Vol. 65
JOHXP. ~ICCULLOUGH AND WILLIAM D. GOOD
1430
TARLE XI1 b301..41> THERMODYXAMIC PROPERTIES O F FORMATION O F CYC1,OPENTANETHIOL IT
Reference state
AHf",
Ref. s t a t e of sulfur
kcaf.
298.15"K.
LFP, kcal.
ASfO cal. de& -1
- 109.08 11.17 -21.35zk0.18 S (c, rhombic) - 84.10 13.65 -11.42 3 ~ 0 . 1 8 Gas S (c, rhombic:) - 103.73 4.00 -26.84h0.19 Gas Sdg) For the reaction: 5C(c, graphite) 5H*(g) S (c, rhombic) or l/&z(g) = CsHl~S(liq. or g). Liquid
a
+
+
ite,g hydrogen gas,Qrhombic sulfur,'O and diatomic sulfur gas,'O all a t 298.15"K.
KI 8.19 -10.01 - 3.00 log
-
Acknowledgment.-The help of Derek 21. Fairbrother and Thelma C. Kincheloe in some of the experimental work is gratefully acknowledged.
CORRELATION OF HEAT OF FORMATIOX DATA FOR ORGAKIC SULFUR COMPOUNDS' B Y JOHN P. MCCULLOUGH AND
~%71LLIAR.l D.
GOOD
Contribution nTo. 105 from the Thermodynamics Laboratory, Petroleum Research Center, Bureau of 3firzes, I'. S . Department of the Interior, Bartlesville, Oklahoma Reeeiaed April 3, 1961
The method of Allen2 was used to correlate unpublished and recently published Bureau of Mines results for the heats of formation of organic sulfur compounds. Six parameters were evaluated from data for 25 acyclic alkane thiols, sulfides and disulfides. With the inclusion of appropriate strain energies, the results for seven cyclic sulfur compounds also were correlated. For all 32 compounds, the average deviation between calculated and experimental values, 0.17 kcal. mole-', was a little lesri than the average experimental uncertainty interval, 0.22 kcal. mole-'. The correlation can be used to predict reliable vzlues of heat of formation for many other organic sulfur compounds.
Allen? recently described one of the most accurate methods of correlating and predicting heats of formation of organic compounds. Selecting appropriate values for thermochemical bond energies and using them as constant in all compounds, he evaluated a small number of interaction energy parameters for use in equation (1) for the heat of atomization of paraffin hydrocarbons AHa"zss16 =
J'CHECH 4-NccEcc
+ X%cc
- TPccc - S A ( 1)
where NCE and Nc,: are the number of C-H and C-C bonds in the molecule ECH and ECC are the C-H and C-C thermochemical bond energies (YCCC is the interaction energy for a pair of next-nearestr neighbor carbon atoms joined to a common carbon atom X is the number of such pairs pccc 1s a trigonal interaction energy involving three carbon atoms, each of which is a next-nearest neighbor of the other two T is the number of trigonal interactions A is the gauche-n-butane interaction energy3 S is the number of such interactions
This relationship is equivalent to assuming that the heat of formation of a paraffin hydrocarbon can be calculated by adding to the heat of formation of methane the appropriate number of methylene increments4 (assumed constant for all com(1) This investi.gation was p a r t of American Petroleum Institute Research 'Project 48A on "The Production, Isolation a n d Purification of Sulfur Compounds a n d Measurement of their Properties," which the Bureau of hl.ines conducts a t Bartlesville, Okla., and Laramie. WcVyO.
( 2 ) T. I,. Allen, J . Chem. Phys., 11, 1039 (1959). (3) K. R. Pitzer, ibid., 8, 711 (1940). (4) W . B. Person and G . C . Pimentel, 3. Am. Chem. S o c . , 7 6 , 532 (1S531.
pounds) and appropriate interaction energy terms; that is, for C,HP,+~hydrocarbons A H ~ O Z S15S = AHf(CH*,g)
+ ( n - 1)[AHf0(CzH6,g)
- AHf"(CHa,g)] - Xaccc - TPccc + SA ( 2 ) For cyclic hydrocarbons, C,H2,, similar reasoning leads to the equation afozes
16
- n[AHfo(CtH6,g) - AHf"(CH4,g)I - Xaccc + TBCCC + 8-4+ E.
(3)
where E, is the strain energy of the cyclic molecule. Correlation for Organic Sulfur Compounds.Allen also determined some interaction energy terms for organic sulfur compounds, but not enough data were available to him for a thorough correlation. Nevertheless, the value he predicted for the heat of formation of methanethiol, -20.8 kcal. mole-l, is in excellent agreement with that recently determined experimentally in this Laboratory, -20.88 kcal. mole-' (both values for formatioil a t 298.1EioE
