Catalytic Hydrogen Isotope Exchange Research Articles

Highly active iridium(i) complexes for catalytic hydrogen isotope exchange

Practically convenient methods have been developed for the preparation of new iridium complexes, possessing bulky N-heterocyclic carbene and phosphine ligands; these routinely handled complexes are highly active catalysts within directed hydrogen isotope exchange processes.

Application of 1‐butyl‐3‐methylimidazolium hexafluorophosphate to Ir(I)‐catalyzed hydrogen isotope exchange labelling of substrates poorly soluble in dichloromethane

AbstractSubstrate solubility remains a major limitation in Ir(I)‐catalyzed isotopic hydrogen exchange labelling. In the search for an alternative to the solvent dichloromethane, which is critical to the success of the reaction, we examined a series of ionic liquids for their suitability. Commercially available 1‐butyl‐3‐methylimidazolium hexafluorophosphate (abbreviated to [BMI][PF6]) was found to support efficient deuterium and tritium exchange labelling of N‐(4‐methoxyphenyl)‐N‐methyl benzamide 1 under standard conditions. The solvent dissolves both polar hydroxyl and carboxylic acid substituted acetanilides, providing isotopomers in unprecedentedly high deuterium incorporation as compared to dichloromethane. We report the application of [BMI][PF6] and its potential for extending the scope of Ir(I)‐catalyzed H/T exchange to more polar compounds. Copyright © 2003 John Wiley & Sons, Ltd.

Synthesis of tritium-labelled diazines and their analogues

Some 40 diazines have been tritiated to high specific activities using a variety of labelling procedures such as catalytic hydrogen isotope exchange both in solution and the solid state, reduction and hydration. For purine derivatives it is shown that the solid state catalytic isotope exchange reaction is the most effective method. With pyrimidines this reaction is accompanied by a parallel hydration reaction of the 5,6-double bond to form a complex mixture of products. Identification and quantitative estimation of these products has been accomplished in terms of the reaction condition (solvent, nature of catalyst). Copyright © 1998 John Wiley & Sons, Ltd.

Organoiridium catalyzed hydrogen isotope exchange: ligand effects on catalyst activity and regioselectivity

Several iridiu complexes [Ir(cod)L 2]X ( L = phosphine ligand) were used as precatalysts for the exchange labeling of a range of model compounds with deuterium gas. Complexes with monodentate L (e.g. PMePh 2, PPh 3 and substituted derivatives thereof) catalyzed exchange selectively of hydrogens four bonds away from a coordinative heteroatom in the substrate, while those with bidentate L (bis(diphenylphosphino)ethane (dppe) and bis(diphenylphosphino)butane) catalyzed exchange of hydrogens both four and five bonds away from a coordinative heteroatom. At heavier loadings, some monodentate complexes also catalyzed five-bond labeling of some substrates. [Ir(cod)(dppe)]BF 4 catalyzed the tritium labeling of methyl 6-methoxynaphth-2-ylacetate at C1 and C3.

Application of solid state catalytic hydrogen isotope exchange to the tritium labeling of lysozyme

AbstractSolid state catalytic hydrogen isotope exchange has been employed to label hen egg lysozyme with tritium. Optimization of reaction conditions so that amino acids and peptide bonds remained intact led to a tritiated product with 97% of the original enzymatic activity and 94% radiochemical purity. The specific activity when using a T2:H2 mixture of 1:1000, was 16 mCi·mmol−1. It is suggested that the currently adopted approach may have wide applications for other proteins able to tolerate lyophilization conditions without loss of activity.

Heterogeneous palladium‐catalyzed exchange labelling of representative organic compounds with tritium gas

AbstractA range of organic substrates was successfully exchanged with tritium gas using NaBH4‐reduced palladium oxide or chloride as catalyst. Exchange conditions involved a reaction temperature of 100 °C, a reaction time of 3 days, and products were analyzed by radio‐gas chromatography and 3H NMR spectroscopy. Both aromatic and aliphatic compounds underwent exchange, 18 of the 22 substrates incorporated > 35% of the available tritium, and most products showed high radiochemical purity. 3H NMR analyses showed that both alkanes and the alkyl chains of alkylbenzenes were rapidly and evenly labelled. Some aromatic compounds showed general ring exchange while others showed high specificity. These results for bulk palladium catalyst are strikingly different from those obtained with bulk platinum and supported palladium catalysts. The results are discussed in terms of currently accepted mechanisms of heterogeneous metal catalyzed hydrogen isotope exchange reactions.

Reactant Correlation Effects Study of Hydrogen Isotope Exchange Reaction on Supported Metal Catalysts

ABSTRACTNon-classical results due to reactant correlation effects have been observed in the study of Monte Carlo simulations of the A2 + B2 → 2AB reaction. These simulation results, interpreted by the Pair Density Analysis method and the experimental kinetic studies, may provide an explanation of the early time anomalous kinetic behavior of the catalytic hydrogen isotope exchange reaction exhibited for surface-diffusion limited conditions on alumina supported platinum islands.

