Studies in detoxication. 44. The metabolism of benzene. The muconic acid excreted by rabbits receiving benzene. Determination of the isomeric muconic acids

Abstract

A colorimetric method for the detn. of the 3 geometrical isomers of muconic acid is based on the production of a red color by heating muconic acid with phenol and concentrated H2SO4 and then dissolving the product in absolute ethanol. The same amt. of color is produced on heating the cis-cis- and cis.trans. acids at 100[degree] for 6 hrs. as on heating the trans-trans acid at 160[degree] for 20 min. By this method the cis-acids can be distinguished from the trans-trans-acid and estimated when they occur separately. This method has also been applied to urine. When the cis-acids and the trans-trans.acid occur together the same colorimetric method can be used for their estimation, if the cis-acids are 1st estimated in the mixture and then converted to the trans-trans-acid by u.-v. light followed by an estimation of the total muconic acid as the trans-trans-isomer. By this colorimetric method it was shown that rabbits receiving an oral dose of benzene excrete about 0.5% of the dose as trans.trans-muconic acid, there being none of this cis-isomers in the urine. trans-trans-Muconic acid was isolated from the urine and characterized as its benzhydryl ester. It was shown that if cis-cis-muconic acid had been excreted after admn. of benzene, it could not have been destroyed by bacteria. The 3 isomers of muconic acid were also injd. into rabbits and no evidence was found for their in vivo isomerization, 50-65% of unchanged acid being recovered in the urine. trans-trans-Muconic acid is probably a true metabolite of benzene and is not produced in vivo from the cis_cis_acid. The cis-cis-acid need not be an intermediate in the formation of the trans-trans-acid in the animal body.