4-Mercapto-4-methyl-2-pentanone

4-Mercapto-4-methyl-2-pentanone (MMP) is an aliphatic ketone thiol that surprisingly shows up in  several natural settings. In 1948, MMP first appeared in the chemical literature in an article by Hungarian chemists Zoltán Földi and Jano Kollonitsch as an example of the addition of thiols across double bonds. The compound also appeared in articles by Russian and Turkish authors the same year.

MMP appears most often in the literature because of its characteristic olfactory property, that is, its foul smell. It is one of the three major odor components of cat urine, along with 3-mercapto-3-methylbutanol¹ and 4-methoxy-2-methyl-2-butanethiol². MMP is often called “cat ketone”.

But to some people, MMP resembles the aroma of blackcurrants, the fruit of the deciduous shrub Ribes nigrum. MMP’s low concentration in the currants gives them a somewhat pleasant smell that is still reminiscent of cat urine odor.

As our reader who suggested this molecule commented, “Cat ketone! Makes my blackcurrant tea and my cat boxes smell the same!” For more details on the currant–urine connection, see Andy Brunning’s excellent article “Blackcurrants & Cat Urine—The Chemistry of Blackcurrants”.

Finally, MMP shows up in other natural settings, such as Japanese green tea, Sauvignon grapes, and boxwood trees.

1. CAS Reg. No. 34300-94-2.
2. CAS Reg. No. 94087-83-9.