Hydroxide anion

There are several cases of hydroxylation according to the hidden-radical mechanism, within a solvent cage. As assumed (Fomin and Skuratova 1978), hydroxylation of the anthraquinone sulfonic acids (AQ—SO3H) proceeds by such a reticent pathway, and OH radicals attack the substrate anion-radicals in the solvent cage. Anthraquinone hydroxyl derivatives are the final products of the reaction. In the specific case of DMSO as a solvenf, hydroxyl radicals give complexes with the solvent and lose their ability to react with the anthraquinone sulfonic acid anion-radicals (Bil kis and Shein 1975). The reaction stops after an anion-radical is formed  

The hidden-radical mechanism (also dubbed the mechanism of biradical origin ) does not, however, take into account all the peculiarities of the reaction participants. The redox potential of OH/ OH couple is equal to 0.9 V with regard to the saturated calomel electrode in AN (Tsang et al. 1987). In conventional reference to the normal hydrogen electrode and in water, this potential is equal to 1.9 (Berdnikov and Bazhin 1970) or 1.3 V in AN (Eberson 1987, Chapter 4, p. 62). 

These values are not appropriate for reducing the majority of the organic acceptors. Of course, there are some cases of single electron transfer from OH ion to an organic acceptor. All these cases, however, refer to substrates with very strong electron affinity, such as tetracyanoethylene or dinitrobenzene (Blumenfel d et al. 1970). Quinones, ketones, and other substrates have less affinity. In the ground (unexcited) states, they are unable to capture an electron from the OH ion (Sawyer and Roberts 1988). 

It should be pointed out that the possibility of an OH OH transformation with one-electron 

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Example Solvation can have a profound effect on the potential energy profile for a reaction. Jorgensen s research group provided important insights into the role of solvation. Consider the nucleophilic addition of the hydroxide anion to formaldehyde ... 

Inspired by the many hydrolytically-active metallo enzymes encountered in nature, extensive studies have been performed on so-called metallo micelles. These investigations usually focus on mixed micelles of a common surfactant together with a special chelating surfactant that exhibits a high affinity for transition-metal ions. These aggregates can have remarkable catalytic effects on the hydrolysis of activated carboxylic acid esters, phosphate esters and amides. In these reactions the exact role of the metal ion is not clear and may vary from one system to another. However, there are strong indications that the major function of the metal ion is the coordination of hydroxide anion in the Stem region of the micelle where it is in the proximity of the micelle-bound substrate. The first report of catalysis of a hydrolysis reaction by me tall omi cell es stems from 1978. In the years that... 

In contrast to the reaction of the betaine 58 in wet diethylether, wet THF, in which the betaine is better soluble, gives the methyl isoanhydroberberilate 64 in 71% yield. The mechanism seemingly involves an unusual carbon to nitrogen acyl migration as shown in Scheme 23. Hydration and air oxidation of the betaine to the peroxide leads to the formation of an aziridine intermediate and loss of a hydroxide anion (77TL3787). 

The reaction is induced by nucleophilic addition of the hydroxide anion to one of the two carbonyl groups. Then the respective substituent R migrates with the bonding electrons to the adjacent carbon atom (a 1,2-shift). Electron excess at that center is avoided by release of a pair of r-electrons from the carbonyl group to the oxygen ... 

The key step of the Cannizzaro reaction is a hydride transfer. The reaction is initiated by the nucleophilic addition of a hydroxide anion to the carbonyl group of an aldehyde molecule 1 to give the anion 4. In a strongly basic medium, the anion 4 can be deprotonated to give the dianionic species 5 ... 

The o. o. o -trihaloketone 7 can further react with the hydroxide present in the reaction mixture. The hydroxide anion adds as a nucleophile to the carbonyl carbon the tetravalent intermediate suffers a carbon-carbon bond cleavage ... 

Using squares to represent atoms of one element (or cations) and circles to represent the atoms of die other element (or anions), represent die principal spedes in die following pictorially. (You may represent die hydroxide anion as a single drde.)... 

Hydroperoxides react with transition metals in lower oxidation states (TiJ, Fe", Cu+, etc.) and a variety of other oxidants to give an alkoxy radical and hydroxide anion (Scheme 3.38)46 224,22"... 

Sulfonic acids themselves are unfit for electrophilic transfer of sulfonyl groups because of the poor nucleofugality of the hydroxide anion. However, the high acidity obviously leads to an equilibrium between the acids and their anhydrides and water, from which water can be removed either by special reaction conditions (i.e., azeotropic distillation with appropriate solvents) or chemically with anhydride forming agents316 (equation 63). sulfonic acid anhydride sulfonylations are compiled in Table 10. 

As shown in this table, the metal catalysts used in the literature are mostly complexes of Ni or Cu and less often Co or Pd. For soft nucleophiles, on the left of the table, the efficiency of the nickel catalysts was already reported. Here, are presented the investigations concerning the arylation of hard nucleophiles such as amines, alcohols or hydroxide anion, using Ni, Pd and Cu catalysts. 

In connexion with the arylation of hard nucleophiles, it was interesting to reinvestigate the hydrolysis of arylhalides in presence of copper catalysts, which is in fact the arylation of hydroxide anion and represents an important industrial challenge (eqn. 2). 

