Kinetics acetate

LACTATE MONOOXYGENASE LEUCINE KINETICS ACETATE KINASE... 

Acetalization of ketones was also effected using Noyori s kinetic acetalization protocol. Thus, bis-trimethylsilyl-ethers readily react with cyclohexanones to give 1,3-dioxanes in good yield (Equation 73) <1997J(P1)2789>. 

The strong tendency for acetalization of cA-l,2-diols is exemplified by the reaction of glucopyranose A, which on treatment with acetone in the presence of a catalytic amount of H2SO4 furnishes the l,2 5,6-di-D-isopropylidene-a-D-glucofuranose B (thermodynamic product). However, kinetic acetalization with 2-methoxypropene in DMF in the presence of TsOH as a catalyst at 0 °C occurs without rearrangement to give the 4,6-isopropylidene glucopyranose... 

Oikawa,Y. Nishi,T. Yonemitsu, O., Kinetic Acetalization for 1,2- and 1,3-Diol Protection by the Reaction of p-Methoxyphenylmethyl Methyl Ether with DDQ. Tetrahedron Lett. 1983, 37, 4037. 

The Lewis acid-catalysed acetaladons of alkyl D-gluco- and D-galactopyranoside-4,6-diols and their 4,6-bis(trimethylsilyl) ethers with methyl 2,2-(diphenylthio)propanoate or methyl pyruvate, respectively, have been studied in detail. It was observed that these reactions are often accompanied by anomerization and by isomerization of the initial, kinetic acetal to the thermodynamically stable diastereomer with an axial COjMe group. An example is given in Scheme 2. The 4,6-0-methyl pyruvate-based acetal 14 has been synthesized from benzyl a-D-mannopyranoside via the 4,6-0-(1,1,3,3-tetraisopropyldisUoxane-l,3-diyl)-piotected derivative 13 this procedure requires fewer protection/deprotection steps than use of the more common 4,6-bis(trimethylsilyl) ether as intermediate. ... 

OT Synthesis of 1,2 4,5-Di-O (3,3-pentylidene) arabitol via Kinetic Acetal Formation... 

Much of the early work was inconclusive confusion sprang from the production by the reaction of water, which generally reduced the rate, and in some cases by production of nitrous acid which led to autocatalysis in the reactions of activated compounds. The most extensive kinetic studies have used nitromethane,acetic acid, sulpholan,i and carbon tetrachloride as solvents. 

Nitration in acetic acid, in sulpholan and in carbon tetrachloride showed kinetic phenomena similar to those shown in nitromethane this is significant for it denies nitromethane a chemical involvement in the slow step. (Originally the rate of isomerization of nitromethane to its aci-form was believed to be a factor in the reaction. )... 

The anticatalytic effect of nitrous acid in nitration The effect of nitrous acid was first observed for zeroth-order nitrations in nitromethane ( 3.2). The effect was a true negative catalysis the kinetic order was not affected, and nitrous acid was neither consumed nor produced by the nitration. The same was true for nitration in acetic acid. In the zeroth-order nitrations the rate depended on the reciprocal of the square root of the concentration of nitrous acid =... 

The kinetics of nitration of anisole in solutions of nitric acid in acetic acid were complicated, for both autocatalysis and autoretardation could be observed under suitable conditions. However, it was concluded from these results that two mechanisms of nitration were operating, namely the general mechanism involving the nitronium ion and the reaction catalysed by nitrous acid. It was not possible to isolate these mechanisms completely, although by varying the conditions either could be made dominant. 

Chloroanisole and p-nitrophenol, the nitrations of which are susceptible to positive catalysis by nitrous acid, but from which the products are not prone to the oxidation which leads to autocatalysis, were the subjects of a more detailed investigation. With high concentrations of nitric acid and low concentrations of nitrous acid in acetic acid, jp-chloroanisole underwent nitration according to a zeroth-order rate law. The rate was repressed by the addition of a small concentration of nitrous acid according to the usual law rate = AQ(n-a[HN02]atoioh) -The nitration of p-nitrophenol under comparable conditions did not accord to a simple kinetic law, but nitrous acid was shown to anticatalyse the reaction. 

The effect of nitrous acid on the nitration of mesitylene in acetic acid was also investigated. In solutions containing 5-7 mol 1 of nitric acid and < c. 0-014 mol of nitrous acid, the rate was independent of the concentration of the aromatic. As the concentration of nitrous acid was increased, the catalysed reaction intervened, and superimposed a first-order reaction on the zeroth-order one. The catalysed reaction could not be made sufficiently dominant to impose a truly first-order rate. Because the kinetic order was intermediate the importance of the catalysed reaction was gauged by following initial rates, and it was shown that in a solution containing 5-7 mol 1 of nitric acid and 0-5 mol 1 of nitrous acid, the catalysed reaction was initially twice as important as the general nitronium ion mechanism. 

