Transition metal catalyst free catechol oxidation to quinone via photo-catalysis

Abstract

Transition metal complexes as catalysts and, occasionally, basic pH 9-11 as a reaction condition were employed to imitate the catecholase activity. Using base as a catalyst, under photo- mediated condition the catalytic aerobic oxidation of the proxy substrate 3,5-di-tert- butylcatechol (DTBC) in polar protic solvent very fast was shown in this invention to be a functional mimic of catecholase activity. The Michaelis-Menten kinetic model's enzymatic substrate inhibition pattern was used to describe the kinetic manifestation of 3,5-di-tert- butylcatechol (DTBC) oxidation. Under photo-mediated condition the oxidation of 3,5-di-tert- butylcatechol (DTBC) was observed very fast which may be due to the higher energy increases the activation energy and under basic pH condition catechol oxidizes to 3,5-di-tert- butylcyclohexa-3,5-diene-1,2-dione (DTBQ).

Description

[0001] TRANSITION METAL CATALYST FREE CATECHOL OXIDATION TO QUINONE VIA PHOTO-CATALYSIS

[0002] FIELD OF THE INVENTION

[0003] The present invention relates to transition metal catalyst free catechol oxidation to quinone via photo-catalysis. Particularly, present invention relates to a photo-mediated fast oxidation of 3,5-di-tert-butylcatechol (DTBC) to 3,5-di-tert-butyl-c>-benzoquinone(DTBQ). More particularly, the present invention relates to an eco-friendly process for the formation of 3,5-di-tert-butyl-c>-benzoquinone (DTBQ) from 3,5-di-tert-butylcatechol (DTBC) which involves no external transition metal base as a catalyst and is carried out under photo-irradiation.

[0004] BACK GROUND OF THE INVENTION

[0005] The metal free catechol oxidation under photo-mediated in basic pH condition which is very fast is studied in the present invention. It involves the use of metal free condition, under photon mediated the electron of the molecule excited from ground state and oxygen which may be form ozonide J. Org. Chem. 1987, 52, 5616-5621 in intermediate step and the oxidation of the catechol occurred in excited state which is stable in room temperature (25 °C - 30 °C).

[0006] Reference may be made to the article “Angew. Chem. Int. Ed. 2016, 55, 4759-4762”, wherein only photons / electron used as catalyst in presence of copper the pseudo oxidative process is disclosed. In this invention we have showed that photon used as a catalyst to form 3,5-di-tert-butylcatechol (DTBC) to 3,5-di-tert-butyl-c>-benzoquinone (DTBQ).

[0007] Reference may be made to the journals “Inorg. Chem. 2002, 41, 1788-1794”, wherein the pH dependence on catecholase activity is investigated in the presence of an appropriate buffer using synthetic model (Copper complex). In this invention, we have shown that the 3,5-di-tert-butylcatechol (DTBC) oxidized to 3,5-di-tert-butyl-o-benzoquinone (DTBQ) in the presence of base without any transition metal complex as an activating agent or the catalyst.

[0008] Reference may be made to the journals “Dalton Trans. 2018, 47, 9385-9399”, wherein it describes how metal complexes' (copper complex) catecholase activity is increased. In this invention, we have shown that the 3,5-di-tert-butylcatechol (DTBC) oxidized to 3,5-di-tert-butyl-o-benzoquinone (DTBQ) in the presence of base without any transition metal complex as an activating agent or the catalyst.

[0009] Reference may be made to the article “Dalton Trans. 2014, 43, 14726” wherein it describes the catechol oxidase activity that is the catalytic aerobic oxidation of catechol to o-quinone at the presence of molecular oxygen where a hydroxo bridge dicupper centre acted as the active catalytic centre. In this invention, we have shown that the 3, 5 -di-tert-butyl catechol (DTBC) oxidized to 3,5-di-tert-butyl-o-benzoquinone (DTBQ) in the presence of base without any transition metal complex as an activating agent or the catalyst.

[0010] Reference may be made to the journals “Inorg. Chem. 2011, 50, 7540-7554”, wherein the catecholase activity of several biomimetic synthetic model complexes has been investigated to determine the precise function of metal ions in catechol oxidation. DTBC, or 3,5-di-tert-butylcatechol, was frequently employed as a model substrate. In this invention, we have shown that the 3,5-di-tert-butylcatechol (DTBC) oxidized to 3,5-di-tert-butyl-o-benzoquinone (DTBQ) in the presence of base without any transition metal complex as an activating agent or the catalyst.

