Sulfonation Reactions

As in most electrophilic reactions, the abiUty to stabilize the positive charge generated by the initial addition strongly affects the relative rates. MX reacts faster than OX and PX because both methyl groups work in conjunction to stabilize the charge on the next-but-one carbon. Sulfonation was, at one time, used to separate MX from the other Cg aromatic isomers. MX reacts most rapidly to form the sulfonic acid which remains in the aqueous phase. The sulfonation reaction is reversible, and MX can be regenerated. 

Sulfonate Esters. Sucrose sulfonates are valuable intermediates for the synthesis of epoxides and derivatives containing halogens, nitrogen, and sulfur. In addition, the sulfonation reaction has been used to determine the relative reactivity of the hydroxyl groups in sucrose. The general order of reactivity in sucrose toward the esterification reaction is OH-6 OH-6 > OH-1 > HO-2. 

Benzene. The reaction of sulfur trioxide and ben2ene in an inert solvent is very fast at low temperatures. Yields of 90% ben2enesulfonic acid can be expected. Increased yields of about 95% can be reali2ed when the solvent is sulfur dioxide. In contrast, the use of concentrated sulfuric acid causes the sulfonation reaction to reach reflux equiUbrium after almost 30 hours at only an 80% yield. The by-product is water, which dilutes the sulfuric acid estabhshing an equiUbrium. 

Sulfur dioxide is usefiil as a solvent for sulfur trioxide in sulfonation reactions for example, in the large-scale production of alkylbenzenesulfonate surfactant (329). A newer use for sulfur dioxide is in cyanide detoxification in connection with cyanide leaching of precious metals from mine dumps. 

Pyridinium sulfate, bis-l,2,4,6-tetramethyl-hydrogen isotope exchange reactions, 2, 194 Pyridinium-1 -sulfonates reactions, 2, 34... 

The process is shown schematically in Fig. 1. During the first stage of the process, a-olefins are sulfonated with diluted S03 gas in a falling film reactor. The optimum molar ratio of S03/olefin varies from 1.0 to 1.2. As the sulfonation reaction is very rapid and exothermic, the reaction temperature can rise to... 

The actual sulfonation reaction consists largely of a concerted 2+2 cyclo addition of S03 and a-olefin yielding a highly reactive, unstable p or 1,2-sultone that can (1) react further to give alkenesulfonic acid and (2) rearrange itself to form y- or 1,3-sultone (a fast reaction), and 8- or 1,4-sultone (a slow reaction). Possible side reactions have been identified by Bakker and Cerfontain [28]. At molar ratios of S03/olefin below 1.0 the major sulfonation product is 1,3-sultone but larger proportions of alkenesulfonic acids will be formed for ratios... 

Schmid et al. studied in detail the sulfonation reaction of fatty acid methyl esters with sulfur trioxide [37]. They measured the time dependency of the products formed during ester sulfonation. These measurements together with a mass balance confirmed the existence of an intermediate with two S03 groups in the molecule. To decide the way in which the intermediate is formed the measured time dependency of the products was compared with the complex kinetics of different mechanisms. Only the following two-step mechanism allowed a calculation of the measured data with a variation of the velocity constants in the kinetic differential equations. 

In the first step an S03 molecule is inserted into the ester binding and a mixed anhydride of the sulfuric acid (I) is formed. The anhydride is in a very fast equilibrium with its cyclic enol form (II), whose double bonding is attacked by a second molecule of sulfur trioxide in a fast electrophilic addition (III and IV). In the second slower step, the a-sulfonated anhydride is rearranged into the ester sulfonate and releases one molecule of S03, which in turn sulfonates a new molecule of the fatty acid ester. The real sulfonation agent of the acid ester is not the sulfur trioxide but the initially formed sulfonated anhydride. In their detailed analysis of the different steps and intermediates of the sulfonation reaction, Schmid et al. showed that the mechanism presented by Smith and Stirton [31] is the correct one. 

As can be seen, water is set free by the reaction. The presence of water retards the sulfonation reaction or prevents it altogether. This is why a very large excess of H2S04 is used to bring the reaction to completion. (The oleum excess is used for the same reason.)... 

High temperatures because the sulfone formation reaction has a higher activation energy than the main sulfonation reactions A high concentration of H+ ions (probably)... 

Only the a-olefins are sulfonated commercially to make a-olefinsulfonate (AOS). The chemistry of a-olefin sulfonation is usually described in terms of three stages. The initial sulfonation reaction involves the formation of 3-sul-tones. This initial step is so fast as to be almost instant. Reaction of the initially formed B-sultones with more S03 is competitive with sulfonation of the olefin. This side reaction produces a byproduct believed to be a cyclic pyro-sulfonate ester, i.e., a pyrosultone ... 

Me-ester sulfonation has to be carried out at relatively high temperatures as the initial reactions and the decomposition of intermediate products is relatively slow compared with sulfonation reaction rates for alkylbenzenes, primary alcohols, ethoxylated alcohols, and a-olefins. The required aging time for conversion of the intermediates to FAME sulfonation acid is long (about 45 min at 85°C). It is not possible to sulfonate Me-esters without an excess of S03. 

Sulfonvlated PPO. The sulfonylation is achieved by sulfonation reaction on PPO, followed by the reaction with aromatic compounds as outlined in Scheme 1. 

BINAP-Ru catalysts also show high enantioselectivity in the hydrogenation of/ -keto sulfonates. Reaction of sodium yS-keto sulfonates with (R)-BINAP-Ru catalyst quantitatively gives the (R)-/1-hydroxy sulfonates in up to 97% ee (Fig. 32.21) [15]. In the same manner, hydrogenation of / -keto sulfones in the presence of an (R)-MeO-BIPHEP-Ru catalyst affords the (R)-hydroxy sulfones in >95% ee [71]. 

Poly(arylether ketone), conducting, 7 524 Poly(aryl ether ketone)s, sulfonation reaction of, 23 717-718 Poly(di-n-alkylsilanes), thermochromic materials, 6 619... 

Sulfonation reaction profiles, 23 548—549 Sulfonation reagents, highly acidic, 23 539 Sulfonation-sulfation systems, 23 544 Sulfonation/sulfation processes, 23 513-563. See also Sulfation entries Sulfonation entries selection of and options for, 23 515 Sulfonation technology, uses for, 23 514-516... 

Al-Omran and Rose controlled the location and extent of sulfonation on poly (ary lene ether) backbones by copolymerizing 4,4 -dichlorodiphenyl sul-fone, durohydroquinone, and hydroquinone to form random copolymers, where only the hydroquinone residue would be expected to be susceptible to sulfonation by sulfuric acid. Although these authors observed sulfonation at positions other than at the desired hydroquinone locations, designing sulfonation sites into a polymer backbone remains an attractive strategy for producing copolymers with known structures. This allows the chemical structure and composition of the material to dictate the extent of sulfonation rather than trying to externally control sensitive and sometimes unpredictable macromolecu-lar sulfonation reactions. 

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