Is possible associate a reserved public ip address to Web App int the azure portal?
I need to replace this ip (40 112 ...) for the reserved ip.
No. From the FAQ:
Can I use a reserved IP for all Azure services?
Reserved IPs can only be used for VMs and cloud service instance roles exposed through a VIP.
Reserved IP Overview
https://azure.microsoft.com/en-us/documentation/articles/virtual-networks-reserved-public-ip/