Sulfinic anhydrides

Sulfur Acids. Organic oxy acids of sulfur, that is, —SO3H, —SO2H, and —SOH, are named sulfonic acid, sulfinic acid, and sulfenic acid, respectively. In subordinate use, the respective prefixes are sulfo-, sulfino, and sulfeno-. The grouping —SO2—O—SO2— or —SO—O—SO is named sulfonic or sulfinic anhydride, respectively. 

Thionyl chloride is another activating agent employed for reactions between aromatic carboxylic acids and phenols in pyridine solution. The mechanism suggested does not involve the formation of an acid chloride but assumes the existence of an intermediary mixed sulfinic anhydride which undergoes reaction with phenolic endgroups (Scheme 2.32).311... 

As an alternative, Harpp and coworkers reacted benzenesulfinyl chloride with the trimethylsilyl derivative of menthol to form the diastereomeric esters in 91% yield the epimer of configuration R could be isolated by crystallization in unspecified yield. Grossert and coworkers prepared ester 19 in 51% yield as a mixture of diastereomers by treating p-toluenesulfonyl chloride with sodium p-toluenesulfinate in DMF containing menthol. It was postulated that initial nucleophilic attack by the sulfinate oxygen on the sulfonyl sulfur atom gave the mixed sulfonate-sulfinate anhydride 21, which then reacted... 

With sulfinyl chlorides the isolated product of their reaction with sulfinate ions is the sulfinyl sulfone (126) (Bredereck et al., 1960). However, whether this results because S-sulfinylation is kinetically preferred, or rather comes about because the sulfinic anhydride resulting from initial O-sulfinylation is readily converted by some of the remaining sulfinate ion to the thermodynamically more stable sulfinyl sulfone (126a), does not appear to have ever been definitely established. 

The anhydride of ethane- 1,2-disulfinic acid has structure [31b] (Mueller and Dines, 1969). In this instance the strain associated with the four-membered ring in [31a], which is absent in the five-membered sulfinic anhydride, is sufficient to ... 

While the anhydride of butane-1-sulfinic acid has the usual sulfinyl sulfone structure ([30a], R = n-Bu), the anhydride of 2-methylpropane-2-sulfinic acid has the sulfinic anhydride structure ([30b], R = t-Bu) Kice and Ikura, 1968). Presumably there is some steric interference between the bulky t-butyl groups in [30a] which is absent in [30b] where, because of the oxygen bridge, they are now further away from each other. However, since it seems unlikely that the... 

Thus these results suggest that although a sulfinyl sulfone [30a] is normally thermodynamically more stable than the isomeric sulfinic anhydride [30b] the actual difference in free energy between the two isomers is not likely to be large. The situation appears reminiscent of the thermodynamics for sulfoxides vs. sulfenates discussed earlier. 

Knoevenagel and Polack733 have given directions for the preparation of aromatic sulfinic anhydrides by the action of acetic anhydride on a suspension of the dry sulfinic acid in a little acetic acid. The reaction is catalysed by sulfuric acid or a 0.1% solution of iron(m) chloride in glacial acetic acid or acetic anhydride. Benzene-, / -toluene-, / -xylene-, pseudocumene-, mesitylene-, and / -bromo- and / -iodo-benzene-sulfinic anhydride have been obtained in this way. 

A very surprising sulfone formation has been investigated by Oae and coworkers . On heating p-toluenesulfinic acid with dimethylaniline in ethanol for 15 h, the reaction mixture shown in equation 100 has been obtained. Obviously, the observed products arise from an equilibrium between the sulfinic acid and its pseudo-anhydride (disulfide trioxide), which is able to attack the amine nitrogen and degrade the tertiary amine corresponding to a Polonovsky reaction . 

Among the oxyacids of sulfur the predilection to form an anhydride with a sulfur-sulfur bond, rather than one with an oxygen bridge between the two sulfurs, is not restricted to sulfenic acids. We will see in a subsequent section that sulfinic acids also do this. Their anhydrides have the sulfinyl sulfone structure. RS(0)S02R, rather than RS(0)0S(0)R. What is unique about the sulfenic acid-thiolsulfinate system, however, is the fact that the anhydride (thiolsulfinate) is strongly preferred thermodynamically over the acid at equilibrium. With any other type of common acid the reverse is true, of course. The uniqueness of the sulfenic acid-thiolsulfinate situation can perhaps best be appreciated by realizing that, if the same stability relationship between acid and anhydride were to exist for carboxylic acids, acetic acid would spontaneously dehydrate to acetic anhydride ... 

