328 VII. ACIDS, AMIDES, ALDEHYDES AND HYDROCARBONS 



(2) Aromatic Hydrocarbons 



With the exception of the cyclopentenophenanthrene nucleus and the 

 triterpenes, the distribution of the aromatic hydrocarbons in biologic ma- 

 terials is limited. Such aromatic hydrocarbons as do exist are quite re- 

 sistant to chemical changes in the animal body. The reactions which 

 occur usually involve oxidations to form hydroxyl or carboxyl groups; 

 these new compounds are water-soluble, and may become conjugated with 

 detoxicating products. Wilhams,"" in his excellent monograph entitled 

 Detoxication Mechanisms, described the metabolic fate of a large group of 

 organic compounds, including the hydrocarbons. A second excellent col- 

 lection of articles, also edited by Williams,"^ entitled Biological Oxidation 

 of Aromatic Rings, has been published in Biochem. Soc. Symposia No. 5. 



a. Benzene and Related Compounds. Although benzene as such can 

 scarcely be considered to be a physiologic substance, the body possesses 

 certain mechanisms for its oxidation and metabolism when it does gain 

 access to the body. The general pattern of these reactions varies not only 

 with the cychc compound employed but even, in the case of benzene, with 

 the site of substitution. 



(a) Benzene, o! . The Elimination of Unchanged Benzene: A con- 

 siderable proportion of the administered benzene can be eliminated from 

 the body through the Imigs and by way of the kidney, especially after large 

 doses of the hydrocarbon have been fed. As early as 1883, Nencki and 

 Sieber^^^ stated that about one-third of the quantity of benzene given was 

 excreted by the respiratory route. Lehmann and co-workers^^' later 

 placed the figure at 40 to 45% of the quantity absorbed. In the latest 

 experiments of Parke and Williams, ^^^ in which C'Mabeled benzene was 

 employed, 43% of the total benzene was excreted unchanged in the ex- 

 pired air by the rabbit within two days after a single oral dose. Earher, 

 these investigators ^^^ had reported an excretion of ordinary benzene via 

 the lungs amounting to 40% when the dose employed was 0.25 and 0.50 

 g. per kg., and to 64% when it was given at a level of 1.0 g. per kg. 



The kidney is a much less important route of elimination of unchanged 



1™ R. T. Williams, Detoxication Mechanisms, The Metabolism of Drugs and Allied Or- 

 ganic Compounds, 2nd ed., Wiley, New York, 1949. 



"1 R. T. Williams, Biological Oxidation of Aromatic Rings, Biochem. Soc. Symposia, 

 No. 5, Cambridge Univ. Press, 1950, pp. 1-96. 



1" M. Nencki and N. Sieber, Arch. ges. Physiol. (Pfluger's), 31, 319-349 (1883). 



1" K. B. Lehmann, S. O. Gundermann, O. Stohr, and R. Kleiner, Arch. Hyg., 72, 307- 

 326(1910). 



"* D. V. Parke and R. T. Williams, Biochem. J., 5U, 231-238 (1953). 



1" D. V. Parke and R. T. WiUiams, Biochem. J., 46, 236-243 (1950). 



