R . J. NIEDZIELSKI, R. S. DRAGO,AND R. L. MIDDAUGH
1694
[CONTRIBUTION FROM
THE
Vol. 86
WM. A . SOYES LABORATORY, UNIVERSITY OF ILLINOIS,CRBASA, ILLIKOIS]
Donor Properties of Some Sulfur Compounds1 BY ROBERTJ. NIEDZIELSKI, RUSSELL
s. DRAGO,AND RICHARD L. MIDDAUGH
RECEIVED X O V E X B E R 13, 1963 Evidence is presented to indicate that the compounds CH,C(S)h'( CH3)2, ( CH3)2h-C(S)r\'(CH,)2,and C6H5SCH3 form sulfur coordinated adducts with iodine and phenol, while C H X ( O)SCH3forms oxygen coordinated adducts. The thermodynamic data for formation of these adducts in CCI, solution are reported, and the donor properties are interpreted in terms of the electronic structure of the donor and the nature of the donor-acceptor interaction. These interpretations are substantiated by the CL3proton n.m r . coupling constants. Evidence is presented to indicate substantial C-S r-bonding in CHsCOSCHs.
Introduction In contrast to the large amount of quantitative data available for oxygen donors, very little information is available for sulfur donors. Thermodynamic data for adduct formation between dialkyl sulfides and the acids BH3,j.' BF3,6 and BC1$ have been reported. Similar studies have been carried out with a series of saturated cyclic ~ u l f i d e s . ~ JAdducts formed by iodine and diethyl disulfide, CzH&CzHj, and those formed by halogens and interhalogens with the phosphine sulfidesghave been studied quantitatively. The sulfur donors studied interact more strongly than the analogous oxygen donors with the acids Iz and BH3 but less strongly with BF3and BC13. In previous articles,]" the magnitude of the donoracceptor interaction has been rationalized in terms of the ease with which the electronic structures a t the reactive sites of the acceptors and donors can be distorted. Donors and acceptors t h a t are both easily distorted form stronger adducts with each other than with acids and bases t h a t are less easily distorted. Certain acceptors are polar and not so easily distorted. The magnitude of the interaction with this type of acceptor is more sensitive to the polar nature of the donor, and oxygen donors are often better than the analogous sulfur donors. Iodine is an example of a distortable acid, while the hydrogen bonding interaction of phenol is found to be quite sensitive to the polarity of the donor. The enthalpy of formation of the adducts formed between sulfur or oxygen donors and the acids Iz,BH3, BF3, and BC13can be rationalized with these arguments. Data on. a large number of other systems have also been interpreted" b y similar arguments. Acids or bases whose electronic structure is easily distorted are referred to as soft and those which are not are referred to as hard. \Vith these considerations in mind it was of interest to inxrestigate and compare the magnitude of the in( 1 ) Ahntracted in p a r t f r o m t h e Ph.1). Theses of R o b e r t J . Niedzielski and Richard I , , M i d d a u g h , University of I l l i n d q , U r b a n a , Ill. ( 2 ) N. W Tideswell a n d J I ) hIcCullnugh, J . A m . Chem. S O C 79, , 1031 (1957) (:I) H 'l'suhomura a n d R . I,ang, ibrd , 83, 2085 (1961). ( 4 ) ?d Guod, A Major, J . S a g - C h a u d h u r i , and S. P M c G l y n n . ibid , 83, 4329 (1061). [.5) W , A G. G r a h a m and P. G. A . Stone, J . I n o v g . Nucl. f h e m . , S, 164 (1956) ((i) RI 'l'nmres, private communication. ( 7 ) J I ) hlcCullough a n d I ) L l u l v e y , .I A m Chem. S o c . , 81, 1291 ( 1 9.-,!u (8) hI. T a m r e s and S. Searles, J r , J . P h y s . C h r m , 6 6 , 1089 (1962) \ ! I ) R A Zingarc,, R E . McGluthlin, a n d E. A Meyers, ibid , 66, 2879 ;l962) ( I O ) If,I).Joesten and R. S. I>rago, J . A m C h e m . Sol.., 84, 2037 ( 1 9 6 2 ) ; I< S . 1)rng.i. I ) . W Rleek, 12 Tnnphi, a n d M 1) Joesten, i n o r g . Chem , 2 ,
im i
i m )
(11) K
C. Prarson, J . A m . Chem Soc , 86,
teraction of the Lewis acids iodine and phenol with the donors N,S-dimethylthioacetamide, CH3C(S)N(CH3)2, tetramethylthiourea, (CH3)~NC(S)N(CH3)2, S-methyl thioacetate, CH3C(0)SCHa, and phenyl methyl sulfide, C6HjSCH3. This comparison also demonstrates the effects of substituents on the donor properties of sulfur. Experimental Preparation and Purification of Materials.-Fisher Spectranalyzed carbon tetrachloride was used without further purification. The purification procedure for iodine has been reported.'* Baker and Adarnson reagent grade phenol was distilled a t atmospheric pressure. The fraction boiling a t 182" was collected. Tetrainethylthiourea was prepared by the regulated thermal decomposition of bis(diniethylthiocarbaniy1) disulfide as described by Shaw and U'alker.13 This was accoinplished by heating the starting material under air reflux for several hours. The resulting mass was recrystallized three times from water. A nul. Calcd. for CLH12SIS: C , 45.41; H , 9.15; N , 21.19. Found: C,45.62; H,9.16; S , 2 1 . 1 3 . S,S-Dirnethylthioacetamide was synthesized from S , S dimethylacetamide and phosphorus pentasulfide according to the general procedure given by Hofmann The compound was recrystallized from water. Anal. Calcd. for C4H,NS: C, 46.56; H, 8.79; ri, 13.58. Found: C , 46.40; H , 8.62; S , 13.59. Phenyl methyl sulfide was prepared from C&SSa and CH31.'4h The colorless liquid was distilled at atmospheric pressure, b.p. 192-196", and redistilled a t reduced pressure, b.p. 65.0-65.5" (5 mm.). A n d . Calcd. for C,H,S: C, 67.69; H , 6.49. Found: C , 67.58; H , 6.64. The apparatus and procedure for determining and calculating equilibrium constants have been reported previously .15 The procedure employed for accurate determination of the enthalpies has also been described.'& T h e infrared spectra of donor-iodine systems were obtained with a Perkin-Elmer Model 21 doublebeam spectrometer employing sodium chloride optics. The 0-H stretching frequency shifts of the donor-phenol systems were obtained on a Beckman Model IR-7 double-beam spectrometer with a fore-prism-grating optical system. Nuclear magnetic resonance spectra were obtained using a Varian Model A-60 n.m .r. spectrometer. Tetramethylsilane was used as an internal reference, and all spectra were recorded a t room temperature.
Results The data employed for calculation of equilibrium constants of the systems studied are contained in Table I Enthalpies were determined by measuring the change in absorbance of a single solution as a function of temperature. Readings were taken about every 3 O over the temperature range 25.0 to 40.0°. Enthalpies were calculated from a least-squares determination of (12) C. n. Schmulbach a n d R . S . I h a g o , ibid., 8.2. 4484 (1960). (13) U' H. R S h a w a n d I>. G Walker. i b i d . , 79, 4329 (19.57) (14) (a) A. W H
