Aqueous reactions disulfides

The second application of the CFTI protocol is the evaluation of the free energy differences between four states of the linear form of the opioid peptide DPDPE in solution. Our primary result is the determination of the free energy differences between the representative stable structures j3c and Pe and the cyclic-like conformer Cyc of linear DPDPE in aqueous solution. These free energy differences, 4.0 kcal/mol between pc and Cyc, and 6.3 kcal/mol between pE and Cyc, reflect the cost of pre-organizing the linear peptide into a conformation conducive for disulfide bond formation. Such a conformational change is a pre-requisite for the chemical reaction of S-S bond formation to proceed. The predicted low population of the cyclic-like structure, which is presumably the biologically active conformer, agrees qualitatively with observed lower potency and different receptor specificity of the linear form relative to the cyclic peptide. 

General Reaction Chemistry of Sulfonic Acids. Sulfonic acids may be used to produce sulfonic acid esters, which are derived from epoxides, olefins, alkynes, aHenes, and ketenes, as shown in Figure 1 (10). Sulfonic acids may be converted to sulfonamides via reaction with an amine in the presence of phosphoms oxychloride [10025-87-3] POCl (H)- Because sulfonic acids are generally not converted directiy to sulfonamides, the reaction most likely involves a sulfonyl chloride intermediate. Phosphoms pentachlotide [10026-13-8] and phosphoms pentabromide [7789-69-7] can be used to convert sulfonic acids to the corresponding sulfonyl haUdes (12,13). The conversion may also be accompHshed by continuous electrolysis of thiols or disulfides in the presence of aqueous HCl [7647-01-0] (14) or by direct sulfonation with chlorosulfuric acid. Sulfonyl fluorides are typically prepared by direct sulfonation with fluorosulfutic acid [7789-21-17, or by reaction of the sulfonic acid or sulfonate with fluorosulfutic acid. Halogenation of sulfonic acids, which avoids production of a sulfonyl haUde, can be achieved under oxidative halogenation conditions (15). 

Sulfur combines directly with hydrogen at 150—200°C to form hydrogen sulfide. Molten sulfur reacts with hydrogen to form hydrogen polysulfides. At red heat, sulfur and carbon unite to form carbon disulfide. This is a commercially important reaction in Europe, although natural gas is used to produce carbon disulfide in the United States. In aqueous solutions of alkaU carbonates and alkaU and alkaline-earth hydroxides, sulfur reacts to form sulfides, polysulfides, thiosulfates, and sulfites. 

When the Claus reaction is carried out in aqueous solution, the chemistry is complex and involves polythionic acid intermediates (105,211). A modification of the Claus process (by Shell) uses hydrogen or a mixture of hydrogen and carbon monoxide to reduce sulfur dioxide, carbonyl sulfide, carbon disulfide, and sulfur mixtures that occur in Claus process off-gases to hydrogen sulfide over a cobalt molybdate catalyst at ca 300°C (230). 

Manufacture. An extensive technology was developed initially ia the 1930s for isolation of ammonium thiocyanate from coke-oven gases, but this technology is no longer practiced ia the United States (372). However, such thiocyanate recovery processes are used iadustrially ia Europe. Likewise, the direct sulfurization of cyanides to thiocyanates is not practiced commercially ia the United States. The principal route used ia the United States is the reaction of carbon disulfide with aqueous ammonia, which proceeds by way of ammonium dithiocarbamate [513-74-6]. Upon heatiag, the ammonium dithiocarbamate decomposes to ammonium thiocyanate and hydrogen sulfide. 

In a typical batch operation, carbon disulfide is added to four molar equivalents of 25—30 wt % aqueous ammonia in a stirred vessel, which is kept closed for the first one to two hours. The reaction is moderately exothermic and requires cooling. After two to three hours, when substantially all of the disulfide has reacted, the reaction mixture is heated to decompose dithiocarbamate and trithiocarbonate and vented to an absorption system to collect ammonia, hydrogen sulfide, and any unreacted carbon disulfide. 

One patent describes a continuous process involving an aqueous alkah metal hydroxide, carbon disulfide, and an alcohol (82). The reported reaction time is 0.5—10 min before the mixture is fed to the dryer. The usual residence time is on the order of hours. A study ia the former USSR reported the use of the water—alcohol azeotrope for water removal from isobutyl or isoamyl alcohol and the appropriate alkah hydroxide to form the alkoxide prior to the addition of carbon disulfide (83). 

