104 JEPIXCOTT THE PHYSICAL CONSTANTS OF NICOTINE. PART I. X.-The Physical Constants of Nicotine. Part I. Spectjic Rotatory Power of Nicotine in Apueous Solution. By HARRY JEPHCOTT. NICOTINE has been purified and its constants have been recorded by Landolt (" Optical Rotation of Organic Substances ") Nasini and Pezzolato (Zeitsch. physikal. Chem. 1893 12 Sol) Gennari (ibid. 1896 19 130) Rein (Diss. Berlin 1896) Piibram and Glucksmann (Monutsh. 1897 18 303) Ratz (ibid. 1905 26, 1241) and Winther (Zeitsch. p'hysilcal. Chem. 1907 60 563). All with the exception of Ratz relied on the distillation in hydrogen of anhydrous nicotine. Ratz utilised two methods, namely fractional distillation in a vacuum and the formation of nicotine zinc chloride followed by distillation.Their results for the specific rotation which show considerable variation are as follows : Landolt .................................... Nasini and Pezzolato .................. Gennari .................................... Hein ....................................... Pfibram and Glucksmann ............ Rrttz (by fractional distillation) ...... .. (from double salt) ............... Winther .................................... bl?. D;*. 161.55 1~01101 161.29 -162.84 1.01071 164.18 1.01049 164.91 1.0095 166.77 -169.0 to 169.54 1.00925 163.85 JEPHCOTT THE PHYSICAL CONSTANTS OF NICOTINE. PABT I. 105 It appeared probable that the variation was due to the presence of the alkaloids nicoteine nicotelline and nicotimine which occur with nicotine and it was decided to purify nicotine by the method utilised by Pictet and Rotschy (Ber.1901 34 696) when isolating these alkaloids. Nicotine which had been prepared from tobacco by steam distillation was dissolved in a slight excess of hydro-chloric acid and treated with sodium nitrite a t low temperature. The nicotine was subsequently liberated by alkali dehydrated and fractionally distilled under diminished pressure. Considerable loss of nicotine occurred owing to the formation of oxidation producte during the treatment with nitrite. A quantity about 2600 grams in all of commercial nicotine was also converted into nicotine zinc chloride twice recrystallised, and the nicotine liberated dehydrated and fractionally distilled under diminished pressure in a manner similar to that of Ratz In the cold, nicotine readily f orrns highly-coloured oxidation products on ex-posure to the air.When hot this oxidation is extremely rapid, and water is also absorbed. At the temperature of distillation the vapour readily attacks cork or rubber used for connexions. Well.-fitting ground-glass joints are essential but there proved to be na necessity to flood the apparatus with hydrogen if a sufficiently high vacuum were maintained (20-40 mm. pressure). The nicotine prepared in this way was colourless and almost without oidour in the cold. When kept in bottles filled to the stopper and away from the light nicotine remains colourless only the slightest yellow tint being noticed after six months and no change in rotatory power (compare Piibram lac.&t. p. 303). For pure nicotine the density and rotatory power were found t o be as follows: (loc. cit.). The distillation was a source of much trouble. D?. [a];,". Purified through nitroso-compound . . . . . . 168.52 Purified through double chloride (1) . . . 1.00925 168.61 168.40 1.00920 Y Y YP , (2) ... 1.00925 ? Y YY Y 99 ) (3) ... 1.00925 168.66 The three sets of figures for the double chloride method refer to three separate and distinct preparations of pure nicotine in that way. Many dilutions of this nicotine with water were prepared and the specific gravity and specific rotatory power for them observed. The rotations were measured with a Schmidt and Haensch half-shade polarimeter using a tube having a length of 100.04 mm 106 JEPHOTT ; TRE PHYSICA5 CONSTANTS OF NICOTINE.PA€LT 1. Percen-t a p by weight. 95.068 91.084 89.471 88.338 83.336 81-842 77-006 750538 84.868 69.202 67-538 64.423 63.960 60.773 59.898 59.649 56.241 64.289 53.096 51.969 60.134 48.949 46.632 46.183 46.015 100 Grams in 100 100.926 96.801 93.323 91.781 90-820 86.132 84-632 79.921 78.551 77.764 71.963 70.231 66.91 8 66.440 63.110 62.131 61.895 58.260 56.245 54,934 53.750 51.777 50.513 48.062 47.629 47.412 C.C. D?. 1.00925 1.01823 1.02458 1.02583 1*02810 1.03356 1-03439 1-03784 1.03836 1.03839 1,03990 1.03988 1-03890 1.03894 1-03846 1.03728 1-037 65 1.03614 1.03603 1.03463 1.03428 1.03278 1.03194 1.03065 1.03 13 1 1.03037 cay:.168.61 153-06 141.65 138.73 134.11 123.21 121.48 111.47 108.39 108.69 100.47 97-82 95.63 94.02 93.69 95.12 91.27 89.27 90.12 86-91 89.03 88.19 86.23 86-79 --Percen-tage by weight. 44.004 41-718 40.237 38.798 38,065 37.986 35.098 34.877 32-141 30.973 30,637 30,291 28.151 26,473 24.975 20.963 20-726 169023 12.963 11.508 10.012 9.921 7.417 6.604 4-998 2-505 Grams in 100 45-296 42.882 41.308 39.804 39.025 38.950 35,920 35-696 32.810 31.607 31.253 30.915 28.664 26.930 25.369 21.235 20.995 15.156 13.027 11.579 10.061 9.971 7.441 6.622 5.006 2.504 C.C. DT . 