Description:DESCRIPTION:
Field of the invention:
[0001] The present disclosure generally relates to the technical field of organic chemistry, and in specific relates to an efficient, cost-effective, and versatile synthesis method for production of high-performance anthracene-based dyes with desirable properties for a wide range of applications.
Background of the invention:
[0002] Fluorescent dyes are indispensable in various scientific and industrial applications, including biological imaging, chemical sensing, and optoelectronics. These dyes operate by absorbing light at a particular wavelength and then emitting light at a different wavelength, allowing for the visualization and measurement of various biological and chemical processes. Among the various classes of fluorescent dyes, anthracene-based compounds have gained significant attention due to their excellent photophysical properties, such as high fluorescence quantum yield, good photostability, and strong absorbance in the UV-visible spectrum.
[0003] Despite the favourable properties of anthracene derivatives, their application is often limited by challenges in their synthesis, especially in achieving specific substitution patterns on the anthracene ring. One of the most critical challenges is the regioselective substitution at the 2nd and 6th positions of the anthracene ring. Achieving such substitution is essential for fine-tuning the electronic properties of the dye, which directly impacts its fluorescence efficiency and sensitivity. Additionally, the existing methods for synthesizing these derivatives often involve complex, multi-step processes, leading to low yields, poor solubility in common solvents, and suboptimal fluorescence efficiency.
[0004] To address these challenges, several synthesis methods have been developed for anthracene derivatives. Common approaches include the Friedel-Crafts acylation reaction, followed by various nitration and reduction processes, and the use of transition metal-catalysed coupling reactions. These methods have enabled the synthesis of a wide range of substituted anthracenes with varying degrees of success in terms of regioselectivity, yield, and photophysical properties.
[0005] A prior art US7005176B2 discloses a method for synthesizing anthracene derivatives using specific catalysts to achieve desired substitution patterns. Another patent, US9080992B2, describes the preparation of anthracene derivatives for use in organic light-emitting devices, highlighting the significance of these compounds in advanced technological applications.
[0006] However, despite these advancements, significant issues remain with the existing synthesis methods for anthracene derivatives. One of the primary drawbacks is the difficulty in achieving regioselective substitution at the 2nd and 6th positions, which limits the ability to design dyes with optimal electronic and photophysical properties. Additionally, the multi-step synthesis routes often result in low yields and require extensive purification processes to obtain the desired products with sufficient purity.
[0007] Moreover, some existing anthracene-based dyes suffer from poor solubility in common solvents, which restricts their applicability in various fields, particularly in biological systems where solubility in aqueous media is crucial. Furthermore, the fluorescence efficiency of many anthracene derivatives is often suboptimal, leading to reduced sensitivity and reliability in sensing and imaging applications.
[0008] Therefore, there is a need for a more efficient, cost-effective, and versatile synthesis method for production of high-performance anthracene-based dyes with desirable properties for a wide range of applications. There is also a need for an anthracene-based dye that has longer wavelength of emission and exhibits good solvatochromic behavior in different organic solvents. There is also a need for an anthracene-based dye that exhibits excellent photophysical properties.
Objectives of the invention:
[0009] The primary objective of the invention is to provide a more efficient, cost-effective, and versatile synthesis method for production of high-performance anthracene-based dyes with desirable properties for a wide range of applications.