Synthesis of Tritiated Components of Nucleic Acids Part 3

At the catalytic tritiation of 5-Formyluracil (5-FU), different compounds are generated. The kind of the species depends on the reaction conditions. 5-FU is one of the derivatives of uracil which are slightly approachable to a catalytic hydrogen isotope exchange. This isotope exchange in the formyl group seems to be favoured above the 6-position in the uracil ring, because of its greater reactivity. After separation of the impurities, we obtained tritiated 5-FU with a specific radioactivity of nearly 1480 GBq/mmol and a radiochemical purity >98%. The pressure of tritium gas was <25 kPa. The catalyst we used was PdO(1.4%)/BaSO4. With the same catalyst we obtained 5-Hydroxymethyl[hydroxymethyl-3H]- uracil by raising the pressure of tritium gas to 50 kPa. Hydrogenation of the 5.6 double bond occurred by an additional raising of the pressure to 75 kPa and we obtained 5-Hydroxymethyldihydrouracil (5-DHMU) [1].

ChemInform Abstract: Catalyzed Hydrogen Isotope Exchange on Five‐Membered Heterocyclenes of the Furan, Pyrrole, and Thiophene Series

ChemInform Abstract: Catalyzed Hydrogen Isotope Exchange on Five‐Membered Heterocyclenes of the Furan, Pyrrole, and Thiophene Series

Hydrogen isotope exchange between boranes and deuterated aromatic hydrocarbons: evidence for reversible hydroboration of benzene

Pentaborane, B/sub 5/H/sub 9/, and diborane, B/sub 2/H/sub 6/, undergo hydrogen isotope exchange with deuterated aromatic hydrocarbons. Lewis acid catalyzed hydrogen isotope exchange occurs between benzene-d/sub 6/ and the apical hydrogen atom of B/sub 5/H/sub 9/ to form 1-DB/sub 5/H/sub 8/ at ambient temperature. In uncatalyzed exchanges, B/sub 5/H/sub 9/ reacts with deuterated aromatic hydrocarbons to produce 1,2,3,4,5-D/sub 5/B/sub 5/H/sub 4/ at +45/sup 0/C and B/sub 5/D/sub 9/ at +120/sup 0/C. This thermally induced hydrogen isotope exchange apparently occurs via a reversible hydroboration of the aromatic ring. Diborane undergoes a similar isotope exchange with benzene-d/sub 6/ under mild thermal conditions. 18 references, 6 figures, 3 tables.

Preparation of tritium‐labelled jasmonic acid, ethyl dihydrojasmonate and itaconic acid

AbstractA method for tritium labelling of jasmonic acid, ethyl dihydrojasmonate, and itaconic acid involving metal catalyzed hydrogen isotope exchange is described. The procedure is a convenient one‐step synthesis and specific activities in the range of 3 to 30 GBq/mmol were obtained.

Application of immobilized hydrogenase for the detritiation of water

AbstractDetritiation of contaminated water is an essential part of nuclear power production. Most promising methods used for this process are based on catalyzed hydrogen isotope exchange reactions. It is proposed herein to replace the platinum catalysts which are currently used in industry with immobilized hydrogenase. Whole bacterial cells of Alcaligenes eutrophus immobilized in calcium alginate or κ‐carrageenan gels were found to be efficient catalysts of the reaction of hydrogen–tritium (H–T) exchange in both a batch tank reactor and in a column. The dependence of the reaction rate on the amount of immobilized cells in the system, and on the concentration of the cells in the matrix, indicate that enzymatic H–T exchange is not controlled by diffusion. Immobilized A. eutrophus cells are enzymatically active over a wide range of pH, with a broad maximum from pH 6.0 to 8.0, and are quite resistant to inhibitors of hydrogenases such as O2 and CO. Upon increasing the temperature from 4 to 37°C, the rate of hydrogenase‐catalyzed H–T exchange increases by a factor of 5. From the standpoint of catalytic efficiency, 1 g of PtO2 is approximately equivalent to 10 g of cells (wet weight). In contrast of platinum‐based catalysts, bacterial hydrogenases (1) are potentially inexpensive; (2) can be readily available in bulk quantities; (3) are maximally active in liquid water.

Hydrocarbon acidities and Brønsted Correlations

We had previously reported [1] two separate Brønsted correlations relating methanolic sodium methoxide catalyzed hydrogen isotope exchange rates of hydrocarbons with p K CsCHA values. One correlations having a slope of 0.37 at 45 °C applies to fluorenyl and related compounds having a cyclopentadienyl moiety. This correlation has now been extended an additional 2 p K units to higher acidity by study of 1,3-diphenylindene. This compound shows a normal primary isotope effect despite being only 3 p K units less acidic than methanol itself [2]. The second linear correlation having a slope of 0.58 at 45 °C (0.46 at 100 °C) applies to polyarylmethanes. This correlation has been extended up to p-methylbiphenyl and toluene without significant deviation. The important region between the two correlations has been studied with derivatives of phenalenes, hydrocarbons as acidic as fluorene and indene but without a cyclopentadienyl moiety. These hydrocarbons actually define the nature of the intersection between two related but different Brønsted correlations.

390. The kinetics of hydrogen-isotope exchange reactions. Part VII. Aromatic hydrogen exchange in the solvent systems ZnCl2–CH3·CO2H and ZnCl2–HCl–CH3·CO2H

The rate of the acid catalyzed hydrogen-isotope exchange between p- deuteroanisole and the solvent systems ZnCl/sub 2/--CH/sub 3/COOH and ZnCl/sub 2/- -HCl--CH/sub 3/COOH has been measured at 25 deg . The rate parallels, to a close approximation, the extent of ionization of indicators such as 4-chloro-2- nitroaniline and p-nitrodiphenylamine in these systems. The ionization process of these compounds is, therefore, considered to involve only hydrogen transfer. The details of the exchange mechanism are discussed. (auth)