When mercuric acetate reacts with coumarinic acid in cold aqueous solution it adds on to the double bond and mercurates the benzene ring in positions 3 and 5. When the product is dissolved in sodium hydroxide the addenda get eliminated so that 3 ∶ 5-diacetoxymercuri-coumaric acid is produced on acidification. These compounds yield pure coumaric acid on being decomposed with hydrogen sulphide in alkaline solution. 5-Nitrocoumarinic acid adds only at the double bond and does not get mercurated. The product therefore yields the nitrocoumaric acid easily on dissolving in aqueous alkali and subsequently acidifying the solution.
In methyl alcoholic solution mercuric acetate adds on to the double bond in coumaric acids and their esters and mercurates positions 3 and 5 if they should be free. The constitution of these compounds has been established by treatment with bromine in glacial acetic acid and by examination of the action of caustic alkali on the bromocompounds. They give rise to brominated coumarilic acids.