In most uses especial can be replaced with special without a change in meaning, although especial can also mean 'in particular'.
But there is one very important difference!
Especial is an extremely rare word in English. Although you can find examples of literate native speakers of English using it, they are hundreds of times less common than the usual word, special. It's almost always used by non-native speakers, and is basically never used in conversation. Why is that?
There are two reasons this word is used by non-native speakers:
- The adverb especially (meaning 'in particular') is quite common, so it's natural for a learner to believe that especial might be a common word, too. But although special and especially are both common, the adjective especial is rare.
- In some languages such as Spanish, especial is a common word. Speakers of languages such as Spanish may transfer this over into English, especially if they look the word up in an English dictionary and are able to find the word listed with the same meaning.
Because of this, it's usually best to treat production of especial in English as a mistake made by non-native speakers. If you're an English language learner, I would like to encourage you to use the word special instead.
It's true that it's technically a word in English, so if you really want to use especial in English, I won't tell you that you can't. But most uses of the word are now quite rare or are entirely archaic, and it will sound quite odd to most speakers. Using it repeatedly when special is expected will mark you as a non-native speaker, so if you want to speak English naturally, stick to special.