Process for One Pot Synthesis of Tin Porphyrins

Abstract

The present invention relates to a streamlined, one-pot process for the synthesis of tin porphyrins of Formula I. The process involves reacting a substituted benzaldehyde, pyrrole, and stannous chloride dihydrate in presence of a phosphovanadotungstic acid catalyst and DMF solvent. This efficient protocol bypasses the traditional multi-step synthesis and harsh reagents, providing tin porphyrins in high spectroscopic yields and high purity, promoting greener chemistry and improved scalability for applications in photodynamic therapy and catalysis.

Description

FIELD OF THE INVENTIONThe present invention relates to a process for synthesis of tin porphyrins. Particularly,the present invention relates to a streamlined, efficient, one-pot process for synthesis of tinporphyrins by reacting a substituted benzaldehyde, pyrrole, and stannous chloride dihydrate inpresence of phosphovanadotungstic acid (HPVW) catalyst and DMF as solvent. This efficientsynthesis approach enhances both the practicality and versatility of tin porphyrins for their widerange of applications, including catalysis, photodynamic therapy, solar energy harvesting, etc.BACKGROUND TO THE INVENTIONDespite their exceptional functional characteristics and wide-ranging applications-fromcatalysis and light harvesting to medical therapies - porphyrins and metalloporphyrins remainunder-utilized due to the challenges associated with their synthesis. Traditional methods, suchas those developed by Rothemund (5%), Alder-Longo (20%), and Lindsey (30-40%), have laidthe foundation for porphyrin chemistry but often suffer from significant drawbacks. Theseinclude multi-step procedures, the use of stoichiometric amounts of corrosive reagents,chlorinated solvents, and strong oxidants, all of which limit scalability and yield.The situation becomes even more complex when synthesizing metalloporphyrins,particularly tin porphyrins, which are highly valuable in antimicrobial photodynamic therapyand photocatalysis. Incorporating metal ions into the porphyrin macrocycle typically requiresstrict reaction conditions to ensure proper coordination, further compounding the difficulty ofthe process. Some of the prior-art documents discloses synthesis of porphyrins are given below:CN102850358A discloses a synthesis method of tailed asymmetric porphyrin, withpyrrole and aromatic carbonyl compound as raw material. The method includes firstlysynthesizing dipyrrylmethane type compound at room temperature with water as solvent, twopyrrole and aromatic carbonyl compound as raw materials and phosphotungstic acid as catalyst,and one-step synthesizing the tailed asymmetric porphyrin in methanol or mixed solvent ofwater and methanol with tetrachloroquinone as an oxidizing agent. The yield of tailedasymmetric porphyrin is 20%-35%.CN112939992B discloses a synthesis method of a tetra (4-aminophenyl) porphyrinmetal complex, which comprises the following steps: 1) organic acid is taken as a solvent,pyrrole and 4-halogen benzaldehyde are taken as substrates, and condensation reaction iscarried out to obtain (4-halogen phenyl) porphyrin solid; 2) dissolving the (4-halophenyl)porphyrin solid in an organic solvent, adding metal salt, and reacting to obtain a (4-halophenyl)porphyrin metal complex; 3) and (4-halophenyl) porphyrin metal complex and ammonia waterare used as substrates, and carbon-nitrogen coupling reaction is carried out in the presence ofa catalyst and an organic solvent to obtain the tetra (4-aminophenyl) porphyrin metal complex.The method has mild reaction conditions, low toxicity and environmental protection.CN102993206A discloses a method for synthesising a tetraphenylporphyrin metalcomplex via a one-step process, comprising the following steps of: (1) dissolving metal acetatein DMF (dimethyl formamide), wherein the ratio of the metal acetate to DMF is 1 g: (8 to 16ml); (2) adding a solvent, namely, propionic acid, in a reaction container, then sequentiallyadding benzaldehyde, the DMF solution dissolved with the metal acetate, and a pyrrole solutiondiluted by propionic acid, and refluxing for 30-120 