For desulfonization

Problem 11.7 Use the principle of microscopic reversibility (Problem 6.26) to write a mechanism for desulfonation. 

Desulfonation.1 Magnesium, activated by 10 washes with dilute aqueous HC1 followed by 5 washes with distilled water, effects desulfonation in dry CH3OH at 50° in satisfactory yield. For example, phenyl p-phenethyl sulfone is converted into ethylbenzene in 68% yield. It is also useful for desulfonation of 1,1- and 1,2-disulfones. 

Desulfonation Sulfonation is reversible, and a sulfonic acid group may be removed from an aromatic ring by heating in dilute sulfuric acid. In practice, steam is often used as a source of both water and heat for desulfonation. 

This reaction is noticeable only if ipso attack triggers rearrangement, or loss of a group on the ring, or if a deuterated acid is used. One possible mechanism for desulfonation of an aromatic ring is shown below. 

The reaction coordinate diagram in Figure 15.5 shows that the rate-determining step for sulfonation is the slower of the two steps, whereas the rate-determining step for desulfonation is the faster of the two steps. Explain how the faster step can he the rate-determining step. 

Processes for Triacetate. There are both batch and continuous process for triacetate. Many of the considerations and support faciUties for producing acetate apply to triacetate however, no acetyl hydrolysis is required. In the batch triacetate sulfuric acid process, however, a sulfate hydrolysis step (or desulfonation) is necessary. This is carried out by slow addition of a dilute aqueous acetic acid solution containing sodium or magnesium acetate (44,45) or triethanolamine (46) to neutrali2e the Hberated sulfuric acid. The cellulose triacetate product has a combined acetic acid content of 61.5%. 

Naphthalenesulfonic Acid. The standard manufacture of 2-naphthalenesulfonic acid involves the batch reaction of naphthalene with 96 wt % sulfuric acid at ca 160°C for ca 2 h (13). The product contains the 1- and 2-isomers in a ratio of ca 15 85. Because of its faster rate of desulfonation,... 

Many aminonaphthalenesulfonic acids are important in the manufacture of azo dyes (qv) or are used to make intermediates for azo acid dyes, direct, and fiber-reactive dyes (see Dyes, reactive). Usually, the aminonaphthalenesulfonic acids are made by either the sulfonation of naphthalenamines, the nitration—reduction of naphthalenesulfonic acids, the Bucherer-type amination of naphtholsulfonic acids, or the desulfonation of an aminonaphthalenedi-or ttisulfonic acid. Most of these processes produce by-products or mixtures which often are separated in subsequent purification steps. A summary of commercially important aminonaphthalenesulfonic acids is given in Table 4. 

Another example of manufacture in this series is the sulfonation of an aminonaphthalenesulfonic acid, followed by selected desulfonation, to make 6-amino-l,3-naphthalenedisulfonic acid (21). Thus, 2-amino-l-naphthalenesulfonic acid made by amination of 2-hydroxy-1-naphthalenesulfonic acid is added to 20 wt % oleum at ca 35°C. At this temperature, 65 wt % oleum is added and the charge is stirred for 2 h, is then slowly heated to 100°C and is maintained for 12 h to produce 6-amino-l,3,5-naphthalenetrisulfonic acid. The mass is diluted with water and maintained for 3 h at 105°C to remove the sulfo group adjacent to the amino group. After cooling to ca 20°C and filtration, 6-amino-l,3-naphthalenedisulfonic acid is obtained in 80% yield (55). 

Hydroxynaphthalenesulfonic acids are important as intermediates either for coupling components for a2o dyes or a2o components, as well as for synthetic tanning agents. Hydroxynaphthalenesulfonic acids can be manufactured either by sulfonation of naphthols or hydroxynaphthalenesulfonic acids, by acid hydrolysis of arninonaphthalenesulfonic acids, by fusion of sodium naphthalenepolysulfonates with sodium hydroxide, or by desulfonation or rearrangement of hydroxynaphthalenesulfonic acids (Table 6). 