[0010] Another objective of the invention is to synthesize an anthracene-based dye that has longer wavelength of emission and exhibits good solvatochromic behavior in different organic solvents.
[0011] The other objective of the invention is to synthesize an anthracene-based dye that exhibits excellent photophysical properties.
[0012] Another objective of the invention is to provide a highly regioselective method for substituting the 2nd and 6th positions of the anthracene ring, allowing for precise control over the electronic properties of the anthracene-based dye.
[0013] Another objective of the invention is to provide a synthesis process that achieves higher yields compared to existing methods, reducing waste and lowering production costs.
[0014] The other objective of the invention is to synthesize an anthracene-based dye that exhibits improved fluorescence efficiency, leading to better performance in applications such as biological imaging and chemical sensing.
[0015] The other objective of the invention is to synthesize an anthracene-based dye that is more soluble in a wider range of solvents, including aqueous media.
[0016] Yet another objective of the invention is to provide a method that simplifies the synthesis of anthracene derivatives by reducing the number of steps required, making the process more efficient and less time-consuming.
[0017] Another objective of the invention is to provide a synthesis method that can be adapted to produce a wide variety of anthracene-based compounds, making it applicable to multiple fields, from biochemistry to materials science.
[0018] Another objective of the invention is to provide a method that improves yields, and simplifying the synthesis process, whereby reduces the overall cost of producing high-quality anthracene derivatives.
[0019] Further objective of the invention is to provide a method that minimizes the use of hazardous reagents and reduces the need for extensive purification, leading to a more environmentally friendly synthesis process.
Summary of the invention:
[0020] The present disclosure proposes a synthesis method for production of high-performance anthracene-based dyes. The following presents a simplified summary in order to provide a basic understanding of some aspects of the claimed subject matter. This summary is not an extensive overview. It is not intended to identify key/critical elements or to delineate the scope of the claimed subject matter. Its sole purpose is to present some concepts in a simplified form as a prelude to the more detailed description that is presented later.
[0021] In order to overcome the above deficiencies of the prior art, the present disclosure is to solve the technical problem to provide an efficient, cost-effective, and versatile synthesis method for production of high-performance anthracene-based dyes with desirable properties for a wide range of applications.
[0022] According to an aspect, the invention provides a method for synthesizing 2-chloro-6-nitro anthracene dye. At first, 1 g to 2 g of phthalic anhydride is subjected through a nitration process to form 4-nitrophthalic acid. At least 3.1 g (0.021 moles) of the phthalic anhydride is heated with a mixture of fuming nitric acid and concentrated sulfuric acid at a temperature ranging from 100 °C to 110 °C to obtain a mixture of nitrophthalic acid. The mixture comprises 1.3 ml of fuming nitric acid and 1 ml of concentrated sulfuric acid. The mixture of nitrophthalic acid comprises 3-nitrophthalic acid and 4-nitrophthalic acid. The 4-nitrophthalic acid isolated from the mixture of nitrophthalic acid.
[0023] Next, the isolated 4-nitrophthalic acid is mixed with at least 2.4 ml (0.016 mol) of acetic anhydride to obtain 4-nitrophthalic anhydride. Next, the obtained 4-nitrophthalic anhydride is heated with chlorobenzene to obtain 2-(4-chlorobenzoyl)-4-nitrobenzoic acid. In a preferred embodiment, the obtained 4-nitrophthalic anhydride is subjected to a friedel-crafts reaction at a temperature varying from 80 °C to 100 °C with at least 50ml excess chlorobenzene to obtain 2-(4-chlorobenzoyl)-4-nitrobenzoic acid and its isomer.
[0024] Next, the obtained 2-(4-chlorobenzoyl)-4-nitrobenzoic acid is subjected through cyclization with at least 0.0 5ml to 7.7 ml of phosphorus oxychloride (POCl₃) at a temperature ranging from 60 °C to 80 °C to form 2-chloro-6-nitro-9, 10-anthraquinone, represented as formula 1.
Formula 1

