T H E COMPLEXES O F MANNITOL AND SORBITOL WITH SODIUM ARSENITE AND BORAX 1LI. SRINIVASAN
AND
M. SREENIVASAYA
Department of Biochemistry, Indian Institute of Science, Bangalore, India Received September 8, 1933
It is known that boric acid, on addition to polyhydric alcohols, enhances their optical rotation and suffers an increase in acidity (5, 8, 14, 20). These properties have been utilized for the estimation of mannitol (17), . and for the titrimetric determination of boric acid (13). van't Hoff (19) assumes in this reaction the formation of a complex having the cyclic grouping
where R represents the inorganic constituent. Magnanini (15) by conductivity measurements supports the formation of a compound from one molecule of mannitol and three of boric acid, while, according to Ageno and Elena Valla (1) the ratio of mannitol to boric acid is 1:l. Fox and Gauge (9) claim to have isolated mannito-boric acid as a definite compound. The work of Boeseken and his coworkers at Delft for the past twenty years has revealed that this property is more generally shared by a large number of polyhydroxy compounds. The ease with which these boric acid-diol complexes are formed is dependent on the positions of the hydroxyl groups, the most favored configuration being the situation of the two hydroxyl groups in the same plane and on the same side of the carbon atoms to which they are bound (4). Irvine and Steele (12) support the findings of Boeseken by a study of electrical conductivity and specific rotation of the methylated mannitols. Dubrisay (6) indicates compound formation between boric acid and mannitol, by measuring the optical rotation and surface tension of the system, as also the critical solution temperature of phenol and water in presence of the complex. The possibility of boric acid and its salts forming more than one complex with mannitol is shown by the work of Grun and Nossowitsch (11) and by Gilmour (10) from optical rotation data. The last-mentioned author obtains a maximum rotation of 37.6" by treating sodium mannito703
704
M. SRINIVASAN AND M. SREENIVASAYA
borate and sodium metaborate in molecular proportions. Thus is explained the exaltation of rotation on mannitol from 22.5” (Vignon) to 28.3’ (Fischer) under the influence of an excess of borax. The theory of ring structures of the boric acid complexes first suggested by van? Hoff and later adopted by Boeseken, is extended in the work of Meiilenhoff (16) who ascribes to the boric acid complex of mannitol the formula
[
C6H1206:H ] ; : < > :
Bancroft and Davis (a), however, in a paper on “The Boric Acid Problem” doubt the compound formation between boric acid and organic hydroxy bodies, and attribute the enhanced acidity of boric acid to its increased dissociation in presence of the organic compounds dissolved therein, while the change in optical rotation is explained by “the abnormal effect of boric acid solutions.” Besides borax, sodium arsenite also induces dextrorotation (Vignon (ZO)), providing a method for the estimation of mannitol (2). In a solution in which the ratio of arsenious acid to mannitol is not less than 17.5, the specific rotation of the hexitol is 46.53’. From a study of the increase in solubility and neutralization values of arsenious acid in presence of mannitol, sorbitol, and other polyhydroxy compounds, Englund (7) has postulated that this acid forms with hydroxy bodies compounds similar to those formed by boric acid. In spite of the large number of physicochemical measurements like optical rotation, electrical conductivity, hydrogen-ion concentration, solubility, and phase study, that have been applied to reveal the nature of combination of boric acid and arsenious acids with mannitol and other polyhydroxy compounds, the question remains yet unsettled. The measurement of volume changes, should they accompany the formation of these “complexes,” would throw new light on the problem. The present communication relates t o a dilatometric investigation of the complexes of mannitol and sorbitol with sodium arsenite and borax. NATERIALS AND METHODS
The dilatometer devised by Sreenivasaya and Sreerangachar (IS) was used in these investigations, as being best suited for the study of reactions in which the equilibrium is attained almost immediately when the reacting components are mixed. All dilatometric measurements were made at 30°C. in a thermostat. A triple shade polarimeter illuminated by a mercury arc was employed for determining the optical rotations in a 200mm. tube a t room temperature (27°C. =tl.O’C.). &Mannit ol a,nd d-sorbitol (B.D.H. products) were recrystallized from
FORMATION OF COMPLEXES
705
,
water, samples dried a t 100°C., and kept in a vacuum desiccator over phosphorus pentoxide. Solutions of these were prepared by dissolving weighed amounts of the substance in distilled water and made to volume. Arsenite solutions were prepared by boiling 198 g. of arsenious oxide with 132.5 g. of sodium carbonate, and the solution was made up to a liter (2). The strength of arsenite solution was determined iodometrically. Borax solutions saturated at 30°C. were used, the amount of dissolved borax (Na2B40,-10H20) being estimated by acidimetric and alkalimetric titrations. TABLE 1 Dilatometers and reaction mixtures REACTION M I X T U R E DILATOiMETER
Small bulb
Big bulb
Control. ...........................
