Ethoxide anion

Figure 3.9 Calculated electrostatic potential maps for acetate anion and ethoxide anion. Although both molecules carry the same -1 net charge, acetate stabilizes the charge better by dispersing it over both oxygens.

The negative charge is localized on its oxygen in ethoxide anion. 

The ethoxide anion resulting from hydride transfer to acetaldehyde is then protonated by the enzyme to form ethanol. 

Nucleophilic attack of the enolate anion to the carhonyl carhon of another ethyl acetate gives an alkoxide tetrahedral intermediate. The resulting alkoxide reforms the carhonyl group hy ejecting the ethoxide anion. This ethoxide anion deprotonates the a-hydrogen, and produces a new enolate anion of the resulting condensed product, which is protonated in the next step upon acidification during work-up and yields the ethyl acetoacetate. 

So, a catalyhc synthesis of solefinacin (2) was developed at Dr. Reddy s Laboratories [28]. Mechanishc analysis reveals that the use of stoichiometric NaH is not required, as ethoxide anions are liberated. This anion is basic enough to deprotonate the (R)-quinuclidin-3-ol (31) and is capable of driving the reachon to completion, as shown in Scheme 14.8. The entire process is thus catalytic with respect to NaH ... 

Exercise 18-2 Make atomic-orbital models of ethanoic acid and ethanol and of the ethanoate anion and ethoxide anion. Show how these models can be used to explain the greater acidity of ethanoic acid relative to ethanol. 

The electrons on the negative oxygen reform the pi bond as the ethoxide anion leaves. 

Ketoesters that have two substituents on the a-carbon undergo fragmentation when treated with ethoxide anion as shown in the following equation. Suggest a mechanism for this reaction. 

Anhydro bases resulting from the proton abstraction by a base at an activated a -methyl group of a quaternary salt (see Section 4.19.2.3.3(iv)(a)) are active C-nucleophiles. These attack the C-2 position of a thiazolium salt affording adducts whose further reaction may lead to thiacyanines. Scheme 28 summarizes the successive steps in the reaction resulting from the addition of sodium ethoxide to a fairly concentrated ethanolic solution of 2,3-dimethylbenzothiazolylium salt (45) (c =0.1 moll-1). The initially formed anhydro base (46) cannot be isolated, it reacts as a nucleophile with a second molecule of benzothiazoly-lium salt yielding an adduct (47) which is deprotonated by ethoxide anion affording the dimeric anhydro base (48) whose reactivity will be discussed later (see Section 4.19.2.3.3.i). Monocyclic thiazolylium salts react similarly. 

The clue to the reaction is the polarity of the double bond. The lowest electron density is at the carbon linked to hydrogen, and is due to the strong inductive effect of the difluoromethylene groups and a slight effect of the vinylic chlorine. The attacking species, ethoxide anion, which is in an equilibrium with hydroxide ion in alcoholic potassium hydroxide, reacts in an SN2 reaction by joining the carbon bonded to hydrogen. The subsequent shift of the double bond facilitates ejection of fluorine as an anion and leads to an ether, compound O [77]. 

In the presence of an excess of potassium ethoxide, the ethoxide anion joins the less negative end of the double bond. Strong electron back-donating power of fluorine increases negativity at the carbon linked to chlorine and causes the addition of the ethoxide ion to the carbon linked to fluorine. Subsequent ejection of fluoride anion restores the double bond, and the final product is a diether, compound P [7/J. 

However, because of a small difference in the polarity of the double bond, the ethoxide anion joins also the carbon linked to bromine, and the result is 2-chloro-l-ethoxytetrafluorocyclobutene, compound R, formed in a smaller amount than compound Q [72]. 

The double bond in l,4-dibromohexafluoro-2-butene surrounded by fluorines and difluoromethylene groups is prone to undergo a nucleophilic addition of ethanol. From the addition product, hydrogen bromide is eliminated in the alkaline medium by E2 mechanism, and the compound C6H5BrF60 is formed. Another explanation of the reaction is addition of ethoxide anion followed by elimination of bromide anion [76],... 

The double bond in chlorotrifluoroethylene is polarized by back-donation of electrons of fluorine in such a way that the negative charge is on the carbon linked to chlorine and fluorine. Consequently, the difluorome-thylene end of the double bond is more electrophilic and is attacked by the ethoxide anion. Subsequent ejection of fluoride anion gives an unsaturated intermediate, l-chloro-l,2-difluoro-2-ethoxyethylene, compound V. This compound reacts with another ethoxide anion in a similar way and yields l-chloro-2,2-diethoxy-1-fluoroethylene. Nucleophilic addition of a third molecule of ethanol gives the final product, the orthoester of chlorofluoroacetic acid, compound W [75]. 

