Hydrolysis rate

The first was proposed by Iraoto and Otsuji (511) and Otsuji et al (512) and concerned the pK of substituted 2-, 4-, and 5-carboxylic acids and the alkaline hydrolysis rate k of their respective ethyl esters (259, 260, and 261, where Y = Et). When Hammett cr , values were used for... 

Under conditions of photochemical chlorination (CH3)3CCH2C(CH3)3 gave a mixture of two monochlorides in a 4 1 ratio The structures of these two products were assigned on the basis of their SnI hydrolysis rates in aqueous ethanol The major product (compound A) underwent hydrolysis much more slowly than the minor one (compound B) Deduce the structures of com pounds A and B... 

Sodium Chloroacetate Sodium chloroacetate [3926-62-3] mol wt 116.5, C2H2C102Na, is produced by reaction of chloroacetic acid with sodium hydroxide or sodium carbonate. In many appHcations chloroacetic acid or the sodium salt can be used interchangeably. As an industrial intermediate, sodium chloroacetate may be purchased or formed in situ from free acid. The sodium salt is quite stable in dry soHd form, but is hydrolyzed to glycoHc acid in aqueous solutions. The hydrolysis rate is a function of pH and temperature (29). 

Commercial condensed phosphoric acids are mixtures of linear polyphosphoric acids made by the thermal process either direcdy or as a by-product of heat recovery. Wet-process acid may also be concentrated to - 70% P2O5 by evaporation. Liaear phosphoric acids are strongly hygroscopic and undergo viscosity changes and hydrolysis to less complex forms when exposed to moist air. Upon dissolution ia excess water, hydrolytic degradation to phosphoric acid occurs the hydrolysis rate is highly temperature-dependent. At 25°C, the half-life for the formation of phosphoric acid from the condensed forms is several days, whereas at 100°C the half-life is a matter of minutes. 

Steric and inductive effects determine the rate of formation of the pentacovalent siUcon reaction complex. In alkaline hydrolysis, replacement of a hydrogen by alkyl groups, which have lower electronegativity and greater steric requirements, leads to slower hydrolysis rates. Replacement of alkyl groups with bulkier alkyl substituents has the same effect. Reaction rates decrease according to ... 

Hydrolysis of TEOS in various solvents is such that for a particular system increases directiy with the concentration of H" or H O" in acidic media and with the concentration of OH in basic media. The dominant factor in controlling the hydrolysis rate is pH (21). However, the nature of the acid plays an important role, so that a small addition of HCl induces a 1500-fold increase in whereas acetic acid has Httie effect. Hydrolysis is also temperature-dependent. The reaction rate increases 10-fold when the temperature is varied from 20 to 45°C. Nmr experiments show that varies in different solvents as foUows acetonitrile > methanol > dimethylformamide > dioxane > formamide, where the k in acetonitrile is about 20 times larger than the k in formamide. The nature of the alkoxy groups on the siHcon atom also influences the rate constant. The longer and the bulkier the alkoxide group, the lower the (3). 

Sulfur monochloride is hydrolyzed at a moderate rate by water at room temperature but rapidly at higher temperatures. In the vapor state, the hydrolysis rate is slow and involves disproportionation of the primary hydrolysis products ... 

Sulfates having alkyl groups from methyl to pentyl have been examined. With methyl as an example, the hydrolysis rate of dimethyl sulfate iacreases with the concentration of the sulfate. Typical rates ia neutral water are first order and are 1.66 x lO " at 25°C and 6.14 x lO " at 35°C (46,47). Rates with alkaH or acid depend on conditions (42,48). Rates for the monomethyl sulfate [512-42-5] are much slower, and are nearly second order ia base. Values of the rate constant ia dilute solution are 6.5 X 10 L/(mol-s) at 100°C and 4.64 X 10 L/(mol-s) at 138°C (44). At 138°C, first-order solvolysis is ca 2% of the total. Hydrolysis of the monoester is markedly promoted by increasing acid strength and it is first order. The rate at 80°C is 3.65 x lO " ... 

