by Marek Ples
| Introduction: The Joy of Synthesis | |
| Triboluminescent copper complex | |
| Lophine | |
| Lucygenin | |
| Luminol | |
| Zinc dithizonate | |
| More |
Creating is a marvelous pleasure that brings immense satisfaction. Whether it's crafting, painting, or even cooking, the act of bringing something new into existence is a source of pure joy. For a chemist, this delight takes on a unique form – the joy of personally synthesizing diverse substances.
Chemistry is a world of endless possibilities, where compounds and elements dance together, transforming into fascinating structures with distinct properties. The chemist becomes an alchemist in this one scientific way, wielding knowledge and skills to manipulate matter and uncover its secrets.
With each successful synthesis, a chemist experiences a profound sense of accomplishment. It's the thrill of witnessing ideas and hypotheses come to life, turning abstract concepts into tangible realities.
The joy of synthesis extends beyond the laboratory walls. In the realm of chemistry, the joy of creating is not just a pursuit of knowledge; it's a profound expression of the human spirit's capacity to explore, innovate, and shape the world.
In this laboratory snapshot, I want to present a few examples (selected from many) of preparing diverse compounds by me. You can find the details of the described syntheses in the footnotes.
Triboluminescence is a phenomenon characterized by the emission of light by crystalline materials during deformation, such as compression, fracture, or crushing. Triboluminescence is a relatively common phenomenon, but in most cases, its effect is weak and difficult to observe. Among substances that exhibit distinct triboluminescence, noteworthy examples include N-acetylanthranilic acid, uranyl(V) nitrate, coumarin, and sucrose. The copper complex [Cu(NCS)(py)2(PPh3)] is a highly efficient triboluminophore and can be easily synthesized in a laboratory.
The synthesis of the complex involves the reaction of copper(I) thiocyanate CuSCN with triphenylphosphine C18H15P (abb. PPh3) in the presence of pyridine C5H5N (abb. py) [1]. This results in the formation of a pale yellow complex (Fig.1) [2].
Fig.1 - Crystalline complex
The crystals of this compound exhibit very strong fluorescence and triboluminescence (Vid.1).
Vid.1 - Triboluminescence
The mechanism of triboluminescence is still a subject of investigation. The proposed mechanism suggests that during the crushing of crystals, the Cu-NCS bond breaks, leading to the separation of electric charges. The electric discharge may excite atmospheric nitrogen molecules, which subsequently emit light, including ultraviolet radiation. This excitation can also be transferred to molecules with fluorescent properties, explaining the similarity between the emission spectra of triboluminescence and fluorescence in this case. The phenomenon continues to be studied as certain aspects of it are far from being fully understood.
There are certain groups of chemical reactions that always attract great interest from students and teachers due to their educational value and stunning visual effect. One of such groups of reactions is chemiluminescent reactions, during which visible light is emitted. Although these reactions may seem rarely encountered, they can be observed even using substances relatively easy to synthesize.
One of the interesting chemiluminescent compounds is lophine C21H16N2. It was first synthesized in the second half of the 19th century by the Polish chemist Bronisław Radziszewski. Historically, the first method of synthesis relied on the use of hydrobenzamide C21H18N2, a compound described by Alexander Borodin. Borodin, primarily known as a classical music composer, was also a chemistry enthusiast [3].
In the process of lophine synthesis conducted by me, a simple method was applied, utilizing readily available and inexpensive chemicals such as benzoin C14H12O2, benzaldehyde C7H6O, ammonium nitrate NH4NO3, and copper acetate (Cu(CH3COO)2). In the synthesis process, benzoin is obtained from benzaldehyde and then transformed into benzil C14H10O2 [4]. Finally, benzil reacts with benzaldehyde in the presence of ammonium nitrate and glacial acetic acid CH3COOH, ultimately yielding lophine (Fig.2).
Fig.2 - Lophine
The obtained chemiluminophore can be used to conduct chemiluminescence experiments. The chemiluminescent reaction of lucigenin can be induced by a solution containing ethanol CH3COOH, hydrogen peroxide H2O2 and sodium hypochlorite NaOCl. During the reaction, lophine undergoes oxidation and emits greenish-yellow light (Fig.3).
Fig.3 - Chemiluminescence of lophine
The brightness of the light depends on temperature and other factors.
Chemiluminescence is a fascinating chemical process in which light is emitted as a result of a chemical reaction. One of the interesting compounds with chemiluminescent properties is lucigenin C28H22N4O6.
