1911 Encyclopædia Britannica/Tropine

TROPINE, C₈H₁₅NO, a base formed together with tropic acid, C₉H₁₀O₃, 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, C₇H₈ (A. Ladenburg, Ann. 1883, 217, p. 74), the same hydrocarbon being also obtained when it is destructively methylated, a certain amount of tropiline, C₇H₁₀O, being produced simultaneously. When heated with fuming hydrochloric acid to 150–180° C. it yields tropidine, C₈H₁₃N, and with hydriodic acid similarly forms an iodo-compound, C₈H₁₅NI₂, which, on reduction with zinc and hydrochloric acid, is converted into hydrotropidine, C₈H₁₅N. 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, C₈H₁₃NO; and with chromic acid in the presence of sulphuric acid it yields tropinic acid, C₆H₁₁N(CO₂H)₂.

Tropidine, C₈H₁₃N, 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, C₈H₁₅N, is also a liquid. its hydrochloride on distillation loses methyl chloride and yields norhydrotropidine, C₇H₁₃N, a compound which is a secondary base, and whose hydrochloride when distilled over zinc dust yields α-ethyl pyridine. Tropinic acid, C₆H₁₁N(CO₂H)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, C₇H₁₃NO, is a secondary base.

The most important of the oxidation products of trop1ne is tropinone, C₈H₁₃NO, which is a ketone containing the grouping —CH_2⋅⋅CO⋅CH₂-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

H₂C CH—CH₂ H₂C⋅CH—CH₂ H¢C-CH-CH₂-CO₂H H₂C⋅CH—CH₂

I I I I I I I

NMe CHOH NMe CO NMe NMe CH

I I I I I I I

H₂C⋅CH—CH₂ H₂C⋅CH—CH₂ H₂C⋅CH⋅CO₂H   H₂C⋅CH—CH

Tropine Tropinone Tropinic acid Tropidine.

On the synthesis of tropine, see R. Willstatter, Ber., 1901, 34, pp. 130, 3163.

Tropic acid, C₉H₁₀O₃, the other decomposition product of atropine, is a saturated hydroxy-acid which is readily converted into atropic acid, C₉H₈O₂, by dehydrating agents. This latter acid is shown by all its reactions to be C₆H₅C(:CH₂)⋅CO₂H, 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 C₆H₅⋅CH(CH₂OH)⋅CO₂H or C₆H₅C⋅(OH)(CH₃)⋅CO₂H, 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—

H₂C⋅CH—CH₂   CH₂OH

NMe CH⋅O⋅CO⋅CH

H₂C⋅CH—CH₂   C₆H₅

Atropine.