Thiohydroxamic acid

The following discussion of hydroxamic acids includes saturated systems, e.g., 2, compounds such as 3, derived from aromatic systems, 7V-hydroxyimides such as 7V-hydroxyglutarimide (78), and certain of their derivatives including thiohydroxamic acids. Naturally occurring cyclic hydroxamic acids are discussed to show the range of structural types that has been found, hut macrocyclic polyhydroxamic acids are mentioned very briefly, because several comprehensive reviews of these compounds are already available. The main purpose of this review is to summarize the methods available for the synthesis of cyclic hydroxamic acids, to outline their characteristic reactions, and to present some useful physical data. Their synthesis and some biological properties have previously been reviewed by Coutts. ... 

In a variation of this method, 2-bromopyridine A-oxide (60) has been converted by sodium sulfide to the thiohydroxamic acid (61). 

However, the 0-alkyl derivatives are potentially unstable with respect to thermal elimination of a carbonyl compound and consequent reduction to the corresponding lactam. A combination of steric and electronic factors may permit this decomposition, i.e., 133 -a- 134, to occur at quite moderate temperatures. The 0-methyl derivative of the benzalphthalimidine (132) undergoes slow loss of formaldehyde at 177° (Ti/a in dimethyl sulfoxide 40 minutes), but this elimination is much faster in certain thiohydroxamic acid derivatives, e.g., 135, which lose benzaldehyde readily at 139° in dimethyl sulfoxide (T1/2 6 minutes). The outstanding example of this decomposition, however,... 

Thiohvdrates metal complexes, 2, 516 Thiohydroxamic acid meta complexes, 2, 806 Thiolates... 

The reactions of salts of nitro compounds (113) (Scheme 3.95) with silylated thiols (308), hexamethyldisilathiane (308, 309), and hexamethyldisilane (310) afford oximes (114), thiohydroxamates (115), or thiohydroxamic acids (116) as final products depending on the structures of the starting nitronates and the reagents used. 

TABLE 3. Periodic system showing the number of reagents from the group of hydroxamic acids with which a certain element can be determined. Superscripts denote the number of reagents considered as hydroxamic acids and subscripts denote the number of elements considered as thiohydroxamic acids... 

Other molecules containing C=S linkages, for example thioamides, RC(=S)NH2, or thiohydroxamic acid derivatives, such as PhC(=S)N(Ph)OH, form stable complexes with gold(I).211,212 The complex ion formed from 2-thioamidopyridine is thought to contain tetrahedral gold(I) with structure (8). Similarly, complexes derived from Ph3P=S such as [AuCl(SPPh3)] are stable complexes.214,215... 

RCOOH — ROH.1 This transformation can be carried out by reaction of the ester (2), prepared from a carboxylic acid and the thiohydroxamic acid 1, with... 

Other thiohydroxamic acid derivatives have been used for the generation of radicals. Acyl derivatives of iV-hydroxythiazole-2-thione (75) have been explored by Barton as precursors for carbon radicals [86JCS(P1)39]. It has also been shown that similar precursors can be used for the generation of dialkylaminium cation radicals, N-hydroxy-4-methyl-thiazole-2-thione carbamates, TTOC carbamates 76 (91JOC1309). In contrast to... 

Lawesson s reagent (LR) is a very effective thionating agent of carbonyl compounds. However, attempted thionation with LR of iV-alkylhydroxamic acids gave maximum yields of 55-60%. Previous work had established that the thionation products, the thiohydroxamic acids (THA), were accompanied by the corresponding amides (A) formed by reduction and the thioamides (TA), the products of thionation of the amides (A) (Scheme 16). Now the reaction of (V-isopropylhydroxamic acid (HA R = IV) with LR has been followed by 31P NMR spectroscopy and several P-containing intermediates have been identified. This has permitted the delineation of a rational, but complex, pathway to each of the products of the reaction.45... 

The high electrophilicity of dithioesters towards amines was applied to the synthesis of phosphonothioamides [35, 36] and thiohydroxamic acids [37]. Dithioacid salts may also be used as starting materials for this thio-acylation with catalysis by boron trichloride [38]... 

With so much good radical chemistry based on acyl derivatives of thiohydroxamic acids, we naturally wondered if the corresponding derivatives of ordinary hydroxamic acids would show similar reactivity. Of the hydroxamic acids studied, only the dihydrocinnamoyl derivative of 138 gave a good yield (97 %) of the hydrocarbon in a tin hydride-initiated reduction. The next best was the derivative of A-hydroxy-2-pyridone which gave 73 % of hydrocarbon. These results,89 as well as... 

The reactions based on A-hydroxy-2-thiopyridone derivatives are clearly radical chain reactions. In a recent paper,91 we have reported quantum yield measurements for a number of reactions based on iV-hydroxy-2-thiopyridone. Most of the reactions had quantum yields of 10-30. Synthesis of the N-hydroxyquinazolin-4-thione 139 (Ar = Ph, An, 1-Naph) by an improved route gave thiohydroxamic acids which were more sensitive to light than iV-hydroxy-2-thiopyridone. The quantum yield for bromination was in the range 30-60. More important, while the JV-hydroxy-2-thiopyridone system at — 30 °C, makes21 radicals only in a non-chain fashion, the derivatives of 139 continue radical chain reactions even at — 60 °C. 

Radical-based dephosphorylation via a phosphonyl radical constitutes one formulation for the mechanism of C-P bond cleavage during microbial degradation of organophospho-nates.80 Frost has demonstrated that anhydrides 117 derived from phosphonic acid and thiohydroxamic acid react in a chain sequence with thiols, Bu3SnH and CC14 to give dephosphoryl-... 

Heating the mixed anhydrides of thiohydroxamic acids and carboxylic acids with diaryl ditellurium compounds under illumination caused decarboxylation and the formation of aryl alkyl tellurium derivatives8. 

Complexes of Hydroxamic Acid, Thiohydroxamic Acid and Derivatives 233... 

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