Sulfoxidation of alkanes

The sulfoxidation of aliphatic hydrocarbons is the easiest method for the synthesis of alkylsulfonic acids. Their sodium salts are widely used as surfactive reactants in technology and housekeeping. Platz and Schimmelschmidt [1] were the first to invent this synthetic method. Normal paraffins (Ci4-Cig) are used for the industrial production of alkylsulfonic acids [2-4]. Olefins and alkylaromatic hydrocarbons do not produce sulfonic acids under the action of sulfur dioxide and dioxygen and retard the sulfoxidation of alkanes [5-9],... 

The very important factor for the efficient sulfoxidation of alkanes is the partial pressure of sulfur dioxide. The study of alkanes sulfoxidation under S02 pressures higher than 1 atm proves that an optimal temperature exists for alkane sulfoxidation. The data (vmax) on different alkane sulfoxidation are listed below [25], The reaction rate v was the maximal rate measured in the experiment. 

Water retards the sulfoxidation of alkanes [25]. The results of experiments on decane sulfoxidation with addition of water (T=333K, pO2 = 980kPa, [S02]o = 6.2mol L 1, vio=5.0x 10-7 mol L-1 s 1) are given in the following table. The rate of sulfoxidation was observed to increase in time due to the accumulation of alkylsulfonic peracid and, hence, v0 -c vmax. 

The sulfoxidation of alkanes occurs with heat evolution. This is the basis for rate of oscillation of rapid sulfoxidation at a relatively high pressure when the feedback arises between reaction rate, diffusion of reactants into liquid phase, and heat evolution [27],... 

When the hydrocarbon concentration is high enough for the reaction of the sulfonyl-peroxyl radical with hydrocarbon not to limit the chain propagation, the following equation describes the dependence of the initial rate v of initiated (Vj) chain sulfoxidation of alkane [25] ... 

MA Saitova. Kinetics and Mechanism of Sulfoxidation of Alkanes. Ph.D. thesis, Institute of Chemical Physics, Chernogolovka, 1975. 

The sulfoxidation of alkanes to alkane sulfonic acids using a combination of sulfur dioxide and dioxygen and catalyzed by vanadium compounds has been reported [20]. The mechanism involves intermediacy of alkyl radicals which are trapped by sulfur dioxide and then further oxidized to the product. 

Hagemeyer, A. and Kuhlein, K., Photoinitiation of sulfochloration or sulfoxidation of alkanes using UV-excimer radiation for the manufacture of alkylsulfonyl chlorides and aUcylsulfonates, European Patent Application EP 1,028,107, 2000. 

Scheme 6.13 A possible reaction mechanism for the sulfoxidation of alkanes.

TABLE 6 Specifications of Sulfoxidation-Derived Alkane-sulfonates (HCils MARLON PS 65)... 

In the homologous series of alkane 1-sulfonates, micellization in aqueous solutions begins with the pentanesulfonate at cM = 1 mol/L. The critical micelle concentrations of the technical alkanesulfonates are cM = 0.002 mol/L (sulfo-chlorination route) and cM = 0.44 g/L (sulfoxidation route). 

The mechanism of alkane sulfoxidation includes the following elementary steps [13,21 24] initiation, three steps of chain propagation, and a few steps of chain termination. 

Recently, Punniyamurthy and co-workers applied the same catalyst 5a as used for the oxidation of alkanes [152] (Sect. 4.2) for the selective oxidation of aromatic sulfides to the corresponding sulfoxides with H2O2 (Eq. 19) [236]. Addition of 5 mol % TEMPO dramatically improved the selectivity and conversion with methylphenylsulfide as the substrate, only traces of sulfone were observed. 

Of the large number of possible ways of synthesizing alkanesulfonates, only sulfochlorination of alkanes (conversion with sulfur dioxide and chlorine to form alkane sulfonyl chlorides and their saponification with sodium hydroxide Table 1, entry 10) and sulfoxidation (reaction with sulfur dioxide and oxygen and neutralization of the sulfonic acids Table 1, entry 11) are of industrial importance [18]. 

The reaction of 60 with an excess of alkane- or arenesulfinyl chloride affords sulfinate esters 61-(R) and 61-fSj in good yields and moderate selectivity [(4-10) 1]. The diastereomeric sulfinates were separated either by crystallization or by column chromatography. Two arene- and two alkanesulfinates were prepared optically pure by the reported method (Scheme 18). The major isomer of the methanesulfinate was used in the synthesis of o.p. (R) methyl p-tolyl sulfoxide 62 in 76% yield, while the p-toluenesulfinate was used to obtain the (S)-p-phenoxyphenyl p-tolyl sulfoxide 63 in 70% yield. 

Oxidations by oxygen and catalysts are used for the conversion of alkanes into alcohols, ketones, or acids [54]-, for the epoxidation of alkenes [43, for the formation of alkenyl hydroperoxides [22] for the conversion of terminal alkenes into methyl ketones [60, 65] for the coupling of terminal acetylenes [2, 59, 66] for the oxidation of aromatic compounds to quinones [3] or carboxylic acids [65] for the dehydrogenation of alcohols to aldehydes [4, 55, 56] or ketones [56, 57, 62, 70] for the conversion of alcohols [56, 69], aldehydes [5, 6, 63], and ketones [52, 67] into carboxylic acids and for the oxidation of primary amines to nitriles [64], of thiols to disulfides [9] or sulfonic acids [53], of sulfoxides to sulfones [70], and of alkyl dichloroboranes to alkyl hydroperoxides [57]. 

Perfluorodecalin has been used in aerial oxidations catalyzed by transition metal complexes," e.g., aromatic aldehydes to aroic acids, sulfides to sulfoxides, alkenes to epoxides. The mild conditions for oxidation of alkanes to ethers with the (Ph,P),PdBr,-NaOMe-0, are valuable. 

Photochemical sulfochlorination of saturated hydrocarbons has been used in the production of long-chain alkanesulfonyl chlorides, again as precursors to the salts as surfactants. These processes involve free radical intermediates. Analogous to the sulfoxidation of long-chain alkanes, these processes also provide mixtures of alkanesulfonyl chloride and chloroalkane products. Nonetheless, pure products can be obtained for short C1-C3 alkyl chain lengths. A high-pressure gas phase process for the reaction of CH4 with CI2 and excess SO2 is used in one commercial manufacturing route to... 

The applications reported for polymer-supported, soluble oxidation catalysts are the use of poly(vinylbenzyl)trimethylammonium chloride for the autooxidation of 2,6-di-tert-butylphenol [8], of copper polyaniline nanocomposites for the Wacker oxidation reaction [9], of cationic polymers containing cobalt(II) phthalocyanate for the autooxidation of 2-mercaptoethanol [10] and oxidation of olefins [11], of polymer-bound phthalocyanines for oxidative decomposition of polychlorophenols [12], and of a norbornene-based polymer with polymer-fixed manganese(IV) complexes for the catalytic oxidation of alkanes [13], Noncatalytic processes can also be found, such as the use of soluble polystyrene-based sulfoxide reagents for Swern oxidation [14], The reactions listed above will be described in more detail in the following paragraphs. 

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