Method for preparing surfactant compositions comprising alkyl liduronamides d-glucuronamides and l-rhamnosides from ulvans

1) Process for preparing a composition comprising a mixture of alkyl D-glucuronamides (I) in pyranoside form of formula (Ia) and in furanoside form of formula (Ib), of alkyl L-iduronamide of formula (II) and of alkyl L-rhamnoside of formula (III):

• in which
• R1 is a linear or branched, saturated or unsaturated alkyl chain of 2 to 22 carbon atoms;
• R2 is a hydrogen, R1, a linear or branched, saturated or unsaturated alkyl chain of 2 to 22 carbon atoms including an amine end function,
• and characterized in that said process comprises:
• a) a step of butanolysis reaction and of Fischer glycosylation starting with ulvans and/or green algae;
• b) a step of aminolysis reaction on the reaction medium obtained from step a), in the presence of a linear or branched, saturated or unsaturated amine of formula R′NH2 in which R′ is composed of from 2 to 22, preferably from 8 to 18, preferentially from 12 to 18 carbon atoms.