A previous paper 1 from this laboratory described the electroreduction of tris-(pnitrophenyl) phosphate (TNP) and suggested a mechanism involving cleavage to give 4,4'-dinitrobiphenyl and 4-nitrophenyl phosphate. It is of interest to consider the case where one of the nitrophenyl groups is replaced by hydrogen, yielding bis-(p-nitrophenyl) phosphate (BNP) [(NO2 C6H40)2 (OH)P=O], to see whether reduction of this compound involves cleavage of both nitrophenyl ring systems in a manner similar to TNP or only one after electroreduction. Analysis of the products and electrochemical data for the electrochemical reduction of BNP provided a mechanism for the reduction generally in agreement with that proposed for TNP.
The polarographic half-wave potentials obtained for the three waves in the reduction of BNP at a dropping mercury electrode in N,N-dimethylformamide (DMF) containing 0.1 M tetra-n-butyl ammonium iodide (TBAI) were -0.94 V, -1.23 V, and -2.6 V vs. an aqueous saturated calomel electrode (SCE). By varying the height of the mercury column above the capillary, the first wave was found to be an adsorption wave (id/h = constant, where id is the diffusion current and h the head of the DME) and the second wave was shown to be a diffusion controlled process (id/h 1/2 = constant). Measurements on the third wave were obscured by maxima. The number of electrons involved in the reduction of BNP at the second wave was estimated to be about two with the calculated diffusion coefficienf of BNP, 1.22 X 10 -s cm 2 s -i (calculated from the known diffusion coefficient of TNP corrected for differences in molecular weights) and the measured diffusion current. The wave height of the third reduction was twice that of the second wave suggesting that the reduction involved twice the number of electrons in the second step and so corresponds to an n of about 4.
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The reduction of BNP was also examined by cyclic voltammetry, typical results are given in Table and Fig. . The shape and position of the peak at -1.02 V was dependent on scan rate and shifted towards more cathodic values with increasing scan rate. This peak disappeared on repeated cycling between -0.83 V and -1.05 V. However, if the