[0025] Next, at least 6.9 g (0.024mol) of the 2-chloro-6-nitro-9, 10-anthraquinone (formula 1) is mixed in at least 500 ml of isopropanol in an inert atmosphere. Subsequently, at least 11 g (0.5 mol) of sodium borohydride is added in portions, with continuous stirring under reflux temperatures to form a reaction mixture.
[0026] Next, the reaction mixture is hydrolysed with a strong mineral acid to obtain a precipitate, thereby filtering the precipitate. In one embodiment, the strong mineral acid is hydrochloric acid (HCl). The reaction mixture is subjected to hydrolysis with HCl in crushed ice.
Scheme 2

[0027] Later, the precipitate is subjected through a purification process, and followed by recrystallization to yield 2-chloro-6-nitro anthracene, represented as formula 2.
Formula 2

[0028] Further, objects and advantages of the present invention will be apparent from a study of the following portion of the specification, the claims, and the attached drawings.
Detailed description of drawings:
[0029] The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, explain the principles of the invention.
[0030] FIG. 1 illustrates a flowchart of a method for synthesizing 2-chloro-6-nitro anthracene dye, in accordance to an exemplary embodiment of the invention.
[0031] FIG. 2 illustrates an excitation spectrum of 2-chloro-6-nitro anthracene, in accordance to an exemplary embodiment of the invention.
[0032] FIG. 3 depicts an emission spectrum of 2-chloro-6-nitro anthracene, in accordance to an exemplary embodiment of the invention.
Detailed invention disclosure:
[0033] Various embodiments of the present invention will be described in reference to the accompanying drawings. Wherever possible, same or similar reference numerals are used in the drawings and the description to refer to the same or like parts or steps.
[0034] The present disclosure has been made with a view towards solving the problem with the prior art described above, and it is an object of the present invention to provide an efficient, cost-effective, and versatile synthesis method for production of high-performance anthracene-based dyes with desirable properties for a wide range of applications.
[0035] According to an exemplary embodiment of the invention, FIG. 1 refers to a flowchart 100 of a method for synthesizing 2-chloro-6-nitro anthracene dye. At step 102, 1 g to 2 g of phthalic anhydride is subjected through a nitration process to form 4-nitrophthalic acid. In a preferred embodiment, at least 3.1 g (0.021 moles) of the phthalic anhydride is heated with a mixture of fuming nitric acid and concentrated sulfuric acid at a temperature ranging from 100 °C to 110 °C to obtain a mixture of nitrophthalic acid. The mixture comprises 1.3 ml of fuming nitric acid and 1 ml of concentrated sulfuric acid. The mixture of nitrophthalic acid comprises 3-nitrophthalic acid and 4-nitrophthalic acid. The 4-nitrophthalic acid isolated from the mixture of nitrophthalic acid.
[0036] At step 104, the isolated 4-nitrophthalic acid is mixed with at least 2.4 ml (0.016 mol) of acetic anhydride to obtain 4-nitrophthalic anhydride. At step 106, the obtained 4-nitrophthalic anhydride is heated with chlorobenzene to obtain 2-(4-chlorobenzoyl)-4-nitrobenzoic acid. In a preferred embodiment, the obtained 4-nitrophthalic anhydride is subjected to a friedel-crafts reaction at a temperature varying from 80 °C to 100 °C with at least 50ml excess chlorobenzene to obtain 2-(4-chlorobenzoyl)-4-nitrobenzoic acid and its isomer.
[0037] At step 108, the obtained 2-(4-chlorobenzoyl)-4-nitrobenzoic acid is subjected through cyclization with at least 0.0 5ml to 7.7 ml of phosphorus oxychloride (POCl₃) at a temperature ranging from 60 °C to 80 °C to form 2-chloro-6-nitro-9, 10-anthraquinone, represented as formula 1. In one embodiment, with this process at least 70% of 2-chloro-6-nitro-9, 10-anthraquinone is yielded.
Formula 1

[0038] The method for synthesis of Formula 1 is illustrated in scheme 1.
Scheme 1

[0039] At step 110, at least 6.9 g (0.024mol) of the 2-chloro-6-nitro-9, 10-anthraquinone (formula 1) is mixed in at least 500 ml of isopropanol in an inert atmosphere. Subsequently, at least 11 g (0.5 mol) of sodium borohydride is added in portions, with continuous stirring under reflux temperatures to form a reaction mixture.
[0040] At step 112, the reaction mixture is hydrolysed with a strong mineral acid to obtain a precipitate, thereby filtering the precipitate. In one embodiment, the strong mineral acid is hydrochloric acid (HCl). The reaction mixture is subjected to hydrolysis with HCl in crushed ice. Further, the obtained precipitate is a light yellow precipitate.
[0041] At step 114, the precipitate is subjected through a purification process, and followed by recrystallization to yield 2-chloro-6-nitro anthracene, represented as formula 2.
Formula 2

