Influence of n-butyl and n-hexyl alcohols in the dehydrohalogenation of DDT in cationic micelles of n-cetyl-N,N,N-trimethylammonium bromide, chloride, and hydroxide

An Improved Method for the Flow-Injection Determination of Iodine Using the Luminol Chemiluminescence Reaction in a Reversed Micellar Medium of Cetyltrimethylammonium Chloride in 1-Hexanol-Cyclohexane

To eliminate the use of chlorinated hydrocarbons, we have improved the method for the flow-injection (FI) determination of iodine based on the chemiluminescence reaction of iodine with luminol in a chloroform-free reversed micellar medium of the surfactant cetyltrimethylammonium chloride (CTAC) using a mixture of 1-hexanol-cyclohexane as a bulk solvent. The FI procedure used simply involves the mixing of an iodine solution in cyclohexane with the chemiluminescent reagent solution of luminol in the reversed micellar medium of CTAC in 0.38 M 1-hexanol in cyclohexane/water (buffered with sodium carbonate). The optimum conditions for the iodine determination were evaluated and a detection limit (DL) of 0.05 ng cm(-3) iodine was achieved. The calibration graph obtained was linear with a dynamic range from the DL to 10 ng cm(-3) iodine. The relative standard deviations (n=5) observed at all concentrations within the linear range were less than 2.5%. The improved FI method is rapid and equally sensitive like the original one and was found to be suitable for the determination of trace iodine.

Influence of the addition of alcohol on the reaction methyl-4-nitrobenzenesulfonate + Br(-) in tetradecyltrimethylammonium bromide aqueous micellar solutions

The reaction methyl-4-nitrobenzenesulfonate + Br(-) was studied in tetradecyltrimethylammonium bromide (TTAB) aqueous micellar solutions in the absence and in the presence of various amounts of n-hexanol, n-pentanol, and n-butanol. Kinetic micellar effects provoked by the addition of the linear alcohols can be rationalized by using simple pseudophase kinetic models. The equilibrium binding constants of the methyl-4-nitrobenzenesulfonate molecules to the cationic micelles decreases when [alcohol] increases. The (k(2)(m)/V(m)) values found are practically the same for the different TTAB-alcohol micellar solutions studied, independent of the nature and concentration of the alcohol present in the reaction medium. This has been explained by considering the balance of two factors operating on reactivity in opposite ways: (1). an increase in the volume of the micellar interfacial region upon increasing alcohol concentration, and (2). a decrease in the polarity of the interfacial region as the amount of alcohol present in the micellar solutions increases.

Kinetic Micellar Effects in Tetradecyltrimethylammonium Bromide–Pentanol Micellar Solutions

The reactions 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane + OH(-) and 2-(p-nitrophenyl)ethyl bromide + OH(-) were studied in tetradecyltrimethylamonium bromide, TTAB, and TTAB-pentanol micellar solutions. The influence of changes in the surfactant concentration as well as changes in the hydroxide ion concentration on the observed rate constant was investigated. If changes in the cmc and ionization degree provoked by the presence of the different amounts of n-pentanol in the micellar solutions are taken into account, the experimental kinetic data can be rationalized quantitatively by using the PIE model. Assuming that the ion-exchange equilibrium constant, K(OH(-)/Br(-)), for the competition between the bromide and the hydroxide ions in all TTAB and in TTAB-pentanol micellar solutions studied is the same, a good agreement between the theoretical and the experimental kinetic data was found in all the micellar media for the two processes studied. This assumption was checked by experimentally determining the ion-exchange equilibrium constant K(OH(-)/Br(-)) in TTAB and TTAB-pentanol micellar solutions through a spectroscopic method, results showing that the presence of n-pentanol does not affect substantially the value of K(OH(-)/Br(-)). The second-order rate constants obtained from the fittings decrease slightly when the amount of pentanol increases, being greater than that in aqueous solution. This acceleration can be explained considering that micelles accelerate the reactions in which the charge is delocalized in the transition state.

The complete dechlorination of DDT by magnesium/palladium bimetallic particles

The complete dechlorination of 1,1-bis(4-chlorophenyl)-2,2,2-trichloroethane (DDT) by a magnesium/palladium bimetallic system has been accomplished. The reaction takes place under ambient temperature and pressure and mild reaction conditions requiring only 0.25 g of magnesium and 0.3% palladium (wt/wt) to drive the dechlorination of 100 microg DDT (50 ppm in 2 ml). The process is both rapid and complete requiring less than 10 min to attain total dechlorination within the detection limit (approximately 10 pg for DDT) of electron capture detection gas chromatography (GC-ECD). The major product formed, as deduced from mass spectrometry (GC-MS) is the hydrocarbon skeleton, 1,1-diphenylethane. This technology may allow for the development of an economic and environmentally benign method of DDT remediation.