888 Wisconsin Academy of Sciences, Arts, and Letters . 
Aloeemodin. — TriKydroxy-2, 4\ 5-methyl-l-anthraquinone. 
Aloeemodin, a primary alcohol, occurs with aloin in various 
species of aloes, 1 senna 2 and rhubarb. 3 It crystallizes in orange 
red needles which melt at 224°. It is easily soluble in ether, 
hot alcohol, and benzene, soluble in concentrated sulphuric acid 
with a cherry red color. Aloeemodin yields a triacetyl and a 
tribenzoyl derivative. Upon reduction it forms methyl anth¬ 
racene. Oxidized with chromic acid mixture it yields rhein. 
O COOH 
CH C 
Since rhein is produced upon the oxidation of aloeemodin, 
one of its hydroxy groups must be in the side chain. The po¬ 
sitions of the other hydroxy groups is uncertain. Robinson 
and Simonson 4 have suggested for it the formula given above. 
P entity dr oxides of methyl-1 -anthraquinone. 
Only one penthy dr oxide of methyl-l-anthraquinone is known 
to exist in plants. This is rhein, a dihydroxyanthraquinone 
carboxylic acid. Rhein is an oxidation product of aloeemodin 
which it accompanies in several species of aloes, and also of 
rhubarb. 
1 Whemer, Die PflanzenstofEe, p. 90; C.r., 150, p. 983; Arch. f. Pharm. 
247, p. 413. 
2 Rupe, Natuerliche Farbstoffe, 2, p. 134. 
8 Arch. Pharm., 243, p. 443 ; 247, p. 413. 
4 Proc. Chem. Soc., 25, p. 76 ; Jr. Chem. Soc., 95, p. 1085. 
