POLARISTROBONETRIC-CHEXICAL ANALYSIS.
59
POLARISTROBOMETRIC-CHEMICAL ANALYSIS. BY H. LAXDOLT.* +Translated by J. F. GEISLER. INTRODUCTORY.
In determining the rotatory power of optically active substances in solution the following factors are of practical bearing : a. The observed angular rotation of a ray of light (usually D) by a solution a t a definite temperature (generally 20"). 1. The length of the tubes used (in decimeters). d. The sp. gr. of the solution (generally determined a t 20", calculated upon water a t 4"). p. The $, L e . the weight of active substance in 100 parte by weight of the solution. q. The $ of optically inactive substance. c = pd the concentration, L e . the number of grammes of active substance in 100 e. c. of the solution. From these the sp. rotatory power is found by lOOa - l O O U
( [ u l = x --
(1) 1Pd which gives the angular rotation which a column of the solution 1 dm. in length would cause, if each c. c. contained l g of the optically active substance. The sp. rot. power is affected not only by the wave length of t h e ray of light and the temperature, but usually also by the nature of the solvent as well as the percentage (p) and the concentration (c) * T h e increae or decrease of the specific rotation of nearly all optically active substances, which is shown by the varying composition of the solutions and attributable to the action of the solvent upon t h e active molecules, may be represented by :
* Ztschr.
anal. Chem., 28, p. 203-218, from Ber. d. chem. Ges. 21, p. 191. +Owing to the importance and general usefulness of this branch of analytical chemistry, this paper, which tends to systematize the methods and introduce correct formulas for calculating poloristrobometric analyses is given almost complete. J. F. G.
60
POLARIBTROROJIETRIC-CHE3lICAL ANALYSIS.
1. The percentage-content of inactive solvent [ n ] = A + Bq + CCt2 2 . The percentage content of active substance [ ~ =1a +*bp + cpe 3. The concentration [a]=%+
gc + a c z
(2)' (3).
(4).
If the constants of the equations ( 2 ) and (3), determined by the examination of a number of solutions, are to be transposed, we have a = A + 100B + l O O O O C A = a + lOOb + 1 0 0 0 0 ~ b =- B - 2OOC I3 =-b - 200c c=c c=c (5). Formula (3) inny be used for calculating the concentration and (4) for percentage-content when the sp. gr. of the solution is
j
known, and by using 1) =-C or c= prl. d If for an active sabstance whose molecular weight is M, the constants in the equation (3) have been determined by trial, and these latter are to be calculated so as to represent one derivative affected by the molecular weight MI, and whose formula shall be [a], = a1 bp + c, pz, then all the quantities of equation (3)
+
ill whence for the new constants must be multiplied by the factor M,
For changing Ventzke's saccharimeter degrees into angular degrees for the ray (D) the ratio is.usually taken as 1"Ventzke = 0.3455 degrees (sodium light). This ratio varies, however, for different substances, so that when accuracy is required, the factor should be determined by comparisons with t h e respective instruments. Thns
POLARISTROBOJIETRIC-CHEMICAL ANALYSIS.
61
1" Ventzke (Gas light) = Cane sugar - - - - - - - .-0.3465 f 0.0005 degrees (Na flame). " i< Milk sugar - - - - - - - 0.3452 f 0.0002 (I '' Grape sugar- - - - - - -0.3448 f 0.0008 '' 66 Invert sugar- - - - - - - -0.3132 f 0.0007 " (r Cholesterin - - - - - - - -0.3416 f 0.0012 " 66 Turpeii tine - - - - - - - - 0.3494 f 0.0009 The values are, moreover, affected somewhat by the degree of concentration. The values for the concentration will be affected somewhat by the value of the unit volume-Le. the true c. c., or Mohr's c. c. I n most of the scientific determinations of the specific rotatory power of optically active substances the true c. c. was used, L e . the 100 c. c. mark on the flasks indicates the volume of 99.728 of water a t 20"; the solutions were weighed out a t 20°, and the specific gravities were determined a t the same temperature based upon water at 4". For saccharimetric work 100 c. c. flasks ha,ve come into use, which were prepared according to the directions of Mohr, accordingly the 100 c. c. mark indicates the volume of lOOg of water a t 17.5". The latter volume is used in the preparation of the normal sugar (26.0483) solution, which on the Ventzke scale causes a deviation of 100"*. Hence Mohr's c. c. (17.5') + 0.9977 will give the value for true c. c. a t 20". The sp. rot. powers
__
determined with Mohr's concentration
would ( pd 17.5 17.5)
have to
be multiplied by 0.9977 if the true c. c. is to be used as the unit volume. Of the many compositions of which a solntion may consist, the' following shall be considered.
