4775This 5050 ratio also agrees with the results reported by Burrington et al." They observed very nearly equal amounts of CD2=CHCH0 and CH2=CHCD0 produced during the oxidation of CH3CH=CD2 over antimony-based catalysts. They suggest that this ratio is a result of an irreversible addition of oxygen to the r-allyl intermediate to form the o-allyl intermediate. This sequence provides a reasonable explanation for our suggestion that with antimony-based catalysts oxygen is added before the 13CH2=CHCD0 and CD2=CH13CH0. Each of the two deuterium signals in CD2=CH13CH0 will be split into a doublet due to the vicinal coupling between D and 13C. The coupling constants ( J C D ) can be calculated from the results obtained for 3JCH by Vogeli et al.*' from the following equation:where y H and yD are the gyromagnetic ratios for a proton and a deuteron, respectively.The experimental results presented in Table VI are in good agreement with those calculated from eq 3. The coupling constant for the trans deuterium is 2.4 Hz (2.5 from 3JCH) and 1.6 Hz (1.6 from 3JcH) for the deuterium cis to the carbonyl carbon. Using these coupling constants, it is possible to assign the chemical shift at 6.42 ppm to the deuterium trans to the carbonyl carbon (D,) and the chemical shift at 6.24 ppm to the cis deuterium (D2).The small signal at 6 6.38, Figure 8c, can be assigned to acrolein with a deuterium a t C-2 by comparing the results obtained for the oxidation of CH2=CDCH3 (Figure 11). Only one signal, corresponding to CH2==CDCH0, is detected (6 6.38). The DEFT I3C spectrum (Figure 12) also indicates that a deuterium atom is located a t C-2. This very minor product is produced by a mechanism not yet explained.The ratio of the various forms of deuterated acrolein, CD2= CHCHO and CH2=CHCD0, were calculated by comparing the amount of D2 (preferred due to better resolution) or D, with that of -CDO. The data summarized in Table VI1 indicate that a 50:50 ratio was obtained for the oxidation of CD2=CHCH3, CH2=CHCD3, and I3CH2=CHCD3 over iron-antimony catalysts. This suggests that a common intermediate is formed from CD2=CHCH3 and CH2=CHCD3. As suggested earlier, this intermediate is a symmetrical ?r-allylic intermediate.second hydrogen is abstracted.Another possible explanation of the 50:50 ratio of the deuterated acrolein would be rapid double bond isomerization of propylene before the *-allylic intermediate is formed. This possibility can be ruled out, however, by examining the position of D (or I3C) in the recovered unreacted propylene. The data in Table VI1 indicates that less than 8% of deuterium scrambling takes place before reaction. The I3C data indicates that less than 2% double bond isomerization takes place. Thus, the evidence is quite conclusive that the 50:50 ratio cannot be explained by a rapid isomerization of propylene.
ConclusionsThe selective oxidation of propylene over iron-antimony catalysts is kinetically and mechanistically very similar to the selective oxidation of propylene reported for USb3010.13 The reaction proceeds via a...
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