Please read Dr. Sears Discipline Book. It would greatly help both of you:
http://www.amazon.com/Discipline-Book-Better-Behaved-Chil...
Some of his advice is online here. This link is advice on helping control your temper:
This link is general discipline and behavior issues and advice:
http://www.askdrsears.com/html/6/T060100.asp
http://www.askdrsears.com/html/6/T061800.asp
In all reality though, you absolutely NEED to make time to play with him, every single day. Neglecting him of that positive attention will only make things worse for him.
I'm a working mom as well and know it's tough, but you have to redefine who you are. A mother first, a businesswoman second. If you fail in the home, it doesn't matter where else you have succeeded, because that isn't lasting like a family is.
Get home, relax for a half hour, read your child a book (i's recommended to read for 15 minutes every day with your child), do a little craft with him or color with him, play a game like hide n seek, tag or a board game like memory, hold him on your lap and cuddle as you watch a television show, get on the floor and play blocks or legos or cars... make a list to do at least 2 of these things with your child every day.
Children thrive on this attention, not simply because it's fun, but because they need that bond with their mothers and the assurance that they have their mother's attention and care. Even if their physical needs are met, they can be emotionally neglected and hindered if their play and bonding needs are not met.
Also, it's 4 year olds business to be noisy and naughty... it's what they do. It's how they have fun and discover, how they test their boundaries, how they learn you are paying attention to them. They also act out in order to get attention. A quiet child playing nicely in the corner won't guarantee a busy mother to come over and visit with him, hence why children act out. They would rather get negative attention than no attention, so do all you can to turn that situation into something positive for once.
Also, the book "Playful Parenting" by Lawrence Cohen helps give a new perspective on how to interact with your children on a regular basis in a more loving and playful way:
http://www.amazon.com/Playful-Parenting-Lawrence-J-Cohen/...