How is what Quine (Methods of Logic, 1959, p. 254) called "the law of infinite conjunction" different from the compactness theorem for propositional logic?
The former states that if a finite or infinite set C of truth-functional formulas is consistent, then there is some truth-assignment that makes all members of C true.
Compactness states that a set of propositions is satisfiable if and only if every finite subset is satisfiable.