “It was not until two decades later that its explosive properties were fully understood and explored.”
According to Dr. Davis, two important differences separate TNT from picric acid. The first is that TNT is slightly more difficult to detonate than picric acid, so it’s more stable. Second, TNT features a methyl group instead of picric acid’s hydroxyl, which makes TNT molecules unable to hydrogen-bond together. He said this lowers TNT’s melting point, so it can be melted down and poured into artillery shells more easily and safely than picric acid.
“TNT was adopted by the German military prior to World War I, and it had striking results. In a bit of a counterintuitive twist, the greater resistance to detonation made TNT a more damaging weapon. Shells that were filled with TNT had that extra fraction of a second to penetrate armor before exploding, whereas shells using picric acid tended to explode instantaneously on the slightest contact with their target.”
The rest of the world caught on, and TNT became the “ordnance of choice” for militaries worldwide. Now, teams of rodents just like Magawa are sniffing out TNT land mines for safe removal.
Dr. Ron B. Davis, Jr., contributed to this lecture. Dr. Davis is an Associate Teaching Professor of Chemistry at Georgetown University, where he has been teaching introductory organic chemistry laboratories since 2008. He earned his PhD in Chemistry from The Pennsylvania State University.