[0011] Reference may be made to the journals “During the oxidation of catechol, the catalytically active metal centre of mono, di-, or polynuclear complexes comprising mostly Ni, Inorg. Chem.

[0012] 2013, 52, 13442-13452, Mn, Inorg. Chem. 2003, 42, 6274-6283, and Co, New J. Chem. 2015, 39, 200-205 metal ions experiences one or two electron reduction, after which the metal centre regenerates its active state when Chreoxidizes it. In this invention, we have shown that the 3,5-di-tert-butylcatechol (DTBC) oxidized to 3,5-di-tert-butyl-o-benzoquinone (DTBQ) in the presence of base without any transition metal complex as an activating agent or the catalyst.

[0013] Reference may be made to the journal “Inorg. Chem. 2012, 51, 8750-8759, wherein the catecholase activity is influenced by ligand centre reduction. In this invention we have showed that very fast catechol oxidation without used any ligand and metal.

[0014] Reference may be made to the journal “Chem. Biodiversity 2023, 20”, which disclosed organic bases like triethylamine and diethylamine can effectively catalyse the aerobic oxidation of 3,5-di-tert-butylcatechol (DTBC), but the rate is very slow and the reaction mechanism occursthrough radical mechanism. However, the mechanistic pathway and its specific kinetics are still completely unknown, and there was no in-depth knowledge of the insight of base-only catalysed catechol oxidation. In this invention we have showed photo induced metal free very fast catechol oxidation with detailed kinetic study.

[0015] Reference may be made to the journal “Inorg. Chem. 2006, 45, 7480-7487”, wherein two pathways are used for the catechol oxidation reactionin which one is base catalyzed pathway where catalyst is base, but the detail kinetics and the mechanistic pathway is totally unknown. In this invention we have studied detail in the very fast catechol oxidation process.

[0016] Therefore, the present invention shows the photo-mediated metal free catecholase activity under basic pH condition that is very fast. At first bases are used as a catalyst where no transition metal was used and showed the detailed kinetic manifestation but the rate was slow. Interestingly it was observed that the rate is very fast under photo irradiation process which is totally unknown till now.

[0017] OBJECTS OF THE INVENTION

[0018] Main object of the present invention is to provide a transition metal catalyst free catechol oxidation to quinone via photo-catalysis.

[0019] Another object of the present invention is to provide a process of photo -mediated very fast catechol oxidation in presence of stoichiometric amount of base.

[0020] Yet another objective of the present invention is to activate molecular di-oxygen under ambient conditions.

[0021] SUMMARY OF THE INVENTION

[0022] The following is a condensed description of the disclosure to give the reader with a basic understanding. Its main goal is to present some of the principles described in this document in a simpler version as a prologue to the more extensive exposition that follows.In accordance with the main aspect, the present invention provides a photo-mediated transitionmetal catalyst free process for the catechol (DTBC) oxidation to quinone (DTBQ), comprising the steps of:

[0023] i. mixing3,5-di-tert-butylbenzene-l,2-diol (DTBC), 1.0 equivalent to 5 equivalent of an electrolyte and a polar protic solvent followed by stirring at a temperature in the range of 25°C- 30°C for a time period in the range of 10 to 20 minutes and bubbling O2 through the solution;

[0024]

[0025] 3 , 5-di-tert-butylbenzene- 1 ,2-diol (DTBC)

[0026] ii. applying LED lights under basic pH condition for a time period in the range of 10 to 20 minutes and at a temperature in the range of 25 °C - 30 °C to obtain 3,5-di-tert- butylcyclohexa-3,5-diene- 1,2-dione (DTBQ);

[0027] >

[0028]

[0029] 3, 5-di-tert-butylcyclohexa-3,5-diene-l, 2-dione (DTBQ).

[0030] In another embodiment of the present invention, the yield of the 3,5-di-tert-butylcyclohexa-3,5-diene- 1,2-dione is in the range of 85 to 97 %.

[0031] In another embodiment of the present invention, the LED light applied under basic pH condition is selected from the group consisting of blue LEDs, Green LEDs or Violet LEDs.

[0032] In another embodiment of the present invention, the wavelength of the blue LEDs is 410-430 nm.

[0033] In another embodiment of the present invention, the wavelength of the Green LEDs is 520-560 nm.In another embodiment of the present invention, the wavelength of the Violet LEDs is 320-400 nm.

[0034] In another embodiment of the present invention, the basic pH conditions have pH in the range of 9- ll.

