Acetic acid deprotonation

Chemical off—on switching of the chemiluminescence of a 1,2-dioxetane (9-benzyhdene-10-methylacridan-l,2-dioxetane [66762-83-2] (9)) was first described in 1980 (33). No chemiluminescence was observed when excess acetic acid was added to (9) but chemiluminescence was recovered when triethylamine was added. The off—on switching was attributed to reversible protonation of the nitrogen lone pair and modulation of chemically induced electron-exchange luminescence (CIEEL). Base-induced decomposition of a 1,2-dioxetane of 2-phen5l-3-(4 -hydroxyphenyl)-l,4-dioxetane (10) by deprotonation of the phenoHc hydroxy group has also been described (34). 

Fig. 2. Synthesis of uma2enil (18). The isonitrosoacetanihde is synthesized from 4-f1iioroani1ine. Cyclization using sulfuric acid is followed by oxidization using peracetic acid to the isatoic anhydride. Reaction of sarcosine in DMF and acetic acid leads to the benzodiazepine-2,5-dione. Deprotonation, phosphorylation, and subsequent reaction with diethyl malonate leads to the diester. After selective hydrolysis and decarboxylation the resulting monoester is nitrosated and catalyticaHy hydrogenated to the aminoester. Introduction of the final carbon atom is accompHshed by reaction of triethyl orthoformate to...

Most diaziridines are not sensitive towards alkali. As an exception, diaziridines derived from 2-hydroxyketones are quickly decomposed by heating with aqueous alkali. Acetaldehyde, acetic acid and ammonia are formed from (162). This reaction is not a simple N—N cleavage effected intramolecularly by a deprotonated hydroxy group, since highly purified hydroxydiaziridine (162) is quite stable towards alkali. Addition of small amounts of hydroxybutanone results in fast decomposition. An assumed reaction path — Grob fragmentation of a hydroxyketone-diaziridine adduct (163) — is in accord with these observations (B-67MI50800). 

The reaction is generally performed between 0 and 100 °C with the majority of the reactions being mn at reflux. Polar protic solvents such as methanol, ethanol, isopropanol, and water are commonly used as solvents. Addition of acid or use of acetic acid as solvent generally helps push sluggish reactions. The use of P-ketoesters as the dicarbonyl partner occasionally requires added base for cyclization to occur to form the pyrazolone. When using alkyl hydrazine salts, base may be required to deprotonate the hydrazine for the reaction to take place. 

However, deprotonation of rc-rf-butyldimethylsilyl-protected products 2 (prepared according to the classical Henry conditions )22, and consecutive reprotonation, provides the silylated nitroaldols 2 with high (R, R ) selectivity. Deprotonation of 2 by treatment with lithium diisopropylamide in tetrahydrofuran at — 78 C furnishes nitronates which are stable against / -elimination at that temperature. Protonation of these intermediates is achieved with an acetic acid/tetrahydrofuran (1 1) solution at —100 C. To achieve maximum yields, the mixture should be warmed up slowly before aqueous workup. 

Acetic acid, on the other hand, is a weak acid in water. Only a small fraction of its molecules undergo deprotonation, according to the equation... 

Solutions of different acids having the same concentration might not have the same pH. For instance, the pH of 0.10 M CH3COOH(aq) is close to 3 but that of 0.10 M HCl(aq) is close to 1. We have to conclude that the concentration of H,() ions in 0.10 M CH3COOH(aq) is lower than that in 0.10 M HCl(aq). Similarly, we find that the concentration of OH ions is lower in 0.10 M NH,(aq) than it is in 0.10 M NaOH(aq). The explanation must be that in water CH.COOH is not fully deprotonated and NH3 is not fully protonated. That is, acetic acid and ammonia are, respectively, a weak acid and a weak base. The incomplete deprotonation of CH3COOH explains why solutions of HC1 and CH3COOH with the same molarity react with a metal at different rates (Fig. 10.14). 

Our first task is to calculate the pH of a solution of a weak acid, such as acetic acid in water The initial concentration of the acid is its concentration as prepared, as if no acid molecules had donated any protons. For a strong acid HA, the H30+ concentration in solution is the same as the initial concentration of the strong acid, because all the HA molecules are deprotonated. However to find the H30 concentration in a solution of a weak acid HA, we have to take into account the equilibrium between the acid HA, its conjugate base A-, and water (Eq. 8). We can expect the pH to lie somewhere between 7, a value indicating no deprotonation, and the value that we would calculate for a strong acid, which undergoes complete deprotonation. The Technique, which is based on the use of an equilibrium table like those introduced in Chapter 9, is set out in Toolbox 10.1. 

