Sulfur trioxide-based sulfonation

Sulfonated aromatic polymers have been widely studied as alternatives to Nafion due to potentially attractive mechanical properties, thermal and chemical stability, and commercial availability of the base aromatic polymers. Aromatic polymers studied in fuel cell apphcations include sulfonated poly(p-phenylene)s, sulfonated polysulfones, sulfonated poly(ether ether ke-tone)s (SPEEKs), sulfonated polyimides (SPIs), sulfonated polyphosphazenes, and sulfonated polybenzimidazoles. Representative chemical structures of sulfonated aromatic polymers are shown in Scheme 3. Aromatic polymers are readily sulfonated using concentrated sulfuric acid, fuming sulfuric acid, chlorosulfonic acid, or sulfur trioxide. Post-sulfonation reactions suffer from a lack of control over the degree and location of functionalization, and the... 

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 mechanical stability and ion exchange capacity of these condensation resins were modest. A better approach is to prepare a suitable crosslinked base membrane, which can then be converted to a charged form in a subsequent reaction. Ionics is believed to use this type of membrane in many of their systems. In a typical preparation procedure, a 60 40 mixture of styrene and divinyl benzene is cast onto a fabric web, sandwiched between two plates and heated in an oven to form the membrane matrix. The membrane is then sulfonated with 98 % sulfuric acid or a concentrated sulfur trioxide solution. The degree of swelling in the final membrane is controlled by varying the divinyl benzene concentration in the initial mix to control crosslinking density. The degree of sulfonation can also be varied. The chemistry of the process is ... 

Sulfonation of LAB. The sulfonation of alkylbenzenes leads to sulfonic acid tyre product, which is then neutralized with a base such as sodium hydroxide to produce sodium alkylbenzene sulfonate. The sulfonation reaction is highly exothermic and instantaneous. An efficient reactor heat removal system is used to prevent the decomposition of the resultant sulfonic acid. The sulfonation reaction takes place by using oleum (SO3H2SO4) or sulfur trioxide (SO3). Although, the oleum sulfonation requires relatively inexpensive equipment, the oleum process has major disadvantages compared to sulfur trioxide. The need for spent acid stream disposal and the potential corrosion owing to sulfuric acid generation increased the problems related to oleum process [1]. 

Sulfonation.43 In concentrated sulfuric acid solution, it has been shown experimentally that there is sulfur trioxide present.44 Consequently we may consider sulfuric acid or sulfur trioxide as the reactive species in sulfonation processes. One mechanism which has been suggested involving sulfuric acid,46 is based upon a preliminary ionization similar to that which has been proposed for nitration ... 

A typical example of the process to produce a metallized layer involves the development of a sulfonated layer of micrometer thickness using the techniques discussed above. A degree of surface sulfonation of only 0.2 micrograms of sulfur trioxide equivalents per square centimeter is achieved by contacting the surface with dry air containing 2 percent sulfur trioxide at 25°C for approximately one second. A metallizing bath based on one part of each of the following is conveniently used ... 

ANILINE-4-SULFONIC ACID (121-57-3) Decomposes on contact with strong acids, forming sulfur trioxide. Aqueous solution is acidic violent reaction with strong bases. Incompatible with alkylene oxides, aliphatic amines, alkanolamines, amides, ammonia, epichlorohydrin, organic anhydrides, isocyanates, oxidizers, vinyl acetate. 

Liquid, mp 2.2°, bpjj 100-101. njf 1,5733, pKa 3,58. The base neutralizes HCI but does not react with alkyl halides or boron trifluoride. Undergoes nuclear sulfonatlon with sulfur trioxide forming a sulfonic acid, Cl3H2,NSOy mp 310° (decompn),... 

Sulfonation is the final step for the preparation of polystyrene-based membranes for fuel cell apphcations. In this reaction a sulfonic acid group is added to the aromatic ring by electrophihc substitution. Sulfonation can be performed by several agents such as sulfiu ic acid, sulfur trioxide, sulfonyl chloride, acetyl sulfate, and chlorosulfonic add. 

Anionic surfactants with the general structure RpCONH-X-COONa (e.g., X = -(0112)5-) have been reported in the patent literature. These surfactants are synthesized from the corresponding isopropyl ester and 6-amino-hexanoic acid sodium or ammonium salt (H2N(CH2) 5COOM). Another class of anionic surfactants derived from PFCA derivatives are perfluoroacylbenzenesulfo-nates (Scheme 18.11). This group of surfactants is synthesized by Friedel-Crafts acylation of benzene with a PFCA halide (e.g., perfluorooctanoyl chloride) in the presence of at least one equivalent of a Lewis acid (e.g., anhydrous aluminum chloride). This reaction proceeds smoothly and in good yields at subambient or ambient temperatures. The perfluoroacylbenzene is sulfonated with oleum or sulfur trioxide and neutralized with a base (e.g., sodium hydroxide). 

The sulfonation of LAB can be achieved using oleum, sulfuric acid, or gaseous sulfur trioxide. On an industrial scale, sulfonation with SO3 is the most cxirrent process. In a continuous process, the major reaction products are various sulfonic acids, the free oil involving mainly unsulfonated alkylbenzene, anhydrides (which are hydrolyzed later by the addition of 1% or 2% water), and sulfuric acid. The sulfonate is obtained after neutralization of the sulfonic acid mixture with an appropriate base (generally sodium hydroxide). 

In order to prepare advanced molecules of poly(arylene ether sulfones) for fuel cell apphcations without sacrificing their excellent physical properties, Noshay and Robeson developed a mild sulfonation procedure for the commercially available bisphenol-A-based poly(ether sulfone) [62,63]. The sulfonation agents that have been used for this polymer modification are chlorosulfonic acid and a sulfur trioxide-triethyl phosphate complex. Recently, Kerres and co-workers [102] reported an alternative sulfonation process of commercial polysulfone based on a series of steps, including metalation-sulfmation-oxidation reactions. 

SMEs are prepared by the addition of sulfur trioxide to the alpha carbon of a methyl ester and subsequent neutralization with a base. Two surfactant moieties are formed (see Fig. 1). The primary surfactant formed is SME. The secondary surfactant formed is a sulfonated fatty acid. This molecule contains two different acid groups, a sulfonic acid and a carboxylic acid group. At a pH of roughly 4.5 to 9 the sulfonated fatty acid is present as a mixture of monoanion and dianion [1]. Below pH 4, the diacid is present as a monoanion. At pH < 9, the sulfonated fatty acid is present in a disodium salt form. 

Many compounds which at first glance seem to offer no possibility of behaving as acids or bases may be forced to do so by reaction with strong bases or acids. For example, in the sulfonation of benzene by sulfur trioxide, the simplest explanation would seem to be that the SO3 molecule coordinates with two of the electrons from the benzene molecule as follows ... 

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