Greener and sustainable method for alkene epoxidations by polymer-supported Mo(VI) catalysts

A polybenzimidazole supported Mo(VI) (PBI.Mo) catalyst has been prepared and characterised. The catalytic activities of the PBI.Mo catalyst in epoxidation of alkenes with tert-butyl hydroperoxide (TBHP) as an oxidant have been studied under different reaction conditions in a batch reactor. As alkene representatives we have chosen cyclohexene, limonene, α-pinene and 1-octene (a less reactive terminal alkene). The order of reactivity of the alkenes was found to be: cyclohexene>limonene>α-pinene>1-octene. The stability of each polymer catalyst was assessed by recycling a sample in batch reaction using conditions that will form the basis of the continuous process. The loss of Mo from each support has been investigated by isolating any residue from the reaction supernatant solutions, following removal of the heterogeneous polymer catalyst, and then using the residues as potential catalysts in epoxidation reactions

A continuous-flow apprach to alkene epoxidation catalysed by Polystyrene 2-(Aminomethyl)Pyridine supported Mo(VI) complex

Epoxides are raw materials for a broad range of products, from pharmaceuticals to plastics and paints to adhesives. The production of epoxides often uses peracids including peracetic acid and m-chloroperbenzoic acid in batch reactions. The employment of peracids is not an environmentally friendly synthetic procedure since equivalent amounts of acid wastes are produced. Hence, there is a strong need for cleaner catalytic epoxidation methods that employ safer oxidants and produces little waste. There have been considerable amount of research efforts on developing stable heterogeneous catalysts for epoxidation by immobilisation of catalytically active metal species on organic or inorganic materials such as polymers, ion-exchange resins, alumina; zeolite and silica. Polymers have gained attention as suitable supports for transition metal catalysts as they are inert, nontoxic, insoluble and often recyclable. In this work, we report a new process which is considered to be clean as it employs an efficient and selective Polystyrene 2-(aminomethyl) pyridine supported molybdenum complex, i.e. Ps.AMP.Mo as a catalyst for epoxidation of 4-vinyl-1-cyclohexene. The process uses environmentally benign tert-butyl hydroperoxide (TBHP) as a terminal oxidant. Experiments have been carried out to study the effect of reaction temperature, catalyst loading and feed molar ratio of alkene to TBHP on the conversion of TBHP to 4-vinyl-1-cyclohexene 1,2-epoxide for optimisation of reaction conditions in a batch reactor. The long term stability of the heterogeneous catalyst has been evaluated by recycling a sample of the catalyst several times in batch experiments. The extent of Mo leaching from the polymer supported catalyst has been investigated by isolating any residue from reaction supernatant studies after removal of the heterogeneous catalyst and using the residue as potential catalyst for epoxidation reaction. Furthermore, the efficiency of the heterogeneous catalyst for continuous epoxidation studies have been assessed using a FlowSyn continuous flow reactor by studying the effect of reaction temperature, feed molar ratio of alkene to TBHP and feed flow rate on the conversion of the oxidant and the yield of epoxide. The continuous flow epoxidation using FlowSyn reactor has shown considerable time savings, high reproducibility and selectivity along with remarkable improvements in catalyst stability compared to reactions carried out in a batch reactor

Efficient and selective polymer supported Mo(VI) catalyst for alkene epoxidation in batch and continuous reactors