I.
Solutio?is,iuhich coizsist qf' hut tive solvelit.
oizc
nctiive substn)rce a d an iiiac-
The conditions hcre resolve themselves into two, according to
* At least foi*the inetrunients manufactured by Schmidt & Haensch in Berlin.
the greater or lfss degrcae t o liicli t h e SIP. rot. power is affected by the concentr:ition. A . If t h e drterniinations slioiv that the sp. rot. power of the substaiirrx is ~ ~ v r n i ~ ~ i i ti.~ ie.i t iiroiJortionai , t o tile concentratiori, t h e n tlicn c1ii.intit! (( or p) in : i l l iinknowii colution is found by the ec 111at i o 11
TIN iiiinitl for1nn1,t 1113y i w u s e d f t i i *~tbstancesi i 1 which the rariiitions d u e to ctoiiceiitiation :tic b u t slight, by ~ubatitutingan 31 cmgcx rc~,iilt for [:1]. ‘l’lie metliotl m i ? accordingiv lie used for t h (x €011o TV i n Q b nbst it ii c tib . 1. Cane Sug;ir.--‘I’Iit. well known iiictliod for dctci mining cane bugar by nieiiiis of tliti ~rolanscope.or special baccharinieters, is bawd on tlic suppobitloii that the rittio between rotation and conctltitration is uniform. The i i i i c s t i p t i o n s of Schmitz arid Tollens sliow, Iio~$ccver.that t h e J n l u e of [ ( I ] decreases as t h e iboncentratioii incie:tsus. tTp to :t concentr:ition of ( ‘ = ? O the lariation
[tr],O=GG.b.!--~J.OO!,i,. 2
c.(Mohr’s c. c. tl
Whence for c. = J 10 1:) 20 2.5 30 T r u e C . c‘. [a]=Oij.G:! (36.5s (jL.33 GG.4S 66.43 66.38 Mohr’s c. c. [w]=GG.;S GG.73 G(i.Gb OC;.G3 CjG.58 66.54 If an average factor is titlten a s 20 80 [ C I ] ~ ~ = G G for . ~ trliec. c.. [ ~ t ] ~ ) = 6 6 . G . 3for AI. C. (a.
tliw tlie coiicentratio~imay tw ioiind from tlie o1)ser~ed augular rotation by the formulas U
t.
Cl
c.. c = 1.5004-for 11.c. c. 1 gi1 ing for the extreme percentage-content of 5 and 30g variations of respectively +0.01 and -0.05 from the true result. c =1.5038-f0r1
C.
POLARISTROBOMETRIC-CHEMICAL ANALYSIS.
63
If the variations are to be taken into account then thc formula of Schmitz* C E O . ~ ~ ~ G ~ ~ L + O . O O O O 'nx ~ G(true G c. c.) may be used, in which n is the angular rotation observed in a 2 dm. column. 2. Milk Sugar.-Schmcigert iound the specific rotatory power of solutions of milk sugar uniform u p to a percentage-content of 36 (c=41.5) and gives f o r t h e hydrate C,, H,, O,, +H,O the value [a]?=52.53"
(t. c. c. d 240).
The rotation decreases as the temperature rises, and a t about 20" the above value is increased or diminished 0.075 for each 1" temp. The birotation which crystallized milk sugar shows shortly after solution can be changed to the constant by warming the solution. But if sugar dried at 100" is dissolved in cold water, the solution shows a t first a lower rotation than the normal, which latter it attains after several hours on standing a t ordinary temperatures or immediately after heating. Schmoger,t Erdmann. (1 3. Maltose.-C,,' H,, 0, +H,O. Dextro-rotatory. Meisslg gives for the dependence of the sp. rot. power upon the $-content of the water solutions and the temperature of the same the formula [aJD=140.375-0.01837. t
p-0.095
t ( t . c. c. cI',~)
which is true for variations of p = 5 to 35 and t -15 to 35". Owing to the relatively smadl variation, by inserting an average €actor 20 [ a ]17.5 I) -138.3or[a) D=138.L in formula ( 7 ) the error, even when p=30, would be within hundredths $. "Ztschr. d.V. f. d. Riibenzucker-Ind. d. D. R. 1879, 950. t Ber. d. chem. Ges., 1880,885. SBerr. d. chem. Ges., 1880, 1915, 2130. 1 (' " ' I " 1880, 2180. 8 Jour. f. Prakt. Chem. (II.), 25, 114.