minutes at a temperature ranging from 120to 150 DEG C, wherein the molar ratio of benzaldehyde to pyrrole to the metal acetate is 1: 1:(0.25 to 2.5), and the volume ratio of the solvent, namely, propionic acid, to DMF is 1: 1 to 1:1.5; and (3) after the reaction is concluded, cooling, removing the solvent, and separating toobtain the product.Sruti Mondal et al., ACS Omega 2021, 6, 35, 22922-22936, discloses new methodologyfor porphyrin synthesis. This is a simple two-step protocol. The first step involves thecondensation of pyrrole and aldehyde in an H2O-MeOH mixture using HCl. The obtainedprecipitate from the first step was dissolved in reagent-grade dimethylformamide (DMF) andrefluxed for 1.5 hour, followed by stirring overnight in the air at room temperature. Subsequentpurification through column chromatography or crystallization resulted in the formation of pureporphyrins.The prior-art documents disclose processes for porphyrin and metalloporphyrinsynthesis that rely on harsh and environmentally unfavourable reagents. These methodstypically result in complex multi-step reaction procedures and often yield suboptimal results.In view thereof, there was a need for a novel, simplified catalytic route that overcomesthe limitations of the prior-art documents.OBJECTIVES OF THE INVENTIONThe objective of the present invention is to develop an efficient and sustainablesynthetic route for the one pot synthesis of Sn(II)porphyrins. The objective, well aligned withthe Sustainable Development Goals (SDG), eliminates the need for strong mineral acids,chlorinated solvents and oxidizing agents. The present invention intends the use ofphosphovanadotungstic acid as catalyst for the scalable synthesis of Sn(II)porphyrins,represented by Formula 1, with substituted benzaldehydes, pyrrole and stannous chloridedihydrate as precursors and DMF as solvent. The objective of the present invention is to achievea high yield of tin porphyrins without contamination of chlorins and N-confused porphyrins.The objective enables the facile synthesis of tin porphyrins and open doors for their wideapplications in photocatalytic technologies in the realm of energy harvesting and health care.SUMMARY OF THE INVENTIONThe present invention relates to a one-pot process for synthesis of tin porphyrin ofFormula I:Formula Icomprising the steps of:i) mixing a substituted benzaldehyde of Formula II, a catalyst, stannous chloridedihydrate and pyrrole in a solvent to obtain a reaction mixture; andFormula IIii) heating the reaction mixture at a temperature in a range of 140-155°C for aperiod of 6-9 hours to obtain the tin porphyrin of Formula I.In an embodiment of the present invention, R is selected from -H, Cl, Br, COOH,COOCH3, OCH3 and 2,5-dimethyl; and X is -OH / H2O.In an embodiment of the present invention, the catalyst is phosphovanadotungstic acidof formula H4[PVW11O40] and is in an amount of 40-60 mg.In an embodiment of the present invention, the substituted benzaldehyde, pyrrole andstannous chloride dihydrate are in a molar ratio of 1:1:4.In an embodiment of the present invention, the solvent is dimethylformamide (DMF).In an embodiment of the present invention, the solvent is in an amount of 10 mL.In an embodiment of the present invention, the temperature is 155 °C and the period is8 hours.In an embodiment of the present invention, the tin porphyrin is obtained with aspectroscopic yield in a range of 48-98% and isolated yield in a range of 35-81% withoutcontamination of chlorins or N-confused porphyrins.BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS / FIGURESThe accompanying drawings, which are incorporated in and constitute a part of thespecification, illustrate the synthesis and structure / elements of the invention and, together withthe description, explain the principles / concepts of the present invention.Figure 1 illustrates characterization of HPVW by (a) XRD (b) FTIR (c) UV-Visspectroscopy.Figure 2 illustrates (a) SEM image of HPVW (b) EDS of HPVW.Figure 3 illustrates Deconvoluted spectra of High resolution XPS of HPVW (a) P2p (b)W4f (c) V2p (d) O1s.Figure 4 illustrates NH3-TPD profile of HPW and HPVW.Figure 5 