[0035] In another embodiment of the present invention, the polar protic solvent is selected from the group consisting of methanol, isopropanol, ethanol or propanol.

[0036] In another embodiment of the present invention, the electrolyte is selected from the group consisting of tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutylammonium iodide, or tetrabutylammonium perchlorate.

[0037] In another embodiment of the present invention, the process conditions were exothermic in range of 25 °C - 30 °Cat elevated concentrations.

[0038] In yet another embodiment of the present invention, the process is versatile in varieties of concentrations from 0.05 M to 6.0 M concentration with a desired volume of 2.0 mL to 1.0 Litre.

[0039] BRIEF DESCRIPTION OF THE DRAWING

[0040] FIG. 1 represents Sketch of three electrodes (1) Pt wire: Counter electrode, (2) Ag / AgCl electrode: Reference electrode and (3) Glassy carbon electrode: Working electrode.

[0041] FIG. 2 represents Sketch of set up for photo-mediated metal free catechol oxidation. (A) 410 -430 nm, 320 - 400 nm and 520 - 560 nm (Light source), (B) Glassy carbon electrode, (C) Pt wire, (D) Ag / AgCl electrode, (E) Alligator clip, (F) Cable for electrode, (G) Electrochemical cell, (H) Teflon lid for G, (I) Retard stand and (J) Magnetic stirrer.

[0042] FIG. 3 represents 'H NMR spectrum of the product 3,5-di-terZ-butyl-o-benzoquinone (DTBQ) in CDCh.

[0043] FIG. 4 represents13C NMR spectrum of the product 3,5-di-terLbutyl-o-benzoquinone (DTBQ) in CDCh.FIG. 5 represents Electronic absorption spectral change for the reaction of 3,5-di-tert-butylcatechol (DTBC) (10‘4- 10'1) M, cyclic hindered amine (10‘4- 10'1) M and O2 (excess) in polar protic solvent.

[0044] FIG. 6 represents Plot of rate vs. [DTBC] for the aerobic oxidation of 3, 5 -di -tert-butyl catechol (DTBC) in polar protic solvent at 25 °C - 30 °C using (10'5- 10'3) M [cyclic hindered amine] as catalyst under normal light. Inset. Double reciprocal Plot of rate vs. [DTBC] . (\^max 3.34 x IO'4MS'1, KM = 2.2x1 O'4M).

[0045] FIG. 7 represents Plot of v / (Vmax- v) vs. 1 / [DTBC] for the aerobic oxidation of 3,5-di-tert-butylcatechol (DTBC) in polar protic solvent at 25 °C - 30 °C using (1O'5-1O'3)M [cyclic hindered amine] as catalyst.] (Double reciprocal plot).

[0046] FIG. 8 represents Cyclic voltammogram of 3,5-di-tert-butylcatechol (DTBC) (blue line) and the stoichiometric mixture of 3,5-di-tert-butylcatechol(DTBC) and Base (cyclic hindered amine) (red line) in polar protic solvent under argon atmosphere. The stoichiometric mixture of 3,5-di-tert-butylcatechol(DTBC) and Base (cyclic hindered amine) in other polar protic solvent saturated with O2 (scan speed: 100 mV / s, 0.1 M supporting electrolyte, glassy carbon working electrode, Pt-wire counter electrode, Ag / AgCl reference electrode, RT). Arrow indicates the direction of the scan.

[0047] FIG. 9 represents Cyclic voltammogram of 3,5-di-tert-butylcatechol(DTBC) (10‘3- 10'1) M and the mixture of 3,5-di-tert-butylcatechol (DTBC) and change in Base (cyclic hindered amine) concentration in polar protic solvent under argon atmosphere (scan speed: 100 mV / s, 0.1 M supporting electrolyte, glassy carbon working electrode, Pt-wire counter electrode, Ag / AgCl reference electrode, 25 °C - 30 °C). The arrow indicates the direction of the scan.

[0048] FIG. 10 represents Electronic absorption spectral change for the reaction of 3,5-di-tert-butylcatechol(DTBC) (10‘4- 10'1) M, cyclic hindered amine (10'4-10'x) M and O2 (excess) in another polar protic solvent.

[0049] FIG. 11 represents Plot of rate vs. [DTBC] for the aerobic oxidation of 3,5-di-tert-butylcatechol (DTBC) in polar protic solvent at 25 °C - 30 °C using (10'5- 10'3) M [cyclic hindered amine] ascatalyst. Double reciprocal Plot of rate vs. [DTBC], (Vmax = 3.8 x 10'4MS'1, KM = 2.9 x 10'4M).