1). '[lollens. by nieaiis of a half sliailow instrument and Ka. light, [ct]
"0 ",)=104.44
t o 104.0 for ~ = 1 0 .
e. Itieschbiet arid TolIe~is,* [u]
;;=
1OP.41- 104.9 for c = 10.
ci. von Lippmaiin [a] T)=104.'3ii for p=.'.ii7. e. Finally Tolienst calculates from the data of Losseau [ a ] D= 105.7, and of yon Iiitthansen [ a ] 1) =104.0. From which it appears that the sp. rotation is affected but little by the concentratioii. and that 2111average factor
In alcohol of 7 5 s raffinose shows, accordlug to Scheibler, the same rotatory p o w ~ as r in wtcr. Dextrose.-For the v:iriatioiis in sp. rot. power of dextrose solutions due to the $-coiltent of the solutions, '[lollens supplied the formn1:t
[u]
90
D
= 53.0
p
=>
p =XI [a] = 53.52 For solutions containing n o t over 20 g. I I I 100 c. c.. the factor wlience for
[(I
etc.
= .i?.G1
is satisfactory.
For greater c,oncentratioiis more accurate results are obtained by the author's new formula, p = 0.948.a - 0.0032.a2: in which n is the angular rotation observed in a 2 dm. column. 'Ann. Chem. (Liebig) 232,169.
t Ann. Chem. (Liebig) ?32, 170.
Z. V. J. R.
I., 1886, 2114.
POLAKISTROBOMETRIC-CHEMICAL ANALYSIS.
65
The birotation of a fresh solution of dextrose is destroyed by heating, or by letting the solution stand for twenty-four hours. 6. Levulose. - The Izvo-rotation of the aqueous solutions increases with the degree of concentration and diminishes as the temperature riscs. The only reliable data are those of Herzfeld* and Winter! who used levulose derived from inulin. From these data i t follows that the dependence of the sp. rotation a t 20" temp. upon the $-content is expressed by 20 = 69.53-0.0935.~ [u] -
D
whence for p = 5
-
-
30
According to Herzfeldl, between the temp. of 2O"-4Oo for each increase of 1' temp., the value of [ u ] 20 is lowered 0.5' for $-content of 10 to 40. D According to Winter,g levulose dissolved in absolute alcohol, possesses a much lower sp. rot. power, namely, 20 [a]-=
- 47.0 for p = 7 . 7 8 . D 7 . Invert Sugar.-The sp. rot. power of invert sugar obtained from cane sugar by the action of dilute acids, shows considerable variations, subject to the conditions of (a,) The concentration.-Gubbe** found that for aqueous solutions of invert sugar, prepared by heating cane sugar solutions (containing 1 part of oxalic acid for every 100 parts invert sugar) for several hours a t 60", the sp. rot. p. a t the temp. of 20" depended upon the %-content of water, as follows :
["I
20 = - 23.305+0.01648, q+0.000221, qe -
D
* Z. V. f. R. Z.I., 1884, p. 445, and 1886, p. 114.
t LOG.cit.,
1887, p. 797. $ Z. V. R. Z. I., 1884, p. 444. 0 Z.V. R. Z. I., 1887, p. 807. ** Ber. d. chem. Ges., 1885, p. 2207. Z. V. R. Z.I. 1884, p. 1345.
66
I'OLARISTROBO~iETRIC-CHE31ICAL ANALYSIS.
which for p. gives the formula 20
= 19.4.1; - 0,06068, pt0.000221. p*. 1) This formula holds good for $-content up to p = 68. For weaker solutions Gubbe gives for the concentration c the for mu la
[a]
2U [u]-=-19.657-0.0361.c t. c. c. d 1) 4 which is true for c up to 3 5 . (b. j According t.o Tuchschmid t8he fip. rot. power diminishes 0.32 for each rise of l Ctemp. between the temp. of 5' to 35', when c = 17.01. Gnbbe gives the more accurate formulas :
(
["I6=t
t =Go to 30" [a] --+0.3041 20 (t-~0)+0*001G5 (t-20)*
D t = 2 0 to 100: t 90 ["I T_+0.3216 ( t - 20)- 0.00021 ( -20)s 11 1) (c.) The kind and quantity of acid used for the immersion, as well as the quantity of acid remainingin the solution. Gubbe found that oxalic acid did not affect the rotatory power, but hydrochloric and sulphurid acid increased it. The increased rotation in 9 per cent. solutions of invert sugar amounted to 0.362 per 1 g. hydrochloric acid, and 0.170 per 1 g. of sulphuric acid present. For increased concentrations these variations are much diminished. (d.) The time and degree of lieat used during the inversion. I n Clerget's method the cane sugar solutions, to which are added 5$ by sol. of concentrated hydrocliloric acid (sp. gr. 1.88=38$), are heated for fifteen minutes a t 67-70' and then mpidly cooled, Creydt*. If heated longer or a t a higher temperature, t h e rotation mav he diminished on account of decomposition. [ a ]- =
* Z. V. K. 2. I., 1887, p.
