Kinetic of acid hydrolysis

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. 

Cellulosic materials are quite variable from source to source, not only in cellulose, hemicellulose, and lignin content but also in the crystallinity of the cellulose. As a consequence, each natural substrate would be expected to have its own unique set of process conditions to optimize glucose yield and minimize secondary product contamination. The next section on kinetics of acid hydrolysis will examine this point. 

A considerable amount of experimentation has been done on the kinetics of acid hydrolysis of pure cellulose substrates. Little experimentation has been done on natural cellulosic materials. Typical examples of kinetic studies of acid hydrolysis of cellulose can be found in the papers of Saeman (33) and Grethlein (13). These researchers depict the acid hydrolysis process as a pseudo-first-order sequential process, with the rate constants as a function of the acid concentration raised to a power, i.e.,... 

In this book, he emphasized the importance of the microscopic and the submicroscopic structure of fibrous high polymers. The reactions of cellulose with water, aqueous alkalis, organic bases, ammonia, and strong salt solutions were all stressed. Special attention was given to various types of cellulose esters, to cellulose xanthate, and to the cellulose ethers. The oxidation of cellulose under a variety of conditions was described, as were the hydrolysis reactions. The latter included discussions on reversion and on the kinetics of acid hydrolysis. It is interesting to note that Heuser, who earlier had criticized the terms hydrocellulose and oxycellulose, and had... 

The /i.-amido-/x-carbonato complex (11) has been prepared and characterized, and the kinetics of acid hydrolysis leading to the iit>amido-/Lt-hydroxo>bis(bis(eth> ylenediamine)cobalt(III)) ion studied in detail/ Values of kobs are independent of [H" ] over the acidity range [H ] = 0.9 M to 0.01 M. The kinetics of base hydrolysis were also studied over the range [OH ] = 0.7 M to 0.025 M The results are consistent with a kinetic scheme involving a rapid preequilibrium followed by a rate-determining step resulting in a /i-amido-dihydroxo complex. 

The kinetics of acid hydrolysis of the p-methoxybenzaldehyde-O-acyloximes (7) in SDS micelles modified by BuOH has also been fitted to the PIE model [86]. The substrates differ only in their hydrophobicities, and while the acetyl derivative partitions between water and micelles, the octanoyl derivative is wholly micelle-bound. The simple PIE model fits rate data in dilute HCl [Eq. (6)], but it underpredicts observed rate constants in more concentrated acid. This increased rate was analyzed in terms of a model that does not involve a constant value of a but allows concentrations of reactive and inert ions, and Na" ", in the micellar pseudophase to increase, following Langmuir isotherms [106]. This model was reasonably satisfactory except at high 1-butanol concentration. Alternatively, the rate data in more concentrated acid can be fitted in terms of Eq. (12). 

Kinetics of acid hydrolysis of a series of pyridioraethyl-carbonyl and -TT-cyclopentadienyl derivatives of molybdenum, tungsten, manganese, and iron have been reported. In the case of the 4-pyridiomethyl derivatives the mechanism is dissociative, and may be described either as 51 1 with respect to the metal or 5 eI with respect to the carbon of the pyridiomethyl ligand. For the 3-pyridiomethyl derivatives homolysis is important. ... 

Singh, S.K. Kinetics of acid hydrolysis of x-carrageenan as determined by molecular weight (SEC-M, LLS-RI), gel breaking strength, and viscosity measmements. Carbohydrate Polymers, 23 (1994) 89—103. 

In recent works, we have studied the kinetics of both hydrolysis and degradation of a acrylamide-acrylic acid copolymer containing 17% of acrylate groups. The purpose of this paper is to give some predictions of the thickening properties evolution based upon semi-empirical viscosity laws. 

The kinetics of the hydrolysis of compound 33 was studied (86MI2). The hydrolysis of aminomethylenemalonates (1441) under acidic conditions gave the corresponding amines (68MI1). 

