STEWART AROMATIU SULPHONYL CHLORIDES. 2555 CCCV1.-Aromatic Sulphonyl Chlorides. By JESSIE STEWART. DURING an investigation of certain properties of aromatic disulphides some difficulty was met in obtaining these substances in a pure condition and in sufficient quantity. Undoubtedly the best method of preparation is by reduction of the corresponding sulphonyl chlorides but the usual method of obtaining these substances from the sulphonates by interaction with phosphorus pentachloride is somewhat troublesome when applied to large quantities and does not always yield a pure product whilst thionyl chloride which in some cases gives excellent yields of pure material is not always applicable. Other drawbacks to the use of phosphorus penta-chloride are illustrated by the case of m-sulphobenzoic acid.This yields the dichloride which requires partial hydrolysis before reduction to the thiol derivative can be advantageously effected. I n this case it was found (T. 1921 119 1792) that the required chlorosulphonyl derivative could be readily obtained from benzoic acid by reaction with chlorosulphonic acid. It therefore seemed desirable to apply this process to other disulphides and sulphinic acids which were required. Several cases of the use of chloro-sulphonic acid in preparing aromatic sulphonyl chlorides are recorded in literature; in some of these the isolated sulphonate or sulphonic acid was treated with the reagent whilst in others the sulphonyl chloride was directly obtained by reaction of the aromatic com-pound with chlorosulphonic acid.Without attempting quite completely to enumerate the cases recorded the following may be mentioned to illustrate the scope of the material submitted to this reagent. Thus benzenesulphonyl chloride (Ber. 1909 42 1802, 2057) the toluenesulphonyl chlorides (Harding T. 1921,119,1261), m-nitrobenzenesulphonyl chloride (D.R.-P. 89997 1896) o-nitro-phenol-p-sulphonyl chloride (2. angew. Chem. 1920 33 S) tetra-hydronaphthalenesulphonyl chloride (D.R. -P. 336615 192 1 ) and veratrolesulphonyl chloride (Brown and Robinson T. 1917 111, 953) have been obtained by this process and except in the case of benzenesulphonyl chloride the yield and quality of the product appear to have been excellent. These isolated examples seemed to indicate the possibility of a more general application of the reagent.The experiments now described were undertaken for the purpose of this extension with the ultimate object of finding satisfactory methods for the preparation of disulphides and sulphinic acids which are otherwise not easily obtained in quantity. I n the majority of the cases studied the results have been entirely satisfactory 2556 STEWART AROMATIC SULPHONYL CHLORIDES. The mechanism of the formation of the sulphonyl chlorides by this inethod has been fully discussed by Harding (Zoc. cit.) in the case of the toluene derivatives; the observations made in the progress of the experiments now described support his conclusion that these substances are formed in a secondary reaction of the sulphonic acid with excess of chlorosulphonic acid the complete process being represented as follows : (i) ArH + S0,HCl = Ar*SO,H + HC1.(ii) Ar*SO,H + S0,HCl = Ar*SO,Cl + H,SO,. In the cxperirnental part of this paper the preparation of sulphonyl chlorides from p-dichlorobenzene acetanilide salicylic acid p-tolyl methyl ether cinnamic acid and phenylacetic acid is described. I n the case of p-dichlorobenzene the constitution of the sulphonyl chloride and of the corresponding disulphide is evident. The derivative obtained from acetanilide was the p-sulphonyl chloride, for the substance was identical with that obtained by the action of phosphorus pentachloride on sodium acetanilide-p-sulphonate (Schroeter Ber. 1899 39 1566) and yielded on reduction the characteristic 4 4'-dithioacetanilide which exists in two isomeric forms (Hinsberg Ber.1906 39 2429); both these were isolated. O*CH OH ' OH (1. ) (11.) (111.) p-Tolyl methyl ether yielded a sulphonyl chloride of the consti-tution (I); this follows from the facts that it is identical with the Bubstance obtained from the sulphonic acid of the given structure and yields a sulphonic acid which is the same as that obtained from the amino-derivative by Gattermann's method (Ber. 1899 39, 1139). The structure of the sulphonyl chloride yielded by salicylic acid was also