illustrates solvent optimisation for Sn porphyrin synthesis.Figure 6 illustrates (a) Temperature of optimisation (b) Reactant to metal salt ratiooptimisation (reactant- pyrrole) (c) Time optimisation (d) Catalytic amount optimisation.Figure 7 illustrates (a) 1 H NMR (b) MALDI TOF (c) UV-Vis spectra of compound 1.Figure 8 illustrates (a) 1H NMR (b) MALDI TOF (c) UV-Vis spectra of compound 2.Figure 9 illustrates (a) 1H NMR (b) MALDI TOF (c) UV vis spectra of compound 3.Figure 10 illustrates (a) 1H NMR (b) MALDI TOF (c) UV-Vis spectra of compound 4.Figure 11 illustrates (a) 1H NMR (b) MALDI TOF (c) UV-Vis spectra of compound 5.Figure 12 illustrates (a) 1 H NMR (b) MALDI TOF (c) UV-Vis spectra of compound 6.Figure 13 illustrates (a) 1H NMR (b) MALDI TOF (c) UV-Vis spectra of compound 7.DETAILED DESCRIPTION OF THE INVENTIONThe present invention will now be described in detail in connection with certainpreferred and optional embodiments, so that various aspects thereof may be more fullyinterpreted and comprehended. However, any skilled person or artisan will appreciate theextent to which such embodiments could be generalized in practice.It is further to be understood that all terminology used herein is for the purpose ofdescribing particular embodiments only and is not intended to be limiting in any manner orscope. Unless defined otherwise, all technical and scientific expressions used herein have thesame meaning as commonly understood by one of ordinary skill in the art to whichembodiments of the invention pertain. In describing and claiming the embodiments of thepresent invention, the following terminology can be used in accordance with the definitions setout below which are known in the state of art.In an aspect of the present invention, the present invention relates to a one-pot processfor synthesis of tin porphyrin of Formula I:Formula Icomprising the steps of:i) mixing a substituted benzaldehyde of Formula II, a catalyst, stannous chloridedihydrate and pyrrole in a solvent to obtain a reaction mixture; andFormula IIii) heating the reaction mixture at a temperature in a range of 140-155°C for aperiod of 6-9 hours to obtain the tin porphyrin of Formula I.In an embodiment of the present invention, R is selected from -H, Cl, Br, COOH,COOCH3, OCH3 and 2,5-dimethyl; and X is -OH / H2O.In an embodiment of the present invention, the catalyst is phosphovanadotungstic acidof formula H4[PVW11O40] and is in an amount of 40-60 mg.In an embodiment of the present invention, the substituted benzaldehyde, pyrrole andstannous chloride dihydrate are in a molar ratio of 1:1:4.In an embodiment of the present invention, the solvent is dimethylformamide (DMF).In an embodiment of the present invention, the solvent is in an amount of 10 mL.In an embodiment of the present invention, the temperature is 155 °C and the period is8 hours.In an embodiment of the present invention, the tin porphyrins are obtained with aspectroscopic yield in a range of 48-98% and isolated yield in a range of 35-81% withoutcontamination of chlorins or N confused porphyrins.EXAMPLES / EXPERIMENTS:Having described the basic aspects of the present invention, the following non-limiting examplesillustrate specific embodiments thereof. Those skilled in the art willappreciate that many modifications may be made in the invention without changing the essenceof invention.MaterialsPhosphotungstic acid (HPW, 98%) was purchased from Sigma Aldrich and used forcomparative analysis. Disodium hydrogen orthophosphate (Na2HPO4, 98%), concentratedsulfuric acid (H2SO4, 98%) and dimethylformamide (DMF, ≥ 99.8 %), and benzaldehyde(C6H5CHO, >99%) were purchased from Merck. Sodium tungstate dihydrate (Na2WO4.2H2O,99%), ammonium metavanadate (NH4VO3, 99%), diethyl ether ([C2H5]2O, >99%), pyrrole(C4H4NH, >99%) and stannous chloride dihydrate (SnCl2.2H2O, >98%) were purchased fromSpectrochem. Pyrrole was distilled before use, while all other reagents and solvents were ofanalytical grade and used without any further purification.Catalyst Preparation and CharacterizationPhosphovanadotungstic acid was prepared by procedure reported in prior-art documents.In short, a mixture of disodium hydrogen orthophosphate (0.71 g in 10 mL of water) andammonium metavanadate (0.61 g in 10 mL of water) was heated to boiling and subsequently cooledto room temperature followed by acidification. 