Explain what happens to (a) the concentration of H,0+ ions in an acetic acid solution when solid sodium acetate is added (b) the percentage deprotonation of benzoic acid in a benzoic acid solution when hydrochloric acid is added (c) the pH of the solution when solid ammonium chloride is added to aqueous ammonia. 

Gold is generally considered a poor electro-catalyst for oxidation of small alcohols, particularly in acid media. In alkaline media, however, the reactivity increases, which is related to that fact that no poisoning CO-hke species can be formed or adsorbed on the surface [Nishimura et al., 1989 Tremihosi-Filho et al., 1998]. Similar to Pt electrodes, the oxidation of ethanol starts at potentials corresponding to the onset of surface oxidation, emphasizing the key role of surface oxides and hydroxides in the oxidation process. The only product observed upon the electrooxidation of ethanol on Au in an alkaline electrolyte is acetate, the deprotonated form of acetic acid. The lack of carbon dioxide as a reaction product again suggests that adsorbed CO-like species are an essential intermediate in CO2 formation. 

The condensation of acetone can also occur over acidic sites as shown by a number of authors [1,9], Generally, when this occurs other products are formed such as isobutene and acetic acid, by the cracking of DAA. Additionally mesitylene can be formed by the internal 2,7-aldol condensation of 4,6-dimethylhepta-3,5-dien-2-one which is in turn obtained by the aldol condensation of MO with a deprotonated acetone molecule [7, 8], As these species are not observed we can concluded that any acidic sites on the silica support are playing no significant role in the condensation of acetone. 

Sample preparation requires only dissolution of the sample to a suitable concentration in a mixture of water and organic solvent, commonly methanol, isopropanol, or acetonitrile. A trace of formic acid or acetic acid is often added to aid protonation of the analyte molecules in the positive ionization mode. In negative ionization mode ammonia solution or a volatile amine is added to aid deprotonation of the analyte molecules. 

In fluorosulfonic acid the anodic oxidation of cyclohexane in the presence of different acids (RCO2H) leads to a single product with a rearranged carbon skeleton, a 1-acyl-2-methyl-1-cyclopentene (1) in 50 to 60% yield (Eq. 2) [7, 8]. Also other alkanes have been converted at a smooth platinum anode into the corresponding a,-unsaturated ketones in 42 to 71% yield (Table 1) [8, 9]. Product formation is proposed to occur by oxidation of the hydrocarbon to a carbocation (Eq. 1 and Scheme 1) that rearranges and gets deprotonated to an alkene, which subsequently reacts with an acylium cation from the carboxylic acid to afford the a-unsaturated ketone (1) (Eq. 2) [8-10]. In the absence of acetic acid, for example, in fluorosulfonic acid/sodium... 

Homocoupling of aryl acetic acid derivatives has been achieved by deprotonation and oxidation by I2 as outlined... 

It has to be emphasized that the resulting bis(pyrazoI-l-yI)acetic acid Hbpza (3a) (Fig. 4) would not be available via the Otero route, since his synthesis is restricted to pyrazoles with substituents in 5-position of the p5rrazoIes. Other bis(pyrazoI-l-yI)methanes would be deprotonated at the CH2 bridge but also in position five of the pyrazole, due to ortho metallation. For the sterically more hindered bis(3,5-di-fert-butylpyrazole)acetic acid (3c) we followed Otero s synthetic pathway. In analogy to the synthesis of bis(3, 5-dimethylpyrazoI-l-yI)methane (2b) (72) 3,5-tert-butyIpyrazoIe... 

Deprotonation of a methylene group in 2d followed by reaction with carbon dioxide and acidic workup yielded a racemic mixture of (3,5-di-ter -butylpyrazol-l-yl)(3, 5 -dimethylp5rrazol-l-yl)acetic acid (Hbpa ) (3d) (Scheme 14). Reaction of 3d with base and anhydrous ZnCl2 5delded [Zn(bpa )Cl] that crystallized as a cross-linked dimer [(bpa )ZnCl]2 (16) (Scheme 15, Fig. 16). 

As reported by Steel et al. three structural isomers of bis(camphor-pyrazol-l-yl)methane (21a, 21b and 21c) are formed by coupling of camphorpyrazole 10 [i.e., (4S,7i )-7,8,8-trimethyl-4,5,6,7-tetrahydro-4,7-methano-l(2)H-indazole] with CH2CI2 (121). Isomer 21c can be separated from the other two structural isomers by crystallization or column chomatography. Deprotonation at the bridging carbon atom, subsequent reaction with carbon dioxide and acidic workup yields the enantiopure bis(camphorpyrazol-l-yl)acetic acid Hbpa (8) (Scheme 17, Fig. 19) (116). Due to missing substituents at the p5rrazolyl carbon C5 and a hence likely ortho metallation, isomers 21a and 21b are not suited for his reaction (72). 

---