42 BoWACK AND LAPWORTH : VI.-Derivatives of Menthyl Cyanoucetate. By DOUGLAS ANDERSON BOWACE and ARTHUR LAPWORTH. THE esters of acetoacetic, cyanoacetic, and malonic acids contain hydrogen atoms, which, although directly attached to carbon atoms, a1 8 easily replaced by sodium, and the resulting metallic derivatives, a t least in the case of the first two classes, appear to be derived from the enolic modifications of the esters. The stability of the enolic forms o f the free esters appears to vary considerably, and only in the case of the derivatives of the acetoacetates is there any direct evidence that a measurable amount of free enol is present when an equilibrium is attained. I n the hope of obtaining further evidence on this point, some optically active derivatives of cyanoacetic acid were prepared, with the view of determining whether they exhibited any measurable mutarotation, as this phenomenon is apparently always associated with change in molecular structure, and, moreover, was well marked in the cape of certain derivatives of menthyl acetoacetate (Trans., 1902,81, 1502, and 1903,83, 1117).The following investigation had been practically completed when a paper by Tschugaeff appeared (J. RW8. Phys. Chem. ~ o c . , 1902, 34, 6069),in wbich fhe rotatory power of menthyl cyanoacetate was given, SO that the first compound described in the present paper is not new. We have not been able to consult the original paper, but the rotatory power of the ester as given in an abstract (Abstr., 1903, ii, 1) agrees satisfactorily with the number we had previously obtained.Menthyl cyanoacetate does not appear to exhibit a trace of muta- rotation, even in presence of traces of bases or acids, agents which have been found t o accelerate this change whenever it occurs. The rotatory power of the monobromo-derivative in benzene, however, altered somewhat rapidly from [a], - 23.42' to [a], - 32.919 It was expected that if mutarotation occurred in any of the deriv- atives of this ester, it would probably be most readily detected in the azo-compounds, particularly as the a zo-derivatives of ment hy 1 aceto-DERIVATIVES OF MENTHY L CYANOACETATE. 43 acetate exhibited this property in an extraordinary degree (compare Trans., 1903, 83, 1117). Moreover, Weissbach (J. pr. Chern., 1903, [ii], 6’7, 395) has shown that ethyl phenylazocyanoacetate may be obtained in three different forms, two of which he regards a s stereo- isomeric azocyanoacetates, and the third as ethyl a-phenylhydrazone- cyanoacetate.No appreciable change in the rotatory powers of the menthyl esters, however, could be detected. It is worthy of note that the rotatory powers of- the azo-compounds described in the present paper, unlike those of menthyl acetoacetate (compare Trans., 1903, 83, 1117), are within the usual limits found for menthyl esters of ordinary carboxglic acids. Menthyl bromo- cyanoacetate, however, has initially an abnormally small rotatory power, which, a s in similar cases, may perhaps be due to the presence of the asymmetric carbon atom present in the acyl residue. EXPER I MENTAL.Menthy2 Cyamoacetata, CN.CH2*C0,*C,,H,,. Menthol (43 grams) and ethyl cyanoacetate (30 grams), mixed in a distilling flask connected with a condenser, are gently heated over a n Argand burner a t such a temperature that about one drop of alcohol per minute is collected, and the heating is continued until the theoretical amount of liquid has thus been obtained. The product is then submitted to fractional distillation under a pressure of about 30 mm., so as to remove the considerable amount of menthene which is always formed; when the temperature of the vapour has risen t o about 150°, the distillation is interrupted, and the residue, which partly solidifies on cooling, is triturated with alcohol and spread on porous earthenware, the solid being 6nally recrystallised from alcohol. 0.2018 gave 0,5167 CO, and 0.1726 I1,O.C = 69.8 ; H= 9.5. C,,II,,O,N requires C = 70.0 ; H = 9.4 per cent. The ester is somewhat readily soluble in most of the ordinary organic media, and crystallises from alcohol in well-defined, small prisms or Ant needles melting a t 83 -84O. In plane polarised light, the crystals show straight extinction, and the directions of greatest elasticity and length are coincident, the double refraction being strong. When melted between glass slips, the compound solidifies readily in very long, flat needles, crystallographically identical with those obtained from alcohol ; in these, the optic axial plane cuts the crystals longitudinally, and in some cases a bisectrix, probably the obtuse, of a figure of wide angle, emerges noimally to the field, so that the acute44 BOWACK AND LAPWORTH : bisectrix is probably emergent at the apices of the crystah.For the determination of the rotatory power, a solution of 0.5000 gram of the ester in benzene (25 c.c.) was examined in a 2 dm. t u b e ; the rotation observed was ay = - 3*25O, giving [.ID = - 81.15'; no altera- tion of this value was noticed after the lapse of some days, and no change was effected by the introduction of traces of piperidine or t richloroacetic acid. The rotatory power of menthyl cyanoacetate was given by Tschugaeff as [air, = -SO.7l0 (Zoc. cit.). Menth) bronzocyanoacetnte, CN*OHBr*C02.C,oHlo, was made by add- ing the requisite quantity of bromine t o a solution of menthyl cyano- acetate in chloroform, the product being allowed to remain until the reaction was complete, when it was shaken repeatedly with water, dried over calcium chloride and evaporated, the solid residue being then crystallised from alcohol.0-1908 gave 0.1176 AgBr. Br = 26.4. C,9H2002NBr requires Br = 