Sultan Qaboos UniversityCollage of ScienceDepartment of ChemistryOrganic Chemistry Laboratory (CHEM4425)

Experiment 79: Preparation of lophine and conversion into its piezochromic and photochromic dimers

Done by:Fatma AhmedSubmitted to Dr:Date:13/5/2015

Abstract:A simple and efficient synthesis of 2,4,5-triphenylimidazole(Lophine) is achieved by refluxing a solution of benzil, benzaldehyde and ammonium ethanoate in ethanoic acid.Oxidation Of lophine in a solution of potassium hydroxide and ethanol with a dilute aqueous potassium ferricyanide solution at 5C produces a light violet solid(2,4,5-triphenylimidazolyl),which dimerizes to yield two dimers,photochromic and piezochromic dimers.

Introduction:

Imidazoles are a class of heterocyclic compounds that contain nitrogen .Heterocyclic imidazole derivatives have attracted considerable attention because of their unique optical properties. These compounds play a very important role in chemistry as multipurpose analytical tools. Lophine (2,4,5-triphenyl-1H-imidazole) (I) is an attractive fluorescence and chemiluminescence compound. The chemiluminescence properties of this synthetic organic compound was reported for the first time by Radziszewski (1877). He showed that lophine emits a yellow light when it reacts with oxygen in the presence of a strong base. Since then many lophine derivatives have been synthesized and studied with regards to their optical properties. Lophine was chosen as the molecule of the week (December 15, 2008) by the American Chemical Society with the following summary "Lophine (2,4,5-triphenyl-1H-imidazole) exhibits lemon yellow chemiluminescence in solution and is one of the few long-lasting chemiluminescence molecules. It forms dimmers that have piezochromic and photochromic properties .They are useful as radical-forming agents or as photo-oxidizing agents for photo-resists, PS plates or proofing materials, or as photochromic agents for sun glasses or window glasses.

3.Results and discussion:The reaction started by dissolve benzyl, benzaldehyde and ammonium ethanoate in ethanoic acid and heated this mixture to reflux for one hour. The color was yellow during this time. After one hour water was added to the mixture and yellow precipitate was formed and it was collect by filtration with suction .Then the filtrate was neuturlized by and yellow precipitate was formed and it was collect by filtration with suction again .The two crops were combined and recrystilize with aqueose ethanol. The melting point (94-95) shows that the reaction of preparing lophine doesn't occur. So lophine was shared to prepare the next step .Preparation of lophine can be explained by the following reaction:

scheme1: A shows the mechanism of the lophine preparation. Next step was preparation of piezochromic and photochromic dimers by dissolve the potassium hydroxide and 2,4,5-triphenylimidazole in ethanol with heating and stirring .A 1.5g lophine was added. A solution of potassium ferricyanide and water was added to the ethanoic mixture at such a rate that the temperature of the reaction does not exceed 10 C with vigorously stirring to make sure that the precipitate formed and does not dissolve if the temperature is higher than 10 C. In the initial stages of the addition , violet coloration developed to be replaced by a light grey precipitate. After addition was complete, precipitate was filtered with suction , washed and dried. About 2.42 g violet powder produced with poor yield .. The low yield probably due to experimental errors, impurities and losses of some product during transferring between glassware .The melting point was(144.3-146.5C) while the literature isThis difference is due to presence of impurities in the product.

scheme1B :shows the mechanism of the piezochromic and photochromic dimers preparation.When the preparation was finished 20mg of the product was dissolve in toluene. Then it was stored in the dark after the solution had become colourless, it was stand in strong sunlightAnd a small amount of the product was grind using a mortar .The color turns from light violet to dark violet.

