ENDOTHIA PIGMENTS 
Alcoholic solutions of sodium and barium acetates yield insoluble 
sodium and barium salts. 
Silver nitrate and Fehling's solution are both reduced, the former even 
in the cold. 
When heated between watch glasses a portion of the substance sublimes 
without melting, giving rise to a ''Brazil red" sublimate. A carbonaceous 
mass remains in the lower watch crystal. 
Combustions were made of separate portions of the pigment, one purified 
from alcohol, dried at i5o°-2oo° C, and the other purified from water and 
dried at 100° C. The results are given in table I. 
Table i. Combustions of Endo thine Red 
Samples A and B from alcohol and samples C and D from water. 
Sample 
Weight 
CO2 
H.2O 
C. Percent 
'H, Percent 
0, Percent 
A 
.1719 
•3467 
•0543 
55-00 
3-53 
41.47 
B 
.1591 
.3186 
.0509 
54.62 
3-58 
41.80 
C 
.1572 
■3136 
.0504 
5440 
3-58 
42.02 
D 
.1803 
.3628 
.0565 
54-87 
3-51 
41.62 
Arithmetic mean of four de- 
terminations 
54-73 
3-55 
41.72 
Required for C7H5O4 
54.88 
3-29 
41-83 
Since the combustions of the material purified by the two methods and 
dried at the different temperatures are in excellent accord, it is evident that 
endothine red contains no water of crystallization. 
Diacetylendothine red. Attempts to obtain the acetyl derivative of 
endothine red by the employment of anhydrous sodium acetate were un- 
successful. The material was, therefore, boiled with acetic anhydride for 
several hours, and toward the end the excess of reagent was removed by 
evaporation. On cooling a semicrystalline mass separated, which was 
filtered with suction, washed with absolute alcohol and ether, and recrystal- 
lized several times from warm absolute alcohol. A portion of the acetyl 
derivative is hydrolyzed to the original pigment w^hen the alcohol contains 
an appreciable quantity of water. Even when preserved in a sealed tube 
for several months, darkening of the acetyl compound takes place. This 
change is rather remarkable when the pigment itself is so stable that cold 
concentrated nitric acid fails to attack it. The acetyl derivative was dried 
at 100° C. and combustions were made, with the results shown in table 2. 
Table 2. Comhusion of Acetyl Derivative of Endothine Red 
Sample 
Weight 
CO2 
HoO 
C, Percent 
H, Percent 
0, Percent 
A 
.2000 
•4034 
.0720 
55-01 
4-03 
40.97 
B 
.2007 
.4047 
.0723 
54-99 
4-03 
40.98 
C 
•1576 
.3217 
•0553 
55-60 
3-93 
40.47 
Arithmetic mean of three de- 
terminations 
55-20 
4.00 
40.80 
Required for 
C7H304(C2H30)2 
55-67 
3.82 
40.51 
