Deprotonation with water

Methylation of nicotine to the pyridinium iodide with methyl iodide, followed by its conversion to the hydroxide with silver oxide in water, oxidation with potassium permanganate to the A -methyl nicotinic acid hydroxide and subsequent deprotonation with silver oxide yielded Trigollenine as colorless needles (1897CB2117). In a later publication, the formation of nicotinic acid from nicotine was described. Esterification followed by aminolysis and methylation yielded the A -methylnicotinamide... 

The breakthrough came with stopped-flow techniques, applied first by Ritchie and Wright (1971a, 1981b). Stopped-flow measurements allow evaluation of observed rates in more detail. It was possible to show that the forward reaction occured not only with hydroxide ions but also with water molecules, followed by fast deprotonation by hydroxide ions. The mechanism of the latter reaction will be discussed in Sections 5.2 and 5.3. 

These ions then precipitate as a hydrated iron(III) oxide, Fe203-H20, the brown, insoluble substance that we call rust. The oxide ions can be regarded as coming from deprotonation of water molecules and as immediately forming the hydrated solid by precipitation with the Fe3+ ions produced in reaction F ... 

According to this scheme, 192 first affords the anion 195 in an initial protonation/ deprotonation equilibrium 195 then undergoes rate-determining unimolecular decomposition to the metaphosphorimidate 197, which reacts fast with water to give the phosphoric acid 197. 

Compounds with an acidity constant, pK, in the range of 4 to 10, i.e. weak organic acids or bases, are present in two species forms at ambient pH. This pA a.i. range includes aromatic alcohols and thiols, carboxylic acids, aromatic amines and heterocyclic amines [15]. Conversely, alkyl-H and saturated alcohols do not undergo protonation/deprotonation in water (pA iw 14). 

Deprotonation with the generation of the radical counterpart can be favorable as it is manifested by the low value. The dimethyl sulfide cation-radical in water is deprotonated in the following way [(CH3)2S] —> CH3SCH2 + H+. Accordingly, pA, value of [(CH3)2S] is 0.3 from B3LYP calculations and about 1.8 from experiments (Brunelle and Rank 2004). 

The y-chloro alcohol 160 was lithiated, after deprotonation with a n-butyllithium in THF at —78°C, using lithium and a catalytic amount of naphthalene (1%) at the same temperature to give the corresponding intermediate 161, which was quenched with water, yielding 1-phenylpropanol (162) (Scheme 57). ... 

Acid-catalysed hydrolysis. Under acidic conditions, the hydrolysis of an amide resembles the acid-catalysed hydrolysis of an ester, with protonation of the carbonyl group yielding an activated carbonyl group that undergoes nucleophilic attack by water. The intramolecular proton transfer produces a good leaving group as ammonia. Simultaneous deprotonation by water and loss of ammonia yields a carboxylic acid. 

Compounds that are more polar, and which can better hydrogen-bond with water, require less drastic alterations to the solvent environment to cause dissolution to occur. On the right side of Figure 3, we associate solute polarity with each formulation concept. Drugs that are good hydrogen donors, in the extreme sense, have acidic properties. Likewise, those that are very good acceptors have basic properties. For these compounds, formation of a salt by protonation or deprotonation is a feasible route. 

The origin of these pKa values has been explored by H NMR studies on cobalt LADH,546 which suggest that the pKa value of 9.0 in Co(c)2Zn(n)2-LADH is due to the S-NH group of His-67, one of the ligands. In the complex with NAD+ the same group shows a pH-dependent shift without deprotonation, with a p a of 8.3 0.2, which is suggested to correspond to the pKa of 7.6 obtained from kinetic data on the native enzyme, and to be due to coordinated water. The suggestion that His-67 is involved in the acid-base equilibria is novel and requires substantiation. 

The Sumitomo Metal Mining Co. in Japan uses a 40% solution of tri- -octylamine in xylene to separate cobalt and nickel in chloride media.44-163 194 The traces of zinc that are present are coextracted with the cobalt and, owing to the strong extraction of zinc, remain in the organic phase when the cobalt is stripped with water (cf. Figure 11). The zinc is then removed from a bleed stream of the organic phase by deprotonation stripping with sodium hydroxide solution ... 

Aliphatic thioketones result tautomerically pure from the reaction of H2S with ketals in the presence of ZnCl2. Deprotonation with LDA gives the enethiolate which can be silylated to form the silyl vinyl sulphide. These are fairly stable to traces of water but react with MeOH to give the enethiol (equation 3)7. 

It might seem surprising that a nucleophilic reaction with water competes with proton loss from the phenanthrenonium ion considering the stability of the aromatic product. As discussed by Richard24 (and considered further below) this reflects a higher intrinsic reactivity of the cations toward nucleophilic attack which compensates for the thermodynamic disadvantage of this reaction. For the phenanthrenonium ion the ratio of rate constants for deprotonation and nucleophilic attack on the cation (kp/kH2o) is 25 25 for the 1-protonated naphthalene it is 1600,106 for 9-protonated anthracene, 1.8.75... 

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