Addition of hydroxide ion

Mercury(II) oxide, HgO, occurs in both yellow and red forms the yellow form is precipitated by addition of hydroxide ion to a solution containing mercury(II) ions, and becomes red on heating. Mercury(II) oxide loses oxygen on heating. 

Step 1 Nucleophilic addition of hydroxide ion to the carbonyl group ... 

The trihalomethyl ketone (RCCX3) so formed then undergoes nucleophilic addition of hydroxide ion to its carbonyl group triggering its dissociation... 

The alkaline fission may be represented similarly. (8-Addition of hydroxide ion to the benzylidene double bond would lead to 130 which by a rather surprising elimination of the A-hydroxyl group could give the acyl dioxopiperazine (128). Cleavage of 128 by ammonia to give a benzamide is unexceptional. Birch et al. noted in 1966 that no... 

Base catalyzed nitrile hydrolysis involves nucleophilic addition of hydroxide ion to the polar C N bond to give an imine anion in a process similar to nucleophilic addition to a polar C=0 bond to give an alkoxide anion. Protonation then gives a hydroxy imine, which tautomerizes (Section 8.4) to an amide in a step similar to the tautomerization of an enol to a ketone. The mechanism is shown in Figure 20.4. 

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. 

The main problem of interest, however, is that of finding a way to determine Kx and K2 separately for cases where Kx < K2. Such a separation of Kx and K2 is possible by taking advantage of the fact that the addition of hydroxide ion to the diazonium ion (rate constant kx in Scheme 5-1) is slower than the deprotonation of the diazohydroxide (rate constant k2). An analogous relationship holds for the two reverse reactions (k 2>k i). From the values of kx and k x one can, of course, calculate Kx and, if KXK2 is known, K2. Such measurements of Kx and K x were, however, difficult in the 1950s. 

As discussed in Sections 5.1-5.3, arenediazonium ions are Lewis acids in which the (3-nitrogen forms the center of electrophilic character. This was demonstrated by the addition of hydroxide ions and water molecules. Other nucleophiles can also be added and, in principle, these reactions display the same mechanistic characteristics as those with OH and H20. According to the nature of the atom of the nucleophile that provides the lone pair of electrons, O-, S-, Se-, N-, P-, or C-coupling can occur. With N- and C-coupling, important and large groups of compounds are formed, namely azo compounds (mainly important as azo dyes) and triazenes, respectively. These compounds will be discussed in Chapters 12 and 13, respectively. 

Ab initio molecular orbital calculations are being used to study the reactions of anionic nucleophiles with carbonyl compounds in the gas phase. A rich variety of energy surfaces is found as shown here for reactions of hydroxide ion with methyl formate and formaldehyde, chloride ion with formyl and acetyl chloride, and fluoride ion with formyl fluoride. Extension of these investigations to determine the influence of solvation on the energy profiles is also underway the statistical mechanics approach is outlined and illustrated by results from Monte Carlo simulations for the addition of hydroxide ion to formaldehyde in water. 

Ab initio calculations addition of hydroxide ion to formaldehyde, 212 energy surfaces, 201-211 Adaptive continuation method, hydrogen-air flame, 417 Adaptive mesh... 

Organoboranes undergo fragmentation if a good leaving group is present on the 8-carbon.102 The reactive intermediate is the tetrahedral borate formed by addition of hydroxide ion at boron. 

The bromo-substituted azacyanine 79 undergoes addition of hydroxide ion and then the resultant adduct 80 undergoes ring-opening reaction to form compound 81 in good yield (Scheme 3) <2001JOC1310>. 

ESR spectroscopy, however, revealed that 75, which one may call a ketyl radical, was not present in alkaline solutions of 77 in absence of oxidizing agents. The signal actually observed was that of 9-hydroxy-N,N -dimethyl-9,9 -biacridan radical 76. It was suggested that this radical was formed by one-electron transfer from N-methyl-acridone radical anion 75 to lucigenin monocarbinol 77, or by addition of hydroxide ion to lucigenin radical cation 78 (formed from lucigenin by one-electron transfer by the ketyl 75). 

