Pyridine sulphonic acids

Little work has been done on the pyridine-sulphonic acids. Alkyl halides do not react with pyridine-2-sulphonic acid or its amide, and with its silver salt give the iV-alkyl betaines which are incapable of forming salts s. With methyl iodide, potassium pyridine-3-sulphonate may have given the methyl ester methiodide, although working up produced the iV-methyl-... 

Examples are known of the conversion of pyridine-sulphonic acids into chloropyridines by reaction with phosphorus pentachloride40 8 7 hut they are of no importance. l-Methyl-2-pyridthione is converted by phosgene into... 

The sulphonic acids are usually prepared by the action of sulphuric acid upon a compound. The concentration of the acid and the temperature of reaction are varied according to the reactivity of the compound. Often oleum is used or even chiorosulphonic acid. Alternatively sulphur trioxide complexed to pyridine or dioxan can be used with reactive substrates. Aminosulphonic acids such as sulphanilic and naphthionic acids are most conveniently prepared by heating the sulphate of the amine at ISO C. 

The presence of certain substituents e.g., the amino group) may markedly affect the solubibty and other properties of the sulphonic acid or carboxylic acid. Thus such sulphonic acids as the aminobenzenesul-phonic acids, pyridine- and quinoline-sulphonic acids exist in the form of inner salts or zwitter-ions that result from the interaction of the basic amino group and the acidic sulphonic acid. Sulphanilic acid, for example, is more accurately represented by formula (I) than by formula (II) ... 

The value of the second-order rate constant for nitration of benzene-sulphonic acid in anhydrous sulphuric acid varies with the concentration of the aromatic substrate and with that of additives such as nitromethane and sulphuryl chloride. The effect seems to depend on the total concentration of non-electrolyte, moderate values of which (up to about 0-5 mol 1 ) depress the rate constant. More substantial concentrations of non-electrolytes can cause marked rate enhancements in this medium. Added hydrogen sulphate salts or bases such as pyridine... 

Unsymmetrical thiosulphinates and thiosulphonates are both oxidized by potassium superoxide in pyridine in the presence of 18-crown-6 ether to produce sulphinic and sulphonic acids and a disulphide, under mild conditions (equation 84)200,201. Sulphinic and sulphonic acids were produced from both the R and R substituents whilst the disulphide was derived only from the sulphenyl side of the reactant. Thus, the reaction mixture contained five products, making the reaction not synthetically useful. Pyrolysis of thiosulphinates also produces mixtures of products, one being the thiosulphonate again this is not a synthetically useful reaction202. 

Polymeric adsorbents have also been found to be very useful, and even highly water-loving undesired materials like p-toluene sulphonic acid from waste streams can be recovered via ad.sorption and regeneration with solvents like fv -propanol. In such instances, the regeneration of activated carbons is not satisfactory, even with aqueous sodium hydroxide. Solutes like phenols, substituted phenols, aromatic amines, heterocyclic amines (pyridine, picolines, etc.) can be recovered, in a rewarding way, from aqueous solutions. 

The amides derived from sulphonic acids are called sulphonamides. They are obtained from amines by the reaction with sulphonyl chloride (R SOCl2) in pyridine. 

A somewhat similar method of cyanide preparation is applicable in the aromatic series aromatic sulphonic acid potassium salts, on fusion with potassium cyanide or potassium ferrocyanide, yield aromatic nitriles. The reaction can be extended to derivatives of pyridine. 

Methanesulphonyloxypropyl)phenthiazine-2-sulphonic acid dimethylamide, was obtained by condensing methanesulphonyl chloride in anhydrous pyridine with 10-(3-hydroxypropyl)phenthiazine-2-sulfonic acid dimethylamide. 

Although better results have been achieved with the sulphonation of pyridine to give the sulphonic acid 5.16, electrophilic substitutions on an inactivated pyridine ring are in general not preparatively useful. 

Details have been published of the pyridine-type molecule approach for the construction of carbocyclic compounds,11 in particular ( )-D-homo-oestrone. Treatment of (39) with toluene-p-sulphonic acid in hot benzene for one minute gave12 compound (40) of the elusive A8(9)-structure further reaction led to the expected oestrapentaene (41) from which by suitable reduction procedures 8aH-, 9 8H,14j3H-, 8aH,14 3H-, and 9/3H-oestrone methyl ethers were obtained. The well known compound (42) on electrocatalytic reduction13 (palladinized platinium... 

