Thiadiazole structures

The corresponding 1,3,4-thiadiazole structure has been assumed, without further evidence, by Chakrabarti and De.60... 

Wohler143 first described the formation, from concentrated aqueous thiocyanic acid, of a compound, C2H2N2S3 later named isoperthiocyanic acid, and now formulated as 3-imino-5-thiono-l,2,4-dithia-zolidine (144). Solutions of isoperthiocyanic acid in alkali deposit sulfur this redissolves presently giving a liquid containing144-147 the salt of an isomeric acid, later named perthiocyanic acid, for which the 3,5-dimercapto-l,2,4-thiadiazole structure is now accepted (see Section III, J, 1). This acid, isolated from its barium salt by treatment with mineral acid and ether extraction,144,145 readily reverts to isoperthiocyanic acid,144 but fairly stable specimens are obtainable under carefully controlled conditions.148 148... 

The chemistry of the isothiocyanate oxides and sulfides for which 1,2,4-thiadiazole structures have been considered at various times3 (see especially... 

The chemical reactions described in this Section are classified, as far as possible, according to the functions of the 1,2,4-thiadiazole structure, but some overlap has occurred when related results are summarized more effectively and briefly in one place. For the same reason some reactions have already been dealt with in the context of the syntheses. 

It is significant that these reactions are restricted exclusively to the 5-methyl-group in 3,5-dimethyl-1,2,4-thiadiazole, even when an excess of the appropriate reagent is employed,287 reflecting the superior reactivity of 5- compared with identical 3-substituents in the 1,2,4-thiadiazole structure.3 The point is further illustrated in the metallation of the 3,5-dimethyl compound (392, R = Me) with butyllithium after further treatment with carbon dioxide, the 5-heteroarylacetic add (396) is the sole product (62%).291... 

The reactivity of 5-halogen substituents in the 1,2,4-thiadiazole structure is well established3 nucleophilic substitution at this center has proved a convenient route to other 1,2,4-thiadiazoles, including 5-hydroxy, alkoxy, mercapto, alkylthio, amino, sulfonamido, hydrazino, hydroxylamino, and azido derivatives. All these reactions have been previously described.3... 

Thiadiazoles. Sulfonyl hydrazide resin 74 could also serve as a sulfone linker in SPS. Porco and coworkers have demonstrated the use of resin 74 for the preparation of sulfonylhydrazone resin 112, which was subsequently applied to the synthesis of 1,2,3-thiadiazoles 113 (Scheme 12.27a).Resin 74 has also been efficiently employed in the resin capture of ketones in a hybrid solution/solid-phase synthesis of 1,2,3-thiadiazoles (Scheme 12.27b). The resin-bound sulfonylhydrazones with aryl halide substituents 112a could be subjected to Stille reaction for the generation of more diverse thiadiazole structures 113a. 

Physical Properties.—The spectral properties of a series of 3-amino-4-aryl-5-aryl(or alkyl)-imino-4,5-dihydro-l,2,4-thiadiazoles are in accord with the proposed structures. The n.m.r. spectra indicate the preferred existence of the dihydro- rather than the tautomeric tetrahydro-thiadiazole structure. Mass spectral fragmentation patterns were proposed for these, and for compound (70). ... 

Cycloaddition. 4-Aryl-3-arylimino-5-imino-l,2,4-thiadiazolidines (69) ( Hector s Bases ) undergo 1,3-dipolar cycloaddition with arylcyanamides to yield 1 1 adducts, for which the condensed l,2,4-thiadiazolo-[5,l-e][l,2,4]thiadiazole structure (70) has been proposed. The alternative guanidino-thiadiazolidine... 

A series of azo-dyes (46), (47) incorporating the benzo-l,2,3-thiadiazole structure have been produced from the 5-amino-heterocycle by conventional methods, and their properties as dyes evaluated. ... 

Fig. 1-6). The structure obtained for thiazoie is surprisingly close to an average of the structures of thiophene (169) and 1,3,4-thiadiazole (170) (Fig. 1-7). From a comparison of the molecular structures of thiazoie, thiophene, thiadiazole. and pyridine (171), it appears that around C(4) the bond angles of thiazoie C(4)-H with both adjacent C(4)-N and C(4)-C(5) bonds show a difference of 5.4° that, compared to a difference in C(2)-H of pyridine of 4.2°, is interpreted by L. Nygaard (159) as resulting from an attraction of H(4) by the electron lone pair of nitrogen. 

Rg. 1-7. Molecular structures of thiophene and 1,3,4-thiadiazole bond lengths in A (left), bond angles in degrees (right). 

The precise geometrical data obtained by microwave spectroscopy allow conclusions regarding bond delocalization and hence aromaticity. For example, the microwave spectrum of thiazole has shown that the structure is very close to the average of the structures of thiophene and 1,3,4-thiadiazole, which indicates a similar trend in aromaticity. However, different methods have frequently given inconsistent results. 

Thiadiazole-2-suifonamide, 5-acetamido-carbonic anhydrase inhibitor, 6, 576 crystal structure, 6, 548... 

The structure of the isomeric benzo-l,2,3-thiadiazole 11.30 is unknown, but the 1 1 adduct with AsFs (11.31) has been structurally characterized. The AsFs molecule is coordinated to the carbon-bonded nitrogen atom. Cycloocteno-l,2,3-selenadiazole is an effective source of selenium for the production of semi-conductors such as cadmium selenide." ... 

The mechanism of the Hurd-Mori reaction has been discussed extensively in the review by Stanetty. The mechanism of the reaction was initially postulated by Hurd-Mori based on the isolation of intermediate 10. This intermediate was shown to transform into the desired thiadiazole upon heating in ethanol, either with or without acid. The reaction was thought to proceed via the four-membered intermediate 11, which would release the volatile ethylformate as a by-product. In 1995, Kobori and co-workers were able to isolate and determine crystallographically a very similar intermediate structure to 10 in their mechanistic studies of the reaction. ... 

The structure of only one 1,2,4-thiadiazole salt has been determined. Unambiguous synthesis of the imino compound obtained on alkali treatment of the salt formed by the reactions of methyl iodide with 5-amino-1,2,4-thiadiazole established that the salt possesses structure 7 136 pjjjg quatemization exactly parallels the reaction occurring in... 

A reliable calculation of polarizabilities requires an adequate description of the outer part of the electron density. For this reason Kassimi and Lin [98JPC(A)9906] used augmented basis sets of triple- quality to study polarizabilities and dipole moments of thiazoles and thiadiazoles. They expect their results to be reliable within 5%. In addition, the authors provide MP2/6-31G geometries for most of their structures. Hyperpolarizabilities for substituted thiazoles obtained from calculations at lower levels are also provided [99MI2]. 

Chemical Name 4-amino-N-(5-methyl-1,3,4-thiadiazol-2-yl)benzenesulfonamide Common Name Sulfamethylthiadiazole Structural Formula A ... 

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