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Kinetics of acetylation

Table 2-3. Kinetics of Acetylation of Isopropyl Alcohol by Acetic Anhydride Catalyzed... Table 2-3. Kinetics of Acetylation of Isopropyl Alcohol by Acetic Anhydride Catalyzed...
Akiyama, S. IC, and Hamme.s, G. G., 1980. Elementary. step.s in die reaction mechani.sm of die pyruvate dehydrogena.se mnltienzyme complex from Escherichia coli Kinetics of acetylation and deacetylation. Biochemistry 19 4208-4213. [Pg.672]

Figure 3.4 The reaction kinetics of acetylation plotted as WPG against time (a) and in terms of diffusion (WPG against square root time) (b). Figure 3.4 The reaction kinetics of acetylation plotted as WPG against time (a) and in terms of diffusion (WPG against square root time) (b).
In a study on the aminolysis of O-acetylethanolamine (185, R =H) and 0-acetylserine (185, R =COOH), it was observed (41) that the kinetics of acetyl-transfer reaction of these two aminoesters indicate that the breakdown of 186 yields mainly the amidoalcohol 187 only 1.5-3% of aminoester 185 was detected. The breakdown of 186 was compared with that of 188 obtained from imidate 94 (cf. p. 130) which gave only the aminoester 95 by C-N bond cleavage. Contrary to the conclusion reached by these authors (41), the difference in behavior between 186 and 188 can be readily understood. Imidate salt 94 reacts with hydroxide ion to give conformer J89 (R=CH3) which can only give the aminoester 95 with stereoelectronic control the amino-... [Pg.82]

K Selden, MD Klein, TW Smith. Plasma concentration and urinary excretion kinetics of acetyl strophanthidin. Circulation 47 744, 1973. [Pg.317]

A partial conformational analysis of a series of substituted thian-4-ols, based on a study of the kinetics of acetylation, has been reported. ... [Pg.246]

In addition to the initial reaction between nitric acid and acetic anhydride, subsequent changes lead to the quantitative formation of tetranitromethane in an equimolar mixture of nitric acid and acetic anhydride this reaction was half completed in 1-2 days. An investigation of the kinetics of this reaction showed it to have an induction period of 2-3 h for the solutions examined ([acetyl nitrate] = 0-7 mol 1 ), after which the rate adopted a form approximately of the first order with a half-life of about a day, close to that observed in the preparative experiment mentioned. In confirmation of this, recent workers have found the half-life of a solution at 25 °C of 0-05 mol 1 of nitric acid to be about 2 days. ... [Pg.81]

First-order nitrations. The kinetics of nitrations in solutions of acetyl nitrate in acetic anhydride were first investigated by Wibaut. He obtained evidence for a second-order rate law, but this was subsequently disproved. A more detailed study was made using benzene, toluene, chloro- and bromo-benzene. The rate of nitration of benzene was found to be of the first order in the concentration of aromatic and third order in the concentration of acetyl nitrate the latter conclusion disagrees with later work (see below). Nitration in solutions containing similar concentrations of acetyl nitrate in acetic acid was too slow to measure, but was accelerated slightly by the addition of more acetic anhydride. Similar solutions in carbon tetrachloride nitrated benzene too quickly, and the concentration of acetyl nitrate had to be reduced from 0-7 to o-i mol 1 to permit the observation of a rate similar to that which the more concentrated solution yields in acetic anhydride. [Pg.85]

The rates of nitration of benzene in solutions at 25 °C containing 0-4-2-0 mol 1 of acetyl nitrate in acetic anhydride have been deter-mined.2 The rates accord with the following kinetic law ... [Pg.86]

Nitrations of the zeroth order are maintained with much greater difficulty in solutions of acetyl nitrate in acetic anhydride than in solutions of nitric acid in inert organic solvents, as has already been mentioned. Thus, in the former solutions, the rates of nitration of mesi-tylene deviated towards a dependence on the first power of its concentration when this was < c. o-05-o-i mol 1 , whereas in nitration with nitric acid in sulpholan, zeroth-order kinetics could be observed in solutions containing as little as 10 mol 1 of mesitylene ( 3.2.1). [Pg.88]

Since nitration produces acetic acid, the concentration of this as well as of acetyl nitrate can be shown to depend upon the nitric acid concentration giving kinetics third-order in nitric acid (3.16 actually observed). It follows that in the presence of acetic acid the order in nitric acid should fall to 2 (2.31 observed). Likewise, in the presence of added sulphuric acid, from equilibrium (31) it follows that the order in nitric acid should fall, the observed order in this being 1.4 and 1.7 in added sulphuric acid. The retardation by added nitrate was attributed to competition by this ion for protonated acetyl nitrate, viz. [Pg.38]

Solvolytic experiments specifically designed to test Bartell s theory were carried out by Karabatsos et al. (1967), who were primarily interested in an assessment of the relative contributions of hyperconjugation and non-bonded interactions to secondary kinetic isotope effects. Model calculations of the (steric) isotope effect in the reaction 2- 3 were performed, as well as that in the solvolyses of acetyl chloride... [Pg.16]

