A process for base metal catalysed conversion of glycerol into lactic acid

Abstract

The present invention relates to a process for base metal catalysed conversion of glycerol into lactic acid. The present invention provides an earth-abundant, inexpensive and environmentally benign base metal containing ore for the conversion of glycerol dehydrogenation to lactic acid. The process of the present invention provides lactic acid in a range of 32-33% at 44-45% selectivity along with hydrogen generation. Further, the present invention provides 88-97% yield of lactic acid at 96% selectivity along with isopropanol by taking acetone as a hydrogen acceptor.

Description

[0001]“A PROCESS FOR BASE METAL CATALYSED CONVERSION OF GLYCEROL INTO LACTIC ACID” FIELD OF THE INVENTION The present invention relates to the field of catalytic conversion of organic compounds. More particularly, the present invention relates to a process for base metal catalysed conversion of glycerol into lactic acid. BACKGROUND OF THE INVENTION Depletion of fossil fuel have raised the demand of biodiesel production that leads to a considerable amount of glycerol generation as a side product. The industries involved in cellulose hydrogenolysis and fermentation processes, gives rise to non-toxic waste glycerol that are considered as a feedstock for various value-added chemicals. Glycerol is widely used as a hydrogen donor or solvent in various metal-aided catalytic transformations. The lactic acid (LA) along with hydrogen generation obtained by transformation of glycerol is employed as a solvent and versatile feedstock in various fields. LA also finds its application in various industries like pharmaceutical, cosmetics, food, detergent and polylactic acid synthesis (PLA). US9085521B2 discloses about catalyst system and process for converting glycerol to lactic acid. The citation discloses a process for producing lactic acid from glycerol comprising of forming a reaction mixture comprising glycerol, an alkaline component, water, and a dehydrogenation catalyst that is selected from a copper catalyst selected from the group of metallic copper (Cu), cuprous oxide (CuO), cupric oxide (CuO), copper chromite (CuCrOs), a Raney nickel catalyst or a Raney cobalt catalyst; or an elemental catalyst selected from the elemental palladium, or elemental rhodium. However, the elemental catalyst is supported on a support that is selected from carbon, silica, aluminas, titania, zirconia or zeolites. WO2017087657A1 discloses about methods of forming and using metal alloy oxidative catalysts. The citation discloses a process comprising the steps of combining a metal precursor of a first metal, a metal precursor of a second metal and a solid support in a solvent; co-precipitating said first metal precursor and said second metal precursor to form alloy complex. However, the citation discloses the use of expensive metals such as platinum or gold for the preparation of metal catalyst. Crabtree et. al., in Nature Communications, 5:5084, 2014; doi: 10.1038 / ncomms6084, discloses about the acceptorless dehydrogenation of glycerol using Ir(I)-NHC complex. The method disclosed in the citation is applied to the glycerol waste derived from the biodiesel industry that provides somewhat lower activity while maintaining the same high selectivity. Beller et. al., in Green about ruthenium-catalyzed hydrogen generation from glycerol and selective synthesis of lactic acid. The citation discloses a protocol for hydrogen generation from glycerol and the selective synthesis of lactic acid with 67% using pincer-type ruthenium complexes. The citation provides insights into hydrogen generation from more complex carbohydrate-based biomass. Crabtree and Hazari in, Chem. Commun., 2015, 51, 16201-16204, discloses about selective conversion of glycerol to lactic acid with iron pincer pre-catalysts. The citation discloses superior selectivity compared with previous heterogeneous systems but further improvements are required to match the activity of homogeneous precious metal catalysts. Tu et. al., in ACS Catalysis 2015, discloses about iridium NHC-based catalysts for transfer hydrogenation processes using glycerol as a solvent and hydrogen donor. The citation proposes a mechanism that involves O−H oxidative addition of glycerol, σ-bond metathesis to eliminate hydrogen, β-hydride elimination and O−H reductive elimination to expel the dehydrogenation products. However, the results highlight the importance of enhanced catalyst solubility for reactions in highly polar media, and the substantial enhancement by microwave heating for viscous and highly base-concentrated reactions. Williams et. al., in ACS Catalysis, 2016, 6, 3, 2014-2017, discloses about an iridium- based catalysts for selective conversion of neat glycerol to lactic acid with 62% LA yield. The iridium-based conditions for the conversion of primary alcohols to potassium carboxylates (or carboxylic acids) in the presence of potassium hydroxide and either [Ir(2- PyCH2(C4H5N2))(COD)]OTf or [Ir(2-PyCH2PBu2t)(COD)]OTf are required. Voutchkova-Kostal et. al, in Organometallics 2018, 37, 1400-1409, synthesized charged sulfonate based Ir(I), Ir (III) and Ru (II) NHC complexes which have rendered good reactivity towards LA. The catalysts disclosed in the citation consist of Ir(I), Ir(III) and Ru(II) complexes bearing sulfonate-functionalized N-heterocyclic carbene ligands (NHCs). Kumar et. al. in Chemical 56, 9886-9889, discloses about selective and high yield transformation of glycerol to lactic acid using NNN pincer ruthenium catalysts. Fu et. al., in Green Chemistry, 2022, 24, 8477-8483; doi:10.1039 / D2GC03235J, discloses about manganese-catalysed dehydrogenative oxidation of glycerol to lactic acid. The citation provides pincer manganese complex supported by PNP ligands for the conversion of glycerol to sodium lactate with dihydrogen liberation. Sodium lactate is obtained in 96% yield with 96% selectivity under mild reaction conditions at 180°C in 36 hours, with the Mn-complex as the catalyst. Further, the traditional strategies of glycerol to LA conversion involves bacterial fermentation as well as heterogeneous catalysis. However, the conversion method suffers from some limitations like bacterial survival in harsh reaction conditions, low yield and