Anions alcohols

As discussed in Section 11.15.4 on thermodynamic aspects, dinitrotetrazolo[l,5- ]pyridines 11 are electrophiles and can react with nucleophilic species in addition reactions as shown in Scheme 18 <1994IZV1278, 2003OBC2764>. In the presence of alcohols on addition of the alcoholate anion in position 5 of tetrazolo[l,5-tf]pyridine takes place. The primary addition product 12 formed in an equilibrium was characterized by its H NMR spectrum and can be isolated in the form of potassium salts 62 in good to high yields 53-96% <1994IZV1278>. 

Dunn has also proposed a mechanism involving this charge relay system in ternary complex formation, but with the substrate displacing the zinc-bound water, as shown in Scheme 9.1443 Hydride transfer from NADH, to form an alcoholate anion, has been shown to occur before protonation.1398 As well as not requiring penta-coordinate zinc, this mechanism differs from Dworschack and Plapp s in postulating the formation of an alcoholate anion. 

This mechanism, accounting for the observed pH perturbations, does not directly consider the proton charge relay system involving Ser-48 and His-51. However it is probable that this system is important in facilitating, by charge distribution, formation of the alcoholate anion and hydride transfer to NAD+, and in the reverse reaction, neutralization of the alcoholate anion and alcohol dissociation. 

In homogeneous, aqueous solution, alkali metal hydroxides react with carbohydrates to produce negatively charged carbohydrate species. Although the general feeling among chemists is that these species are free alcoholate anions, the possibility that they are composed, at least partially, of carbohydrate-hydroxide ion adducts cannot be dismissed. 

Alkali metal complexes may be analyzed for their metal content by simple acidimetric titration. Analysis for adduct (hydroxide) content is more involved, and entails the assumption that there can be no water of hydration attached to an alcoholate anion. The method involves first, dissolving the complex in anhydrous methanol, and then, treating the resulting solution with an appropriate anhydrous add, such as tartaric acid. The acid serves to convert any hydroxide ion into water (reaction S),... 

A major point of contention is the ionization state of the bound alcohol Is it bound as the alcoholate anion7,22 or as the neutral alcohol The position of the proton cannot, of course, be located in the x-ray diffraction studies. Evidence in support of the alcoholate anion being bound comes from the pH dependence of the binding of substituted alcohols 23 The complexes of the holoen-zyme with various alcohols have the following pKa values trifluorethanol, 4.3 2,2-dichloroethanol, 4.5 2-chloroethanol, 5.4 ethanol, 6.4. These values are some 8 to 9 units below the values of the alcohols in solution. If they represent the ionization of the alcohols in the ternary complexes, then complexing to the enzyme has dramatically lowered the pK s. This does seem to have happened,... 

Loraine GA. Effects of alcohols, anionic and nonionic surfactants on the reduction of PCE and TCE by zero-valent iron. Water Res 2001 35 1453-1460. 

Free energy measurements show that cations are stabilized in alcohol-water mixtures. This is due to the better solvation of the ion because of the inductive effect of the alkyl group from the coordinated alcohol. Anions, on the other hand, are destabilized in alcoholic solutions, due to the same effect.(22)... 

The treatment of 4-chlorobutyronitrile, 3-chloropropyl phenyl sulfone, and other related compounds with a base affords 7-halocarbanions which are usually prone to undergo intramolecular substitution to produce substituted cyclopropanes. However, these carbanionic intermediates can be trapped with external electrophilic partners, such as aldehydes, to give alcoholate anions, which then cyclize to produce 2,3-disubstituted tetrahydrofurans in excellent yields (Scheme 78) <2002CEJ4234>. 

Like alcoholate anions, thiolate, ° dithiocarbamate, ° °° and 0-ethyl dithiocarbonate anions °° add easily in boiling ethanol or acetonitrile at C-2 of 1,3-dithiolium salts (Eq. 39). 

The adducts of the reaction of allyl alcohols with allenic sulfones are especially interesting as they allow the carbanion-accelerated Claisen rearrangement to take place. By deprotonation, or directly by addition of an allyl alcoholate anion, a system is generated, which rearranges much more easily than the uncharged system and with high diastereoselectivity (Scheme 62). 

Protection or reductive deoxygenation of alcohols and ketones. Ireland et al.2 have found that N,N,N, N -tetramethylphosphoroiiamidates (TMPDA derivatives) of alcohols and of ketone enolates are reduced in high yield by lithium-ethylamine. They are readily prepared by phosphorylation of alcoholate or enolate anions. The complete sequence is as follows. The alcoholate anion is simply prepared by treatment of an alcohol with a slight molar excess of n-butyllitliium. The enolate anions of saturated ketones are prepared by treatment with lithium diisopropylamide. In the case of a,/J-unsaturated ketones, lithium-ammonia reduction or conjugate organometallic addition is suitable. For phosphorylation of the Jnion a fivefold excess of N,N,N, N -tetramethyldiamidophosphorochloridate in 4 ] dimethoxyethane (or THF)-N,N,-N. N -tetramethylethylenediamine (TMEDA) is used. The reaction is complete after... 

