スルホン化反応

無水硫酸による脂肪酸のα-スルホン化に関する研究 (第4報)

抄録

α-Sulfonated fatty acids are easily prepared by dropping liquid sulfur trioxide into the solution of fatty acids in carbon tetrachloride.
In this process, however, the color of the reaction mixture becomes gradually dark brown and finally black.
Thus, repeated washing by a solvent (e.g. petroleum benzine) and recrystallization from it are necessary to obtain white powder, and consequently the yield considerably reduces.
The authors tried to use an adduct of dioxane and sulfur trioxide as sulfonating agent to prevent the coloring of the reaction mixture.
In this work, α-sulfonation of palmitic acid dissolved in carbon tetrachloride was carried out with three alternative methods, direct method, adduct method and mixed solvent method, and these results were compared and discussed.
In each method, 1.2, 1.4 and 1.6 moles of sulfur trioxide were used per mole of palmitic acid, respectively.
The samples were taken from the reaction mixture at a definite time interval, followed by measuring the color of each sample by photoelectric colorimeter and the yield of α-sulfopalmitic acid was determined by semimicro methylene blue backtitration method.
The conclusions obtained were as follows :
1. Adduct method gave extraordinary low coloring and the conversion of palmitic acid to its sulfoacid was almost 95% or more. Direct method gave markedly high coloring, and the coloring increased considerably after the conversion reached 80%. Mixed solvent method gave moderate coloring.
2. When the mole ratio of sulfur trioxide vs. palmitic acid increased in the order of 1.2, 1.4 and 1.6, the conversion increased in the same order at any time, but the difference of the conversion almost disappeared after about 2 hours from the beginning of the reaction.
3. This sulfonation reaction was assumed to be of the first order from the data of direct method performed at constant temperature, 30°C, 40°C, 50°C and 60°C.