Chemiluminescence of Luminol

In this experiment, luminol was synthesized in order to perform a chemiluminescent (light emitting) reaction. In the first step of the reaction, triethylene glycol (TEG) was used as a solvent. Hydrazine was mixed with 3-nitrophthalic acid and heated in TEG. Because TEG has a high boiling point (~285 deg.C), the temperature was first raised to 100 deg.C to boil off water, and then raised to ~215 deg.C to drive dehydration of the liquid to completion. In the second step, 3-nitrophthalhydrazide underwent a reduction—the nitro group was reduced to an amino group. Sodium hydrosulfide was the reagent that caused the change. In step three, the energy for the generation of light for the luminol reaction came from luminol being activated with an oxidant. In this case, the oxidant activator was the mixture of 3M sodium hydroxide and hydrogen peroxide, in the presence of the catalyst potassium ferricyanide. The reaction of luminol and 3M sodium hydroxide formed a dianion, which reacted with the oxygen from hydrogen peroxide. The product lost a nitrogen, which caused the electrons to go from an excited state to ground state, and the energy was emitted as a photon of (bluish) light. The reaction is classified as exothermic. The chemiluminescent reaction was very successful resulting in a blue glow when luminol was mixed with the peroxide/iron solution; therefore, luminol was successfully synthesized. The crude product of luminol in the experiment weighed 0.136 g (7.67 x 10^-4 mol), which resulted in a percent yield of 81%. The loss of product can be concluded in different steps of the procedure. In step one, the solution boiled a little bit longer than expected and the precipitate collected by vacuum filtration was collected on filter paper in which some of the precipitate stuck to. In step two, the luminol crude product was also collected on filter paper; therefore, some of the product may have still been on the filter paper. Also, in the two vacuum filtrations, a small amount of product may have went through the filter. An IR, HNMR, and CNMR were provided by the instructor. According to the chemical formula, luminol has 4 double bond equivalents, which represent the aromatic ring. For the IR spectra, the peaks at 3300 and 3400 cm^-1 represent the amine (N-H) groups on the compound. The peaks from 1450 to 1600 cm^-1 represent the aromatic ring, and Benzene is at ~3050 cm^-1. The carbonyl group amide (O=C-N) typically shows a peak at 1690 cm^-1; however, the spectra shows the peak to be ~1670 cm^-1. The HNMR spectra has peaks between 6.5 and 8 ppm, which represents the aromatic ring. The CNMR spectra has peaks ranging from 110 to 160 ppm. The aromatic range for CNMR is 110-170 ppm. The amide peak is usually in a range from 165-175; therefore, the peak at ~162 ppm is probably the amide carbon. The range from 100-150 also represents sp2 hybridized carbons. The CNMR shows 8 carbon signals that coordinate with 8 carbons on the luminol compound.

Conclusion:

In this experiment, the compound luminol was successfully synthesized and underwent a chemiluminescent reaction. The light emitting reaction was also successful, in which a photon of blue light was emitted when luminol/sodium hydroxide solution was combined with the potassium ferricyanide/hydrogen peroxide solution.