selectivity, complexity in product separation. None of the prior art discloses about earth abundant, cost-effective and environment-friendly catalyst-based conversion of glycerol to lactic acid. Therefore, in view of above, there is a need of development of an earth abundant, cost- effective and environmentally friendly base metal catalysed conversion of glycerol into lactic acid along with the generation of valuable by-product. OBJECT OF THE INVENTION The main object of the present invention is to provide a process for base metal catalysed conversion of glycerol into lactic acid. Another object of the present invention is to provide a cost-effective and environmentally benign metal ore catalyst for conversion of glycerol into lactic acid. Yet another object of the present invention is to provide a method for base metal catalysed acceptorless dehydrogenation of glycerol to lactic acid. Yet another object of the present invention is to provide a method for base metal catalysed transfer dehydrogenation of glycerol to lactic acid. Still another object of the present invention is to provide a method for base metal catalysed conversion of glycerol to lactic acid with higher yield. SUMMARY OF THE INVENTION The present invention relates to a base metal ore (cobaltite) catalysed acceptorless dehydrogenation or transfer dehydrogenation of glycerol to lactic acid along with hydrogen generation or isopropanol generation. In an embodiment, the present invention provides a process for base metal catalyzed conversion of glycerol into lactic acid, comprising the steps of: (a) reacting a metal ore and a base to generate a base-metal product; (b) subjecting said base-metal product obtained in step (a) to solvolysis with glycerol to obtain an octahedral metal (II) hydroxide complex; and (c) subjecting said octahedral metal (II) hydroxide complex obtained in step (b) to alcoholysis with glycerol for an in-situ formation of an octahedral metal (II) alkoxide complex along with the removal of a by-product followed by generation of lactic acid and hydrogen. In another embodiment, the present invention provides a method for acceptorless dehydrogenation of glycerol into lactic acid performed by the steps of: (i) adding 0.460- 0.4605 g (5 mmol) of glycerol, 0.0041-0.0043 g (0.025 mmol) of cobaltite, 0.2102-0.2104 g (3.747 mmol) of KOH and 1-2 mL ethanol in a one-necked round bottom flask connected to a burette with a water-cooled condenser to obtain a reaction mixture; (ii) stirring said reaction mixture obtained in step (i) at room temperature for 5-10 minutes to obtain a homogenous green solution; (iii) stirring said homogenous green solution obtained in step (ii) at 160-165 ºC for 40-48 hours in air to obtain final mixture; and (iv) bringing said final mixture obtained in step (iii) to room temperature followed by adding 1-1.2 mL of water and mixing thoroughly to obtain a colorless dehydrogenated oil (lactic acid) and hydrogen along with ethylene glycol and formic acid. In yet another embodiment, the present invention provides a method for transfer dehydrogenation of glycerol into lactic acid performed by the steps of: (i) adding a Teflon liner, 0.460-0.4605 g (5 mmol) of glycerol, 0.0041-0.0043 g (0.025 mmol) of cobaltite, 0.5281-0.5283 g (5.4956 mmol) of NaOtBu and 1-1.2 mL (13.75 mmol) of acetone in a 20 mL stainless steel autoclave to obtain a reaction mixture; and (ii) stirring said reaction mixture of step (i) at 160-165ºC for 40-48 hours followed by bringing said reaction mixture to room temperature while adding 1-1.2 mL of water and mixing thoroughly to obtain dehydrogenated oil (lactic acid) along with isopropanol. In yet another embodiment, the present invention provides a method for transfer dehydrogenation of glycerol into lactic acid performed under microwave heating by the steps of: (i) adding 0.460-0.4605 g (5 mmol) of glycerol, 0.0041-0.0043 g (0.025 mmol) of cobaltite, 0.3082-0.3083 g (5.4956 mmol) of KOH and 1-1.1 mL mL (8.57 mmol) of acetophenone in a 10 mL microwave vial to obtain a reaction mixture; and (ii) stirring said reaction mixture of step (i) at 160-165ºC for 2-2.5 hours under microwave conditions at 50 watt microwave power followed by bringing said reaction mixture to room temperature while adding 1-1.2 mL of water and mixing thoroughly to obtain a dehydrogenated oil (lactic acid) along with isopropanol. The present invention relates to a base metal catalysed acceptorless dehydrogenation or transfer dehydrogenation of glycerol to lactic acid having a glycerol conversion rate in a range of 72-76%. The above objects and advantages of the present invention will become apparent from the hereinafter set forth brief description of the drawings, detailed description of the invention, and claims appended herewith. BRIEF DESCRIPTION OF THE DRAWINGS An understanding of the process for base metal catalysed conversion of glycerol into lactic acid of the present invention may be obtained by reference to the following drawings: Figure 1 is a schematic representation of a mechanism of the glycerol dehydrogenation to lactic acid catalysed by cobaltite involving octahedral Co(II) species, according to an embodiment of the present invention. Figure 2 is a graphical representation of electron paramagnetic resonance (EPR) analysis of the reaction mixture obtained from the optimized acceptorless dehydrogenation of glycerol in part (a); and a graphical representation for determination of magnetic moment through Evan’s method of the reaction mixture obtained from the optimized acceptorless dehydrogenation of glycerol in part (b), according to the present invention. Figure 3 is a graphical representation of high resolution mass spectrometry (HRMS) analysis of the reaction mixture obtained from the optimized acceptorless dehydrogenation of glycerol at time, t=0 at room temperature in part (a); and at time, t=1 hour at 160ºC in part (b), according to the present invention. Figure 4 is a graphical representation of1H NMR spectra of acceptorless dehydrogenation of glycerol at a catalyst loading of 0.25 mol%, KOH (0.75 equivalents), 1-2 mL ethanol as given in S. No.1 in Table 1, according to the present invention. DETAILED DESCRIPTION OF THE INVENTION The present invention will now be described hereinafter with reference to the accompanying drawings in which a preferred embodiment of the invention is shown. This invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiment set forth herein. Rather, the embodiment is provided so that this disclosure will be thorough, and will fully convey the scope of the invention to those skilled in the art. The present invention now will be described hereinafter with reference to the detailed description, in which some, but not all embodiments of the invention are indicated. