Hydroxide ion formation

In addition to the general improvement of transfer in micro reactors, there is evidence that the voltage of electroosmotic flow (for EOF see [14]) in combination with the large internal surface area in glass chips can induce hydroxide ion formation [6]. Concerning catalyst loss, there is no obvious direct correlation rather, micro reactors can act as mini fixed beds fixing heterogeneous catalyst particles. 

Although many other acid-base definitions have been proposed and have been useful in particular types of reactions, only a few have been widely adopted for general use. Among them are those attributed to Arrhenius (based on hydrogen and hydroxide ion formation), Br0nsted-Lowry (hydrogen ion donors and acceptors), and Lewis (electron pair donors and acceptors) [6,67-70]. 

The paper pulp should be basic. Sodium hypochlorite (NaCIO) is a salt prepared from a strong base (NaOH) and a weak acid (HCIO). Salts of strong bases and weak acids are basic. The solution is basic because the hypochlorous ion (CIO1) bonds with hydrogen ions (H+) from water leaving an excess of hydroxide ions (OH1-). The following equations describe the salt formation and the hydroxide ion formation ... 

A key aspect of the process recommended by Acar et al. [64] is to continue electrolysis for a sufficient time to completely acidify the soil mass. The effects of hydroxide ion formation at the cathode can be alleviated further by the addition of a weak acid. Anions of this weeik acid, for example acetic acid, will migrate upstream but upon meeting the downstream H" " ions, associate to form nonconducting molecules. 

Now let s consider a strong base such as potassium hydroxide. Let s say the solution is 1 x 10 M. Since KOH is a strong base, it dissociates completely. So we can confidently say that the concentration of hydroxide-ion formed is also 1 X 10 M. Just like the strong acid, we can ignore the possibility of hydroxide-ion formation from water, since the self-ionization of water is negligible. Since the OH" concentration is 1 x 10 , the pOH is 3. From this, we can say that the pH of this solution is close to 11, since pH + pOH =14. 

Iron hydroxide ion formation, Fe(OFI), depends on solution pFl, that is, the availability of OH ions. As bivalent Fe ions are formed through Eq. (12.6), OH ions are transported from the bulk to the surfice to maintain electroneutrality. Flydroxide ions are also produced via the cathodic oxygen reduction reaction, causing an increase in surface pH. At high pH, the formation of adsorbed [Fe(OH)]ads on the iron surface becomes more favorable than bivalent Fe ions, Eq. (12.6). The electrode potential tends to shift into a more anodic direction to accommodate the formation of Fe(OH)". As time increases, the Fe(OH) concentration at the surface increases. In the next step, Fe(OH) oxidizes to ferric oxide at e° = —0.084Vvs.SCE, resulting in a barrier oxide layer ... 

A probable mechanism for this rearrangement postulates the intermediate formation of a hydroxide-ion addition complex, followed by the migration of a phenyl group as an anion ... 

Obtaining maximum performance from a seawater distillation unit requires minimising the detrimental effects of scale formation. The term scale describes deposits of calcium carbonate, magnesium hydroxide, or calcium sulfate that can form ia the brine heater and the heat-recovery condensers. The carbonates and the hydroxide are conventionally called alkaline scales, and the sulfate, nonalkaline scale. The presence of bicarbonate, carbonate, and hydroxide ions, the total concentration of which is referred to as the alkalinity of the seawater, leads to the alkaline scale formation. In seawater, the bicarbonate ions decompose to carbonate and hydroxide ions, giving most of the alkalinity. 

Dehydrogenation is considered to occur on the corners, edges, and other crystal defect sites on the catalyst where surface vacancies aid in the formation of intermediate species capable of competing for hydrogen with ethylbenzene. The role of the potassium may be viewed as a carrier for the strongly basic hydroxide ion, which is thought to help convert highly aromatic by-products to carbon dioxide. 

The formation of oximes, hydrazones, and related imine derivatives is usually catalyzed by both general acids and general bases. General base catalysis of dehydration of the tetrahedral intermediate involves nitrogen deprotonation concerted with elimination of hydroxide ion. ... 

Addition of hydride ion from the catalyst gives the adsorbed dianion (15). The reaction is completed and product stereochemistry determined by protonation of these species from the solution prior to or concurrent with desorption. With the heteroannular enolate, (13a), both cis and trans adsorption can occur with nearly equal facility. When an angular methyl group is present trans adsorption (14b) predominates. Protonation of the latter species from the solution gives the cis product. Since the heteroannular enolate is formed by the reaction of A" -3-keto steroids with strong base " this mechanism satisfactorily accounts for the almost exclusive formation of the isomer on hydrogenation of these steroids in basic media. The optimum concentration of hydroxide ion in this reaction is about two to three times that of the substrate. 

Inspection of the citrate structure shows a total of four chemically equivalent hydrogens, but only one of these—the pro-/J H atom of the pro-i arm of citrate—is abstracted by aeonitase, which is quite stereospecific. Formation of the double bond of aconitate following proton abstraction requires departure of hydroxide ion from the C-3 position. Hydroxide is a relatively poor leaving group, and its departure is facilitated in the aeonitase reaction by coordination with an iron atom in an iron-sulfur cluster. 