Sulfonic acids are prone to reduction with iodine [7553-56-2] in the presence of triphenylphosphine [603-35-0] to produce the corresponding iodides. This type of reduction is also facile with alkyl sulfonates (16). Aromatic sulfonic acids may also be reduced electrochemicaHy to give the parent arene. However, sulfonic acids, when reduced with iodine and phosphoms [7723-14-0] produce thiols (qv). Amination of sulfonates has also been reported, in which the carbon—sulfur bond is cleaved (17). Ortho-Hthiation of sulfonic acid lithium salts has proven to be a useful technique for organic syntheses, but has Httie commercial importance. Optically active sulfonates have been used in asymmetric syntheses to selectively O-alkylate alcohols and phenols, typically on a laboratory scale. Aromatic sulfonates are cleaved, ie, desulfonated, by uv radiation to give the parent aromatic compound and a coupling product of the aromatic compound, as shown, where Ar represents an aryl group (18). 

Allylic sulfones and a, /5-unsaturated sulfones are known to be in equilibrium314-319. Allylic sulfones, such as 242, isomerize to a, /5-unsaturated sulfones 243 upon treatment with a catalytic amount of potassium t-butoxide in dry THF. The a, /5-unsaturated sulfones can be converted to the corresponding olefins upon desulfonation with sodium amalgam320 or aluminium amalgam294,321. Since treatment of allylic sulfones with potassium-graphite gives 2-alkenes, alkylation of allylic sulfones and subsequent desulfonation is a useful process for the synthesis of olefins, as shown in Scheme 6. 

A review article is an intensive survey of a rather narrow field for example, the titles of some recent reviews are Desulfonation Reactions Recent Developments , Pyrrolizidine and Indolizidine Syntheses Involving 1,3-Dipolar Cycloaddtion , and From Corrin Chemistry to Asymmetry Catalysis—A Personal Account. A good review article is of enormous value, because it is a thorough survey of all the work done in the field under discussion. Review articles are printed in review journals and in certain books. The most important review journals in organic chemistry (though most are not exclusively devoted to organic chemistry) are shown in Table A.3. Some of the journals listed in Table A.l, for example, the Bull Soc. Chim. Fr. and J. Organomet. Chem. also publish occasional review articles. 

Azacanthines, 374, like their deaza analogues (cf. Equation 128), can be prepared by inverse electron demand aza-Diels-Alder reactions of the appropriately tethered amidoalkyl-l,2,4-triazinylindoles 373 (Equation 135) <1995TL6591>. The sulfonyl-substituted derivatives 375 can be prepared similarly in high yield, although the conditions for each individual reaction are important, since an appreciable amount of the desulfonated product 376 may also be formed (Equation 136) <1998TL2487>. 

Excess acidity correlations have been used to show that some aromatic sulfonic acid desulfonations have an A-SE2 mechanism.188,189 This mechanism (alternative terminologies are Ad-E2 and A(E) +A(N))190 has also been found to apply to the hydration of acetylene itself,191 to ynamines192 and to many other alkynes,193-195 as well as to many different alkenes196-199 and vinyl ethers.200-203 The excess acidity method has been used to evaluate aA values for several alkene hydrations.204 205... 

Figure 2.1.1 shows the most common derivatisation methods for anionic surfactants reported in the literature [1]. The first method of LAS determination by GC consisted of a microdesulfonation procedure in which LASs were desulfonated in boiling phosphoric acid at high temperature [2-4] and the corresponding alkylbenzenes analysed. The microdesulfonation method was further improved by introducing additional concentration and clean-up steps [5—11], which allowed the determination of LAS in influent, effluent and river water samples at low qg L-1 levels [7,8] and sediment and sludge samples [8] at pg g-1. In addition to the desulfonation procedure, several derivatisation techniques have been used to make LAS analysis amenable to GC. 

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