17.76 g of sodium tungstate dihydrate was added tothe mixture and conc. sulfuric acid was added dropwise with continuous stirring, when the dark redcolour faded. After extraction with diethyl ether and solvent evaporation in vacuum oven, H4[PVW11O40], designated hereafter as HPVW, was obtained as a crystalline yellow solid and stored in a desiccator for further use.XRD pattern was obtained from Bruker AXS D8 Advance powder diffractometerequipped with graphite monochromatised Cu-Kα radiation (λ= 1.5405 A). FTIR spectra wererecorded on the JASCO model 4100 FTIR spectrometer using the KBr pellet method.Morphological characteristics and elemental analysis of the samples were recorded by SEMeds on JEOL Ltd JSM- 6390LV. Electronic spectra were collected from Thermo ScientificEvolution 220 UV-Vis spectrophotometer. Temperature programmed studies were carried outin MicrotracBEL Corp. chemisorption equipment with a TCD detector. The samples weredegassed at 100°C for 3 hours under vacuum before analysis. For TPD (TemperatureProgrammed Desorption) studies, 90 mg of the sample, after preheating to 350°C for 1 hourunder He flow, was cooled to 100°C and exposed to ammonia flow (5 vol% NH3 / He). Thedesorption was then monitored by a progressive increase of temperature to 400°C.Catalytic activityThe one pot synthesis of tin porphyrins was carried out in a 50 mL RB flask (Scheme1). For a typical run, catalyst, aldehyde and pre-distilled pyrrole (1:1 molar ratio) in 10 mLsolvent, were taken in R.B flask fitted with a condenser. The whole set-up was mounted on amagnetic stirrer equipped with sensitive temperature control. Formation of Sn-porphyrins wasfollowed by spectroscopic analysis in a Thermo Scientific Evolution 220 UV-Visspectrophotometer. The crude dark purple / green reaction mixture after solvent evaporationwas purified by column chromatography and isolated yields were noted.Scheme 1: One pot synthesis of tin porphyrins mediated by HPVWResultsCatalyst characterizationThe detailed characterization of HPAs has been reported in prior-art documents.HPVW was morphologically and structurally characterized using XRD, FTIR, electronicspectra, SEM EDS, TEM and XPS. The XRD pattern (Figure 1a) revealed classic Keggin-typediffraction peaks at 2θ values 10.76 ,° 21.7 ,° 23.56 ,° 25.29 ,° 26.6 ,° and 30.7 .°The sample exhibits high crystallinity, as evidenced by distinct, well-defined and sharppeaks. The typical skeletal vibrations of Keggin oxo anions in the region of 1100-700 cm-1 werereflected in the FTIR spectra (Figure 1b). The asymmetric stretching vibration of the W=Otbond (t-terminal oxygen atoms) may be linked to the peak at 982 cm-1. The vibrations at 1073,879, 804, and 595 cm-1 can be assigned to tetrahedral P-Oa (oxygen atom coupled to three Watoms and P), W-Ob-W (b-corner shared bridging oxygen atoms), W-Oc-W (edge sharedbridging oxygen atoms), and the bending mode of Oa-P-Oa, respectively. A blue shift in thebands corresponding to P-O and W=O vibrational modes, likely attributed to the reduction instructural symmetry, was observed upon substitution of W atom with V in the primary structureof the Keggin anion. Distinctive V-O peaks were probably masked by the strong W-O peaks.A prominent peak below 300 nm appeared in the UV-visible spectra (Figure 1c), whichcorrelated with oxygen-to-metal charge transfer transition.The agglomerated microstructure of HPAs can be observed in the scanning electronmicrographs (Figure 2a). The formation of HPVW and the incorporation of V into the latticestructure were confirmed by EDS (Energy-Dispersive X-ray Spectroscopy) analysis (Figure 2b).XPS (X-ray Photoelectron Spectroscopy) was used to confirm the presence of elementsand their electronic state. The presence of tetracoordinate phosphorus was confirmed by thehigh-resolution XPS profile of P 2p (Figure 3a), which shows BE in the range 133.5-134.7 eV,corresponding to spin-orbit splitting (2p 3 / 2 and 2p 1 / 2)

