Pyridinium sulfate

Pyridinium sulfate, bis-l,2,4,6-tetramethyl-hydrogen isotope exchange reactions, 2, 194 Pyridinium-1 -sulfonates reactions, 2, 34... 

Copolymerization of AN with the quartemary salt of 1,2-dimethyl-5-vinyl-pyridinium sulfate to proceed in accordance with the following scheme ... 

Various alkylamino-artemisinins 155 were synthesized by the nucleophilic displacement of bromoartemisin 149, which was prepared in situ from 148 (Scheme 19), followed by reaction with alkylamines <2004AGE1381>. A more direct route involved treatment of 29a firstly with a mixture of NaBr and TMSCl and then with the amine <2006AGE2082>. HFIP can be used as an additive in the amination step to increase the yield <2005AGE2060>. Similar aminoartemisinins 155 (where NRR = NHAr) were prepared by reacting 29a with anilines, in the presence of a catalytic amount of pyridinium sulfate in pyridine, in good yields (e.g., Ar = Ph, 93% 72% ... 

Pyridine is a typical 3° amine, (a) C,H,N—BMcj (ft) (CsHjNHjjSO ", pyridinium sulfate (c) [CjHjN —Et]I", N-ethylpyridinium iodide (d) C,H5NH Br"-I-MejC=CHMe (the 3° halide undergoes elimination rather than 5 2 displacement) ... 

Coke Manufacture By-products. In United States practice, coking of coal is done almost exclusively by the high-temperature (900-1200c C) process, For many years, the major source of the pyridines was the chemical-recovery coke oven, The volatiles produced in the coke oven are only partially condensed. The noncondensed gases are passed through a scrubber (the ammonia saturator) containing sulfuric acid. After removal of crystals (ammonium sulfate), a solution of ammonium sulfate and pyridinium sulfates is obtained and treated with ammonia to liberate and contained pyridine bases (— 70% is pyndine itself), See also Coal Tar and Derivatives. The balance of the pyndine bases is extracted from the crude coal tar. i.e., the condensed, main portion of the volatilization products from coking. The crude tar contains approximately 0,1 -0.2% pyridine bases, Further separation of the pyridines involves a rather complex series of extractions, distillations, and crystallizations. 

Pyridine-sulfur trioxide adduct 173 Pyridine (1 mole) is added, with stirring and good cooling, to sulfur trioxide (1 mole) in three parts of carbon tetrachloride. The adduct produced is filtered off, washed with a little ice-water (to remove small amounts of pyridinium sulfate), and dried. The yield is about 90%. 

Here cholesterol forms the hydrophobic tail of the surfactant and is attached via a spacer to a hydrophilic pyridinium sulfate ester head. The effect of molecular imprinting in these particles was elegantly demonstrated by an immunoprecipita-tion experiment, in which a,co-cholesterol-functionalized poly(ethylene oxide) was mixed with a suspension of the imprinted particles which led to bridging flocculation and precipitation. 

Fulvene-type enamines, which possess some nonbenzenoid aromatic character, have been synthesized by treating cyclopentadienylsodium with an amide-dimethyl sulfate eomplex (117aJ17b) or quaternary pyridinium salts (117c). One of the simplest ones produced is 6-(dimethylamino)fulvene (117a,117d). 

The nitration of l,2,5-selenadiazolo[3,4-/] quinoline 77 with benzoyl nitrate affords the 8-nitro derivative 78, whereas methylation with methyl iodide or methyl sulfate afforded the corresponding 6-pyridinium methiodide 79 or methosulfate 80, respectively (Scheme 29). The pyridinium salt 80 was submitted to oxidation with potassium hexacyanoferrate and provided 7-oxo-6,7-dihydro derivative 81 or, by reaction of pyridinium salt 79 with phenylmagnesium bromide, the 7-phenyl-6,7-dihydro derivative 82. Nucleophilic substitution of the methiodide 79 with potassium cyanide resulted in the formation of 9-cyano-6,9-dihydroderivative 83, which can be oxidized by iodine to 9-cyano-l,2,5-selenadiazolo [3,4-/]quinoline methiodide 84. All the reactions proceeded in moderate yields (81IJC648). 

C5H5NHBr pyridinium bromide [(CH3)3NH]2S04 trimethylammonium sulfate... 