[0042] In one embodiment, the purification process includes a chromatography process. In the chromatography process, the precipitate is mixed in a mixture of dichloromethane (DCM) and hexane to form a solvent mixture. Next, the solvent mixture is applied to a top of a column filled with silica gel, and gravity or gentle pressure is used to push the mixture of dichloromethane (DCM) and hexane and the precipitate through the silica gel. As the solvent mixture flows down the column, the 2-chloro-6-nitro anthracene in the precipitate interact differently with the silica gel based on their polarity and other chemical properties, thereby by obtaining the 2-chloro-6-nitro anthracene (formula 2). The 2-chloro-6-nitro anthracene is recrystallised from chloroform to obtain at least 60 % of the 2-chloro-6-nitro anthracene as pale yellow crystals. The 2-chloro-6-nitro anthracene is a dye.
[0043] The method for synthesis of Formula 2 is illustrated in scheme 2.
Scheme 2

[0044] In one embodiment, characterization of 2-chloro-6-nitro-9, 10-anthraquinone (formula 1) shown in table 1.
[0045] Table 1:
M.P 190 °C
Molecular formula C14H6NO4Cl
Elemental analysis 1. Calc.(%) : C, 58.43; H, 2.08, N, 4.86; O, 22.26
2. Found(%) : C, 58.41; H, 2.09, N, 4.84; O, 22.23
1H NMR (d6-acetone, TMS), δ 9.04 (d, J = 2.2Hz, 1H), 8.59 (dd, J = 8.4Hz & 2.3Hz, 1H), 8.43 (d, J = 2.3Hz, 1H), 8.42 (d, J = 8.4,1H), 8.27 (d, J = 8.4Hz, 1H), 7.87 (dd, J = 2.4 Hz & 8.4Hz, 1H)
IR (νmax)cm-1 in KBr 3082, 2955, 1680, 1668, 1583, 1465, 1360, 1320, 1174, 1112, 1076, 972, 963, 870, 817, 721, 650.

[0046] In one embodiment, characterization of 2-chloro-6-nitro anthracene (formula 2) is shown in table 2.
[0047] Table 2:
M.P 211 °C
Molecular formula C14H8NO2Cl
Elemental analysis 1. Calc.(%) : C, 65.2; H, 3.10, N, 5.43; Cl, 13.78
2. Found(%) : C, 65.16; H, 3.12, N, 5.41; Cl, 13.73
1H NMR (d6-acetone, TMS), δ 8.60 (d, J = 2.24Hz, 1H), 8.49 (dd, J = 8.4, 2, 24Hz, 1H), 8.37 (s, 1H), 8.39 (s, 1H), 8.02 (d, J=8.4Hz, 1H), 7.89 (d, J = 2.3Hz, 1H), 7.87 (d, J = 8.4 Hz, 1H), 7.77 (dd, J = 8.4Hz & 2.3Hz, 1H)
IR (νmax)cm-1 in KBr 2344, 1630, 1590, 1487, 1437, 1186, 1093, 1050, 820