[40] . W in +6 oxidation state is indicatedby two peaks in 35.8 eV and 37.9 eV (the spin-orbit splitting of 2.1 eV) in the deconvolutedXPS spectrum corresponding to W 4f (Figure 3b). V in the pentavalent state is represented bythe binding energy of 517.1 eV (Figure 3c), while bivalent state of oxygen attributes to bindingenergy at 530-531 eV (Figure 3d).Ammonia TPD studies in prior-art documents reflect the acidic characteristics of thecatalyst. However, due to ammonia's nature as a robust, non-selective base, it can adsorb ontoboth Br(symbol)nsted and Lewis acid sites, resulting in simultaneous desorption from multiplesites and complicating the distinction between these acidity types. The temperature at whichammonia desorbs designates the strength of the acid sites present. Desorption peaks occurringbelow 150°C typically denote weak acid sites, those between 150°C and 300°C are indicativeof moderate sites, and peaks above 300°C are associated with strong acid sites. To get a betterperception on the impact of vanadium substitution on acidity, TPD profile of phosphotungsticacid (HPW) was also recorded. HPW exhibited a single desorption peak at approximately 200°C,signifying moderately strong acidic sites (Figure 4). The incorporation of vanadium into thephosphotungstic acid framework significantly elevates the acidity, particularly in the strongacid domain. HPVW exhibited two distinct desorption peaks, reflecting a considerableincrease in both moderate and strong acid sites. This enhancement in acidity is likelyresponsible for the improved catalytic performance and high yield of tin porphyrins achievedwith HPVW.Catalytic ActivityThe synthesis of metalloporphyrins conventionally involves the coordination of metalions into the porphyrin core, typically achieved through the reaction of metal salts with free-base porphyrins in a suitable solvent medium. In a one-pot synthetic approach, both metalinsertion and porphyrin formation are expected to transpire concurrently, thereby streamliningthe process and minimizing the number of synthetic steps. This method forestalls the need forintermediate isolation and purification of the free-base porphyrin prior to metalation.Preliminary trials in this approach were conducted using benzaldehyde as the substrateand the formation of Sn-TPP was monitored through electronic spectral analysis. Solventoptimization being the most crucial step in any organic synthesis, Sn-TPP yields in varioussolvents were scanned, starting with dimethylformamide (DMF), the most employed inmetallation reactions. After a duration of 8 hours under refluxing conditions (155°C), a 94%yield of Sn-TPP was observed (Figure 5). The Sn-TPP yields in other common solvents,ethanol, toluene, acetonitrile, and dimethyl sulfoxide (DMSO) were also recorded underrespective refluxing temperatures and after 8 hours. The choice of solvent significantly impactsreaction time, with lower boiling solvents like ethanol requiring extended reflux, while higherboiling alternatives like DMF reduce it to a few hours. DMF's effectiveness stems from itsability to coordinate with metal ions and the polar aprotic nature facilitates superior solvationand stabilization of reactive intermediates, leading to enhanced yields. In contrast, proticsolvents such as ethanol can interfere with metalation through competitive hydrogen bonding,while non-polar solvents like toluene exhibit inadequate solvation, resulting in diminishedyields. Considering the marginal yields with other solvents, when compared to DMF, furtherstudies were performed using DMF.To assess the impact of temperature, yields at temperatures ranging from 100 to 155°Cwere monitored in DMF solvent with a 1:4 reactant to metal ratio (Figure 6a). low temperaturesresulted in a lower yield as anticipated. It may be assumed that higher temperatures arebeneficial in surpassing the activation energy barriers and driving the reaction. A spectroscopicyield of 13% was noted at 100°C, which improved to 94% at 155°C. Reactant to metal saltratio (reactant-pyrrole) was pivotal in deciding the metalloporphyrin yields. Herein, the ratiowas altered from 1:3 to 1:6, and the yields were monitored (Figure 6b). While 1:3 ratio wasinsufficient to provide good yield, 1:4 ratio proved to be optimal giving maximum yield. Yielddecreased at higher ratios, perhaps due to the limited solubility of metal salts in solvent. Theoptimal 1:4 ratio not only seems to promote more effective coordination of metal ions but alsoaugments the overall yield, surpassing the side possible reactions.The reaction duration exerts a substantial influence on the yield in tin porphyrinsynthesis. An optimal reaction time of 8 hours has been delineated, at which point the yieldachieves its zenith of 94% (Figure 6c). Shorter reaction times, ranging from 30 minutes to 1hour, result in substantially low yields. As the reaction time is extended, there is a markedimprovement in yields, with significant gains observed up to 8 hours. However, extending thereaction time beyond 8 hours does not confer additional benefits. Consequently, an 8-hourreaction period is deemed optimal for maximizing efficiency. The quantity of catalyst(s) usedplays a key role in determining the reaction outcome. Starting with 10 mg of catalyst gave amodest 23% yield, indicating inadequate catalyst concentration for effective metalation. Theprogressive increase in the Sn-TPP yield with catalyst amount validates a clear link betweenthe