César A. Henriques

Ecofriendly Porphyrin Synthesis by using Water under Microwave Irradiation

Water, under microwave irradiation and at a temperature of 473 K, reaches pressures above 16 bar, being capable to act as catalyst, without the use of organic solvents and oxidants, for meso-substituted porphyrin synthesis. Sustainability of the reaction is proved by E Factor=35 and EcoScale value of 50.5, the highest so far obtained for porphyrin synthesis. Methodologys wide versatility is clearly demonstrated by the good yields obtained for both aryl and alkyl substituted porphyrins. These reaction conditions represent a huge development, not only by using very high concentrations, minimizing organic solvent usage, but also by eradicating toxic expensive solvents and oxidants.

Unsymmetrical porphyrins: the role of meso-substituents on their physical properties

The synthesis of one-step meso-porphyrins type AxBy containing alkyl and pyridyl groups is described. An initial assess of the amphiphilic proprieties were determined by its log Kow using fluorescence detection techniques and values from 1.42 to 2.15 were observed. The melting points of this set of porphyrins was determined and a strong effect of the number and size of the meso-alkyl chain is ascribed.

Solventless metallation of low melting porphyrins synthesized by the water/microwave method

Herein, we unveil a new ecofriendly methodology for the synthesis of low melting point meso-substituted metalloporphyrins. The water/microwave (MW) synthetic method was used to prepare low melting point unsymmetrical meso-aryl substituted porphyrins and meso-alkyl substituted porphyrins, which uses water under MW irradiation, acting as the solvent/acid catalyst/oxidant in sub-critical conditions. A straightforward conceptual method for the preparation of their metal complexes in very high yields, in the absence of either solvent or base was followed. Thermomicroscopy studies were carried out to assess the metallation reaction, showing that the process is a typical solventless reaction. Calculation of sustainability classifications such as E factors and EcoScale values (as low as 283 and as high as 82 respectively, for the metallation procedure) and very favorable EHS classification establishes this methodology as one presenting the best sustainability classification on porphyrin synthesis.

A Cost-Efficient Method for Unsymmetrical Meso-Aryl Porphyrin Synthesis Using NaY Zeolite as an Inorganic Acid Catalyst

Herein we report the synthesis of unsymmetrical meso-aryl substituted porphyrins, using NaY zeolite as an inorganic acid catalyst. A comparative study between this method and the several synthetic strategies available in the literature was carried out. Our method presented a better, more cost-efficient rationale and displayed a significantly lower environmental impact. Furthermore, it was possible to verify the scalability of the process as well as the reutilization of the inorganic catalyst NaY (up to 6 times) without significant yield decrease. In addition, this method was applied to the synthesis of several other unsymmetrical porphyrins, from a low melting point porphyrin to mono-carboxylated halogenated unsymmetrical porphyrins, in yields higher than those found in the literature. Additionally, for the first time, two acetamide functionalized halogenated porphyrins were prepared in high yields. This methodology opens the way to the preparation of high yielding functionalized porphyrins, which can be easily immobilized for a variety of applications, either in catalysis or in biomedicine.

Synthesis of meso-substituted porphyrins using sustainable chemical processes

The easy access and low price of pyrrole and aldehydes, conjugated with the simplicity in preparing meso-substituted porphyrins, makes this type of porphyrins very attractive for a broad range of applications. However, there is an increasing demand for the development of new synthetic processes involving more sustainable chemical principles substituting, whenever possible, dangerous organic solvents by alternative solvents, chromatographic purifications by precipitations and energy-intensive procedures by alternative energy sources such as microwaves and ultrasounds. In this review we will address some recent strategies to synthesize meso-substituted porphyrins using alternative energy sources, reaction media and catalysts, namely microwave irradiation, water as solvent, or solid microporous acid catalysts.

Synthesis of low melting point porphyrins: A quest for new materials

Preparation of porphyrins which do not aggregate, possessing low melting points is an endearing challenge for several applications in materials science. In this contribution a viewpoint regarding the synthesis of low melting point porphyrins, is presented. Herein we review the synthesis of symmetrical and unsymmetrical substituted porphyrins that hold the possibility to be used in several materials science applications and present new results on the spectroscopic and thermal characterization of some low melting point meso-tetrasubstituted porphyrins.

A recyclable hybrid manganese(III) porphyrin magnetic catalyst for selective olefin epoxidation using molecular oxygen

The synthesis and characterization of a hybrid Mn(III)-porphyrin magnetic nanocomposite is described. Moreover, a sustainable methodology for epoxidation of olefins is reported, using O2 as a green oxidant and the magnetic nanoparticle as a recyclable catalyst. High activity in alkene oxidation was observed, with full selectivity for epoxide formation. The magnetic catalyst presented high stability, being recovered and reused in five consecutive runs without loss of catalytic activity or selectivity in cyclooctene oxidation. Moreover, the catalytic system showed very good reactivity toward epoxidation of a range of terminal, substituted, cyclic or acyclic, aliphatic and aromatic olefins, including terpene and steroid derivatives, affording a range of biologically relevant epoxides in excellent yields. The isobutyric acid, formed as side-product, was recovered with high yield and purity, which provides the potential reutilization of this important industrial product.

Hybrid Metalloporphyrin Magnetic Nanoparticles as Catalysts for Sequential Transformation of Alkenes and CO2 into Cyclic Carbonates

The synthesis and full characterization of manganese and chromium metalloporphyrins and hybrid magnetic nanocomposites prepared thereof is described. Their application in homogeneous and heterogeneous sequential epoxidation/CO2 cycloaddition reactions by using O2 or H2O2 as the oxidant showed high activity and selectivity for the preparation of a variety of cyclic carbonates directly from olefins. The combination of manganese and chromium nanocomposites allowed us to set the keystone for the development of a reusable dual catalytic system to transform olefins into cyclic carbonates.