[0050] FIG. 12 represents Plot of v / (Vmax- v) vs. 1 / [DTBC] for the aerobic oxidation of DTBC in polar protic solvent at 25 °C - 30 °C using (1 O'5- 1 O'3) M [cyclic hindered amine] as catalyst.]

[0051] FIG. 13 represents Cyclic voltammogram of 3,5-di-tert-butylcatechol (DTBC) (black line) and the stoichiometric mixture of 3,5-di-tert-butylcatechol (DTBC) and Base (cyclic hindered amine) (red line) in polar protic solvent under argon atmosphere. The stoichiometric mixture of 3,5-di-tert-butylcatechol (DTBC) and Base (cyclic hindered amine) in polar protic solvent saturated with O2 (scan speed: 100 mV / s, 0.1 M electrolyte, glassy carbon working electrode, Pt-wire counter electrode, Ag / AgCl reference electrode, 25 °C - 30 °C. Arrow indicates the direction of the scan.

[0052] FIG. 14 represents EPR spectrum of the reaction mixture of 3,5-di-tert-butylcatechol(DTBC) and base at t = 10 minutes.

[0053] FIG. 15 represents ESLMS mass spectrum of 3,5-di- / / 7-butyl- -benzoc|uinone(DTBQ).

[0054] FIG. 16 represents Cyclic Voltammetry study of polar protic solvents under LEDs (410-430 nm) condition in polar protic solvents.

[0055] FIG. 17 represents Cyclic Voltammetry study of polar protic solvents under LEDs (320-400 nm) condition in polar protic solvents.

[0056] FIG. 18 represents Cyclic Voltammetry study of polar protic solvents under LEDs (520-560 nm) condition in polar protic solvents.

[0057] FIG. 19 represents Cyclic Voltammetry study of 3,5-di-tert-butylcatechol(DTBC) and base under photo irradiation condition in polar protic solvents.

[0058] FIG. 20 represents Photo-mediated metal free synthesis of 3,5-di-terZ-butyl-o-benzoquinone (DTBQ) from 3,5-di-tert-butylcatechol(DTBC).DETAILED DESCRIPTION OF THE INVENTION

[0059] The present invention provides a photo-mediated process for the catechol oxidation which is very fast under basic pH condition, electron may be the catalyst in this very fast oxidation process.

[0060] In a well dried four-neck round bottom flask, 10.0 gm to 20.0 gm of compound (1) 3,5-di-tert-butylbenzene-l,2-diol (DTBC) electrolyte (1.0 equiv. to 5.0 equiv.) 20.0 mL of polar protic solvent were taken, and then the mixture was stirred at 25 °C - 30 °C for around 10.0- 20.0 minutes. Then O2 was bubbled through the solution while blue LEDs / Green LEDs / Violet LEDs (410 - 430 nm, 520 - 560 nm and 320 - 400 nm) was applied under basic pH condition. The reaction was allowed to proceed for 10.0- 20.0 mins at ambient temperature and isolated (Yield = 97 %) (FIG. 20).

[0061] In the irradiation of normal light, it was found that the reaction was observed under an essential medium of pH range 8 to 10, but the reaction rate was very slow. (Chem. Biodiversity 2023, 20, e202201166).

[0062] Under photo-mediated conditions, compound (1) 3,5-di-tert-butylbenzene-l,2-diol (DTBC) was excited at a higher excitation state, and oxygen may be formed ozonide and the product formation occurred by radical mechanism by breaking the oxygen bond which may be the reason for the very fast oxidation of catechol after irradiating the blue LEDs which may be due to the excitation of the compound (1) 3,5-di-tert-butylbenzene-l,2-diol (DTBC) was occurred from ground state (difference in energy levels of normal light to that of the blue light) to excited state under this condition ozone reacts with compound (1) 3,5-di-tert-butylbenzene-l,2-diol (DTBC) to form product (2) 3, 5-di-tert-butylcyclohexa-3,5-diene-l, 2-dione (DTBQ) which is proved by cyclic Voltammetry study.