amount of catalyst and the reaction efficiency. The yield attained its maximum with 50 mgof catalyst, and additional loading beyond this level does not significantly augment the yield(Figure 6d).Substrate scope of the synthesis protocol was also validated using substitutedaldehydes. Sn(IV)meso-(tetracarboxymethyl) phenyl porphyrin was formed with the highestyield (~98%). Anisaldehyde delivered yields above 90%, while 4-chloro and 4-bromobenzaldehyde gave moderate yields of 78% and 58%, indicating lower nucleophilicity and lessefficient coordination with metal ions. It is concluded that both electronic and steric featuresof aldehydes affect metalation efficiency and overall yield (Scheme 2). However, consideringthat the yields reported for porphyrins through Lindsay method are around 30-40%, theversatility of the one-pot strategy can be validated.Scheme 2: Substrate scope using various aldehydes.Reaction conditions: 1:4 ratio of reactants and SnCl2.2H2O, 50 mg HPVWcatalyst, DMF,8 hours; a=spectroscopic yield; b=isolated yield.Yet another remarkable feature of the synthesis protocol is synthesis of Sn-TCPP, widelyused in energy harvesting applications. Normally, ester-functionalized precursor aldehyde ispreferred over the acid counterparts due to better solubility, chemical stability, and minimalinterference with ring formation or metalation. In contrast, free carboxylic acid groups oftenhinder the reaction through poor solubility and unwanted interactions with catalysts or metalions, rendering the direct synthesis of acid-functionalized porphyrins challenging. Thisnecessitates an additional hydrolysis step in the synthesis of TCPP / SnTCPP. However,through a novel one-pot approach, SnTCPP (tin tetra(4-carboxyphenyl)porphyrin) wassuccessfully synthesized in reasonable yields directly, demonstrating that the method caneffectively overcome the typical solubility and reactivity barriers associated with acid-functionalized porphyrins. A key advantage of the present invention is its operationalsimplicity and reduced reaction time, offering a more efficient route to access metalated,carboxylic acid- functionalized porphyrins without the need for multi-step synthesis or post-functionalization.The obtained tin porphyrins were characterized and verified by 1 H NMR, MALDI-TOFmass spectra and UV VIS spectroscopy (Figure 7-13).Compound 1 (SnTPP) (DMSO) δ: 8.29 (d, 4H), 7.96-7.91 (m, 8H), 7.55-7.29 (m, 8H), 6.6-6.59 (d, 4H), 6.28 (d, 4H), 2.90 (s, 4H); MALDI-TOF: 767; UV-Vis spectra: 426, 559, 600 nm.Compound 2 (SnClTPP) (DMSO) δ: 1.23 (s, 4H) 8.02 (d, 8H), 7.66-7.38 (m, 8H), 6.56 (d,4H), 6.35 (d, 4H); MALDI-TOF: 949; UV-Vis spectra: 434, 567, 606 nm.Compound 3 (SnBrTPP) (DMSO) δ: 9.08 (s, 4H), 8.21 (d, 4H), 8.11 (d, 4H), 7.52 (d, 4H),7.26 (d, 4H), 6.81 (d, 4H), 6.29 (d, 4H); MALDI-TOF: 1083; UV-Vis spectra: 425, 559, 599nm.Compound 4 (SnAnis) (DMSO) δ: 8.20 (d, 4H), 7.49 (d, 8H), 7.19 (d, 4H), 7.08 (d, 4H), 6.88(d, 4H), 3.74 (s, 12H), 2.79 (s, 4H); MALDI-TOF: 887; UV-Vis spectra: 434, 562, 609 nm.Compound 5 (Sn25DM) (DMSO) δ: 8.93 (b, 4H), 7.87-7.61 (m, 8H), 7.02 (d, 4H), 6.96 (d,4H), 2.27 (s, 24H); MALDI-TOF: 879; UV-Vis spectra: 428, 562, 600 nm.Compound 6 (SnTCPP) (DMSO) δ: 9.32 (s, COOH), 8.47 (d, 4H), 8.03 (d, 4H), 7.33 (s, 4H),7.23 (s, 4H), 7.13 (s, 4H), 6.25 (s, 4H), 4.38 (OH); MALDI-TOF: 942; UV-Vis spectra: 430,563, 602 nm.Compound 7 (SnTCMP) (DMSO) δ: 8.49 (d), 8.04 (m), 7.68 (d), 7.23 (d), 4.33 (s, OH), 3.88 (s,COOCH3); MALDI-TOF: 999; UV-Vis spectra: 429, 562, 601 nm.ConclusionTin porphyrin(s) play a pivotal role in various domains, including catalysis, materialsscience, and environmental remediation, owing to their distinctive properties and versatilefunctions. A novel one-pot synthetic route for substituted tin porphyrins using DMF as solventand phosphovanadotungstic acid (HPVW) as catalyst is reported. This strategy eliminates theuse of corrosive and expensive acids / oxidising agents and stringent / inert atmosphericconditions and complex multiple-step synthetic pathways. Under optimised reaction conditionsusing H4[PVW11O40], substituted tin porphyrins were obtained with a spectroscopic yield ofaround 48-98% (35-81% isolated yield) without contamination of chlorins or N confusedprophyrins.The process of the present invention offers several key advantages:- Efficiency and Yield: The present invention provides a single-step process whichsignificantly reduces synthesis steps and complexity while enhancing yield. Thetraditional route requires initial synthesis of free base porphyrins and purificationthrough column chromatography. In the second stage, metal insertion is carried out andpure metalloporphyrins are retrieved through column chromatography, and the yield islimited. In the present one pot process, high yields of tin porphyrins (spectroscopicyield in a range of 48-98% and isolated yield in a range of 35-81%) obtained withoutmuch complicated procedures.- Reduced Use of Harsh Reagents: The process of the present invention avoids thereliance on chlorinated solvents, strong mineral acids, and oxidising agents.- Environmental Compatibility: The process of the present invention minimizes theuse of hazardous reagents to promotes greener chemistry practices.- Scalability and Practicality: The one-pot synthesis of the present invention enablespractical large-scale production, facilitating broader applications in photodynamictherapy, catalysis, and solar cell technologies.

