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

Abstract

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 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 the 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

“…This fraction was then evaporated to dryness, and the resulting solid was dried under vacuum and weighed. Characterization data from Compounds 1 [ 53 ], 2 [ 52 ], 3 [ 59 ], and 4 [ 60 ] are in accordance with those in the literature. The characterization data for the new compounds are displayed below.…”

“…It is well established that the pKa and the type of acid (organic [ 43 , 44 , 45 ] or solid [ 46 , 47 ]—Lewis or Brønsted) are determining factors for efficient pyrrole and aldehyde condensation. Using acids as catalysts, the current methods for meso -aryl substituted porphyrin syntheses include the classical one-pot Adler-Longo [ 43 ] and Gonsalves-Pereira [ 44 ] strategies and the two-step Lindsey method [ 45 ], along with more recent microwave irradiation methodologies [ 48 , 49 , 50 , 51 , 52 ].…”

“…Considering our interest in highly soluble low melting point porphyrins [ 41 , 52 ], we prepared 5-(4-hydroxyphenyl)-10,15,20-tris(4-ethylhexyloxyphenyl) porphyrin ( 2 ) in 15% yield, higher than the previously reported using other methodologies (7–10%) [ 41 ]. Similarly, and considering the high importance of monocarboxylic acid-substituted porphyrins for further functionalization, 5-(4-carboxyphenyl)-10,15,20-tris(phenyl) porphyrin ( 3 ) was also prepared in 17% yield in just one step, while a careful literature search revealed that the best yields are usually obtained by first preparing the 5-(4-methoxycarbonylphenyl)-10,15,20-tris(phenyl) porphyrin, followed by ester hydrolysis, attaining 6.5% overall yields [ 59 ].…”

The EcoScale as a framework for undergraduate green chemistry teaching and assessment

“…A major strength of this approach is that it allows the direct comparison of different routes towards the same target compound. The EcoScale has found favor as an assessment tool in academic laboratories (13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25) and has been modified for industrial purposes (26). It has also been incorporated into some undergraduate pedagogical laboratory exercises (9,27), although it has not, to our knowledge, been utilized as a formal way to evaluate student learning and understanding of green chemistry.…”

Synthesis and characterization of biocompatible bimodal meso-sulfonamide-perfluorophenylporphyrins

“…The synthetic difficulties and scarce availability of natural porphyrinoids [29,33,34], led to the use of meso-substituted tetrapyrrolic macrocycles, easily obtained by sustainable synthetic methods [12,[35][36][37][38], as the main choice for the development of new generations of PDT agents [8,9,39]. 5,10,15,20-Tetrakis(pentafluorophenyl)porphyrin (TPFPP) is an interesting template to functionalize via nucleophilic substitution reactions [40], making use of nucleophiles such as amines, thiols, alcohols and nitrogen heterocycles [41,42], to improve their avidity for bacteria.…”