CycHc esters show accelerated hydrolysis rates. Ethylene sulfate compared to dimethyl sulfate is twice as fast ia weak acid (first order) and 20 times as fast ia weak alkaH (second order) (50). Catechol sulfate [4074-55-9] is 2 x 10 times faster than diphenyl sulfate ia alkaline solution (52). Alcoholysis rates of several dialkyl sulfates at 35—85°C are also known (53). 

The acetylation reaction is stopped by the addition of water to destroy the excess anhydride, causing rapid hydrolysis of the combined sulfate acid ester (Eig. 7). This is followed by a much slower rate of hydrolysis of the acetyl ester groups. The rate of hydrolysis is controlled by temperature, catalyst concentration, and, to a lesser extent, by the amount of water. Higher temperatures and catalyst concentrations increase the rate of hydrolysis. Higher water content slightly iacreases the hydrolysis rate and helps minimize degradation (85). The amount of water also influences the ratio of primary to secondary... 

GB is unstable in the presence of water. Maximum stability in aqueous solutions occurs from pH 4.0—6.5 with the hydrolysis rate increasing as the pH increases. The half-life in distilled water at 25°C is ca 36 h, but hydrolysis is accelerated in the presence of acids or bases. Because bases are far more effective in this respect than acids, caustic solutions are useful for decontamination. 

The lack of dependence on ionic strength in the first reaction indicates that it occurs between neutral species. Mono- or dichloramine react much slower than ammonia because of their lower basicities. The reaction is faster with CI2 because it is a stronger electrophile than with HOCl The degree of chlorination increases with decreasing pH and increasing HOCINH mol ratio. Since chlorination rates exceed hydrolysis rates, initial product distribution is deterrnined by formation kinetics. The chloramines hydrolyze very slowly and only to a slight extent and are an example of CAC. 

In solution, chlorine dioxide decomposes very slowly at ambient temperatures in the dark. The primary decomposition process is hydrolysis of chlorine dioxide into chlorite and chlorate ions. The hydrolysis rate is a function of the concentration of hydroxyl ions and temperature, proceeding rapidly at solution pH values above 10 ... 

Binary azeotropic systems are reported for all three derivatives (9). The solubiHties of benzyl chloride, benzal chloride, and ben zotricbl oride in water have been calculated by a method devised for compounds with significant hydrolysis rates (10). 

According to a kinetic study which included (56), (56a) and some oxaziridines derived from aliphatic aldehydes, hydrolysis follows exactly first order kinetics in 4M HCIO4. Proton catalysis was observed, and there is a linear correlation with Hammett s Ho function. Since only protonated molecules are hydrolyzed, basicities of oxaziridines ranging from pii A = +0.13 to -1.81 were found from the acidity rate profile. Hydrolysis rates were 1.49X 10 min for (56) and 43.4x 10 min for (56a) (7UCS(B)778). O-Protonation is assumed to occur, followed by polar C—O bond cleavage. The question of the place of protonation is independent of the predominant IV-protonation observed spectroscopically under equilibrium conditions all protonated species are thermodynamically equivalent. 

The influence of temperature, acidity and substituents on hydrolysis rate was investigated with simple alkyldiaziridines (62CB1759). The reaction follows first order kinetics. Rate constants and activation parameters are included in Table 2. 

Successive introduction of two methyl groups at ring carbon increases the hydrolysis rate by a factor of 10 in each step, indicating cation formation in the transition state as in acetal hydrolysis. Equilibrium protonation before hydrolysis becomes evident from an increasing rate of hydrolysis with a decreasing pH value (Table 3). Below pH 3 no further increase of rate is observed, so that protonation is assumed to be complete. 