The kinetic form of the decomposition in various solvents indicates competing unimolecular homolysis of the peroxide link (a) and radical induced decomposition (b). Other diacyl peroxides behave similarly, except that, in the case of acetyl peroxide, induced dceomposition is much less important. More highly branched aliphatic or a-phenyl-substituted diacyl peroxides decompose more readily, partly because induced decomposition is more important again and partly because of the occurrence of decomposition involving cleavage of more than one bond (for a mechanistic discussion of these cases, see Walling et al., 1970). [Pg.82]

Is the paramagnetic adduct between CO and Cluster A a kinetically intermediate in acetyl-CoA synthesis Questions have been raised about whether this adduct is a catalytic intermediate in the pathway of acetyl-CoA synthesis 187, 188) (as shown in Fig. 13), or is formed in a side reaction that is not on the main catalytic pathway for acetyl-CoA synthesis 189). A variety of biochemical studies have provided strong support for the intermediacy of the [Ni-X-Fe4S4l-CO species as the precursor of the carbonyl group of acetyl-CoA during acetyl-CoA synthesis 133, 183, 185, 190). These studies have included rapid ffeeze-quench EPR, stopped flow, rapid chemical quench, and isotope exchange. [Pg.321]

Schols, H.A., and Willfor, S. (2008) Kinetics of acid hydrolysis of water-soluble spruce O-acetyl galac-toglucomannans. /. Agric. Food. Chem., 56, 2429-2435. [Pg.186]

The HM and LM pectins give two very different types of gels the mechanisms of stabilization of the junction zones in the two cases are described and few characteristics given. The different molecular characteristics (DE, distribution of methoxyl or acetyl substituents, neutral sugar content or rhamnose content) play an important role on the kinetic of gelation, mechanical properties of the gel formed and also on the experimental conditions to form the stronger gels. All these points were briefly discussed. [Pg.31]

The UV-spectra of azolides have already been discussed in the context of hydrolysis kinetics in Chapter 1. Specific infrared absorptions of azolides were mentioned there as well increased reactivity of azolides in nucleophilic reactions involving the carbonyl group is paralleled by a marked shift in the infrared absorption of the corresponding carbonyl bond toward shorter wavelength. For example, for the highly reactive N-acetyl-tetrazole this absorption is found in a frequency range (1780 cm-1) that is very unusual for amides obviously the effect is due to electron attraction by the heterocyclic sys-tem.[40] As mentioned previously in the context of hydrolysis kinetics of both imidazo-... [Pg.35]

Xu et al. (2001) synthesized the copolymers of a dimer fatty acid (dimer of oleic and linoleic acids) and sebacic acid (P(DA-SA)) by melt polycondensation of acetylated prepolymers. Degradation and drug release kinetics showed that increasing dimer acid content decreased the release rate (Xu et al., 2001). [Pg.179]

A mixture of acetyl acetone, 1-nitronaphthalene, and naphthalene has been proposed for evaluating reversed-phase packing material [102]. This reveals the usual optimum kinetic chromatographic parameters (the naphthalene peak), the degree of activity or end-capping status of the column (the ratio of the 1-nitronaphthalene and naphthalene retention times) and trace metal activity (the shape and intensity of the acetylacetone peak). [Pg.544]

Further studies of the kinetics of reaction of disulphides with triphenylphosphine and water have been reported,86 87 supporting the previously suggested two-step mechanism.88 The reactions of -labelled acetyl aralkyl disulphides with triphenylphosphine have also been investigated.89... [Pg.16]

Serine peptidases can hydrolyze both esters and amides, but there are marked differences in the kinetics of hydrolysis of the two types of substrates as monitored in vitro. Thus, the hydrolysis of 4-nitrophenyl acetate by a-chy-motrypsin occurs in two distinct phases [7] [22-24]. When large amounts of enzyme are used, there is an initial rapid burst in the production of 4-nitro-phenol, followed by its formation at a much slower steady-state rate (Fig. 3.7). It was shown that the initial burst of 4-nitrophenol corresponds to the formation of the acyl-enzyme complex (acylation step). The slower steady-state production of 4-nitrophenol corresponds to the hydrolysis of the acetyl-enzyme complex, regenerating the free enzyme. This second step, called deacylation, is much slower than the first, so that it determines the overall rate of ester hydrolysis. The rate of the deacylation step in ester hydrolysis is pH-dependent and can be slowed to such an extent that, at low pH, the acyl-enzyme complex can be isolated. [Pg.73]

Like in Chapt. 7, we begin the discussion with acetates, since acetic acid is the simplest nontoxic acyl group, formic acid being less innocuous. An informative study was carried out to compare the kinetics of hydrolysis of two types of corticosteroid esters, namely methyl steroid-21-oates (which are active per se) and acetyl steroid-21-ols (which are prodrugs), as exemplified by methyl prednisolonate (8.69) and prednisolone-21-acetate (8.70), respectively [89]. In the presence of rat liver microsomes, the rate of hydrolytic inactivation of methyl steroid-21-oates was much slower than the rate of hydrolytic activation of acetyl steroid-21-ols. Thus, while the Km values were ca. 0.1 -0.3 mM for all substrates, the acetic acid ester prodrugs and the methyl ester drugs had Vmax values of ca. 20 and 0.15 nmol min-1 mg-1, respectively. It can be postulated that the observed rates of hydrolysis were determined by the acyl moiety, in other words by the liberation of the carboxylic acid from the acyl-enzyme intermediate (see Chapt. 3). [Pg.472]


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See also in sourсe #XX -- [ Pg.270 ]




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Acetylation kinetics

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