Reaction of 1,1-diphenyl-2-picryl-hydrazyl or -hydrazine with sodium borohydride in the presence of 18-crown-6 ether

The reaction between a solution of the stable free radical 1,1 -diphenyl-2- picrylhydrazyl (DPPH), 1, or the corresponding 1,1-diphenyl-2-picrylhydrazi ne (DPPH2), 2, in triethylene chloride and solid sodium borohydride in the presence of 18-crown-6 ether leads to the corresponding anions of the hydra zine 2 and to the following four compounds: 1-(4-nitrophenyl)-1-phenyl-2-pi cryl-hydrazine, (4); 1,1-diphenyl-2-(2,4-dinitrophenyl)-hydrazine, (5); 1,3 ,5-trinitrobenzene, (6), and traces of 1,3-dinitrobenzene, (7). The above a nions were converted into neutral compounds 2, 4, 5, 6 and 7 in the organic phase by treatment with hydrochloric acid, isolated via preparative TLC, i dentified by NMR and UV-Vis spectra, and determined quantitatively in this phase through densitometric TLC. A possible mechanism for this disproportio nation (intermolecular nitro group transfer) and molecular fragmentation is proposed and discussed, by correlating the above results with ESR data obt ained by using the spin traps alpha -phenyl-N-t-butylnitrone (PBN) and 5,5, -dimethyl-1-pyrroline-N-oxide (DMPO).