One of the major differences between penicillins and cephalosporins is the possibility for a concerted elimination of the C-3 substituent in the case of cephalosporins (6->7). There is now considerable evidence to support the idea that an increase in the ability of the C-3 substituent to act as a leaving group results in an increased reactivity of the 8-lactam carbonyl (75JMC408). Thus, both the hydrolysis rate of the 8-lactam and antibacterial activity... 

The behavior of penicillins under hydrolysis conditions has been extensively studied e.g. B-49MI51102,71JPS503), and Some of the early work has been summarized in Section 5.11.3.2. Generally, the rate of /3-lactam hydrolysis for various penicillins reaches a minimum between pH 6 and 7, and increases sharply above and below that minimum (74CPB1186). Under basic conditions, hydrolysis rates are relatively insensitive to the 6-substituent, and the product is the relatively stable penicilloate and, at least in some cases, its 5-epimer (Scheme 51) (77JHC503). 

Diazaspiro[2.5]octane, 1 -methyl-hydrolysis rate constant, 7, 216 (62CB1759)... 

Diaziridine, 1-cyclohexyl-hydrolysis rate constant, 7, 216 (62CB1759) Diaziridine, 1 -cyclohexyl-3,3-dimethyl-hydrolysis rate constant, 7, 216 (62CB1759) Diaziridine, l-cyclohexyl-3-methyl-hydrolysis rate constant, 7, 216 (62CB1759) Diaziridine, l,2-di-t-butyl-3-t-butylimino-IR, 7, 13 <80AG(E)276)... 

Imidazole, 4-acetyl-5-methyl-2-phenyl-synthesis, 5, 475 Imidazole, 1-acyl-reactions, 5, 452 rearrangement, 5, 379 Imidazole, 2-acyl-synthesis, 5, 392, 402, 408 Imidazole, 4-acyl-synthesis, 5, 468 Imidazole, C-acyl-UV spectra, 5, 356 Imidazole, N-acyl-hydrolysis rate constant, 5, 350 reactions, 5, 451-453 synthesis, 5, 54, 390-393 Imidazole, alkenyl-oxidation, 5, 437 polymerization, 5, 437 Imidazole, 1-alkoxycarbonyl-decarboxylation, 5, 453 Imidazole, 2-alkoxy-l-methyl-reactions, 5, 102 thermal rearrangement, 5, 443 Imidazole, 4-alkoxymethyl-synthesis, 5, 480 Imidazole, alkyl-oxidation, 5, 430 synthesis, 5, 484 UV spectra, 5, 355 Imidazole, 1-alkyl-alkylation, 5, 73 bromination, 5, 398, 399 HNMR, 5, 353 synthesis, 5, 383 thermal rearrangement, 5, 363 Imidazole, 2-alkyl-reactions, 5, 88 synthesis, 5, 469... 

Steiic effects of another kind become important in highly branched substrates, in which ionization is facilitated by relief of steric crowding in going from the tetrahedral groimd state to the transition state for ionization. The ratio of the hydrolysis rates in 8OV0 aqueous acetone of t-butyl /F-nitrobenzoate and 2,3,3-trimethyl-2-butyl p-nitrobenzoate is 1 4.4. 

Table 5.14. Relative Hydrolysis Rates of 2-AU l-2-adamantyl p-Nitrobenzoates"...

Acetic anhydride has also been used as the acylating agent. The formation of thiiranes from thiocyanatohydrins having a tertiary hydroxy group is best achieved by p-toluenesulfonic acid-catalyzed acetylation.The analogous thiocyanatohydrins with a secondary hydroxyl and a tertiary thiocyanate function give a predominance of epoxide from thiocyanatohydrin acetates since the hydrolysis rate of the secondary acetate grouping becomes competitive with that of the tertiary thiocyanate. 

In the acidic and alkaline hydrolysis rates of the same ester, the steric and resonance effects. re the same. 

Hydrolysis Rate Constants for Model Oligosaccharides with Lysozyme... 

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