A-sulfo fatty acid methylesters

The preparation of of-sulfo fatty acid methylesters is a two-stage process taking place at two different rates. At first, an addition compound of 1 mol of methylester with 2 mol of SO3 is formed. Then, in the following reaction, 1 mol, of SO3 is split off, to form the final ester. This sulfur trioxide will slowly react further with another methyl ester. Using the fatty acid methylester and SO3 in a molar ratio results in an undesirably long reaction time. Therefore a surplus of sulfur trioxide is used. The reaction mixture then consists of the main product, the a-sulfo fatty acid methylester and also its anhydride with SO3. By neutralization with a solution of caustic soda, on the one hand the desired sodium salt of the required ester is formed, while on the other hand the anhydride is transformed to the corresponding disodium salt and sodium methyl sulfonate. In order to achieve a complete transformation of the fatty acid methylester, a certain amount of the undesired disodium salt has to be expected. 

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