The micellar effects of 1-cetyl-2-methyl-3-(2-hydroxyiminopropyl)imidazolium and 1-cetyl-3-hydroxyiminomethylpyridinium halides in acyl transfer reactions (phosphoryl, phosphonyl, and toluenesulfonyl) were investigated. Variation of the nature of the head group does not lead to change in the reactivity of the oximate group, while the nucleophilicity follows the basicity of the functional fragment. The increase of the observed reaction rates during transfer of the disintegration of the substrates from water to the micellar pseudophase is due both to concentration of the reagents and to change in the reactivity of the oximate group. The new detergent 1-cetyl-2-methyl-3-(2-hydroxyiminopropyl)imidazolium chloride is one of the most effective functional surfactants in the decomposition of organophosphorus compounds. Key words: functional surfactants based on pyridine and imidazole, nucleophilicity, micellar effects.Functional surfactants containing an a-nucleophilic fragment in the head group are usually characterized both by high nucleophilic reactivity and by effective solubilization of electrically neutral polar substrates, including excotoxicants of organophosphorus type [1-10]. During the design of new functional detergents an important role is played by the true solubility of the surfactant in water, the basicity of the functional group, and its reactivity. However, the introduction of the functional fragment often leads to a decrease in the solubility of the surfactant in water [1,2,5,8]. Therefore, during study of the micellar effects of such detergents, as during their use in systems for the decomposition of excotoxicants, it is necessary to introduce an inert surfactant -a co-detergent, and this makes the system multicomponent and less attractive from the practical standpoint. The nucleophilicity of functional detergents can be predicted on the basis of the reactivity of analogs not forming micelles [1,2,[7][8][9][10]. This opens up the possibility of specific modification of the structure of the surfactant with the aim of producing compounds with the required level of nucleophilicity. This is the approach that we used during the creation of functional detergents based on imidazole [7][8][9]. With variation of the position of the oximate group in the series of hydroxyiminomethyl-1-cetylpyridinium halides the variation of the observed rates of decomposition of 4-nitrophenyl diethyl phosphate corresponds likewise to the variation of the basicity of the a-nucleophilic fragment in hydroxyimino-1-methylpyridinium halides [1]. It is important to note that for oximes that are not micelle-forming compounds there is a single Brönsted relationship onto which the points for oximes containing both an imidazole ring and a pyridinium ring fit [11]. In so far as analysis of the experimental results in [1] in terms of the existing models for description of micellar effects was not made 0040-5760/08/4402-0093

We consider the factors responsible for the nucleophilicity and micellar effects of surfactants based on imidazole and pyridine, functionalized by an oximate group. The reactivity of the functional detergents, as for oximes not forming micelles, is described by a nonlinear Brönsted plot with an inflection point at the pK a of the oximate group,~8.5-9.0. The major contribution to the increase in the degradation rate of ecotoxins by supernucleophilic systems based on functional surfactants (by a factor of 10 2 to 10 3 compared with the methyl analogs) comes from the effect of concentration of the substrate. The established characteristics make possible targeted modification of the surfactant structure and obtaining detergents with a specified reactivity level.Design of reagents for fast and irreversible degradation of ecotoxins, including organophosphorus compounds (OPCs), requires designing systems having both high nucleophilicity and high solubilizing ability relative to hydrophobic substrates. Using a-nucleophiles as the basis for such systems makes it possible to provide anomalously high rates of nucleophilic cleavage of organophosphorus compounds [1][2][3]. The special interest in study of the reactivity of typical representatives of this class of reagents, oximate ions (Ox -), is first of all due to the fact that effective antidotes are found among them: re-activators of the acetylcholinesterase inhibited by organophosphorus compounds, the search for which is being vigorously pursued at the moment [4]. There is no doubt that the level of biological activity of the antidotes is directly connected with the high reactivity of Ox -ions [4][5][6][7]. Detailed kinetic analysis of their behavior suggests that the nucleophilicity of Ox -ions cannot be described in terms of a single Brönsted equation [4][5][6][7]. Curvature of the Brönsted plots for reactions of Ox -ions with substrates containing electron-deficient centers and the "leveling off" of the reactivity at p a Ox K -> 8.5-9.0 may be connected with both energetically unfavorable solvation effects of the solvent, the contribution of which becomes more and more significant as the basicity of the nucleophile increases, and also with a change in the structure of the transition state [4][5][6][7]. Nevertheless, for the studied reaction series, it is unlikely that such a considerable change in the structure of the transition state would occur as the basicity of the Oxions increases [7].The similar character of the Brönsted plots for interaction of Ox -ions with different acyl-containing substrates clearly shows that it is hardly possible to modify the structure and synthesize an oxime whose nucleophilicity in aqueous solution 94 0040-5760/10/4602-0094

