Degradation pathways of perfluoro-2-methyl-3-pentanone in different solvents: a multinuclear NMR and DFT study

The perfluorinated ketone perfluoro-2-methyl-3-pentanone (1) is a fire protection fluid of great merchandise importance whose analysis of purity can be easily carried out by NMR techniques. However, while 1 is very stable (at least one year) in the neat state, it reacts with moisture when dissolved in NMR solvents such as acetone-d6, acetonitrile-d3 or dimethylsulfoxide-d6 producing the gem-diol perfluoro-2-methyl-3,3-pentandiol (2) as the major product in acetone-d6 or in acetonitrile-d3; and a perfluoropropionic acid/CF3CFHCF3 (3/4) mixture in dimethylsulfoxide-d6. Good stability was observed in CDCl3 or in C6D6. A multinuclear NMR analysis using both a low-field machine (80 MHz benchtop spectrometer) and a medium-field machine (400 MHz spectrometer) and a DFT study that confirmed the existence of through-space spin-spin coupling for 1, as well as the mechanism of water induced degradation of 1, is reported.