determined. As might be expected it is identical with the chloride obtained from sulphosalicylic acid but the structure of the latter seems by no means firmly established. The method planned by Hirsch (Ber. 1900 33 3238) for determining the orientation of the sulphonic group was not successful but the substance is commonly referred to in literature as 5-sulphosalicylic acid.There is no reason to doubt this structure and it has now been proved to be correct for the sulphinic acid (111) obtained from 5-aminosalicylic acid by Gattermann's process is identical with that formed from the chloroaulphonyhalicylic acid (11) by reduction with sodium sulphite. The corresponding dkulphide is readily obtaine STEWART AROMATIC SULPHONYL CHLORIDES. 2557 from the sulphonyl chloride by the usual methods. It has been stated that a substance of this character is formed by interaetioh of sulphur chloride and salicylic acid (D.R.-P. 46413 lSSS) But the product of this reaction is amorphous and appears not to be the same as the 5 5'-disulphide now obtained.It is worthy of notice that this disulphide like m-dithiobenzoic acid (T. 1921,119 1793), is rcsolved by aqueous alkali hydroxide giving the mercaptan (IV). The alkaline solution when treated with methyl sulphate yields 5-methylthiolsalicylic acid (V). OH OH <C:CH-CO2H (yo" ()CO,H \/ SH SCH w.1 (V- ) \/ 80,Cl Cinnamic acid yields the p-chlorosulphonyl derivative (VI) ; this was identified by oxidation of the corresponding sulphonamide, when p-sulphaminobenzoic acid was obtained. Search for the o-chlorosulphonyl derivative in the product was made by reduction to the thiol. Friedlander has shown (Ber. 1913 46 1003) that thionaphthen is readily formed from o-thiolcinnamic acid by oxida-tion with alkaline ferricyanide; and since this substance is very easily detected the reaction was applied to the crude thiol obtained by reduction of the chlorosulphonyl compound but no thionaph-then was encountered.I t is therefore evident that the o-sulphonyl chloride is not iorined to any appreciable extent during the process of sulphonation under the conditions adopted. Phenylacetic acid is readily attacked by cold chlorosulphonic acid but the isolation of the chlorosulphonyl derivative proved difficult since the sub-stance is somewhat easily attacked by ice-cold water. There is little doubt that the least soluble portion of the product is the para-derivative; but the quantity available was not sufficient to permit this to be determined or to allow investigation of the more soluble portion.The few examples now described together with those previously recorded are sufficient to show the advantage of the method; more recent experiments have shown that it may be applied to derivatives of acetanilide from which the aminosul-phinic acids and the divulphides may thus be satisfactorily obtained. E x P E R I M E N T A L. 2 Ei-Dichloroben~eneff.zIlp~on?/l chloride C,H,Cl2~SO,C1.-A mixture of p-dichlorobenzene with chlorosulphonic acid (o mols.) was heated a t 150" for one hour. The cooled liquid was poured over crushed ice when the required chlorosulphonyl derivative separated in th 2558 STEWART AROMATIC SULPHONYL CHLORIDES. solid state. The yield of crude material was 85 per cent. of that required by theory. After recrystallisation from cold alcohol the substance was obtained in colourless needles which melted a t 39" (Found S = 13.0; C1 = 43.2.Calc. S =5 13.0; C1 = 43.4 per cent.). The corresponding amide prepared in the usual manner, melted after recrystallisation from hot water a t 181" ; Holleman (Rec. trav. chim. 1911,30 331) gives m. p. 185-186". 2 5 2' 5'-Tetrachlorodiphenyl disulphide was prepared by re-duction of the chloride with zinc dust in boiling acetic and hydro-chloric acids. After three hours the filtered liquid was cooled the zinc derivative of the mercaptan which was then precipitated was collected and decomposed with a mixture of alcohol and hydro-chloric acid and ferric chloride added the required disulphide being obtained in the crystalline state. The substance separated from warm alcohol in colourless needles which melted a t 81-82" (Found C = 40.1 ; H = 1.9; S = 18.0.Calc. C = 40.4; H = 1.7; S = 17-97 per cent.). Acetanilide-p-sulphonyl Chloride NHAc*C,H,*SO,Cl.