[0063] All solvents for synthesis and spectroscopic analysis were purchased from commercial sources and were used after drying and degassing.1H and13C-NMR spectra were recorded on a Bruker AV400 Supercon Digital NMR system in deuterated chloroform (CDCh) solvent by using tetramethylsilane (TMS) as standard. The Fourier transform infrared (FTIR) spectra were recorded on a Perkin-Elmer Spectrum 100 spectrometer using a KBr plate in the range of3500-500 cm-1. The absorption spectral analysis was recorded on an Ocean Optics spectrophotometer. All electrochemical experiments were performed using Admiral Instruments. A three-electrode cell consisting of a glassy carbon working electrode for cyclic voltammetry (CV), a platinum wire as the counter electrode, and a Ag / AgCl reference electrode was used and were performed in dry acetonitrile solutions, using 0.1 M electrolyte.

[0064] The present invention has the salient features as follows:

[0065] 1. Development of metal free photo-catalytic protocol for catechol oxidation.

[0066] Metal-free photo-catalytic oxygen activation is a very rare process. The selective activation of the catechol is highlighted and occurred in the presence of light which turns out to be a photo-mediated process. (J. Org. Chem. 1987, 52, 5616-5621).

[0067] 2. Very fast oxidation of catechol under photo-irradiation.

[0068] 3, 5-di-tert-butylcyclohexa-3,5-diene-l, 2-dione (DTBQ) (Inorg. Chem. 2012, 51, 8750- 8759) is a very important chemical source that is utilized extensively in medicinal chemistry, chemical synthesis, and life science applications, Its availability without the use of external transition metal-free catalyst will be cost and energy effective.

[0069] 3. Ambient temperature (25 °C - 30 °C) accessible methodology for oxidation reaction.

[0070] It is very important to know under which conditions the oxidation occurs. The ambient condition (25 °C - 30 °C) is enough to carry out the very fast oxidation under a photomediated process via photons / electrons as an active catalyst in the presence of molecular oxygen and light.

[0071] 4. Photons (electrons) as photocatalysts for the electron mediated oxidation transformation.

[0072] EXAMPLES

[0073] Following examples are given by way of illustration and therefore should not be construed to limit the scope of the present invention.EXAMPLE 1

[0074] In a well dried four-neck round botom flask, 44.0 mg (10.0 mmol) of the compound (1) 3,5-di-tert-butylbenzene-l,2-diol (DTBC) electrolytes (1 equiv. to 5 equiv.), 20.0 mL of polar protic solvent were taken and then the mixture was stirred at 25 °C - 30 °C for around 10.0 - 20.0 minutes. Then O2 was bubbled through the solution and irradiation of photo was applied, then cyclic voltammetry (CV) was studied. After that blue light (410 - 430 nm) was applied on the solution for 10.0 - 20.0 minutes at 25 °C - 30 °C at basic 9-11 pH and then again cyclic voltammetry (CV) was studied. The product (2) 3, 5-di-tert-butylcyclohexa-3,5-diene-l, 2-dione (DTBQ) was isolated (Yield = 85%).

[0075] EXAMPLE 2

[0076] In a well-dried four-neck round botom flask, 44.0 mg (10.0 mmol) of compound (1) 3,5-di-tert-butylbenzene-l,2-diol (DTBC) electrolytes (1 equiv. to 5 equiv.), and 20.0 mL of polar protic solvent were taken, and then the mixture was stirred at 25 °C - 30 °C for around 10.0 -20.0 minutes with photo irradiation. Then O2 was bubbled through the solution and cyclic voltammetry (CV) was studied. After that violet light (320 - 400 nm) was applied on the solution for 10.0-20.0 minutes at 25 °C - 30 °C, pH 9-11 and then again cyclic voltammetry (CV) was studied. The product (2) 3, 5-di-tert-butylcyclohexa-3,5-diene-l, 2-dione (DTBQ) was isolated (Yield = 97%). The optimized reaction condition is 3,5-di-tert-butylbenzene-l,2-diol (DTBC) was dissolved in 20.0 mL polar protic solvent, and O2 was bubbled under photo irradiation (320 - 400 nm), condition giving the product yield (97%).

[0077] EXAMPLE 3

[0078] In a well-dried four-neck round botom flask, 44.0 mg (10.0 mmol) of compound (l)3,5-di-tert-butylbenzene-l,2-diol (DTBC) electrolytes (1 equiv. to 5 equiv.), and 20.0 mL of polar protic solvent were taken, and then the mixture was stirred at 25 °C - 30 °C for around 10.0 - 20.0 minutes with photo irradiation. Then O2 was bubbled through the solution and cyclic voltammetry (CV) was studied. After that green light (520 - 560 nm) was applied on the solution for 10.0 - 20.0 minutes at 25 °C - 30 °C, pH 9-11 and then again cyclic voltammetry (CV) was studied. The product (2) 3, 5-di-tert-butylcyclohexa-3,5-diene-l, 2-dione (DTBQ) was isolated(Yield = 97%). The optimized reaction condition is 3,5-di-tert-butylbenzene-l,2-diol (DTBC)was dissolved in 20.0 mL polar protic solvent, and O2 was bubbled under photo irradiation (520 - 560 nm), condition giving the highest product yield (97%).