The growing concern for the environment, increasingly stringent standards for the release of chemicals into the environment and economic competitiveness have prompted extensive efforts to improve chemical synthesis and manufacturing methods as well as development of new synthetic methodologies that minimise or completely eliminate pollutants. As a consequence, more and more attention has been focused on the use of safer chemicals through proper design of clean processes and products. Epoxides are key raw materials or intermediates in organic synthesis, particularly for the functionalisation of substrates and production of a wide variety of chemicals such as pharmaceuticals, plastics, paints, perfumes, food additives and adhesives. The conventional methods for the industrial production of epoxides employ either stoichiometric peracids or chlorohydrin as an oxygen source. However, both methods have serious environmental impact as the former produces an equivalent amount of acid waste, whilst the later yields chlorinated by-products and calcium chloride waste. There has been considerable effort to develop alternative alkene epoxidation methods by employing an oxidant such as tert-butyl hydroperoxide (TBHP) as it is environmentally benign, safer to handle and possesses good solubility in polar solvents. A notable industrial implementation of alkene epoxidation with TBHP was the Halcon process that employed soluble molybdenum(VI) as a catalyst for liquid phase epoxidation of propylene to propylene oxide. However, homogenous catalysed alkene epoxidation has several drawbacks including deposition of catalyst on the reactor walls and increased difficulties in separation of catalyst from the reaction mixture. In this work, an efficient and selective polystyrene 2-(aminomethyl)pyridine supported molybdenum complex (Ps.AMP.Mo) and a polybenzimidazole supported molybdenum complex (PBI.Mo) have been used as catalysts for epoxidation of 4-vinyl-1-cyclohexene (i.e. 4-VCH) using TBHP as an oxidant in batch and continuous reactors. An extensive assessment of the catalytic activity, stability and reusability of the catalysts has been conducted in a classical batch reactor. Experiments have been carried out to study the effect of reaction temperature, feed molar ratio of alkene to TBHP and catalyst loading on the yield of 1,2-epoxyhexane and 4-vinyl-1-cyclohexane 1,2-epoxide (4-VCH 1,2-epoxide) to optimise the reaction conditions in a batch reactor. A detailed evaluation of molybdenum (Mo) leaching from the polymer supported catalyst has been investigated by isolating any residue from reaction supernatant solutions and then using these residues as potential catalyst in epoxidation reactions. Furthermore, the efficiency of the heterogeneous catalyst for continuous epoxidation studies have been assessed using a FlowSyn continuous flow reactor by studying the effect of reaction temperature, feed molar ratio of alkene to TBHP and feed flow rate on the conversion of the oxidant and the yield of corresponding epoxide. The continuous flow epoxidation using FlowSyn reactor has shown considerable time savings, high reproducibility and selectivity along with remarkable improvements in catalyst stability compared to reactions carried out in a batch reactor

Greener and Sustainable Alkene Epoxidation Process

Epoxides are key raw materials or intermediates in organic synthesis, particularly for the functionalisation of substrates and production of a wide variety of chemicals such as pharmaceuticals, plastics, paints, perfumes, food additives and adhesives. The conventional methods for the industrial production of epoxides employ either stoichiometric peracids or chlorohydrin as an oxygen source. However, both methods have serious environmental impact as the former produces an equivalent amount of acid waste, whilst the later yields chlorinated by-products and calcium chloride waste. There has been considerable effort to develop alternative alkene epoxidation methods by employing an oxidant such as tert-butyl hydroperoxide (TBHP) as it is environmentally benign, safer to handle and possesses good solubility in polar solvents. However, homogenous catalysed alkene epoxidation has several drawbacks including deposition of catalyst on the reactor walls and increased difficulties in separation of catalyst from the reaction mixture. In this work, an efficient and selective polystyrene 2-(aminomethyl)pyridine supported molybdenum complex (Ps.AMP.Mo) and a polybenzimidazole supported molybdenum complex (PBI.Mo) have been used as catalysts for epoxidation of 4-vinyl-1-cyclohexene (i.e. 4-VCH) using TBHP as an oxidant in batch and continuous reactors. An extensive assessment of the catalytic activity, stability and reusability of the catalysts has been conducted in a classical batch reactor. Experiments have been conducted to study the effect of reaction temperature, feed molar ratio of alkene to TBHP and catalyst loading on the yield of 1,2-epoxyhexane and 4-vinyl-1-cyclohexane 1,2-epoxide (4-VCH 1,2-epoxide) to optimise the reaction conditions in a batch reactor. Furthermore, the efficiency of the heterogeneous catalyst for continuous epoxidation studies have been assessed using a FlowSyn continuous flow reactor, which has shown considerable time savings, high reproducibility and selectivity along with remarkable improvements in catalyst stability compared to reactions carried out in a batch reactor