The reactivity of a-nucleophilic groups in functional detergents is comparable with those for analogous compounds which do not form micelles. Methods are proposed for the modification of surface active compounds to produce supernucleophilic systems for the decomposition of organophosphorus compounds. A new functional detergent -1-cetyl-3-(2-hydroxyiminoethyl)imidazolium chloride -is the most powerful of the investigated surface active reagents capable of achieving half lives for the decomposition of 4-nitrophenyl diethyl phosphonate and 4-nitrophenyl diethyl phosphate of £2 and 14 s respectively.Attempts to construct reagents for the effective decomposition of organophosphorus compounds, particularly exotoxicants (pesticides, war gases, etc.), is without doubt a current problem [1]. The high observed rate of reaction is important but so also is the solubilization of organophosphorus compounds which are difficult to dissolve in water. It is frequently these factors which determine attempts to modify the structures of the reagents [2, 3]. Previously we showed [3-6] that a promising direction for the solution of this problem is the creation of microheterogeneous systems based on a new class of functional surface active substances (SAS) in the composition of which imidazole ring and specific a-nucleophilic units (I-III, R = C 16 H 33 ) were included, which decomposed organophosphorus compounds -4-nitrophenyl esters of diethylphosphoric acid (NPDEP) and diethylphosphonic acid (NPDEPS) -anomalously rapidly.The micellar effects of the functional SAS result from the concentration of the substrate (S) in the micellar pseudophase and the change in the ionization rates of the a-nucleophilic unit and its reactivity on transferring the reaction from water (aq) to the 0040-5760/06/4205-0295

we should take into account not only their hydrophobic properties but also the efficiency of substrate solubilization as well as the reactivity of the oximate group in the surfactant micelles.The unflagging interest during recent decades in the synthesis and reactivity of surfactants with nucleophilic functional groups is a consequence of a number of factors. Firstly, microheterogeneous systems derived from functional detergents serve, to some extent, as models for studying the action of hydrolytic enzymes, which provides for the investigation of various features of enzymatic catalysis in simpler systems. The increase in the reaction rate in micelles of functional surfactants in comparison with water may reach factors of 10 2 -10 7 , which makes such systems comparable in efficiency with enzyme systems [1,2]. The observed effects are largely a function of the role of the microenvironment of that part of the micelles, in which the chemical reaction proceeds and the hydrophobic binding of the substrate by the micelle core [1][2][3][4]. Secondly, the intensive study of the reactivity of functional detergents has had and still has marked applied significance related to the decomposition and utilization of environmental toxicants, in particular the highly toxic esters of organophosphorus acids [1,[5][6][7][8].Modification of functional surfactants in order to obtain highly efficient supernucleophilic systems requires us to establish the factors responsible for the micelle effects of detergents. In previous work [9], we showed that, in the case of surfactants with an oximate group, nucleophilicity is directly related to the acid-base properties of the oximate group. In this instance, as in the case of oximes, which do not form micelles, the Brönsted catalysis equation is not linear and has an inflection point at pK a » 8.5-9.0 [9, 10]. Since the concentration of the substrate in the micellar pseudophase makes the major contribution to the increase in the observed reaction rate [10], the hydrophobic properties of the functional surfactants have fundamental importance in the manifestation of their micellar effects [1,[11][12][13].

Hypobromite ion, BrO(-), is an effective alpha-nucleophile that reacts rapidly with activated phosphorus(V) and sulfonate esters. The parent acid rapidly oxidizes organic sulfides and aryloxide ions. At pH 10-11 BrO(-) and HOBr coexist in water and are potentially useful as decontaminants of chlorosulfide blister agents and the phosphonyl nerve agents. Bis(dialkylamide)hydrogen dibromobromates are well characterized, stable, solids which rapidly form HOBr-BrO(-) in mildly alkaline water. Reactions of 4-nitrophenyl diethyl phosphate and phosphonate, which are simulants of the phosphonofluoridate nerve agents, and of 4-nitrophenyl tosylate, with BrO(-) are rapid (t(1/2) = 60-700 s) with 0.1 M BrO(-), under conditions in which oxidations of organic sulfides are too fast to be followed by conventional methods.