PREPARATION AND PROPERTIES OF VERDOHEMOCHROMES 461 



2.3. Preparation and Properties of Verdohemochromes 



Preparation. For the preparation of pyridine verdohemochromes 

 on a large scale the coupled oxidation of pyridine hemochromes with 

 hydrazine gives good results. Great care is required, however, in order 

 to avoid contamination with by-products; so far only amorphous 

 preparations have been obtained.* 



The original method of Warburg and Negelein has been modified by 

 Lemberg (1081,1687). A rapid current of oxygen is passed through a vigor- 

 ously stirred solution of hemin in 20% pyridine at 60° C; the addition of a 

 mixture of hydrazine sulfate and sodium hydroxide starts a rapid reaction 

 with change of the color to green (both the total amount of hydrazine and 

 the ratio of hydrate to sulfate are critical). This reaction is complete in a 

 few minutes. It is essential to control the course of the reaction by examining 

 samples reduced with dithionite under the spectroscope every thirty seconds. 



At first the green hem/chrome of oxyporphyrin is formed (absorption band 

 at 640 m/x)t; on reduction with dithionite this yields a red-brown hemo- 

 chrome with absorption bands similar to those of porphyrin hemochromes. 

 The reaction must be continued until, after dithionite reduction, no trace 

 of the first hemochrome band in the green (557 m/i for proto) is any longer 

 visible, but only the strong band in the red and the two weak bands in the 

 green (530 and 500 mju), which are those of proto verdohemochrome. If this 

 precaution is neglected mixtures of verdohemochromes with hemochromes 

 of oxyporphyrin or intermediate oxidation products of the latter are 

 obti ined. 



After extraction of brown by-products with ether, the verdohemochrome 

 is extracted with chloroform, together with some pyridine. The extract is 

 dried, concentrated to a small volume in vacuo, and the verdohemochrome is 

 precipitated with light petroleum. The precipitate is once more dissolved 

 in dry chloroform containing 1% pyridine and reprecipitated with light 

 petroleum. 



Analysis proves that the ratio of nitrogen to iron is 6:1, i.e., that 

 the substance contains two moles of pyridine; the carbon values, 

 however, were always found too low (about 61% instead of the 65% 

 expected from theory). The preparation also contains a small amount 

 (1.85%, far less than one atom) of chlorine, which may be due to 

 occluded chloroform. 



Verdohemochromes are rather unstable substances. In the presence 

 of atmospheric oxygen they soon lose their solubility in chloroform. 



* Recently a crystalline verdohemin was obtained (168S). The chloroform solution 

 of verdohemochrome is washed with dilute hydrochloric acid to remove the pyridine. 

 After concentration of the chloroform solution in vacuo, verdohemin crystallizes in 

 green prisms. 



t This compound is possibly the hemochrome of the intermediate oxidation product 

 postulated in Figure 3, not the hem/chrome of oxyporphyrin, i.e., dithionite reduces 

 the pyrrolic nucleus, but not the iron. 