Most studies of micellar systems have been carried out on synthetic surfactants where the polar or ionic head group may be cationic, e.g. an ammonium or pyridinium ion, anionic, e.g. a carboxylate, sulfate or sulfonate ion, non-ionic, e.g. hydroxy-compound, or zwitterionic, e.g. an amine oxide or a carboxylate or sulfonate betaine. Surfactants are often given trivial or trade names, and abbreviations based on either trivial or systematic names are freely used (Fendler and Fendler, 1975). Many commercial surfactants are mixtures so that purity can be a major problem. In addition, some surfactants, e.g. monoalkyl sulfates, decompose slowly in aqueous solution. Some examples of surfactants are given in Table 1, together with values of the critical micelle concentration, cmc. This is the surfactant concentration at the onset of micellization (Mukerjee and Mysels, 1970) and can therefore be taken to be the maximum concentration of monomeric surfactant in a solution (Menger and Portnoy, 1967). Its value is related to the change of free energy on micellization (Fendler and Fendler, 1975 Lindman and Wennerstrom, 1980). 

Similarly, pyridine can be 3-sulfonated with hot sulfuric acid, or oleum, if mercuric [mercury(II)] sulfate is present as a catalyst (Scheme 2.5). The process is not straightforward and may involve a C-mecuriated pyridine intermediate [it is known, for example, that pyridine reacts with mercuric acetate at room temperature to form a pyridinium salt that decomposes at 180 °C into 3-(acetoxymercuri)pyridine (X = OAc)]. Without the catalyst, long reaction times and a temperature of 350 C are necessary even then, the yield of pyridine-3-sulfonic acid is poor. 

The first studies on the sulfation of organic compounds, amino acids, and proteins have shown that pyridine/sulfur trioxide complex (pyridine/S03 or pyridine/Cl S03H),168-721 concentrated sulfuric acid,173,74 sulfuric acid//V,A -dicyclohexylcarbodiimide,175,761 and chloro-sulfonic acid177 are the most efficient reagents for the sulfation of tyrosine. More recently, alternative methods based on dimethylformamide/sulfur trioxide complex (DMF/S03),152,781 trimethylamine/sulfur trioxide (Me3N/S03),1152,1531 pyridinium acetylsulfate,137,791 and pyr-idinium trifluoroacetylsulfate1801 have been proposed to minimize side reactions which are difficult to control for the chemical sulfation of tyrosine peptides. 

The main drawback of the pyridinium acetylsulfate reagent arises from its reduced reactivity that is well documented by the rates of sulfation of tyrosine and serine derivatives in comparison to pyridine/S03, as shown in Figure 7/55 ... 

Sulfation of peptide (0.05mmol) in DMF/pyridine (4 1, lmL) with pyridine/S03 complex (5equiv) or pyridinium acetylsulfate (lOequiv) at 25 °C. 

Sulfation of tyrosine peptides with pyridinium acetylsulfate has been mainly carried out in DMF/pyridine mixtures at room temperature (Scheme 8), where various excess reagents and reaction times are required for quantitative sulfation depending on the peptide and reaction conditions. 

Chemical sulfation of unprotected gastrin with pyridine/S03 in aqueous media can lead to serious side reactions and correspondingly to very low yields. 89 In order to solubilize gastrin in DMF/pyridine for sulfation with pyridinium acetylsulfate and tri-fluoroacetylsulfate the protected derivative shown in Scheme 9 was used. 80 ... 

Scheme 9 Sulfation of Gastrin Protected at the Side-Chain Carboxy Groups as /ert-Butyl Esters by Treatment with Pyridinium Trifluoroacetylsulfate/Dimethylformamide[8°l...

Scheme 11 Protection Strategy for Postsynthetic Sulfation of CCK-33 with Pyridinium Acetylsulfate in TFA1561...

The reaction of methyl a-D-mannopyranoside with sulfuryl chloride gave methyl 6-chloro-6-deoxy-a-D-mannopyranoside 2,3,4-tri(chloro-sulfate) even treatment of the product with pyridinium chloride for 12 hours at 50° did not effect further substitution.25 In this case, the lack of displacement of the chlorosulfonyloxy group at C-4 is attributed to the presence of an axial group at C-2. In the (hypothetical) transition state 13 (viewed along the C-4-C-3 bond), there would be... 

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