5n reactions

Contemporaneously with the Berkeley experiments, Zvara et al. (1969, 1970), working at Dubna, produced 3.2 + 0.8 s 259104 by the Pu/ Ne, 5n) reaction. The chloride of this spontaneously fissioning activity was shown using gas chromatography to be slightly less volatile than Hf, but more volatile than the actinides. An international group of reviewers (Barber et al., 1992) has determined that the Berkeley and Dubna groups should share the credit for the discovery of element... 

In a related study, MP2(full)/6-31+G //HF/6-31+G calculations of the 5n reaction between methyl fluoride and the free isothiocyanate ion or the lithium isothiocyanate ion pair108 indicate that the free-ion reaction occurs at the sulfur atom via a normal Sn2 mechanism with inversion of configuration. In the ion-pair reaction, sulfur is again the nucleophilic atom and the reaction occurs with an inversion of configuration but via a six-membered ring transition structure (23). As one might expect, the ion-pair reaction in the gas phase is faster than the free ion gas-phase reaction. 

In the Rf experiments [35] performed at the PSI Philips Cyclotron, 261Rf was produced in the Cm O, 5n) reaction at 100 MeV. The target contained 10% Gd enriched in 152 Gd to produce simultaneously short-lived Hf isotopes that were used to monitor the behavior of Hf and to perform yield checks by Y spectroscopy. Rf and Hf were transported by a He(KCl) gas jet and were collected for 90s by impaction inside ARCA II [7]. The deposit was dissolved in 200 pL 0.1 M HNO3/X M HF (x variable) and was fed onto the 1.6x8 mm cation-exchange column at a flow rate of 1 mL min 1. The effluent was evaporated to dryness as sample 1. In order to elute remaining Rf and Hf from the column, a second fraction of 200 pL 0.1 M HNO3/O.I M HF was collected to strip all group-4 elements from the column. The fraction was prepared as sample 2. 

Studies of the dubnium behavior. 930 experiments were conducted with 262Db produced at the Berkeley 88-Inch Cyclotron in the 249Bk(lsO,5n) reaction. Extractions were performed in the Aliquat336/Cl - HC1 system with a 50 s cyclic collection time of the KC1 aerosol on a Kel-F slider in ARCA II. The reaction products were fed onto the column in 10 M HC1 followed by the elution of a Ta fraction in 6 M HC1 and a Nb,Pa fraction in 6 M HNO3/O.OI5 M HF. The effluents were continuously sprayed through a 60 pm nozzle onto hot Ta discs on which they were evaporated to dryness by hot He gas and infrared light. Start of measurement of the activities was 60 s (Ta fraction) and 76 s (Nb, Pa fraction) after the end of collection, respectively. 

If 50 MeV protons arc available, the (p, 5n) reaction with is the most favourable, because iodine has only one stable nuclide. However, measurable amounts of Xe are produced by the (p, 3n) reaction. The volatile products formed by irradiation of h, Lil, Nal, KI or CH2I2 arc transferred by He. In a first trap, cooled to -ITC, directly formed iodine and iodine compounds arc separated and in a second trap, cooled to -196°C, Xc and Xe are collected. The second trap is taken off and after about 5 h the iodine formed by decay of - Xe is dissolved in dilute NaOH. During this time - Xe has largely decayed, but Xe (t]/2 = 16.9 h) only to some extent. The yields are of the order of 100 to 500 MBq per pAh, and the relative activity of I is of the order of 0.1%. 

AUyl compounds are highly reactive towards nucleophiles and examples of dissociative (5 1) and associative (5 2) reactions, and nucleophilic substitution with rearrangement are well documented . Differentiation between these mechanisms when azide ion is the nucleophile is cften extremely difficult due to the possibility of rearrangement of the allylic azide resulting from substitution, and for this reason the relative nucleophilic strength of azide ion in allylic 5n reactions has not been delineated. 

A full study of some 5n reactions of alkyl halides to give other halides, nitriles, ethers, etc. under triphase catalysis conditions i.e. organic and aqueous liquid phases with a heterogeneous phase-transfer catalyst) has appeared. 

Applications to Phase-transfer Methods.—Dehmlow has published a review on advances in phase-transfer catalysis (PTC) which discusses the introduction of crown ethers into this area. The full details are now available of a study of alkyl-substituted azamacrobicyclic polyethers (78a) as PT catalysts. When the alkyl chains are C14—C20, such molecules are very efficient catalysts in both liquid-liquid and solid-liquid phase-transfer modes, which contrasts with the lower catalytic ability of the less organophilic unsubstituted cryptand (78b). Crown ethers immobilized on polymeric supports have been demonstrated to possess increased PTC activity in 5n reactions, up to that of the non-immobilized systems, when the connection to the polymer involves long spacer chains [e.g. (79)]. 

The discovery of Hs was reported in 1984 (Miinzenherg et al. 1984) with the identification of 265hs a half-life of 1.5 ms. In 1996, Hs with a half-life of about 10 s was observed in the a-decay chain of 112 (Hofmann et al. 1996). Its direct production should be possible in the Cm( Mg,5n) reaction with a cross section of a few picobarns. 