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements. Like numbers refer to like elements throughout. The present invention is described fully herein with non- limiting embodiments and exemplary experimentation. The present invention provides a base metal ore (cobaltite) catalysed acceptorless dehydrogenation or transfer dehydrogenation of glycerol to lactic acid along with hydrogen or isopropanol generation. In a preferred embodiment, the present invention provides a process for base metal catalyzed conversion of glycerol into lactic acid, comprising the steps of: (a) reacting a metal ore and a base to generate a base-metal product; (b) subjecting said base-metal product obtained in step (a) to solvolysis with glycerol to obtain an octahedral metal (II) hydroxide complex; and (c) subjecting said octahedral metal (II) hydroxide complex obtained in step (b) to alcoholysis with glycerol for an in-situ formation of an octahedral metal (II) alkoxide complex along with the removal of a by-product followed by generation of lactic acid and hydrogen. Here, the metal ore in step (a) is cobaltite (CoAsS), and said base in step (a) is potassium hydroxide (KOH) or sodium tertiary butoxide (NaOtBu), sodium ethoxide (NaOEt) or sodium carbonate (Na2CO3). Said base-metal product in step (a) is cobalt hydroxide (Co(OH)2), cobalt tertiary butoxide (Co(OtBu)2), cobalt ethoxide (Co(OEt)2) or cobalt carbonate (CoCO3); and said octahedral metal (II) hydroxide complex in step (b) is octahedral cobalt (II) hydroxide complex. Further, the by-product in step (c) is tertiary butyl alcohol (HOtBu), ethanol (HOEt) or carbonic acid (H2CO3); and said octahedral metal (II) alkoxide complex obtained in step (c) is Co (II) alkoxide complex. Preferably, said octahedral metal (II) alkoxide complex is selected from complex 8a, 8b or 8c. The process of the present invention converts glycerol into lactic acid at a glycerol conversion rate in a range of 72-76%. Additionally, the process of the present invention converts glycerol into lactic acid by acceptorless dehydrogenation or transfer dehydrogenation. In another preferred embodiment, the present invention provides a method for acceptorless dehydrogenation of glycerol into lactic acid performed by the steps of: (i) adding 0.460-0.4605 g (5 mmol) of glycerol, 0.0041-0.0043 g (0.025 mmol) of cobaltite, 0.2102-0.2104 g (3.747 mmol) of KOH and 1-2 mL of ethanol in a one-necked round bottom flask connected to a burette with a water-cooled condenser to obtain a reaction mixture; (ii) stirring said reaction mixture obtained in step (i) at room temperature for 5- 10 minutes to obtain a homogenous green solution; (iii) stirring said homogenous green solution obtained in step (ii) at 160-165ºC for 40-48 hours in air to obtain final mixture; and (iv) bringing said final mixture obtained in step (iii) to room temperature followed by adding 1-1.2 mL of water and mixing thoroughly to obtain a colorless dehydrogenated oil (lactic acid) and hydrogen along with ethylene glycol and formic acid. Here, the acceptorless dehydrogenation generates lactic acid with a yield of 32% to 33% and selectivity ranging from 44% to 45%. Further, acceptorless dehydrogenation generates hydrogen with a yield in a range of 30 to 31%. In yet another preferred embodiment, the present invention provides a method for transfer dehydrogenation of glycerol into lactic acid performed by the steps of: (i) adding a Teflon liner, 0.460-0.4605 g (5 mmol) of glycerol, 0.0041-0.0043 g (0.025 mmol) of cobaltite, 0.5281-0.5283 g (5.4956 mmol) of NaOtBu and 1-1.2 mL (13.75 mmol) of acetone in a 20 mL stainless steel autoclave to obtain a reaction mixture; and (ii) stirring said reaction mixture of step (i) at 160-165ºC for 40-48 hours followed by bringing said reaction mixture to room temperature followed by adding 1-1.2 mL of water and mixing thoroughly to obtain dehydrogenated oil (lactic acid) and isopropanol. In yet another preferred embodiment, the present invention provides a method for transfer dehydrogenation of glycerol into lactic acid performed under microwave heating by the steps of: (i) adding 0.460-0.4605 g (5 mmol) of glycerol, 0.0041-0.0043 g (0.025 mmol) of cobaltite, 0.3082-0.3083 g (5.4956 mmol) of KOH and 1-1.1 mL mL (8.57 mmol) of acetophenone in a 10 mL microwave vial to obtain a reaction mixture; and (ii) stirring said reaction mixture of step (i) at 160-165ºC for 2-2.5 hours under microwave conditions at 50 watt microwave power followed by bringing said reaction mixture to room temperature while adding 1-1.2 mL of water and mixing thoroughly to obtain a dehydrogenated oil (lactic acid) along with isopropanol. Here, said transfer dehydrogenation generates lactic acid with a yield of 88% to 97% and selectivity ranging from 89% to 100%. Referring to Figure 1, a schematic representation of a mechanism of the glycerol dehydrogenation to lactic acid catalysed by cobaltite involving octahedral Co(II) species, is depicted. EXAMPLE 1 Materials and methods Materials All the reactions were carried out in air. All the chemicals were purchased from MERCK or Sigma-Aldrich or HiMedia. Physical measurements1H,13C,1H and2H NMR were recorded either on a Bruker ASCEND 600 operating at 600 MHz for1H and2H and 151 MHz for13C or on a Bruker AVANCE 400 operating at 400 MHz for1H. Chemical shifts (δ) are reported in ppm, spin–spin coupling constants (J) are expressed in Hz, and other data are reported as follows: s=singlet, d=doublet and q=quartet. HRMS measurements were recorded with the help of an Agilent Accurate- Mass QTOF ESI-MS 6520. The X-band EPR spectra was recorded on a JES-FA200 ESR spectrometer. GC analysis (TCD detection) was performed on an Agilent 7820-GC instrument fitted with Agilent Front SSZ Inlet N2 by a HPPLOT Q column (30 m length × 530 μm × 40 μm). Acceptorless