3, 5-dimercapto

Fusion of 4-hydroxyquinazoIine with phosphorus pentasulfide yields 4-mercaptoquinazoline and, similarly, substituted 2,4-dimercapto-quinazolines have been obtained from the corresponding dihydroxy compounds. The greater reactivity of the 4-mercapto as compared with the 2-mercapto group has permitted the preparation of 4-amino-2-mercaptoquinazolines (see 7a). 

Interestingly, the action of cold concentrated hydrochloric add on 2,4-dimercapto- l-butano) (L) and 1,4-dimercapto-2-butanol (U) does not give the chlnro dithiol as does 2>3-dimerc ptopropanol. Instead, the product is 3-mercaptothiophano (Lll), which may be formed via the eyolio sulfonium ion (LIII) (Eq. 30). 

Dimercapto-l,3,4-thiadiazole and its derivatives can be used to crosslink a wide variety of halogen-containing polymers. SuccessM use of the thiadiazole in a given polymer is seen to depend on the particular derivative and any associated accelerator. A review is presented of the various thiadiazoles for crosslinking halogen-containing polymers. 3 refs. 

Thiols have a marked ten dency to bond to mercury and the word mercaptan comes from the Latin mer curium captans which means seizing mercury The drug dimercaprol is used to treat mercury and lead poisoning It IS 2 3 dimercapto 1 propanol... 

Other Accelerators. Amine isophthalate and thiazolidine thione, which are used as alternatives to thioureas for cross-linking polychloroprene (Neoprene) and other chlorine-containing polymers, are also used as accelerators. A few free amines are used as accelerators of sulfur vulcanization these have high molecular weight to minimize volatility and workplace exposure. Several amines and amine salts are used to speed up the dimercapto thiadiazole cure of chlorinated polyethylene and polyacrylates. Phosphonium salts are used as accelerators for the bisphenol cure of fluorocarbon mbbers. 

Dimercapto-l,3,4-thiadiazole derivatives, accelerated by amines, are used to cross-link chlorinated polyethylene. Polyisobutylene containing brominated i ra-methylstyrene cure functionahty can be cross-linked in polymer blends with dimercapto-1,3,4-thiadiazole derivatives accelerated with thiuram disulfides. Trithiocyanuric acid is suggested for use in polyacrylates containing a chlorine cure site and in epichlorohydrin mbbers. 

Chemical Properties. The most significant chemical property of L-ascorbic acid is its reversible oxidation to dehydro-L-ascorbic acid. Dehydro-L-ascorbic acid has been prepared by uv irradiation and by oxidation with air and charcoal, halogens, ferric chloride, hydrogen peroxide, 2,6-dichlorophenolindophenol, neutral potassium permanganate, selenium oxide, and many other compounds. Dehydro-L-ascorbic acid has been reduced to L-ascorbic acid by hydrogen iodide, hydrogen sulfide, 1,4-dithiothreitol (l,4-dimercapto-2,3-butanediol), and the like (33). 

The reaction of toluene-3,4-dithiol(3,4-dimercaptotoluene) and antimony trichloride ia acetone yields a yeUow soHd Sb2(tdt)2, where tdt is the toluene-3,4-dithiolate anionic ligand (51). With the disodium salt of maleonitnledithiol ((Z)-dimercapto-2-butenedinitrile), antimony trichloride gives the complex ion [Sb(mnt)2] , where mat is the maleonitnledithiolate anionic ligand. This complex has been isolated as a yeUow, crystalline, tetraethyl ammonium salt. The stmctures of these antimony dithiolate complexes have apparendy not been unambiguously determiaed. 

Curing Systems. The most commonly used vulcanizing agent for the polyethers not containing AGE, that is, ECH and ECH—EO, is 2-mercaptoimidazoline, also called ethylenethiourea [96-45-7]. Other commercially appHed curing agents include derivatives of 2,5-dimercapto-l,3,4-thiadiazole, trithiocyanuric acid and derivatives, bisphenols, diamines, and other substituted thioureas. 

Bismuthiol I (2,5-dimercapto-l,3,4-thiadiazole) potassium salt [4628-94-8] M 226.4, m 275-276 (dec), pKes,(I) 4.1. Usually contaminated with disulfide. Purified by crystn from EtOH. Reagent for detection of Bi,Cu, Pb and Sb. 

Although the first all-sulfur macrocycles were prepared many years ago " the first systematic study of such compounds was initiated by Busch and his coworkers , who were interested in the cation binding properties of such ligands. A sequential synthesis was utilized to produce 1,4,8,11-tetrathiacyclotetradecane [tetrathia-14-crown-4 (70)] . In the first step, 1,3-propanedithiol is metallated using sodium and alkylated with 2-chloroethanol. The diol was then treated with thiourea to form the dimercapto-dithioether compound 9. The latter was once again metallated with sodium and allowed to react with 1,3-dibromopropane. The yield of 70 in the ring closure step, conducted at high dilution in absolute ethanol, was 7.5% after recrystallization. The entire sequence is illustrated in Eq. (6.8) . ... 

The tautoraerism of certain difunctional derivatives of l-thia-3,4-diazole has received considerable attention. Pala assigned structure 156 to 2,5-dimercapto-l-thia-3,4-diazole on the basis of infrared spectral data, and Thorn" reached the same conclusion by comparing its ultraviolet spectrum (measured in ethanol) with those of the four possible methylated derivatives. However, the infrared spectrum of a chloroform solution of the parent compound showed bands at 2600-2550 cm indicating an SH group and the probable occurrence of form 157 under these conditions, and this conclusion is supported by the occurrence of SH bands in solid state spectra obtained by Swiss investigators. For a summary of earlier work on these compounds, see reference 187. 

G. Reactions and Tautomerism of Quinoxaline-2-thione and Quinoxaline-2,3-dithione (2-Meecapto- and 2,3-Dimercapto-quinoxaline)... 

Chemical Name 2,3-dimercapto-1-propanol Common Name 1,2-dithioglycerol... 

BAL—see Propan-l-ol, 2,3-dimercapto-Bacillus cereus calcium transport, 6,572 Bacillus megaterium calcium efflux, 6, 570 calcium transport, 6,572 sporulation zinc transport, 6, 572 Bacillus spp. sodium ions, 6, 559 sporulation... 

Propane-1,2-diol, 3-mercapto-metal complexes, 2,804 Propan-l-ol, 2-amino-2-methyl-copper(II) complexes, 2,795 Propan-l-ol, 2,3-dimercapto-chelating agent heavy metal poisoning, 6,767 Propan-l-ol, 3-(methylamino)-copper(II) complexes, 2,795 Propan-2-ol... 

Tungsten, tris(2,3-dimercapto-2-butenedinitrile)-structure, 1,63 Tungsten alkoxides physical properties, 2,346 synthesis, 2,339... 

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