Reduction of sulphonyl chlorides

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 ... 

Polarographic reduction of sulphonyl chlorides is evidently also a two-electron process, yielding sulphinate and chloride. Work in this domain has not been analytical, however. An indirect method for determining aromatic sulphonyl chlorides in DMSO has been based on H+ and/or Cl" waves278. 

The reduction of sulphonyl halides RS02X may occur whatever the (aliphatic or aromatic) nature of the R group. Disturbances may be caused either by the solvent (solvolysis with breaking of the S—X bond) or the electrode (interaction between the sulphonyl halide and the mercury). All presently available data concern exclusively the chloride (X = Cl). 

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 ... 

Reduction of a nitro compound to a primary amine. In a 50 ml. round-bottomed or conical flask fitted with a reflux condenser, place 1 g. of the nitro compound and 2 g. of granulated tin. Measure out 10 ml. of concentrated hydrochloric acid and add it in three equal portions to the mixtiue shake thoroughly after each addition. When the vigorous reaction subsides, heat under reflux on a water bath until the nitro compound has completely reacted (20-30 minutes). Shake the reaction mixture from time to time if the nitro compound appears to be very insoluble, add 5 ml. of alcohol. Cool the reaction mixture, and add 20-40 per cent, sodium hydroxide solution imtil the precipitate of tin hydroxide dissolves. Extract the resulting amine from the cooled solution with ether, and remove the ether by distillation. Examine the residue with regard to its solubility in 5 per cent, hydrochloric acid and its reaction with acetyl chloride or benzene-sulphonyl chloride. 

Amides are the least reactive of the carboxylic acid derivatives, and undergo acid or base hydrolysis to produce the parent carboxylic acids, and reduction to appropriate amines (see Section 4.3.10). They can also be dehydrated to nitriles, most commonly with boiling acetic anhydride, (AcO)20, sulphonyl chloride (SOCI2) or phosphoms oxychloride (POCI3) (see Section 4.3.18). Amines (with one less carbon) are prepared from amides by the treatment of halides (Br2 or CI2) in aqueous NaOH or KOH. This reaction is known as Hofmann rearrangement (see Section 4.3.10). 

Aminobenzenesulphonic acid (orthanilic acid, Expt 6.64) is readily prepared by the reduction of 2-nitrobenzenesulphonic acid. The latter may be prepared by the hydrolysis of the corresponding sulphonyl chloride which is obtained from di-o-nitrophenyl disulphide. The preparation of this disulphide involves the use of the reactive aryl halide, 2-chloronitrobenzene (cf. Expts 6.93... 

The syntheses of the pachysandrines and epipachysandrine-A have been effected starting from the diosphenol (214). Reduction of (214) with sodium borohydride leads to an epimer of terminaline, 3)8,4 -dihydroxy-20a-dimethyl-amino-5a-pregnane (221), which readily forms a mono-tosylate (222) on treatment with toluene-p-sulphonyl chloride in pyridine. On treatment with sodium azide in N-methylpyrrolidone, the mono-tosylate (222) gives the azide (224) with... 

Reduction (LiAlH4) of the pachystermines-A and -B gives the pachystermine-diol (232), which was methylated to (233). Treatment of (232) with methane-sulphonyl chloride in pyridine gives the azetidine (234), characterised by an intense peak at m/e 138 in its mass spectrum. Under the same conditions, (233)... 

Sulphonic acids/sulphonates have been determined by conversion to the sulphonyl chlorides. One method of determining the latter has been by reduction to thiols, e.g. with Zn/HCl159 or by LiAlH/60, followed by GLC. 

The difference of reactivity between neutral and acidic solvents could only lie in the fact that the aromatic sulphonyl chloride is protonated and consequently reduced more easily in its protonated form. A potential shift of about 0.5 V for the main reduction step (Figure 10b) can be observed in the voltammetries. The general Scheme 951 fits the two possible routes according to the acidity of the medium. 

Chlorosulphonation of 4 -chloro-o-acetotoluidine yields the eorresponding sulphonyl chloride derivative whieh on amination forms the sulphonamide derivative. Oxidation of the methyl moiety gives the respeetive anthranilamide derivative whieh on hydrolysis eliminates the acetyl group to yield the substituted anthranilic acid. Fusion of this amino acid with propionamide first gives rise to an intermediate by the loss of a mole of water and ultimately helps in the closure of the ring to generate the quinazoline ring system. Catalytic reduction of this finally produces the official compound. 

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