Chemistry 3231 – Organic Chemistry III

Laboratory Report for Experiment #5 – "Synthesis and Chemiluminescence of Luminol"

Objective: To study the reactions necessary to synthesize luminol. Then to carry out the oxidative process to release the chemiluminescence of the molecule.

Theory: In this experiment we will synthesize luminol from 3-nitrophthalic acid. This will be done by the acyl substitution of the carboxyl groups on NTA with aqueous hydrazine and then to reduce the 3-nitro substitutent to an amino group. This has to be done in an anhydrous condition due to the fact that nitrogen is not easily acylated to the amide. Amides tend to react readily with water in an acyl substitution to reform the acid. Which is why we react the NTA in this case at high temperatures to ensure that there is little to no water present to drive the reaction backwards as well as using tiethylene glycol to set a non aqueous solution.

From Luminol we will study the effects of chemiluminescence which this molecule possesses. This property is found when the molecule is in the triplet state. This occurs when the Magnet Spin of the molecule is equal to 3, which is made up from the magnetic spin quantum numbers of the individual valence electrons. In the triplet state the electrons can undergo intersystem crossing (‘flipping’ the direction of the magnetic spin) and which emits radiation in the form of light. There are a few schools of thought in the way in which the luminol can emit this light. Firstly the luminol is reduced to an anion on the nitrogen (or the oxygen, it is resonated). From there it either is reacted with an oxidizing agent to form a diacid, releasing N2 (g) and forming a diacid releasing the photons. Or, it undergoes the reaction of the oxidation to form a negatively charged radical which then couples to form a similar structure to luminol releasing light. Since we did not run spectral data on the product formed from this reaction it is hard to tell which was formed.

Scheme II seems to be the more probable of the 2 for this reaction since to release the chemiluminescence we react the Luminol with a base and potassium ferricyanide with hydrogen peroxide. This inidcates that there will be an oxidation of luminol, which is catalyzed by the the ferric ion in solution (being reduced to ferrous ions)

Table of Chemicals:

Reagents/Products

Amount Used

Molecular Weight

Concentration

Comments
3-Nitrophthalic Acid 0.5155 g      
Hydrazine 1 mL   ~8% Concentration achieved by diluting 35% four times over.
Triethylene glycol 2 mL      
Sodium HydroSulphite 3.0465 g      
Sodium Hydroxide 3 mL   5% 5% achieved by adding 1.5 mL 10% NaOH and 1.5 mL water
Acetic Acid 1 mL   Glacial  
Potassium Ferrocyanide 20 mL   ~3.5%  
Hydrogen Peroxide 20 mL   3% 3% achieved by adding 2 mL 30% H2O2 and 18 mL water
Water 10 mL

200 mL

160 mL

     (HOT)

(COLD)
Luminol 0.1869 g (received)      

Experimental Procedure: followed the lab manual (Chemistry 3231 Lab Manual, Department of Chemistry, Lakehead University) in all steps. Refer to Lab Notebook for exact steps/procedures.

Results:

Observations:

From the synthesis of luminol we received 0.1869g. This was the wet product and should be noted that this weight will be more than the actual weight of just the product. Another reason for a low yield was probably due to the fact that in the filtration of the product that I improperly setup the instruments and had to do it over. Since there was a considerable amount of ‘washing’ involved some of the product may have dissolved into solution and not landed on the filter paper.

After all, when the Luminol and the Ferric ion solutions were added together, indeed a bright neon like light (similar to those seen at certain night clubs around town) was seen and lasted for several minutes.

Yield Data:

%Yield = (0.001055 / 0.002442) x 100%

= 43.2080%

Spectral Data:

There was no spectral data taken from this reaction.

Reference(s):

Dictionary of Organic Compounds, 5th ed. Chapman & Hall. ©1982

http://www.chem.utah.edu/MSDS/N/3-NITROPHTHALIC_ACID

http://www.msu.edu/user/grahamm9/luminol.html (I recommend this site!)

Organic Chemistry 5th ed. Morrison & Boyd. ©1992 Prentice Hall