Methacrolein is prepared in a continuous process by a Mannich condensation reaction of formaldehyde with propanal. A methacrolein polymerization inhibitor is introduced during the production process and a part thereof is recycled back into the reactor where the Mannich condensation reaction is carried out.

Methacrolein is prepared in a continuous process by a Mannich condensation reaction of formaldehyde with propanal. A methacrolein polymerization inhibitor is introduced during the production process and a part thereof is recycled back into the reactor where the Mannich condensation reaction is carried out.

The invention relates to a natural vanillin, which is in the form of an amorphous solid of which the color, in ethanolic solution at 10% by weight, is less than or equal to 200 Hazen, preferably less than or equal to 100 Hazen.