Psychological addiction to Coca-Cola is entirely possible, and sugar/caffeine addiction is also possible, so he may be experiencing either of those when not drinking it for long periods of time.
The “it dissolves a nail” argument only works on the stupid kids. The smart kids will say “I’m not made of metal.” The smart ones who have learned how to learn will look up facts on the Internet, such as how Coke is used as a cure for an upset stomach. Also, they’ll discover that Coke only dissolves nails thanks to its acid content, which will become a problem for you when you are trying to get him to drink Orange Juice, another drink known for its acid content.
Finally, the “teeth will rot” argument falls flat if you’ve convinced him to brush his teeth twice a day. If you haven’t convinced him to brush his teeth, he holds very little regard for your reasoning ability.
Teenagers don’t respond well to being told that something might kill them, or cause pain and frustration. We are talking about teenagers here, people who delight in performing the forbidden and the dangerous.
What you need to do is a gradual conversion. First get him to slowly switch to a non-caffeinated soda, such as a lemon-lime soda. This will wean him off the caffeine. Then switch him to a lemon-lime soda water, such as the lemon-lime twist made by Canada Dry. This will wean him off the additional sugar from the soda pop. You could try switching him to lemon water to get him off the carbonated water (which can cause problems with the swallowing muscle), but you may not be able to get him to give up the carbonation.