Anions solutes

The original SBR process is carried out at. 50° C and is referred to as hot polymerization. It accounts for only about 5% of aU the mbber produced today. The dominant cold polymerization technology today employs more active initiators to effect polymerization at about 5°C. It accounts for about 85% of the products manufactured. Typical emulsion polymerization processes incorporate about 75% butadiene. The initiators are based on persulfate in conjunction with mercaptans (197), or organic hydroperoxide in conjunction with ferrous ion (198). The rest of SBR is produced by anionic solution polymerization. The density of unvulcanized SBR is 0.933 (199). The T ranges from —59" C to —64 C (199). 

The Anionic Solution Polymerization of Butadiene in a Stirred-Tank Reactor... 

Reaction Mechanism. The reaction mechanism of the anionic-solution polymerization of styrene monomer using n-butyllithium initiator has been the subject of considerable experimental and theoretical investigation (1-8). The polymerization process occurs as the alkyllithium attacks monomeric styrene to initiate active species, which, in turn, grow by a stepwise propagation reaction. This polymerization reaction is characterized by the production of straight chain active polymer molecules ("living" polymer) without termination, branching, or transfer reactions. 

A number of synthetic procedures are available (Ai2). (2) For precisely defined stoichiometries, the isobaric, two-bulb method of Herold is preferred H5, H6, H2). (2) To generate compounds suitable for organic synthesis work, graphite and alkali metal may be directly combined, and heated under inert gas (Pl, lA). (5) Electrolysis of fused melts has been reported to be effective iN2). 4) Although alkali metal -amine solutions will react with graphite, solvent molecules co-inter-calate with the alkali metal. Utilization of alkali metal-aromatic radical anion solutions suffers the same problem. 

A hydrophobidty scale based on the migration index from emulsion electrokinetic chromatography of anionic solutes. Anal. Chem. 1996, 68, 1028-1032. 

Consider an anion solution of unknown concentration C0 with volume V0. An appropriate ISE together with a reference electrode is introduced and the emf of the cell measured. Next, a series of additions of a standard solution with concentration C and volume V are made, and after each incremental addition the emf is measured. 

HYDROXYETHYL CELLULOSE ADSORPTION BEHAVIOR IN MULTIVALENT ANION SOLUTIONS... 

The objectives of each theoretical approach are not only the explanation of the experimental results or failures of practice but also the prediction of new possibilities to increase the sensitivity, separation capacity and velocity of the chromatographic procedure under investigation. Numerous theoretical reviews deal with the problems of the CE separation technique. In recent years the methods to enhance the precision in CE by the modification of operational parameters [113], the theory and methodological improvements of sample stacking of cationic and anionic solutes in CE [114-116], and the results and difficulties of the application of conductivity detection in CE technologies [117] have been reviewed. 

Cation derived from a strong base Reaction with water neither ion Solution neutral Examples NaCl, K2SO4, Ca(N03)2 Reaction with water only the anion Solution basic Examples NaCHsCOO, KF, Mg(HS04)2... 

The separation mechanism is based on stereoselective ion-pair formation of oppositely charged cationic selector and anionic solutes, which leads to a difference of net migration velocities of the both enantiomers in the electric field. Thus, the basic cinchona alkaloid derivative is added as chiral counterion to the BGE. Under the chosen acidic conditions of the BGE, the positively charged counterion associates with the acidic chiral analytes usually with 1 1 stoichiometry to form electrically neutral ion-pairs, which do not show self-electrophoretic mobility but... 

The jacketed addition funnel is removed and 1.5 g of cuprous bromide-dimethyl sulfide complex (Note 7) is added through a powder funnel. A 500-mL, pressure-equalizing addition funnel (long-tipped) is attached to the flask and flushed with argon. As the anion solution is cooled in a dry ice-isopropyl alcohol bath, a solution of 530 g (2.08 mol) of sublimed iodine in 500 mL of anhydrous tetrahydrofuran is placed in the addition funnel. This solution is added dropwise to the cooled slurry over approximately 90 min (Note 8). The solution is stirred for about 15 min at low temperature. 

The CMC of this new surfactant is several orders of magnitude lower than the CMC of its parent species. Figure 15 indicates a typical CMC plot versus the composition of the anionic-cationic (e.g., dodecyl sulfate-tetradecyl trimethyl ammomnium chloride) mixture in water. It can be seen that the CMCs of the anionic and cationic species are quite high, e.g., around 0.1 wt. %. As soon as a very small percentage of cationic is added to an anionic solution, the CMC falls several orders of magnitude. The same happens when a very small amount of anionic is added to a cationic solution. In both cases it seems that an equimolar catanionic species forms, and that its very low CMC dominates the mixing rule [84]. 

