The specific steps for the preparation of cinnamic acid from cinnamaldehyde are as follows:

1. Cinnamaldehyde is added to phenol, and an isocyanate catalyst is added, and the reaction produces an isocyanate of cinnamic acid.

2. The reactant solution is added to concentrated sulfuric acid and reacted under cooling and stirring for 1 hour to produce cinnamic acid.

3. The reaction product is filtered, washed and dried to give a final cinnamic acid product.

Reaction equation:

Cinnamaldehyde + isocyanate catalyst + phenol → isocyanate of cinnamic acid

Isocyanate of cinnamic acid + concentrated sulfuric acid → cinnamic acid

Precautions:

1. Because sulfuric acid is strongly corrosive, you need to wear chemical gloves to protect your eyes and so on when you carry out the chemical reaction. After the reaction, wash your hands and furniture countertops, etc. well with water to avoid harm to the human body and the environment.

2. During the preparation of cinnamic acid, the reaction product should be filtered and washed to remove impurities that may affect product quality and purity.