When acetone reacts with hydrazine in ethanol, the primary product formed is azine.

Here's the reaction:

2 CH₃COCH₃ (acetone) + H₂N-NH₂ (hydrazine) → CH₃C(=N-N=CCH₃)CH₃ (azine) + 2 H₂O (water)

The reaction proceeds via a condensation reaction, where a molecule of water is eliminated. The hydrazine acts as a nucleophile, attacking the electrophilic carbonyl carbon of the acetone. This forms a hydrazone intermediate, which then reacts with another molecule of acetone to form the azine.

Note: This reaction can be catalyzed by an acid, and the reaction conditions can influence the yield and selectivity of the reaction.