Role of Acetic Acid Added to the Reaction Media for the Enantio-differentiating Hydrogenation of Methyl Acetoacetate Over a Tartaric Acid-modified Nickel Catalyst

Abstract

The role of acetic acid added to the reaction media for the enantio-differentiating hydrogenation of methyl acetoacetate over a (R,R)-tartaric acid-in-situ-modified nickel catalyst was studied from the viewpoint of the hydrogenation rate during repeated runs. The hydrogenation of methyl acetoacetate on the ''enantio-differentiating sites'' of a tartaric acid-modified nickel catalyst was specifically accelerated by the acetic acid added to the reaction media to increase the enantio-differentiating ability of the catalyst. In order to increase the enantio-differentiating ability, the addition of acetic acid to the reaction media was required in each run during the repeated use of the catalyst.

Studies of the effects of the modification conditions on the hydrogenation rate for the enantio-differentiating hydrogenation of methyl acetoacetate over a tartaric acid–NaBr-modified nickel catalyst

“…[18]. Therefore, the hydrogenation without the addition of modifiers to the reaction media over a recovered catalyst was carried out (the 2nd run).…”

“…This is a significant advantage regarding the in-situ-modification. By using the in-situ-modification, we investigated the effect of the amount of acetic acid added to the reaction media on the hydrogenation rate of methyl acetoacetate over the tartaric acid-modified nickel catalyst and that over the unmodified nickel catalyst [18]. It is known that the addition of acetic acid increases the e.d.a.…”

Studies of the effect of pivalic acid on the hydrogenation rate and the enantio-differentiating ability for the hydrogenation of 2-octanone over a tartaric acid-NaBr-modified nickel catalyst

“…The modification was carried out using an in-situ-modification method [15]. (R,R)-tartaric acid and NaBr (the amounts were stated in the text) were added to the reaction mixture.…”

“…For the hydrogenation of methyl acetoacetate, we recently reported that by using an in-situ modification, the role of the acetic acid for increasing the e.d.a. was attributed to the specific acceleration of the hydrogenation rate on the enantio-differentiating sites, where optically active compounds are produced with the aid of tartaric acid [15]. The in-situ-modification is a powerful method for kinetic investigations, because the effect of the modifier adsorption on the hydrogenation rate can be measured without a change in the nickel surface during the modification [15].…”

“…was attributed to the specific acceleration of the hydrogenation rate on the enantio-differentiating sites, where optically active compounds are produced with the aid of tartaric acid [15]. The in-situ-modification is a powerful method for kinetic investigations, because the effect of the modifier adsorption on the hydrogenation rate can be measured without a change in the nickel surface during the modification [15]. On the other hand, for the hydrogenation of 2-alkanones, a few reports concerning the role of pivalic acid have been published, while the addition of pivalic acid to the reaction media is mandatory for the appearance of the enantio-selectivity.…”