INTERMOLECCLAR HYDROGES BONDINVOLVTXG A T-IJASE
AS
PROTON ACCEPTOR
2895
Intermolecular Hydrogen Bond Involving a n-Base as the Proton Acceptor. I.
Detection by the Refractive Index Method
by Zen-ichi Yoshida, Eiji Osawa, and Ryohei Oda Department of Syvilhctic Chemistry. Faculty of Engineering, Kyoto IJniversity, Kyoto, J a p a n (Receioed March 14,1964)
Complex formation between proton-donating molecules and aromatics and olefins in heptane, dioxane, and water as solvents was studied by the refractive index method. Of 108 pairs of proton donors and acceptors examined, 61 pairs showed complex formation. Hydrogen bond formation of this type seems to increase as the number of conjugated double bonds (and condensed rings) in the acceptor molecule increases. Even in water, a weak interaction was found to exist between alcoholic O H and sulfonated aromatic hydrocarbons. The results obtained lend some support to the current hypothesis on cellulose substantivity which assumes that the O-H r-electron type bond between cellulosic OH and delocalized n-electron clouds of dye is partly responsible for the affinity of dyes for cellulosic materials. 1 . .
Introduction Recently, a new interpretation of the origin of substantive affinity of dyestuff on cellulosic substrates has been made,’.z which suggested that the interaction between cellulosic OH groups and delocalized a-electron clouds of dye molcules may be responsible for the affinity. Although such an association between proton donors and n-bases has long been known,3 previous investigations of this type of hydrogen bonding have been done exclusively in nonaqueous media. Therefore, it appeared of interest to determine whether or not such a weak interaction can survive when exposed to competition with water for n-bases under dyeing conditions. I n this communication, the refractive index method developed by Giles and his school4 was applied to detect the complex of the type X-H. . . a-base. Experimental5 Materials. Sodium Naphthalene-l-sulfonate. Commercial reagent was recrystallized three times from water and dried for 2 hr. a t 100’ under reduced pressure. Anal. Calcd. for ChHSOnNa: Ya. 9.99. Found: .. Na, 9.96. Sodium Phenanlhrene-3-sulfonate. Phenanthrene was sulfonated by the method of Fieser.6 White leaflilte crystals were obtained. Anal. Calcd. for CI4H9S03Na: Ka, 8.21. Found: Ka, 8.07. p-Toluidine salt,: m.p. 221-223’ (lit.6m.p. 222’).
Disodium Pyrene-l,6-disulfmate. Pyrene was sulfoliated according to the direction of Tietz and Bayer.’ Yellow crystalline powder was obtained. Anal. Calcd. for C I ~ H & O ~ N ~Na, Z : 11.32. Found: Na, 11.32. Sodium n-Butane-l-sulfonate. A mixture of 41 g. (0.3 mole) of n-butyl bromide and 300 ml. of saturated aqueous solution of sodium sulfite was refluxed for 10 hr. with stirring. After cooling, water was removed from the reaction mixture under reduced pressure and the residue was extracted with three 200-ml. portions of hot ethanol. From the combined extract ethanol was removed and the residue recrystallized twice from 75% ethanol to give long thin white plates. (1) C H. Bamford, Discussions Faraday SOL.,16, 229 (1954). (2) W. L. Lead, J. Soc. Dyers Colourists, 73, 464 (1957); 75, 195 (1959). (3) (a) G . C. Pimentel and A. L. McClellan, “The Hydrogen Bond,” W. H . Freeman and Co., San Francisco, Calif., 1960, p. 202; (b) P. von R . Schleyer, D. S. Trifan, and R. Bacskai, J . Am. Chem. SOC., 80, 6691 (1958); ( c ) It. West, ibid., 81, 1614 (1959); (d) M. Oki and H . Iwamura, Bull. Chem. SOC.J a p a n , 34, 1395 (1961).
(4) (a) C . H. Giles, et al., J . Chem. Soc., 3799 (1952); (b) 17. M . Arshid, et al., ibid., 67 (1955); 72, 559, 1272 (1956); (c) D. S. E. Campbell, et at., J . SOC. Dyers Colourisb, 73,546 (1957); (d) I. C. L. Bruce, et al., J . Chem. SOC.,1610 (1958); 559 (1959). (5) Melting points are corrected. (6) L. F. Fieser, “Organic Syntheses,” Coll. Vol. 11, John Wiley and Sons, Inc,, New N , y., 1948, u. 482,
(7) E. Tietz and 0. Bayer, Ann., 540, 201 (1939).