dehydrogenation of glycerol to lactic acid catalysed by cobaltite The optimization was started by mixing 5 mmol of glycerol (1), 0.5 mol% of cobaltite, 0.25 equivalents of KOH and 2 mL of ethanol in a 50 mL round-bottom flask (as given in S. No.1 in Table 1). The reaction mixture was homogenized by stirring at room temperature for 10 minutes. The obtained homogeneous green solution was allowed to stirring at 160ºC for 48 hours under air. As a result of ethanol evaporation within few minutes, the green solution turned into a bluish foam which gradually turned into a brown gel with time. There was no trace of ethanol or dehydrogenated products as inferred from the1H NMR spectra. Figure 4 shows the graphical representation of1H NMR spectra of acceptorless dehydrogenation of glycerol at a catalyst loading of 0.25 mol% of KOH (0.75 equivalents), 1-2 mL of ethanol, as depicted in S. No.1 in Table 1. Sodium acetate was taken as an internal standard to calculate the yield of products, namely, lactate (2’), ethylene glycol (3) and formate (4’) from1H NMR. Among the observed products lactate (2’) was the major product and the other side products observed were decarbonylation product of glycerol (ethylene glycol, 3) and decarboxylation product of lactic acid (formate, 4’).24-26% of (2’) was obtained at 38% selectivity with a glycerol conversion of 65-70% (as given in S. No.1 in Table 1). The yield of (2’) increased to 28-30% on increasing the base loading to 0.5 equivalents (as given in S. No. 2 in Table 1). At a higher KOH loading of 0.75 equivalents, the yield of (2’) further increased to 32-33% at 44% selectivity and the yield of side products also increased (as given in S. No. 3 in Table 1). A similar yield of (2’) (30-32%) to the yield mentioned S. No.3 in Table 1 was obtained at a higher base loading of 1 equivalent with higher glycerol conversion of 78-82% (as given in S. No. 4 in Table 1). Hence, further optimizations were performed considering 0.75 equivalents of KOH as the best condition. A decrease in the glycerol conversion (50-55%) as well as yield of (2’) (22-24%) at a selectivity comparable to that of 0.5 mol% of cobaltite (as given in S. No. 3 in Table 1) was observed on decreasing the catalyst loading to 0.25 mol% (as given in S. No. in Table 1). A similar (2’) yield of 31-33% (S. No.6 in Table 1 and S. No.3 in Table 1) was observed at higher catalyst loading with similar glycerol conversion as well as selectivity. A lower yield of LA was obtained at higher temperature probably due to the catalyst deactivation. Table 1: Glycerol acceptorless dehydrogenation to lactic acid catalysed by cobaltite under varying conditions[a] % 32- 26- 05 075 7276 131519 30 [a]-Reaction conditions: 5 mmol glycerol, X mol% cobaltite, KOH (Y equivalents with respect to glycerol), 2 mL ethanol, 160°C, 48 hours in an open vessel (one neck round- bottom flask) under air. [b]-Determined from1H NMR by taking sodium acetate as an internal standard. [c]-Selectivity of lactic acid=(yield of lactic acid / conversion of glycerol)X100. The poor selectivity in some instances (say 59% total yield versus 66% conversion at 89% total selectivity, S. No.1) is attributed to undetectable by-products. [d]- Hydrogen evolution was determined by burette measurements after deducting the blank contribution. Yield of hydrogen was calculated as (moles of H2(as observed from gas chromatography and the amount of gas evolved) / moles of 1)100. [e]-Reaction performed at 170°C. [f]-Reaction performed at 140°C. [g]-1 mL of dioxane was taken. [h]-1 mL of DMF was taken. [i]-1 mL of o-xylene was taken. [j]-1 mL of acetone was taken. [k]-1 mL of water was taken. [l]-1 mL of methanol was taken. A drop in the yield of (2’) (4-5%) was observed when the temperature was decreased to 140ºC (as given in S. No.9 in Table 1). The importance of catalyst was understood from the reaction done in absence of cobaltite where very poor yield was observed (as given in S. No.10 in Table 1). The reaction did not proceed at all in absence of base (as given in S. No.11 in Table 1). The reaction time profile was determined by monitoring the reaction at the best condition (as given in S. No.3 in Table 1) and found that the reaction did not proceed after 48 hours. The optimizations in presence of different solvents like dioxane, o-xylene, water and methanol provided yield of (2’) between 15-18% (as given in S. No.12, 14, 16, and 17 in Table 1). Reactivity was not observed in DMF (as given in S. No.13 in Table 1). The role of the solvents were limited to initial homogenization of the reaction mixture as the solvents evaporate out within the first few minutes (as given in S. No.3, 12 and 16-17 in Table 1). The better activity in the presence of ethanol as the solvent is due to the ease in the generation of Co-H species (catalytically active species) from Co(ethoxide) through β- hydride elimination. A trace of hydrogenated product of acetone (isopropanol) was observed in presence of acetone with a moderate (2’) yield (20-22%) (as given in S. No.15 in Table 1). Transfer dehydrogenation of glycerol to lactic acid by taking acetone as sacrificial hydrogen acceptor catalysed by cobaltite In a closed vessel, transfer dehydrogenation of glycerol with acetone gave (2’) in 50-52% yield at 96% selectivity (as given in S. No.1 in Table 2). An increase in the yield of (2’) was observed with increase in base loading (as given in S. No.2 and 3 in Table 2) and at 1.1 equivalent of KOH 79-81% (2’) yield at 100% selectivity was achieved (as given in S. No. 3 in Table 2). 