Physical properties of thiols

Alcohols and thiols resemble each other in many ways, but they also differ in some significant respects. For example, thiols have lower boihng points than the corresponding alcohols because sulfur does not form intermolecular hydrogen bonds. 

Some alcohols have rather sweet odors, but one of the distinguishing properties of thiols is then-strong, disagreeable odor. The odor of the striped skunk Memphitis mephitis) is due to 3-methyl-1-butanethiol. The human nose can detect thiols at a few parts per billion in air. There is a positive side to the obnoxious odors of thiols Small amounts of thiols are added to natural gas to aid in easy detection of leaks. 

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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. 

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... 

Reactions of the Disulfide Group. Besides the thiol end groups, the disulfide bonds also have a marked influence on both the chemical and physical properties of the polysulftde polymers. One of the key reactions of disulfides is nucleophilic attack on sulfur (eq. 4). The order of reactivity for various thiophiles has been reported as (C2H O) P > R, HS , C2H5 S- >C,H,S- >C,H,P,... 

Table 3 gives the corresponding physical properties of some commercially important substituted pyridines having halogen, carboxyHc acid, ester, carboxamide, nitrile, carbiaol, aminomethyl, amino, thiol, and hydroxyl substituents. 

TABLE 1. Physical Properties of Step 1 Products Prepared by Condensing Diphenyl Carbonate with Selected Thiols Prepared According to the Current Invention... 

Hydroxy- and 5-mercaptotetrazoles and their mono-N1 -substituted derivatives can be involved into keto-enol and thiol-thione tautomeric equilibria (Equation 7). This is the reason for significant differences in chemical and physical properties of these compounds from other 5R-tetrazoles. 

Commercial products are available where n varies from 2 to 7. The flexible epoxy resins based on polyglycol also make excellent reactive diluents because they have a viscosity of 100 cP at 25°C. Table 4.4 shows the effect of two polyglycol diepoxides on the physical properties of a cured epoxy system. Another type of flexible epoxy resin is derived from dimerized unsaturated fatty acid, cashew nut oils, and other vegetable oils. Other flexible epoxy resins can be made with thiols, aliphatic acids, and hydroxyl-terminated compounds. Applications where flexible epoxy resins are valued include... 

The cystine residues, because they may act as cross-linkages between protein chains, have been studied more closely than other residues in keratin. Burley s (1956a) use of the concept of thiol-disulfide interchange to explain the effects of chemical modification on the physical properties of wool fibers has stimulated further work on cysteine and cystine residues. 

The conversion of disulfide bonds to thiol groups has a much greater effect on the physical properties of wool than conversion to (S-methyl groups (Crewther, 1965b). Reduction of relatively few disulfides and the consequent small increase in thiol content give maximum extensions > 100 % and high strains at the end of the yield region. 

Physical Properties of 1,3,4-Thiadiazoles. Ultraviolet spectra of some 2-benzylideneamino-5-phenyl-1,3,4-thiadiazoles have been reported. The n.m.r. spectral properties and conformational preferences of some open-chain and cyclic aromatic sulphides that contain 1,3,4-thiadiazole units, spectroscopic data of metal (Mn, Fe, Co, Ni, Cu, or Zn) chelates of iV-(5-phenyl-l,3,4-thiadiazol-2-yl)dithiocarbamic acids, conductometric and i.r. and Raman determinations on thirteen complexes of Zn, Cd, or Hg with 2-methyl-5-mercapto-1,3,4-thiadiazole, and thermogravimetry of some noble- and common-metal chelates of 5-amino-l,3,4-thiadiazole-2-thiol were also described, as well as the mass-spectral fragmentation of 2-phenyl-... 

The thiol—disulfide bonding system is important in the physical properties of a number of foods (134). Various enzymes catalyze the oxidation of thiols, the rearrangement of disulfide bonds, and the interchange of thiol-disulfide (135-141). The significance of these enzymes, some of which are found in baker s yeast (137), in the rheology of bread doughs, in other food systems, or in modifying novel proteins such as the keratins remains to be determined. 

Many studies have appeared dealing with the properties of crosslinked polymer systems. These include adhesion of epoxy-acrylates onto tin-plate, adhesion of isocyanate and epoxy-resin coatings, adhesion of butadiene-acrylate rubbers onto metals, glass, and ceramics, adhesion of acrylic, thiol, and polyester resins to aluminium bodies, and the mechanical and physical properties of photo-crosslinkable poly(vinyl cinnamate), vinyl-divinyl copolymers,polythiols, acrylates, epoxies, and thiols,epoxy resins, polyesters on wood, ... 

Membrane-s )Anmn have been prepared. Tetraphenylpor-phyrins having jc-carboxy and jc-amino functionalities have been polymerized interfacially to produce chemically asymmetric membrane films.Mercaptoporphyrins have also been polymerized to form ultrathin films of a porphyrin homopolymer based upon 5,10,15,20-tetrakis-(Q -mercapto-j9-tolyl) porphyrin,and thiol-derivatized porphyrins for attachment to electroactive surfaces have been prepared and examined as means of information storage,including those having a ferrocenyl moiety appended in several ways. Various means of linking porphyrins to form arrays have been reviewed. Preparation and investigation of the physical properties of cyclic tetra-, hexa-, hepta-porphyrin and star-shaped multiporphyrin or star-shaped tetra- or octa-porphyrin, or monophthalocyanine arrays have been described and reviewed. As part of this work, methods of forming porphyrins in the presence of acid-labile metalloporphyrins that provide a new route to mixed-metal multiporphyrin arrays have been reported. ... 

Vanin AF, Stukan RA, Manukhina EB (1996) Physical properties of dinitrosyl iron complexes with thiol-containing ligands in relation with their vasodilator activity. Biochim Biophys Acta 1295 5-12... 

One other physical property of carboxylic acids must be mentioned The liquid carboxylic acids, from propanoic acid to decanoic acid, have extremely foul odors, about as bad as those of thiols, though different. Butanoic acid is found in stale perspiration and is a major component of locker room odor. Pentanoic acid smells even worse, and goats, which secrete Ce, Cg, and Qo acids, are not famous for their pleasant odors. 

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