Volume 08,Number 10
October, 1364
z.YOSHIDA, E. OSATVA, AND R. 0 L ) A
2896
Anal. Calcd. for C4H9S03Na: Na, 14.36. Found: K a , 14.19. Other commercially available reagents were purified inmediately before use by the usual manner except for the following: .\[ethanol, Eastinan Kodak Spectrograde reagent, was used without further purification. Naphthalene was purified as the picrate (n1.p. 80.7-80.9'; lit. m.p. 80.2'). Anthracene (crude anthracene) was converted to the maleic anhydride adduct, recrystallized from acetone, m.p. 262-263' (Found: C, 78.24; H , 4.39; 0, 17.37), submitted to thermal decomposition in the presence of soda lime, sublimed, and then recrystallized from cthanol-benzene (m.p. 218.1-218.5'; lit. m.p. 218"). For glucose, sucrose, and cellobiose (0.3H20), the coniniercial reagents were dried and used directly (m.p.: 1 4 9 . 5 150.3O, 168-173' dcc., and 225-230' dec., respectively; lit. m.p.: 147' dec., 160-186' dec., and 225' dec.). Measurements of Refractive Indices. Various amounts of a solution of a proton donor and an equimolar solution of a proton acceptor were introduced into test tubes from the respective burets so as to keep the total concentrations constant, and the ratios of concentrations of each component variant. The test tubes were stoppered, shaken well, and left to stand overnight. The refractive indices of the solutions were measured with the Abbe refractonleterg a t constant temperature. The mean n-values were squared and plotted against the molar concentrations of one of each pair of components. Straight lines were obtained when no complex was formed or its concentration was negligible. Complex formation was found by a sudden change in the slope, the mole ratio at the bending point showing the composition of the 'complex. Complicated complexes, in which the mole ratios of donor to acceptor were above 4 : 1 or below 1 :4,were difficult to detect by the present method.
Results and Discussion All conibinations of proton donors and acceptors, shown in Table I, were examined in three solvents: n-heptane, dioxane, and water. Of 108 pairs of donors and acceptors examined, 61 combinations showed a t least one kind of complex formation. The data are summarized in Table 11. Changes in the slope of the n 2 us. concentration plots were not as sharp and clear-cut as in the case of X-H' . Y hydrogen bond pairs where X and Y = 0 , K, and S 4 As sp2 carbon is less electronegative than either the nitrogen or oxygen atom, both the equilibrium concentration and the polarization (contributing to niolar refraction) of the complex may be smaller than The Journal o j Physical Chemistry
Table I : Proton Donors and Acceptors Donors, D, and acceptors, 4
Solvent
n-Heptane
1)" Ethanol, acetic acid, and phenol A Cyclohexene, benzene, cyclohexylbenzene, biphenyl, p-terphenyl,6 decalin, tetralin, naphthalene, anthracene,* phenanthrene, pyrene, trans-stilbene, and fluorene
Water
D
A
D
Dioxane
A
D-Glucose, sucrose, cellobiose, pentaerythritol, and ethanol Sodium naphthalene-1-sulfonate, sodium phenanthrene-3-sulfonate, disodium pyrene-1,6disulfonate, and sodium n-butane-l-sulfonate Water, methanol, ethylene glycol, acetone, acetonitrile, ethyl acetoacetate, and diethyl malonate Decalin, tetralin, benzene, naphthalene, anthracene, pyrene, cyclohexylbenxene, biphenyl, and p-terphenyl
Chloroform and piperidine, as examples of weak proton donors, were tested with naphthalene as an acceptor a t a total (ioncentration of 0.4 mole/l. a t 27.4 and 27.6") respectively, Benbut complex formation was not observed in either case. zene "as used as a solvent because of the poor solubilities of anthracene and p-terphenyl in n-heptane.
'
those of the X-H'..Y type hydrogen-bonding complexes. n-Heptane Solution. Refractometry was carried out initially in a n inert solvent, n-heptane, to .distinguish the net effect from the solvation problem. A possible interaction between x-electron clouds of phenol and aromatics through dispersion force is not detected by this method, since the benzene-naphthalene system did not show any bending in the refractive index diagram. This kind of interaction appears to produce no observable change in the refractive index of the solution. As is seen in Table 111, as the conjugated system in the aromatic acceptors becomes larger in size, the complex formation tends to be detected more easily and the mole ratio (D/A) of the complex becomes larger. This means that the formation constant of the complex is increased by the use of large aromatics as proton acceptors. Indeed, the cyclohexene complex was not detected by the present method. Since the strengths of X-H . x-base interaction are not varied largely as far as nonsubstituted aromatics and ordinary proton donors are paired,g this tendency will be interpreted '
(8) Accuracy of refractive index was +0.0002. the authentic samples was omitted. (9) 2. Yoshida and E. Osawa, to be published.