The kinetics of the hydrolysis reactions of 4-amino-2-phenethyl- (354 R = PhCH2CH2) and 4-amino-2-cyclohexyl-2,3-dihydro-3-oxo-l,2,5-thiadiazole 1,1-dioxide (354 R = CeHii) have been investigated in the pH range 1-10 at 24-73 °C. The products are the corresponding new compounds 2-anuno-2-[(A -substituted-sulfamoyl)imino]acetic acid salts (355 R = PhCH2CH2 or CeHn) which hydrolyse further, in a slow reaction, to the sulfamide and oxalic acid derivatives. ... 

Another feature of the kinetics of acid-catalysed hydrolysis of amides may be of relevance in connection with the nature of the protonated cation, that is the rate maximum which is found at 3-6 M acid for all amides. The usual interpretation of this is that increasing... 

For 3-aryl-anhydro-5-hydroxy-l,2,3,4-oxatriazolium hydroxides (4 R = Ar) the rate of hydrolysis is dependent not only on acidity but also on the nature of the acid and the ionic strength <82JCS(P2)70i>. Although the kinetics of the hydrolysis of 3-substituted anhydro-5-hydroxy-l,2,3,4-oxatriazolium hydroxides (4) is known, detailed mechanistic aspects, such as the migration of aryl groups from N-3 in (4 R = Ar), remain unexplained. 

Friedman, M., McDonald, G. M., Haddon, W. F. (1993). Kinetics of acid-catalyzed hydrolysis of carbohydrate groups of potato glycoalkaloids a-chaconine and a-solanine. J. Agric. Food Chem., 41, 1397-1406. 

It remains unclear whether or not the rate of cleavage of the gly-cosyl bond in sugar nucleotides depends upon the structure of the nucleotide residue, and the same uncertainty is true for other reactions that affect the glycosyl group no systematic kinetic studies have been reported. However, it may be noted that there appears to be no essential difference between the rates of acidic hydrolysis of the 5 -(a-D-glucopyranosyl pyrophosphates) of uridine and N3-methyluridine, 331... 

Kinetics of the Hydrolysis of Orthoesters A General Acid-Catalyzed Reaction 57... 

Kinetic investigations of amide hydrolysis showed that the rate of hydrolysis in basic media is proportional to the concentration of amide and hydroxide ion. Similarly, early work180-183 on the acid-catalysed hydrolysis of amides showed that the rate of acidic hydrolysis is, in general, proportional to the concentration of amide and hydroxonium ion. In several acidic hydrolyses, however, a maximum is observed in the pH-rate profile at 3-6 pH units, a phenomenon first reported by Benrath184 and since supported by other workers185"190. This behaviour of amides is in contrast to the hydrolysis of nitriles whose rate constant increases continuously with the hydrogen ion concentration191. 

The kinetics for acid hydrolysis of L3Co(OH)3CoL33+ ions have been reported for L3 = (NH3)3, dien, tach, and tacn (132, 185-187, 371). The ammonia system has been studied in detail (132,186,187, 371), and it is now generally accepted that the kinetic data should be interpreted in terms of Scheme 7. 

The kinetics of the hydrolysis of acetic anhydride in dilute hydrochloric acid, Scheme 1.9, may be described by a single pseudo-first-order rate constant, k, and the investigation by calorimetry combined with IR spectroscopy, as we shall see in Chapter 8, provides a clear distinction between the heat change due to mixing of the acetic anhydride into the aqueous solution and that due to the subsequent hydrolysis. This model of the reaction is sufficient for devising a safe and efficient large-scale process. We know from other evidence, of course, that the reaction at the molecular level is not a single-step process - it involves tetrahedral intermediates - but this does not detract from the validity or usefulness of the model for technical purposes. 

The present study investigated the inhibition of Saccharomyces cerevisiae by the liquid hydrolysate and the kinetics of enzymatic hydrolysis of the solid components produced by the pretreatment of aspen wood and corn stover by liquid hot water and hot carbonic acid. Inhibition of yeast was determined by measuring the rate of glucose consumption by yeast growing in hydrolysates produced at various reaction severities. The enzymatic hydrolysis rates of pretreated solids was determined by measuring rates of sugar accumulation of enzyme-digested pretreated solids. 