Thus, starting from the (—)-(S )-a-(methoxymethyl)benzeneethanaminc derived imines at low temperatures, (S )-2-methylcycloalkanones are obtained via the -azaenolates, whereas (R)-configurated products are obtained via the thermodynamically more stable Z-azaenolates by refluxing the anion solutions prior to alkylation. However, a high degree of enantiomeric excess is obtained only under thermodynamic conditions, presumably due to different selectives in the alkylation step (see Table 3). Variation of the base (/ert-butyllithium, lithium diethylamide, lithium 2,2,6,6-tetramethylpiperidide) and additives (hexamethylphosphoric triamide) did not improve the EjZ ratio (enantiomeric excess) significantly9. 

An oven-dried. 50-mL, 3-necked flask equipped wilh a pressure-equalizing dropping funnel, reflux condenser, nitrogen inlet, magnetic stirrer, and vacuum takeoff adapter is evacuated (vacuum pump) and refilled three times with nitrogen. 10 mL of THF and 0.735 mL (5.25 mmol) of diisopropylamine are then added via a double-ended needle. The solution is cooled to 0"C and 2.2 mL of a 2.4 M solution of butyllithium (5.25 mmol) in hexane are added. The lithium diisopropylamide is allowed to form at 0 °C for 15 min and is then cooled to — 20 C. 5 mmol of the chiral acyclic ketone iminc in 5 mL of THF are added (5 min) and anion formation allowed to continue for 1 h at 20 C. The anion solution is then heated to reflux for 2 h and cooled to —78 C. A solution of 5.25 mmol of the iodoalkane in 5 mL of THF is then added, and alkylation is allowed to proceed at — 78 °C for 1 h. Workup and hydrolysis, as described for the cyclic ketones (see Section 1.1.1.4.1.2.L), yields the a-alkylatcd acyclic ketones (see Table 4). 

On the other hand, alkylation of 2-chloromethyl-4,5-dihydrooxazolcs furnishes 2-chloro-alkanoic acids in good chemical yields but in low enantiomeric excess. Attempted alkylation of the deep red anion solution at —98 to —40 C resulted in little or no alkylation. Alkylation at 20 °C occurred in 80 -90 % yield, however, the products were nearly racemic. Alkylation in the presence of 2 equivalents of hexamethylphosphoric triamide proceeds at 78 C in 85-94% yield, however, enantiomeric excesses were low in comparison to alkylations of the corresponding 2-alkyl-substituted 4,5-dihydrooxazoles7. 

Metalation of 4,5-dihydro-3-phenylisoxazole occurs at position 4. Upon warming the anion solution to 25 °C, ring opening13 to the a,/i-unsaturated oximes 1 occurs, however, alkylation at — 78°C or below provides 4-substituted 4,5-dihydro-3-phenylisoxazoles 215. 

In the case of 4,5-dihydroisoxazoles substituted with anion stabilizing groups in position 5 or 5a, ring opening and fragmentation occurs2-3,29 upon warming the anion solution. 

Due to the low solubility of the concave pyridines 3 in diethyl ether, the corresponding pyridine buffers could not be compared with the experiments of Table 4. But when the protonations were carried out in other solvents, no influences of the acids (including the acids of Table 4) on the regioselectivity could be found. The exchange of diethyl ether by other solvents caused a color change of the allyl anion solution which indicated different structures for the anions in diethyl ether and in other, more polar solvents [44],... 

Inverse oxidation the anionic solution Is deactivated by adding It dropwlse Into a solution of THF cooled to -50eC and saturated with oxygen. 

Anionic solutes X- can be solvent extracted from aqueous solution into organic phases containing trialkylammonium (R3NH+) or similar cations ... 

Chelated Metal Ion-Solute. If the metal is first chelated with a relatively hydrophobic chelating agent, solute interactions will increase retention. Cooke et al C25) have developed such a technique using 4-dode-cyldiethylenetriamine and Zn(ll). Not only does this chelated metal greatly increase retention for certain anionic solutes, presumably by an ion pairing interaction, but the relatively rigid conformation of the metal chelate imparts marked selectivities. 

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