Claims

1. A one-pot process for synthesis of tin porphyrin(s) of Formula I: Formula I comprising the steps of: i) mixing a substituted benzaldehyde of Formula II, a catalyst, stannous chloride dihydrate and pyrrole in a solvent to obtain a reaction mixture; and Formula II ii) heating the reaction mixture at a temperature in a range of 140-155°C for a period of 6-9 hours to obtain the tin porphyrin of Formula I.

2. The process as claimed in claim 1, wherein R is selected from -H, Cl, Br, COOH, COOCH3, OCH3 and 2,5-dimethyl; and X is -OH or H2O.

3. The process as claimed in claim 1, wherein the catalyst is phosphovanadotungstic acid of formula H4[PVW11O40] and is in an amount of 40-60 mg.

4. The process as claimed in claim 1, wherein the substituted benzaldehyde, pyrrole and stannous chloride dihydrate are in a molar ratio of 1:1:4.

5. The process as claimed in claim 1, wherein the solvent is dimethylformamide (DMF).

6. The process as claimed in claim 1, wherein the solvent is in an amount of 10 mL.

7. The process as claimed in claim 1, wherein the temperature is 155°C and the period is 8 hours.

8. The process as claimed in claim 1, wherein the tin porphyrin(s) is obtained with a spectroscopic yield in a range of 48-98% and isolated yield in a range of 35-81% without contamination of chlorins or N confused porphyrins.