Sodium complexes solvent-separated

For instance, (kH/kD)a was 1.085 0.011 when the sodium thiophenoxide concentration was 0.0086 mol dm-3 and 1.129 0.010 when the concentration of the sodium thiophenoxide was reduced to 0.0040 mol dm-3 in DMF at 20°C. Conductivity and UV studies of sodium thiophenoxide solutions in DMF, in DMSO, in methanol and in diglyme, and reactions done in the presence of the macrocyclic polyether 15-crown-5 (Westaway and Lai, 1988), showed that the change in the secondary a-deuterium KIE was due to a change in the form of the reacting nucleophile from a solvent-separated ion-pair complex at the higher concentration (see (27)) to a free ion at the lower concentration. 

The nucleophile in the S.v2 reactions between benzyldimethylphenylammonium nitrate and sodium para-substituted thiophenoxides in methanol at 20 °C (equation 42) can exist as a free thiophenoxide ion or as a solvent-separated ion-pair complex (equation 43)62,63. The secondary alpha deuterium and primary leaving group nitrogen kinetic isotope effects for these Sjv2 reactions were determined to learn how a substituent on the nucleophile affects the structure of the S.v2 transition state for the free ion and ion-pair reactions64. 

If the proposed structure was true, then a solvent of higher solvating power, such as dme, should decrease the stability of the intramolecular complex. Using sodium as the counterion part of the active centres should exist in the form of externally solvated contact ion pairs or even solvent-separated ion pairs. With caesium as the counterion there should be little change, because this cation is only poorly solvated by both solvents and consequently the possibility of solvent-separated ion pairs to be found should be extremely small. 

This change is a result of a change in the state of the reacting anion from free thiophenoxide to a solvent-separated sodium thiophenoxide ion-pair complex. 

The above explanation has been corroborated by further studies of a-deuterium K.I.E. in the same reaction carried out in DMSO, DMF and methanol. In all three solvents a smaller isotope effect and a tighter transition state have been found for the reaction with the ion-pair complex569. It has been suggested that the solvent-separated ion pair exists as a complex consisting of several solvent-separated sodium thiophenoxide ion pairs. 

A review on TLC of rf-block elements and their connteranions discnsses types of stationary phases, mobile phases, development modes and detection and qnantitative determination techniqnes . The colored complexes Ni(ttfac)2, Co(ttfac)2, Mn(ttfac)2, Cn(ttfac)2, Fe(ttfac)3, Ce(ttfac)4, Th(ttfac)4 and U(ttfac)6 were prepared by adding a solntion of l-thenoyl-3,3,3-triflnoroacetone (ttfacH) to a solntion of the metal salts bronght to pH 7.5 with sodium acetate buffer. The complexes were separated on silica gel G TLC plates. Best results were obtained with the solvent systems butanone-xylene, acetone-cyclohexane and 4-methyl-2-pentanone-xylene . ... 

The soiution is aliowed to cool and the crystals of the P2P-bisulfite addition compound are then separated by vacuum filtration, washed with a little clean dH20 then washed with a couple hundred mLs of ether, DCM or benzene. The filter cake of MD-P2P-bisulfate is processed by scraping the crystals into a flask and then 300mL of either 20% sodium carbonate solution or 10% HCi soiution are added (HCI works best). The soiution is stirred for another 30 minutes during which time the MD-P2P-bisulfite complex will be busted up and the P2P will return to its happy oil form. The P2P is then taken up with ether, dried and removed of the solvent to give pure MD-P2P. Whaddya think of that ... 

Baker et al, have obtained some kinetic data on the exchange reactions between the 1,10-phenanthroline, 2,2 -dipyridine and 2,2, 2"-tripyridine complexes of Co(III) and Co(ll) in both H2O and D2O solution. The isotopic method ( Co) and separations involving either extraction of Co(II) with organic solvents (n-hexanol-ether or saturated sodium acetate in n-hexanol) or precipitation of Co(III) as Co(phen)3(l3)3 were used. For the 1,10-phenanthroline system, a rate law... 

The collection behaviour of chromium species was examined as follows. Seawater (400 ml) spiked with 10-8 M Crm, CrVI, and Crm organic complexes labelled with 51Cr was adjusted to the desired pH by hydrochloric acid or sodium hydroxide. An appropriate amount of hydrated iron (III) or bismuth oxide was added the oxide precipitates were prepared separately and washed thoroughly with distilled water before use [200]. After about 24 h, the samples were filtered on 0.4 pm nucleopore filters. The separated precipitates were dissolved with hydrochloric acid, and the solutions thus obtained were used for /-activity measurements. In the examination of solvent extraction, chromium was measured by using 51Cr, while iron and bismuth were measured by electrothermal atomic absorption spectrometry. The decomposition of organic complexes and other procedures were also examined by electrothermal atomic absorption spectrometry. 

Among the most important indirect methods of analysis which employ redox reactions are the bromination procedures for the determination of aromatic amines, phenols, and other compounds which undergo stoichiometric bromine substitution or addition. Bromine may be liberated quantitatively by the acidification of a bromate-bromide solution mixed with the sample. The excess, unreacted bromine can then be determined by reaction with iodide ions to liberate iodine, followed by titration of the iodine with sodium thiosulphate. An interesting extension of the bromination method employs 8-hydroxyquinoline (oxine) to effect a separation of a metal by solvent extraction or precipitation. The metal-oxine complex can then be determined by bromine substitution. 

Barker and coworkers have applied gel chromatography in studies of pneumococcal polysaccharides.121 Purification of the type-specific polysaccharide of Pneumococcus Type II was effected by chromatography on Sephadex G-200 in M sodium chloride in this way, the ribonucleic acid, a persistent impurity in preparations of this polysaccharide, was almost completely removed. The complex formed between the polysaccharide and the nucleic acid is largely dissociated in M sodium chloride, so that the two are free in this solvent and may be separated on the basis of their differing molecular size. 

Solvent or ligand Interactions with tight Ion pairs produce externally complexed tight Ion pairs and/or ligand separated Ion pairs. The stability of the complexes depends on solvent, temperature, type of crown and the nature of the cation. For example, In ethereal solvents benzo-15-crown-5 and fluorenyl sodium (Fl-.Na ) form the two Isomeric complexes I and II depicted In reaction 1, but the ratio I/II Is highly solvent sensitive (9) (If the bound solvent In II Is Included In the structure of II, the two complexes of course can actually not be considered Isomeric). 

Virtually quantitative conversions were observed in the hydroformylation of 1-tetradecene with rhodium complexes generated from the lithium salt of tppms or the lithium (sodium) salts of 21 (Table 2 R=Ph n=3,4) and 22 (Table 2) in methanol as solvent.127,334 Catalyst recycling involved evaporation of methanol and addition of water to form a two phase system, separation of the aqueous phase, evaporation to dryness and addition of MeOH. 

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