For example, dithioben2oic acid [121 -68-6] results from the reaction of carbon disulfide, phenyl bromide, ether, and magnesium. Sodium a2idodithiocarbonate [38093-88-8] is prepared by the reaction of aqueous sodium a2ide [26628-22-8] at 40—50°C ... 

Sulfur Compounds. Ethylene thiourea [96-45-7] a suspected human carcinogen, is prepared by reaction of carbon disulfide [75-15-0] CS[) in aqueous EDA (47). 

Section 15.13 Thiols are compounds of the type RSH. They are more acidic than alcohols and are readily deprotonated by reaction with aqueous base. Thiols can be oxidized to sulfenic acids (RSOH), sulfinic acids (RSO2H), and sulfonic acids (RSO3H). The redox relationship between thiols and disulfides is important in certain biochemical processes. 

Thiohydantoin 9 was obtained from the treatment of carbonyl 1 with carbon disulfide and ammonium cyanide in aqueous methanol. The transformation could also be carried out step-wise, that is, treatment of 1 with ammonium cyanide to form aminonitrile 10 followed by reaction with carbon disulfide to produce thiohydantoin 9. Alternatively, 5,5-disubstituted 4-thiohydantoins could be prepared by the reaction of ketones with ammonium monothiocarbamate and sodium cyanide. ... 

The disulfide is dissolved by aqueous potassium hydroxide, yielding a greenish-yellow solution. At low temperatures no perceptible evolution of gas takes place. Since the disulfide in many respects behaves as a pseudo-halogen, Brown et al. have supposed that the reaction described by Eq. (8) takes place, i.e. a reaction analogous to the formation of halide and halite ions from a halogen and alkali. 

The solid disulfide reacts explosively with chlorine or bromine. At low temperatures in certain non-aqueous solvents, e.g. chloroform, CISCSN3 and BrSCSN3 are probably formed, but the extreme instability of these compounds has precluded their exact analysis and description. However, the reaction between cyanogen bromide and the potassium salt of the thiol yields the well-defined cyanide NCSCSN3,... 

Carbethoxycyclohexanone, 46, 82 2-Carbethoxycyclononanone, 47, 22 2-Carbethoxycyclooctanone, 47, 20 2-Carbomethoxycyclopentanone, conversion to 2-benzyl-2-carbometh-oxycyclopentanone, 45, 8 Carbon disulfide, reaction with /i-chloro-aniline and aqueous ammonia,... 

Chloroacetic acid, reaction with salicyl-aldehyde, 46, 28 Chloroacetone, 46, 3 Chloroacetyl fluoride, 45, 6 o-Chloroacetyl isocyanate, 46,16 -Chloroaniline, reaction with carbon disulfide and aqueous ammonia,... 

The reaction of 3-hydrazinophenanthro[9,10-e][l,2,4]triazine 742 with carbon disulfide, thiourea, phenyl isothiocyanate, urea, and phenyl isocyanate led [77ZN(B)569] to the formation of phenanthro[9,10-e][l,2,4]-triazolo[4,3-/j][l,2,4]triazines 743. Alkylation of 743 in aqueous alkaline... 

In contrast with irradiation of ACSO and PCSO, where volatile products were formed (sulfides, disulfides and alcohols), no volatile products were formed in the radiolysis of aqueous solutions of S-(cis- l-propenyl)-L-cysteine. Here the authors found that reactions of OH" radicals are responsible for the formation of propyl-1-propenyl sulfides (cis and trans). 

Thiophenols may also be synthesized via the photochemical decomposition route 156). Thus, treatment of arylthallium ditrifluoroacetates with an aqueous solution of potassium Ar,AT-dimethyldithiocarbamate led in quantitative yields to the formation of the corresponding aryl AT,A -dimethyl-dithiocarbamates. Subsequent photolysis in aqueous acetone then led to disulfides which were reduced to the thiophenols. A small amount of aryldithiocarbamate formed as a by-product in the photolysis was converted to the same thiophenol by hydrolysis. The overall reaction sequence is illustrated in Eq. (18). 

Sodium hydrogen telluride, (NaTeH), prepared in situ from the reaction of tellurium powder with an aqueous ethanol solution of sodium borohydride, is an effective reducing reagent for many functionalities, such as azide, sulfoxide, disulfide, activated C=C bonds, nitroxide, and so forth. Water is a convenient solvent for these transformations.28 A variety of functional groups including aldehydes, ketones, olefins, nitroxides, and azides are also reduced by sodium hypophosphite buffer solution.29... 

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