5 cc. of water
Experimental.. .....................
5 cc. of mannitol or sorbitol solution
I 1 2 3 4 5 6 7
M O L E S OF ARSENITE PER GRAM-MOLE OF MANNITOL
0.0 2.4 4.8 7.2 9.6 19.2 24.0
1
50 cc. of arsenite or borax solution 50 cc. of arsenite or borax solution
TABLE 2 Mannitol-arsenite DILATOMETRIC RISE
1
VOLUME INCREASE P E R GRAM-MOLE OF MANNITOL
cm.
CC.
9.1 12.9 13.8 14.3 17.3 17.3
8.05 10.52 12.14 12.53 15.22 15.22
-
OBSERVED ROTATION
-
-
0.26 0.36 0.39 0.41 0.49 0.49
45.88 63.53 68.84 72.36 86.48 86.48
The dilatometers and the reaction mixtures used were as given in table 1. As large quantities of arsenite or borax are necessary to react with a definite amount of sugar alcohol, the big bulb always received the inorganic salt solution, while the hexitol occupied the small one. The details of the experimental procedure were those followed in a previous communication (18). On mixing the solutions, one observes a depression in the control dilatometric column due to dilution of the salt solution, the order of depression depending on the strength of arsenite or borax solution used. But the experimental dilatometer treated as above records a definite rise. The equilibrium is attained within fifteen minutes, when the final readings
706
M. SRINIVASAN AND M. SREENIVASAYA
of the dilatometers are taken. The difference between the readings of the two dilatometers is a measure of the volume change accompanying the formation of the complex. The solutions are finally polarized. The whole operation takes one and a half hours. TABLE 3 Mannitol-boraz (NmB407.10 € 1 2 0 ) EXPERIMENT
dOLES OF B O R A ) P E R QRAM-MOLE OF M A N N I T O L
DILATOMETRIC RISE
VOLUME I N C R E A S E PER G R A Y - M O L E OF MANNITOL
cm.
1 2 3 4 5 6 7 8 9 10
0.0 0.5 1.0 1.5 2.0 2.5 3.3 5.0 7.5 10.0
OBSERVED ROTATION
[MI
*:::I
[a
cc.
-
-
-
-
16.6 17.5 18.2 19.1 19.5 19.7 20.2 21.0 21.0
16.47 17.34 18.03 18.92 19.32 19.52 20 I02 20.81 20.81
0.20 0.22 0.23 0.25 0.25 0.28 0.25 0.26 0.26
39.73 43.7 45.68 47.67 49.66 49.66 49.66 51.65 51.65
OBSERVED
EXPERIMENT
1 2 3 4 5
Mean.
DILATOMETRIC RISE
” , 6 ” ~ ~ $ ROTATION ~~ (V
)
mg.
cm.
cc.
72.7 87.8 122.1 162.5 254.2
4.95 5.95 8.30 11.05 17.30
15.24 15.17 15.21 15.22 15.22
. . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . .
15.21
La I%;:
0.14 0.17 0.23 0.31 0.49
-
47.15 47.71 46.41 47.02 47.51 47.22
RESULTS
“Complexes” of mannitol
Preliminary experiments were conducted to study the effect of adding increasing quantities of arsenite and borax to a given quantity of mannitol. Five cc. of 5 per cent mannitol and 50 cc. of arsenite or borax solutions of varying concentrations (prepared from the standard stock solutions by dilution) were used. The results are given in tables 2 and 3 and represented graphically in figure 1.
