Abstract: In the production of light-colored pastes of .alpha.-sulfofatty acid alkyl ester alkali metal salts by reaction of fatty acid alkyl esters with gaseous SO.sub.3, subsequent after-reaction in liquid phase, neutralization with aqueous alkali metal hydroxide solutions and bleaching, effective bleaching can be obtained without any reduction in the washing-active substance content by addition of the hydrogen peroxide during neutralization of the .alpha.-sulfofatty acid alkyl ester and subjecting the neutralization product obtained to a temperature-controlled after-reaction.

Abstract: In the production of highly concentrated pastes of .alpha.-sulfofatty acid alkyl ester alkali metal salts by reaction of fatty acid alkyl esters with gaseous SO.sub.3, subsequent after-reaction in liquid phase and neutralization with aqueous alkali hydroxide solutions, the sulfonation product and aqueous alkali metal hydroxide solution are introduced during neutralization into an aqueous phase initially containing 0 to 55% by weight washing-active substance at a pH value in the range from 2 to 8 and washing-active substance contents of 60 to 70% by weight are established.

Abstract: In the production of .alpha.-sulfofatty acid alkyl ester alkali metal salt pastes by reaction of fatty acid alkyl esters with gaseous SO.sub.3, subsequent after-reaction in liquid phase and neutralization with aqueous alkali metal hydroxide solutions, the crude sulfonation product is fed to an at least two-stage cascade of stirred tanks equipped with heating and cooling systems in which it is subjected with mechanical agitation to a temperature-controlled after-reaction until a degree of sulfonation of at least 90% is reached, after which the aged sulfonation product is further processed in known manner to .alpha.-sulfofatty acid alkyl ester alkali metal salt pastes.

Abstract: In the production of highly concentrated pastes of .alpha.-sulfofatty acid alkyl ester alkali metal salts by reaction of fatty acid alkyl esters with gaseous SO.sub.3, subsequent after-reaction in liquid phase and neutralization with aqueous alkali hydroxide solutions, the sulfonation product and aqueous alkali metal hydroxide solution are introduced during neutralization into an aqueous phase initially containing at least 55% by weight washing-active substance at a pH value in the range from 2 to 8 and washing-active substance contents of 60 to 70% by weight are established.

Abstract: In light colored surfactants produced by sulfonation of fatty acid alkyl esters with less than 2 moles of SO.sub.3 per mole of fatty acid alkyl ester and subsequent work-up of the crude sulfonate in aqueous medium to form salts, the content of .alpha.-sulfofatty acid disalts is regulated and reduced by transesterifying the sulfonation product before its treatment with an aqueous medium with at least about 0.5 mole equivalent of an alcohol, based on the SO.sub.3 which is not for .alpha.-sulfonation.

Abstract: In light colored surfactants produced by sulfonation of fatty acid alkyl esters with less than 2 moles of SO.sub.3 per mole of fatty acid alkyl ester and subsequent work-up of the crude sulfonate in aqueous medium to form salts, the content of .alpha.-sulfofatty acid disalts is regulated and reduced by transesterifying the sulfonation product before its treatment with an aqueous medium with at least about 0.5 mole equivalent of an alcohol, based on the SO.sub.3 which is not for .alpha.-sulfonation.