Synergistic Effect of a Palladium‐on‐Carbon/Platinum‐on‐Carbon Mixed Catalyst in Hydrogen/Deuterium Exchange Reactions of Alkyl‐Substituted Aromatic Compounds

Abstract

Abstract:We have found a synergistic effect in the H-D exchange reaction of alkyl-substituted aromatic compounds using the Pd/C-Pt/C-D 2 O-H 2 system. This system would lead to fully H-D exchange results even on the sterically hindered sites which were only low-deuterium incorporated by Pd/C or Pt/C independently. Since the reaction was general for a variety of aromatic compounds, it could be applied to the deuteration of dianiline derivatives as raw materials for polyimides.Keywords: catalysis; deuteration; palladium; platinum; synergistic effect Deuterium-labeled compounds have been extremely useful in many different branches of science including analysis of drug metabolism, investigation of reaction mechanisms and kinetics etc.[1] Recently, deuterium-labeled polymers were recognized as new materials for wave guides in optical communication systems due to their transparency in the infrared wavelength region.[2]The post-synthetic incorporation of deuterium by the hydrogen isotope exchange reaction using D 2 O, which is the cheapest deuterium compound, as a deuterium source is a cost-wise attractive method. A number of H-D exchange procedures of aromatic compounds in D 2 O have been reported, for example, the H-D exchange reaction catalyzed by acids, [3] bases [4] or transition metals (Ir, [5] Ru, [6] Rh, [7] Pt [8] and Pd [9] ) and supercritical [10] or microwave enhancement [6,8f] exchange reactions. However, many such methods involve contraindications with specific functionalities, low deuterium efficiency and/or the requirement of a vast amount of catalyst and special apparatus.We have recently reported a characteristic H-D exchange reaction catalyzed by Pd/C or Pt/C using D 2 O in the presence of a small amount of H 2 gas, [11] that is, Pd/C catalyzed the H-D exchange reaction at inactive alkyl chains [11b] and Pt/C catalyzed it at aromatic rings [11e] efficiently. We also applied the reaction to the stepwise deuteration of alkyl-substituted aromatic compounds using Pt/C and Pd/C and obtained high deuterium efficiency. Meanwhile, when we tried to examine the deuteration using Pd/C and Pt/C at the same time, and a surprisingly high deuterium efficiency by a synergistic effect was observed. Herein, we report the efficient deuterium incorporation into alkyl-substituted aromatic compounds by synergistic effect of the Pd/C-Pt/C-D 2 O-H 2 system. First, we examined the deuteration of 5-phenylvaleric acid using Pd/C and Pt/C independently or mixed them as a catalyst and Table 1 summarizes a comparison of the deuterium efficiencies. 5-Phenylvaleric acid and 10 % Pd/C (10 wt %) in D 2 O at 180 8C under a small amount of hydrogen in a sealed tube for 24 h leads to high deuterium efficiency on the aromatic ring and alkyl chain, except for the C3 (ortho) position (entry 1). On the other hand, using 5 % Pt/C (20 wt %) as a catalyst leads to high deuterium efficiency on the aromatic ring, except for the C3 (ortho) position (entry 3). The low deuterium efficiency of the C3 position is probably caused by steric hindran...

Die Renaissance des H/D‐Austausches

“…[114] Die gängi- [116] Gegenstand zahlreicher, grundlegender Untersuchungen war die Entwicklung von Methoden zur Aktivierung von Platin [117] oder Palladium [118] für den H/D-Austausch an Kohlenstoff. Außer der Aktivierung von Platinkatalysatoren durch vorherige Hydrierung [78c-d, 119] oder durch initiale Belegung der Katalysatoroberfläche mit Sauerstoff [120] nach Reduktions-und Oxidationszyklen ist auch eine Aktivierung des Katalysators durch Reduktion mit organischen Verbindungen wie Benzol möglich.…”

Preparation and Characterization of 4-Dimethylaminopyridine-Stabilized Palladium Nanoparticles

“…[57][58][59] Deuterated molecules can be used in stable isotopic tracer studies where they can be detected using mass spectrometry. Furthermore, deuterium labeling provides a route to obtain tritium labeled molecules for radiotracer studies.…”

Hydrogen/deuterium exchange of cross-linkable α-amino acid derivatives in deuterated triflic acid

“…Many attempts for deuterium introduction in the aromatic portions of compounds have been reported. Hydrogen/deuterium exchange (H/D exchange) [3][4][5] at a specific position and universal H/D exchange in acidic condition 6) and/or metal catalysis 7) on aromatics have been reported in the literature. Although aromatic α-amino acids were considered to be the substrate for H/D exchange, the α-amino acid skeleton sometimes inhibited to apply previous H/D exchange methods due to their solubility in many organic solvent.…”