Pyridine-4-sulfonic acid, sodium salt

For aliphatic amines Dissolve 0.6 g l,2-naphthoquinone-4-sulfonic acid sodium salt in 12 ml water, make up to 200 ml with ethanol (90%) and add 10 ml pyridine [8]. 

Fluoropyridiniumsulfonates 2 can be synthesized by fluorinating the corresponding pyridine-sulfonic acids or sodium or amine salts with fluorine diluted with nitrogen in acetonitrile, aqueous acetonitrile, or a polyfluoro alcohol.40,41... 

Water-insoluble amines are dissolved in a dilute acid, or when necessary in methanol, ethanol, acetone, or even pyridine. Sulfonic acids are used as their sodium salts. If there is a danger that the amine may undergo more than single coupling when this is not desired, then,... 

The sulfonate salts of the --deficient heterocycles will undergo many reactions typical of arenesulfonates, such as displacement by hydroxide, on fusion with alkali (e.g. Scheme 129), or by cyanide on fusion with potassium or sodium cyanide. Also, the sulfonation of pyridine is reversible when pyridine-3-sulfonic acid is heated with 100% sulfuric acid and mercury(II) sulfate at approximately 330 °C a mixture is obtained containing mainly pyridine (58RTC963). 

The method can also be applied to the conversion of 4-chloropyridine (49) to pyridine-4-sulfonic acid (50) (Scheme 28). In compound (49), the chlorine atom is activated to nucleophilic attack by the electron-withdrawing nitrogen atom. Scheme 28 is a useful synthetic sequence since direct sulfonation of pyridine only yields the 3-sulfonic acid as a consequence of the electrophilic nature of the nitrogen atom. Sulfonic acids can also be obtained by oxidation of sulfides, disulfides and sulfinic acids. The introduction of a sulfonic acid group into an organic molecule provides a useful method of increasing the aqueous solubility of the compound. Many sulfonic acids as their sodium salts are... 

If the double salt 158 is heated with sodium sulfite (Na2S03) in water, aromatic nucleophilic substitution 160 leads to the sodium salt of pyridine-4-sulfonic acid 162 or to the sulfonic acid itself 163 after acidification. These are nucleophilic substitutions following electrophilic attack at nitrogen. 

When 3-aminopyndine is diazotized with hydrochloric acid and sodium nitrite and then treated with acetic acid containing sulfur dioxide and cupric chloride, 3-pyridine ulfonic acid can be isolated. Similarly, 4-aminopyridine-l-oxide gives 4-pyridinesulfonic acid-1 -oxide, but the 2-isomer gives very poor yields of the corresponding sulfonic acid. The preparations and reactions of various 3-pyridinediazonium salts have been reported. 3-Amino-2,6-lutidine... 

Treatment of pyridine with fuming sulfuric acid yields pyridine-3-sulfonic acid which is converted to 3-cyanopyridine by distillation of its sodium salt with potassium cyanide . Better yields are claimed by initial bromination of pyridine in the 3-position and subsequent treatment with cuprous cyanide . The 3-cyanopyridine is then hydrolyzed to nicotinic acid. 

Another striking observation is that the formation of the 2-acid can be depressed to as little as 1% by the use of pyridine-sulfur trioxide as the sulfonating agent, even when the reaction is carried out at temperatures (150-175°) that, with oleum, favor substitution in the 2-posi-tion. Although the two sulfonic acids can be separated from each other and from polysulfonic acids fairly adily by fractional crystallization of the sodium or barium salts, the sulfbnation reaction of anthracene is not employed commonly, since the monosulfonic acids are prepared more conveniently from the corresponding derivatives of anthraquinone. 

Systematic studies on micellar size and structure have been published for poly(styrene-h-acrylic acid) (PS-PAAc) [7, 8], poly(styrene-fr-sodium acrylate) (PS-PAAcNa) [9], or quaternized poly(styrene-h-4-vinyl-pyridine) (PS-P4VPMeI) [10, 11]. It was concluded that the polyelectrolyte chains in the micellar corona are almost fully stretched [8]. The effect of salt concentration was investigated by Guenoun et al. on poly(f-butylstyrene-fr-sodium styrene sulfonate) (PtBS-PSSNa) who observed a weak decrease of micellar size and aggregation number when the salt concentration was increased beyond 0.01 mol/1 [12]. Using small-angle neutron scattering (SANS), the authors could provide additional support for the rod-like conformation of the polyelectrolyte chains in the micellar corona [13]. 

Since sulfonation of pyridine iV-oxide is about as difficult as is that of pyridine itself and takes place at the 3-position,17 it has been assumed18 that, in fuming sulfuric acid, pyridine iV-oxide reacts only in the salt form (3), when the prediction is that substitution at C-3 would take place. It is, however, difficult to account for the fact that bromination, even at 110° in the presence of iron powder, does not occur.17 Bromination in chloroform solution in the presence of acetic anhydride and sodium acetate (when the O-acetate is the the probable substrate) take place readily, however, to give 3,5-dibromopyridine JV-oxide.19 The predicted order of nucleophilic reactivity, on the basis of both atom localization energies and ground-state v-electron density calculations, is 4 > 2 > 3. The same order is predicted for the nucleophilic substitution reactions of the salts of pyridine JV-oxide. In actual practice, iV-alkoxypyridinium derivatives undergo nucleophilic attack preferentially at C-2.20-23 The reaction of some pyridine iV-oxides with phosphorus pentachloride may involve the formation... 

---