-A solution of acetanilide in chlorosulphonic acid (5 niols.) was kept a t 60" for two hours. The crude product which formed about 85 per cent. of the theoretical amount was isolated in the usual manner. After recrystallisation from benzene it was obtained in colourless needles which melted a t 149" (Found C1= 15-1 ; S = 13.9; N -- 6.0. Calc. C1 = 15.2; S = 13.7; K = 6.0 per cent.). When this substance was treated with zinc dust in boiling acetic acid the zinc derivative of 4-thiolacetanilide was obtained from which the corresponding 4 4'-dithioacetanilide was prepared in the usual manner.This substance melted at 182" (Found S = 19.2; N = 8.7. Calc. S = 19.3; N = 8.4 per cent.) and was evidently the a-isomeride ; when it was kept a t the atmospheric temperature, the F-isomeride of melting point 213-214" was formed (compare Hinsberg Zoc. cit.). 3-ChZorosuZphonyl-p-tolyl Methyl Ether (I) .-One volume of p-tolyl methyl ether was slowly added to chlorosulphonic acid (5 vols.) a t 0" and the solution poured over crushed ice when an almost theoretical yield of the required chlorosulphonyl derivative separated in the solid condition. When dry the crude material melted at 79-81" and after recrystallisation from alcohol it was obtained in colourless needles which melted at 84" (Found C1 = 15.9; S = 14.7.Calc. C1 = 16.1 ; S = 14.5 per cent.). This material and the amide prepared from it (m. p. 183") were identical with the Corresponding substances prepared from 3-sulpho-p-tolyl methyl ether. 4 4'-Dimethoxydi-m-toZpZ Disulphide (OMe*C,H,Me),S,.-Th STEWART SROMATIC SULPHONYL CHLORIDES. 2559 corresponding mercaptan which was prepared by reduction of the chlorosulphonyl derivative was oxidised by treatment with ferric chloride Thc disulphide after recrystallisation from alcohol, was obtained in pale yellow prisms which melted at 67" (Found : C = 62.3; H = 6.1 ; S = 21.3. C,,H,,O,S requires C = 62.7; H = 5.9; S = 20.9 per cent.). 5-Chlorosu~phor'ylstrlicylic Acid (111) .--Salicylic acid was gradually added to cooled chlorosulphonic acid (5 mols.) the solution kept a t 75" for one hour and the solid chlorosulphonyl derivative isolated in the usual manner particular care being taken to avoid rise of temperature during the decomposition with ice and to remove the material from contact with water as soon as possible.With these precautions the yield was about 60 per cent. of the theoretical but otherwise considerable loss may arise from hydrolysis of the product. 5-Chlorosulphonylsalicylic acid separates from benzene in colourless prisms which melt a t 169-171" (Found C1 = 14.8; S = 13.8. Calc. C1 = 15.0; S = 13.5 per cent.). The same substance was readily obtained from sulphosalicylic acid by treatment with chlorosulphonic acid. 5-Xulphinoaalicylic acid (111) was prepared by two methods. 5-Aminosalicylic acid was converted in aqueous solution to the corresponding diazonium derivative.This was treated with an excess of sulphurous acid in presence of copper powder the latter removed and the required sulphinic acid extracted from the aqueous solution with ether. After purification thc product melted a t 159" and was identical with that obtained by reduction of the chlorosulphonyl derivative. The yields of sulphinic acid from this process were very poor ; but the substance is easily obtained by the following process. Five grams of chlorosulphonylsalicylic acid were gradually added with shaking to an aqueous solution of 20 grams of sodium sulphite, sodium hydroxide being added if necessary to maintain alkalinity. Subsequently excess of dilute sulphuric acid was added and the liberated sulphinic acid removed by solution in ether.The yield of crude material was 3.6 grams. The substance was purified by recrystallisation from ether when it was obtained in colourless needles which melted a t 159" (Found C = 41.4; H = 3.1 ; S = 15.9. Calc. C = 41.6; H = 3.0; S = 15-8 per cent.). This sulphinic acid is readily soluble in cold water; when mixed with phenetole in sulphuric acid it gave the characteristic blue solution. 5 5'-Dithiosalic?/lic dcid.