Emerging catalytic processes for the production of adipic acid

Abstract

Research efforts to find more sustainable pathways for the synthesis of adipic acid have led to the introduction of new catalytic processes for producing this commodity chemical from alternative resources. With a focus on the performance of oxygen and hydrogen peroxide as preferred oxidants, this minireview summarizes recent advances made in the selective oxidation of cyclohexene, cyclohexane, cyclohexanone and n-hexane to adipic acid. Special attention is paid to the exploration of catalytic pathways involving lignocellulosic biomass-derived chemicals such as 5-hydroxymethylfurfural, D-glucose, g-valerolactone and compounds representative of lignin and lignin-derived bio-oils.Scheme 1 Simplified reaction scheme of the current industrial process for AA production by catalytic oxidation of KA oil with nitric acid. Scheme 6 Proposed mechanism for the transformation of cyclohexanone to e-caprolactone over HMSnP-1 in the presence of O 2 . 96 Scheme 7 Baeyer-Villiger oxidation of cyclohexanone with H 2 O 2 . Scheme 8 Hydrogenation of 5-hydroxymethylfurfural to 2,5-di-hydroxymethyltetrahydrofuran with RANEY s -Ni catalysts. 150 Scheme 10 Schematic illustration of the active sites on rhodium-rhenium catalysts for the hydrogenolysis of 2-THPM. Adapted from ref. 152.Scheme 9 Consecutive reaction pathway for the conversion of 2,5-di-hydroxymethyltetrahydrofuran to tetrahydro-2H-pyran-2-ylmethanol via 1,2,6-hexanetriol. 150

Catalytic oxidative cleavage of catechol by a non-heme iron(iii) complex as a green route to dimethyl adipate

“…Selective catalytic catechol cleavage would nevertheless be advantageous, as hydrogenation 4 of the intradiol cleavage product, muconic acid (3a), can provide a greener route to adipic acid or its esters, which are key monomers, e.g., for nylon-6,6. 5 Such a route would make use of non-toxic catalysts and oxidants, be highly atomefficient and employ a renewable substrate, as catechol may be obtained sustainably from lignin 6 or by fermentation of glucose. Que et al have reported the most active system for stoichiometric intradiol cleavage of 3,5-di-tert-butylcatechol reported to date, using the ligand tris(2-pyridylmethyl)amine (tpa).…”

Integrated biorefineries: CO2 utilization for maximum biomass conversion

“…In parallel, other researchers [42,43] proposed cogeneration of fuels and chemicals. While producing biofuel requires a high degree of deoxygenation, the application of biomass for producing chemicals may potentially skip costly oxidative processes and provide viable pathways toward production of alcohols, carboxylic acids, and esters [44,45]. While these integrated biorefineries benefit from economies of scale and diversity of bioresources, they also face a challenge with respect to imbalanced product markets.…”

Production of medium-chain, a, omega-bifunctional monomers from fatty acids and n-alkanes

“…Industrial production of nylon 6,6 is mostly achieved by condensation of hexamethylene diamine and adipic acid (AA). Among DCAs, AA is produced most; its annual global production is prospected to reach 2.7 million tons in 2017 2 . Other DCAs have significantly smaller production volumes 3 ; due to the cumbersome production from petrochemical feedstocks.…”

“…HMF is hydrogenated in a multistep process to yield 1,6-hexanediol. Unfortunately, the hydrogenation of HMF results in the formation of a significant amount byproducts and requires a high H2 pressure 2,74 .…”

“…To produce AA, benzene is converted into a mixture of cyclohexanol and cyclohexanone. This mixture is oxidized with nitric acid to yield adipic acid with the concomitant emission of N2O, a potent greenhouse gas 2,5 C8-C10 DCAs are produced from renewable feedstocks, such as oleic acid and ricinoleic acid, via ozonolysis 16,101 . Although ozonolysis of unsaturated fatty acids is highly selective and effective, it suffers from several drawbacks.…”