Sulfur preparations

Activity is also retained when oxygen at the 21 position is replaced by sulfur. Preparation of one of these compounds follows a route quite analogous to the foregoing thus, displacement of the mesylate group in the cortisone (56) derivative 57 with the anion from thiopivalic acid affords thioester 58. Reduction of the 11-ketone by means of borohydride affords tixocortol pivalate (59)[13j. 

While these agents may cause less skin irritation than benzoyl peroxide or the topical retinoids, several disadvantages exist. Sulfur preparations produce an unpleasant odor when applied to the skin, while resorcinol may cause brown scaling. And although rare, the possibility of salicylism exists with continual salicylic acid use.3,12... 

Thermodynamically stable sulfur forms deep yellow, nonodorous orthorhombic crystals with a space group Fddd-D, containing 16 molecules, i.e., 128 atoms in the unit cell. It has a density of 2.069 gm/cm and is well soluble in CS2. Its molecular unit is Sg, cyclooctasulfur, a crown-shaped molecule with a symmetry of i>4d. The pale flowers of sulfur, prepared by alchemist by distillation, are insoluble in CS2, and the structure is not yet fully understood. Another form, plastic sulfur, is obtained by melting sulfur to about 180°C, where it forms as highly... 

Quenched sulfur vapor has been studied for a long time. Slowly quenched to room temperature it yields flowers of sulfur, which were prepared by alchemists. The flowers can be separated into several phases by elution with CSg. Thermal alnalysis 19) shows that a-sulfur, j3-sulfur, and oD-sulfur are present. The latter melts at 104°C. The X-ray structure of a -sulfur, prepared in this way, and that of Crystex 104), a widely used insoluble form of sulfur, ateo called supersublimation sulfur, are not... 

Tellurium tetrachloride reacted with bis[3-lithio-2,5-dichlorothien-4-yl]sulfur, prepared from 3,4-dibromo-2,5-dichlorothiophene, to give bis[2,5-dichlorolfiieno][3,4-b 4, 3 -e]-l,4-thiatellurin. ... 

Use Wet-grinding of pigments and sulfur preparation of ceramic glazes, oil-well drilling muds, insecticidal mixtures, carbon black in rubber, and water-insoluble dyes. 

S the thermal behavior of depends on its preparation since is a mixture of long chains and large rings and not a well defined chemical substance. This mixture is thermodynamically unstable with respect to a-Ss at 20 °C and in fact depolymerizes slowly at moderate temperatures already. DSC measurements of polymeric sulfur prepared from quenched melts as well as from sublimed sulfur show the polymer to melt at 100 °C followed immediately by the exothermic depolymerization. Stabilized commercial polymeric sulfur (Crystex) starts to melt only at 110 °C but otherwise behaves similarly (heating rate 10 K min ) [55]. 

S/. Polymeric sulfur prepared from liquid sulfur ... 

Dinocap is effective only against powdery mildew fungi. In contrast to the sulfur preparations, it exerts a fungicidal action at low temperatures (5-10°C), making possible the prevention of fungi growth even in early spring (Perrot et al., 1958). It... 

Its purpose is to partially convert heavy fractions highly contaminated by natural compounds such as sulfur, nitrogen, metals Ni, V, and asphaltenes and to prepare feedstocks for deeper conversion or to produce low-sulfur fuel-oil. 

To be able to prepare and study these elusive species in stable form, acids billions of times stronger than concentrated sulfuric acid were needed (so called superacids). Some substituted carbocations, however, are remarkably stable and are even present in nature. You may be surprised to learn that the fine red wine we drank tonight contained carbocations which are responsible for the red color of this natural 12% or so alcoholic solution. I hope you enjoyed it as much as I did. 

Note 2. Sulfur dichloride was prepared by introducing the calculated amount of... 

Halide derivatives may be fluorides, chlorides, or bromides. Fluorides are best prepared by the reaction of hydroxy groups with (diethylamino)sulfur trilluoride ( DAST M. Sharma, 1977) or of glycosyl thioethers with DAST/NBS (K.C. Nicolaou, 1990 B). The other halides are usually only introduced at the glycosidic position, where treatment with hydrogen chloride... 

Similar halogenations have been done on 2-lithio-l-phenylsulfonylindole[2], 2-Lithio-l-phenylsulfonylindole is readily converted to the 2-(trimethylsilyl) derivative[2,3]. 2-Trialkylstannylindoles can also be prepared via 2-lithio-indoles[4,5], 2-Sulfonamido groups can be introduced by reaction of a 2-lithioindole with sulfur dioxide, followed by conversion of the sulfinic acid group to the sulfonyl chloride with A-chlorosuccinimide[6]. 