-Thirty grams of zinc dust and 100 C.C. of concentrated hydrochloric acid were gradually added with shaking to an alcoholic solution of 20 grams of 5-chlorosulphonyl-salicylic acid. When reduction was complete the excess of zin dust was removed and the clear liquid treated with solid ferric chloride care being taken that suflicient hydrochloric acid was present to prevent the formation of the purple iron salt.Partial separation of the required disulphide took place immediately but this was completed by the careful addition of water. The yield of the crude material was about 78 per cent. of the theoretical. To purify the product it was first treated with aqueous sodium car-bonate when some ester which had been formed during the treat-ment in alcohol remained insoluble. The disulphide was recovered from the solution and then recrystallised from a mixture of alcohol and water when it was obtained as a pale yellow crystalline powder, which nielted at 236" (Found C = 49.4; H = 3.2; S = 18.8. Calc. C = 40.7; H = 3.0 S 5-Thiolsalicylic a.cid (IV) was prepared by reduction of the disulphide with glucose according to the method of Claasz (Ber., 1912 45 2424).The mercaptan was set free from the alkaline mixture with dilute sulphuric acid and recrystallised from hot water. It formed small pale yellow needles which melted a t 150-152" and were converted to the disulphide by mild oxidising agents. The same substance may be prepared by hydrolysis of the disulphide with alkali hydroxide. The latter substance was treated with boiling fl-scdium hydroxide (8 mols.) for half an hour ; the mercaptan was preeipitatod in the crystalline state when excess of dilute sulphuric acid was added to the alkaline solution. 5- Methylthiolsalicylic Acid (V).-A solution of 10 grams of the clisulphide in excess of N-sodium hydroxide was boiled for half an hour cooled and shaken with 6 C.C.of methyl sulphate. On adding excess of mineral acid to the clear solution 7.2 grains of 5-methyl-thiolsalicylic acid wcre liberated. This was recrystallised from hot , water and thus obtained as a pale buff' crystalline powder which melted a t 126" (Found C = 52.3; H = 4.2; S = 17.7. Calc., C = 52.2; H = 4.3; S = 17.4 per cent.). It is evident that the methylthiol group is present in this substance since it was not converted to a disulphide by ferric chloride. Moreover methylation of the hydroxyl under these conditions can scarcely be expected when the difficulty experienced by Graebe (Annalen 1905,340,204) in methylating salicylic acid is recalled. 4-C'hEorosulphon~Ecinnamic Acid (VI).-A solution of cinnamic acid in chlorosulphonic acid (about 8 mols.) was kept a t 50-60" for half an hour.The product.was isolated in the usual manner and after recrystallisation from acetic acid 4-chlorosulphonyl-cinnamic acid was obtained in colourless needles which melted and decomposed a t 226" (Found C1 = 14.3 ; S = 12-8. Calc. C1 = 14.4 ; S = 13.0 per cent.). 4-Sulphaminocinnamic acid was obtained 18.9 per centl.) LIMITS FOR THE PROPAGATION OF FLAME ETC. 2561 in the usual manner from the chloride; it formed colourless prisms which decomposed between 250-260" according to the rate of heating (compare Palmer Amer. Chem. J. 1882 4 163) (Found : S == 14.1; N = 6.2. Calc. S = 14.1; N = 6.2 per cent.). This sulphonamide was oxidised by chromic acid in presence of warm dilute sulphuric acid.On cooling the reaction mixture after oxidation was complete the product separated in the crystalline state. After being purified the substance decomposed a t about 280" (Found : S = 15.9; N = 7.1. Calc. S = 15.9; N = 6.9 per cent.). This behaviour agrees with that assigned to 4-sulphaminobenzoic acid by Palmer (Zoc. cit.); moreover the meta-komericle melts a t 233", whilst the ortho-derivative melts indefinitely a t a lower temperature than either of these and loses water. ChZorosuZphonyZphenyZacetic Acid MO,C*CH,*C,HQ*SO,C1.-Phenylacetic acid was gradually added to cooled clilorosulphonic acid (5 mols.). Reaction mas immediate and after the lapse of a few minutes the solution was poured over crushed ice and the solid product isolated from moisture as rapidly as possible. The maxiilium yield obtained was about 35 per cent. of the theoretical. After recrystallisation from benzene in which it was readily soluble the chlorosulphonyl derivative was obtained in colourless prisms which melted a t 136" (Found C1 = 15.1; S = 13.6. Calc. C1 = 15.1; S = 13.6 per cent.). The corresponding ainide is readily soluble in water ; it separates from this solvent in shining plates which melt a t 176". I wish to express my thanks to Professor Smiles for his advice and for the interest he has taken in the work recorded above. KING'S COLLE(XE AND UNIVERSITY COLLEGE, LONDON. [Received October 3nd 1922.