Thymohydroquinone, C10H14O2, has been found in the oil of Callitris quadrivalvis, Algerian fennel oil (?) and in the oil of Monarda fistulosa. Artificially it is obtained by the reduction of thymoquinone with sulphurous acid.3)

Thymohydroquinone occurs in four-sided, shiny prisms. According to Carstanjen3) they melt at 139,5°, according to Ciamician and Silber4) at 143°. According to the latter authorities thymohydroquinone boils at 290°. It is somewhat readily soluble in hot water, but difficultly in cold water. When oxidized it is changed to thymoquinone.

The dimethyl ether of thymohydroquinone is the principal constituent of arnica root oil, also of ayapana oil. It boils at 248 to 250°; d22o 0,998.5)

1) Hantzsch, Journ. f. prakt. Chem. II. 22 (1880), 462. 2) Wichelhaus, Berl. Berichte 12 (1879), 1501, footnote; comp. Hesse, Liebig's Annalen 200 (1880), 254.

3) Carstanjen, Journ. f. prakt. Chem. II. 3 (1871), 54.

4) Atti della Reale Accademia dei Lincei Rendiconti (5) 10, I. (1901), 96. 5) Reychler, Bull. Soc. chim. III. 7 (1892), 33.