The preparation of a series of transition metal complexes (Co. Ni. Pd. Pt, Ir. Au. Cu. Ag) with ambident anion (70) and phosphines as ligands has been reported recently (885). According to the infrared and NMR spectra the thiazoline-2-thione anion is bounded through the exocyclic sulfur atom to the metal. The copper and silver complexes have been found to be dimeric. 

Since the exocyclic sulfur is more reactive in the ambident anion than in A-4-thiazoIine-2-thione. greater nucleophilic reactivity is to be expected. Thus a large variety of thioethers were prepared in good yields starting from alkylhalides (e.g.. Scheme 38 (54, 91, 111, 166-179). lactones (54, 160), aryl halides (54, 152. 180, 181), acyl chlorides (54. 149, 182-184). halothiazoles (54, 185-190), a-haloesters (149. 152. 177. 191-194), cyanuric chloride (151). fV.N-dimethylthiocarbamoyl chloride (151, 152. 195. 196), /3-chloroethyl ester of acrylic acid (197), (3-dimethylaminoethyl chloride (152). l,4-dichloro-2-butyne (152), 1,4-dichloro-2-butene (152), and 2-chloro-propionitrile (152). A general... 

The hydrolysis of 2-benzamidoselenazoles in aqueous phosphoric or sulfuric acid gives 2-aminoselenazOles identical to those prepared from selenourea (Scheme 12). 

The nitration of the 2-anilino-4-phenylselenazole (103) is much more complicated. Even careful nitration using the nitrate-sulfuric acid method leads to the formation of a mixture of variously nitrated compounds in an almost violent reaction. By the use of column chromatography as well as thin-layer chromatography a separation could be made, and the compounds could be partly identified by an independent synthesis. Scheme 33 shows a general view of the substances prepared. Ring fission was not obser ed under mild conditions. 

The first compounds with a Aj selenazoline structure were mentioned in the literature in 1892 by Michels (55). He prepared 2-methyl-A -selenazoline in the course of his investigations into sulfur and selenium... 

The reaction is carried out at low temperature in aqueous medium and then allowed to stand overnight (221). Ammonium thiocarbamate is prepared from a cold saturated solution of ammonium thiocyanate, which is gradually added to dilute sulfuric acid at 25°C. The liberated carbonyl sulfide is passed into a saturated solution of alcoholic ammonia at about 10°C (221). The fairly low yield indicates that the reaction has not been greatly developed. 

This reaction was first described by Gabriel in 1910 (40), when he warmed an acylaminoketone (197a) with an equimolecular amount of phosphorus pentasulfide. The reaction (Scheme 103) is similar to the preparation of other five-membered oxygen- and sulfur-containing rings from 1,4-dicarbonyl compounds. 

Arylthiazoles were prepared either from w-formaminoaceto-phenones and phosphorus pentasulfide in 70% yield (47, 641) or by treating thioformaminoketones with concentrated sulfuric acid in water (344). Thioformaminoacetophenone itself was obtained by the action of potassium dithioformate on aminoacetophenone (251). 

Aminothiazole derivatives (243) can be prepared by treatment of enamines of type 240 with sulfur and cyanamide at room temperature in ethanol (701) yields range from 30 to 70%, and no catalyst is required. Initial formation of the thiolated intermediate (241) is probably followed by addition of cyanamide, yielding 242 (Scheme 124). 

Methyl and 2,4-dimethylthiazole were prepared by the vapor-phase reaction (450 to 500°C) of sulfur with diethylamine and diisopropylamine, respectively (816) yields were 66 and 59%. 

Asinger et a], have developed a simple preparative method for variously substituted A3-thiazolines by the action of sulfur and ammonia on ketones. 

The overall reactivity of the 4- and 5-positions compared to benzene has been determined by competitive methods, and the results agreed with kinetic constants established by nitration of the same thiazoles in sulfuric acid at very low concentrations (242). In fact, nitration of alkylthiazoles in a mixture of nitric and sulfuric acid at 100°C for 4 hr gives nitro compounds in preparative yield, though some alkylthiazoles are oxidized. Results of competitive nitrations are summarized in Table III-43 (241, 243). For 2-alkylthiazoles, reactivities were too low to be measured accurately. 

Trichlorothiazole, which behaves as an insecticide, can be prepared by the reaction at 150 to 200°C of sulfur with either 1.2.2.2-tetrachlorethylisocyanide dichloride (103), JV-(l,2,2,2-tetrachlor-ethyl)formimidine (104), or by the reaction of sulfur chlorides at... 

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