[0079] EXAMPLE 4

[0080] In a well-dried four-neck round bottom flask, 10 gm - 15 gm of compound (l)3,5-di-tert-butylbenzene-l,2-diol (DTBC) electrolytes (tetrabutylammonium Chloride, tetrabutylammonium Bromide, tetrabutylammonium Iodide, tetrabutylammonium Perchlorate) (1 equiv. to 5 equiv.), and 20.0 mL of polar protic solvent were taken, and then the mixture was stirred at 25 °C - 30 °C for around 10.0 - 20.0 minutes with photo irradiation. Then O2 was bubbled through the solution and cyclic voltammetry (CV) was studied. After that green light (520 - 560 nm) was applied on the solution for 10.0 - 20.0 minutes at 25 °C - 30 °C, pH 9-11 and then again cyclic voltammetry (CV) was studied. The product (2) 3,5-di-tert-butylcyclohexa-3,5-diene-l, 2-dione (DTBQ) was isolated (Yield = 97%). The optimized reaction condition is 3,5-di-tert-butylbenzene-l,2-diol (DTBC)was dissolved in 20.0 mL polar protic solvent, and O2 was bubbled under photo irradiation (520 - 560 nm), condition giving the highest product yield (97%).

[0081] NMR Study

[0082] Hl NMR (400 MHz, CDCh): 8 (ppm) = 6.93 (d, 1H, J = 2.28 Hz), 6.21(d, 1H, J = 1.52 Hz), 1.26 (s, 9H), 1.22 (s, 9H).

[0083] 13C NMR (100 MHz, CDCh): 181.16, 180.07, 163.34, 149.98, 133.48, 122.12, 36.05, 35.50, 29.23, 27.90

[0084] EXAMPLE 5: Kinetic study of catechol oxidation in the presence of base

[0085] The progress of the reaction was monitored within a time scan of UV / Vis absorption spectra, which displayed (FIG. 5) an increase in absorbance at 401 nm, indicating the formation of the oxidized species 3, 5-di-tert-butylcyclohexa-3,5-diene-l, 2-dione (DTBQ), and the reaction was completed, which followed first-order rate law with respect to compound (1) 3,5-di-tert-butylbenzene-l,2-diol [DTBC],Thus, considering Michaelis-Menten substrate saturation kinetic model under the lower substrate concentration, the Vmaxand KM values were calculated from the double reciprocal plot (FIG. 6, Inset) which are 3.34 x 10'4Ms'1and 2.2 x 10'4M, respectively.

[0086] The plot of v / (V max-v) vs. inverse of compound (1) 3,5-di-tert-butylbenzene-l,2-diol (DTBC) concentration (FIG.7) showed the linear dependency of reciprocal of 3,5-di-tert-butylbenzene-1,2-diol (DTBC) concentration at higher concentration passing through the origin, and the inhibition pattern is complete type.

[0087] The CV of compound (1) 3,5-di-tert-butylbenzene-l,2-diol (DTBC) oxidation displayed as one electron irreversible oxidation at 0.77 V The mixture of 3,5-di-tert-butylbenzene-l,2-diol(DTBC) and base solution responded to one irreversible oxidation at a lower potential (0.59 V), which disappeared in the presence of O2. These results could be interpreted in a way that the lowering of oxidation potential for compound (1) 3,5-di-tert-butylbenzene-l,2-diol (DTBC) took place due to the electronic effect of hydrogen bonding interaction between 3,5-di-tert-butylbenzene-l,2-diolDTBC- base adduct in polar protic solvent where (-) 8 charge at OH group ofcompound (l)3,5-di-tert-butylbenzene-l,2-diol (DTBC) was formally created such that it will be negatively polarized and hence easy to oxidize. Under this situation, O2 might easily oxidize compound (1) 3,5-di-tert-butylbenzene-l,2-diol DTBC- base adduct before electrode oxidation at the anode (FIG. 8).

