The characterization of alcohol ethoxylates (AE) to determine ethylene oxide (EO) adduct distribution has been studied in our laboratory for many years by using high-performance liquid chromatography-mass spectrometry (LC-MS). This paper describes the LC-MS approach being used to analyze both nonderivatized and derivatized AE. We conclude that the best way to determine EO adduct distribution is by first converting the AE to alcohol ethoxy sulfates (AES) and then by using LC-MS with electrospray ionization in the negative ion mode. A convenient laboratory technique for converting small-scale samples of AE to AES has been discovered and is reported herein. Several examples of EO adduct distributions determined by this method are presented for both linear and isomeric AE samples. A method has been described to characterize the major anionic surfactant linear alkylbenzene sulfonate after derivatization by gas chromatography-mass spectrometry (GC-MS) (1). That method also has been applied to the analysis of sulfoxylated methyl esters (2). In this paper, the development of analytical methods to characterize surfactants is continued with the characterization of alcohol ethoxylates (AE). Aliphatic AE are widely used in household and industrial applications. They are produced by the catalytic addition of ethylene oxide (EO) to mixtures of aliphatic alcohols of oleochemical or petrochemical origin and have the general formula C x H 2x+1 O(CH 2 CH 2 O) y H. Commercially available AE are complex mixtures of linear and/or branched alkyl chains with the number of carbons ranging from 6 to 18 and the degree of ethoxylation varying from 1 to >25 mol. Numerous chromatographic methods, such as GC (3,4) supercritical fluid chromatography (5-8), thin-layer chromatography (9), high-performance liquid chromatography (HPLC) (10-18), HPLC-light-scattering detection (19), HPLC-nuclear magnetic resonance spectrometry (20), and capillary electrophoresis (21), have been published for AE characterization. A paper evaluating the efficiency and reliability of different chromatographic techniques was recently published by Trathnigg et al. (22). All these techniques produce suitable results for AE with linear alkyl chains; however, for branched-chain AE they yield unreliable data. Separation is the critical issue with these techniques. Owing to the complexity of branchedchain alcohol structures, it is difficult to imagine any analytical technique able to separate all AE components by alkyl carbon number and by ethoxy units (ethoxymers). Only MS coupled with HPLC, which combines chromatographic separation with ion detection, can produce the data for a detailed AE characterization. Earlier publications provide few examples of liquid chromatography-mass spectrometry (LC-MS) applied to the characterization of AE as pure sample or as detergent formulations (23-26). Other publications are mainly based on biodegradation studies (27-32). Most publications are evaluations of AE exposure in environmental compartments (33)(34)(35)(36)(37)(38)(39)(40)(41)(4...
AbstractΦ-Sulfo Fatty Methyl Esters sulfonates (Φ-MES) were obtained via sulfoxidation of fatty acid methyl esters (FAME) with SO2, O2, and ultraviolet light of appropriate wavelength. Expectedly, these products may be used as linear alkylbenzene sulfonate (LAS) and alkyl ether sulfate (AES) partners, either in heavy-duty or in hand dishwashing liquids. Φ-MES are new anionic surfactants that can be regarded as potential components for detergent formulations and body care products as well. In this work we summarize the most relevant results of our research started fifteen years ago, on the synthesis, separation and analysis of Φ-sulfo fatty methyl ester sulfonates known as Φ-MES, and we update our last findings. We have to point out that we are for the time being, the only research group in the world to have published our research on Φ-MES. This paper describes the optimum batch conditions for the sulfoxidation of FAME and a reaction mechanism is proposed. The paper depicts an improved workup for the separation of reaction products from non reacted methyl ester and the GC-MS analysis of Φ-sulfo fatty methyl ester sulfonate is shown. Finally, an interpretation of conversion and selectivity of sulfoxydation reaction is given.
