# 1911 Encyclopædia Britannica/Tropine

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​TROPINE, C$_8$H$_{15}$NO, a base formed together with tropic acid, C$_9$H$_{10}$O$_3$, in the hydrolysis of the alkaloid atropine (K. Kraut, Ann., 1863, 128, p. 280; 1865, 133, p. 87). It crystallizes in plates which melt at 63° C. and boil at 233° C.; it is very hygroscopic and easily soluble in water. It is an optically inactive, strongly alkaline tertiary base. On heating with sodium in amyl alcoholic solution it it transformed into a stereoisomer, identical with the ψ-tropine obtained by hydrolysing tropa-cocaine with hydrochloric acid. It possesses alcoholic properties, since it forms esters, the so-called “tropeines.” On distillation with caustic baryta or soda lime it decomposes into methyl amine and tropilidine, C$_7$H$_8$ (A. Ladenburg, Ann. 1883, 217, p. 74), the same hydrocarbon being also obtained when it is destructively methylated, a certain amount of tropiline, C$_7$H$_{10}$O, being produced simultaneously. When heated with fuming hydrochloric acid to 150–180° C. it yields tropidine, C$_8$H$_{13}$N, and with hydriodic acid similarly forms an ​iodo-compound, C$_8$H$_{15}$NI$_2$, which, on reduction with zinc and hydrochloric acid, is converted into hydrotropidine, C$_8$H$_{15}$N. It yields various oxidation products. With an alkaline solution of potassium permanganate it yields tropigenine, C7H,3NO; with chromic acid in the presence of acetic acid it yields tropinone, C$_8$H$_{13}$NO; and with chromic acid in the presence of sulphuric acid it yields tropinic acid, C$_6$H$_{11}$N(CO$_2$H)$_2$.
Tropidine, C$_8$H$_{13}$N, is a liquid having an odour resembling that of conine. It is a strong tertiary base, and is an unsaturated compound, forming addition products with the halogen acids. Hydrotropidine, C$_8$H$_{15}$N, is also a liquid. its hydrochloride on distillation loses methyl chloride and yields norhydrotropidine, C$_7$H$_{13}$N, a compound which is a secondary base, and whose hydrochloride when distilled over zinc dust yields α-ethyl pyridine. Tropinic acid, C$_6$H$_{11}$N(CO$_2$H)$_2$, obtained as above, is inactive; it was resolved by J. Gadamer (Arch. Pharm., 1901, 239, p. 663) by means of its cinchonine salt. It is a dibasic ac1d, and the methiodide of its dimethyl ester on fusion with caustic alkalis yields rt-adipic acid. It is apparently a derivative of N—methyl pyrrollidine, since it may be oxidized ultimately to N—methyl succinimide. Tropigenine, C$_7$H$_{13}$NO, is a secondary base.
The most important of the oxidation products of trop1ne is tropinone, C$_8$H$_{13}$NO, which is a ketone containing the grouping —CH$_{2⋅}$⋅CO⋅CH$_2$-since it yields a di-isonitroso derivative, a dibenzal derivative, and also forms mono- and di-oxalic esters. It is a strong base and has a powerful reducing action. Its constitution is determined by the above facts and also because tropinic acid on destructive methylation yields a diolefine dicarboxylic acid which on reduction is converted into n-pimelic acid. These data point to tropine possessing an unbranched chain of seven carbon atoms and incidentally determine the constitution of the other various oxidation products, &c. (R. Willstätter, Ber., 1895–1901). These compounds may consequently be represented as
H$_2$C CH—CH$_2$ H$_2$C⋅CH—CH$_2$ H¢C-CH-CH$_2$-CO$_2$H H$_2$C⋅CH—CH$_2$
       I I I I I I I
    NMe CHOH NMe CO NMe NMe CH
       I I I I I I I
    H$_2$C⋅CH—CH$_2$ H$_2$C⋅CH—CH$_2$ H$_2$C⋅CH⋅CO$_2$H   H$_2$C⋅CH—CH
    Tropine Tropinone Tropinic acid Tropidine.
On the synthesis of tropine, see R. Willstatter, Ber., 1901, 34, pp. 130, 3163.
Tropic acid, C$_9$H$_{10}$O$_3$, the other decomposition product of atropine, is a saturated hydroxy-acid which is readily converted into atropic acid, C$_9$H$_8$O$_2$, by dehydrating agents. This latter acid is shown by all its reactions to be C$_6$H$_5$C(:CH$_2$)⋅CO$_2$H, a fact which is confirmed by its synthesis from ace top hen one by the action of phosphorus pentachloride, followed by the decomposition of the resulting chloride with an alcoholic solution of potassium cyanide and subsequent hydrolysis of the nitrile so formed. These results show that tropic acid must be either C$_6$H$_5$⋅CH(CH$_2$OH)⋅CO$_2$H or C$_6$H$_5$C⋅(OH)(CH$_3$)⋅CO$_2$H, and since the latter compound has been prepared from ace top hen one by the addition of the elements of hydrocyanic acid, followed by subsequent hydrolysis and is an isomer of tropic acid, it follows that tropic acid must be represented by the former of the two formulae. Hence the alkaloid atropine, being a tropine-tropate, must have the annexed formula—
H$_2$C⋅CH—CH$_2$   CH$_2$OH
NMe CH⋅O⋅CO⋅CH
H$_2$C⋅CH—CH$_2$   C$_6$H$_5$
          Atropine.