Catalysis of Organic..

134Aminoalcohols to Aminocarboxylic Acid Saltseffects are present as well. One possibility is that the reactant is bound to the catalystsurface partly via the nitrogen lone pair so that if this is absent, or the H of NH 2 isreplaced by a more bulky alkyl group, then the strength of attachment is reduced.This might also explain why 2-(2-aminoethylamino)ethanol, which has a secondnitrogen to aid attachment, is relatively reactive.If a diol is oxidatively dehydrogenated to form a diacid via an intermediate withone OH group, then a first order plot based on hydrogen evolution can exhibit somecurvature. This is because the slope at any time will reflect the instantaneousconcentrations of the diol and intermediate as well as their intrinsic reactivities. Firstorder plots for the reaction of ethylene glycol, 1,4-butanediol and diethanolamine areshown in Figure 2. All plots are reasonably linear, consistent with reaction via anintermediate with a rate constant rather similar to that of the starting diol (or a directreaction with no intermediate whatsoever).-ln(1-X H2)2.01.51.00.50.0EG (CrCu)DEA (CrCu)EG (Cu)DEA (Cu)BD (CrCu)0 1 2 3Reaction time, hoursFigure 2. First order plots based on hydrogen evolution for the reaction of ethyleneglycol (EG), diethanolamine (DEA) and 1,4-butanediol (BD) over unpromotedcopper (Cu) and chromia-promoted copper (CrCu).Apparent rate constants, k H2 ′, calculated from the slopes of these plots are shownin Table 3. Comparison against Table 2 shows that the reactivity of ethylene glycolover the promoted catalyst is about 60% that of ethanolamine, while that of 1,4-butanediol is more than an order of magnitude lower. The implication is that thereaction is facilitated through activation by neighbouring groups, with an OHsubstituent somewhat less activating than an NH 2 one, and that this activation isgreatly attenuated by intervening CH 2 groups. As found previously for the reactionof ethanolamine (10, 11), the chromia-promoted catalyst is two or three times asactive as the unpromoted one. However with both catalysts, the CH 2 OH groups indiethanolamine react at less than one-half the rate of those in ethanolamine. Theimplication is that either a CH 2 CH 2 OH side chain is less activating than is H alone,or that a second bulky group hinders reaction or adsorption.