Acid hydrolysis kinetics

Index Entries Reaction kinetics glucose decomposition dilute acid hydrolysis kinetic modeling acid-soluble lignin acid-base catalysis rules. 

Carboxyhc acid ester, carbamate, organophosphate, and urea hydrolysis are important acid/base-catalyzed reactions. Typically, pesticides that are susceptible to chemical hydrolysis are also susceptible to biological hydrolysis the products of chemical vs biological hydrolysis are generally identical (see eqs. 8, 11, 13, and 14). Consequentiy, the two types of reactions can only be distinguished based on sterile controls or kinetic studies. As a general rule, carboxyhc acid esters, carbamates, and organophosphates are more susceptible to alkaline hydrolysis (24), whereas sulfonylureas are more susceptible to acid hydrolysis (25). 

Orthoesters. The value of cycHc orthoesters as intermediates for selective acylation of carbohydrates has been demonstrated (73). Treatment of sucrose with trimethylorthoacetate and DMF in the presence of toluene-/)-sulfonic acid followed by acid hydrolysis gave the 6-0-acetylsucrose as the major and the 4-0-acetylsucrose [63648-80-6] as the minor component. The latter compound underwent acetyl migration from C-4 to C-6 when treated with an organic base, such as / fZ-butylamine, in DMF to give sucrose 6-acetate in >90% yield (74). When the kinetic reagent 2,2-dimethoxyethene was used,... 

Reduction of the sodium salt of equilenin 17-ethylene ketal with lithium, sodium or potassium in ammonia at —70° occurs predominantly in the B-ring, affording, after acid hydrolysis, equilin (29) in up to 76% yield (55% isolated). The preferential reduction of the B-ring reflects the relative, but not absolute, resistance to reduction conferred on the A-ring by the naphthoxide ion. Some A-ring reduction does compete kinetically with B-ring reduction, since the epimeric 3-hydroxyestra-5,7,9-trien-17-ones are the major reaction by-products. Simple phenoxide ions usually reduce slowly... 

The acid hydrolysis of diaziridines has been investigated kinetic-ally. The reaction is first order and shows a relatively high temperature coefficient. Thus one finds a relatively high activation enthalpy (23-28 kcal) and a positive activation entropy (2-6 eu). The influence of substitution on nitrogen is small. The velocity of the diaziridine hydrolysis depends only in the weakly acid region on the acid concentration. Between pH 7 and 3 the fc-values rise by nearly 10 . For the... 

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. 

Blecker, C., Fougnies, C., van Herck, J.-C., Chevalier, J.-P., and Paquot, M. (2002) Kinetic study of the acid hydrolysis of various oligofructose samples. 

The redox potential and the reactivity of this oxidation state depend strongly upon the anion (Table 11). Strong complexes are formed with SO ". Even in perchloric acid, hydrolysis and polymerisation greatly complicate kinetics. The co-ordination number of Ce(lV) in solution is not established . 

Rates of hydrolysis may be influenced by the presence of dissolved organic carbon, or organic components of soil and sediment. The magnitude of the effect is determined by the structure of the compound and by the kinetics of its association with these components. For example, whereas the neutral hydrolysis of chlorpyrifos was unaffected by sorption to sediments, the rate of alkaline hydrolysis was considerably slower (Macalady and Wolf 1985) humic acid also reduced the rate of alkaline hydrolysis of 1-octyl 2,4-dichlo-rophenoxyacetate (Perdue and Wolfe 1982). Conversely, sediment sorption had no effect on the neutral hydrolysis of 4-chlorostilbene oxide, although the rate below pH 5 where acid hydrolysis dominates was reduced (Metwally and Wolfe 1990). 

Bank S, RJ Tyrrrell (1984) Kinetics and mechanism of alkaline and acidic hydrolysis of aldicarb. JAgric Food Chem 32 1223-1232. 

In order to elucidate the causes of the increased stability of the hydrolyzed cluster ions compared with the unhydrolyzed ions, further studies were made of the behaviour of [Te2X8]3 (where X = Cl,Br, or I) in solutions of hydrogen halides [43,52,80,87]. The studies were performed mainly in relation to the most stable and most readily synthesized [Tc2C18]3- ion (Fig. la) kinetic methods with optical recording were employed. The identity of the reaction products was in most cases confirmed by their isolation in the solid phase. The studies showed that the stability of the [Tc2X8]3 ions (where X = Cl, Br, or I) in aqueous solutions is determined by the sum of competing processes acid hydrolysis complex formation with subsequent disproportionation and dissociation of the M-M bonds, and oxidative addition of atmospheric oxygen to the Tc-Tc multiple bond. 

Exhaustive studies on well-defined systems are rather scarce (4) nevertheless 3 systems thoroughly analyzed by independant research groups are of outstanding interest a) the quaternization of polyvinylpyridines by alkyl halogenides (20-25) b) the chlorination of polyethylene (13,26-28) c) the basic or acid hydrolysis of PMMA (29-31). On the other hand, neighbouring groups effects have been quantitatively taken into account for the kinetic analysis of periodate oxidation of amylose (32,33). 

The next example is 1,3-dibenzoylurea (4.222), a diacetylated linear urea. The hydrolysis kinetics and enzymatic cleavage of 1,3-dibenzoylurea together with various other /V-acylbenzamides were studied to assess the suitability of these compounds as prodrugs for the amido group [113]. At pH 7.4 and 37°, 1,3-dibenzoylurea was hydrolyzed quantitatively to benzoic acid and N-benzoylurea (4.223) with a tm value of 39 h. Since the hydrolysis of 1,3-di-benzoylurea was not catalyzed by human plasma, it was concluded that the acyclic diureide structure is not appropriate in prodrug design. 

In the reverse direction, a proton may be effective by aiding ring-opening directly or via a reactive protonated species. It may intervene with the ring-opened species. A splendid example of these effects is shown in the acid hydrolysis of ferrioxamine B (9). Four stages can be separated and the kinetics and equilibria have been characterized by stopped-flow and rapid-scan spectral methods. 

Kinetics of the acid hydrolysis of A-alkenyl derivatives of phenoxazine, phenoth-iazine, and carbazole in aqueous dioxane suggest an ASe2 mechanism, based on the activation parameters and isotope effects. ... 

The kinetics and mechanism of the acid hydrolysis of tris[4-(2 -phenylisopropyl) phenyl] phosphate (249) have been reported. 

Kinetic studies of the acid hydrolysis of iV-alkyl dithiocarbamates (372) have been reported. " The tertiary amine-catalysed addition of CS2 (373) to 1,2-diaminobenzene (375) involves initial formation of the zwitterionic adduct (374), which then reacts with the diamine (375) to yield 2-mercaptobenzimidazole (376). ... 

In a sediment system, the hydrolysis rate constant of an organic contaminant is affected by its retention and release with the sohd phase. Wolfe (1989) proposed the hydrolysis mechanism shown in Fig. 13.4, where P is the organic compound, S is the sediment, P S is the compound in the sorbed phase, k and k" are the sorption and desorption rate constants, respectively, and k and k are the hydrolysis rate constants. In this proposed model, sorption of the compound to the sediment organic carbon is by a hydrophobic mechanism, described by a partition coefficient. The organic matrix can be a reactive or nonreactive sink, as a function of the hydrolytic process. Laboratory studies of kinetics (e.g., Macalady and Wolfe 1983, 1985 Burkhard and Guth 1981), using different organic compounds, show that hydrolysis is retarded in the sohd-associated phase, while alkaline and neutral hydrolysis is unaffected and acid hydrolysis is accelerated. 

Acid-catalyzed hydrolysis kinetics are described by the expression... 

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