0.5 mol% catalyst loading in presence of 1.1 equivalent base loading provided the best results (as depicted in S. No. 3 versus S. No. 4 and 5 in Table 2). A similar glycerol conversion was obtained at 0.5 mol% and 0.75 mol% of cobaltite, however, a slightly lower yield of (2’) was obtained in the latter case was due to the formation of undetectable side products. At lower temperature, relatively lower yield was observed (as given in S. No.3 vs. S. No. 6 and 7 in Table 2). Acetone served as the best acceptor among the other screened acceptors (as depicted in S. No.3 vs. S. No.8 and 9 in Table 2). CoCl2.6H2O gave lower yields in comparison to that of cobaltite (as given in S. No. 3 vs. S. No. 10 in Table 2). The reaction was also tested under microwave conditions by taking acetophenone as an acceptor owing to the higher boiling point where 57-58% yield of (2’) was achieved at 98% selectivity (as given in S.No.11 vs. S. No.12 and 13 in Table 2). Among all the screened bases, NaOtBu gave the best yield in terms of yield of 2’ (93±4%) as well as selectivity (96%) (as depicted in S. No.15 vs.3, 14 and 16-21 in Table 2). LA was obtained in pure form upon work-up with dilute HCl. There was no reactivity in absence of base (as given in S. No.23 in Table 2) and very poor yield of 2’ was obtained in absence of catalyst (as given in S. No.22 in Table 2). Higher turnover numbers were observed in case of catalyst loading of 0.05 mol% (1080 TONs) and 0.005 mol% (as given in S. No.27 in Table 2). Mechanistic studies on the dehydrogenation of glycerol to lactic acid catalysed by cobaltite The generation of hydrogen under the optimized condition of acceptorless condition was evident from gas chromatography (GC) analysis (as given in S. No. 3 in Table 1). The hydrogen evolved was quantified by burette measurements. The hydrogen evolution was determined by burette measurements after deducting the blank contribution. The yield of hydrogen was calculated as (moles of H2(as observed from gas chromatography and the amount of gas evolved) / moles of 1) × 100. When reactions were done under the optimized condition in presence of well-known catalyst poisons PPh3 and CS2 only a slight decrease was observed for (2’), as depicted in equations 3, 4 and 5. (1) (5) Since, 1 equivalent of the poison (PPh3and CS2) with respect to the catalyst does not deactivate the catalyst, gives an indication of the presence of molecular-Co species. The result obtained from the mercury poisoning test under the optimized conditions (as given in S. No. 15 in Table 2) gives an indication of the presence of homogeneous catalytic species (as depicted by equation 6). (6) 5 (12) Freshly prepared Co(OH)2, as depicted in equation 7, presented similar reactivity to that of cobaltite under the optimized reaction condition (as given in S. No.15 in Table 2). The result suggests that Co(OH)2act as an intermediate in the reactions. On contrary, from the poor reactivity in presence of freshly prepared Co(OH)2and NaOtBu, formation of Co(OtBu)2, Co(OEt)2and CoCO3in presence of NaOtBu, NaOEt and Na2CO3was anticipated in the reactions. From the EPR and Evan’s method indicates the presence of Co(II) octahedral species. The EPR silent nature as well as the magnetic moment (1.9 BM) of the reaction mixture obtained from the Evan’s method gives evidence of the presence of Co(II) octahedral species. In-situ formation of molecular octahedral Co(II) species were detected in the HRMS analysis of the reaction mixture. Table 2: Glycerol acceptorless dehydrogenation to lactic acid catalysed by cobaltite under varying conditions[a] Cobaltite Base % Glycerol 2’ Yield[b] 7[e]0.50.5 KOH(1.1) 5a 58-60 58-59% (98%) 26 0.5 NaOtBu(0.25) 5a 17-18 14-16% (89%) [a]-Reaction conditions: 5 mmol of glycerol, X mol% cobaltite, KOH (Y equivalents with respect to glycerol), 1 mL of acceptor, at 160°C, in a 20 mL autoclave under air. [b]- Determined from1H NMR analysis by taking sodium acetate as an internal standard. [c]- Selectivity of lactic acid=(yield of lactic acid / conversion of glycerol)100. [d]-Reaction was done at 140°C. [e]-Reaction was done at 120°C. [f]-Reaction was done with CoCl2.6H2O. [g]-Reaction was done under microwave conditions: 5 mmol of glycerol, 0.5 mol% of cobaltite, KOH (1.1 equivalent with respect to glycerol), 1 mL of 5b, sealed vessel, 50 Watt microwave power for 2.5 hours. [h]-Reaction was done at 160°C. [i]-Reaction was done at 140°C. [j]-Reaction was done at 180°C. [k]-LA 2 was isolated in the pure form after workup of the reaction with dilute HCl. [l]-Average of two runs. In a deuterium labelling experiment, deuterated glycerol (1a) and normal glycerol (1) were taken in equal ratio (1:1), and the reaction was done under the optimized transfer dehydrogenation conditions (as given in S. No 15 in Table 2).44-46% of LA was afforded and a modest kinetic isotope effect (KIE) of 1.68 was obtained. The value of secondary KIE indicates that C-H activation takes part in the catalytic cycle. From the results obtained from different control experiments a plausible mechanism is inferred, as shown in Figure 1. The first step involves the reaction of Cobaltite and KOH that give rise to Co(OH)2. Almost similar yield of (2’) was obtained in the reaction under the optimized condition in presence of cobaltite (as given in S. No.3 in Table 2) and Co(OH)2(as depicted in equation 7) and is an indication of formation of Co(OH)2in the reaction. Further, the solvation of Co(OH)2with glycerol gives rise to octahedral Co(II) hydroxide 7 which then undergoes alcoholysis with glycerol and leads to the formation of octahedral Co(II) alkoxide (8) along with removal of water molecule. In the similar way, there is possibility of involvement of Co(OtBu)2, Co(OEt)2and CoCO3which lead to (8) with the release of HOtBu, HOEt and H2CO3. From the HRMS analysis, several derivatives of 8 (8a, 8b and 8c) have been detected. Then, β-hydride elimination takes place from (8) resulting in the generation of the Co(II) hydride species (9) along with extrusion of glyceraldehyde (11), as depicted in Figure 1. The transformation of glyceraldehyde to (2’) involves subsequent uncatalyzed organic transformations like dehydration of glyceraldehye (11) to acrolein (12), tautomerism of (12) to pyruvaldehyde (13), and the final step involves intramolecular Cannizzaro reaction which transforms (13) to lactate (2’). In acceptorless dehydrogenation of glycerol, σ-bond metathesis of the Co-H bond in (9) and O-H bond of glycerol leads to the regeneration of (8) and release hydrogen. In transfer dehydrogenation conditions, carbonyl of acetone is inserted in the Co-H bond of (9) leading to the generation of Co-isopropoxide species (10), as depicted in Figure 1. Further, σ-bond metathesis of (10) with hydrogen (hydrogenolysis) or glycerol (alcoholysis) leading to regeneration of (9) or (8) and alongside isopropanol. Even in open vessel the hydrogenated product of acetophenone was observed along with LA, as depicted from equation 10 that leads to the fact that there is contribution from both