G. K. Helmkamp and D. J. Pettitt. Trimethyloxonium 2,4,6-Trinitrobenzenesulfonate. Org. Synth. 1966, 46: 122. doi:10.15227/orgsyn.046.0122.
Ross, S.; Bassin, M.; Finkelstein, M.; Leac, A. L. Molecular Compounds. I. Picryl Chloride-Hexamethylbenzene in Chloroform Solution. J. Am. Chem. Soc. 1954, 76: 69–74. doi:10.1021/ja01630a018.