Table1: IR- spectral dataWavenumber (cm -1)

Function GroupPeak Strength

745C-H(aromatic)Strong

1560C=Cmedium

1604C=Nmedium

Strong peaks appeared at cm-1 , cm-1 for C N andaromatic C H groups. In addition, at cm-1 medium peak was appeared for (Aromatic) C C group.Table2: 1H-NMR spectral data.(ppm)

#of H

splittingGroupJ (Hz)

Table3: 13C-NMR spectral data.(ppm)

# of C

130.71

128.82

129.73

138.44

166.95

77.66

149.57

4. Experimental:4.1.General: 1H and 13C NMR spectra were determined in CDCl3. IR spectra were recorded by Agilent Technologies ,Cary 630 FTIR.Apparatus condition:A 250 RBF and a 1L beaker were drying in ahot oven Equipments:Magnetic stirrer, oil bath, Hotplate, Apparatuses for reflux, , Suction filtration, recrystallization Materials:

Name of compound and PurtyMolar mass(g/mol)QuantitySafety

Benzaldehyde 106.12.65gtoxic

Benzil210.25.25 girritant

Ammonium ethanoat77.1Ca.10 g

Glacial ethanoic acid(100%)_Corrosive

Ethanol(95%)_Flammable,toxic

Ammonium hydroxide(ca.30% )-Corrosive, irritant

2,4,5-triphenylimidazole296.41.5 g-

Potassium ferricyanide-4.5 g-

Potassium hydroxide pellets -12.0 gCorrosive,hygroscopic

Light petroleum(bp40-60 oC)-flammable

Toluene-flammable

Procedure:

1. Preparation of 2,4,5-triphenylimidazole: Dissolve the benzyl, benzaldehyde and ammonium ethanoate in 100 mL glacial ethanoic acid in a 250 mL round-bottomed flask containing a magnetic stirrer bar, and heat the mixture to reflux for 1h with stirring (the solution must be stirred). After this time, cool the mixture to room temperature and filter to remove any precipitate which may be present. Add 300 mL of water to the reaction filtrate and If the precipiate is gooey, dont do the filtration and simply decant the solution, add the water to the decanted solution, and proceed with the neutalization.collect the precipitate by filtration with suction. Neutralize the filtrate with ammonium hydroxide and collect the second crop of solid Combine the two crops of precipitate and recrystallize from aqueous ethanol. Record the yield and mp of your purified material.

2. Preparation of piezochromic and photochromic dimers :

Dissolve the potassium hydroxide in 100 mL of 95% ethanol with heating and to this add 1.5 g of 2,4,5-triphenylimidazole. When fully dissolved add the mixture to a 1 L beaker containing a large magnetic stirrer bar and cool to 5C in an ice-water bath with stirring. Prepare a solution of the potassium ferricyanide in 450 mL of water and place this in an addition funnel clamped securely over the beaker. Add the potassium ferricyanide solution to the vigorously stirred ethanolic mixture at such a rate that the temperature of the reaction does not exceed 10C. (This should require about 1 h.) Near the end of addition, the rate can be increased. In the initial stages of the addition, a violet colouration develops to be replaced by a lightlycoloured precipitate. After addition is complete, filter off the precipitate with suction, washing thoroughly with water (5 x 50 mL). Dry the precipitate on the filter by rapid washing with cold 50% ethanol (10 mL) followed by light petroleum(2 x 25 mL). Record the yield, appearance and mp of your material and store it in the dark. Place a small quantity of your product in a mortar, grind it and observe the colour change. Dissolve 20 mg of the material in 30 mL of toluene, stopper and store the mixture in the dark. After the solution has become colourless or nearly so, stand the solution in strong sunlight or irradiate it with a bright tungsten light and note the effect. Return the solution to the dark and observe it after a day or so. Interpret the results.

5. Conclusion:Finally, the lophine and its dimers were synthesised7. References: http://pubs.sciepub.com/wjoc/1/1/2/ http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2968781/ D. M. White , J. Sonnenberg, Oxidation of Triarylimidazoles. Structures of the Photochromic and Piezochromic Dimers of Triarylimidazyl Radicals, J. Am. Chem. Soc., 1966, 88 (16), pp 38253829, Publication Date: August 1966. Kenichiro Nakashima, a* Yuriko Fukuzaki, a Rie Nomura, a Ryo Shimoda, a Yasuko Nakamurafl Naotaka Kurodafl Shuzo Akiyama ~ & Knut Irgum b, Fluorescence and Chemiluminescence Properties of Newly, Developed Lophine Analogues, Department of Analytical Chemistry, University of Umea, S-901 87 Umea, Sweden, Received 9 September 1997; revised version received 13 October 1997.