[0048] In one embodiment, the melting points (M.P) are determined using a hot plate, with the values reported as uncorrected. The 1H NMR spectra are recorded on a spectrometer operating at a frequency of 90 MHz. Deuterated acetone (d6-Acetone) served as the solvent, while tetramethylsilane (TMS) is utilized as the internal standard to ensure accurate chemical shift referencing.
[0049] Infrared (IR) spectral analysis is conducted using an IR spectrophotometer, with samples prepared in potassium bromide (KBr) pellets. This method provided a detailed assessment of the functional groups present in the compound, contributing to the structural characterization of the synthesized molecules.
[0050] Fluorescence spectra were acquired using a Shimadzu RF-540 fluorescence spectrometer, which employed a xenon arc lamp as the excitation source. The measurements were conducted in a quartz cell with a path length of 10 mm, ensuring precise and reliable data collection.
[0051] Given the poor solubility of the newly synthesized 2-chloro-6-nitro anthracene in low-polarity solvents, the absorption and fluorescence emission spectral properties were specifically examined in highly polar solvents, including methanol, ethanol, acetonitrile, and acetone. The use of these solvents is essential to fully dissolve the formula 2, enabling accurate spectroscopic analysis.
[0052] The fluorescence spectra for the compound (formula 2) are recorded across a broad excitation wavelength range of 230-720 nm and an emission wavelength range of 250-800 nm. This comprehensive spectral analysis allowed for the detailed investigation of the photophysical properties of the formula 2, providing insight into its behavior in various solvent environments and contributing to the understanding of its electronic transitions and potential applications in optoelectronic devices or fluorescent probes.
[0053] According to another exemplary embodiment of the invention, FIG. 2 refers to an excitation spectrum 200 of 2-chloro-6-nitro anthracene (referred to as Formula 2). FIG. 3 depicts an emission spectrum 300 of Formula 2. To investigate the fluorescence and photophysical properties, Formula 2 is subjected to a comprehensive analysis. Formula 2, characterized by a chlorine atom substitution at the C-2 position and a nitro group at the C-6 position, demonstrates significant intramolecular charge transfer effects. These effects, akin to electron-donating and electron-withdrawing behavior through the anthracene core, are reflected in the observed fluorescence and photophysical properties of the molecule.
[0054] The study involved measuring various properties of Formula 2, including absorption, fluorescence, and Stokes shift, in highly polar solvents such as methanol, ethanol, acetonitrile, and acetone, as summarized in Table 3. The absorption maximum is used as the excitation maximum for these measurements. The concentration of Formula 2 is maintained at 10-5 M. When excited at 400 nm and 495 nm, Formula 2 exhibited emission at 475 nm in both methanol and ethanol. The Stokes shift in ethanol is observed to be 80 nm, the highest among the tested solvents.
[0055] Table 3:
S. No Solvent Excitation max(nm) Emission max(nm) Stokes shift
1. Methanol 400 475 75
2. Ethanol 395 475 80
3. Acetonitrile 395 460 65
4. Acetone 410 445 35

[0056] In one embodiment, FIG. 2 and FIG. 3 present the excitation and emission spectra (fluorescence) of Formula 2. The polarity of the solvent has a pronounced effect on the emission wavelength of the compound. As shown in Table 3, the emission wavelength shifted to longer wavelengths (red shift) in polar protic solvents such as methanol and ethanol compared to non-protic solvents. This solvatochromic behaviour is attributed to the reorientation of the solvent dipoles around the excited state dipole moment of Formula 2. Upon excitation from the ground state to the excited state, solvent relaxation occurs, which stabilizes the excited state, resulting in a lower energy state and a corresponding red shift in the emission spectrum. The magnitude of this effect increases with solvent polarity, leading to a more significant red shift in emission.
[0057] Numerous advantages of the present disclosure may be apparent from the discussion above. In accordance with the present disclosure, an efficient, cost-effective, and versatile synthesis method is disclosed here for production of high-performance anthracene-based dyes with desirable properties for a wide range of applications.
[0058] The synthesized 2-chloro-6-nitro anthracene (formula 2) has longer wavelength of emission and exhibits good solvatochromic behavior in different organic solvents. The synthesized formula 2 exhibits excellent photophysical properties. The proposed method is a highly regioselective method for substituting the 2nd and 6th positions of the anthracene ring. The proposed method allow for precise control over the electronic properties of an anthracene-based dye.
[0059] The proposed synthesis method achieves higher yields compared to existing methods, reducing waste and lowering production costs. The synthesized formula 2 exhibits improved fluorescence efficiency, leading to better performance in applications such as biological imaging and chemical sensing. The synthesized formula 2 is more soluble in a wider range of solvents, including aqueous media.
[0060] The proposed method simplifies the synthesis of formula 2 by reducing the number of steps required, making the process more efficient and less time-consuming. The proposed synthesis method is adapted to produce a wide variety of anthracene-based compounds, making it applicable to multiple fields, from biochemistry to materials science.
[0061] The proposed method improves yields, and simplifying the synthesis process, whereby reduces the overall cost of producing high-quality anthracene derivatives. The proposed method minimizes the use of hazardous reagents and reduces the need for extensive purification, leading to a more environmentally friendly synthesis process.
[0062] It will readily be apparent that numerous modifications and alterations can be made to the processes described in the foregoing examples without departing from the principles underlying the invention, and all such modifications and alterations are intended to be embraced by this application.
, Claims:CLAIMS:
I/We Claim:
1. A method for synthesizing 2-chloro-6-nitro anthracene dye, comprising:
subjecting phthalic anhydride through a nitration process to form 4-nitrophthalic acid;
mixing the 4-nitrophthalic acid with acetic anhydride to obtain 4-nitrophthalic anhydride;
heating the obtained 4-nitrophthalic anhydride with chlorobenzene to obtain 2-(4-chlorobenzoyl)-4-nitrobenzoic acid;
subjecting the obtained 2-(4-chlorobenzoyl)-4-nitrobenzoic acid through cyclization with phosphorus oxychloride (POCl₃) to form 2-chloro-6-nitro-9, 10-anthraquinone, represented as formula 1;
Formula 1