26.5 per cent. The substance is somewhat readily soluble in chloroform, benzene, and glacial acetic acid, but more sparingly so in alcohol and light petroieum. It separates from alcohol in well-defined, small prisms, which in plane polarised light have straight extinction and strong double refraction, the directions of greatest length and elasticity being coincident ; when melted between glass slips, i t solidifies in masses of very small, ill-defined, flat needles. For the determination of the optical activity, a solution of 0.4056 gram of the compound dissolved in benzene (25 ex.) had a n initial rotation in a 2 dm.tube of a, = 0*76O, whence [.ID = - 23.42'. The value rose within half an hour t o [a]* = - 3 2 * 9 O , afterwards remaining constant at this point, Menthyl p- ToZyZaxocya rzoacetate, C H,*C,H,*N,* CH(C N)* GO,* C,,H,,. It was not found possible to obtain menthyl phenylazoaceto- acetate in a crystalline form, but the preparation of the corresponding p-tolylazo-compound presented little difficulty. Menthyl cyanoacetate was dissolved in a large quantity of warm alcohol containing a n excess of sodium acetate, and t o the well-cooled liquid was slowly added one molecular proportion of p-tolyldiazonium sulphate dissolved in the smallest possible quantity of water.After some hours, during which the mixture remained a t the temperature of the laboratory, the whole was poured into water and the deposited oil collected, washed repeatedly with water, and dissolved in an equal bulk of alcohol. After some weeks, the azo-compound was deposited i n large crystals, which were freed from adherent oil and recrystallised from alcohol.DERIVATIVES OF MENTHYL CYANOACETATE. 45 0.2120 gave 0.5467 CO, and 0.1509 H,O. C,,H,70,N, requires C = 70.4 ; H = 7.9 per cent. The compound dissolves readily in ether, ethyl acetate, acetic acid, chloroform, and benzene, but is much more sparingly soluble in alcohol and light petroleum. It separates very slowly from warm super- saturated solutions in alcohol i n the form of beautiful, large, trans- parent, yellow plates which melt a t 93-95'.When crushed fragments of the crystals are examined in cedar-wood oil in convergent polarised light, a biaxial interferencefigure of wide angle is occasionally noticeable. If, as is probable, the figures observed were those surrounding the acute bisectrix, the double refraction is positive in sign and strong. After melting between glass slips, the substance could not be made to resolidify. For the determination of the optical activity, a solution of 0.7543 gram of the compouud in benzene (50 c.c.) was examined in a 2 dm. tube. The rotation observed as a mean of several concordant readings was uD = - 1-62', whence [.ID = -53.7'. The rotatory power did not change after the solution had remained for several days ; the addition of piperidine, however, caused a n immediate alteration of the observed rotation by 0.04', but this new value was also constant, so that the change was probably not due t o mutarotation ; no effect was produced by the addition of trichloro- acetic acid.The azo-compound does not appear to Cissolve in cold 30 per cent. aqueous sodium hydroxide, even if very finely powdered, and i t com- municates no colour whatever t o the liquid; even if the alkali is added to the alcoholic solution of the substance, when the liquid is poured into water, the latter is found to be colourless after the pre- cipitate has settled. The corresponding ethyl ester dissolves somewhat readily in dilute alkali, and the difference in properties between the two esters is doubtless to be attributed to the very great relative difference between their solubilities in water rather than to any chemical dissimilarity (compare Trans., 1903, 83, 11 17).C=70.3; H=7.9. iVe?xth?/l p-.Bromo~~enylazoc?/unoacetate, Br*C,5H,*N,*CH( CN) CO,* 910H19. This compound was prepared by a method exactly similar to that used in making the foregoing compound. It crystallised readily when its alcoholic solution was sown with a trace of the cryntals of the corresponding p-tolyl compound. 0.2005 gave 0.4155 CO, and 0.1092 H,O. C=56*5 ; H=6.0. C:,,H,,O,N,Br requires C: -- 56.15 ; H = 5.9 per cent.46 HA" AND LAPWORTH: OPTICALLY ACTIVE ESTERS OF The substance closely resembles that just described in regard to it8 solubility in various media, but appears to be somewhat less readily soluble.It separates from warm alcohol in the form of magnificent, transparent, yellow prisms or thick plates which melt at 97-98'. Crystallographically, the description given of the p-tolyl compound applies equally well to the [present substance. Occasionally it was found that another form of the compound separated during the crystallisation from alcohol. This modification presented the appear- ance of very fine needles and melted somewhat indefinitely between 95' and 105'. The difference between the two forms, however, appears to be of a crystallographicd and not a chemical character, as the rotatory powers in both cases are constant and identical, and by seeding the supersaturated solution of the acicular modification with a trace of the other the whole may be converted into the transparent tables characteristic of the form melting at 97-98". For the determination of the rotatory power, ft solution containing 0.3450 gram dissolved in benzene (25 c.c.) was examined in a 2 dm. tube. The rotation observed was a,, = - 1-18', whence [a],, -- -42.75". The authors desire to express their thanks to the Research Fund Committee of the Chemical Society for a grant which defrayed part of the cost of the investigation. CHEMICAL DEPARTMENT, THE GOLDSMITHS' INSTITUTE, NEW CROSS, S.E.