A photochemical technique for the synthesis of iV-acyl-imines has been reported. Photolysis of the azido-ketone (78) in the presence of pyridine or NEts yielded the AT-acyl-imine (79) which was hydrated to (80a) on alumina or sulphonic acid ion-exchange resin. Irradiation of (78) in MeOH afforded (80b), (79) being an intermediate. Catalytic reduction of (79) furnished the lactam (81). In refluxing... 

This ring is formed at room temperature when pyridine-2-acetic acid is stirred with hydroxylamine-<9-sulphonic acid. 

Triaza-Compounds. 2-(Ethoxymethyleneamino)pyridine is converted into the triazolopyridine (564) by the action of hydroxylamine-O-sulphonic acid. Anodic oxidation of the hydrazone Ar NHN=CHAr (Ar =p-NO2C6H4, Ar = /7-MeC6H4) in the presence of pyridine and tetraethyl-ammonium perchlorate affords the salt (565). Oxidative cyclization of the pyridylhydrazone PyCH=NNHPy (Py = 2-pyridyl) by means of mercury(II) acetate yields compound (566). 2,4,6-Triphenylpyrylium fluoroborate reacts with amidrazones ArC(NH2)=NNH2 in the presence of triethylamine to give the pyrazolopyrimidines (567). The tricyclic compound (568) is... 

Chloro-[35S]sulphonic acid (84) and pyridine were reacted at 0°C in a standard scintillation vial, sealed with a rubber cap at stirring. The solid pyridine-[3 5S]sulphur trioxide (85) was coupled with 2-amino tricarballylate to give radio-labelled 35S -SAT (83). The low yield of 83 in the second step of the synthesis was assumed to be caused by steric hindrance around the amino group of 2-amino tricarballylate. 

Chromones.- Enamines have previously been converted into chromones and in another approach, the enamine (104) reacted with thionyl chloride to give the chromone (105 n=2) in moderate yield. The sulphinic acid was readily oxidized to the sulphonic acid (105 n=3) by 3-chloroperoxybenzoic acid.110 A convenient synthesis has been described of 2-methylchromene-4-thione in 57% yield from 4-(2-hydroxyphenyl)butane-1,3-dione.111 The t-amino-methylchromones (106) have been synthesized and shown to be central nervous system depressants. A new synthesis of 2-substituted chromones (including flavones) uses 2-acetoxyphenacyl bromide (107) which is converted into its phosphorane (108). Heating this with an alkanoyl or aroyl chloride or anhydride in pyridine gave good yields of the chromone (109).113... 

Pyridine is a tertiary amine its aqueous solution shows an alkaline reaction and precipitates the hydroxides of metals, some of which are soluble in an excess of the amine. Salts of pyridine like those of other amines form characteristic double salts with metallic halides. The ferrocyanide of pyridine and the addition-product of pyridine and mercuric chloride are difficultly soluble in water these compounds are used in the purification of the base. Pyridine is a very stable compound it can be heated with nitric acid or chromic acid without undergoing change but at 330° it is converted by a mixture of nitric acid and fuming sulphuric acid into nitropyridine, a colorless compound that melts at 41° and boils at 216°. At a high temperature pyridine is converted into a sulphonic acid by sulphuric acid. Chlorine and bromine form addition-products, e.g., C5H5N.CI2, at the ordinary temperature when these are heated to above 200°, substitution-products are formed. The hydroxyl derivative of pyridine is made by fusing the sulphonic acid with sodium hydroxide it resembles phenol in chemical properties. The three possible carboxyl derivatives of pyridine are known. The a-acid is called picolinic acid, the jS-acid nicotinic acid (664), and the 7-acid isonicotinic acid. 

Grignard reagents RMgX into the amines RNH2 succeeds with the former but fails with the latter. The two reagents gave comparable yields in the iV-amination of pyridine and quinoline but for indole and carbazole the first was more effective. It was concluded that, in general, hydroxylamine-O-sulphonic acid was more versatile. 1,2,3-Triazole reacts with hydroxylamine 0-sulphonic acid in aqueous potassium hydroxide to yield a mixture of 53% 1-amino-l,2,3-triazole and 14% of the 2-amino isomer (equation 37) . ... 

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