Luminol Formal Report

Fatima SaavedraLuminol Formal ReportSection 10

IntroductionChemiluminescence is a process where light is generated by a chemical reaction. This occurs when the reaction produces a product in an excited electronic state that relaxes the ground electronic state with concomitant emission of energy in the form of a photon-light. The excited state may relax to the ground state through radiationless (loss of energy through emission of visible light). This can also be seen when fluorescence and phosphorescence occur (involve singlet and triplet electronic states).A number of living organisms emit light through chemiluminescene reactions (they involve naturally occurring compounds). Bioluminescence is an example of chemiluminescence in which a biochemical process results in the emission of light. An example of this would be fireflies. When they are in search of a mate, the male will emit flashes of visible light that result from the reaction of luciferin with molecular oxygen in a process catalyzed by the enzyme luciferase (Reaction 1).

Reaction 1The light that is produced by fireflies and other bioluminescent organisms has baffled observers for years. There are many organisms that have developed the ability to emit light. They include jellyfish, corals, squids, fishes, insects, and marine worms. Other than fish, this list doesnt include higher forms of life. The chemiluminescent compound in fireflies is called luciferin. The enzyme is the one that induces it to emit the light-which is called luciferase. The chemiluminescent properties of luminol have a number of practical applications. A forensic assay that used to identify the presence of blood at a crime scene is one of these. When the alkaline solution of luminol and hydrogen peroxide is exposed to blood, then the characteristic of the blueis-green light associated with the chemiluminescence of luminol is observed. The iron catalyst is required for the reaction is provided by the hemoglobin present in blood.Data and Observation1.0236 grams of 3-nitrophthalic acid was used. Some of the product got stuck on the stirring rod.Diluted stock solution caused a blue luminescence. When the stock was added, the luminescence increased. The bright color faded out to a died out purple.DiscussionLuminol is synthesized by a sequence of reactions that involves the condensation of 3-nitrophthalic acid with hydrazine to produce 3-nitrophthalhydrazide, which is then reduced by sodium dithionite to form luminol (Reaction 2). The chemiluminescent reaction is demonstrated by mixing luminol with hydrogen peroxide and potassium ferricyanide (Reaction 3).

Reaction 2

Reaction 3The formation of 3-Nitrophthalhydrazide is basically a reaction in which 1,2-dicarboxylic acid and 1,2-diamine react to form a cyclic diamide or hydrazide (Reaction 4). The acid and amine are in rapid equilibrium with the corresponding ammonium salt and the carboxylate ion (the latter is not subject to a nucleophilic attack at the carbonyl carbon atom). The acid may undergo nucleophilic attack; however, the small amount of it that exists in equilibrium reacts with the free amine to produce the tetrahedral intermediate.

Reaction 4The reaction was purified by crystallization and vacuum filtration. This purification takes advantage of the fact that the impurities often have a different solubility than the compound that is being purified. Acetic acid was used in the reaction instead of HCl because acetic acid is a weak acid. Acetic acid will weakly ionize, which would lead to fewer H+ ions, while HCl would ionize strongly.ConclusionThe expected blue fluorescence was observed upon the combination of the solutions for the luminal preparation. This would mean that the synthesis occurred correctly. Luminol is used in forensic investigations in order to trace blood that could have been left behind at crime scenes. Luminol reacts with the iron that is found in the hemoglobin. Luminol can be sprayed across an area, and the trace amounts of the activating oxidant will cause the lumiol to emit a blue glow that can be seen in a dark room. The glow doesnt last long, but it can be captured with a photograph. Sources of error that could have contributed to the experiment would be unclean glassware, incorrect measurements of products, and mixing the wrong compounds.ReferenceExperimental Organic Chemistry 10th Edition