4-NITRO-5-METHYL-2-SULPHOBENZOIC ACID 
183 
preparation of the chlorides, and the condensed phosphorous 
oxychloride formed is kept in the mixture, a much larger per 
cent of the unsymmetrical chloride is produced, although the 
absolute yield seems to he smaller. Holmes^^ used phosphorous 
oxychloride in sealed tubes for the preparation of the pure un- 
symmetrical acid chloride of p-nitro-o-sulphobenzoic acid. In 
this case we found it not necessary, and the shorter process 
was used. 
The purification of the unsymmetrical acid chloride by frac- 
tional crystallization from carbon tetrachloride was not difficult. 
It crystallized in short, tufted, rather soft needles, yellowish in 
color. An attempt was made to use the method of List and 
Stein^^ for the purification of the acid chlorides by distillation 
in vacuo. It was expected that the symmetrical chloride would 
decompose at the distillation temperature, while the unsymmet- 
rical would distil unchanged. Distillation took place at the 
following temperatures and pressures. 
Pressure in mm. mercury 
Boiling point 
21 
218-220° 
11 
214° 
10 
212° 
It was found that both acid chlorides distilled unchanged 
under these conditions. The distillation mixture was composed 
of nearly pure 83° melting chloride; no attempt was made to 
distil the 134° melting acid chloride either alone or when there 
was any large per cent of it in the mixture. No difference was 
made in the melting point of the pure 83° melting point sub- 
stance, though its color was nearly destroyed by the distillation. 
The acid chloride melting at 83° was analyzed, the methods 
used being the same as in the case of the high melting chloride. 
.3849 g. acid chloride gave .3626 .g. silver chloride. 
.3848 g. acid chloride gave .3646 g. silver chloride. 
.2780 g. acid chloride gave .2636 g. silver chloride. 
.2780 g. acid chloride gave .2180 g. barium sulphate. 
.2869 g. acid chloride required 9.06 cc 1084N HCl. 
.1823 g. acid chloride required 5.80 cc 1084N HCl. 
Theory for CgHsOsNSCL Found 
Chlorine, 23.80 per cent. 23.3 - 23.40- 23.46 per cent. 
Nitrogen, 4.70 per cent. 4.82 - 4.79 per cent. 
Sulphur, 10.74 per cent. 10.77 per cent. 
“Am. Chem. J., 25, 204, 1901. 
“Ber., 31, 1648, 1898. 