For meitnerium, element 109, the isotope Mt to be produced in the U( Cl,5n) or Cm( Al,5n) reactions is anticipated to have a half-life on the order of a second and should, thus, be suitable for chemical studies with one of the fastest separation techniques,for example, with SISAK. 

These and other studies and reanalysis of data for Sg decay products of Hs alpha-decay by Diillmann and Tiirler (2008) have shown that the originally reported 21s Sg (Tiirler et al. 1998) was in error and was actually due to Sg, which has two isomeric states with half-lives of 8.9 s and 16.2 s, respectively. The good news is that the 8.9 s Sg isomer is produced preferentially via the Cm( Ne,5n) reaction with an estimated cross section of a few hundred picobarns Now it should be quite feasible to perform more in-depth detailed studies of the chemistry of Sg, such as stability of its oxidation states both in solution and in gas-phase studies and complex formation under a variety of conditions. 

The chemistry of rutherfordium has been shown to be similar to the chemistry of hafnium rather than the chemistry of the heavier actinides, a clear demonstration of the expected end of the actinide series at lawrencium. This demonstration involved both aqueous and gas-phase chemistry. In the gas-phase experiments by Zvara etal. (1972a,b) the 3-s isotope produced in the " Pu ( Ne, 5n) reaction was used. Zvara and co-workers attempted to use thermochromatography to show a difference in volatility of RfC which seemed to condense at 220°C as compared to the chlorides of the heavier actinides which have much higher condensation temperatures. 

The ring opening of thiiranes with an emphasis on the regiospecificity of the ringopening reaction with different nucleophiles and on the effect of such nucleophiles on the 5n reactions, alkene formation, and polymerization reactions, has been reviewed. 

The tetrakis-sulphoxides (67) have been reported as a new type of PT catalyst in a solid-liquid mode, for example in 5n reactions of 1-bromo-octane. Nucleophilic substitutions of 1-bromo-octane and benzyl bromide are again the test reactions in a report on the use of the sucrose-ethylene oxide adducts (68a) as PT catalysts in both solid-liquid and liquid-liquid modes. The methacrylate ester derivative (68b) has been polymerized to a cross-linked gel that acts in a TC capacity for the same reactions. In a related approach some modified dextran anion exchangers carrying lipophilic substituents, such as the modified hydroxypropylated dextran gel shown in (69), have been synthesized and shown to catalyse displacement reactions including the alkyl bromide to iodide transformation under TC conditions. ... 

Pu( Ne,4n) [139, 143], Cm( 0,4n) [144, 145], and " Bk( N,4n) [145-148]. The a-emitting isotopes Rf Ty2 — 4.7 s) and Rf Ty2 = 2.8 s) were produced in Berkeley in 1969 in irradiations of " Cf targets with and ions, employing the technique of gas-jet transport to the periphery of a stepped wheel [144, 149] (see Sect. 3.3 and Experimental Techniques for more technical details). Though disputed at the time [150, 151], the results have stood up [152, 153]. The 9% SF branch in the decay of Rf is the likely source of the detected fission events in the earlier Russian chemistry experiments. The SF activities Rf Th2 =13 ms) [144] and Rf Ty2 — 8 ms) [145] were observed in these same reactions, using the spinning-drum or tape-transport methods (see Sect. 3.3). A mainstay of subsequent chemical studies (see Liquid-Phase Chemistry of Superheavy Elements and Gas-Phase Chemistry of Superheavy Elements ), 68-s a-emitting is produced in the Cm( 0,5n) reaction with a cross... 

Bk( 0,5n) reactions, respectively, with corresponding cross sections of 5 nb and 6 nb [168-171]. The " Cm( F,5n) reaction has also been used to produce Db [170] and the Cf( N,4n) reaction has been used to produce Db [168]. The SF decay branch of the isotope Db (Ti/a = 27 s) was first observed in the products of the " Bk( 0,4n) reaction with a cross section of 6 nb [168], and was positively identified in subsequent radiochemical experiments [161]. Until recently, chemistry experiments were usually performed with Db (see Liquid-Phase Chemistry of Superheavy Elements and Gas-Phase Chemistry of Superheavy Elements ). 

Decay by emission of a particles (with ANIAZ — 1) is a proton-rich process, and in the known transactinides results in daughter nuclei that lie closer to the line of /i stability than do their parents. The decays of the superheavy cold-fusion nuclei lead to long chains of sequential a emissions and a progressive increase in neutron richness in the lower members of the chain. In this way, cold fusion can be used to produce isotopes that rival the neutron richness of those produced in hot-fusion reactions. This has been referred to as overshooting [22, 47]. For example, 10-s Hs can be produced directly in the Cm( Mg,5n) reaction with a cross section of 7 pb [179, 180]. The most neutron-rich isotope of hassium that can be produced directly by cold fusion is Hs, in the Pb( Fe,n) reaction [241-243]. However, Hs is also the third member of the Cn decay chain. 

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