In a
12-l. round-bottomed flask are placed 7.2 kg. of cracked ice and
2.4 kg. (1300 cc., 23.4 moles) of concentrated sulfuric acid (sp. gr. 1.84). The mixture becomes very cold and is kept at −5° to 0° by means of an
ice-salt bath. Mechanical stirring is started and
600 g. (3.4 moles) of crude benzenesulfonyl chloride (p. 84) is gradually introduced (one-half hour) (Note
1). Then
1.2 kg. (16.5 atoms) of zinc dust (90 per cent) is added (Note
2) in portions as rapidly as possible without allowing the temperature to rise above that mentioned (this requires about one-half hour) (Note
3). The contents of the flask are stirred for one to one and one-half hours longer, the temperature being kept at 0° or below during the whole period. A
stopper holding an
efficient reflux condenser (lower end not constricted) and stirrer is now attached; the ice bath is removed (Note
4); and the reaction mixture is allowed to warm up spontaneously or it may be warmed up with a low flame, the stirring being continued. Within a very few (two to five) minutes, in many runs, a rather vigorous reaction with the evolution of much
hydrogen takes place. Under these circumstances it is advisable to cool the flask momentarily by a stream of water. The reflux condenser will, however, generally take care of the vapors satisfactorily.
After the first ebullition has subsided, no further attention is required, and the mixture is heated to boiling over a
ring burner until the solution becomes clear. The stirring should be continued during the refluxing, and the stirrer should be arranged so as to suck the liquid downward from the surface. This helps distribute the
zinc which holds
hydrogen and floats on top of the liquid. About four to seven hours are required for the heating (Note
5). The
thiophenol is then distilled with steam, this process requiring about one hour. The product is separated from the water, dried with
calcium chloride (shaking with
calcium chloride for three to five minutes is generally sufficient), and distilled. The crude material weighs
359 g. (
96 per cent of the theoretical amount), and the pure compound boiling at
166–169° (71°/15mm.) weighs
340 g. (
91 per cent of the theoretical amount). Ten to twelve hours are required for the whole experiment up to the final distillation.