The Chemistry of Low Valent Sulfur Compounds in the S-H2O System

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Abstract

The primary goal of this thesis is to analyze geometrical trends of thermodynamic and related functions of low valent sulfur polymer groups in order to determine the thermodynamic properties of these species.

The following geometries were observed or inferred. a). H₂2S_n(g,aq, n ≥ 2): analogy with other isostructural molecular polymer groups indicates that all of its thermodynamic properties will be linear functions of n. b). S_nS^-2 (aq, n ≥ 1): a speciation model is developed that is in agreement witb the best experimental data, which proposes that Δ G°_f,n has an inverted gaussian geometry with respect to n with the curve minima being centered at n_e. This model is extrapolated to high temperatures. c). S_n(g,n ≥ 2): n-logfs_tot data appears to have the same geometry at all temperatures and to exhibit iso-n linearity on a logfs_tot vs. 1/T plot, implying that Cp °_n and Δ H°_f,n but not S°_n or ΔG°_f,n are linear functions of n over the temperature range of the data. A multi-temperature speciation model is developed based on the assumption that S_n(g,chains,n = 2-5) and S_n(s,rings, n = 6-8) constitute separate isostructural homologous groups. d). S_m(aq, m > 0): Analysis of the behaviour of polysulfides in various media suggests that Kd_m, which governs the scission of S_nS^-2 to S_m radicals, increases with m.

Secondarily, the isostructural-isovalent non-polymeric O-S-Se-Te(=X) group is discussed in light of Sverjensky's (1984) observations and reactions like logK (H₂X,g = HX· + H⁺) are shown to be linear functions of ΔG°_f(H₂X,g). These Sverjensky correspondence plots (SCPs) will allow pKa₂(H₂S) tobe determined from H₂Se and H₂Te. A restricted isocoulumbic extrapolation technique termed 'twinning', that matches isostructural-isovalent products and reactants, is used to extrapolate some types of data to high temperatures, including ΔG°_f(S₂O₃^-2). Tue twinning of 25°C SCPs can generate adundant multi-temperature data.

Table of Contents

Chapter I. The Sulfide Species ... p1
1). Introduction ... pl
2). Henry's Constant, K_H ... pl
3). Ka₁ ... p2
4). Ka₂ ... p6
5). ∑s^-2 and Sverjenski Correspondence Plots ... p7
6). The Combination of Twinning with Sverjensky Correspondence
Plots ... p10
7). Conclusions ... p16

Chapter II. The Unprotonated Polysulfid es Nea r Room Temperature ... p19
1). lntroduction ... p19
2). Mathamatical Representation of Polysulfide Equilibria ... p20
3). Experimental Data and Speciation Models ... p22
3a). Be, n_e and n.. ... p23
3b). Speciation ModeJs ... p26
4). Symmetry Considerations ... p29
4a). ΔG°_f,n vs. n ... p29
4b). Constructing the Model ... ... p29
5.) Conclusions ... p36

Chapter III. Hydrogen Polysulfides (H₂SS_n,g,aq) ... p37
1). lntroduction ... p37
2). The Homologous Group Approach ... p37
3). H₂SS_n,g ... p40
4 ). H₂SS_n,aq ... p42

Chapter IV. Elemental Sulfur ... p46
1). Introduction ... p46
2). S_n,g ... p46
2a). Introduction ... p47
2b). Representation of Equilibria ... p47
3). Experimental Data on S_n,g ... p48
3a). Saturated Vapor Pressure ... p48
3b). n-fs_tote ... p48
3c). Analysis of n-log(fs_tote) Data ... p57
4). S_n,g Speciation Models ... p59
4a). Previous Work ... p59
4b). New Model ... p62
4c). Comparison of Models ... p64
4d). Conclusions ... p69

Chapter V. The Hypersulfides (S_m) ... p70
1). Introduction ... p70
2). S₃ ... p72
3). S₂ ... p72
4). S₄ ... p73
S). S₁ ... p74
6). Graphical Representation of Equilibria ... p74
6a). u_n and u_m ... p75
6b ). u_n,t and u_m-,t ... p76
7). The Interpertation of Published Spectra ... p78
7a).Dubois, Lelieur and Lepoutre's Studies ... p78
7b ). K_dm trends ... p85
7c). Other Studies ... p86
8). Conclusions ... p89

Chapter VI. High Temperature Equilibria ... p90
1). Introduction ... p90
2). The Polysulfides ... p90
3). The Hypersulfides ... p96
4). Disproportionation of Elemental Sulfur ... p105
4a). Basic Solutions ... p105
4b). Acidic Solutions ... p106
5). Free Energy of S₂0₃^-2 ... p108
5a). Giggenbach (1974a) ... p108
5b). Uyama, Chiba, Kusakabe and Sakai (1985a,b) ... p109
5c). Mel, Hugus and Latimer (1956) ... p113
6). Inter-Species Relationships ... p114
7). Conclusions ... p121

Chapter VII. Comments on Applied S-H₂0 Chemistry ... p 122

References ... p129