NOTES
444
connection with this article. We are also grateful for financial support of this research furnished by the National Science Foundation (NSF G P 3789), the
Army Research Office (Durham) (DA 31 124 ARO D 241), and a NASA grant (NGR-24-005-063) to the Space Science Center of the University of Minnesota.
NOTES
Hydrogen-Bonding Interaction between Alcohols and Ethylene Trithiocarbonate
grahi.‘ If the base B forms a 1:l complex with a pro ton donor A, then
[AI -- _ by Sadhan Kumar De and Santi R. Palit Department of Physical Chemistry, Indian Association for the Cultivation of Science, Jadavpur, Calcutta 52,India (Received March 85, 1966)
Hydrogen-bonding interaction with C=S chromophore has been but little studied except for some preliminary investigation^.'-^ We report herein some results of our preliminary studies of the hydrogen-bondinginteractionof ethylene trithiocarbonate (ETTC) with alcohols. Following the suggestion of Chandra and Sannigrahi,* we have allowed for self-association of alcohols5-9 in calculating the stability constant of the hydrogen-bonded complexes.
Experimental Section ETTC was obtained as a gift from Evans Chemetics, Inc. The nonhydrogen-bonding solvent used was RIerck’s n-heptane which showed cutoff at 220 mp. The alcohols were purified by standard methods1° and distilled before use. The solutions were made gravimetrically and all of the spectral measurements were taken on freshly prepared solutions in a Hilger UVspeck spectrophotometer using 1-cm stoppered quartz cells at 24” (a temperature constant within *0.5” being maintained by circulating water through the cell holder).
Results The obseived blue shift of the n-r* transition of ETTC with increasing concentration of alcohols as shown in Figure 1 was utilized to calculate the equilibrium constant by determining the slope and intercept of an [A]/D us. [A] plot (Figure 2) in accordance with the following equation due to Chandra and SanniThe Journal of Physical Chemistry
D
[A1 +-[Bloc
1 K[B]oi
where D = OD - ea[B]o, a = ec - EB, K is the equilibrium constant of the complex, OD is the optical density of the mixture, [BIois the formal concentration of solate, [A] is the monomer concentration of alcohol, and EC and EB are the molar extinction coefficients of the complex and solute, respectively. Calculation of monomer concentration of alcohols requires dimerization constant values and these values of benzyl alcohol, n-propyl alcohol, and n-butyl alcohol were those as reported by Coggeshall and Saier,5 those of ethyl alcohol and t-butyl alcohol as reported by Becker,6 and of isopropyl alcohol as reported by Blanks and P r a u ~ n i t z . ~ The results are summarized in Table I where the average values of the equilibrium constants measured at several wavelengths near the shifted peak are given. The values of equilibrium constant for a given system are constant within 10%. I n order to study any effect due to solute concentration, the ETTC-n-butyl al(1) L. J. Bellarny and P. E. Rogasch, J. Chem. Soc., 2218 (1960). (2) M. J. Janssen, Rec. Trav. Chim., 79, 454, 464 (1960). (3) A. Balasubrarnanian and C. N . R. Rao, Spectrochim. Acta, 18, 1337 (1962). (4) A. K. Chandra and A. B . Sannigrahi, J. Phys. Chena., 69, 2494 (1965). (5) N. D . Coggeshall and E. L. Saier, J . Am. C h m . Soc., 73, 5414 (1951). (6) E. D. Becker in ”Hydrogen-Bonding,” D. Hadzi, Ed., Pergamon Press Ltd., London, 1959. (7) J. C.Davis, Jr., K. 9. Pitzer, and C. N. R. Rao, J . Phys. C h m . , 64, 1744 (1960). (8) B.D . N . Rao, P. Venkateswarulu, A. S. N . Murthy, and C. N . R. Rao, Can. J . Chem., 40,387 (1962). (9) R. F. Blanks and J. M. Prausnitz, J . Chem. Phys., 38, 1500 (1963). (10) “Techniques of Organic Chemistry,” A. Weissberger, Ed., Vol. VII, Interscience Publishers, Inc., New York, N. Y . , 1955.
NOTES
445
Table I : Equilibrium Constants of the Hydrogen-Bonded Complexes between ETTC and Alcohols
Concn of ETTC X 108, M
Alcohols
Benzyl alcohol
4.414
Ethyl alcohol
4.942
n-Propyl alcohol
4.406
n-Butyl alcohol
3.692 6.572
0
Isopropyl alcohol
4.229
&Butyl alcohol
3.965
Range of alcohol concn,O M
Range of monomer concn in the range of alcohol concn used, M
0.096490.4824 0.34221.711 0.26721.7368 0.32731.4183 0.76372.182 0.78061.9515 0.31772.645
0.08040.2826 0.23890.7352 0.18790.6850 0.21200.5741 0.38480.7484 0.45950.8506 0.21520.8906
Equilibrium constant, M -1
P& of alcohol a t 25"b
Taft's n* of R in
R-ow
0.620
15.4
0.215
0.286
15.93
-0. loo
0.245
16.1
-0.115
0.192
16.1
-0.130
0.137
17.1
-0.190
0.038
19.2
-0.300
0.198
The concentration of benzyl alcohol was kept low because of its limited solubility in n-heptane. See ref 14.
* J. Murto, Acta Chem. Scund.,
IS, 1043 (1964).
I
'201 440
I
I
I
450
x,
I
4 /O
n??60-
Figure 1. Absorption spectra of E T T C in 0 (I), 1.706 (11), 3.412 (111), and 4.265 (IV) M ethyl alcohol. Concentration of E T T C was 5.171 x 10-3 M for all absorption curves.
coho1 system was studied at two different concentrations of ETTC and no significant variation in the equilibrium constant was observed.