The synthesis of lucigenin begins with stage I, where 2-chlorobenzoic acid ClC6H4CO2H, aniline C6H5NH2, potassium carbonate K2CO3, copper(I) oxide Cu2O, and activated carbon C are used. After the reaction, N-phenylanthranilic acid C13H11NO2 is obtained, which is purified through extraction and reaction with hydrochloric acid HCl(aq). This acid is then dried and used in subsequent stages [5].
Stage II involves the transformation of N-phenylanthranilic acid into crude acridone C13H9NO through a reaction with sulfuric acid (VI) H2SO4. Then, acrydone is purified by recrystallization.
In stage III, acrydone is converted into N-methylacrydone C14H11NO through a reaction with iodomethane CH3I. The obtained crude N-methylacrydone is then purified by recrystallization from ethanol [6].
In the final stage, N-methylacrydone is transformed into lucigenin (Fig.4). This reaction occurs in the presence of zinc Zn, concentrated hydrochloric acid, and ethanol.
Fig.4 - Lucigenin
Lucigenin exhibits the ability to chemiluminescence during oxidation. Under suitable conditions, the lucigenin chemiluminescent reaction can produce multi-colored (green->blue, Fig.5) light.
Fig.5 - Chemiluminescence of the solution of lucigenin
The using of chemiluminescent reactions, such as those involving lucigenin, holds great potential in education, engaging students and facilitating the understanding of chemical processes. Additionally, studying chemiluminescent reactions allows for the exploration of various aspects, such as reaction kinetics, energy transfer, and the influence of different reagents and conditions on the reaction's progress.
Luminol C8H7N3O2 is one of the most commonly used chemiluminescent compounds because it emits a very bright blue light upon oxidation, making it ideal for demonstrations.
Preparing luminol is a simple process. The required ingredients include acetone C3H6O, sodium nitrate NaNO3, phthalic anhydride C8H4O3, polyethylene glycol, aluminum Al, concentrated sulfuric acid H2SO4, sodium acetate C2H3NaO2, sodium metabisulfite K2S2O5, hydrazine sulfate NH2NH2·H2SO4, and sodium hydroxide NaOH [7].
The synthesis of luminol begins with the nitration of phthalic anhydride or phthalic acid, resulting in the formation of 3-nitrophthalic acid C8H5NO6 (Fig.6). This acid then undergoes condensation with hydrazine, and the resulting 3-nitrophthalhydrazide is finally reduced to 3-aminophthalhydrazide. After conducting the reaction and removing impurities, raw luminol is obtained.
Fig.6 - Nitration
The obtained luminol can be used for conducting chemiluminescence experiments. The reaction can be activated using a catalyst such as potassium hexacyanoferrate(III) K3[Fe(CN)6]. The effects of this reaction can be observed as streaks of light that disperse in the solution (Fig.7).
Fig.7 - Brilliant blue chemiluminescence of oxidized luminol
Luminol can also react with copper complexes or heme, which has found applications in forensics (blood detection).
Photochromism, as we know, refers to the reversible alteration of a specific substance, known as a photoswitch, between two distinct forms through the absorption of electromagnetic radiation, specifically by undergoing photoisomerization. These two forms exhibit different absorption spectra, which means they absorb light at different wavelengths. In simpler terms, photochromism can be described as a color change that is reversible and occurs when the substance is exposed to light.
Dithizone C13H12N4S is a sulfur-containing organic compound and it may be prepared by reacting phenylhydrazine C6H8N2 with carbon disulfide CS2, followed by reaction with potassium hydroxide KOH. It is a good ligand, and forms complexes with many toxic metals such as lead Pb, thallium Tl and mercury Hg. Interestingly, some of these complexes possess photochromic properties. One of them is the zinc dithizonate [8].
I synthesized the complex by combining a benzene solution of dithizone with an aqueous solution of zinc chloride ZnCl2. After purification, the complex solution was evaporated, and the remaining solid was purified by recrystallization from a mixture of benzene and ethanol.
The solution of the complex in dichloromethane CH2Cl2 is pinkish red, but exposure to green, blue, or ultraviolet light causes a reversible color change to dark blue (Vid.2).
Vid.2 - Photochromic liquid
It is also possible to prepare a photochromic polymer. The video shows the color change of a film that I obtained by introducing a small amount of the described complex into the structure formed by polystyrene chains (Vid.3).
Vid.3 - Photochromic polymer
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