Catalysis of Organic..

Disselkamp et al. 223Scheme 4.cis-2-buten-1-olHOυ 1Ni surface+H (or D)HOcis-2-buten-1-olHOυ 2trans-2-buten-1-ol-H (or D) HOυ 3 -H (or D)υ 4Ni surface[I] - intermediate1-butanol+H HO(or D)The results of our olefin exchange experiments are summarized in Figure 2. Thedeuterium number is given as a function of extent of reaction. The deuteriumnumber is defined as the fractional amount of a given species that has gained +1 amurelative to the hydrogenation-only expected mass. The extent of reaction is simplythe progress of the reaction where at c=0 all substrate exists, whereas at c=1 allproduct(s) exist. In our discussion here, substrate refers to the cis-olefin with zerodeuterium number, and the (only) product is the saturated alcohol (e.g., 1-butanol)not of general interest here. A beneficial feature of our GC/MS analysis approach ofthe cis and trans olefins was the presence of a strong parent ion signal and weakparent-1 mass feature. Thus it was straightforward to quantify parent+1 olefinexchange. We did not observe parent+2, or larger, mass signals indicative of higherorder exchange processes. It is seen that the substrate (cis) deuterium values aremuch less than those of the newly formed trans-olefins. This is expected as initially(at c=0) only H-containing cis-olefins are present. Significantly, the cavitatingultrasound trans values (trans-US) are much larger than the conventional processingvalues (trans-MS). This data will be analyzed further, after a model of thedeuteration process is presented.Deuterium number0.60.50.40.30.20.10.2Cis-MSTrans-MSCis-USTrans-US0.4 0.6 0.8χ (extent of reaction)Figure 2. Deuterium number is shown versus extent of reaction for control (MS) aswell as ultrasound (US) experiments.Two limiting cases of this C3(-H) or C3(-D) elimination chemistry are possible.In one mechanism, rapid energy input into the C-H/D reaction coordinate suggeststhat an excess of energy, beyond the barrier height, can occur. Here one expects anearly statistical distribution of reaction pathways. Thus, the deuterium number(deuterium exchange fraction) should be 0.5. At more moderate vibrational