Ingold makes no differentiation in principle between pseudo bases and those derivatives which are formed by the action of nucleophilic reagents. The latter he denotes by the general term "pseudo salts and considers their formation parallel to the formation of the car-binolamines themselves. If the mesomeric cation combines with a hydroxide ion, a pseudo base is formed if it combines with another nucleophilic ion or molecule, then a pseudo salt is formed. 

During the next fifty years the interest in derivatives of divalent carbon was mainly confined to methylene (CHg) and substituted methylenes obtained by decomposition of the corresponding diazo compounds this phase has been fully reviewed by Huisgen. The first convincing evidence for the formation of dichlorocarbene from chloroform was presented by Hine in 1950. Kinetic studies of the basic hydrolysis of chloroform in aqueous dioxane led to the suggestion that the rate-determining step was loss of chloride ion from the tri-chloromethyl anion which is formed in a rapid pre-equilibrium with hydroxide ions ... 

Under the influence of thermal motion and on endothermic electron transition from the OH ion to the Me ion in alkali metal hydroxides the formation of the Me. and OH. radicals takes place. As a result, free va-... 

Following formation of the amide intermediate, a second nucleophilic addition of hydroxide ion to the amide carbonyl group then yields a tetrahedral alkoxide ion, which expels amide ion, NHZ-, as leaving group and gives the car-boxylate ion, thereby driving the reaction toward products. Subsequent acidification in a separate step yields the carboxylic acid. We ll look at this process in more detail in Section 21.7. 

As an example of enolate-ion reactivity, aldehydes and ketones undergo base-promoted o halogenation. Even relatively weak bases such as hydroxide ion are effective for halogenation because it s not necessary to convert the ketone completely into its enolate ion. As soon as a small amount of enolate is generated, it reacts immediately with the halogen, removing it from the reaction and driving the equilibrium for further enolate ion formation. 

Once again, the formation of NH accounts for ammonia having the properties of a base. Reaction (27) produces hydroxide ion, which, by our postulate, accounts for the taste and feel properties of solutions of bases. Reaction (28) shows... 

It is appropriate at this juncture to address some of the more useful transformations of 2,3-epoxy alcohols.913 A 2,3-epoxy alcohol such as compound 14 possesses two obvious electrophilic sites one at C-2, and the other at C-3. But in addition, C-l of a 2,3-epoxy alcohol also has latent electrophilic reactivity. For example, exposure of 14 to aqueous sodium hydroxide solution results in the formation of triol 19 in 79% yield (see Scheme 5). In this interesting transformation, hydroxide ion induces the establishment of an equilibrium between 2,3-epoxy-l-ol 14 and the isomeric 1,2-epoxy-3-ol 18. This reversible, base-induced epoxide migration reaction is a process known as the Payne rearrangement.14... 

A base was originally defined as a substance which, when dissolved in water, undergoes dissociation with the formation of hydroxide ions OH- as the only negative ions. Thus sodium hydroxide, potassium hydroxide, and the hydroxides of certain bivalent metals are almost completely dissociated in aqueous solution ... 

The hydrogen ions required for this reaction can be obtained only from the further dissociation of the water this dissociation produces simultaneously an equivalent quantity of hydroxyl ions. The hydrogen ions are utilised in the formation of HA consequently the hydroxide ion concentration of the solution will increase and the solution will react alkaline. 

Complex formation reactions. These depend upon the combination of ions, other than hydrogen or hydroxide ions, to form a soluble, slightly dissociated ion or compound, as in the titration of a solution of a cyanide with silver nitrate... 

In Sections 5.2 and 5.3 it was shown that experimental data are consistent with a direct rearrangement of the (Z)- to the (ii)-diazohydroxide rather than with a recombination after a primary dissociation of the (Z)-isomer into a diazonium ion. Positive evidence for direct formation of the (ii)-diazohydroxide from the diazonium ion and a hydroxide ion (or water) is still lacking (see Scheme 5-15 in Sec. 5.2). For diazo ethers, however, Broxton and Roper (1976) came to the conclusion that there is no direct (Z) >(E) conversion, but rather that in the system ArNj + OCH3/(Z)-diazo ether/(Zi)-diazo ether the (Z)-ether is the kinetically determined product and the (iE )-isomer the thermodynamic product, as shown in Scheme 6-3. 

The reaction with nitrite proceeds smoothly and with relatively high yields of the corresponding nitroarene (see Sec. 10.6). Obviously a major part of the driving force of this reaction is the formation of a stable, i. e., an energetically favorable, radical, nitrogen dioxide. With the hydroxide ion — a much stronger nucleophile than the nitrite ion — the reaction is expected to produce very unstable radicals, the hydroxy radical OH and the oxygen radical anion O, from the diazohydroxide (Ar - N2 — OH) and the diazoate (Ar-N20 ) respectively. Consequently, dediazoniation in alkaline aqueous solution does not follow the simple Scheme 8-41 with Yn = OH, but instead involves diazoanhydrides (Ar — N2 —O —N2 —Ar) as intermediates (see Sec. 8.8). 

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