1-02936 1.02790 1.02661 1.02592 1.02522 1.02538 1-02341 1-02351 1.02107 1.02048 1.02010 1.02060 1.01820 1.01725 1.01588 1.01300 1.01239 1.00880 1.00492 1-00611 1.00611 1.00494 1-00317 1.00276 1,00163 0.99970 [.I:.86.47 86.7 1 85.09 83-79 85-2 1 84-98 83.52 83-39 81.83 82.48 82.67 82.60 81.95 81.78 81.67 80.64 80.06 79-79 79.43 78.66 79.20 79.94 79-25 80.48 83.15 8a.99 The effect of temperature on the density and rotatory power both of pure nicotine and certain of its aqueous solutions has also been observed. For t.his purpose a jacketed polarimeter tube was Nicotine in aqueous 9olution. 1-05 1.04 1-03 .g 2 1.02 6 1.01 Percmtage by weight. employed a Sprengel tube being used for t,he densities.It was not convenient in every cas0 to observe both density and angle at, t.he same temperature and the density a t the temperature a JEPHCOTT THE PHYSICAL CONSTANTS OF NICOTINIS. PART I. 107 which the rotatory power was observed was obtained from a graph constructed from the recorded densit,ies. Pure Nicotine. Temperature. 20". 21.1'. 40". 60". 80". 97.7'. Dz O ............ 1.00925 1.00865 0.99424 0.97799 0.96184 0-94534 Temperature. 20° 29.5 41.5 62 62 69.6 86.4 92.0 Df (from graph). 1.00926 1.0017 0.9924 0.9840 0,9760 0.9699 0-9567 0.9521 [a];. 168.20" 168.71 169.09 169.61 169.74 169.94 169.73 169.7 1 Owing t o the so-called closed curve of solubility of nicotine in water it is not possible to observe the rotatory power and density of solutions containing between 7 and 87 per cent.of nicotine a t all temperatures up to looo since separation occurs at about 60°. Two solutions were therefore prepared which would fall outside this closed curve and contained 6-638 per cent. and 88.338 per cent. of nicotine. For these the following figures were found: Percentage Grams in Temperature. by weight. 100 C.C. D" [a]:. 20" ............... 6.638 6-682 140275 76.82 85 ............... 6.638 6.4188 0.96328 95.29 20 ............... 88.338 90.820 1.02810 134.16 90 ............... 88.338 86.936 0.98412 150.34 It will be observed that the change in rotmatory power is marked. On cooling to 20° the 6 per cent. solution a t Once showed its original rotatory power but the 88 per cent.solution did not revert to its former value for some days although an immediate fall to about [a]," 138.0 took place. Difficulty occurs in determin-ing the rotatory power of pure nicotine and its more concentrated solutions since owing presumably to light absorption it is zuxes-sary to match a greyish-pink against a grey when taking polari-metric readings. I n the case of the more concentrated aqueous solutions the difficulty is greatly increased owing to the very marked changes in density. In observing the angle of the 88 per cent. solution a t 90° even with a rapid stream of water circu-lating round the jacket the change in density by cooling a t the exposed surface of the end plates was so marked as t o make i t almost impossible t o get light to pass khrough the tube and th 108 JEPHCOTT !FHE PHYSICAL CONSTANTS OF NICOTINE.PART I. rotation recorded must be considered liable to an error of lo. No such difficulties were experienced with the 6 per cent. solution. The graphs for density and specific rotatory power of nicotine in aqueous solution both exhibit a series of maxima and these agree with molecular proportions of nicotine and water. This indica.tion of the formation of a series of hydratea is confirmed by an examination of the freezing points of nicotine solutions. Between 40 and 80 per cent. the time taken for hydrate-form-ation is appreciable and t h e abnormal points marked were found in cases of solutions when the rotation was observed immediately after mixing.A solution containing 69.2 per cent. of nicotine showed no change in rotation after keeping for twelve months. The ‘‘ OJosed Curve of Solubility ’’ fop Nicotime. The formation of hydrates of nicotine and their decompositlion at higher temperatures shows the true nature of the “closed curve of solubility.” Nicotine is only sparingly soluble in water and water is only sparingly soluble in nicotine but hydrates of nicotine are miscible wit,h either a state of balance existing a t any given temperature between nicotine its hydrates and water. When the temperature rises the hydrate-formation reverses, and on the concentration of fr0e nicotine becoming greater than the solubility of nicotine in water at that temperature separation occurs. By choosing concentrations of nicotine and water such that the limit of solubility of the one in the other was not exceeded, it was possible as shown above to note the marked rise in rota-tory power as tqhe concentration of free nicotine increased with the rise in temperature and it is to be expected that with conve~ence for observing the angle a t a sufficiently high temperature the true rotatory power of nicotine in water would be obtained. I am indebted to Mr. George Dean Head of the Chemistry Department of the Institute for valuable suggestions and advice, and t o tihe Chemical Society for a grant towards the cost of this research. WEST HAM MUNICIPAL TECHNICAL INSTITUTE. [Received November l l t h 1918.