Greener and Sustainable Alkene Epoxidation Process

Epoxides are key raw materials or intermediates in organic synthesis, particularly for the functionalisation of substrates and production of a wide variety of chemicals such as pharmaceuticals, plastics, paints, perfumes, food additives and adhesives. The conventional methods for the industrial production of epoxides employ either stoichiometric peracids or chlorohydrin as an oxygen source. However, both methods have serious environmental impact as the former produces an equivalent amount of acid waste, whilst the later yields chlorinated by-products and calcium chloride waste. There has been considerable effort to develop alternative alkene epoxidation methods by employing an oxidant such as tert-butyl hydroperoxide (TBHP) as it is environmentally benign, safer to handle and possesses good solubility in polar solvents. However, homogenous catalysed alkene epoxidation has several drawbacks including deposition of catalyst on the reactor walls and increased difficulties in separation of catalyst from the reaction mixture. In this work, an efficient and selective polystyrene 2-(aminomethyl)pyridine supported molybdenum complex (Ps.AMP.Mo) and a polybenzimidazole supported molybdenum complex (PBI.Mo) have been used as catalysts for epoxidation of 4-vinyl-1-cyclohexene (i.e. 4-VCH) using TBHP as an oxidant in batch and continuous reactors. An extensive assessment of the catalytic activity, stability and reusability of the catalysts has been conducted in a classical batch reactor. Experiments have been conducted to study the effect of reaction temperature, feed molar ratio of alkene to TBHP and catalyst loading on the yield of 1,2-epoxyhexane and 4-vinyl-1-cyclohexane 1,2-epoxide (4-VCH 1,2-epoxide) to optimise the reaction conditions in a batch reactor. Furthermore, the efficiency of the heterogeneous catalyst for continuous epoxidation studies have been assessed using a FlowSyn continuous flow reactor, which has shown considerable time savings, high reproducibility and selectivity along with remarkable improvements in catalyst stability compared to reactions carried out in a batch reactor

A continuous-flow apprach to alkene epoxidation catalysed by Polystyrene 2-(Aminomethyl)Pyridine supported Mo(VI) complex

Epoxides are raw materials for a broad range of products, from pharmaceuticals to plastics and paints to adhesives. The production of epoxides often uses peracids including peracetic acid and m-chloroperbenzoic acid in batch reactions. The employment of peracids is not an environmentally friendly synthetic procedure since equivalent amounts of acid wastes are produced. Hence, there is a strong need for cleaner catalytic epoxidation methods that employ safer oxidants and produces little waste. There have been considerable amount of research efforts on developing stable heterogeneous catalysts for epoxidation by immobilisation of catalytically active metal species on organic or inorganic materials such as polymers, ion-exchange resins, alumina; zeolite and silica. Polymers have gained attention as suitable supports for transition metal catalysts as they are inert, nontoxic, insoluble and often recyclable. In this work, we report a new process which is considered to be clean as it employs an efficient and selective Polystyrene 2-(aminomethyl) pyridine supported molybdenum complex, i.e. Ps.AMP.Mo as a catalyst for epoxidation of 4-vinyl-1-cyclohexene. The process uses environmentally benign tert-butyl hydroperoxide (TBHP) as a terminal oxidant. Experiments have been carried out to study the effect of reaction temperature, catalyst loading and feed molar ratio of alkene to TBHP on the conversion of TBHP to 4-vinyl-1-cyclohexene 1,2-epoxide for optimisation of reaction conditions in a batch reactor. The long term stability of the heterogeneous catalyst has been evaluated by recycling a sample of the catalyst several times in batch experiments. The extent of Mo leaching from the polymer supported catalyst has been investigated by isolating any residue from reaction supernatant studies after removal of the heterogeneous catalyst and using the residue as potential catalyst for epoxidation reaction. Furthermore, the efficiency of the heterogeneous catalyst for continuous epoxidation studies have been assessed using a FlowSyn continuous flow reactor by studying the effect of reaction temperature, feed molar ratio of alkene to TBHP and feed flow rate on the conversion of the oxidant and the yield of epoxide. The continuous flow epoxidation using FlowSyn reactor has shown considerable time savings, high reproducibility and selectivity along with remarkable improvements in catalyst stability compared to reactions carried out in a batch reactor