PORPHYRIN COMPLEX SALTS 93 



phyrin, the benzoylated liydroxyporphyrin remains spectroscopically similar 

 to phylloporphyrin, tautomerization being prevented by the esterification. 



Fisher names the compounds isooxyporphyrins, "oxy" connoting hydroxy 

 in the German language. 



9. PORPHYRIN COMPLEX SALTS 



The ability of porphyrins to combine with various metals has 

 repeatedly been mentioned in the preceding pages. The most impor- 

 tant of these complexes are the iron compounds, the hematins. They 

 will be discussed fully in Chapter V, together with the theory of 

 complex salt formation and the properties of some metal compounds 

 (cobalt, nickel, and manganese) which resemble hematin compounds 

 in certain aspects and which allow interesting comparisons. The 

 nature of the porphyrin metal compounds as internal complexes 

 was recognized by Willstatter (3091), who described magnesium com- 

 plexes of porphyrins as phyllins. Compounds with zinc had been 

 obtained by Schulz {21^87), with cobalt by Laidlaw {1632), with nickel 

 and tin by Milroy {1957), and with manganese by Zaleski {3156). 

 Hill {1275) used the following methods for the preparation of a large 

 number of porphyrin complex salts: (a) heating with metal acetate 

 in acetic acid; (6) heating with metal salt in ammonia; (c) introduc- 

 tion of sodium and potassium by alcoholates in pyridine; {d) intro- 

 duction of magnesium by Grignard reagent {cf. also 3091 and 861^ 

 p. 611); {e) introduction of aluminum and arsenic by using the tri- 

 chlorides in pyridine; (/) introduction of silver with silver oxide or 

 silver carbonate in alcohol. 



A better way of preparing phyllins is by heating porphyrins with 

 magnesium bromide in pyridine {810). The stability of the metal 

 complexes varies greatl3\ Water removes sodium, potassium, and 

 arsenic; dilute acetic acid, magnesium and lead; hydrochloric acid, 

 silver, zinc, tin (Sn-"'') and iron (Fe-"*"); concentrated sulfuiic acid, 

 copper, iron (Fe-"^), nickel and cobalt; while tin (Sn^"*") and alumi- 

 num could not be removed. 



Hill distinguishes between three types of spectra: those of the alkali 

 metals and thallium {263^) resemble the acid porphyrin spectrum in that the 

 first band is much weaker than the broad second. (The similarity to the 

 one-banded hemoglobin spectrum may be fortuitous or may be due to pre- 

 dominantly ionic linkage of the alkali metals.) The second class has two 

 bands of about equal strength comparable to oxyhemoglobin, while in the 

 third the first band is the stronger, comparable to hemochromes {cf. Chap- 

 ter V). These similarities are probably fortuitous, particularly since Stern 



