Inner salts of sulfonic acids

Inner Salts of Sulfonic Acids (Alkali Blue Types) 541... 

Two types of insoluble triarylcarbonium compounds are used industrially as pigments. Both are salts of these basic dyes. So-called Alkali Blue type triarylcarbonium pigments are inner salts of sulfonic acids, while the second group comprises salts of complex inorganic anions of heteropolyacids. 

There are two groups of triarylcarbonium pigments inner salts of triphenyl-methane sulfonic acids, and complex salts with heteropolyacids containing phosphorus, tungsten, molybdenum, silicon, or iron. 

The thus prepared product, however, being the inner salt of a sulfonic acid, turned out to be entirely insoluble in water. The compound only became a suitable textile dye after it had been converted into its sodium salt, i.e., through application in a slightly alkaline medium (= Alkali Blue). 

These diazonium salts are good electrophiles for activated aromatic rings, such as amines and phenols, and this is how azo dyes are prepared. Diazotization of the salt of sulfanilic acid, which we have just made by sulfonation of aniline, gives an inner salt that combines with N,N-dimethylaniline to form the water-soluble dye, methyl orange. 

Diazo compounds which contain a sulfo group are usually quite insoluble and precipitate as white or yellow crystals of the inner salt. Since many of the aminosulfonic acids themselves are also relatively insoluble, it is desirable to diazotize them by the indirect method. This is done by adding the necessary amount of nitrite to the solution of the sodium sulfonate, and pouring the solution into the acid. 

Like other alkaloids having a free position para to a hydroxyl or methoxyl in an aromatic ring, papaverine can be sulfonated with cold sulfuric acid. The interpretation of the position of the sulfonic acid group in papaverine-6 -sulfonic acid is supported by the inability of the compound to couple with diazonium salts. The compound probably has an inner salt structure... 

Acid solutions of iron salts react with water solutions of 8-hydroxy-7-iodo-quinoline-5-sulfonic acid (I) to produce a green color due to the inner complex anion (II),... 

In addition to these inner salts, a number of monomeric salt pairs have been prepared [93]. In these systems a vinyl acid such as vinyl sulfonic acid was reacted with a vinyl base such as vinyl pyridine in THF. The precipitated salt was washed and purified. Polymerization of the salt was accomplished in the aqueous solution with a thermal initiator. Other salt pairs include acrylate and acrylamide derivatives with sulfonic groups as the anionic constituents and tertiary or quaternary amino pendant groups as the cationic constituents [94]. 

Direct polymerization from sulfonated monomers is the most widely used method for the synthesis of the SPIs. The synthesis is usually performed by polycondensation reaction of sulfonated diamine monomers with tetracarboxylic dianhydride monomers in m-cresol in the presence of triethyl amine (EtjN) and benzoic acid at around 180°C [4,7,10,11,13,28-34]. Sulfonated diamines are inner salts that are formed due to the interaction of the sulfonic add groups and the basic amino groups, and the function of the EtsN is to liberate the protonated amino groups of sulfonated diamines for polymerization with the 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA),... 

The most widely used chemically modified PPO in the development of thin film composite membranes is sulfonated polyphenylene oxide (SPPO). The polymer in the acid form as well as salt form has been used by Bikson to produce multilayer composite membranes. These types of membranes have been described to have at least two chemically distinct layers deposited on a porous substrate in a single coating step process. The outer layer forms a protective defect-sealing surface whereas the inner layer is the selective SPPO layer. This layer is adjacent to the porous support membrane. The two top layers are formed simultaneously on top of porous polysulfone support hollow fibers. A coating solution of SPPO in the lithium salt form (SPPO-Li ) and amine functional silicone fluid was coated on top of the polysulfone fibers. These coated fibers were used to construct a hollow fiber separator permeator. 

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