Rotate a cube around pivot in four direction

I want my cube to drop down to left right up or down with some animation. So what I have done is that I have made an empty game object and made it my cube parent. Now when ever a key is pressed I move the pivot to right position and make it fall in that direction.

It works perfect for left and right but not for up and down please help.

 if(roatationAxis=="z")
         {
             if(rotateDirection=="left")
             {
                 if(transform.localRotation.eulerAngles.z + 10  < rotationAngle)
                 {
                     this.transform.RotateAround (transform.position, transform.forward, 10);
                 }
                 else
                 {
                     this.transform.eulerAngles=new Vector3(0f,0f,rotationAngle);
                     doAnimate=false;
                 }
             }
             else
             {
                 if(transform.localRotation.eulerAngles.z + 10  < rotationAngle)
                 {
                     this.transform.RotateAround (transform.position, -Vector3.forward, 10);
                 }
                 else
                 {
                     this.transform.eulerAngles=new Vector3(0f,0f,rotationAngle);
                     doAnimate=false;
                 }
             }
         }
         if(roatationAxis=="x")
         {
             if(rotateDirection=="up")
             {
                 if(transform.localRotation.eulerAngles.z + 10  < rotationAngle)
                 {
                     this.transform.RotateAround (transform.position, transform.right, 10);
                 }
                 else
                 {
                     this.transform.eulerAngles=new Vector3(rotationAngle,0f,0f);
                     doAnimate=false;
                 }
             }
             else
             {
                 if(transform.localRotation.eulerAngles.x + 10  < rotationAngle)
                 {
                     this.transform.RotateAround (transform.position, -transform.right, 10);
                 }
                 else
                 {
                     this.transform.eulerAngles=new Vector3(rotationAngle,0f,0f);
                     doAnimate=false;
                 }
             }
         }