Discussion It is evident from our data that alcohols form weak 1:l hydrogen-bonded complexes with ETTC and the stability constants follow the order: benzyl alcohol >
ethyl alcohol > n-propyl alcohol > n-butyl alcohol > isopropyl alcohol > t-butyl alcohol. Balasubramanian and Rao3 found that the hydrogen-bond energies in an ETTC-alcohol system increase in the order: methyl alcohol > ethyl alcohol > isopropyl alcohol > t-butyl alcohol. However, these values of hydrogen-bond energies do not represent the energy of one hydrogen bond, since the concentration of the proton-donor solvents was very large in their experiments thereby leading t o considerable self-association of the solvent molecules. A similar trend has also been observed in various basealcohol systems. For example, Bec1ter1l found that the equilibrium constants for 1:1 complex formation between alcohsls and different proton acceptors follow the order: methyl alcohol > ethyl alcohol > t-butyl alcohol. Chandra and Basu12 and Murthy13 found that the equilibrium constants for the formation of 1:1 hydrogen-bonded complexes decrease in the order : primary, secondary, and tertiary alcohol. However, the equilibrium constants reported by Chandra and Basu as well as by hllurthy do not correspond to any definite composition of the complexes since alcohols would exist appreciably as dimers and polymers in their working range of concentrations and no correction was (11) E. D. Becker, Spectrochim. Acta, 17, 436 (1961). (12) A. K. Chandra and S. Basu, Trans. Faraday Soc., 56, 632 (1960). (13) A. S. N. M u r t h y , Ph.D. Thesis, T h e Indian Institute of Science, Bangalore, 1964.
Volume 7 1 , Number 9 January 1967
NOTES
446
I
Mass Spectrometric Studies at High Temperatures.
4 2
XIV. The Vapor Pressure
and Dissociation Energy of Silver Monofluoride
by K. F. Zmbov and J. L. Margrave Department of Chemistry, Rice University, Houston, Texas (Received July $2, 1066)
The vaporization behavior of AgC1, AgBr, and AgI has been studied, 1-4 but quantitative vapor pressure data have not been available for silver monofluoride. The object of the present work was to study the sublimation and vaporization of AgF and to determine the dissociation energy of AgF(g).
r
Experimental Section
01
I
I
*
I
4
I
I
I
[A] XI0
I
6
*
I
10
Figure 2. Plot of ( A ] / Dus. [A] : I, benzyl alcohol (4.414 X lo-.’ M ) ; 11, ethyl alcohol (4.942 X M); 111, n-propyl alcohol (4.406 X M ) ; IV, n-butyl alcohol (3.692 X M ) ; V, n-butyl alcohol (6.572 X 10-8 M ) ; VI, isopropyl alcohol (4.229 X 10-8 M ) ; VII, t-butyl alcohol (3.965 X lo-* M ) . The concentrations of E T T C are indicated in the parentheses. All of the spectral measurements were made at 454 mp.
applied for the same. Nevertheless, all these trends are consistent with the concepts of acidities of the alcohols. Table I shows that the equilibrium constants for hydrogen bond formation run parallel with the acidic strength or proton-donating power of alcohols and also with Taft’s polar substituent constant (,*).l4 Such a correlation between the acidity of proton donor and stability of the hydrogen-bonded complex shows in an indirect way the contribution of the electrostatic part in the over-all strength of a hydrogen bond. Acknowledgments. The authors are grateful to Evans Chemetics, Tnc., for a gift sample of ethylene trithiocarbonate. Thanks are due to the Council of Scientific and Industrial Research, India, for awarding a Junior Research Fellowship to S. K. D. (14) R. W. Taft, Jr., in “Steric Effects in Organic Chemistry,” M. S. Newman, Ed., John Wiley and Sons, Inc., New York, N. Y., 1956, Chapter 13.
The Journal of Physical Chemistry
The mass spectrometer has been de~cribed.~The AgF sample was obtained from Research Inorganic Chemicals Co., Sun Valley, Calif., and was used without further purification. The sample was evaporated from a platinum Knudsen cell; the temperature of the cell was measured with a Pt-Pt-lO% Rh thermocouple, calibrated against a National Bureau of Standards standard thermocouple, and is believed accurate to =k0.5”, although the maximum temperature gradient in the cell could be as great as f5”.
Results The vaporization of AgF was studied over the temperature range 854-1024°K. The only ions formed by electron bombardment of the vapors effusing from the Knudsen cell were AgF+ and Ag+ in the ratio 0.25 to 0.17 a t 7 5 ev. KOpolymeric species (AgF).+ were observed in the mass spectrum. The appearance potentials of Ag+ and AgF+ ions, determined by the vanishing-curre nt method and using background mercury as a standard, were found to be 11.5 and 11.4 ev, respectively, with probable errors of zk0.3 ev. The heat of vaporization of AgF was determined from the plot of log I+T (for the AgF+ ion) vs. 1/T as ALHV,935.6 = 42.8 0.3 kcal mole-’, where the uncertainty given represents the standard deviation of the least-squares treatment of the data. The true uncer-
*
-~~~
~
(1) H. Von Wartenberg and 0. Besse, 2. Elektrochem., 28, 384 (1922). (2) K. Jelinek and A. Rudat, 2. Physik. Chem., A143, 55 (1929). (3) A. V. Gusarov and L. N. Gorokhov, Vestn. Mosk. Univ. Ser. 11, Khim., 17, No. 5, 14 (1962). (4) H. M.Rosenstock, J. R. Walton, and L. K. Brice, U. S. Atomic Energy Commission Report ORNL-2772 (1959). (5) G. Blue, J. W. Green, R. G. Bautista, and J. L. Margrave, J. Phys. Chem., 67, 877 (1963).