hydrogenolysis as well as alcoholysis in the transfer dehydrogenation reaction. As there is no hydrogenated product when acetone or acetophenone were allowed to react with hydrogen independently under the optimized transfer dehydrogenation conditions as depicted from equation 11 and equation 12, indicates the sole contribution of the alcoholysis step in the catalytic cycle. In the salt metathesis, only 1 mol% of the base is taken, and the remaining 1.1 equivalents of the base carries forward the Cannizzaro reaction and also trapping the LA in Na / K lactate form. Both the productivity and rate of the reaction are dependent on the concentration of base. General procedure for the acceptorless dehydrogenation of glycerol under conventional heating A 50 mL one-necked round bottom flask containing 0.460-0.4605 g (preferably 0.460 g, 5 mmol) of glycerol, 0.0041-0.0043 g (preferably 0.0041 g, 0.025 mmol) of cobaltite, 0.2102- 0.2104 g (preferably 0.2102 g, 3.747 mmol) of KOH and 1-2 mL (preferably 2 mL) of solvent connected to a burette (to determine the amount of gas evolved) through a water- cooled condenser, were added. The reaction mixture was stirred at room temperature for 5–10 minutes to make a homogeneous solution. The resulting homogeneous green solution was then allowed to stir at 160-165°C for 40-48 hours (preferably 160°C in 48 hours) in air. After 40-48 hours, the reaction mixture was brought to room temperature and 1-1.2 mL (preferably 1 mL) of water was added and mixed thoroughly. An aliquot was drawn from the reaction mixture for NMR analysis. The conversion yield of lactate 2’, ethylene glycol 3 and formate 4’ were determined from1H NMR analysis by taking sodium acetate as standard and D2O as the NMR solvent. The amount of hydrogen evolved was quantified through measurement of water displacement in a burette after deducting the contribution from a blank experiment done under identical conditions but without any cobaltite. General procedure for the transfer dehydrogenation of glycerol under conventional heating In a 20 mL stainless steel autoclave containing a teflon liner, 0.460-4605 g (preferably 0.450 g, 5 mmol) of glycerol followed by 0.0041-0.0043 g (preferably 0.0041 g, 0.025 mmol) of cobaltite, 0.5281-0.5283 g (preferably 0.5281 g, 5.4956 mmol) of NaOtBu and 1- 1.2 mL (preferably 1 mL, 13.75 mmol) of acetone were added. The reaction mixture was then allowed to stirring at 160-165°C for 40-48 hours (preferably 160°C for 48 hours). After 40-48 hours, the reaction mixture was brought to room temperature and 1-1.2 mL (preferably 1 mL) of water was added and mixed thoroughly. An aliquot was drawn from the reaction mixture for NMR analysis. The yield of lactate 2’ was determined as 93% from1H NMR analysis with the help of sodium acetate as standard and D2O as the NMR solvent. Solvent was evaporated from the rest of the reaction mixture under reduced pressure. The residue was washed with dilute HCl and extracted with ethyl acetate. The organic portion was separated and dried over anhydrous Na2SO4prior to removal under reduced pressure to yield lactic acid (LA 2) as a colorless oil (0.36 g, 80%).1H NMR (400 MHz, Deuterium Oxide): δ 4.04 (q, J=6.3 Hz, 1H), 1.26 (d, J=6.7 Hz, 3H).31C {1H} NMR (151 MHz, Deuterium Oxide): δ 181.62, 67.59, 19.14. General procedure for the transfer dehydrogenation of glycerol under microwave heating In a 10-mL microwave vial, 0.460-0.4605 g (preferably 0.460 g, 5 mmol) of glycerol followed by 0.0041-0.0043 g (preferably 0.0041 g, 0.025 mmol) of cobaltite, 0.3082-0.3083 g (preferably 0.3083 g, 5.4956 mmol) of KOH and 1-1.1 mL (preferably 1 mL, 8.57 mmol) of acetophenonone were added. The reaction mixture was then allowed to stirring at 160- 165°C for 2-2.5 hours (preferably 160°C for 2.5 hours) under microwave conditions (50 watt microwave power). After 2-2.5 hours, the reaction mixture was brought to room temperature and 1-1.2 mL (preferably, 1 mL) of water was added and mixed thoroughly. An aliquot was drawn from the mixture for NMR analysis. The yield of lactate was determined from1H NMR analysis by taking sodium acetate as standard and D2O as the NMR solvent. The glycerol dehydrogenation to lactic acid was successfully accomplished in both acceptorless and transfer dehydrogenation conditions in presence of different bases by taking 0.5 mol% of earth abundant, cost-effective and environmentally friendly base metal ore cobaltite at 160-165ºC. In acceptorless fashion, 0.5 mol% of cobaltite in presence of 0.75 equivalents of KOH at 160-165ºC, afforded lactic acid (32-33%), ethylene glycol (13- 15%), formic acid (26-28%) along with hydrogen at a glycerol conversion of 72-76%. Under transfer dehydrogenation conditions, in presence of acetone, a sacrificial hydrogen acceptor, 0.5 mol% of cobaltite in presence of 1.1 equivalents of NaOtBu at 160-165ºC, gave the maximum yield of lactic acid (88-97%) at a very high selectivity (96%) along with isopropanol. Comparable results obtained in the presence of PPh3or CS2or mercury and absence of PPh3or CS2or mercury under the optimized reaction conditions (0.5 mol% of cobaltite, 1.1 equivalents of NaOtBu, at 160-165ºC) gave an indication that the reaction mixture is homogeneous in nature. The presence of Co(II) octahedral species in the reaction mixture was evident from Evan’s method, EPR analysis, as shown in Figure 2 and HRMS analysis, as shown in Figure 3. The involvement of C-H activation in the catalytic species was evident from the deuterium labelling experiment, where a secondary KIE of 1.68 also suggests that C-H activation is not a part of RDS. Therefore, the present invention provides a cost-effective and environmentally benign base metal ore (cobaltite) catalysed acceptorless dehydrogenation or transfer dehydrogenation of glycerol to lactic acid along with hydrogen or isopropanol generation. Many modifications and other embodiments of the invention set forth herein will readily occur to one skilled in the art to which the invention pertain having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is to be understood that the invention is not to be limited to the specific embodiments disclosed and that modifications and other embodiments are intended to be included within the scope of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

