Abstract
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.
Highlights
Substituted porphyrin design has been applied for several decades, at first, using porphyrin β-pyrrolic substituting patterns such as the 3+1 route [27,28,29], employing the chemistry proposed in the well-known MacDonald 2+2 method [30], which essentially relied on the cumbersome synthesis of tripyrranes [31], later mitigated by Sessler’s advances on their syntheses [32]
Following our previously reported method, where NaY was used as a porous solid acid catalyst [40], and since the legitimate establishment of any porphyrin synthetic methodology implies the demonstration of its flexibility and general usability, we established first a direct correlation between applied methodologies and the yields of desired compounds
The tested NaY zeolite acts as an efficient co-catalyst in the synthesis of unsymmetrical porphyrins in solution
Summary
Substituted porphyrin design has been applied for several decades, at first, using porphyrin β-pyrrolic substituting patterns such as the 3+1 route [27,28,29], employing the chemistry proposed in the well-known MacDonald 2+2 method [30], which essentially relied on the cumbersome synthesis of tripyrranes [31], later mitigated by Sessler’s advances on their syntheses [32]. The development of profitable synthetic methodologies for the preparation of porphyrins bearing at least one bridgeable chemical group, concomitantly with other property-enhancing groups, is presumably one of the main aims in synthetic porphyrin chemistry at present
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