How to Send BTC from my address to another using private key
If you don't want to use any wallet software, you could install bitcoind on your local host and 

https://stackoverflow.com/questions/38493893/heres-how-to-send-raw-transaction-btc-using-bitcoin-cli-command

You could use an online version of bitcoind RPC endpoint, but I am not sure you want to submit your private key over the network.