Luminol: Structure, Synthesis, chemical

reaction, and its function.

By: Hau Huynh

Abstract

• Chemiluminescence is the emission of light during a chemical reaction. Luminol is used to reveal a light-producing chemical reaction between chemicals and hemoglobin, an oxygen-carrying protein in the blood. The focus of this presentation will be on the synthesis of luminol, the chemical reaction, and how investigators use luminol to solve the crimes.

Outline

• A. What is chemiluminescene?• B. The structure of Luminol.• C. Spectroscopic features

• IR, C NMR, H NMR

• D. Synthesis of Luminol • E. The chemical reaction • F. Applications• G. Conclusion• H. Reference

What is chemiluminescence?

• Chemiluminescence is the emission of light during a chemical reaction.

• A molecule that is chemiluminescent is oxidized in a chemical reaction to an excited state product and emits light upon deexcitation.

• Chemiluminescence is distinct from fluorescence and phosphorescence in that a chemical is used to excite a molecule and an external source of photons is not needed.

• Luminol is chemiluminescent molecule which was discovered by the German scientist H.O. Albrecht in 1928. It has been used in many chemical applications because of its chemiluminescent properties.

Structure of luminol

• Name: 5-amino-2,3-dihydro-1,4-phthalazine-dione .

• Formula : C8H7N3O2

• Melting point: 319 -320oC

IR

http://www.aist.go.jp/RIODB/SDBS/cgi-bin/direct_frame_top.cgi?lang=eng

C=0

C NMR

C3C2

C1

C4 C5

C6C7

C8

H NMR

HaHb

Hd

Hc

The synthesis of Luminol

hydrazine

3-nitrophthalic acid

The synthesis of Luminol

• 3-nitrophthalic acid (1) combines with aqueous hydrazine in a triethylene glycol solution and under heat, which substitutes the carboxylic acid -OH groups with -NH groups.

• This releases two water molecules and creates 3-nitrophthalhydrazide (2). 3-nitrophthalhydrazide combines with aqueous sodium hydrosulfite, which substitutes amino groups for the nitro groups on the benzene ring.

The chemical reaction of Luminol

3-aminophthalate

The chemical reaction of Luminol

• 3-aminophthalhydrazide (4) combines with a basic solution, which removes the hydrogen protons from the nitro groups to release two water molecules.

• The resulting molecule (5) undergoes keto-enol tautomerization to move the negative formal charges onto the carbonyl oxygens.

• A metal ion catalyst (such as copper (II), iron (III) or cobalt (II)) decomposes the hydrogen peroxide (or other oxidizing molecule) solution to make peroxide molecules available.

• A peroxide molecule is cyclically added to the enolate form (6) of the intermediate molecule. Nitrogen gas is released and 3-aminophthalate is formed in its triplet state (7). The electrons undergo intersystem crossing and then decay to their ground state, which emits a photon of light (8)

Applications A basic luminol solution combined with hydrogen peroxide and a thickening agent can be sprayed on surfaces with suspected blood traces. The solution will glow if catalyzed by the presence of a metal ion, such as iron in blood hemoglobin.

• Disadvantage

– Luminol can be catalyzed by substances such as bleach, copper, potassium permanganate (found in many dyes), saliva, brain tissue, bone marrow, rust, and vegetable enzymes.

– Secondly, luminol can destroy some genetic markers in cell DNA.

– Thirdly, it can smear bloody impressions and make prints and splatters more difficult to analyze.

Applications

Biology and Chemistry

Research – In biology research, Luminol can detect

proteins and DNA in very small concentrations.

– In chemistry research, concentration of a metal ion can be detected and reaction rate analysis of oxidizers can be tracked by the intensity of the glow of luminol.

Commercial an emergency light source for vehicles, businesses, schools, and the military.  Glowsticks are occasionally made using luminol, which are sold at many events

Conclusion

• Luminol is a chemiluminescent compound, which means that a release of light is a result of a chemical reaction.

• When luminol is placed in a basic solution, the luminol is oxidized.

• Luminol is used in biology and biochemistry for a multitude of testing

• This hemoglobin reacts with the luminol as the catalyst.

Reference

• http://www.sas.upenn.edu/~hickeyj/lumrxn.html• http://cas.bellarmine.edu/chem117a/lab/luminol.ht

m• http://people.howstuffworks.com/luminol4.htm• Journal of Physical Chemistry B July 26, 2001

v105 i29 p6993-6999• The American Journal of Physiology April 2000

v278 i4 pC646• Journal of the American Chemical Society Sept 4,

2002 v124 i35 p10250(2)