701
FORMATION O F C O M P L E X E S
The above results show that the dilatometric change and optical rotation reach a steady maximum, beyond which further additions of arsenite or borax are no more accompanied by increases either in volume or in optical activity. To bring about this maximum change, about 19.2 moles of arsenite (see reference 2) or 7.5 moles of borax (decahydrate) per gram-mole of mannitol is found necessary. Further, this maximum corresponds to a volume increase of 15.22 cc. with arsenite and 20.81 cc. with borax per gram-mole of mannitol.
a 20
2
11
.5 9,
ur U R
12
9,
roo
:. Q 8
BO
E
t
2
2
Bonax(DiIahome,ten) 60 r h-ManniCof-Arseni6e 19 C - M a n n i k o l -Ansenihe ( R o t a i i o n ) 40 d-Mannitol- B o n a x I9 5- M a n n i t o l -
4
l
z
20
0
4
Molecules oP
8
arsenite
OP
12 16 20 24 2 I borox pen g ~ a m - m o l e c u l e OP monnitc t
FIG.1 The experiments were repeated with varying concentrations of the sugar alcohol and calculated amounts of arsenite and borax to induce maximum changes, and the results, incorporated in tables 4 and 5 and figure 2, confirm the above findings.
“Complexes” of sorbitol
A dilatometric study of the sorbitol-arsenite and sorbitol-borax systems has given the results embodied in table 6 and figure 2. It will be seen that the dilatation constants per gram-mole of sorbitol are 16.93 cc. and 22.38 cc. with arsenite and borax, respectively.
708
M. SRINIVASAN AND M. SREENIVASAYA ACCURACY OF T H E M E T H O D S
Table 7 gives the dilatometric and polarimetric readings (taken from the previous tables) and their errors corresponding to maximum and minimum amounts of mannitol. DISCUSSION
On mixing solutions of mannitol and sorbitol with a solution of either arsenite or borax, there occurs an appreciable increase in volume corresponding to the exaltation in optical activity (tables 2 and 3 and fig-
2
E
I ,
.p,
’
91
2
c
.:c I
-a
r)
U
2
a
- MS oarnbniittooll c - Mannitol a
b
d
40
80
120
- Sorbikol 160
(Sodium apsenise) (Sodium arwenrt..) (Bor~ax) (8o~ax)
200
240
230
S u g a m a l c o h o l in m3
FIG.2
ure 1). This volume change observed in the case of the two hexitols is a new property found to accompany the formation of the “complexes.” A strict proportionality exists between volume change and the amounts of mannitol and sorbitol forming the complex (tables4,5, and 6 and figure2). As compared with the polarimetric estimation of mannitol or sorbitol now adopted, the dilatometric method offers a more convenient mode of determination, ensuring greater accuracy. Table 7 gives the errors in estimating mannitol in two concentrations by the two methods. It will be seen that the error in the dilatometric estimation is about 0.2 to 1 per
709
FORMATION O F COMPLEXES
TABLE 5 Mannitol-borax EXPERIMENT
hlean.
,
,
,
(17)
em.
mg.
CC.
6.05 7.39 7.55 12.86 13.10 15.15 21.00
65,OO 79.20 81.25 138.00 140.00 162.50 225.80
OBSERVED ROTATION
DILATATION CONSTANT
DILATOMETRIC RISE
MANA'ITOL
20,83 20,87 20.80 20.77 20.81 20.85 20.81
.. .... . ...., . . . . ... . ... ... . , , /
30.33 27,80 30.33 28.57 28.16 28.82 28.38
0.08 0.09 0.10 0.16 0.16 0.19 0.26
____
28.91
20.82
TABLE 6 Sorbitol-arsenite and sorbitol-borax
1 EXPERIMEiVT
I
ARSENITE
1
2 3
Dilatometric rue
rise c m. 1.5 1.9 3.8
mg.
1
BORAX
SORBITOL
20 25 50
cc.
cm.
16,78 17.00 17.00
Mean. , . . . . . . . . . . . , . . . .. . . . . . . . . . . . . . .
Dilatation constant ( V ) CC.
2.0 2.5
22.38 22.38 22.38
5.0
16.93
22.38
.
TABLE 7 Accuracy of the methods DILATOMETRIC
POLARIMETRIC
MANNITOI
I ,
Reading
Arsenite . . . . . . , . . . . Borax . . . . . . . .
'{I
mnz.
