The pure product tends to crystallize in perfect large purple crystals. Single-crystal X-ray diffraction revealed a triclinic P-1 space group (Table ). Two opposed hexyloxycarbonyl groups on each ring are oriented parallel to the plane of the nitrogen atoms and the other two are rotated by ~70E out of this plane (Figure ). Conversion of 3 into 2 requires hydrolysis followed by decarboxylation of the intermediate tetracarboxylic acid, and can be accomplished by heating in a concentrated sulfuric acid solution. However, even in the absence of oxygen, much of the porphyrin turns into a black tar and the yield rarely exceeded 60%. As an alternative, concentrated orthophosphoric acid effects the decarboxylation well, but it cannot be used to hydrolyze the ester. The original onepot synthesis was therefore divided into two separate reaction steps. The first is an alkaline ester hydrolysi and the second is acidic decarboxylation. Both steps are almost quantitative and they can be carried out in the same flask.