VOL.
XLI.
NOVEMBER] 1919.
No. 11.
THE. JOURNAL OF THE
American Chemical Society with which has been incorporated the
American Chemical Journal (Founded by Ira Remsen)
[CONTRIBUTION FROM THE LABORATORY OF PHYSICAL CHEMISTRY OF THE UNIVERSITY OF ILLINOIS. PUBLICATION No. 35.1
SOME PHYSICAL PROPERTIES OF MANNITE AND ITS AQUEOUS SOLUTIONS.' BY JOSEPH M.
BRAHAM.
Received June 21, 1919.
This study was made in connection with an investigation on the laws of aqueous solutions. The compound, which is also termed mannitol and hexanhexol, is of interest in the latter connection since it contains a comparatively large number of hydroxyl groups. The literature on the subject is not very complete and very little recent work has been done on it. This paper presents the results of the study and includes a brief statement of earlier work on the subject. I. Purification of Mannite. An investigation was first made to ascertain the number of recrystallizations of commercial mannite that are required to yield a pure product, the melting point being the criterion of purity. The material was dissolved h distilled water a t a temperature near 80°, forming an almost saturated solution. This solution was filtered to remove the suspended impurities which were present in considerable quantity, then cooled to 1 This article is based on a thesis submitted by the writer in 1915 to the Graduate School of the University of Illinois in partial fulfillment of the requirements for the degree of Master of Science.
170s
TOSEPH M. BRAH.ihI.
about 40' and alcohol added to reduce the solubility. The crystals were freed from the liquid as completely as possible and then dried in an electric oven a t 120-13o0 for several hours. ?'he second crystallization was made by dissolving the crystals, from which the mother liquor had been removed, in pure, hot water, allowing the solution to cool and then adding alcohol; a similar procedure was followed in the third and fourth crystallizations. Another lot was purified in precisely the same manner except that no alcohol was used and contact of the crystals with the filter paper was avoided, but no difference in the purity of the two lots could be distinguished. 11. Melting Point of Pure Mannite. The most extensive set of determinations described in the literature was made by Landolt.' He found the freezing point of a mass consisting of 620 g. of mannite to be 165 .69'; with a much smaller quantity of matexial the melting point was 165.73' and the freezing point 165.64'. Using an apparatus designed to avoid stem correction, the values 166.97' and 167.04' were obtained; the latter values are undoubtedly too high. The results obtained by other investigators are: Favre,2 166' (freezing point 162'); Stohmann and Langhein,j 166'; and Kroft and Dyes,* 166'. Since the true value is thus uncertain, this property was investigated. A nitrogen filled mercury thermometer which had been checked by the Bureau of Standards was employed. It was graduated in 0.I ', ruled directly on the stem; readings to o . O I ' were made with the aid of a reading glass. Three auxiliary thermometers were employed to determine the temperature of the emergent stem a t various heights. The equilibrium mixture of mannite crystals and liquid was contained in a small Dewar tube closed by a tin foiled cork and stirred With a small glass rod with a loop a t one end. The mannite was heated to about 175' in an electric oven or very carefully over a gas flame and the liquid poured into the previously heated Dewar tube. It was found impossible to obtain a perfectly clear liquid by either method of heating, the slight brown color seeming to indicate that carbonization occurs to a very limited extent; the color was first ascribed to the presence of fine filter paper shreds, but it was later observed in fused material with which special precautions had been taken to avoid contamination from that source. When the temperature of the liquid in the Dewar had dropped to about I ~ o ' , pure crystals were added. A temperature which remained constant for several minutes was soon reached. The following results were obtained: l
2. playszk. Chem., 4, 366 (1889). A n n . cliim. phys., [3] 11, 7 1 (1844). J . prakt. Chetn., 121 45, 305 ( 1 8 g z j . Ber , 28, 2583 (1895)
'709
PHYGICAL PROPISRTIBS Ol? MANNITE. Mannite.
Melting point.
original material., ............................... First crystallization. .............................. Second crystallization............................. Third crystallization.............................. Fourth crystallization.,...........................
165.10' 165.84 166 .os 166.os 166.os
It is evident from these data that two crystallizations of commercial mannite are necessary as well as sufliaent for the production of pure mannite.
III. Specific Rotation. Of the 3 optical forms of mannite, the so-called dextro form, which is actually levorotatory, is the most common. Very few determinations of the specific rotation of pure mannite in aqueous solutions have been made, although the literature contains numerous references to measurements on solutions of mannite with some other constituent such as borax, boric acid or sodium hydroxide. In 1873, G. Bouchardatl found that the rotation was less than 0.2 ' which was the smallest value then measurable, but the fact that it really was optically active was shown the following year by I,. Vignon2 in his researches on mannite solutions containing borax or boric acid. Using a greatly improved apparatus, G. BouchardatJ later found the specific rotation to be [aIj = -0.25' (estimated to be -0.23' referred to the sodium D line), the temperature of the solution not being given. In 1875, L. Vignon4 again studied this property of mannite in pure aqueous solutions and found the following values, each of which is the average of IO readings : [a],,= 0.204 ', 0.260 ', and 0.232'. The temperature of the solution was not stated. Since no more recent determinations had been made, it seemed desirable to determine this constant with greater accuracy. A sample of purified mannite was fused to eliminate completely all traces of moisture and then finely powdered; but solutions from this material possessed a slight brown color which made satisfactory illumination of the solution impossible. Samples which had been thoroughly dried but not fused were therefore used. The solutions were prepared by dissolving 17.6067 g. of mannite in distilled water and making up to 100cc. a t 25'. A triple field Schmidt and Haensch polarimeter fitted with a 100cm. jacketed tube was used, and the solution under examination kept at 25". A quartz mercury vapor lamp furnished the light, which was further purified by passing it through a spectroscope, the green E-line of mercury being employed. The specific rotation was found to be [a]*&= -0.244' f 0.002. The values of -0.244' and -0.245 * 0.002 were 1
Compt. rend., 76, 1550 (1873).
I N . ,77, 1191(1874). *IN.,80,122 (1875). 2
4
Ana. chim. phys., [5 J 2,440 (1875).
obtained a t the same time by X r . C. Scholl in this laboratory. Assuming that the same factor ( o . 8 p q ) I may be used in converting the value re~ sodium 1) line as found for quartz, ferred to the mercury €? iinc t ( the the rotation becomes la]?;= i)2 0 8 3- 0.002. IV. Solubility--Freezing-Point Measurements. At the time this investigation was begun, the data on the solubility of mannite in water and on the freezing points of relatively concentrated solutions were very meager. 'fhe solubilit!~data contained in the literature are summarized in the following table. Solvent.
Temp.
negrees.
Water Water Water Water Water Urater Water Ethyl alcohol ( d = o 898q I Ethyl alcohol ~ahuolute
G.mannite per
100 6. of solvent. 12.8
16 .o 15 .(I
18.5 20
.gf,
29.93 '16 . hq 1.2
',. ds
@ dt
= b$-. I
-am
de and dt
de
Similarly they obtain
