Processes for the preparation of citral and interrelated products

Process for the preparation of 3,7-dimethyl-octa-2,6-dienal (citral) comprising the steps of:

• a) reacting at least one formaldehyde source and isobutylene to obtain isoprenol;
• b) isomerizing isoprenol obtained in step a) to obtain prenol by bringing a reactant stream comprising isoprenol into contact with at least one heterogeneous isomerization catalyst;
• c) providing prenal by at least one of c-i) and c-ii):
• c-i) subjecting isoprenol obtained in step a) to oxidative dehydrogenation so as to obtain prenal and/or isoprenal by bringing a reactant stream comprising isoprenol into contact with at least one heterogeneous oxidative dehydrogenation catalyst, in the presence of molecular oxygen, and optionally isomerizing at least part of the isoprenal to prenal;
• c-ii) oxidizing prenol obtained in step b) so as to obtain prenal by bringing a reactant stream comprising prenol into contact with at least one oxidant and at least one oxidation catalyst;
• d) condensing prenol obtained in step b) with prenal obtained in step c) to obtain diprenyl acetal of prenal;
• and
• e) subjecting diprenyl acetal of prenal obtained in step d) to cleaving conditions to obtain citral via prenyl (3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene;
• wherein step c-i) is characterized by maintaining in the reactant stream a weight ratio of aldehydes to isoprenol of less than 0.04, and
• optionally, step b) is characterized by maintaining in the reactant stream a concentration of aldehydes of less than 0.5 wt.-%, based on the total weight of the reactant stream, and,
• optionally, the concentration of aldehydes in the reactant stream is not lower than 10 ppm, based on the total weight of the reactant stream.

Process for the preparation of 3,7-dimethyl-octa-2,6-dienal (citral) comprising the steps of:

• a) reacting at least one formaldehyde source and isobutylene to obtain isoprenol;
• b) isomerizing isoprenol obtained in step a) to obtain prenol by bringing a reactant stream comprising isoprenol into contact with at least one heterogeneous isomerization catalyst;
• c) providing prenal by at least one of c-i) and c-ii):
• c-i) subjecting isoprenol obtained in step a) to oxidative dehydrogenation so as to obtain prenal and/or isoprenal by bringing a reactant stream comprising isoprenol into contact with at least one heterogeneous oxidative dehydrogenation catalyst, in the presence of molecular oxygen, and optionally isomerizing at least part of the isoprenal to prenal;
• c-ii) oxidizing prenol obtained in step b) so as to obtain prenal by bringing a reactant stream comprising prenol into contact with at least one oxidant and at least one oxidation catalyst;
• d) condensing prenol obtained in step b) with prenal obtained in step c) to obtain diprenyl acetal of prenal;
• and
• e) subjecting diprenyl acetal of prenal obtained in step d) to cleaving conditions to obtain citral via prenyl (3-methyl-butadienyl) ether and 2,4,4-trimethyl-3-formyl-1,5-hexadiene;
• wherein step b) is characterized by maintaining in the reactant stream a concentration of aldehydes of less than 0.5 wt.-% based on the total weight of the reactant stream, and,
• optionally, the concentration of aldehydes in the reactant stream is not lower than 10 ppm based on the total weight of the reactant stream;
• and
• optionally wherein step c-i) is characterized by maintaining in the reactant stream a weight ratio of aldehydes to isoprenol of less than 0.04.