We have therefore studied the kinetics of cellulose hydrolysis and glucose decomposition under extremely dilute H2S04 (0.05-0.2 wt%, pH 1.5-2.2) and high-temperature (200-230°C) conditions. Our ultimate goal is to better understand the kinetics of dilute-acid hydrolysis of biomass and develop promising acid hydrolysis processes that can give both high... 

The current method for the hyalurcnidase assay described in the United States Pharmacopeia (USP) [132] is based on the inability of hydrolyzed potassium hyalurooate to form a complex precipitate with proteins from added serum, reflected in a decreased turbidity of the reaction mixture (measured after 30 min). The method is, from the enzymological point of view, not well defined since it does not actually evaluate the kinetics of the hydrolysis of the substrate. An assay with end-point determination is only valid if the reaction rate does not change during this reaction time. We found that only with the two lowest test concentration (0=15 nnH 0=3 PJ) was this condition fulfilled, while with the three higher test concentrations the reaction is not linear. Commercially available hy aluronates can be contaminated with chondroitln sulfates. They are more acidic than... 

When the kinetics of the hydrolysis of rac-pantolactone by Lph were investigated a decrease in the reaction velocity was observed this was found to be because of competitive inhibition by D-pantolactone (Eq. 1) [19] and slight product inhibition of Lph. Under the same conditions of pH (7.5) and temperature (30 °C), l-pantolactone was completely converted to L-pantoic acid. This is certainly a disadvantage of Lph-catalyzed kinetic resolution, because space-time yields come to levels as low as 6 g L 1 h 1. 

Sydnones and sydnonimines are stable in acid solution at room temperature but are subject to rapid hydrolysis in basic solution. The kinetics of alkaline hydrolysis of 3-alkylsydnonimines was found to be third order, first order in sydnonimine and second order in hydroxide ion at pH 8 (63ZOB3699). The mechanism shown in Scheme 3 rationalizes the kinetics of the hydrolysis. The nitrosonitrile (29) is hydrolyzed to the nitrosoamide at higher pH (65KGS328). The rate law for 3-arylsydnonimines is fc[syd][OH-]. 

Since 1,3-dioxolanes are cyclic acetals it follows that they are readily hydrolyzed by acids. The kinetics of this hydrolysis have been extensively reviewed (57MI43000). The acidic hydrolysis of 1,3-oxathiolanes is of theoretical importance in that there are conflicting reports as to whether the C—O or the C—S bond is ruptured first. It is known that protonation of 2,2-dimethyl-l,3-oxathiolane in fluorosulfonic acid leads to the exclusive formation of dication (68) (71BSF541). Based on deuterium labelling studies, however, the present data suggest that the C—O bond is broken first in aqueous systems (72TL2569). 

Interest in the kinetics of alkaline hydrolysis of esters in DMSO + water mixtures was stimulated by the observation that the rate constant often increased gradually as x2 increased. This is observed, for example, in the alkaline hydrolysis of ethyl acetate. For higher esters, e.g. ethyl p-nitrobenzoate, the rate constant drops slightly at low x2 but then rises again until k/k x2 = 0) > 1 (Tommila, 1964). The rate of alkaline hydrolysis of esters of benzoic acid is accelerated when DMSO is added (Tommila and Palenius, 1963), as also is the rate of alkaline hydrolysis of 2,4-dinitrofluorobenzene. In the latter case the effect is less dramatic because the rate constant for spontaneous hydrolysis also increases (Murto and Hiiro, 1964). The rate constants also increase when DMSO is added to aqueous solution for reactions between hydroxide ions and benzyl chloride (Tommila... 

The kinetics of acid-catalysed ester hydrolysis in DMSO + water mixtures (Tommila and Murto, 1963) is similarly complex, reflecting the importance of intercomponent association. Nevertheless the analysis is made more difficult because the mechanism of reaction involves at least two stages (Wolford, 1964). 

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