Metal detector finds are an example of an exception to the general rule "never clean coins". Keep them uncleaned and you might have an "interesting historical artifact", but you don't really have a "coin" - especially if it's unidentifiable as to country, denomination and date.
Acids (including tomato juice) are towards the "strong" end of cleaning agents. Acetone is towards the "weak" end, as it only removes organic "goo" and leaves the metal and any metal corrosion by-products alone. This coin was covered in green corrosion by-products; acetone would have done nothing.
Quote: Actually, I rather prefer amonia + soap water and boil it for few min.
Ammonia and soap-water are also "weak"; I do not know how they work when mixed together and boiled. I do know concentrated ammonia alone, on copper/bronze coins, tends to leave an ugly, bright orange discolouration once the corrosion is removed. This Romania 10 lei coin is made of "nickel-brass", and so would probably also have enough copper in it to turn orange too. I think you made the right choice in going straight to mild acid.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis