Aliphatic sulfinic acids

The acidity of sulfinic acids is quite substantial. Benzenesulfinic acid has a pAg-value of 1.2 in water (Ritchie et al., 1961). Aliphatic sulfinic acids are somewhat weaker (p/fa = 2.2-2.3) (Rumpf and Sadet, 1958 Wudl et al., 1967). For the ionization of a series of arenesulfinic acids ArS02H in water pis +0.97 (Ritchie et al., 1961). 

Aliphatic sulfinic acids (1) are much less stable than the aromatic derivatives sulfinic acids decompose on heating (30-100°C) into the corresponding thiol sulfonates (3) and sulfonic acids (4) (Scheme 3). Alphatic sulfinic acids can be oxidised or reduced. Oxidation,... 

There are many parallels between phosphates and sulfates of aliphatic alcohols. Both types of surfactants contain ester bonds undergoing hydrolysis in acid solutions. In that case the starting materials are received once more. By dry heating of the salts above a temperature of 140°C destruction will occur forming the corresponding alkenes and an inorganic acid salt. In the same way as sulfonic and sulfinic acids are formed by C-S bonds, C-P bonds lead to phosphonic and phosphinic acids. 

A third method of access to sulfines is the oxidation of thiocarbonyl compounds. When the starting material is available it is an attractive route. There has been some dispute in the past whether enethiolisable thiocarbonyl derivatives would lead to the corresponding sulfines or to divinyl disulfides [101, 102]. It is now clear from our research that, even if the C=S molecules bear highly acidic a-protons, oxidation occurs on C=S and does not touch the a-protons. There are many examples of this behaviour. The most easily enethiolised compounds are thioketones. We have shown that their reaction with a peroxycarboxylic acid, mCPBA, is very fast at 0°C and quantitatively provides the corresponding sulfines [103]. In many examples the aliphatic sulfines are not very stable and have to be used in subsequent reactions that will be faster than their decomposition (t1/2 from some hours to days). 

Zwanenburg and his group [105] have addressed the question of the tautomeric interconversion of aliphatic sulfines into vinyl sulfenic acids. They have synthesised dithioesters bearing an a asymmetric carbon centre. Oxidation with mCPBA did produce chiral sulfines, which did not racemise except when a phenyl group was attached to the a carbon. 

Alkyl iodides. Although this mixture reduces arsenesulfonic acids, it converts aliphatic sulfonic acids,1 sulfinic acids, thiols, sulfonates, and disulfides to alkyl iodides in 70-100% yield.2... 

Finally mixing of aliphatic or aromatic nitroso compounds with benzene sulfinic acid leads immediately to formation of benzene-sulfonylaminyloxides75. Aminyl-oxide anion 62 was detected when nitrosobenzene was allowed to react with aqueous hydrogensulfite in presence of lead dioxide76. With nitroso trifluoromethane radical 63 was formed. With tetraphenylarsonium cation this radical anion even formed a solid, paramagnetic precipitate77. ... 

Saturated aliphatic hydrocarbons undergo this reaction most satisfactorily under pressure and at elevated temperatures,238 but alkenes give sulfinic acids even at atmospheric pressure.239... 

When fused with sodium hydroxide aromatic sulfonic acids are converted to corresponding phenols with the simultaneous formation of sodium sulfite. Sulfinic acids and sulfones react in a similar manner. The presence of these groups in the original sample can be detected on the basis of the evolution of sulfur dioxide after the acidification of the melt [this reaction is also given by aliphatic sulfonic acids (23)], or by detecting phenols in the melt, using some of the known reactions. The phenol may also be identified paper chromatographically (24). 

Sulfinic acids are generally unstable compounds (especially aliphatic ones), and they can be identified either as phenylhydrazine salts (58), or, better, by alkylation of their sodium salts with methyl iodide, during which sulfones are formed (59). 

A general way to achieve thiophilic addition is to use sulfines [149]. The sulfur atom of thiocarbonyl oxides is selectively attacked by carbanions. We have applied this property to aliphatic dithioester oxides and shown [150] that, despite the probably high acidity of the a-protons, thiophilic addition of alkyllithiums is observed, leading to stabilised carbanions. After treatment with electrophiles, dithioacetal oxides were obtained. From a synthetic point of view, it is worthy of note that these adducts are much more easily... 

A simple method of preparing sulfinic esters consists of oxidative chlorination of aliphatic thiols, thiophenols, or disulfides with chlorine in glacial acetic acid, followed by alcoholysis of the resulting sulfinyl chlorides 626... 

Both aromatic and aliphatic sulfonyl halides react with the iridium(I) complex (XI) to form octahedral S-bonded sulfinate derivatives such as (XLIX) 3S), These are characterized by intense infrared stretching frequencies centered near 1235 and 1065 cm , reminiscent of sulfones. The low frequencies of these absorptions suggest that the S-bonded sulfinate group is a strong ar-acid. Certain of the aromatic sulfinates eliminate SO2 upon heating, yielding iridium(III) aryls such as (L) 38). The scope of this gas-forming elimination reaction is uncertain. 

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