LACTOBACILLIC ACID 



2. STRUCTURE OF LACTOBACILLIC ACID 



The behavior of lactobacillic acid (8, 9) which provides 

 the key to its chemical constitution is illustrated on Fig. 1.3. 

 The acid is stable toward oxidizing agents but undergoes 

 hydrogenolysis in presence of platinum and hydrogen with 

 absorption of one mole of hydrogen. The resulting mixture 

 of hydrogenation products contains nonadecanoic acid plus 

 a product also containing 19 carbon atoms which melts at 

 13 to 14°, and on the basis of C-methyl determinations, 

 possesses a branched carbon-chain. The latter material 

 consists of a mixture of branched chain acids later recog- 

 nized as DL-11- and DL-12-methyloctadecanoic acids. These 

 materials arise from the simultaneous hydrogenolysis of the 

 carbon-carbon bonds 2 and 3 in the lactobacillic acid mole- 

 cule. Treatment with hydrogen bromide in glacial acetic 

 acid converts lactobacillic acid into a mixture of mono- 

 bromononadecanoic acids (see Chapter 2, section 4). 



The chemical behavior of lactobacillic acid, i.e., its stabil- 

 ity toward oxidation and its lability toward hydrogen bro- 

 mide and hydrogenolysis, coupled with the fact that hydro- 

 genolysis produces three acids— one of which contains a 

 straight carbon chain (nonadecanoic acid)— pointed to the 

 presence in lactobacillic acid of a cyclopropane ring. Sta- 

 bility toward oxidation and lability to hydrogenolysis and 

 hydrogen bromide are characteristic properties of this par- 

 ticular ring system. The infrared absorption spectrum (Fig. 

 1.4, curve 1) supports the cyclopropane nature of lactobacil- 

 lic acid. The spectrum exhibits the characteristic cyclopro- 

 pane absorption maximum at 9.8 ^ (19), which disappears on 

 hydrogenation (curve 2). 



