618 3. DEHYDROACETATE 



Dehydroacetic acid was found to be rather inactive against most of the 25 

 types of bacteria studied and no further mention was made of it. McGowan 

 et al. (1948) investigated 80 compounds with ethylenic linkages for the pur- 

 pose of correlating fungistatic activity with the abihty of the substituents 

 to withdraw electrons from these double bonds, and found dehydroacetate 

 to exert very little effect. An investigation stimulated by the antibacterial 

 effects of usnic acid from lichens led Ukita et al. (1949) to examine dehydro- 

 acetate, which they found to inhibit staphylococci and mycobacteria slight- 

 ly; however, other substances were more potent and of greater interest. 

 The Dow Chemical Company meanwhile had been studying the antimicro- 

 bial action of dehydroacetate and on June 28, 1949 issued three patents for 

 its use in food preservation.* These were based on work started in 1946 in 

 cooperation with the Department of Pharmacology of the University of 

 Michigan Medical School, the results of which were published in a series of 

 papers in 1950. Almost all of our present basic knowledge of dehydroacetate 

 stems from this work and essentially no fundamental biochemical reports 

 have been made since, although a great many papers on its practical use 

 appear annually. 



CHEMICAL PROPERTIES 



The structure of dehydroacetic acid was debated for many years until 

 Rassweiler and Adams (1924) proved that the formula suggested by Feist 

 (1890) is basically correct. The dipole moment of 2.83 was claimed by Le- 



Dehydroacetic acid 



Fevre and LeFevre (1937) to be consistent with this structure if restrictions 

 were imposed on the rotation of the acetyl group. The formula is commonly 

 written in the keto form, but it is likely that a tautomeric equilibrium with 

 the following enolic forms occurs: 



H,c. o ^o H,C 



(a) (b) (c) 



* Dehydroacetate is actually a rather weak inhibitor of microbial growth but can 

 be used to ^reserve food because it is so little toxic to humans. 



