Abstract
F-Sulfo Fatty Methyl Esters sulfonates (F- MES) are new anionic surfactants obtained via sulfoxidation of fatty acid methyl esters (FAME) with SO2, O2, and ultraviolet light of appropriate wavelength. The designation of Φ refers to the random positioning of SO3 in the alkyl chain.
In this work we summarize the most relevant results of our research started fifteen years ago, on the synthesis, separation, analysis and performance of F-sulfo fatty methyl ester sulfonates known as F-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 F-MES.
This work 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 F- sulfo fatty methyl ester sulfonate is shown. Besides, an interpretation of conversion and selectivity of sulfoxydation reaction is given.
Finally, performance of water solutions based on sulfoxylated methyl ester of palmitic acid (F-MES C16) have been studied and compared to two leading types of surfactants used today: linear alkylbezene sulfonate (LAS) secondary alkane sulfonate (SAS) and to a-sulfo fatty methyl ester sulfonate (a-MES) with regard to solubility, performance and skin compatibilty. The experimental results obtained indicate that F-MES can be regarded as a potential component of detergent formulations and most likely of body care products.
Introduction
Fatty acid methyl esters are products derived from fats. The chain length is within 12 to 18 carbon atoms. The names of the detergent range are lauric(C12), myristic (C14), palmitic (C16) and stearic (C18).
α-Sulfo fatty methyl esters sulfonates (α-MES) are well known surfactants derived from natural fats and oils, obtained via traditional sulfonation with SO3. During recent years there have been a number of studies on their surface properties, calcium tolerance, detergency and environmental behavior [1–5].
However, one of the distinct limitations in the use of α-MES is their poor water solubility, which makes them less satisfactory products compared to alkylaryl sulfonates (LAS).
α-MES exhibit a remarkable specificity in that sulfonate group is added almost exclusively to the α position of the long chain when conventional processes using SO3 is employed, presumably being the reason for their low water solubility. To overcome this drawback some authors [6,7] suggested the use of randomly sulfonated FAME, produced by ultraviolet (UV) irradiation–sulfoxidation that apparently would eliminate the performance gap between MES and LAS.
Sulfoxidation or sulfoxylation processes have already been used in the detergent industry to produce paraffin secondary sulfonate (SAS) [8,9]. Sulfoxidation is the addition of sulphur dioxide and oxygen in the presence of UV light of appropiate wavelength to some organic compounds, such as aliphatic hydrocarbons or fatty acid methyl esters.
As a result of our investigation on F-MES started in 1993, several papers have been published [10-17]. These studies have led to two patents accepted in 1999 [18] and 2006 [19] by the Spanish Patent and Trade Mark Office.
The sulfoxydation reaction [14] proceeds through a radical mechanism unlike the a-MES traditional sulfonation, which proceeds through an electrophilic substitution.
Due to the former, a characteristic of these compounds is that the sulfonate group is randomly distributed over all , except the α and ω positions, of the alkyl chain, being this the reason why they are named Φ- MES, as we will see later.
The main reaction product is monosulfonic acid: