Can phosphoric acid be used to substitute sulfuric acid in the synthesis of thymolphthalein?

I am planning to synthesize thymolphthalein, a pH indicator. I am wondering if phosphoric acid can be used to substitute sulfuric acid in the preparation. I know it can catalyze Friedel-Crafts reactions, which are a part of the synthesis. Any advice would be appreciated.

• It would be appreciated if you could attach an image of the normal synthesis involving sulphuric acid. Would help those who are not aware of the compound. Thank you :)
– TRC
Jul 25 at 14:44
• If you use polyphosphoric acid (PPA) I think it will work. PTSA will also probably work Jul 25 at 15:05
• What is your reasoning for, what is your reasoning against the substitution of the strong Bronsted acid $\ce{H2SO4}$ by phosphoric acid (i.e., review of the literature)? By the way, the waxy polyphosphoric acid may be considered, too (an elder review, a current application). Jul 25 at 15:06
• I do chemistry in a workspace with wooden benches, and sulfuric acid would eat through them quickly. Thanks for suggesting those, I can make or get both of those. Jul 25 at 15:19
• But the question is: would straight phsophoric acid work? Jul 25 at 16:13