S. J. GILL,J. HUTSON, J. R. CLOPTOS ASD A I . DOWKIKG
1432
Dithiaaikanes
VOl. 65
Discussion Acyclic Sulfur Compounds.--Eyuatioss 5a and (ia represent the values of AHfozvs.15 for 22 acyclic alkane thiols and sulfides with ai1 average deviation + + + of 0.13 kcal. mole-', or 0.009 Itral. per valence bond, which is a somexhat better fit tlmi Allen obtained + + + for hydrocarbons.2 Only two of the deviations Thiacycianes and cycloalkylthiaalkanes are greater than experimental uncertainty by as AHf"ms.16 AHf0(C&SCH3,g) - AHfo(CzHe,g) much as 0.1 kcal. mole-'. a[AHfO(C&Hs,g)- AHf"(CH4,g)I - XCYCCC- X ' ~ C CS The definite trend in the deviations for the threc ( X V - 1)acsc ITBCCC - T'bccs sa4 E. (€9 dithianlkanes is puzzling. Neither experimentnl errors nor unaccounted-for interactions should bc AflfOZSS.lS = -1.111 - 2.35U - 2.58X - 3.30X' - 2.97X" + O.G5T + 1.20T' + 0.58 + Ea (83,) so large, but obviously one or the other must be. Cyclic Sulfur Compounds.-There are not enough Cycloalkanethiols d s t s for cyclic compounds to provide a real test AHf"(CH,SH,g) - AHf"(CH4,g) f A F f j f 0 2 ~16s of the correlation. However, the results for thii cL[AFff"(CJ%j,g) - AHf"(CH,,g)] - X ~ C C-C two thiacyclopentanes are consistent with a strain S ' ~ C CTBCCC S '~''PCCS S A E. (9) energy of 1.59 f 0.04 kcal. mole-l, and the absence AHf'298.16 = -2.!30 - 2 . 3 5 ~- 2.58X - 3.30X' + of significant strain in thiacyclohexane is to bc 0.652' 1.207" 0.5s E. (9a) expected. The results of the two cyclopentyl comThe numerical constants in the foregoing equa- pounds are consistent with Allen's value of 6.1 tions were evaluat,ed from the parameters in Table kcal. mole-' for the strain energy in cyclopentane. Comparison with Other Correlations.-Estimates 11, the selected' heats of formation of the sulfur compounds, and the heats of formation of methanea of heat of formation for sulfur compounds by most and ethane.6 The heats of formation of CH,SCH3 earlier correlations, like that of Franklin,' are not and CHSSSCH3 obtained in this correlation were very accurate because no reliable experimental data were available for evaluating the necessary paramused instead of t'he experimental values. Equations 8 and 9 include a ring strain energy eters. However, Lovering and Laidlers recently term, which Allen evaluated for cyclopentane and used a scheme of bond and group energies to corcyclohexane. The strain energy for the thia- relate published Bureau of Mines data for many of cyclopentane ring was evaluated from the data for the sulfur compounds in Table I. The deviations thiacyclopentarie and 2-methylthiacyclopentane they report between observed and calculated (S = 0 was assumed for the latter compound). values are somewhat larger than those reported For thiacj-clohexane, E, apparently is about zero here but, nevertheless, are comparable to the accuracy uncertainty of the experimental results. at. room temperature, as it is for cyclohexane.
+
,If