Two different reactions are possible when ethyl acetoacetate reacts with ethoxide anion. One possibility involves attack of ethoxide ion on the carbonyl carbon, followed by elimination of the anion of ethyl acetate—a reverse Claisen reaction similar to the one illustrated in 23.40. More likely, however, is the acid-base reaction of ethoxide ion and a doubly activated a-hydrogen of ethyl acetoacetate. 

Whereas 2,4,6-triphenylthiopyrylium cation (9) reacts with methoxide or ethoxide anion to give the corresponding IH adduct, it undergoes an electron transfer with isopropoxide or rer/-butoxide anion to yield the neutral radical 51 (86ZC400). 

Ellenberger, M. R., Farneth, W. E., and Dixon, D. A., Gas-phase isotope fractionation factor for the proton-bound dimer of the ethoxide anion, J. Phys. Chem. 85, 4-7 (1981). 

Dieckmann cyclization of diethyl adipate can be described by the two successive equilibria shown below. Use SpartanView to obtain the energies of diethyl adipate, the keto ester, the keto ester enolate ion, ethanol, and ethoxide anion, and calculate AH° for both steps. Which step is more favorable ... 

Thus, for example, when 1,1-dichloroethene is treated with ArS-, in the presence of a catalytic amount of ethoxide anion, the product is the 1,2-dithiophenoxy derivative. Suggest a route for this reaction. 

The first reaction we will study in this section is similar to one that we looked at in the previous section. We saw earlier a reaction that involved the substitution of 1,1-dichloroethene by the ArS-anion, using a catalytic amount of ethoxide anion. If the concentration of the ethoxide anion is increased, and the substrate altered to cis-1,2-dichloroethene, then the first reaction is an elimination step, instead of an addition step. Suggest what the subsequent steps might be, and the geometry of the final product. 

Meisenheimer complex. On the addition of a protic acid, the complex may fragment with the elimination of either the ethoxide or methoxide anions. If the ethoxide anion is eliminated this results in an overall substitution of an ethoxy group for methoxy group at the ipso position of the aromatic ring. Another example would involve the use of 2,4-dinitrofluorobenzene, which is used to form the derivative of the amino terminal of polypeptides. 

The effect of resonance may be seen when the acidity of a simple carboxylic acid such as acetic acid is compared with the acidity of an alcohol such as ethanol. Both compounds can ionise to liberate a proton, but while the anion formed on ionisation of acetic acid is resonance-stabilised, the ethoxide anion formed on ionisation of ethanol is not so stabilised and the negative charge resides wholly on the oxygen atom (see Figure 3.3). 

The first step is in basic medium ethoxide has a pATabH of 16. Sources The ethoxide anion. Leaving groups Only ethoxide on the ester. Sinks The ketone is a polarized multiple bond, and the ester is a polarized multiple bond with a leaving group. Acidic Hs The CH2 between the two carbonyls the most acidic, p/fa 10.7 the methyl on the carbonyl is the next most acidic, pA a 19. Resonance forms help us understand the polarization of our reactants. 

Dibromocarbene undergoes addition to alkenes in a stereospecific manner. The sole case of nonstereospecific dibromocyclopropanation using bromoform/base/phase-transfer catalyst concerns ( )-cyclooctene, and is explained by isomerization of this cycloalkene caused by reversible addition of tribromomethyl or ethoxide anion the latter is formed from the ethanol present in bromoform (see also ref 2 and Houben-Weyl, Vol. El 9b, p 1617 for stereomutation in the reactions of dibromocarbene, generated from organomercury reagents, with low-active alkenes, see Section 1.2.1.4.3.1.5.1. and Vol. E19b, pp 1615 1616). 

J Does the fact that bromoethane undergoes substitution faster with the ethoxide anion than with ethanol fit with the order of reactivity of nucleophiles ... 

The reactant in this problem is the same as in Problem 9.38a. However, the reaction conditions are different. In Problem 9.38a, the reaction was conducted with the strong base, ethoxide anion, so the mechanism was E2 and anti elimination was preferred. In this problem, there is no strong base present, so the mechanism is S I/EI. First the Cl leaves to form a carbocation. Because the carbocation is planar, stereochemistry is lost and anti elimination is not required. So both products are formed. Product 2 should be the major elimination product because E1 reactions follow Zaitsev s rule. 

The first step in these transformations is the addition of nucleophiles, such as methyllithium and sodium ethoxide, resulting in the corresponding neutral osma- or iridacyclohexa-1,4-diene complexes. Oxidation of these o -intermediates with oxidizing agents, such as oxygen, copper chloride, or DDQ, affords the final cationic Sn products. This approach is demonstrated by the reaction of cationic iridabenzene with the ethoxide anion (Scheme 28) [113]. 

Acid-catalysed alcoholysis of D-fructose with 2-chloroethanol affords the crystalline B-pyranoside (1) in 90% yield, and an extensive range of further derivatives have been reported. For example, treatment of (1) with ethoxide anion gave the spiro-product (2), and the dlsulphonate (3) afforded the tricyclic epoxide... 

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