Quaternary ammonium compounds, degradation

Acids such as sulfuric or nitric acids or bases such as sodium hydroxide may catalyze the hydrolysis of PET. It has been demonstrated that the rate of alkaline PET hydrolysis increases in the presence of quaternary ammonium compounds.26 27 Niu et al.26 reported an increase in the rate of alkaline PET degradation in the presence of dodecylbenzyldimethylammonium chloride at 80°C. Polk et al.27 reported increases in the rate of sodium hydroxide depolymerization of PET in the presence of trioctylmethylammonium chloride, trioctyl-methylammonium bromide, and hexadecyltrimethylammonium bromide at 80° C. 

Taking into consideration its physico-chemical properties, removal efficiencies, low biodegradability, predicted environmental levels, toxicity, and the need to provide sufficient safety margins for aquatic organisms, the demand for alternative cationic surfactants arose. Since 1991, DTDMAC has been replaced in some European countries due to producer s voluntary initiatives with new quaternary ammonium compounds, the esterquats. These contain an ester function in the hydrophobic chain (Table 1.3) that can be easily cleaved, releasing intermediates that are susceptible to ultimate degradation [24-26]. The effects of the phasing-out and replacement of DTDMAC can be demonstrated by the results of a Swiss study, where the surfactant... 

Tlie neurotransmitter acetylcholine is both a quaternary ammonium compound (see Box 6.7) and an ester. After interaction with its receptor, acetylcholine is normally degraded by hydrolysis in a reaction catalysed by the enzyme acetylcholinesterase. This enzyme contains a serine residue that acts as the nucleophile, hydrolysing the ester linkage in acetylcholine (see Box 13.4). This effectively acetylates the serine hydroxyl, and is an example of transesterification (see Section 7.9.1). For continuation of acetylcholine degradation, the original form of the enzyme must be regenerated by a further ester hydrolysis reaction. 

Most uses of quaternary ammonium compounds can be expected to lead to these compounds eventual release into wastewater treatment systems except for those used in drilling muds, Useful properties of the quaternaries as germicides can make these compounds potentially toxic to sewer treatment systems. It appears, however, that quaternary ammonium compounds are rapidly degraded in the environment and strongly sorbed by a wide variety of materials. 

Many cosmetics, paints, ointments, foods, shampoos, and medicines contain preservatives to combat biological degradation. Toxic chemicals used as preservatives include mercury compounds, formaldehyde, methyl and propyl p-aminobenzoic acids, butylated hydroxyanisol, butylated hydroxytoluene, benzoic acid, and quaternary ammonium compounds. 32 ... 

The alkaline hydrolysis of PET involves treating the polyester with an aqueous solution of sodium hydroxide (4-20 wt%) under pressure at temperatures between 200 and 250 °C for periods of several hours.53,54 Under these conditions the sodium salt of TPA is formed and by acidification TPA is recovered from the solution as a precipitate. It has been observed that the rate of the PET alkaline hydrolysis increases in the presence of quaternary ammonium compounds. Thus, Niu et al.55 have reported on the alkaline degradation of PET fibres with addition of dodecylbenzyldimethylammonium chloride (DBDMAC) into the reaction mixture. A sharp increase in the PET hydrolytic degradation at 80 °C was observed with DBDMAC concentrations in the range 0-1.0 g/1, especially for the least crystalline fibres. The authors concluded that the rate enhancement by quaternary ammonium compounds occurs preferentially on the amorphous regions of the PET fibres. 

Hofmann degradation usually occurs with -elimination (El reaction). Wittig and Polster85 86 discovered a variant in which quaternary ammonium compounds are converted by strong bases such as phenyl- or butyl-lithium into olefins, by way of ylides, with intramolecular cw-elimination 87... 

Carbon isotope effects (kyjku) have been measured for both the beta and alpha carbon atoms in some Hofmann degradations of quaternary ammonium compounds (Table 5). Three methods were used to determine the isotope effects (a) comparison of molar specific activity of reactant remaining after a measured extent of reaction, (b) comparison of molar specific activity of the... 

Selecting an appropriate microbicide one has always to take into consideration the pH of the medium to be protected. Degradation/hydrolysis of the microbicide may occur at certain pH values. There are microbicides which are effective only within certain pH ranges (optimum pH), e.g. glutaraldehyde (III.2.3), acids (III.6), phenolics (III.5), quaternary ammonium compounds (III.16.1). 

Preservation of a water-based packer fluid. The role of the biocide in a packer fluid is to prevent the degradation of the organic polymer and to prevent the growth of potentially harmful microorganisms once the fluid is in the annular space. The biocide should have long lasting preservative qualities, be compatible with the other components of the fluid, and be tolerate of the conditions it will see once the fluid is in-place. Commonly used biocides include quaternary ammonium compounds, glutaraldehyde and isothiazolone. 

The isocyanurate reaction occurs when three equivalents of isocyanate react to form a six-membered ring, as shown in the fifth item of Fig. 1. Isocyanurate linkages are usually more stable than urethane linkages. Model compound studies show no degradation of the trimer of phenyl isocyanate below 270°C [10,11]. Catalysts are usually needed to form the isocyanurate bond. Alkali metals of carboxylic acids, such as potassium acetate, various quaternary ammonium salts, and even potassium or sodium hydroxide, are most commonly used as catalysts for the isocyanurate reaction. However, many others will work as well [12]. 

Esterquats, quaternary carboxyalkyl ammonium compounds, have been developed as substitutes for the quats, especially DTDMACs which are applied as softeners in household products because they are resistant to degradation [42] and toxic [43,44]. Today, the esterquats are preferentially used (see Fig. 2.12.1(b)). As previously noted, the detection of all types of esterquats in environmental samples is difficult because of their tendency to adsorb at surfaces. Even in the inflows of wastewater treatment plants (WWTP) it is extremely difficult to find these compounds, which are reduced in toxicity [45] compared with the DTDMACs. One reason is that these carboxyalkyl ammonium compounds are not very stable in the environment. A second reason is that these compounds are not stable during the ionisation process. 

EMDE DEGRADATION. Modification of the Hofmann degradation method for reductive cleavage of the carbon-nitrogen bond by treatment of an alcoholic or aqueous solution of a quaternary ammonium halide with sodium amalgam. Also used as a catalytic method with palladium and platinum catalysts. The method succeeds with ring compounds not degraded by the Hofmann procedure. 

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