A method to prepare coumalic acid comprising (a) heating a solution in dichloroethane of malic acid and sulfuric acid or a solution in dichloroethane of malic acid and a perfluorosulfonic acid or (b) adding an acid comprising sulfuric acid or a perfluorosulfonic acid to a solution of malic acid in dichloroethane to yield a solution that is heated for a period of time so as to convert the malic acid into a major amount of coumalic acid and, optionally, a minor amount of fumaric acid.