Non-micellar Medium Research Articles

New Protocol for Oxidation in Water: Micellar Oxidation Systems Composed of Novel Amphiphilic Hydroperoxides

A series of novel amphiphilic hydroperoxides, alpha-alkoxyalkyl hydroperoxides (alpha-AHPs) and their related hydroperoxides, were designed and prepared with the intention of developing new oxidizing agents bearing a micelle-forming character in water. After their fundamental physical and interfacial properties were elucidated, both oxidation of benzyl sulfide and epoxidation of geraniol promoted by these hydroperoxides were investigated in detail under various conditions. Effective oxidation ofbenzyl sulfide to the corresponding sulfoxide was achieved in aqueous micellar systems composed of alpha-AHPs la-d and a catalytic amount of MoO2(acac)2 at 30 degrees C. Up to 100% conversion was observed under the optimum conditions. In the case of epoxidation of geraniol in water, the corresponding 2,3-epoxide was selectively formed in good yields. Because the conversion of each substrate in the micellar systems was higher than that in nonmicellar media, the solubilization of substrates into micelles was certainly effective in promoting oxidations of insoluble substrates in aqueous media. Micellar oxidation systems composed of novel amphiphilic hydroperoxides afford a new protocol in order to derive safer conditions under which these reactions may be carried out.

Flow-injection spectrophotometric determination of nicotinic acid in micellar medium of N-cetylpyridinium chloride

A simple flow-injection (FI) method with spectrophotometric detection at 440 nm is proposed for the determination of nicotinic acid, which is based on the formation of a polymethine dye at room temperature. In the FI system, nicotinic acid is hydrolyzed with 0.2 M cyanogen bromide at pH 5 (acetic-acetate buffer) in a non-micellar medium. The glutaconic aldehyde formed is injected into a stream containing 0.1 M aniline at pH 7, in a 0.1 M micellar medium of the cationic surfactant N-cetylpyridinium chloride (NCPC), to produce the polymethine. The performance of NCPC is compared with that of other surfactants: cetyltrimethylammonium bromide (CTAB, cationic), sodium dodecyl sulphate (anionic), and Triton X-100 (non-ionic). In the presence of NCPC and CTAB, the coupling reaction increases its sensitivity in ×3.3 and ×2.6 factors, respectively. This effect is explained by the higher concentration of glutaconic aldehyde and aniline on the micelle surface due to electrostatic attraction and hydrophobic association to the cationic surfactant. The dispersion coefficient of the FI system was D=2.4, and the sampling rate, 95 samples per hour. The limit of detection was 1.2×10 −6 M and the coefficient of variation 1.0 and 0.8% for 1×10 −5 and 1×10 −4 M nicotic acid, respectively. The optimized manifold was applied to the determination of commercial pharmaceuticals containing nicotinic acid, with recoveries in the 96.7–101% range.

Flow-Injection Analysis of Pyridoxine Hydrochloride by Coupling with the Diazonium Ion of p-Sulfanilic Acid

ABSTRACT A flow-injection (FI) procedure is proposed for the determination of pyridoxine. In the FI manifold, a solution of p-sulfanilic acid in a micellar medium of N-cetylpyridinium chloride (NCPC) was diazotized with nitrite in acidic medium, and the pH was then adjusted to 7 with monohydrogenphosphate; the sample was injected into this stream and the absorbance measured at 450 nm. The surfactant catalyzed the derivatization reaction and enhanced the sensitivity of the FI procedure. Consequently, the addition of toxic mercury(II) acetate, used in the conventional procedure performed in non-micellar medium, was no longer required. The signals obtained with other surfactants, such as sodium dodecyl sulfate or Triton X-100, were smaller. Under optimized FI conditions, the calibration curve was linear from the limit of detection, 5×10−5 M, up to 1×10−3 M, and the sampling frequency was 60 h−1. The procedure was applied to the determination of pyridoxine hydrochloride in commercial pharmaceutical preparations, with recoveries close to 100%.

Spectrophotometric Determination of B6 Vitamins by Coupling with Diazotized P-Sulfanilic Acid in Micellar Medium of N-Cetylpyridinium Chloride

The water-soluble B6 vitamins pyridoxine, pyridoxal and pyridoxamine were determined by coupling with the diazonium ion of p-sulfanilic acid, in a micellar medium of N-cetylpyridinium chloride (NCPC), with spectrophotometric measurement in the visible region (450 nm). A stable azo dye, with increased sensitivity with respect to the derivative obtained in non-micellar medium, was rapidly formed. The addition of toxic mercury(II) acetate, recommended in a previous procedure to develop the colour for pyridoxine and pyridoxamine, was not required in the presence of NCPC. The procedure was applied to the determination of pyridoxine hydrochloride in commercial pharmaceutical preparations, with recoveries between 94 and 107%, and repeatabilities below 1%. The differences in the coupling reaction rates of the B6 vitamins, in the presence of boric acid and NCPC micellar medium, permitted the differential-kinetic analysis of binary mixtures of the three B6 vitamins.

