IS Sobrero Casale, Monferrato, Italy
Have you ever heard about lophine? It works similar to luminol, the substance widely used in TV series such as C.S.I. to detect blood stains.
Both are chemiluminescent organic compounds which can emit mysterious light as you might know from glow sticks. We (Fig. 1) had the unique chance to have a very close look at lophine (while the synthesis of luminol is more difficult and dangerous).
Everything started thanks to the collaboration of our chemistry teacher Elisabetta Gaita with the Università del Piemonte Orientale Avogadro of Alessandria. Our aim was to synthesize lophine, which chemists call 2,4,5-triphenylimidazole. Wearing the classic white coats and protective goggles we enthusiastically started work under the supervision of the scientists Katia Sparnacci and Guido Panzarasa. The first step was the synthesis of benzil by oxidation of benzoin with nitric acid (HNO3). This reaction needs heat and produces red-brown fumes of NO2 (Figs. 2,3) until a bright yellow solid is obtained when the liquid product has cooled down. This product is not very pure, so it must be dissolved in ethanol until a clear liquid is formed, that has to be recrystallized by putting it in ice. During our work we had to use a Buchner funnel to separate the solid component from the liquid.
The second step was the synthesis of lophine by condensation of benzil with benzaldehyde (Fig. 4), which we accomplished by heating a solution of benzil and benzaldehyde in glacial acetic acid. The product was obtained as a cream-white solid upon addition of aqueous ammonia, recovered by vacuum filtration and air-dried.
We were very excited when we tested our own lophine. We dissolved it in ethanol and went into a darkroom. To observe the chemiliuminescence, a basic solution of hydrogen peroxide (NaOH+H2O2) was added to the ethanolic solution of lophine followed by a diluted solution of sodium hypochloride commercial bleach): A yellow-green light was emitted by the mixture which was visible in the dark (Fig. 5). This experience was so impressive that a follow-up project was set up by our teacher and by professor Nadia Semino from the Marconi Institute of Tortona. Now it was our turn to teach our fellow students all about chemiluminescence and make them produce such glowing stuff themselves.
The results were presented at the European Science on Stage Festival 2013 in Slubice (Poland) and you can also fi nd an interactive poster at www.sobrero.it/liceo/clil.htm
NOTE: WHEN DEALING WITH CHEMICALS YOU MUST OBSERVE UTMOST CAUTION TO NOT HARM YOURSELF, OTHERS, OR THE ENVIRONMENT. THE EXPERIMENT DESCRIBED HERE MUST BE CONDUCTED UNDER SUPERVISION OF TEACHERS!Artikel als PDF (731 KB)
- K. Nakashima (2003). Lophine derivatives as versatile analytical tools. Biomedical chromatography 17, 83-95.
- E. Welsh (2011). What is chemiluminescence? Science in School 19, 62-68.
- “practical instruction of our teachers”