Preparation of the hydroxypentanoic acid fragment was initiated by addition of the protected propargyl alcohol anion 109 to ethylene oxide. After silylation of the resulting alcohol, the ethoxy ethyl group was removed and the alkyne partially reduced to afford the (2)-alcohol 110 in 52% overall yield. Enantiospecific epoxidation of 110 under Sharpless s conditions and subsequent oxidation provided a 69% yield of diastereomerically pure epoxy acid 111. Treatment with trimethylaluminum gave almost exclusively the p-methyl acid, which was acylated to afford 112 (78%). 

These and related methods allowed us recently to reevaluate the structure of active centers in anionic polymerization of simple, unsubstituted lactones, 5-propiolac-tone. The rationale was put forward in terms of stereo -electronic factors to explain why g-propiolactone propagates on carboxylate and e-caprolactone on alcoholate anions. This is shown in scheme below ... 

In anionic polymerization, B-propiolactone initiated with potassium alcoholate, gives,in initiation,both alco-holate and carboxylate anions. Alcoholate ions in every next step convert partially into carboxylate whereas carboxylate reproduce themselves quantitatively. Thus, after a few steps only carboxylate anions are left (14). Related situation was observed in the polymerization of styrene oxide (15). Here, however, it is only due to the structure of the initiator used. Thus, when in the initiation step both secondary and primary alcoholate anions are formed, due to the low steric requirements, in the next step apparently only the attack on the least substituted carbon atom takes place and already in the second step exclusively secondary alcoholate anions are present. 

The active site of alcohol dehydrogenase contains two cysteine residues (Cys 48 and Cys 174) and a histidine residue (His 67), all of which are coordinated to a zinc ion (Figure 6.20a). After NAD+ binds to the active site, the substrate ethanol enters and binds to the Zn2+ as the alcoholate anion (Figure 6.20b). The electrostatic effect of Zn2+ stabilizes the transition state. As the intermediate... 

The complexing agents were acetylacetonate (acac) and alcoholate anions. The electrolyses were carried in ethereal solvents, employing tetraalkylammonium salts as supporting electrolytes. 

The SN-2 attack of the alcoholate anion take place preferentially at the a-carbon atom of the oxiranic ring (normal SN-2 attack), which is explained by the low steric hindrance of this atom and by the electron release effect of the methyl group, which increases the electron density at the carbon atom in the (3 position [2, 4, 5, 9-14, 17, 49-54]. An high electron density carbon atom is less susceptible to the attack of the anions. As an immediate consequence, the terminal hydroxyl groups are predominantly secondary, thus proving that this is a predominantly normal SN-2 attack [4, 74] ... 

Equation (4.13) is a more general equation of the PO anionic polymerisation of PO, where the propagation constant is a function of the hydroxyl group concentration and of the dissociation constant of the alcoholate anion. 

The potassium cation is retained, by complexation, at the same chain end, the alcohol -alcoholate equilibrium is perturbed, and EO reacts preferentially with this template structure and the resulting primary hydroxyl content decreases. In the case of bivalent cations with two positive charges, the alcoholate anion is linked more strongly by electrostatic forces and the coordination of the cation with the formed poly[EO] chains takes place to a much smaller extent. 

The PO polymerisation is reduced to the classical nucleophilic attack of the alcoholate anion on the a-carbon atom of the oxiranic ring, the counter ion being the big phosphazenium cation instead of the potassium cation ... 

The mechanism of alkylene oxide anionic polyaddition to hydroxyl groups, catalysed by alkali hydroxides, is discussed in chapters 4.1-4.1.5, the real active centre being the alkaline alcoholate, and the propagation reaction being the repeated SN-2 attack of the alcoholate anion on the a-carbon atom of the oxirane rings. The rapid equilibrium of the alcohol - alcoholate assures that each hydroxyl group from the reaction system is a chain initiator. 

The intramolecular SN-2 nucleophilic substitution is based on the SN-2 attack of the alcoholate anion to the a-carbon atoms of the four alkylic substituents of the nitrogen atom, the a-carbon atoms being activated by the positively charged nitrogen atom present in the quaternary ammonium alcoholate (reactions 13.10). 

The mechanism of this equilibrium is typical for base catalysed transesterification reactions, the alcoholate anion of the catalyst (for example sodium or potassium methoxide) attacks the carbonyl group of the ester bonds first (reactions 17.6). 

Aldehydes, ketones, alcohols Anion Ketones and aldehydes held as bisulphite addition compounds. Eluted with hot water and NaCl respectively. 

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