158.
67
POLARISTROBOMETRIC-CHEMICAL ANALYSIS.
(e.) T h e sp. rot. power of invert sugar is changed when acidfree solutions of invert sugar are evaporated in a vacuum to a syrupy consistency, probably owing to the formation of hydrated products (dextro-rotatory lmulosan?). On resolution dextrorotation may be obtained, or a t least a l m o rotation less than the normal. The latter may be reobtained by adding hydrochloric acid and setting the solution aside for several hours, or by heating for a short time a t 67-70" (g.) Further, the rot. power of invert sugar solutions is affected by the presence of other substances snch as alcohol, acetate of lead, or lime. 8. Galaktose (Lactose). Dextro-rotatory.-Meissl found that the specific rotatory power of aqueons solutions of lactose as affected by $-content and temperature, is expressed by [~]-=83.883+0.0785 t p-0.209t
D
4
which equation is good for p = 5 to 35, and Rindell gives
t
[ u ]-=83.037+0.199.p
D
=lo"
to 30"
- (0.276 -0.0025.~)
("*
c-2)
when p = 11 to 20, and t = 4 O to 40". This would yield a value of 81.25 when p = 15 and t =20, whereas the formula of Meissl gives 80.88, or 81.07 when based on Mohr's c. c. Fresh aqueous solutions of lactose show birotatim, but after standing about six hours the normnl rototion is obtained. 13. When the sp. rot. power of a substance is dependent upon the concentration to such a degree that the simple formula
can not be used, another form of calcnlation is adopted. I n all such cases where the variation in sp. r. power can be expressed by a linear function and the third term of the equations (3) and (4) does not appear, the $-content of a solution may be found by
68
POLhRISTROB0~fIETRIC-CHEMICAI~ AN.%LYSIS.
p= -
whence
aZb
+/(;!)’ /
Ifr
- -----_____---
+o;‘
:
(8a)
a
i 7
These formulas need be used only when only tlie formulas (3) and (4) are given for the active substance. If the data of the determination are at one’s disposal, it is simpler to deduct the con stants of the equation of the form p=al
Cl --
1
+ b,
(9 a)
hence taking p and c direct as functious of the angular rotation. These latter equations are also applicable when the variation of the sp. rot. power are represented by a curve, and hence equations (3) and (4) appear with all three members. For example, a number of mixtures of nicotin and alcohol are given, the rotatory power of which had been determined by the author. The rapidly diminishing rotatory power as the $ of alcohol q increased i s expressed by the formula
[“ITj20
= - 160.83
+ 0.8224 ‘1,
which transposed for p, the value of nicotin, gives 20 [a]- = - 138.59 - 0.2224. p t. C. C. d
(
D “O 4 and by inserting the constants of tlie equation (8 a)
+ 311.58 -
J
,
~_________
U
97‘082.5 - 440.64 I d By use of formula (9 b), based upon calcnlations and experiments*, the following formula results a c = 0.704 - - 0.000525 1 With these formulas very accurate deterniinatiolls of nicotiii
p
(W
*
Ann. Chem., (Liebig) 189, p. 520.
69
POLARISTROBOMETRIC-CHEMICAL ANALYSIS.
can be made, which suggests their use for determining the quantity of nicotin i n tobacco. I n like manner the quantity of camphor in alcoholic solution may be determined. According to the author's experiments* the rapid increase of the sp. rot. power as the concentration increases is expressed by the formula 20 [ a ] - = 41.982 0.11824. c t. C. C. d 2 D "O4 whence with formula (8 b) as a basis the following results,
+
c=-
177.53
+
31516.45
1
(
+ 845.74 51 ,
(I.)
From dircct observations for the constants of equations (9 b) results c = 2.3614
1
(
- 0.01158 5 1 )8
(11.)
I n the table supplied Z. A. C. 28, p. 217, the results obtained by t h e use of the formulas are shown t o be subject to a n error of but - .16 to + 0.13 as extremes. Instead of the above method another may be adopted for the calculation by first ineerting in c = - lOOa [a1 1 an approximate value for [ a ] and recalculate with the value of c, obtained from [ a ] = 3 g c , the value [ a ] . The latter result is then inserted in the first formula and the recalculations repeated 4 or 5 times until c becomes a constant quantity.
+
*
Ann. Chem., (Liebig) 189, p. 333. (TO B E CONTINUED.)
