Titanium is a rather unreactive metal, making it difficult to dissolve. There are several ways to oxidize titanium.
Hydrochloric acid: Boiling concentrated hydrochloric acid will slowly dissolve titanium, forming a purple solution of titanium trichloride. When I tried this, hardware store hydrochloric acid was unable to dissolve the titanium. It might work if it was boiled for an extended period of time, however.
Sulfuric, acetic, nitric acid: Titanium is quite resistant to all of these acids. It may dissolve extremely slowly in boiling sulfuric acid but that is a generally poor way of dissolution.
Bromide dissolution: I found somewhere on the internet that titanium has a weakness for bromine. Therefore, I decided to dissolve it by electrolyzing it in a sodium bromide solution with a nine volt battery. I was really amazed that absolutely no bromine was produced. All of the bromine reacted with the titanium, which appeared for form a soluble tetravalent complex with the bromine. When this contacted the sodium hydroxide produced at the cathode, a clumpy white precipitate began forming. The titanium gradually grew thinner until it was just a brittle fragment remaining that was no longer electrically connected. I noticed that the titanium hydroxide had a purplish tint to it, showing that some titanium was found in the trivalent state.
The titanium foil completely dissolved within a short period of time, showing the efficacy of this method. The product is also soluble in hydrochloric acid, forming a colorless solution which turns bright red upon addition of hydrogen peroxide. However, a smell of bromine is noticed, so is the red coloration the titanium peroxo complex or the bromine water? I will need to do more research into this.