Sulfonic acids from aromatic sulfonation

Aromatic sulfonic acids from aromatic hydrocarbons... 

Most phenohc foams are produced from resoles and acid catalyst suitable water-soluble acid catalysts are mineral acids (such as hydrochloric acid or sulfuric acid) and aromatic sulfonic acids (63). Phenohc foams can be produced from novolacs but with more difficulty than from resoles (59). Novolacs are thermoplastic and require a source of methylene group to permit cure. This is usually suppHed by hexamethylenetetramine (64). 

Acidic Hydrolysis. Hydrolysis of esters by use of water and a mineral acid leads to an equiUbrium mixture of ester, alcohol, and free carboxyHc acid. Complete reaction can only be achieved by removal of alcohol or acid from the equiUbrium. Because esters have poor solubiUty in water, the reaction rate in dilute acids is fairly low. Therefore, emulsifiers such as sulfonated oleic acid or sulfonated aromatic compounds (TwitcheU reagent) are added to facihtate the reaction. 

Equilibrium constants for sulfinyl sulfone formation from aromatic sulfinic acids at 21 °C in acetic acid containing 1 to 5% H20 ... 

Another concern for polystyrene- and some aromatic-based PEMs is hydrolysis of fhe sulfonic acid group from aromatic rings as well as hydrolytic cleavage of polymer backbone under fuel cell conditions for aromafic polymers including polyimides, poly(arylene ethers), poly(ether ketones), and poly(ether sulfones). It is well known that the sulfonation of aromafic rings is a reversible process especially at low pH and at elevated temperature (Scheme 3.3). The reversibility of sulfonation, for example, is used in fhe preparafion of trinitrotoluene or picric acid. Por the simplest membrane of the class of arylsulfonic acids (i.e., benzenesulfonic acid), fhe reacfion occurs upon freatment with a stream of superheated steam at 180°C.i ... 

Sulfonation is the introduction of a sulfonic acid group (-S03H) into an organic compound as, for example, in the production of an aromatic sulfonic acid from the corresponding aromatic hydrocarbon. 

Fluorescence arises from aromatic by-products which, however, can be entirely separated by careful work. Pure ac-tetrahydro-/5-naphthylamine gives no color with diazobenzene sulfonic acid. 

Phenols can be prepared from aromatic hydrocarbons by sul-fonalion and hydrolysis of the resulting sulfonic acid. 

In the laboratory, simple phenols can be prepared from aromatic sulfonic acids by melting with NaOH at high temperature (Section 16.2i. Few functional groups can survive such harsh conditions, though, and the reaction is therefore limited to the preparation of alkyl-substituted phenols. We ll see a better method of phenol preparation from aromatic amines in Section 24.8. 

A sodamide melt can be used at atmospheric pressure but gives poorer yields.383 However, use of sodamide in boiling piperidine has proved an excellent method of preparing 1-arylpiperidines from aromatic sulfonic acids.1191... 

Instead of allowing the sulfonating agent proper (or the spent acid from it) to function as the reaction solvent, it is sometimes customary to dissolve or suspend the organic compound (e.g., an aromatic amine) in monohydrate acid or low-strength oleum, followed by addition of the sulfonating agent (e.g., 65 per cent oleum). 

Polybenzimidazoles are synthesized from aromatic tetraamines (bis-o-diamines) and dicarboxylates (acids, esters or amides). Generalized monomers are shown in FIGURE 1 and polybenzimidazoles from those monomers are shown in FIGURE 2. In either figure, R(l) and R(2) can be aromatic or aliphatic and may contain other groups as ether, ketone, sulfone, etc. The structures shown do not exhaust all possible benzimidazole polymers. 

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