Tritium catalysts

Boron Bromide. Approximately 30% of BBr produced in the United States is consumed in the manufacture of proprietory pharmaceuticals (qv) (7). BBr is used in the manufacture of isotopicaHy enriched crystalline boron, as a Etiedel-Crafts catalyst in various polymerization, alkylation, and acylation reactions, and in semiconductor doping and etching. Examples of use of BBr as a catalyst include copolymerization of butadiene with olefins (112) polymerization of ethylene and propylene (113), and A/-vinylcarbazole (114) in hydroboration reactions and in tritium labeling of steroids and aryl rings (5). 

Isotopic Exchange Reactions. Exchange reactions between the isotopes of hydrogen are well known and well substantiated. The equihbrium constants for exchange between the various hydrogen molecular species have been documented (18). Kinetics of the radiation-induced exchange reactions of hydrogen, deuterium, and tritium have been critically and authoritatively reviewed (31). The reaction T2 + H2 — 2HT equiUbrates at room temperature even without a catalyst (30). 

A number of studies of the acid-catalyzed mechanism of enolization have been done. The case of cyclohexanone is illustrative. The reaction is catalyzed by various carboxylic acids and substituted ammonium ions. The effectiveness of these proton donors as catalysts correlates with their pK values. When plotted according to the Bronsted catalysis law (Section 4.8), the value of the slope a is 0.74. When deuterium or tritium is introduced in the a position, there is a marked decrease in the rate of acid-catalyzed enolization h/ d 5. This kinetic isotope effect indicates that the C—H bond cleavage is part of the rate-determining step. The generally accepted mechanism for acid-catalyzed enolization pictures the rate-determining step as deprotonation of the protonated ketone ... 

Another example of this preference is found in the enantiospecific syntheses of tritium-labeled leukotrienes(/i). Commercially available 3-nonyn-l-ol was converted to its phosphorane (16) and Wittig-coupled with the unsaturated aldehyde (17) to afford 18, which was reduced over Lindlar catalyst to give 19. 

Table IV presents the results of the determination of polyethylene radioactivity after the decomposition of the active bonds in one-component catalysts by methanol, labeled in different positions. In the case of TiCU (169) and the catalyst Cr -CjHsU/SiCU (8, 140) in the initial state the insertion of tritium of the alcohol hydroxyl group into the polymer corresponds to the expected polarization of the metal-carbon bond determined by the difference in electronegativity of these elements. The decomposition of active bonds in this case seems to follow the scheme (25) (see Section V). But in the case of the chromium oxide catalyst and the catalyst obtained by hydrogen reduction of the supported chromium ir-allyl complexes (ir-allyl ligands being removed from the active center) (140) C14 of the...

Comyns et al.516 first observed the rate enhancement by Lewis acid catalysts in hydrogen exchange in the tritiation of toluene by tritium chloride. Second-order rate coefficients were given approximately by... 

SO the Sgl mechanism and not the usual arenium ion mechanism is operating. Aromatic rings can also be deuterated by treatment with D2O and a rhodium(III) chloride or platinum catalyst or with CeDs and an alkylaluminum dichloride catalyst," though rearrangements may take place during the latter procedure. Tritium ( H, abbreviated T) can be introduced by treatment with T2O and an alkylaluminum dichloride catalyst. " Tritiation at specific sites (e.g., >90% para in... 

Neither tritium or deuterium gas, with zero dipole moments, can be expected to interact positively with microwave radiation. Their low solubilities are seen as a further disadvantage. Our thoughts therefore turned towards an alternative procedure, of using solid tritium donors and the one that has found most favor with us is formate, usually as the potassium, sodium or ammonium salt. Catalytic hydrogen transfer of this kind is remarkably efficient as the results for a-methylcinnamic acid show [50]. The thermal reaction, when performed at a temperature of 50 °C, takes over 2 h to come to equilibrium whereas the microwave-enhanced reaction is complete within 5 min. A further advantage is that more sterically hindered al-kenes such as a-phenylcinnamic acid which are reduced with extreme difficulty when using H2 gas and Wilkinson s catalyst are easily reduced under microwave-enhanced conditions. 

Several versions of this reaction have been used for separating deuterium and tritium the G-S version operates in the liquid phase, without a catalyst, at two temperatures. Used at the Savannah River plant of the U.S. Atomic Energy Commission and at several Canadian plants. 

The tritium labelled V.fischeri AHL 31 was prepared with a specific activity of 45-55 Ci/mmol by the tritiation of the corresponding unsaturated precursor, AT-(3-oxo-4-hexenoyl)-L-HSL 30 in the presence of a homogeneous Wilkinson s catalyst, tris(triphenylphosphine)rhodium[I] chloride (Scheme 13) [71]. 

Deuterioammonia, 188, 190 Deuteriobor ation, 191 Deuteriobromic acid, 214 Deuteriodiborane, 191 Deuterio-Raney nickel, 215 Deuterium gas and a surface catalyst, 199 Deuterium and tritium gas, 179 3,17/8-Diacetoxyestra-3,5-diene, 486 3,20-Diacetoxypregna-3,5,20-triene, 411 (20S)-2/3,3j3-Diacetoxy-5a-pregn-7-en-6 one-20-carboxylic acid methylester, 301 Diborane, 89, 100... 

Tracer studies have been used in an attempt to determine the nature of the ends of the chain but these were as unsatisfactory as for propylene. Feldman and Perry (83) used triterated methanol to react the polyethylene from a titanium tetrachloridetrialkylaluminum catalyst. They found a continual increase in the number of polymeric chain ends which react with the tritium. This agrees with the results of Roha and Beears (84) who showed the very rapid exchange of alkyls which took place when ethylene was grown on a Ziegler catalyst in the presence of excess alkylaluminum chloride. In these experiments only an extremely small... 

In the 18 years since its discovery, Wilkinson s catalyst has been used to hydrogenate all kinds of unsaturated compounds and great efforts have been made to develop other phosphorus ligand-containing catalysts of both rhodium and other metals. This in turn has led to catalytically active complexes which do not contain phosphorus. In Table 1 the hydrogenation of various unsaturated compounds catalysed by [RhCl(PPh3)3] is summarized. In some cases the addition of deuterium and tritium to the substrate was investigated.84,95,101,102... 

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