The　specific　roles　of　solvents　in　the　synthesis　of　meso-tetraphenylporphyrin　(TPP)　using　a　classical　mixed-solvent　of　acetic　acid,　propionic　acid,　and　nitrobenzene　are　unclear　to　date.　In　this　work,　we　explored　the　acid-activation　process　between　benzaldehyde　and　pyrrole　using　DFT　calculations.　The　catalytic　role　of　carboxylic　acids　was　proven　by　the　formation　of　a　carbocation　intermediate.　Moreover,　the　oxidation　behavior　of　nitrobenzene　or　its　analogs　was　studied　by　UV/Vis　spectroscopy.　In　particular,　the　formation　of　the　corresponding　amides　derived　from　the　reduction　of　nitrobenzene　and　its　analogs　directly　confirmed　their　oxidation　behaviors.　Specifically,　yields　of　up　to　38%　of　TPP　can　be　obtained　from　nominally　pure　to　quite　pure　using　the　mixed-solvent　method　with　meta-nitrotoluene　as　the　oxidant.