The benzilic acid rearrangement, though catalyzed by hydroxide ion, probably belongs in the same category as carbonium ion rearrangements. Kinetic and isotopic exchange experiments show that there is a rapid reversible addition of hydroxide ion.841 242... 

This is a synthetically useful procedure because the a-halo acids are useful starting materials for other reactions. For example, the addition of hydroxide ion leads to the replacement of the halogen with an -OH group. The reaction with ammonia replaces the halogen with -NH2. The reaction with cyanide ion, CN , converts the halide to a nitrile. Figure 12-33 illustrates this reaction. 

In this section we generated an -value of by taking the family of identity exchange reactions of benzyl derivatives (109) (Pross, 1983). That particular -value is sufficiently anomalous to deter any possible application to questions of transition state structure. Yet there are cases that are, in principle, quite similar to the identity exchange reaction in which a-values are utilized as a measure of transition state structure. In such cases we believe the conclusions may not be valid. A typical example (Bell and Sorenson, 1976) is the addition of hydroxide ion to substituted benzaldehydes (110). For this system the sensitivity of rates and equilibria to substituent effects was similar. 

The tetramer is the main polymerization product obtained (21% yield) on addition of hydroxide ion (3 days, 25°C, pH = 3.8) to solutions of the pure dimer (11, 70, 79). On acidification, the tetramer splits into [Cr(OH2)6]3+ and the trimer. Careful investigation of the tetramer showed that two rapidly interconverting species could be detected (Fig. 10). The proposed structure of TC (80), with a square pyrimidal tetraco-... 

The addition of hydroxide ions to substituted benzaldehydes (ArCHO + OH <=> ArCH(0H)0 ) is used to establish J-acidity scales in water-ethanol and water-DMSO mixtures containing sodium hydroxide as a base. The pK-values in such mixtures are linearly correlated with Hammett substituent constants. The independence of reaction constant p of solvent composition confirms that substituted benzaldehydes are suitable J- indicators for hydroxide solutions in water-ethanol and water-DMSO mixtures. Dependence of J- values on sodium hydroxide concentration is only slightly affected by ethanol up to 90 % and at a constant sodium hydroxide concentration shows only small increase between 90 and 98 % ethanol. J- increases more with increasing DMSO concentration, but the effect is much smaller than that of DMSO on H- values based on proton abstraction from aniline. 

Nevertheless, validity of acidity function H cannot be expected to extend to reactions involving addition of hydroxide ions rather than dissociation of a proton. For addition of hydroxide ions, the acidity function J- has been defined (8, 9,1 1, 12) as in Equation 1, where ax are activities, cx concentrations,... 

Substituted benzaldehydes have proved useful as acid-base indicators for reactions involving the addition of hydroxide ions n strongly alkaline aqueous media (19). It seemed logical to extend their use to solutions of sodium hydroxide in water-ethanol and water-DMSO mixtures. In ethanol-water, it was of interest whether the competition between addition of hydroxide and ethoxide ions will be reflected in the dependence of the J- function on ethanol concentration. In water-DMSO mixtures, it was important to investigate whether the radical change at higher DMSO concentrations, observed for H values and attributed to changes in solvation of the hydroxide ion, will be observed for the addition reaction as well. 

Provided that the influence of the water-ethanol composition on the reaction involving addition of hydroxide ions to benzaldehydes can be characterized by any parameter Yj (the application of Y- used for benzoic acid dissociations in ethanol-water mixtures (28) might be doubtful), application of the relation pYt - pyo = C(Yi - Y0) would indicate that the value of C (0.638) for benzoic acids (28) and —0.573 for anilines (29) is close to zero for the benzaldehyde reaction (4). 

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