Sulfates reactions catalyzed

Colonna, S., Gaggero, N., Carrea, G. and Pasta, P., Oxidation of organic cyclic sulfites to sulfates a new reaction catalyzed by cyclohexanone monooxygenase. Chem. Commun., 1998, 415. 

Sunamoto et al. 94) have studied the reaction of (14) with 2,4-dinitro-phenyl sulfate in aqueous organic solvent with 0.1 A sodiiun hydroxide. The rate of esterolysis by (14) was greater than the rate of the reaction catalyzed by -cyclodextrin. Better binding by the paracyclophane cavity and the greater nucleophilicity of the oxime group as compared to the secondary hydroxyl group of jS-cycdextrin were cited to explain the difference in catalytic efficiency. 

Reactions other than those of the nucleophilic reactivity of alkyl sulfates involve reactions with hydrocarbons, thermal degradation, sulfonation, halogenation of the alkyl groups, and reduction of the sulfate groups. Aromatic hydrocarbons, eg, benzene and naphthalene, react with alkyl sulfates when catalyzed by aluminum chloride to give Friedel-Crafts-type alkylation product mixtures (59). Isobutane is readily alkylated by a dipropyl sulfate mixture from the reaction of propylene in propane with sulfuric acid (60). 

Comparison of the various mechanistic facets of the above sulfate reactions to those of the acid-catalyzed hydrolysis of the Bunte salts (RSS03 ) suggests that the mechanisms are identical, i.e. A-1163... 

Tetrahydropyranylation The reaction of an alcohol (even tertiary) with dihydropyran is catalyzed efficiently by [(CH3)3Si0]2S02. The resulting ether is isolated in 90-100% yield by addition of pyridine and concentration of the solvent. The sulfate also catalyzes alcoholysis of the derivative at 25° (10-90 minutes). It is also useful in some transesterifications. 

The rate of the reaction (86-90) is about two orders of magnitude slower than the O2/C reaction, consistent with the greater strength of the NO bond than that in O2. The CO/CO2 ratio in the products of the reaction increases with increasing temperature (86, 87). At low temperatures (850 K), a stable chemisorbed oxygen compled (86) forms and inhibits the reaction. At AFBC temperatures, however, it has been observed that the reaction is accelerated in the presence of oxygen (91). This latter result may be a consequence of the increase in the CO concentration within a char particle as the 0 concentration is raised. Because the O2/C reaction is so much faster than the NO/C or the carbon catalyzed CO/NO reaction (86, 91), the situation exists in which the effectiveness factor for the O2/C reaction is small and little O2 penetration into char occurs at a time when the effectiveness factor for the NO reduction reactions are near unity. Additional NO reduction reactions that may occur are the CO/NO reaction catalyzed by bed solids (90 - 92) and the reduction of NO by sulfite-containing, partially sulfated limestone (93). 

Vascular fragility may also result from reduced sulfation of proteoglycans in connective tissue, as may also occur in hyperhomocysteinemia (Section 10.3.4.2). Dehydroascorbate catalyzes the oxidation of homocysteine to ho-mocysteic acid, which is the precursor of PAPS, the sulfate donor for sulfation reactions (McCuUy, 1971). 

Dehydroascorbate catalyzes the oxidation of homocysteine to ho-mocysteic acid, which is the precursor of PAPS, the sulfate donor for sulfation reactions (McCully, 1971). 

Although polyethyleneimine possesses moderate catalytic effects on several hydrolysis reactions, the polymer modified with long allQrl chains show mudi enhanced reactivity toward hydrophobic substrates. Remaikable catalytic effects were observed in the hydrolysis of phenyl esters and a sulfate ester catalyzed by the methylene-imidazole-modified polymer. These results were explained as arising from the hi y brandied, compact stmcture of the polyediyleneimine derivative. Klotz called the imidazole-containing polyethyleneimine synzyme (synthetic enzyme), on the basis of its stmctural characteristics and catalytic activity which are comparable to hydrolytic enzymes. 

Scheme 37. Sequential One-pot Selenenylation-Deselenenylation Reactions Catalyzed by Phe-nylselenyl Sulfate...

Homocysteine is metabolized in the liver, kidney, small intestine and pancreas also by the transsulfuration pathway [1,3,89]. It is condensed with serine to form cystathione in an irreversible reaction catalyzed by a vitamin B6-dependent enzyme, cystathionine-synthase. Cystathione is hydrolyzed to cysteine that can be incorporated into glutathione or further metabolized to sulfate and taurine [1,3,89]. The transsulfuration pathway enzymes are pyridoxal-5-phosphate dependent [3,91]. This co-enzyme is the active form of pyridoxine. So, either folates, cobalamin, and pyridoxine are essential to keep normal homocysteine metabolism. The former two are coenzymes for the methylation pathway, the last one is coenzyme for the transsulfuration pathway [ 1,3,89,91 ]. 

The rates of reactions with different precatalysts also pointed to Cu(I) species. The initial rate of the reaction initiated with Cul was larger than that of the reaction catalyzed by cupric sulfate. However, a steady state of reactions catalyzed by CuCl was rapidly established (<3 min), and at this steady state, the rate was almost the same as that when cupric sulfate was used. The identity of the steady-state rates was probably observed because cuprous chloride was converted to cupric species, and the reaction took the same course as when the cupric salt was added. 

Introduction. Sulfation reactions consist of a sulfate being transferred from the cofactor 3 -phosphoadenosine 5 -phosphosulfate (19) (PAPS Fig. 13.17)to the substrate under catalysis by a sulfotransferase. The three criteria of conjugation are met in these reactions. Sulfotransferases, which catalyze a variety of physiological reactions, are soluble enzymes that include aryl sulfotransferase (phenol sulfotransferase EC 2.8.2.1), alcohol sulfotransferase (hydroxysteroid sulfotransferase EC... 

In view of the probable course of the addition reaction, it is not surprising that, besides mineral acids, acetic acid, trifluoroacetic acid, and acidic resins should catalyze the addition, or that efforts to detect carbohydrate sulfates amongst the products of the reaction catalyzed by sulfuric acid should have been unsuccessful. ... 

The sulfotransferase (SULT) enzymes belong to a superfamily of enzymes that catalyze sulfation reactions. The sulfation reaction involves high-energy inputs from the cell because two molecules of ATP are necessary for the synthesis of one molecule of 3 -phosphoadenosine 5 -phosphosulfate (PAPS). The amino acids cysteine and methionine are the major sources of sulfate required for PAPS synthesis, Cellular concentrations of PAPS arc considerably less than those of UDPGA and glutathione, limiting the capacity for sulfation. 

---