Benzoyllævotetrahydroquinaldine, C10H12N CO. CH5.

On suspending purified lævotetrahydroquinaldine in warm caustic soda solution and running in rather more than the calculated quantity of benzoic chloride with continual agitation, an opaque, yellowish oil separates which rapidly solidifies to a hard, crystalline mass; this is ground in a mortar and filtered, being well washed with water and dilute hydrochloric acid. The substance is best purified by crystallisation from acetone; if, as sometimes happens, a green colouring matter is produced, this is best destroyed by crystallisation from ethylic acetate. After ultimately crystallising from absolute alcohol, the benzoyl derivative is obtained in colourless crystals melting at 117.5-118°. It is very soluble in benzene and moderately soluble in cold alcohol, less so in cold acetone or ethylic acetate; it is nearly insoluble in light petroleum or boiling water. This substance is, as would be expected, appreciably more soluble than the corresponding racemic compound. The following results were obtained on analysis:

2

0.1996 gave 0.5934 CO2 and 0·1230 H2O. C-81·08; H=6·84. 0.2066 0-6139 CO2 " 0.1276 H2O. C-81.04; H=6.86. 0.6108 300 c.c. of dry nitrogen at 21° and 7.55 mm. N=5.69. C1HON requires C=81.27; H=6·77; N = 5·58 per cent.

17 17

99

In order to obtain evidence as to the racemic nature of externally compensated benzoyltetrahydroquinaldine, it was necessary to compare the densities and crystalline forms of the active and inactive substances. The densities were determined by Retgers' method (Zeit. physikal. Chem., 1889, 3, 497), using a solution of barium mercuric iodide diluted with water; the results seem slightly more accurate than those obtained by Retgers with isomorphous mixtures, using organic liquids. The following results were obtained with crystals of benzoyllavotetrahydroquinaldine deposited from acetone or ethylic acetate solutions :

d1-2119; 1-2113; 1-2116; mean = 1.2116;

the molecular volume of the crystalline material is thus 207.16 at 14.5°/4°.

The crystallographic properties of the benzoyl derivatives of levoand dextro-tetrahydroquinaldine were fully studied and compared ; the crystals of the two substances being enantiomorphously related, as was to be expected, the following crystallographic description includes both compounds.

The optically active benzoyltetrahydroquinaldines are so soluble in benzene that good crystals could not be obtained from this solvent ;

cold solutions in acetone or ethylic acetate, however, deposit on spontaneous evaporation well-developed crystals suitable for goniometrical examination. The crystals are usually elongated in the direction of

the c-axis, and then are generally developed only at one end; frequently, however, crystals of the typical habit shown in Figs. 6 and 7 are obtained, and the examination of these crystals shows them to be

hemimorphic, the b-axis being polar. The pinacoids a{100} and b{010} are predominant, and generally of about the same facial development; neither of these forms gives very good reflections. The form pw{111} is usually fairly large, whilst the pyramid po{111} is quite small;

crystals exhibiting the number of faces required in the holohedral division of the monosymmetric system are often deposited from ethylic acetate solution, but the hemimorphism is generally betrayed by the unequal sizes of the faces, as in Figs. 8 and 9.

There is a very perfect cleavage parallel to a{100}, and the acute bisectrix emerges through a cleavage fragment at the edge of the field; observation of the extinction in b(010) shows that the acute bisectrix lies in the plane of symmetry at 17.5° to the face-normal to a(100). Both optic axes are visible in convergent light under a 1/12th inch oil immersion objective; the optic axial dispersion is marked, the optic axial angle for red being greater than that for blue light. The double refraction is positive in sign, and the optic axial plane is perpendicular to the plane of symmetry.

Crystalline system.-Monosymmetric: Hemimorphic.

a:b:c=1·0277:1:0·4261.

B=88° 15'.

Forms present on benzoyllævotetrahydroquinaldine (Figs. 6 and 8). -a{100}, b{010},+po{111} and +pw{111}; sometimes also - po{111} and -pw{111}.

Forms present on benzoyldextrotetrahydroquinaldine (Figs. 7 and 9).—a{100}, b{010}, -po{111}, -pw{111}; sometimes also + po{111} and +pw{111}.

