Diethanolamines

The formation of the diethanolamine complexes can be thought of as a three-step process, with the reaction of an alcoholic function to initially form an alkoxo complex. At this stage, there will be little perturbation of the electronic environment around the vanadium nucleus. As described previously, electron density at vanadium 

FIGURE 9.5 The formation constants (V04H2 + H2L V02L ) for various diethanolamine vanadate complexes are shown as a function of the pKj of the ligand. The solid line is provided as a guide and has no theoretical significance. The values are for 0.40 M KC1 solutions at room temperature and are taken from the work of Crans and Boukhobza [21]. 

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Here the ethylene oxide undergoes parallel reactions, whereas the monoethanolamine undergoes a series reaction to diethanolamine and triethanolamine. 

Two principal secondary reactions occur, to diethanolamine and triethanolamine ... 

Cmea = molar concentration of monoethanolamine Cdea = molar concentration of diethanolamine... 

An excess of ammonia in the reactor decreases the concentrations of monoetha-nolamine, diethanolamine, and ethylene oxide and decreases the rates of reaction for both secondary reactions. 

The use of an excess of ammonia is home out in practice. A mole ratio of ammonia to ethylene oxide of 10 1 3delds 75 percent monoethanolamine, 21 percent diethanolamine, and 4 percent triethanolamine. Using equimolar proportions under the same reaction conditions, the respective proportions become 12, 23, and 65 percent. 

In cases where Noyori s reagent (see p. 102f.) and other enantioselective reducing agents are not successful, (+)- or (—)-chlorodiisopinocampheylborane (Ipc BCl) may help. This reagent reduces prochiral aryl and tert-alkyl ketones with exceptionally high enantiomeric excesses (J. Chandrasekharan, 1985 H.C. Brown, 1986). The initially formed boron moiety is usually removed hy precipitation with diethanolamine. Ipc2BCl has, for example, been applied to synthesize polymer-supported chiral epoxides with 90% e.e. from Merrifield resins (T. Antonsson, 1989). 

COMPOSITEMATERIALS - POLYTffiR-MATRM - THERMOSETS] (Vol 7) -diethanolamine surfactant [SURFACTANTS] (Vol 23)... 

Solvents used for hydrogen sulfide absorption include aqueous solutions of ethanolamine (monoethano1 amine, MEA), diethanolamine (DEA), and diisopropanolarnine (DIPA) among others ... 

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