Look, man, if you scaled down all reactants, you must scale down HCl too!(quantity not percentage) But in this case add to cold reaction mixture about 500 ml benzene and after few time you'll obtain crude methadone hydrochloride.
For this step see
Patent US2601323
,
Example 3. Next, then you add HCl, don't remove heating, reaction must be very vigorous and all xylene must be removed during addition of HCl.
Good luck, Murmur.
