This sentence contains the particle de (part of the verb venir de) followed by the personal pronoun l' followed by the verb acheter. The usual form of this pronoun is le when referring to a masculine noun, and la when referring to a feminine noun. However, when the article is followed by a word that begins with a vowel, the pronoun is always elided to l'. The form l' exists for both genders.
This elision is also done when le or la is a definite article: le matin, la nuit, l'après-midi. It is also done when le or la is part of a partitive article: du pain, de la confiture, de l'eau.
Furthermore, note thatNow let's suppose the verb didn't start with a vowel: “je viens de le vendre”. Why don't we say “je viens du vendre”? There are two cases where de le contracts into du is only a partitive article. In your sentence:
- When it is a partitive article (i.e. it means “some amount of”), as in du pain.
- When it the preposition de is introducing a noun group that begins with the definite article le, as in “je descend du train” (“je descend de la voiture”).
On the other hand, there is no contraction when de and le happen to be next to each other but they do not form a single unit. Therefore we would sayHere, de is part of the verbal compound venir de and le is a personal pronoun which forms a complement of this verb. There is no contraction when le is a pronoun: “Jeje viens de le voirvendre”.