Convert Non-Date to Date

SELECT to_char(trunc(TO_date('05-SEP-2015 8:30:25', 'DD-MON-YYYY HH:MI:SS')),'DD
-MON-YYYY') FROM dual;
SELECT TO_DATE('2015/05/15 8:30:25', 'YYYY/MM/DD HH:MI:SS')
FROM dual;