mixing the obtained 2-chloro-6-nitro-9, 10-anthraquinone in isopropanol under an inert atmosphere, and adding sodium borohydride to form a reaction mixture;
hydrolysing the reaction mixture with a strong mineral acid to obtain a precipitate, thereby filtering the precipitate; and
subjecting the precipitate through a purification process followed by recrystallization to yield 2-chloro-6-nitro anthracene, represented as formula 2,
Scheme 2

wherein the obtained 2-chloro-6-nitro anthracene is a fluorescent dye.
2. The method for synthesizing 2-chloro-6-nitro anthracene dye as claimed in claim 1, wherein the nitration process involves heating at least 3.1 g (0.021 moles) of the phthalic anhydride with a mixture of fuming nitric acid and concentrated sulfuric acid at a temperature ranging from 100 °C to 110 °C.
3. The method for synthesizing 2-chloro-6-nitro anthracene dye as claimed in claim 1, wherein the 4-nitrophthalic acid is mixed with at least 2.4 mL (0.016 mol) of acetic anhydride.
4. The method for synthesizing 2-chloro-6-nitro anthracene dye as claimed in claim 1, wherein at least 50 ml of chlorobenzene is mixed with the obtained 4-nitrophthalic anhydride.
5. The method for synthesizing 2-chloro-6-nitro anthracene dye as claimed in claim 1, wherein the obtained 2-(4-chlorobenzoyl)-4-nitrobenzoic acid subjected through the cyclization with 0.0 5ml to 7.7 ml of phosphorus oxychloride (POCl₃).
6. The method for synthesizing 2-chloro-6-nitro anthracene dye as claimed in claim 1, wherein at least 6.9 g (0.024mol) of the 2-chloro-6-nitro-9, 10-anthraquinone is mixed in at least 500 ml of isopropanol in an inert atmosphere.
7. The method for synthesizing 2-chloro-6-nitro anthracene dye as claimed in claim 1, wherein at least 11 g (0.5 mol) of the sodium borohydride is added to the isopropanol, in portions, with continuous stirring under reflux temperatures to form the reaction mixture.
8. The method for synthesizing 2-chloro-6-nitro anthracene dye as claimed in claim 1, wherein the strong mineral acid is hydrochloric acid (HCl), wherein the reaction mixture is subjected to hydrolysis with HCl in crushed ice.
9. The method for synthesizing 2-chloro-6-nitro anthracene dye as claimed in claim 1, wherein the purification process includes a chromatography process that comprises:
mixing the precipitate in a mixture of dichloromethane (DCM) and hexane to form a solvent mixture, and
applying the solvent mixture to a top of a column filled with silica gel, and allowing the solvent mixture to flow down, thereby obtaining the 2-chloro-6-nitro anthracene.
10. The method for synthesizing 2-chloro-6-nitro anthracene dye as claimed in claim 1, wherein the2-chloro-6-nitro anthracene is recrystallised from chloroform to obtain at least 60 % of the 2-chloro-6-nitro anthracene as pale yellow crystals.