72.7 254.2
49.5
173.0
Error in reading
Error
mm.
percent
50.5 10.5
51.0
Reading
____
60.5 10.5 210.0 f0.5
Error in reading
Error
deorees
per cent
-~ degrees
0.3
0.14 fO.01 &7.0 0.49 50.01 2.0
0.8 0.2
0.08 f0.01 0.27 zto.01
12.5 3.7
cent, while the polarimetric method involves an error of about 2 to 12.5 per cent, which gets considerably multiplied if the test solutions happen to be colored. This limitation does not affect dilatometric estimations.
710
M. SRINIVASAN AND M. SREENIVASAYA
Since the volume change per gram-mole of mannitol or sorbitol is greater with borax than with arsenite, borax complexes are to be preferred for the dilatometric estimation of these sugar alcohols. The dilatometric data obtained in this investigation strongly point to the existence of a definite compound in the systems studied. Solutions of arsenite or borax which suffer a decrease in volume on dilution with water (shown by controls) should undergo further decrease on mixing with mannitol or sorbitol solutions, if it is only a question of enhanced electrical conductivity, according to Bancroft and Davis (3). On the other hand, a definite increase in volume on mixing the two solutions has been recorded in all the experiments. Further, mannitol and sorbitol (at the concentrations used) do not register any volume change on mixing with water. Hence the dilatometric changes are more the characteristics of the formation of a new entity than the additive behavior of the preexisting constituents. These, along with the strict proportionality found to hold between the volume increase and the amounts of hexitol reacting, point to the formation of a compound as shown by Boeseken in the course of his extensive researches. SUMMARY
1. The formation of the “complexes” of mannitol and sorbitol with sodium arsenite and borax has been investigated in the dilatometer and also followed by polarimetric estimations in the case of mannitol. 2. The reaction is accompanied by appreciable increases of volume, which correspond to 15.21 cc. and 20.82 cc. a t 30°C. per gram-mole of mannitol with arsenite and borax, respectively. The corresponding dilatation constants for sorbitol are 16.93 cc. and 22.38 cc. 3. The dilatation constants of the hexitols being higher with borax than with arsenite, borax complexes have to be preferred for the dilatometric estimation of these hexitols. It is shown that this method is more convenient and accurate than the polarimetric one now in vogue. 4. The volume expansions attending the “complex” formation and their definite relationship t o the concentration of mannitol and sorbitol, suggest the formation of compounds as shown by Boeselten. In conclusion, one of us wishes to thank the Government of Madras for the award of a scholarship that has enabled him to pursue this investigation. REFERENCES (1) AGENOAND VALLA,ELESA: Chem. Ztg. 36, 221 (1913); Gam. chim. ital. 43, ii, 163 (1913). (2) BADREU:J. pharm. chim. 24, 12 (1921). (3) B.4NCROFT AND DAVIS: J. Phys. Chem. 34, 2479 (1930).
FORMATION OF COMPLEXES
(4) (5) (6) (7)
711
BOESEKEN:Rec. trav. chim. 34, 96 (1915). BOUCHARDAT: Compt. rend. 80, 120 (1875); Jahresber. 1876, p. 145. DUBRISAY:Compt. rend. 176, 762 (1922). ENGLUND: J. prakt. Chem. 122, 121 (1929); 124, 191 (1930), 129, 1 (1931); Rec. trav. chim. 61, 135 (1932). (8) FISCHER: Ber. 23, 385 (1890). (9) F o x AND GAUGE:J. Chem. Soc. 99, ii, 1075 (1911). (10) GILMOUR:J. Chem. Soc. 121, 1333 (1922). (11) GRUNAND NOSSOWITSCH: Monatsh. 37, 409 (1916). (12) IRVINEAND STEELE: J. Chem. Soc. 107, 221 (1915). (13) JONES: Am. J. Sci. 7, 147 (1899); 8, 127 (1899). (14) KLEIN:Compt. rend. 86,826 (1878); Bull. soc. chim. 29, 195 (1878). (15) MAGNANINI: Z. physik. Chem. 6, 58 (1890). (16) MEULENHOFF: Rec. trav. chim. 44, 150 (1925). (17) MULLER:Bull. soc. chim. 11,329 (1894). (18) SREENIVASAYA AND SREERANGACHAR: J. Indian Inst. Sci. 16A, 17 (1932). (19) VAN'T HOFF: Lagerung der Atome in Raume, 2nd edition, p. 133. (20) VIGNOX:Compt. rend. 77, 1191 (1873); Ann. chim. phys. 2,433 (1874).
