842 X. THE VITAMIN K GROUP 



more readily soluble in water. Thus, although menadione dissolves to the 

 extent of only 0.013% in water, the esters of the hydroquinones are quite 

 soluble in this solvent. 



Although the K vitamins are fairly thermostable,*^ they are readily de- 

 stroyed by alkali, ^^'^^ alcohol,^^-^^ and by various kinds of light, including 

 sunlight, ^^'^^ light from ordinary Mazda bulbs," and, especially, ultraviolet 

 light.«8 



One of the most characteristic properties of the vitamins K which is use- 

 ful in their identification is the ultraviolet absorption pattern. Maxi- 

 mum absorption bands occur at 243, 249, 260, 269, and 325 m.^.^^ The 

 absorption cui-ves for vitamins Ki and K2 are reproduced in Figure 1, and 

 those of the 1,4-naphthoquinones in Figure 2. The extinction coefiicients 

 are recorded in Table 1. 



TABLE 1 

 Absorption Coefficients of Vitamin Ki in Hexane at Maximum and Minimum 



Wave Lengths" 



" Adapted from J. R. Loofbourow, Vitamins and Hormones, 1, 109-155 (1943). 



The positions for the maxima and minima are similar for vitamins Ki 

 and 1^2,^^^ but the e values are somewhat lower for vitamin K2. Ewing et 

 aU^ report the maxima on the synthetic vitamin Ki prepared by Mac- 

 Corquodale et aL" to be X 243, 249, 260, 269, and 325; the corresponding 

 E (1%, 1 cm.) values were 410, 425, 395, 395, and 75, respectively. Thus, 

 the data on the synthetic product correspond within experimental limits 

 to those of the natural vitamin. 



Vitamin Ki is a yellow oil melting at about — 20°C., while vitamin K2 

 is a yellow crystalline solid melting at 53.5-54.5°C.2^ Menadione is also a 

 crystalline lemon-yellow powder, which melts at 106°C. It has a faint but 

 characteristic odor. Vitamin Ki has a redox potential. En, of +0.005 

 volt. According to Almquist and Klose,^* its solutions exhibit a white 

 fluorescence when exposed to the light of the argon lamp. The latter 



" H. J. Almquist, J. Nutrition, U, 241-245 (1937). 

 «8 H. J. Almquist, /. Biol. Chem., 117, 517-523 (1937). 



