Properties of Thiols

When one encounters a thiol for the first time, especially a low-molecular-weight thiol, its most obvious property is its foul odor. Ethanethiol is added to natural gas so that leaks can be detected without special equipment—your nose is so sensitive that it can detect less than one part of ethanethiol in 10,000,000,000 parts of air The odor of thiols weakens with the number of carbons, because both the volatility and the sulfur content decrease. 1-Dodecanethiol, for example, has only a faint odor. 

The S—H bond is less polar than the O—H bond, and hydrogen bonding in thiols is much weaker than that of alcohols. Thus, methanethiol (CH3SH) is a gas at room temperature (bp 6°C), and methanol (CH3OH) is a liquid (bp 65°C). 

Thiols are weak acids, but are far more acidic than alcohols. We have seen that most alcohols have values in the range 10 to 10 (pK = 16 to 19). The corresponding values for thiols are about = 10 ° (pK = 10). The significance of this difference is that a thiol can be quantitatively converted to its conjugate base (RS ), called an alkanethiolate anion, by hydroxide  

Thiols, therefore, dissolve in aqueous media when the pH is greater than 10. 

Another difference between thiols and alcohols concerns their oxidation. We have seen earlier in this chapter that oxidation of alcohols gives compounds having carbonyl 

PROBLEM 15.15 The main components of a skunk s scent fluid are 3-methyl-1-butanethiol and cis- and frans-2-butene-1-thiol. Write structural formulas for each of these compounds. 

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Sulfides (RSR ) are the sulfur analogs of ethers Just as m the preceding chapter where we saw that the properties of thiols (RSH) are different from those of alcohols we will explore differences between sulfides and ethers m this chapter... 

RAFT polymerization lends itself to the synthesis of polymers with thiol end groups. Several groups have utilized the property of thiols and dilhioesLers to bind heavy metals such as gold or cadmium in preparing brushes based on gold film or nanoparticles1 8 761 763 and cadmium selenide nanoparticles.763 76 1... 

A thiol contains an —SH group covalently bonded to carbon. Sulfur is just below oxygen in the periodic table, so a thiol is somewhat similar to an alcohol. Still, the chemical and physical properties of thiols differ significantly from those of alcohols. For example, whereas alcohols have inoffensive odors, thiols smell bad. The stench of skunk scent is due to thiols, including 3-methylbutanethiol. Thiols are important in proteins because of their abilities to form S—S linkages, which we describe in Section 13-1. 

Pan, L., Tamai, N., Kamada, K. and Deki, S. (2007) Nonlinear optical properties of thiol-capped CdTe quantum dots in nonresonant region. Appl. Phys. Lett., 91, 051902-1-051902-3. 

Table 6.1 Individnal Properties of Thiols (1-13) in Dynamic Transthiolesteri-fication...

A characteristic of organic sulfur compounds, especially volatile (low molecular mass) thiols, is their disagreeable odors. For example, 3-methyl-1-butanethiol and 2-butene-1-thiol are ingredients of a skunk s perfume, and methanethiol or ethanethiol is usually added, in small amounts, to natural gas, which is odorless by itself, so that leaks can be readily detected. The chemical properties of thiols and sulfides differ from those of alcohols and ethers in that thiols are somewhat stronger acids than alcohols and the sulfur atoms of these compounds are considerably more nucleophilic than the oxygen of their analogs. They are excellent nucleophiles in substitution reactions. 

Hydrogen-atom donation from thiols to carbon-centered radicals was too often assumed to be the only property of thiols that is important in free radical processes in biology. Moreover, it was a common presumption that reaction (1) was the end of the biological pathway in which thiols repair radicals. Equilibria turned out to be much more important in sulfur radical chemistry than was first thought. For instance, the hydrogen-donation reaction was found to be a reversible equilibrium over 30 years after it was first observed. ... 

The heavy-metal chelating properties of thiols were taken advantage of in the design of dimercaprol ( British Anti-Lewisite, BAL) as counter poison of the arsenical war gas lewisite (Figure 20.43). Today dimercaprol is used to treat poisoning by compounds of gold, mercury, antimony and arsenic. The toxic nature of the heavy metals is masked and chelate is stable enough to be excreted as such in the urine. 

Synthesis, structure, and properties of thiols, particularly, those of heterocyclic series 05ZOR647. 

The conversion of cysteine to cystine requires additional comment. The —SH group of cysteine makes cysteine a thiol. One property of thiols is that they can be converted to disulfides by mild oxidizing agents. This conversion, moreover, can be reversed by mild reducing agents ... 

Properties of Thiol Proteinase Inhibitor from Rat Liver"... 

Many of the chemical properties of thiols stem from the fact that the sulfur atom of a thiol is oxidized easily to several higher oxidation states. The most common reaction of thiols in biological systems is their oxidation to disulfides, the functional group of which is a disulfide (—S—S —) bond. Thiols are readily oxidized to disulfides by molecular oxygen. In fact, they are so susceptible to oxidation that they must be protected from contact with air during storage. Disulfides, in turn, are easily reduced to thiols by several reagents. This easy interconversion between thiols and disulfides is very important in protein chemistry, as we will see in Chapter 18 ... 

The S—H bond is nonpolar covalent, and the physical properties of thiols are more like those of hydrocarbons with comparable molecular weight. 

The chemical and physical properties of thiol-stabilized II-VI semiconductor nanocrystals were reviewed by EychmuUer and Rogach [30]. The materials prepared... 

Spectroscopic and Related Properties of Thiols.— The n.m.r. absorption of the thiol proton moves to lower field in the order PhCHa SH, PhjCH SH, PhaC SH corresponding hydrotrisulphides RSS SH show the opposite sequence, due to over-riding inductive and anisotropic effects within the cumulative sulphur chain. 

Many of the chemical properties of thiols stem from the fact that the sulfur atom of a thiol is oxidized easily to several higher oxidation states, the most common of which are shown in the following flow diagram. 

The radioprotecting properties of thiols and aminothiols have been known for some time and this is generally attributed to their quenching of radiation-induced radicals such as Oj. Compounds which remove endogenous thiols thus increase radical lifetime and can have sensitizing properties. This mechanism contributes to the action of, for instance, A-ethylmaleimide [90] and any thiol depletion by artificial means should indeed produce enhancement of sensitization [91]. 

The reducing properties of thiols, suggest that mercaptan... 

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