Scale calibration to
INTERMOLECT-LAR HYDROGEN BONDINVOLVING T-BASEAS PIZOTON ACCEPTOR
Table I1 :
2897
Complexes Detected by Refractometry
Proton acceptor, A
Proton donor, D
Total concn., Temp., Complex mole M 'C. ratio, A : D
Fig no.
Proton acceptor, A
n-Heptane solution" Benzene Cyclohexylbenzene Biphenyl p-Terphenylb p-Terphenyl* Naphthalene Naphthalene Naphthalene Anthracene Anthracene Phenanthrene Phenanthrene Pyrene Pyrene Pyrene trans-Stilbene Fluorene Fluorene '
0 2
28 2 1:l
Decalin
Acetonitrile
Ethanol 1.:thanol Phenol Acetic acid Xthanol Phenol Acetic acid Ethanol Phenol Phenol Acetic acid Ethanol Phenol Acetic acid Phenol Ethanol Acetic acid
0 2
27 0 27.1 27 3 27.9 28.0 27.6 27.0 28.0 27.0 26 4 27.3 27.6 27.5 27.1 20.0 22.2 22.2
Tetralin Tetralin Tetralin T e tralin Benzene Benzene Benzene Naphthalene Naphthalene Kaphthalene Naphthalene Naphthalene Naphthalene Anthracene Anthracene Anthracene Pyrene Pyrene Pyrene Cyclohexylbenzene Biphenyl Biphenyl Biphenyl Biphenyl Biphenyl p-Terphenyl p-Terphenyl p-Terp hen yl p-Terphenyl p-Terphenyl
Water Methanol Ethylene glycol Ethyl acetoacetate Ethylene glycol Acetonitrile Ethyl acetoacetate Water Methanol Ethylene glycol Acetonitrile Ethyl acetoacetate Diethyl malonate Ethylene glycol Ethyl acetoacetate Diethyl malonate Ethylene glycol Acetonitrile Diethyl malonate
0.2 0.05 0.05 0.3 0.2 0.3 0.05 0.05
0.1 0.1 0.1 0.1 0.1 0.05 0.1 0.1
Di-Na pyrene1,6-dlSUlfOnate
Pentaerythri to1
0.2
Glucose Sucrose Cellobiose Pentaerythritol
18.0 0.1 17.8 0.05 18.1 0.1 17.7
Glucose Sucrose Pen taerythritol
0.1
0 05 0 05 0 05
Fig. no.
Dioxane solution
Ethanol
1:l 1:2 1:1, 1:3 1:l 1:l 1:l 1:l 1:1, 1:2 1:2,1:3 1:2 1:l 1:1, 1:2 1:2 1:l 1:1, 1:3 1:l 1:l
1
Aqueous solution" N a naphthalene-l-sulfonate Xa phenanthrene-3-sulfonate
Total concn., Temp., Complex mole M OC. ratio. A : D
Proton donor, D
23.4 1:2,2:l
2
1:l 1:l 1:l 1:l
18 8 1:l 18 0 1:l 17 3 1:1
21.0 22.0 0.1 20.4 0.1 19.8 0.1 21.7 0 . 1 20.9 0.1 22.0 0 4 25.9 0.1 21.3 0.1 18.8 0.1 19.7 0.1 22.5 0.1 18.9 0.1 18.9 0.1 19.0 0.05 26.2 0.05 27.2 0.05 27.2 0.1 27.0 0.1 27.0 0.1 27.0
1:1d
01 01 01 01
1:1 1:1 1:1
0.1
Ethylene glycol Water Methanol Ethylene glycol Ethyl acetoacetate Diethyl malonate Water Methanol Ethylene glycol Ethyl acetoacetate Diethyl malonate
0 1
01 0 05 0 05 0 05 0 05 0 05
220 192 193 224 191 198 25 1 25 2 26 0 24 6 24 6
1:1
1:1 1:1 1 : 1 (1) 1:1 1:1 1 : 1 (?)
1:1, l:2,1:3 1:2 1:2(1) 1:2 (1) 1:2 1:2 1:2
1:1 1:1,1:2 (7) 1:2 1:1 2:3 3
1:1
1:2 1:2(?), 1:3 (1) 1:1 1 : l (1)
1:1, 1:2 (?) 1:l (?), 1:a (?) 1:l (?)
a Decalin showed no complex formation with any donor in n-heptane. I n benzene. Sodium butane-1-sulfonate showed no complex formation with any donor. Decalin showed complexing only with acetonitrile, in dioxane. Measurements were repeated a t two different temperatures.