The kinetics of nitration in acetic anhydride are complicated. In addition to the initial reaction between nitric acid and the solvent, subsequent reactions occur which lead ultimately to the formation of tetranitromethane furthermore, the observation that acetoxylation accompanies the nitration of the homologues of benzene adds to this complexity. 

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. ... 

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. 

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 ... 

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). 

In the nitration and acetoxylation of o-xylene the addition of acetic acid increased the rate in proportion to its concentration, the presence of 3-0 mol 1" accelerating the rate by a factor of 30. In the presence of a substantial concentration (2-2 mol 1 ) of acetic acid the rate of reaction obeyed the following kinetic expression... 

Similarly, acetic acid catalysed the zeroth-order nitration of mesitylene without affecting the kinetic form... 

Other substituents which belong with this group have already been discussed. These include phenol, anisole and compounds related to it ( 5.3.4 the only kinetic data for anisole are for nitration at the encounter rate in sulphuric acid, and with acetyl nitrate in acetic anhydride see 2.5 and 5.3.3, respectively), and acetanilide ( 5.3.4). The cations PhSMe2+, PhSeMe2+, and PhaO+ have also been discussed ( 9.1.2). Amino groups are prevented from showing their character ( — 7 +717) in nitration because conditions enforce reaction through the protonated forms ( 9.1.2). 

The kinetics of the nitration of benzene, toluene and mesitylene in mixtures prepared from nitric acid and acetic anhydride have been studied by Hartshorn and Thompson. Under zeroth order conditions, the dependence of the rate of nitration of mesitylene on the stoichiometric concentrations of nitric acid, acetic acid and lithium nitrate were found to be as described in section 5.3.5. When the conditions were such that the rate depended upon the first power of the concentration of the aromatic substrate, the first order rate constant was found to vary with the stoichiometric concentration of nitric acid as shown on the graph below. An approximately third order dependence on this quantity was found with mesitylene and toluene, but with benzene, increasing the stoichiometric concentration of nitric acid caused a change to an approximately second order dependence. Relative reactivities, however, were found to be insensitive... 

It has not been found possible to reconcile all these observations with a simple kinetic scheme. A major difficulty is that whilst the stoichiometric concentrations of nitric acid and of acetic acid can be varied independently, the actual concentrations of these species cannot, because of the existence of the equilibrium ... 

In one of the earliest kinetic studies of an organic reaction earned out m the nine teenth century the rate of hydrolysis of ethyl acetate m aqueous sodium hydroxide was found to be first order m ester and first order m base... 

Mixtures of trioctylamine and 2-ethylhexanol have been employed to extract 1—9% by volume acetic acid from its aqueous solutions. Reverse osmosis for acid separation has been patented and solvent membranes for concentrating acetic acid have been described (58,59). Decalin and trioctylphosphine were selected as solvents (60). Liquid—Uquid interfacial kinetics is an especially significant factor in such extractions (61). 

The monomer pair, acrylonitrile—methyl acrylate, is close to being an ideal monomer pair. Both monomers are similar in resonance, polarity, and steric characteristics. The acrylonitrile radical shows approximately equal reactivity with both monomers, and the methyl acrylate radical shows only a slight preference for reacting with acrylonitrile monomer. Many acrylonitrile monomer pairs fall into the nonideal category, eg, acrylonitrile—vinyl acetate. This is an example of a nonideality sometimes referred to as kinetic incompatibiUty. A third type of monomer pair is that which shows an alternating tendency. 

T[[dotb]he nature of the initial attack by the water (eq. 10) is a matter of some controversy (205,206). Stereochemical and kinetic studies of model systems have been reported that support trans addition of external water (207,208) or internal addition of cis-coordinated water (209), depending on the particular model system under study. Other paHadium-cataly2ed oxidations of olefins ia various oxygen donor solvents produce a variety of products including aldehydes (qv), ketones (qv), vinyl acetate, acetals, and vinyl ethers (204). However the product mixtures are complex and very sensitive to conditions. 

In studies of the polymerization kinetics of triaUyl citrate [6299-73-6] the cyclization constant was found to be intermediate between that of diaUyl succinate and DAP (86). Copolymerization reactivity ratios with vinyl monomers have been reported (87). At 60°C with benzoyl peroxide as initiator, triaUyl citrate retards polymerization of styrene, acrylonitrile, vinyl choloride, and vinyl acetate. Properties of polyfunctional aUyl esters are given in Table 7 some of these esters have sharp odors and cause skin irritation. 

An especially interesting case of oxygen addition to quinonoid systems involves acidic treatment with acetic anhydride, which produces both addition and esterification (eq. 3). This Thiele-Winter acetoxylation has been used extensively for synthesis, stmcture proof, isolation, and purification (54). The kinetics and mechanism of acetoxylation have been described (55). Although the acetyhum ion is an electrophile, extensive studies of electronic effects show a definite relationship to nucleophilic addition chemistry (56). 

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