Carbon acid promoted

The first of these reactions is a hydrolysis process, the second is a carbonic acid-promoted dissolution, and the third is a proton-promoted dissolution. Equations 3.59b and 3.59c are the forward reactions in Eqs. 3.17 and 3.15, respectively. They provide a mechanistic underpinning for the dependence of kd in Eq. 3.14 on pH or pc0, as discussed in Section 3.1. Indeed, if Eq. 3.7 is applied to the forward reaction in Eq. 3.14 and rate laws for Eq. 3.59 are developed consistently with the hypothesis leading to Eq. 3.7, the result is7,33,34... 

The carbonic acid-promoted dissolution of calcite (Eq. 3.59b) can be described in an open system by the sequence of heterogeneous reactions ... 

In the discussion of the relative acidity of carboxylic acids in Chapter 1, the thermodynamic acidity, expressed as the acid dissociation constant, was taken as the measure of acidity. It is straightforward to determine dissociation constants of such adds in aqueous solution by measurement of the titration curve with a pH-sensitive electrode (pH meter). Determination of the acidity of carbon acids is more difficult. Because most are very weak acids, very strong bases are required to cause deprotonation. Water and alcohols are far more acidic than most hydrocarbons and are unsuitable solvents for generation of hydrocarbon anions. Any strong base will deprotonate the solvent rather than the hydrocarbon. For synthetic purposes, aprotic solvents such as ether, tetrahydrofuran (THF), and dimethoxyethane (DME) are used, but for equilibrium measurements solvents that promote dissociation of ion pairs and ion clusters are preferred. Weakly acidic solvents such as DMSO and cyclohexylamine are used in the preparation of strongly basic carbanions. The high polarity and cation-solvating ability of DMSO facilitate dissociation... 

The enzyme carbonic anhydrase promotes the hydration of COg. Many of the protons formed upon ionization of carbonic acid are picked up by Hb as Og dissociates. The bicarbonate ions are transported with the blood back to the lungs. When Hb becomes oxygenated again in the lungs, H is released and reacts with HCO3 to re-form HgCOj, from which COg is liberated. The COg is then exhaled as a gas. 

The effect of C ,C -disubstituted amino acids (aaAAs) on peptide secondary structure has been studied in recent years.2a d While longer side-chain C ,C -di-n-alkyl amino acids promote extended peptide conformation,23 alicyclic aaAAs, in which the Ca carbon forms a cyclic bridge with itself, such a 1-aminocyclopentane-l-carboxylic acid (Ac5c) and 1-aminocyclohexane-l-carboxylic acid (Ac6c), have helix-forming characteristics similar to those of 1 -aminoisobutyric acid (Aib).2ax... 

To determine if the overaii caicuiation is reasonable, notice that the hydronium concentration in acid rain is five orders of magnitude higher than in pure water. This increased hydronium ion concentration can convert a substantiai amount of carbonate anions into hydrogen carbonate anions, promoting the soiubiiity of caicium carbonate. The resuiting equiiibrium concentration of caicium cations is about five orders of magnitude iarger than the concentration in a saturated soiution in pure water. 

In analogy to the mechanism of the palladium-catalyzed enyne cyclization, it is postulated that exposure of palladium(O) to acetic acid promotes in situ generation of hydridopalladium acetate LnPd"(H)(OAc). Alkyne hydrometallation affords the vinylpalladium complex A-10, which upon r-carbopalladation of the appendant alkyne provides intermediate B-7. Silane-mediated cleavage of carbon-palladium bond liberates the cyclized product along palladium(O), which reacts with acetic acid to regenerate hydridopalladium acetate to close the cycle (Scheme 33). 

The presence of a positively charged substituent on the a carbon atom promotes the acidity of P hydrogen. 