Table I11 : Complex Detecting Frequency (%) and the Number of Conjugated Double Bonds in Acceptor Molecules No. of conjugated double bonds
----
3
4.2 18.9 6.3 6.3 12.6 12.6
5 6
7 8 9
1:l
Complex mole ratio (D/A), %--1:2 1:3 Sum
0 0 3.2 6.3 12.0 0
0 0 0 4.2 6.3 6.3
4.2 18.9 9.5 16.8 31.5 18.9
%
1.9510
-
1.9470
-
1.9430 -
1.9390 -
as follows. As Lead2 has pointed out briefly, the fact that the interaction we now discuss is weak and the proton acceptors are extended n-electron clouds would suggest that the bonds formed are located indefinitely and have a higher degree of freedom than in the case of
Donor Acceptor
0
100
20 80
40
60
60
40
80 20
100 0
Mole %.
Figure 1. Pyrene-acetic acid in heptane; total concentration 0.1 mole/l. at 27.1 '.
Volume 68, Number 10
October, 1964
Z. YOSHIDA, E.
2898
1.8270
1.8230
f 1.8190
1.8150
1.8110 I
Donor Acceptor
0 100
I
I
40 60 Mole %.
20 80
I
60 40
80 20
100 0
Figure 2 . Sodium naphthalene-1-sulfonate-pentaerythritol in water; t,otal concentration 0.2 mole/l. at 23.4'.
I
I
Donor Acceptor
0 100
20
80
40
60 Mole %.
I
I
I
60 40
80
20
100 0
Figure 3. Biphenyl-water in dioxane; total concentration 0.1 mole/l. at 19.2".
I
I
1
2.0490
I Donor Acceptor
0
I00
I
20 80
I
40
60 Mole %.
I
60 40
I
80 20
I 100 0
Figure 4. Decalin-acetonitrile in dioxane ; total concentration 0.1 mole/l. at 21".
the X-H . . Y type hydrogen bonding. Therefore, the entropy of the system increases as the conjugation of 8-base is extended, favoring complex formation. e
The Journal of Physical Chemistry
OSAW-A,A N D R. ODA
According to a more recent report by West,Io - A S o of association of phenol with naphthalene and phenanthrene in CCI, solution (2.8 and 1.0 cal. deg.-l mole-l) are smaller than that of benzene-phenol (4.0 cal. deg.-' mole-I), which in turn is considerably smaller than that of alkyl ether-phenol (10-18 cal. deg.-' mole-I), consistent with the above reasoning. Aqueous Solution. .4s shown in Table 11, even in water, several complexes were barely detected between alcohols and sulfonated aromatics, although the bending in the refractive index diagram is obscure. There is no possibility of electrostatic interaction between the sulfonate group and the alcoholic OH group because sodium n-butane-l-sulfonate produced no complexes with hydroxyl compounds (glucose, sucrose, cellobiose, and pentaerythritol) , Dioxane Solution. As the changes of slopes in the n 2us. concentration plots in water were all very obscure compared to those observed in heptane, refractometry was carried out in dioxanc, whose proton-accepting power is less than that of water.ll As shown in Table 11, many instances were added for the existence of X-H.. . a-base interaction in hydrogen-bonding solvents. Complex formation in hydrogen-bonding solvents must be preceded by the desolvation of components, an energetically unfavored process. Indeed, it is suggested by Giles'* on the basis of refractive index measurements and surface film experiments that ordinary hydrogen bonding to the solvated OH group of cellulose in water could not occur. Therefore, it is to be expected in the present experiments that the entropy effect referred to above might have played a subtle role in the free energy balance of the desolvation-complexing equilibrium. The present result, however, seems to provide some indirect support for the hypothesis's2 that this type of hydrogen bonding may contribute to substantive adsorption of dyes to highly solvated cellulosic materials in water. I n both heptane and dioxane solution, decalin naturally proved not to be a proton acceptor, since it has no r-electron, but the case of decalin-acetonitrile in dioxane was an exception. A 1 : l complex was detected on repeated measurements a t two temperatures (Fig. 4). The nature of the intermolecular forces acting in this complex is yet unknown. (10) R. W e s t , I n t e r n a t i o n a l Symposium of l l o l e c u l a r S t r u c t u r e a n d Spectroscopy, T o k y o , Sept., 1962, D-117. (11) M. Tsuboi, Bull. Chem. SOC. Japan, 2 5 , 385 (1952). (12) F. M . Arshid. C. H . Giles, a n d S. K. J a i n , J . Chem. Soc., 559 (1956). (13) I n this connection, further work is in progress in o u r l a b o r a t o r y
on t h e t h e r m o d y n a m i c s of X - H .
.
rr-base t y p e hydrogen bonding.