Derivatization of a C 12 Φ-methyl ester sulfonic acid by using iodide-trifluoroacetic anhydride in dimethylformamide in a one-step reaction yielded derivatized sulfonic thiotrifluoroacetates. The latter have been analyzed by gas chromatography-mass spectrometry (MS) and liquid chromatography-MS techniques so that, for the first time, the acid composition and the mono sulfonic acid isomer distribution are shown.Paper no. S1298 in JSD 6, 151-154 (April 2003).KEY WORDS: C 12 Φ-sulfoxylated methyl ester, composition, derivatization, isomer identification.In our previous work (1), a C 16 Φ-methyl ester sulfonic acid (Φ-MES C 16 ) sample was derivatized by methylation with trimethylorthoacetate in excess to give the dimethylester sulfonate. Different analytical techniques were used to analyze the sample, such as gas chromatography (GC)-mass spectrometry (MS), 1 H nuclear magnetic resonance (NMR), liquid secondary ionization mass spectrometry (LSIMS), and tandem MS. The main conclusions drawn from that investigation were as follows: (i) The SO 3 group was positioned randomly. (ii) GC-MS showed the presence of at least 11 isomers that could not be characterized. (iii) 1 H NMR indicated that the major species present contained one CHSO 3 and one CH 2 CO 2 group, confirmed the presence of different isomers, and suggested the presence of polysulfonates. (iv) LSIMS and LSIMS/MS confirmed the presence of CH 3 (CH 2 ) m CH(SO 3 Me)(CH 2 ) n CH 2 CO 2 Me (M.W. = 364 where m + n = 12); very little α or β substitution; and the presence of polysulfonated species of the forms CH 3 (CH 2 ) m CH(SO 3 Me)(CH 2 ) n CH(SO 3 Me)(CH 2 ) p CH 2 CO 2 Me and CH 3 (CH 2 ) m C(SO 3 Me) 2 (CH 2 ) n CH 2 CO 2 Me. Probably as a result of the instability of the derived methyl esters, the research (1) could not be completed and the identification of each isomer remained a goal to be reached.Therefore, in the present investigation a C 12 fatty acid methyl ester was sulfoxidized with SO 2 , O 2 , and ultraviolet light of 257.3 nm wavelength as described previously (2). The sulfonic acid was further extracted from the reactor outlet product with n-hexane as described previously (3), and a different derivatization technique was applied using potassium iodide and trifluoroacetic anhydride (TFAA) (4).Although the random position hypothesis was confirmed for Φ-MES C 16 (1), the present work describes the sulfonic acid composition and identifies each positional isomer for the first time by means of GC-MS and liquid chromatography (LC)-MS. EXPERIMENTAL PROCEDURESDerivatization of Φ-MES C 12 . According to a method developed by Li and Lin (5) and applied by Pratesi et al. (4), a sulfonic acid methyl ester sample, obtained through sulfoxidation (2) and further hexane extraction (3), was derivatized by the TFAA/potassium iodide method (4), and the derivatives were analyzed by GC-MS and LC-MS [electrospray ionization (ESI) source].In this procedure (4), the sulfonic group is first reduced to an alkyl-thiol group. Then the trifluoroacetic acid group is added to ...
Sulfonation with SO3 of an oleic methyl ester has led to a mixture of sulfonates with potential properties as a surfactant, an emulsifier or even a wetting agent that can be used in detergent formulations. For the first time, the products from the sulfonation reaction with SO3 are identified.
In this work several batch sulfoxidation reactions of different fatty acid methyl esters, having chain lengths of C12 to C18, in the presence of SO 2 , O 2 , and ultraviolet light of 253 nm have been carried out. The average reaction conversion for each methyl ester has been calculated and the selectivity determined by liquid chromatography. The results indicate that conversion increases dramatically with the increase of carbon chain length, whereas selectivity to monosulfonate seems to increase slightly as the chain length increases.Paper no. S1499 in JSD 9, 47-50 (Qrt. 1, 2006). KEY WORDS: Conversion, selectivity, sulfoxylated methyl esters (Φ-MES).In previous papers (1-6) different aspects of the sulfoxidation reaction of fatty acid methyl esters have been covered. A gap still remains regarding conversion and selectivity as a function of the hydrocarbon chain length. After completion of the sulfoxidation reaction, the products in the reactor consist mainly of mono-and polysulfonic acids, some fatty acids, and all the unreacted fatty acid methyl ester.To determine conversion, the unreacted methyl ester must first be separated from the reaction products. To determine selectivity, the fastest way has been to analyze the separated product by liquid chromatography-mass spectrometry (LC-MS). The results of both procedures are depicted herein.The hot water extraction method (3) has been applied to obtain the unreacted methyl ester. A volume of hot water (250 mL at 60°C) approximately equivalent to the volume of the reactor outlet is added to the latter by means of a separatory funnel; then the mixture is well shaken and the two phases are immediately separated. The upper organic layer contains all the unreacted methyl ester and a very small amount of fatty acid, and the lower aqueous phase has all the sulfonic acids produced.The hexane extraction method (3) has been used to obtain the monosulfonic-polysulfonic acids mixture. The reactor outlet is transferred to a liquid-liquid extractor. The extractor has two outlets, one connected to a round-bottomed flask filled with 600 mL of hexane, the other (the overhead) to a water condenser. The round-bottomed flask is heated to reflux for 6 to 8 h. The sulfoxylated methyl ester (Φ-MES) sulfonic acids remain in the extractor while the unreacted methyl ester is recovered in the hexane-containing roundbottomed flask. The acid is then neutralized with a 30% sodium hydroxide solution and analyzed by LC-MS chromatography on a reversed-phase column (Octyl column; length = 150 mm; diameter = 4.6 mm) in order to calculate mono-and disulfonates. A methanol/water gradient is used to perform the chromatographic separation. An electrospray ionization interface is used to generate the ions, and the mass spectrometer is operated in the negative ion mode. RESULTS AND DISCUSSIONConversion. Conversion is calculated as the amount of starting methyl ester minus the recovered unreacted methyl ester divided by the starting amount, which in all the experiences was 250 mL. The results from six expe...
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