2-(Triphenylphosphoranylidene)-butanedioic Acid 1,4-Diethyl Ester-14C4 is an intermediate in the synthesis of Itaconic Acid-13C5 (I931004) which is a labelled analogue of Itaconic Acid, a fermentation product of carbohydrates such as glucose using Aspergillus terreus. Itaconic Acid is widely used as a co-monomer in the production of styrene-butadiene-acrylonitrile and acrylate latexes.