Z 0 U < 3 0g 2 0 -1 0 -I I I I I -1 0 -0 6 -0 2 0 2 0 6 1 0 1 4 l o g 8 [, -P rO H I 1 [Ox H21' Figure 1. The dependence of the ratio of oxidation products on the substrate ratio in the chromic acid cooxidation of isopropyl alcohol and oxalic acid. The solid line is calculated from eq 9, using the value of k2/k6 = 0.27. the total yield of COz is 2(2m). COz:acetone ratio, x, is given by eq 8 and 9.The experimental Equation 10 (from eq 7 and 8) relates the ratio of reaction products to the ratio of the concentrations of the substrates Plotting the data from Table I according to eq 10, one obtains a reasonably good straight line (Figure 2), with a slope k j / k 6 = 0.27. Oxalic acid is thus about 3.7 times more reactive toward chromium(V) than isopropyl alcohol.This approach is of general utility and will permit the determination of the reactivity of a variety of compounds, relative to oxalic acid, toward chromium(V), provided that they can participate in a cooxidation reaction with oxalic acid similar to isopropyl alcohol.It is interesting to compare the relative reactivities of the two substrates, oxalic acid and isopropyl alcohol, toward chromium(V) and chromium(V1). Under conditions comparable to these reactions in which chromium(V) reacts 3.7 times faster with oxalic acid than with isopropyl alcohol, chromium(V1) is about 120 times more reactive.j The higher reactivity of chromium(V1) toward oxalic acid is most likely due to the availability of the three-electron oxidation mechanism' for the latter reaction.It should be noted that in Figures 1 and 2 all points lie on single lines, regardless of acidity.6 One can thus conclude that the chromium(V) oxidations of both alcohols and of oxalic acid exhibit the same dependence on acidity. As the chromium(V) oxidation of oxalic acid is independent of a~i d i t y ,~ it follows that the chro-( 5 ) In 0.097 M perchloric acid, the rate of reduction of chromium(V1) by 0.10 M isopropyl alcohol is 1.41 X 10-5 sec-' and by 0.097 M oxalic acid is 1.70 X 10-3 sec-1.(6) This is true only provided that undissociated oxalic acid, rather than the total analytical concentration of oxalic acid, is taken into account. This indicates that only undissociated oxalic acid is kinetically active as a reducing agent toward chromium(V). This conclusion parallels our reported findings for chromium(V1). 1 (7) V. Srinivasan and J. Ro'cek, unpublished results. 4 0 -7 3 0 -n . -2 2 0 -1 0i G 4 0 6'0 8'0 I d G I 2 0 1 4 0 [ -PrOH]/[OxH2] Figure 2. Determination of the relative rates of chromium(V) oxidation of isopropyl alcohol and oxalic acid-perchloric acid : (0),0.063 M ; (e), 0.125 M ; (@),0.63 M.mium(V) oxidation of isopropyl alcohol is also acidity independent within the acidity region covered by the present study. In this respect, the chromium(V) oxidation of isopropyl alcohol differs significantly from the chromium(V1) oxidation, which is well known to be acid catalyzed.8 (8) F. H. Westheimer and A. Novick, J . Chem. Phys., 11, 506 (1943).
Generation and Reactions of Anions ct to the Carbene...