ISSN:
0018-019X
Keywords:
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The complex formation of silver(I) has been studied with the anions of simple mercaptans RSH which have been rendered soluble by replacing some H in the substituent R by OH. All equilibria constants refer to a solvent of ionic strength μ = 0,1 and 20°C.Monothioglycol HO—CH2—CH2—SH (pK = 9.48) forms an amorphous insoluble mercaptide {AgSR} (s), ionic product [Ag+] [SR-] = 10-19.7. The solution in equilibrium with the solid contains the molecule AgSR at a constant concentration of 10-6.7 M which furnishes the formation constant of the 1:1-complex: K1 = 1013. 0. The solid is soluble in excess of mercaptide (AgSR+SR- → Ag(SR)2-: K2 = 104. 8) as well as in an excess of silver ion (AgSR + Ag+ → Ag2SR+K ≍ 106).With the bulky monothiopentaerythrite (HO—CH2—)3C—CH2—SH (pK = 9.89) no precipitation occurs with silver when the mercaptan concentration is below 10-3. 2M. A single polynuclear Ag10(SR)9+ (β10.9 = 10175) is formed in acidic solutions which breaks up with the formation of Ag2SR+ (β2.1 = 1019.0) when an excess of silver ion is added. Below the mononuclear wall ([RS]total 〈 10-6) Ag2SR+ is formed via the mononuclear AgSR (K1 = 1013). At higher mercaptan concentrations ([RS]tot 〉 10-3.2) an amorphous precipitate is formed which has almost the same solubility product as silver thioglycolate ([Ag+] [SR-] = 10-19.1).Apparently silver(I) forms with mercaptans always the complexes Ag2SR+, AgSR and Ag(SR)2-. Above the mononuclear wall, these species condense to chain-like polynuclears which are cations Ag(SRAg)n+ in presence of an excess of Ag+, and anions SR (AgSR)n- when the concentration [RS-] is larger than [Ag+]. Usually n becomes rapidly very large as soon as the condensation starts (n → ∞: precipitate). The decanuclear Ag(SRAg)9+ formed with thiopentaerythrit is somewhat more stable than the shorter chains (n 〈 9) and larger chains (n 〉 9), because it can tangle up to a ball by coordination of bridging mercapto-sulfur to the terminal silver ions (figure 12, page 2179). This ball seems to be further stabilized by hydrogen bonds between the many alcoholic OH groups of the substituent R = (HO—CH2)3C—CH2—. The stability of the bonds Ag—S, however, is little influenced by the substituent R which carries the mercaptide sulfure.
Additional Material:
12 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/hlca.19710540751
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