Trimethyloxonium 2,4,6-trinitrobenzenesulfonate (CAS NO.: 13700-00-0) could be produced through the following synthesis route.

The apparatus is shown in Fig. 1. Two 500-ml. round-bottomed flasks without standard-taper joints (which could cause diazomethane to detonate) are used. The gas inlet C is connected to a cylinder of . Gas inlet C is long enough to reach near the bottom of flask A, but tubing D extends only about halfway into flask B. A calcium chloride drying tube is attached to the gas outlet E. Flask B contains a ®-covered stirring bar. The pieces of the apparatus are dried in an oven at 110°; well-dried apparatus is essential for a good yield.

                                              Fig. 1.

A solution of diazomethane in 200 ml. of xylene is prepared from 15.0 g. (0.146 mole) of nitrosomethylurea. The diazomethane solution is decanted into flask A, and about 20 g. of potassium hydroxide pellets is added to the solution. The mixture is swirled for a few seconds to ensure removal of most of the water. About 4.2 g. (0.10 mole) of diazomethane is present. Flask A is then immersed in a water bath at 20–25°.

2,4,6-Trinitrobenzenesulfonic acid (14.7 g., 0.050 mole), previously dried for at least 1 hour at 80–100° (1 mm.), is placed in flask B, which is then immersed to the level shown in Fig. 2 in a bath of acetone maintained at -35° to -40° by addition of small amounts of dry ice. About 200 ml. of dimethyl ether is rapidly poured from an ampoule into flask B. Flasks A and B are connected as shown in Fig. 2, and magnetic stirring is started in flask B. When most of the sulfonic acid has dissolved, gaseous dimethyl ether is introduced through C at such a rate that a rapid stream of individual bubbles passes through the diazomethane solution in flask A. In the course of the reaction all the acid goes into soution and is replaced by a fluffy precipitate of the oxonium salt. The introduction of dimethyl ether is discontinued as soon as the supernatant solution in flask B turns yellow.

Flask B is separated from the apparatus but kept in the cooling bath, and 200 ml. of anhydrous ethyl acetate is added; addition is slow so as to avoid excessive boiling of the dimethyl ether. The flask, with a tube of calcium chloride attached, is gradually brought to room temperature; most of the dimethyl ether evaporates during this operation. Crystalline trimethyloxonium 2,4,6-trinitrobenzenesulfonate is separated on a coarse sintered-glass funnel, washed with two 25-ml. portions of ethyl acetate and with 50 ml. of high-boiling petroleum ether, and dried over phosphorus pentoxide at 25° (<1 mm.); yield 12–14 g. (68–79%), m.p. 181–183°.