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SULPHONIC ACIDS

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Originally appearing in Volume V26, Page 61 of the 1911 Encyclopedia Britannica.
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SULPHONIC ACIDS , in organic See also:

chemistry, a See also:group of compounds of the type R•S03H, where R is an alkyl or an aryl group. Aliphatic Sulphonic Acids.—The members of this class may be prepared by the See also:direct sulphonation of some paraffins (I. Worstall, Amer. Chem. Journ., 1898, 20, p. 664) , by the oxidation of See also:mercaptans with concentrated nitric See also:acid (H. See also:Kopp, See also:Ann., 1840, 35, p. 346); in the See also:form of their salts from the alkyl halides and alkaline sulphites, and as See also:esters from the alkyl halides and See also:silver sulphite. They are colourless See also:oils or crystalline solids which are extremely hygroscopic, very soluble in See also:water and have a strongly acid reaction. They are unaffected by See also:heating with aqueous alkalis or acids and are See also:stable towards concentrated nitric acid. See also:Phosphorus pentachloride converts them into the corresponding acid chlorides, R•SO2C1, which are decomposed slowly by water. These chlorides, on reduction by See also:zinc and sulphuric acid, pass readily into the mercaptans, whilst if zinc dust and See also:alcohol be used they are converted into the sulphinic acids, R•S02H.

Methyl sulphonic acid, See also:

CH3•SO3H, was obtained by H. See also:Kolbe (Ann., 1845, 54, p. 174) by reducing trichloromethyl sulphonic chloride (formed from See also:chlorine and See also:carbon bisulphide in the presence of water :CS2+5C12+2H2O=CC13•SO2C1+4HC1+SCl2) with See also:sodium See also:amalgam. It is a colourless See also:syrup which decomposes when heated above 13o° C. The corresponding acid chloride is an extremely stable solid which melts at 135° C. It is formed by the See also:action of carbon bisulphide on See also:potassium bichromate in the presence of nitric and hydrochloric acids (Loew, Zeit. f. Chem., 1869, p. 82). When heated under pressure it decomposes with the final See also:production of carbonyl and thionyl chlorides: CC13•SO2C1=CCla+SO2= COC12+SOC12. See also:Ethyl sulphonic acid, See also:C2H6.SO3H, is a crystalline deliquescent solid formed by oxidizing ethyl mercaptan or by reducing vinyl sulphonic acid, See also:CH2:CH•SO3H (Kohler, Amer. Chem. Journ., 1898, 20, p.

687). Thiosulphonic acids of the type R•SO2•SH are formed by the action of the sulphochlorides on a concentrated See also:

solution of potassium sulphide: R•SO2CI + K2S = R•SO2K+S+KCl=KCI+R•SO2•SK: or by the action of the See also:salt of a sulphinic acid on an alkaline sulphide in the presence of See also:iodine (See also:Otto, Ber., 1891, 24, p. 144). Aromatic Sulphonic Acids.—The acids of this group are very similar to the corresponding aliphatic sulphonic acids and are usually obtained by the direct heating of an aromatic hydro-carbon with concentrated sulphuric acid, fuming sulphuric acid or See also:sulphur chlorhydrin. After the action is completed they may frequently be " salted out " by adding See also:common salt to the acid solution until no more dissolves, when the sodium salt of the acid separates (L. Gattermann, Ber., 1891, 24, p. 2121). They are also formed by oxidizing thiophenols or by decomposing diazonium salts with sulphurous acid. The See also:free acids are usually hygroscopic, crystalline solids which are readily soluble in water. When heated under pressure with concentrated hydrochloric acid to about 15o° C. they yield See also:hydrocarbons and sulphuric acid. The salts usually crystallize well, and those of the See also:alkali metals are employed in the preparation of phenols, into which they pass when fused with the See also:caustic alkalis. When distilled with potassium See also:cyanide they yield the aromatic nitriles.

The sulphonic acids with phosphorus pentachloride are converted into sulphochlorides which are stable to See also:

cold water, but with See also:ammonia they yield sulphonamides, R•S02NH2, and with See also:alcohols esters of the sulphonic acids. See also:Benzene sulphonic acid, See also:C6H5•SO3H,1H2O, crystallizes in small plates and is very deliquescent. Benzene sulphochloride, C6H5-SO2CI, is a colourless fuming liquid which boils at 120° C. (io mm.). The aminobenzene sulphonic acids, particularly the See also:meta and See also:para compounds, are of importance owing to their employment in the See also:colour See also:industry. The direct sulphonation of See also:aniline yields the para acid, sulphanilic acid, See also:C6H4(See also:NH2)(SO3H), which crystallizes in small plates and is sparingly soluble in cold water. When fused with caustic potash it yields aniline, whilst oxidation with chromic acid yields benzoquinone. In constitution it is probably to be regarded /NH3N as a cyclic ammonium salt, C3H4 SO3/. When diazotized in ~ acid solution and coupled with dimethyl aniline it yields helianthine, the sodium salt of which is used as an See also:indicator (q.v.). Metanilic acid See also:C6H,(NH2) (SO2H) [1.3], which crystallizes in prisms, is formed by the reduction of meta-See also:nitrobenzene sulphonic acid and is used In the preparation of various See also:azo dyes. Sulphinic acids, R•S02H, are formed by reducing sulpho= chlorides with zinc dust; by the action of sulphur dioxide on the zinc alkyls (Hobson, Ann, 1857, 102, p. 72; 1858, Io6, p.

287) ; by the action of sulphochlorides on mercaptans in alkaline solution; and by the action of the Grignard reagent on sulphur dioxide or thionyl chloride (See also:

Rosenheim, Ber., 1904, 37, p. 2152; Oddo, R. Accad. Lin., 1905 (5), 14 (i.), p. 169). The free acids are unstable. They are readily oxidized to sulphonic acids and reduced to mercaptans.. Their alkali salts on treatment with the alkyl halides yield sulphones, R2S02. Ethyl sulphinic acid, C2H5•SO2H, is a colourless syrup. Benzene sulphinic acid, C6H5•S02H, crystallizes in large prisms and acts as .a reducing See also:agent. It decomposes when heated with water under pressure: 3C6H5•SO2H=C6H5•S02H+C6H5•S02•S•C6H5+H20. The potassium salt when fused with caustic potash yields benzene and potassium sulphite.

End of Article: SULPHONIC ACIDS

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