[0088] The CV of 3,5-di-tert-butylbenzene-l,2-diol(DTBC) oxidation displayed as one electron irreversible oxidation at 0.77 V. The mixture of 3,5-di-tert-butylbenzene-l,2-diol(DTBC) and base solution responded to one irreversible oxidation at a lower potential, which disappeared in the presence of O2. Actually increasing the base concentration gradually lowers the oxidation potential which is clearly reflected in FIG. 9. The electronic effect of the hydrogen bonding interaction between compound (1) 3,5-di-tert-butylbenzene-l,2-diol (DTBC) and the base adduct in polar protic solvent, where the (-) 8 charge at the OH group of compound (1) 3,5-di-tert-butylbenzene-l,2-diol (DTBC) was formally created so that it will be negatively polarized and hence easy to oxidize, could be interpreted as the reason for this result. In this case, O2 may be able to readily oxidize the [DTBC»base] adduct before electrode oxidation at the anode.EXAMPLE 6: Kinetic study of catechol oxidation in presence of cyclic hindered amine

[0089] The progress of the reaction was monitored within time scan of UV / Vis absorption spectra which displayed (FIG. 10) an increase in absorbance at 401 nm indicating the formation of the oxidized species compound (2) 3, 5-di-tert-butylcyclohexa-3,5-diene-l, 2-dione (DTBQ) and the reaction was completed within 183 mins which follow first order rate law with respect to3,5-di-tert-butylbenzene- 1 ,2-diol [DTBC] .

[0090] Thus, considering Michaelis-Menten substrate saturation kinetic model under the lower substrate concentration, the Vmax and KM values were calculated from the double reciprocal plot (FIG. 11, Inset) which are 3.8 x 10'4Ms'1and 2.9 x 10'4M, respectively.

[0091] The plot of v / (Vmax- v)vs. inverse of 3,5-di-tert-butylbenzene-l,2-diol(DTBC) concentration (FIG. 12) showed the linear dependency of reciprocal of 3,5-di-tert-butylbenzene-l,2-diol (DTBC) concentration at higher concentration passing through origin resulted k’=0 and the inhibition pattern is complete type.

[0092] At 0.77 V, the CV of 3,5-di-tert-butylbenzene-l,2-diol (DTBC) oxidation showed irreversible oxidation of one electron. At lower potential, the 3,5-di-tert-butylbenzene-l,2-diol(DTBC) and base solution mixture underwent an irreversible oxidation that vanished when O2 was present. The electronic effect of the hydrogen bonding interaction between 3,5-di-tert-butylbenzene-l,2-diol(DTBC) and the base adduct in polar protic solvent, where the (-) 8 charge at the OH group of 3,5-di-tert-butylbenzene-l,2-diol(DTBC) was formally created so that it will be negatively polarized and hence easy to oxidize, could be interpreted as the reason for this result. In this case, Chmay be able to readily oxidize the [DTBC»base] adduct before electrode oxidation at the anode (FIG. 13).

[0093] EXAMPLE 7: EPR study

[0094] EPR spectrum of the reaction mixture of 3,5-di-tert-butylbenzene-l,2-diol(DTBC) and base in aerobic condition showed (FIG. 14) the typical organic radical nature having g = 2.0034 with peak-to-peak line width of ca. 30 gauss. This result demonstrated the oxidation of 3,5-di-tert-butylbenzene-l,2-diol(DTBC) proceeded via one-electron oxidation in the first step through the radical mechanism.EXAMPLE 8: Mass spectroscopy study

[0095] In ESI+ion mass spectrum (FIG. 15) of the reaction mixture of 3,5-di-tert-butylbenzene-l,2-diol (DTBC), base and O2 in polar protic solvent displayed most intense peak at 243.10 for[DTBQ+Na]+ion.

[0096] EXAMPLE 9: Cyclic Voltammetry study under photo-irradiation condition

[0097] It was observed that under photo irradiation condition at different intensity of 410 - 430 nm, there is no change of polar protic solvent (FIG. 16). It is stable at also under photo irradiation condition of blue light.

[0098] It was also observed that under photo irradiation condition at different intensity of 320 - 400 nm, there is also no change of polar protic solvent (FIG. 17). It is stable at also under photo irradiation condition of violet light. Hence any change was observed for 3,5-di-tert-butylbenzene-l,2-diol (DTBC).

[0099] We checked it then under green light irradiation (FIG. 18). It was also observed that under photo irradiation condition at different intensity of 520 - 560 nm, there is also no change of polar protic solvent. It is stable at also under photo irridation condition of green light. Hence any change was observed for 3, 5 -di -tert- butylbenzene- 1,2-diol (DTBC) after photo irridation and product was formed after 10.0 - 20.0 minutes.