CLAIMS We claim:

1. A process for base metal catalyzed conversion of glycerol into lactic acid comprising the steps of: a) reacting a metal ore and a base to generate a base-metal product; b) subjecting said base-metal product obtained in step (a) to solvolysis with glycerol to obtain an octahedral metal (II) hydroxide complex; and c) subjecting said octahedral metal (II) hydroxide complex obtained in step (b) to alcoholysis with glycerol for an in-situ formation of an octahedral metal (II) alkoxide complex along with the removal of a by-product followed by generation of lactic acid and hydrogen; wherein, said metal ore in step (a) is cobaltite (CoAsS); said base in step (a) is potassium hydroxide (KOH), sodium tertiary butoxide (NaOtBu), sodium ethoxide (NaOEt) or sodium carbonate (Na2CO3); said base-metal product in step (a) is cobalt hydroxide (Co(OH)2), cobalt tertiary butoxide (Co(OtBu)2), cobalt ethoxide (Co(OEt)2) or cobalt carbonate (CoCO3); said octahedral metal (II) hydroxide complex in step (b) is octahedral cobalt (II) hydroxide complex; said by-product in step (c) is tertiary butyl alcohol (HOtBu), ethanol (HOEt) or carbonic acid (H2CO3); said process converts glycerol into lactic acid by acceptorless dehydrogenation or transfer dehydrogenation; and said octahedral metal (II) alkoxide complex obtained in step (c) is octahedral Co (II) alkoxide complex.

