IRS considers cryptocurrency as property, and exchanging one for another is a taxable event.
See "Q16. Will I recognize a gain or loss if I exchange my virtual currency for other property?" [1]:
A16. Yes. If you exchange virtual currency held as a capital asset for other property, including for goods or for another virtual currency, you will recognize a capital gain or loss. For more information on capital gains and capital losses, see Publication 544, Sales and Other Dispositions of Assets.
I think that’s more a function of Puerto Rico not having federal taxes than anything about crypto (ie, no capital gains or income tax on anything, including crypto).
Then again, I'm operating under the impression most people cheat on their taxes w.r.t cryptos