Son spits in my face

Whenever I try to talk to my son after he does something like kicks the dog or hurts his brother he spits in my face. I put him in time out and take away toys but he doesn’t seem to bother him. He pushed his brother down who is only 10 months old and learning to walk. I got in front of my son and said “why did you do that? That’s not nice. You do not push people, especially your baby brother.” He wouldn’t make eye contact with me and then he spit in my face. What do I do? I’m at a loss. He is not even 3 yet.