2. The process as claimed in claim 1, wherein said octahedral metal (II) alkoxide complex is selected from:.

3. The process as claimed in claim 1, wherein said process converts glycerol into lactic acid at a glycerol conversion rate in a range of 72-76%.

4. The process as claimed in claim 1, wherein said acceptorless dehydrogenation is performed by the steps of: i. adding 0.460-0.4605 g (5 mmol) of glycerol, 0.0041-0.0043 g (0.025 mmol) of cobaltite, 0.2102-0.2104 g (3.747 mmol) of KOH and 1-2 mL of ethanol in a one-necked round bottom flask connected to a burette with a water- cooled condenser to obtain a reaction mixture; ii. stirring said reaction mixture obtained in step (i) at room temperature for 5- 10 minutes to obtain a homogenous green solution; iii. stirring said homogenous green solution obtained in step (ii) at 160-165ºC for 40-48 hours in air to obtain final mixture; and iv. bringing said final mixture obtained in step (iii) to room temperature followed by adding 1-1.2 mL of water and mixing thoroughly to obtain a colorless dehydrogenated oil (lactic acid) and hydrogen along with ethylene glycol and formic acid.

5. The process as claimed in claim 1, wherein said acceptorless dehydrogenation generates lactic acid with a yield of 32% to 33% and selectivity ranging from 44% to 45%.

6. The process as claimed in claim 1, wherein said acceptorless dehydrogenation generates hydrogen with a yield in a range of 30 to 31%.

7. The process as claimed in claim 1, wherein said transfer dehydrogenation is performed by the steps of: i) adding a Teflon liner, 0.460-0.4605 g (5 mmol) of glycerol, 0.0041-0.0043 g (0.025 mmol) of cobaltite, 0.5281-0.5283 g (5.4956 mmol) of NaOtBu and 1-1.2 mL (13.75 mmol) of acetone in a 20 mL stainless steel autoclave to obtain a reaction mixture; and ii) stirring said reaction mixture of step (i) at 160-165ºC for 40-48 hours followed by bringing said reaction mixture to room temperature while adding 1-1.2 mL of water and mixing thoroughly to obtain dehydrogenated oil (lactic acid) along with isopropanol.

8. The process as claimed in claim 1, wherein said transfer dehydrogenation under microwave heating is performed by the steps of: (i) adding 0.460-0.4605 g (5 mmol) of glycerol, 0.0041-0.0043 g (0.025 mmol) of cobaltite, 0.3082-0.3083 g (5.4956 mmol) of KOH and 1-1.1 mL mL (8.57 mmol) of acetophenone in a 10 mL microwave vial to obtain a reaction mixture; and (ii) stirring said reaction mixture of step (i) at 160-165ºC for 2-2.5 hours under microwave conditions at 50 watt microwave power followed by bringing said reaction mixture to room temperature while adding 1-1.2 mL of water and mixing thoroughly to obtain a dehydrogenated oil (lactic acid) along with isopropanol.

9. The process as claimed in claim 1, wherein said transfer dehydrogenation generates lactic acid with a yield of 88% to 97% and selectivity ranging from 89% to 100%.

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