To develop a new method for the manufacture of anionic surfactants such as alkanesulfonates, which are completely biodegradable, we used linear aliphatic hydrocarbons C 12 and C 14 as raw material. These hydrocarbons were transformed into the corresponding sulfochlorides in quantitative yield by photosulfochlorination with sulfuryl chloride. The operating conditions led to reaction mixtures containing all the position isomers of sulfochlorinated and chlorinated alkanes. These compounds have been identified by gas chromatography-mass spectrometry. The isomeric distribution of different reaction products, as well as the molar ratio of the main product, the alkanesulfochlorides, vs. the by-products, the alkanechlorides, were determined by the gas chromatography method. The particular isomeric distribution observed during these reactions was different from that of classic chain reactions, as highlighted by the values of calculated relative reactivities. After separation, purification, and alkaline hydrolysis steps, the resulting dodecane and tetradecanesulfonates showed good surface activity. Indeed, the values of the surface tensions at the critical micelle concentration (CMC) compare well with those in the literature. CMC values of these mixtures are given, and the influence of isomeric distribution on CMC values and on the surface tension values at the CMC is presented.
Using different reaction conditions of photosulfochlorination of n-dodecane, two samples of anionic surfactants of sulfonate type are obtained. Their micellar behavior has been already reported and the relationship between their isomeric distribution and their chemical structures and micellar behaviors have been more thoroughly explored. In this investigation, we screened the foaming properties (foaming power and foam stability) by a standardized method very similar to the Ross-Miles foaming tests to identify which surfactants are suitable for applications requiring high foaming, or, alternatively, low foaming. The results obtained for the synthesized surfactants are compared to those obtained for an industrial sample of secondary alkanesulfonate (Hostapur 60) and to those of a commercial sample of sodium dodecylsulfate used as reference for anionic surfactants. The foam formation and foam stability of aqueous solutions of the two samples of dodecanesulfonate are compared as a function of their isomeric distribution. These compounds show good foaming power characterized in most cases by metastable or dry foams. The highest foaming power is obtained for the sample rich in primary isomers which also produces foam with a relatively high stability. For the sample rich in secondary isomers we observe under fixed conditions a comparable initial foam height but the foam stability turns out to be low. This property is interesting for applications requiring low foaming properties such as dishwashing liquid for machines. The best results are observed near and above the critical micellar concentrations and at 25°C for both the samples.
Increasing concentration of sulfuryl chloride during the photosulfochlorination reaction under visible light shows that under these conditions n-alkanes react at high conversion rates instead of the conversion rate of 15% reported in the literature. This photosulfochlorination with sulfuryl chloride leads to better and more interesting results compared with those of photosulfochlorination by gas mixture. Indeed, nearly total conversion of n-alkanes, specifically n-heptane, n-dodecane, n-tetradecane, and n-hexadecane, occurred in pure phase, with a quantitative global yield, a sulfochlorination-tochlorination molar ratio of about 1, and a relative reactivity of secondary to primary hydrogen of about 2.5, at a reaction temperature of 30°C and a reaction time of 120 min, using 2 × 10 −2 mol L −1 of pyridine. Under these conditions, no polysulfochlorinated compounds are detected. These results are further improved using chlorobenzene as the solvent, instead of benzene. Indeed, the sulfochlorination of n-heptane at a conversion rate of 80% in the presence of chlorobenzene leads also to a quantitative reaction yield, a higher RSO 2 Cl/RCl molar ratio, and, as expected, a high selectivity of secondary over primary hydrogen. Under these conditions, sulfochlorination of long-chain nalkanes leads to the highest RSO 2 Cl/RCl molar ratio for n-dodecane, n-tetradecane, and n-hexadecane belonging to detergent range, and the value of the molar ratio for these is between 1.45 and 1.7. The isomeric distribution of sulfochlorinated compounds obtained during sulfochlorination in the presence of solvent resembles that of secondary alkanesulfonates produced by sulfoxidation reaction, whereas that obtained in pure phase has a similar conversion rate, is rich in primary isomer, and thus is different from that of classic radical reactions such as photochlorination or photosulfochlorination with gas mixture.Paper no. S1521 in JSD 9, 249-257 (Qtr. 3, 2006).
Using different reaction conditions of photosulfochlorination of n-alkanes, various samples of anionic surfactants of sulfonates type have been obtained. Their micellar behavior was researched and the relationship between their isomeric distribution and so, their chemical structures and micellar behaviors were more thoroughly explored. Their critical micelle concentrations (CMC) were determined with surface tension measurements, the surface activities (c CMC ) were obtained, the surface absorption amounts (Gm) and the molecular areas (Am) at the interface of air-water gained by using Gibbs' equation. In addition, under the conditions of adding electrolyte NaCl, the critical micellar concentrations (CMCs) of two samples were also examined, and the effects of the addition of electrolyte on their micellar behaviors were studied. The experiment results show that the samples rich in secondary isomers have characteristic micellar behavior: CMC are higher, and the abilities to decrease surface tension are better, which well compared to common anionic surfactants, especially Hostapur 60, commercially available. Besides, the effects of addition of electrolyte on the micellar behaviors of the anionic surface-active agents are similar to common anionic surfactants.
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