Mercapto radical

When free radicals or other reactive organic species are generated in the electron transfer step, the pattern of surface coverage may have a dramatic impact on the yields of various possible organic oxidation products. Consider the oxidation of mercaptans (RSH) by a metal oxide surface. One-equivalent oxidation forms mercapto radicals (RS1) which quickly couple with neighboring radicals to form a disulfide product (36). 

Electron transfer from sulfur to copper would now give a copper(I) complex, and the mercapto radical which is uncharged could now be readily displaced by another ligand, or the complex could be oxidized further by oxygen to give... 

Unless the drop size is very small, the micelles, with their relatively large surfaces at which the lauryl mercaptan and the persulfate can react, will initiate the polymerization. It may well be that there is even some enrichment of the mercaptan in the surface of the micelle, leading to a still faster reaction. It seems that it is the mercapto radicals held in the... 

Another puzzling point of the mechanisms proposed to explain the autooxidation of thiols in basic solutions (in particular see Scheme 4) is the assumption that mercapto radicals dimerize almost quantitatively without interacting with the solvents in which the reaction was studied. 

Lippard et al. proposed several possible mechanisms of the alkane hydroxylation [9]. One possible mechanism is shown in Scheme 3, in which an T 2,T 2-peroxo-bridged diiron(III) acts as an active intermediate which directly transfers oxygen to an alkane substrate [9]. This mechanism suggests the participation of a mercapto radical of Cys-151. This amino acid occupies the equivalent region of space to the tyrosyl radical of ribonucleotide reductase, as indicated by sequence homology and the X-ray crystallographic results [53, 55]. 

Grignard reagents from, 5, 106 reactions, 5, 104 6, 274, 292 reactivity, 6, 292 synthesis, 6, 297 Thiazoles, imino-reactivity, 6, 250 Thiazoles, isopropenyl-radical polymerization, 6, 278 Thiazoles, mercapto-industrial uses, 6, 330 reactions, 5, 102 synthesis, 6, 298-299 tautomerism, 6, 247, 248, 269, 289 Thiazoles, methyl-... 

Halogenation of 2-methyl-l,3,4-thiadiazole 9 can be achieved under free radical conditions. Trichloro- and tribromomcthyl-l, 3,4-thiadiazolcs have been obtained by this method <1980LA1216>. Rapid and selective free radical monochlorination of the 2-mercapto-5-methyl-l,3,4-thiadiazole 9 was achieved using sodium hypochlorite under microwave conditions (Equation 27) <1998JCM586>. 

Semitelechelic HPMA polymers were synthesized by free radical polymerization of HPMA using 2,2 -azobis(isobutyronitrile) (AIBN) as the initiator and alkyl mercaptans as chain transfer agents. Alkyl mercaptans with different functional groups, namely, 2-mercaptoethylamine, 3-mercapto-propionic acid, 3-mercaptopropionic hydrazide, and methyl 3-mercapto-propionate, were used as the chain transfer agents ST HPMA polymers... 

The best evidence for the photolytic decomposition of mercaptans and disulfides into free radicals involves photoinitiation of polymerization of olefins. Thus, photolysis of disulfides initiates the copolymerization of butadiene and styrene,154 as well as the polymerization of styrene207 and of acrylonitrile.19 Thiophenol and other thiols promote polymerization upon ultraviolet irradiation.19 Furthermore, the exchange of RS-groups between disulfides and thiols is greatly accelerated by light. Representative examples are benzothiazolyl disulfide and 2-mercapto-thiazole,90 tolyl disulfide and p-thiocresol, and benzyl disulfide and benzylmercaptan.91 The reaction probably has a free radical mechanism. Similar exchange reactions have been observed of RS-groups of pairs of disulfides have been observed.19... 

Free radical polymerization of styrene, of acrylate and of methacrylate monomers in solutions at 60° C in the presence of this preformed polymer produced graft copolymers in high efficiency, the chain transfer constants for these mercapto groups with styrene and methyl methacrylate being similar to those found with simple mercaptans (80, 85). 

The authors reported that methyl 4-mercapto-2-alkenoates 710, obtained by irradiation of 2(5H)-thiophenones 709 in MeOH, undergo light-induced S-H bond homolysis to give thio radicals 710 (84HCA2198 85HCA2350 87HCA125). Intermediate 710 can be trapped by alkenes to afford 3-thia-hex-5-enyl radical 711, which cyclize selectively to radicals 712, precursors of thiolane-3-acetates 714. 

Fig. 1.7. Surface modification of 45 A Ti02 colloids with different mercapto-carboxylic acids. EPR spectra of degassed aqueous Ti02 colloids (0.3 M) illuminated with 308 nm excimer laser (a) in the presence of different surface modifiers illuminated at 77K and recorded at 8K (b) the same samples recorded at 150 K at the bottom irradiation of pure TLA acid in N20 leads to formation of sulfur centered radical dimmer of TLA.

The heteroaromatic thioles, in particular 2-mercapto-6-nitrobenzothiazole, were studied in regard to their abilities to function as coinitiators in free-radical photopolymerizations induced by camphorquinone and isopropylthioxanthone [598],... 

The redox noninnocence of the 2-mercapto-3,5-di-tert-butylaniline ligand has recently been investigated with nF ions. The spectroelectrochemistry of the complex displays a range of electron transfers where the monocation, the neutral species, and the mono- and dianions have been characterized. In a related manner, Wieghardt and coworkers have reported the first example of a stable N, O-coordinated o-iminobenzoquinone via air oxidation of the initial nF complex with 2-anilino-4,6-di-tert-butylphenol (94). The analogous o-iminobenzosemiquinonate 7r-radical complex was also isolated for this system and earlier for the bis-(o-immobenzosemiquinonate)nickel(II) complex. ... 

Rule 2. Different names for a few common ligands hydro, hydroxy, peroxy, mercapto, thio, dithio, hydroperoxy. In case of doubt, the charge on a ligand is indicated thus tartrato(3-) for 00CCH(0 )CH2-C00 . Organic radicals listed with neutral groups. 

Thiols, unlike alcohols, form insoluble salts (mercaptides) (4) and (5) by reaction with heavy metals like mercury and lead (Scheme 3) this is the origin of the former name mercaptan for thiols, which comes from the Latin mercurium captans, meaning mercury seizing. In modern nomenclature the name thiol is preferred to mercaptan although the prefix mercapto is still allowed for the unsubstituted SH radical. 

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