Method for synthesising partially N-hydroxyethylated tertiary 1,6-hexanediamines

A synthesis method for N,N′-dimethyl-N,N′-di(2-hydroxyethyl)-1,6-hexanediamine of formula (I2) as follows:

• comprising two reaction steps, and
• comprising at least a first reaction between a first halogen atom-free precursor compound and a second halogen atom-free precursor compound,
• and wherein none of the two reaction steps comprises a halogenated organic reactant,
• wherein the first halogen atom-free precursor compound being 1,6-hexanediamine and the second halogen atom-free precursor compound being ethylene oxide,
• said method comprising:
• a first reaction step between the 1,6-hexanediamine and the ethylene oxide so as to form at least one intermediate compound selected from the group consisting of N-(2-hydroxyethyl)-1,6-hexanediamine, N,N′-di(2-hydroxyethyl)-1,6-hexanediamine, N,N-di(2-hydroxyethyl)-1,6-hexanediamine and N,N,N′-tri(2-hydroxyethyl)-1,6-hexane-diamine;
• a second step of methylation of the primary or secondary amine functions of said at least one intermediate compound so as to form at least N,N′-dimethyl-N,N′-di(2-hydroxyethyl)-1,6-hexanediamine, said second methylation step being carried out by reaction between said intermediate compound, formaldehyde and hydrogen in the presence of a hydrogenation catalyst, or by reaction between said intermediate compound, formaldehyde and formic acid according to the Eschweiler-Clarke reaction.