The following angular measurements were obtained :

After melting the substance on a microscope slide under a cover slip, the liquid film can usually be cooled to the ordinary temperature without any solidification occurring; sometimes, however, crystallisation sets in whilst the film is very hot and then proceeds rapidly at the high temperature, but stops entirely when the slide cools. The crystallisation, having once started, can be caused to proceed rapidly until complete by cautiously heating the film at a temperature

below its melting point. The crystalline film consists of large, welldefined individual flakes; the larger faces of some of these are nearly perpendicular to the acute bisectrix of a fairly small optic axial angle showing positive double refraction, but those of others are nearly perpendicular to the obtuse bisectrix, in which the double refraction is apparently negative in sign. The optic axial dispersion is marked, the optic axial angle for red being greater than that for blue light. At the ordinary temperature, the liquid film solidifies very slowly indeed to a mass of interlaced needles showing aggregate polarisation; some of these needles can be seen to lie perpendicularly to the optically negative bisectrix of a large optic axial angle. Both the films obtained at high and low temperatures are probably structurally identical and also identical with the crystals deposited from solution.

The rotation constants of benzoyllæ votetrahydroquinaldine are of considerable interest, and show that the introduction of the acidic group has converted the lavorotatory base into a highly dextrorotatory compound. This is the more remarkable since the piperidine bases, dextro a-pipecoline, dextroisopipecoline, coniine, and dextroisoconiine, have the specific rotatory powers [a] +36-9°, +33-29°, +13-79°, and +8.19° respectively, whilst their benzoyl derivatives are also dextrorotatory and have the values [a] + 35.3°, +33·35°, +37·7°, and 29.1° respectively; the introduction of the benzoyl group into the pipecolines scarcely alters the specific rotatory power (Ladenburg, Ber., 1893, 26, 854). A case somewhat similar to that of lævotetrahydroquinaldine and its benzoyl derivative has been investigated by Forster (Trans., 1898, 73, 386), who finds that dextrobornylamine having [M]+69-6° yields a benzoyl derivative having the molecular rotatory power in alcoholic solution of [M] - 56.0°, the molecular rotatory power thus changing by 125.6°; in the case now recorded, a change of nearly 1000° in molecular rotatory power attends the conversion of the base into its benzoyl derivative. It is further of interest to note that, whilst the change of rotatory power occurs in the same sense on passing from either bornylamine or neobornylamine to its hydrochloride and then to its benzoyl derivative, the direction of the change in rotatory power alters in the case of tetrahydroquinaldine, as is shown in the following table:

The variation of the rotation constants of non-electrolytes with change of solvent has up to the present been but little studied, as, with the exception of the work of Freundler (Ann. Chim. Phys., 1895, [vii], 4, 286), few results of theoretical importance have been derived from such determinations. As, however, we show in a subsequent paper (this vol., p. 1111) that valuable information concerning the state of molecular aggregation of optically active substances is derivable from the variations in rotation constants referred to, a series of determinations of the specific rotatory powers of benzoyllævotetrahydroquinaldine in various solvents has been made. The results are stated in the following table, in which w denotes the weight of substance contained in v c.c. of solution at temperature t, and c is the concentration in grams per 100 c.c. of solution :

Hydrolysis of Benzoyllævotetrahydroquinaldine.-Since we proposed to prepare pure dextrotetrahydroquinaldine by hydrolysing its benzoyl derivative, and since racemisation frequently accompanies chemical change, it was desirable to ascertain whether benzoyllævotetrahydroquinaldine yields only the parent base on hydrolysis. The powdered benzoyl derivative was hydrolysed by boiling for some days with concentrated hydrochloric acid; after rendering alkaline with soda, and extracting with ether, the ethereal solution was washed with water and evaporated to dryness, hydrochloric acid being added towards the end. The crystalline hydrochloride was then ground up with acetone in an agate mortar, separated by filtration, and spread on a porous plate; it was colourless, and 0.5009 gram, dissolved in water and made up to 25.2 c.c. at 23.0°, gave ap - 2.63° in a 200 mm. tube, whence [a]p - 66.2°. This being the specific rotatory power of the lævohydrochloride, it is obvious that no racemisation attends the hydrolysis,