Sulphinates

One method of preparing sulphlnic acids has already been described (diazo reaction. Section IV,65). Reduction of a sulphonyl chloride with zinc powder and water affords the zinc salt of the sulphinic acid, converted by sodium carbonate to the sodium salt (in which form it is conveniently isolated), and by hydrochloric acid into the somewhat unstable sulphinic acid, for example ... 

Thiophenols (or aryl mercaptans) are obtained by more vigorous reduction of sulphonyl chlorides (or of sulphinic acids), for example with zinc and dilute sulphuric acid, and are isolated by steam distillation ... 

To prepare the free sulphinic acid, dissolve some of the sodium salt in cold water and cautiously acidify with hydrochloric acid avoid an excess of mineral acid since it dissolves the sulphinic acid to a certain extent. The resulting p-tolueneaulphinic acid is difflcult to dry without partial conversion into the sulphonic acid and thiolsulphonic ester... 

Sulphonic acids, sulphinic acids, sulphuric acids, and sul-phonamides... 

The following classes of sulphur compounds occur in Solubility Groups II, III and VII sulphonic acids and derivatives, ArSO,OR sulphinic acids and derivatives, ArSOOR mercaptans, RSH thiophenols, ArSH sulphides or thioethers, RSR disulphides, RSSR sulphoxides, RR S->0 ... 

Sulphinic acids. Aromatic sulphinic acids are found in Solubility Group II. They may be detected by dissolving in cold concentrated sulphuric acid and adding one drop of phenetole or anisole when a blue colour is produced (Smiles s test), due to the formation of a para-substituted aromatic sulphoxide. Thus the reaction with benzenesulphinic acid is ... 

Aromatic sulphinic acids are oxidised by potassium permanganate.to sulphonio acids and are reduced by zinc and hydrochloric acid to thiophenols. 

XI XI, 1st 1928 1505-1591 Other Acids. Sulphinic acids Benzenesulphinic acid. 

Notes, (a) Commercial p-toluenesulphinic acid sodium salt was dissolved in water and acidified with dilute sulphuric acid. The precipitated sulphinic lacid was filtered off and dried at 20 C/0.1 mmHg. 

TMSOTf, 111-12.119,122-3,139 p-Toluene-sulphinic acid, 16 Transannular bromodesilyladon, 15 Transmetallation, 10 Tributytin methoxide, 115 Trichlorosilane, 9,10,58 ( )-l-Trichlorosilylhex-l-ene, 9 Tridcca-l,2-dienc, 69... 

The polarography of sulphones has been fairly extensively studied, sometimes with an analytical bias and sometimes with more theoretical interest. It is generally accepted that a two-electron reduction takes place, to sulphinate ... 

D. Reaction of Organometallic Compounds with Sulphinic Add Derivatives 258... 

Detailed study of the reaction of methyl benzenesulphinate 97 and two cyclic sulphinates 98 and 99 with a number of Grignard reagents was carried out by Harpp and coworkers159. 

As an extension of the reaction of sulphinates with organometallic compounds, the Claisen-type condensation between ketone enolate anions 101 and arenesulphinates may be considered. It was found161,162 that this reaction provides an interesting synthetic approach to a-ketosulphoxides 102 (equation 54 Table 9). 

I. Cycloaddition of Sulphur Monoxide and Sulphines to Unsaturated Compounds... 

Due to the presence of a heterocumulene unit, sulphines may be considered as a group of compounds which are able to undergo cycloaddition reactions. Reaction of sulphines with enamines and phosphorus ylides reported by Sheppard217 and Trippett218 and their coworkers may be considered formally as an example of [2 + 2] cycloaddition. In fact, Sheppard and Dickman217 obtained a 1 1 adduct from thiofluorenone S-oxide and 1-morpholinocyclohexene to which they assigned the dipolar sulphoxide structure 168. 

Phenylsulphine prepared in situ from phenylmethanesulphinyl chloride and triethyl-amine reacted with 1 -morpholinocyclohexene to form the addition product 169 having the enamine structure218. A similar experiment with phenylsulphine and 2-pyrrolidinocyclo-hexene gave only 2-phenylmethanesulphinyl cyclohexanone 170. The latter is most probably formed by hydrolysis of the corresponding enamine sulphoxide upon isolation. The reaction of sulphines with enamines is apparently a stepwise process involving the transient formation of the dipolar intermediate 171 which is stabilized by proton transfer, giving the enamine sulphoxide. 

The synthesis of chiral dialkyl sulphoxides of high optical purity from dia-stereoisomeric alkanesulphinates has a serious limitation because the sulphinates are not... 

Further utility of the Andersen sulphoxides synthesis is demonstrated by the preparation of optically active unsaturated sulphoxides which were first prepared by Stirling and coworkers359 from sulphinate 276 and the appropriate vinylic Grignard reagents. Later on, Posner and Tang360 prepared in a similar way a series of ( )-l-alkenyl p-tolyl sulphoxides. Posner s group accomplished also the synthesis of (+)-(S)-2-(p-tolylsulphinyl)-2-cyclopentenone 287, which is a key compound in the chiral synthesis of various natural products361 (equation 159). 

Optically active sulphoxides 311 and 312 have been prepared stereospecifically either by hydrolysis of the optically active sulphonium salt 313 or by the reaction of p-tolyl magnesium bromide with optically active sulphinate 314, respectively377 (equations 167 and 168). 

Thus, the enantiomeric contents in a pair of sulphoxides can be determined by the NMR chemical shifts in the methine or methylene protons in the two diastereomeric complexes which are stabilized by the hydrogen bond between the hydroxyl and the sulphinyl groups147-151 (Scheme 13). Similarly, the enantiomeric purity and absolute configurations of chiral sulphinate ester can be determined by measuring the H NMR shifts in the presence of the optically active alcohols152. 

The interaction of sulphones with other electrophiles—formation of sulphoxides and sulphinates... 

Truce also examined a few examples of the cleavage of sulphones with sodium in liquid ammonia97 and found essentially similar results except that diaryl sulphones were reduced to sulphinate salts instead of to arylthiolates as with the lithium reductions. Dialkyl sulphones were unreactive towards sodium in liquid ammonia. 

Relatively few reports have been published subsequently on the use of these reagents. Hope and coworkers99 have used sodium in liquid ammonia to cleave the benzyl sulphonyl derivatives of cysteamine, L-cysteine and L-homocysteine to prepare the corresponding sulphinic acids, as in equation (42). 

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