Hydrolysis accelerated with acid

ASA undergoes the normal reactions of acid anhydrides. Of particular interest in conjunction with sizing is the reaction with alcoholic hydroxy groups to yield an ester, and the hydrolysis with water. Both reactions occur in the papermaking system. ASA is highly reactive, and the reactions proceed rapidly and irreversibly. Although this would provide satisfactory development of sizing on a paper machine, the hydrolysis of ASA is undesirable. The hydrolysis accelerates with pH, time, and temperature and leads to deposits and runnabiHty problems on the paper machine. In order to Hmit the hydrolysis of ASA emulsions, the pH can be lowered immediately after the emulsification by addition of aluminum sulfate. 

Manufacture of Fatty Acids and Derivatives. Splitting of fats to produce fatty acids and glycerol (a valuable coproduct) has been practiced since before the 1890s. In early processes, concentrated alkaU reacted with fats to produce soaps followed by acidulation to produce the fatty acids. Acid-catalyzed hydrolysis, mostly with sulfuric and sulfonic acids, was also practiced. Pressurized equipment was introduced to accelerate the rate of the process, and finally continuous processes were developed to maximize completeness of the reaction (105). Lipolytic enzymes maybe utilized to spHt... 

In general, hydrides react exothermically with water, resulting in the generation of hydrogen. This hydrolysis reaction is accelerated by acids or heal and. in some instances, by catalysis. Because the flammable gas hydrogen is formed, a potential fire hazard may result unless adequate ventilation is provided. Ingestion of hydrides must be avoided because hydrolysis ill form hydrogen could result in gas embolism. 

The rates of hydrolysis of amino acid esters or amides are often accelerated a million times or so by the addition of simple metal salts. Salts of nickel(n), copper(n), zinc(n) and cobalt(m) have proved to be particularly effective for this. The last ion is non-labile and reactions are sufficiently slow to allow both detailed mechanistic studies and the isolation of intermediates, whereas in the case of the other ions ligand exchange processes are sufficiently rapid that numerous solution species are often present. Over the past thirty years the interactions of metal ions with amino acid derivatives have been investigated intensively, and the interested reader is referred to the suggestions for further reading at the end of the book for more comprehensive treatments of this interesting and important area. 

Menger et al. synthesized a Ci4H29-attached copper(II) complex 3 that possessed a remarkable catalytic activity in the hydrolysis of diphenyl 4-nitrophenyl phosphate (DNP) and the nerve gas Soman (see Scheme 2) [21], When 3 was used in great excess (ca. 1.5 mM, which is more than the critical micelle concentration of 0.18 mM), the hydrolysis of DNP (0.04 mM) was more than 200 times faster than with an equivalent concentration of the nonmicellar homo-logue, the Cu2+-tetramethylethylenediamine complex 9, at 25°C and pH 6 (Scheme 4). The DNP half-life is calculated to be 17 sec with excess 1.5 mM 3 at 25°C and pH 6. The possible reasons for the rate acceleration with 3 were the enhanced electrophilicity of the micellized copper(II) ion or the acidity of the Cu2+-bound water and an intramolecular type of reaction due to the micellar formation. On the basis of the pH(6-8.3)-insensitive rates, Cu2+-OH species 3b (generated with pK3 < 6) was postulated to be an active catalytic species. In this study, the stability constants for 3 and 9 and the thermodynamic pvalue of the Cu2+-bound water for 3a —> 3b + H+ were not measured, probably because of complexity and/or instability of the metal compounds. Therefore, the question remains as to whether or not 3b is the only active species in the reaction solution. Despite the lack of a detailed reaction mechanism, 3 seems to be the best detoxifying reagent documented in the literature. 

The amides are derived from oxazolidinones and yield "Z"-enolates with high stereoselectivity. The alkylating agent reacts in both cases from the side that is opposite to the side of the substituent highlighted in red. Alkaline hydrolysis accelerated by hydrogen peroxide proceeds with retention of configuration and yields enantiomerically pure a-alky-lated carboxylic acids X t and X 2 are the chiral amide groups. 

The reason for interest in the details is that the acceleration with I was very large compared with that which had been observed previously with cyclodextrin reactions. In fact, in a system with 60% DMSO-40% H20 and hydroxide supplied by a buffer that in H20 would have a pH of 6.8, the Vmax was 0.18 sec-1. This represented an acceleration 750,000-fold compared with hydrolysis by the hydroxide ion alone in this same buffered medium in the absence of cyclodextrin. The product of this reaction was the ferrocinnamate ester of cyclodextrin, which then hydrolyzed slowly in a second step to the salt of the free acid. 

Catalytic action of cationic surfactants (quaternary pyridinium chlorides) in the hydrolysis of 2,4-dinitrochlorobenzene and in the reaction with aniline in a foam has been observed as well [109,110]. For example, in the presence of quaternary pyridinium bases, the rate constant of the hydrolysis in a foam increased from 1.4210 7 (without the surfactant) to 2.7 1 O 2 m3 mol 1 s 1 (with surfactant) which is greater than in the case of catalysis in micelles (8.3-10 6 m3 mol 1 s"1). A similar acceleration of acid hydrolysis occurs also in the presence of anionic surfactants [112,113]. 

Two different types of enzymatic time-temperature integrators are described. The first, under the tradename of I-point, is based on a lipase-catalyzed hydrolysis reaction (125). The lipase is stored in a nonaqueous environment containing glycerol. The indicator contains two components that are mixed when the indicator is activated. The operating principle is as follows Upon activation, two volumes of reagents are mixed with each other. Lipase is thereby exposed to its substrate, here a triglyceride. At low temperatures there will be almost no hydrolytic reaction. As the temperature increases, hydrolysis accelerates and protons are liberated. A pH indicator is dissolved in the system. The indicator is selected to shift color after a certain amount of acid has been liberated by the enzyme-catalyzed process. Since the catalytic activity is influenced both by temperature and time, this indicator strip is said to be a time-temperature integrator. 

Smit followed the equilibration of acetic acid and aqueous hydrogen peroxide by titrating the hydrogen peroxide with permanganate, which does not react with peracetic acid. In dilute solution at 0° the hydrolysis of peracetic acid is so slow that one can titrate the peracid by iodimetry. At room temperature, equilibrium is reached only after several days. The reaction is markedly accelerated by 1% sulfuric acid or by warming to 70°. Thus Fernholz heated a mixture of 30 ml. of 30% hydrogen peroxide and 300 ml. of acetic acid for 5 hrs. at 70° and then let the solution stand for 2 days at ambient temperature and obtained a solution containing 2-2.5% of peracetic acid. 

These represent hydrolysis of diethyl ether, synthesis of iV-mono-ethylaniline from alcohol and aniline, and dehydration of alcohols to olefins. Promoting the catalyst differently effects these reactions, in accord with the multiplet theory. Thus, the addition of the oxides of Fe, Ni, and Zn accelerates the first reaction and slows down the second and the third one 351). Incidentally, as has been found by the author and Sokolova 352), Nb20s and TaEOs are good catalysts in obtaining monoethylamine as well as in esterification of alcohols with acids, and they carry out the condensation of acetaldeyde into crotonaldehyde 353). 

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