The carbonyl group of an acid chloride is also a sufficiently electropositive center that acylation of a sulfinate ion occurs at oxygen (123) rather than sulfur (Schank, 1967 Kobayashi, 1966b). The mixed sulfinic-carboxylic anhydrides... 

The anhydrides of sulfinic acids normally have the sulfinyl sulfone structure... 

Sulfinyl sulfone (anhydride of a sulfinic acid) PhS(0)S02Ph + HjO - 2PhS02H 0 O II II -1.5... 

Although anhydride formation is more favorable thermodynamically for a sulfinic acid than for most types of acids, it is still true that in media containing any significant amount of-water the equilibrium in (132) for acyclic sulfinyl sulfones lies far to the left, and when placed in such media sulfinyl sulfones are hydrolyzed completely to the corresponding sulfinic acid. Let us now discuss what is known about the mechanism of this hydrolysis reaction. 

Thiolsulfonates have the structure shown in [58]. That they may be considered the mixed anhydride of a sulfenic and a sulfinic acid is indicated by one of the principal synthetic methods for their preparation, namely reaction (166) of a sulfinic acid with a sulfenyl chloride (Stirling, 1957). Once again, as we have... 

That an a-disulfone may properly be considered to be a mixed anhydride of a sulfinic and a sulfonic acid is shown by the fact that a-disulfones undergo relatively easy spontaneous hydrolysis (188) to give one molecule each of a sulfinic and a sulfonic acid (Kice and Kasperek, 1969). 

A structure isomeric to [73] for a mixed anhydride of a sulfinic and a sulfonic acid would, of course, be RS(0)0S02R. Oae and Ikura (1966, 1967)... 

Unlike sulfinyl sulfones (the anhydrides of sulfinic acids), whose heat of hydrolysis is much less than that for most anhydrides, the heat of hydrolysis of an cr-disulfone (see Table 5, p. 114) is comparable to that for typical anhydrides (Kice et al., 1977). 

A variant that eliminates the production of water and that has proved effective for esterification of hydroxy and aromatic amino acids involves the use of thionyl chloride instead of acid. At a low temperature, the alcohol reacts with the chloride, generating methyl sulfinyl chloride, which produces the ester, probably through the mixed carboxylic acid-sulfinic acid anhydride (Figure 3.18, B). p-Toluenesulfonyl chloride added to the acid and benzyl alcohol serves the same purpose in the preparation of benzyl esters. 

Kohn et developed a one-step preparation of a stable carboxylic-sulfinic acid anhydride by oxidizing 3,3,4,4-tetraphenyl-) -propionothiolac-tone with a peracid (Eq. 50). 

Oxidation of sulfides and sulfoxides, as discussed above, and alkylation of sulfinate salts are the most common methods used to obtain sulfones for synthetic purposes [71, 109-113], A hydrogen peroxide-urea-phthalic anhydride system was recently proposed as a mild convenient reagent for the efficient preparation of sulfones from organic sulfides [114]. 

Disulfides, diselenides, and ditellurides can be oxidized by hypervalent iodine compounds quite easily. Depending on the reaction conditions disulfides can be oxidized to sulfinic esters [59] or thiosulfonic S-esters [60,61]. Diselenides can be transformed into selenosulfonates [62]. Arenetellurinic mixed anhydrides are mild oxidants and can be obtained by oxidation of the corresponding ditellurides as shown in Scheme 9 [63]. Recently it was shown that a thioacetal based linker for solid-phase synthesis can be cleaved oxidatively using [bis(trifluoro-acetoxy)iodo]benzene 4 [64]. 

Single crystals of difluoromethane bis(sulfinic acid) anhydride 17 were isolated, after the cesium salt 119 was stored in the presence of traces of water vapor for several weeks <1998JFC(89)55>. Treatment of difluoromethane-l,l-bis(sulfonyl fluoride) 120 with liquid ammonia led to the formation of the cyclic ammonium imide 121 <1997ZNB359, 1997WO9731909>, while reaction of sulfamide 122 with trifluoroacetaldehyde O-ethyl hemiacetal afforded the cyclic aminal 60 (Scheme 41) < 1999S1731 >. 

In the reaction of carbodiimides with inorganic acids, usually the corresponding anhydrides are formed. For example, sulfinic acids 518 react with carbodiimides to give the corresponding anhydrides 519." Sulfonic acids react similarly. 

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