Micellar modified spectrophotometric determination of nitrobenzenes based upon reduction with tin(II), diazotisation and coupling with the Bratton–Marshall reagent

Nitrobenzenes, such as the antibiotic chloramphenicol, the vasodilator nicardipine, and the herbicides dinitramin, dinobuton, fenitrothion, methylparathion, oxyfluorfen, parathion, pendimethalin, quintozene, and trifluralin, were determined by using a spectrophotometric method in the visible region (540 nm). The method was based on the reduction of the nitrobenzenes to arylamines with tin(II) chloride, diazotisation of the arylamines and coupling of the diazonium ions with the Bratton–Marshall reagent. The two latter reactions were performed in a micellar medium of sodium dodecyl sulphate. The linear calibration range was 2×10 −6 to 7×10 −5 M ( r>0.999), with limits of detection in the 10 −7 M level, which is 2–6 fold lower with respect to the corresponding spectrophotometric procedure in non-micellar medium. The procedure was applied to the analysis of the compounds in commercial preparations (pharmaceuticals and herbicide formulations) and in water samples, with good recoveries.

Spectrophotometric Determination of the Antihistamines, Carbinoxamine Maleate and Doxylamine Succinate, in anN-Cetylpyridinium Chloride Micellar Medium

Abstract The pyridine antihistamines carbinoxamine maleate and doxylamine succinate were derivatized by hydrolysis with cyanogen bromide and coupling with aniline to form a polymethine dye, and determined by colorimetry. In a micellar cationic medium of N-cetylpyridinium chloride (NCPC), the reaction times were reduced and the sensitivities improved. In 0.1 M NCPC the apparent molar absorptivities of the derivatives were 5,900 and 3,500 M−1 cm−1, and the limits of detection (as 3s) were 8.6x10−7 M and 1.7x106 M, for carbinoxamine and doxylamine, respectively. The sensitivity was enhanced in a three- to six-fold factor with respect to a non-micellar medium. The reproducibility was 0.8% for 1.6x10−4 M carbinoxamine, and 1.8% for 1.3x10−4 M doxylamine. The procedure was applied to the evaluation of the drugs in pharmaceutical preparations.

Determination of Pyrrole Derivatives and Hydroxyproline with 4-(Dimethylamino)benzaldehyde in a Micellar Medium

Abstract The spectrophotometric determination of pyrrole derivatives and hydroxyproline with 4-(dimethylamino)benzaldehyde (Ehrlich's reagent) in a sodium dodecyl sulphate micellar medium is studied. Pyrrole and pyrrole-2-carboxylic acid were used as model compounds for the optimization of the procedure. In the micellar medium with 0.2 M HCl at 90° C, pyrrole reacts in 15 min, whereas a HCl concentration larger than 5 M is required in the absence of the surfactant. The sensitivity increases from 1.3 to 5.6-fold with respect to the use of a non-micellar medium, for some pyrrole derivatives. The procedure is applied to the determination of hydroxyproline in meat samples.

Catalytic oxidation of p-nitrodiphenylamine with peroxydisulphate in micellar and non-micellar media

The kinetics of oxidation of p-nitrodiphenylamine (p-NO2 -DPA) with the peroxydisulphate ion has been investigated spectrophoto-metrically. The uncatalyzed oxidation process was so slow but was accelerated tremendously upon the incorporation of Ag+ as catalyst. At moderate concentration of the catalyst, the reaction proceeds with first order kinetics with respect to the substrate, oxidant and catalyst concentrations. In the presence of high concentration of Ag+ , the order of reaction for the substrate species turned to zero, resulting in an overall second order reaction consisting of first order kinetics for the Ag+ and S2 O8 2- individually. Sodium dodecyle sulphate (SDS) micelles showed further enhancement in the catalyzed reaction rate when its concentration was ≤ 3 x 10-3 M. Above this limit an inhibition occurred. Such enhancement has not been observed with cetyltrimethylam-monium bromide (CTAB) but only a retardation was observed. Mixed solution of both SDS and CTAB also inhibited the rate considerably. Mechanisms describing the oxidation processes have been suggested.