(define replacements (list (list "a" "A")(list "b" "B") (list "c" "C")))

(define (string-replace-multi str lst)
  (cond
    [(empty? lst) str]
    [(eq? (length lst) 1)
     (string-replace str
                     (first (first lst))
                     (last (first lst)))]
    [else
     (string-replace-multi (string-replace str
                                           (first (first lst))
                                           (last (first lst)))
                           (rest lst))]))