Neutralization Chemical Hydrolysis

Neutralization (chemical hydrolysis) Low-temperature technology for hydrolysis of neat chemical agents and binary precursors... 

Carbamates are subject to chemical hydrolysis, which takes place relatively slowly under neutral or acid conditions, but more rapidly under alkaline conditions. 

Chemical detoxification uses oxidation, reduction, neutralization, and hydrolysis to reduce the toxicity of the contaminants. The basic theory is similar to that of treating pumped groundwater. 

R = Me, Et, and PhCH2, respectively Fig. 8.1). In 80% human plasma at pH 7.4 and 37°, these model prodrugs were hydrolyzed with tm values of 3.5, 16, and 2.6 min, respectively [59]. Such rates of enzymatic hydrolysis are comparable to those of various carbamoylmethyl esters of benzoic acid (Table 8.2). It is important to note that the direct liberation of benzoic acid by Reaction a (Fig. 8.1) was severalfold faster than the competitive Reaction b. Reaction c was very slow in human plasma (tm > 100 h). In HO -catalyzed hydrolysis, the opposite regioselectivity was seen, with the terminal ester bridge being cleaved markedly faster than the central one. No data appears to be available on chemical hydrolysis at neutral pH. 

Sulfuric acid esters also undergo chemical hydrolysis, which can be acid- or base-catalyzed [170], As a rule, the former reaction is faster than the latter, the slowest rates being found around neutrality. High dependence on chemical structure is another characteristic of sulfuric acid ester hydrolysis. 

Transformation of triazines is primarily the result of degradation caused by microorganisms. However, triazines are also subject to a slow chemical degradation process known as hydrolysis. Chemical hydrolysis of atrazine, for example, is a process where the chlorine atom is removed from the atrazine molecule and replaced with a hydroxyl (OH) group. Chemical hydrolysis is relatively fast in acidic and alkaline soils, but it is relatively slow in neutral soils. In neutral soils, the rate of chemical hydrolysis of triazines increases when the triazine is adsorbed on the surfaces of soil particles. Hydroxytriazines, the products of chemical hydrolysis, are very strongly held by soil surfaces and hence move very slowly in soils. The hydroxytriazines have no biological activity. 

Acid-Base Catalyzed Hydrolysis of Neutral Chemicals... 

The terms neutralization and hydrolysis are often used interchangeably in the literature on chemical agent demilitarization. Hydrolysis is the more appropriate term from a chemical process perspective. Neutralization is more in keeping with the notion of neutralizing and thereby rendering innocuous. It may be found in the literature to refer to hydrolysis in either aqueous or nonaqueous media. 

The reader is reminded here that NECDF uses a neutralization (caustic hydrolysis) process to destroy the bulk VX stored at the Newport Chemical Depot. An incinerator is not part of the... 

Recently, Brill and co-workers (43, 44) have isolated mutant strains of Azotobacter vinelandii which produce an inactive nitrogenase component. This component can be reactivated by treatment with the neutralized acid-hydrolysis products of other nitrogenases (which themselves become inactive on such a treatment) but not apparently with any other molybdenum enzymes. This may either reflect a difference between the cofactor in nitrogenase and other molybdenum enzymes or may be caused by the reconstitution conditions used which may not have been sufficiently varied to allow for different molybdenum oxidation states to be attained. In any event, the chemical characterization and authentication of the molybdenum cofactor should reveal some of the intimate details of the molybdenum site. 

When primary aliphatic isocyanates that show the lowest reactivity compared to secondary or aromatic isocyanates are used in combination with hydrophilic (pre-) polymers, crosslinking may be performed in aqueous solution without the use of additional crosslinkers. At neutral pH, hydrolysis of isocyanates to carbaminic acid with subsequent decarboxylation yields amines. These amines react much more rapidly than water with isocyanates, resulting in crosslinking if the functionality per macromolecule is more than two [43], This crosslinking reaction can be quenched by adjustment of the pH value. At pH values above 10, carbamate formation is faster than decarboxylation, whereas at pH values below 3 an almost quantitative protonation of the formed amino groups results in the formation of ammonium. In both cases, chemical crosslinking is prevented. 

Offidani et al. compared chemical hydrolysis with enzymatic hydrolysis utilizing hair samples obtained from heroin users. Hair samples were subjected to incubation in a solution of 1 M NaOH, then neutralized with hydrochloric acid and pH 7, 1 M phosphate buffer. Samples were also treated with a 1-mg/mL pronase solution in 0.05 M Tris buffer for 24 h at 39°C, followed by neutralization with pH 7, 1 M phosphate buffer. Both procedures yielded comparable results for morphine by RIA. 

Poly(3-hydroxybutyrate) (PHB) and its copolymer poly(3-hydroxybutyrate-co-3-bydroxyvalerate) (PHBV) are ratber resistant towards moisture and tbeir cbemical hydrolysis at neutral pH and ambient temperature proceeds slowly through random chain scission [78,79]. The rate of chemical hydrolysis decreases with increasing crystallinity [80]. There is no agreed explanation to how the copolymer composition affects the hydrolysis rate. It has been suggested that it is the crystalhnity, rather than the composition that affects the hydrolysis rate. On the other hand, PHBVs of the same crystalhnity, but different compositions (45-71 mol% HV), showed decreasing hydrolysis rates with increasing HV-content [81]. 

In this chapter, the committee briefly reviews some other applications of neutralization and hydrolysis elsewhere in the world to provide historical perspective for the technology being used in the United States to destroy recovered chemical weapons, as described in Chapter 1. Detailed descriptions and evaluations of the Russian two-stage neutralization/ bitumenization process and incineration processes follow that review. 

An industrial process must be economic and safe for the environment. The chemical hydrolysis of nitrile in acid is well known (ref. 1). Nearly all nitriles react with either basic or acid catalysts, but considerable quantities of inorganic salts are always produced as by-products. The only way to suppress these by-products is to produce the ammonium carboxylate under neutral pH and then to recover the ammonia by dissociation of the salt between the weak base and acid. Therefore, we suggest the route shown in Figure 1. 

---