One of the most fundamental chemical reactions is the combination of a hydroxide ion (OH ) and a hydronium ion (H3 0+) to produce two molecules of water OH" (a g) + H3 (a g) 2 H2 O (/) A molecular view of this reaction (Figure 4-7f shows that the hydroxide anion accepts one hydrogen atom from the hydronium cation. Taking account of charges, it is a hydrogen cation (H ) that is transferred. The reaction occurs rapidly when H3 O and OH ions collide. The hydroxide anion accepts a hydrogen cation from the hydronium cation, forming two neutral water molecules. 

Any reaction in which a proton is transferred from one substance to another is an acid-base reaction. More specifically, the proton-transfer view is known as the Bronsted-Lowiy definition of acids and bases. In an acid-base reaction, an acid donates a proton, and a base accepts that proton. Any species that can give up a proton to another substance is an acid, and any substance that can accept a proton from another substance is a base. The production of two water molecules from a hydroxide anion (a base) and a hydronium ion (an acid) is just one example of an acid-base reaction acids and bases are abundant in chemistry. 

In Figure the hydronium ion acts as an acid because it donates a proton to a base. The hydroxide anion acts as a base because it accepts a proton from an acid. When a hydronium ion with charge +1 transfers a proton to a hydroxide ion with charge -1, the two resulting water molecules have zero charges. The pair of charges becomes a neutral pair. A proton transfer reaction such as this one, in which water is one product and a pair of charges has been neutralized, is called a neutralization reaction. 

C15-0009. What are the units of the rate constant for the reaction of hydroxide anions with hydronium cations, which proceeds by the single collision shown in Section 15-1 ... 

These examples of acid-base reactions show that water can act as either an acid or a base Water accepts a proton fixtm an HCl molecule, but it donates a proton to a PO4 anion. As an acid, water donates a proton to a base and becomes a hydroxide anion. As a base, water accepts a proton from an acid and becomes a hydronium cation. A chemical species that can both donate and accept protons is said to be amphiprotic. Water is an amphiprotic molecule. 

A substance that generates hydroxide ions quantitatively in aqueous solution is a strong base. The most common strong bases are the soluble metal hydroxides, among which NaOH perennially ranks among the top ten industrial chemicals. When a soluble metal hydroxide dissolves in water, it generates metal cations and hydroxide anions NaOH (5 ) H2 O Na (a q) + OH (a q)... 

When ammonia dissolves in water, the resulting solution has a pH greater than 7.00, indicating that the solution is basic (Eigure 17-31. In other words, the concentration of hydroxide ions in aqueous ammonia is greater than that in pure water. Ammonia molecules accept protons from water molecules, generating ammonium cations and hydroxide anions NH3((2 q) + H2 0((3 q) NH4 (a q) + OH (i2 q)... 

The reaction generates hydroxide anions, so the solution is basic. Fluoride acts as a base, so the equilibrium constant is a base dissociation constant, Zj,. 

Hydronium cations, neutral water molecules, and hydroxide anions illustrate the effect of charge on acid-base behavior. 

The water equilibrium always exists in aqueous solution. In general, we can focus our initial attention on the equilibria involving other major species (NH3 in this example). Nevertheless, the water equilibrium does exert its effect on the concentrations of OH and H3 O. In this example, the concentration of hydroxide anion is established by the ammonia equilibrium, but the concentration of hydronium cations must be found by applying the water equilibrium. We use this feature in several of our examples in this chapter. 

Healthy humans do not suffer these ailments, because blood pH is tightly regulated by a pair of reactions that involve H2 CO3 and HCO3. Hydronium ions that enter the bloodstream react with hydrogen carbonate, and hydroxide anions react with carbonic acid. These reactions work together to maintain the pH of blood at HC03 + H3 0+ H2 CO3 + H2 O... 

A second way to prepare a buffer is by adding strong base to a solution of a weak acid. This produces a buffer solution if the number of moles of strong base is about half the number of moles of weak acid. As a simple example, if 1 L of 0.5 M NaOH is mixed with 1 L of 1.0 M CH3 CO2 H, hydroxide anions react quantitatively... 

The pH of the buffer solution, both before and after adding the solid NaOH, is close to the p of the conjugate acid-base pair. Moreover, the pH increases when NaOH is added. The solution becomes more basic as a consequence of the added hydroxide anions. 

Examples are CO2, SO2, and SO3. Each of these molecules can form a a bond betw een its central atom and a Lewis base, at the expense of a jrbond. For example, the hydroxide anion, a good Lewis base, attacks the carbon atom of CO2 to form hydrogen carbonate ... 

In this reaction, the oxygen atom of the hydroxide ion donates a pair of electrons to make a new C—O bond. Because all the valence orbitals of the carbon atom in CO2 are involved in bonding to oxygen, one of the C—O ITT bonds must be broken to make an orbital available to overlap with the occupied orbital of the hydroxide anion. 

X-ray diffraction studies on several forms of the enzyme have demonstrated that the active site is composed of a pseudo-tetrahedral zinc center coordinated to three histidine imidazole groups and either a water molecule [(His)3Zn-OH2]2+ (His = histidine), or a hydroxide anion [(His)3Zn-OH] +, depending upon pH (156,157). On the basis of mechanistic studies, a number of details of the catalytic cycle for carbonic anhydrase have been elucidated, as summarized in Scheme 22... 

The binding energy increases more rapidly for the sulfide anion than for the oxide or hydroxide anion (Figure 2.5). Sulfide donates or shares electrons more readily than does oxide or hydroxide. 

In a more detailed study, it was shown that MW effects are strongly dependent on the temperature and the nature of the cation associated with hydroxide anion [66] (for example Eq. (46) and Tab. 5.20). 

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