The alkoxycarbenium ions generated by the cation pool method react with various carbon nucleophiles such as substituted allylsilanes and enol silyl ethers to give the corresponding coupling products in good yields. It should be noted that the reactions of alkoxycarbenium ion pools with such nucleophiles are much faster than the Lewis acid promoted reactions of acetals with similar nucleophiles. A higher concentration of the cationic species in the cation pool method seems to be responsible. 

The axially chiral (allenylmethyl) silanes 110 were also prepared in optically active form using chiral Pd catalysts [98]. For the asymmetric synthesis of 110, a Pd/(R)-segphos system was much better in terms of enantioselectivity than the Pd/(R)-binap catalyst. Under the optimized conditions, 110m and llOt were obtained in 79% ee (57% yield) and 87% ee (63% yield), respectively (Scheme 3.56). The enantio-merically enriched (allenylmethyl) silanes 110 served for Lewis acid-promoted SE reaction with tBuCH(OMe)2 to give conjugated dienes 111 with a newly formed chiral carbon center (Scheme 3.56). During the SE reaction, the allenic axial chirality was transferred to the carbon central chirality with up to 88% transfer efficiency. 

In a review on the addition of carbenium ions to alkenes (equation 19) as a general procedure for carbon-carbon bond formation50, Mayr reported on investigations which also include the reactions of a variety of 1,3-dienes toward electrophilic carbon species generated by Lewis acid-promoted heterolysis of alkyl chlorides. 

Regiospecific mono-C-alkylation (60-90%) of trimethylsilyl enol ethers is promoted by benzyltriethylammonium fluoride [34, 35]. A similar alkylation of tin(IV) enolates is aided by stoichiometric amount of tetra-n-butylammonium bromide and has been utilized in the synthesis of y-iminoketones [36]. Carbanions from weakly acidic carbon acids can be generated by the reaction of their trimethylsilyl derivatives with tetra-n-butylammonium triphenyldifluorosilicate [37] (see also Section 6.3). Such carbanions react readily with haloalkanes. Tautomeric ketones in which the enol form has a high degree of stabilization are O-alkylated to form the enol ether, e.g. methylation of anthrone produces 9-methoxyanthracene [26],... 

Ethanol is membrane-permeable and is quickly resorbed. The maximum blood level is already reached within 60-90 min after drinking. The resorption rate depends on various conditions, however. An empty stomach, a warm drink (e.g., mulled wine), and the presence of sugar and carbonic acid (e.g., in champagne) promote ethanol resorption, whereas a heavy meal reduces it. Ethanol is rapidly distributed throughout the body. A large amount is taken up by the muscles and brain, but comparatively little by adipose tissue and bones. Roughly 70% of the body is accessible to alcohol. Complete resorption of the ethanol contained in one bottle of beer (16 g) by a person weighing 70 kg (distribution in 70 kg 70/100 = 49 kg) leads to a blood alcohol level of 0.33 per thousand (7.2 mM). The lethal concentration of alcohol is approximately 3.5 per thousand (76 mM). 

Lewis acid-promoted [3+2] cycloadditions of aziridines and epoxides proceeding via carbon-carbon bond cleavage of three-membered ring heterocycles are demonstrated for the first time. This proposal details plans for extending these initial results into a general synthetic method for the enantioselective synthesis of structurally diverse pyrrolidine- and tetrahydrofuran-containing organic compounds. Expected outcomes of the proposed work will include... 

A summary of the in situ use of the azobenzene probases is given in Table 2. Apart from the generation of ylid, referred to above, the main applications have been for N- and C-alkylation of weak nitrogen and carbon acids, for the promotion of condensation and substitution reactions involving carbanions such as the cyano-methyl anion, for an interesting carboxylation reaction (entries 4 and 17), and for base-promoted cyclisations (entries 5 and 6). 

Ref la). It is miscible with w, ale and eth (See also Ref 7). Various methods of prepn are given in Refs 1.3 9 In Ref 2 is described the catalytic production of acetaldehyde from acetylene and steam over activated carbon and promoted by phosphoric acid. 

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