[0100] The cyclic voltammetry' (CV) analysis of 3,5-di-tert-butylbenzene-l,2-diol (DTBC) oxidation revealed a process characterized by a one-electron irreversible oxidation event. Under conditions of photo irradiation, when 3,5-di-tert-butylbenzene-l,2-diol(DTBC) was mixed with a basic pH solution, the electrochemical response exhibited two distinct irreversible oxidation peaks at lower potentials. Notably, these oxidation signals were no longer detectable in the presence of molecular oxygen (O2), indicating a potential interference or inhibition effect from O2 on the oxidation process. This suggests that the presence of oxygen may significantly alter the electrochemical behaviour of 3,5-di-tert-butylbenzene-l,2-diol (DTBC) under irradiated conditions.P_W0100772

[0101] In-effect under photo-irradiation conditions, the molecule excited to a higher excited state and increases the reactivity; then at this condition, O2 forms ozonide and breaks the bond, and very fast oxidation of catechol occurs, which is occurs at radical mechanism, which is very fast oxidation under basic pH medium. These results could be interpreted in a way that the lowering of oxidation potential (FIG. 19) for 3,5-di-tert-butylbenzene-l,2-diol(DTBC) was taken place due to the electronic effect of hydrogen bonding interaction in higher excited state between 3,5-di-tert-butylbenzene-l,2-diol(DTBC) and base in polar protic solvent where (-) 5 charge at OH group of 3,5-di-tert-butylbenzene-l,2-diol(DTBC)was formally created such that it will be negatively polarized and hence easy to oxidize. Under this situation, O2 might be able to oxidize [DTBC base] adduct very easily.

[0102] ADVANTAGES OF THE INVENTION

[0103] • The synthesis of photo-mediated metal free protocol for 3,5-di-tert-butylcyclohexa-3,5- diene- 1 ,2-dione (DTBQ) formation from 3,5-di-tert-butylbenzene-l,2-diol(DTBC) is eco-friendly and can be performed under 25 °C - 30 °C.

[0104] • The process involves utilization of molecular oxygen and the product transformation occurred under photo irradiation process mediated under 25 °C - 30 °C that involves O2 activation.

[0105] • The process is also cost-effective due to synthesis of the product in metal free condition.

Claims

WE CLAIM:

1. A photo-mediated transition-metal catalyst free process for the catechol (DTBC, 1) oxidation to quinone (DTBQ, 2), comprising the steps of:iii. mixing3,5-di-tert-butylbenzene-l,2-diol (DTBC, 1), 1.0 equivalent to 5 equivalent of an electrolyte and a polar protic solvent followed by stirring at a temperature in the range of 25°C- 30°C for a time period in the range of 10 to 20 minutes and bubbling O2 through the solution;3,5-di-tert-butylbenzene-l,2-diol (DTBC, 1)iv. applying LED lights under basic pH condition for a time period in the range of 10 to 20 minutes and at a temperature in the range of 25 °C - 30 °C to obtain 3,5-di-tert- butylcyclohexa-3,5-diene- 1,2-dione (DTBQ, 2);3, 5-di-tert-butylcyclohexa-3,5-diene-l, 2-dione (DTBQ, 2).

2. The process as claimed in claim 1, wherein the yield of the 3,5-di-tert-butylcyclohexa-3,5- diene- 1 ,2-dione is in the range of 85 to 97 %.

3. The process as claimed in claim 1, wherein the LED light applied under basic pH condition is selected from the group consisting of blue LEDs, Green LEDs or Violet LEDs.

4. The process as claimed in claim 1, wherein the wavelength of the blue LEDs is 410-430 nm.

5. The process as claimed in claim 1, wherein the wavelength of the Green LEDs is 520-560 nm.

6. The process as claimed in claim 1, wherein the wavelength of the Violet LEDs is 320-400 nm.

7. The process as claimed in claim 1, wherein the basic pH conditions have pH in the range of 9 - 11.

8. The process as claimed in claim 1, wherein the polar protic solvent is selected from the group consisting of methanol, isopropanol, ethanol or propanol.

9. The process as claimed in claim 1, wherein the electrolyte is selected from the group consisting of tetrabutylammonium chloride, tetrabutylammonium bromide, tetrabutyl ammonium iodide, or tetrabutylammonium perchlorate.

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