Protonated 1.2-ethanediol

Since double bonds may be considered as masked carbonyl, carboxyl or hydroxymethylene groups, depending on whether oxidative or reductive methods are applied after cleavage of the double bond, the addition products from (E)-2 and carbonyl compounds can be further transformed into a variety of chiral compounds. Thus, performing a second bromine/lithium exchange on compound 4, and subsequent protonation, afforded the olefin 5. Ozonolysis followed by reduction with lithium aluminum hydride gave (S)-l-phenyl-l,2-ethanediol in >98% ee. 

Kemkes256 assumes that the overall order relative to the esterification of terephthalic acid by 1,2-ethanediol in oligo(l,2-ethanediyl terephthalate) is two no mechanism has however been suggested. Mares257 considers that during the esterification of terephthalic acid with 1,2-ethanediol, two parallel kinetic paths take place, one corresponding to a reaction catalyzed by non-dissociated add and the other to a non-catalyzed process. In fact, Mares257 is reserved about the existence of protonic catalysis. Some other orders were found for the system terephthalic atid/l,2-ethanediol 0 (overall)318 2 (add) andO (alcohol)203 1 (add) and 1 (alcohol)181 1 (add)194 . These contradictory results could be partly due to the low solubility of terephthalic acid in 1,2-ethanediol. 

Perhaps the most important parameter involved in aqueous-organic mixtures is their effective protonic activity (denoted by pH or pan). This parameter has been measured for most commonly used buffers in all selected mixtures down to their freezing point (Hui Bon Hoa and Douzou, 1975 Douzou ei al., 1976). Values of pH depend on solvent and temperature in a way that varies for different buffers, but with the data available a medium of known pH under any desired condition may be prepared. An example of the effect of solvent and temperature is provided by Tris-HCl buffer a solution of this at pH 8.0 in water at 20 C will be pH 10.5 in 50% (v/v) ethanediol at -40 C (Douzou et al, 1976). On the other hand, neutral buffers such as phosphate undergo... 

Monoalkyl ethers of (R,R) 1,2-bis[3,5-bis(trifluoromethyl)phenyl]ethanediol, 24, have been examined for the enantioselective protonation of silyl enol ethers and ketene disilyl acetals in the presence of SnCU (Scheme 12.21) [25]. The corresponding ketones and carboxylic acids have been isolated in quantitative yield. High enantioselectivities have been observed for the protonation of trimethylsilyl enol ethers derived from aromatic ketones and ketene bis(trimethylsilyl)acetals derived from 2-arylalkanoic acids. 

According to protonation thermochemistry of simple a,(0-diols (1,2-ethanediol, 1,3-propanediol, 1,4-butanediol), the diols show enhanced proton affinities in the gas phase compared with primary alcohols attributed to the formation of a strong intramolecular hydrogen bond.59 60... 

Monoethers of diols are at the borderline between mono-ols and diols. Both enantiomers of 1-phenyl-1.2-ethanediol are commercially available. The isomeric monoethers 8 and 9 are obtained from mandelic acid by the reaction sequences shown14, and have been applied as auxiliaries in chiral dienophiles (Section D. 1.6.1.1.1.1.2.) and for enantioselective protonation (Section C.). 

The complex [Cp2U N(C2H5)2 2] reacts with ligands that have protons of more acidic nature than that of diethylamine [244], like toluene-3,4-dithiol, 0-mercaptophenol, catechol, and 1,2-ethanediol (Eq. 46) ... 

These reactions require removal of a proton from -OH or H2O, respectively, so the reaction is promoted by increasing pH consequently, the surface area of the gel rises over the pH range from 4 to 6. Organic molecules, such as glycerol or ethanediol, inhibit the reaction by adsorbing on the hydroxyls. Conversion to bayerite is inhibited in dioxane, not because of adsorption, but because transfer of the proton is prevented by the aprotic solvent [45]. 

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