THE CATALYTIC ACTION OF IODINE IN SULPHONATION. 1405 CLllI.-The Catalytic Action of Iodine in Sulphonation. Part r. By J~ANEKDRA NATH RAY and MANIK LAL DEY. THE present investigation was undertaken with the view of ascer-taining whether the addition of a trace of iodine to sulphuric acid (D 1.84) facilitates the sulphonation of aromatic compounds (com-pare Heinemann Brit. Pat. 12260 of 1915). It has been found that ordinary sulphuric acid and a trace of iodine can advan-tageonsly be used in place of fuming sulphuric acid with o r witthout the addition of phosphoric olxide et'c. The nature of the product is changed in certain cases, thus making ela,sy the preparation of some of the acids difficult to obtain. The catalytic sulphonation is facilitated by the presence of an amino- hydroxy- or halogen group in the molecule but proceeds with less ease in the case of carboxylic acids and is inhibited in the case of nitro-compounds.This fact probably explains the non-formation of disulphonic acids in the product. It is significant that there is an optimum tempera-ture for each reaction in which maximum transformation takes place. It has also been noticed that there is some liberation of iodine vapour but no trace of sulphur dioxide or hydrogen iodide could be detected in the space above the reaction mixture. The discrepancy between the actual yield and that theoretically possible was accounted for in nearly all cases by the unchanged original material. EXPERIMENTAL. I n the experiments to be described below the general method of work was to heat a mixture of a few grams of the substance and the calculated quantity or an excess of sulphuric acid (D 1-84) together with a trace of iodine for a few hours a t the temperature determined by trial a t which the transformation was greatest.The product was poured into water the free sulphuric acid removed with barium carbonate or hydroxide and the acid liberated from the filtrate by exactly neutralising with sulphuric acid. The solution of the free acid was concentrated whereupon it was obtained in a crystalline condition. I n some cases the product was poured into a saturated solution of potassium chloride when the potassium salt separated in fine crystals (0-nitrophenol etc.). The acid or the potassium salt was converted by the usual method into the sulphonyl chloride 1406 T H ~ CATALYTIC ACTION OF IODINE IN SULPHONATION.from which the amide mercaptan etc. were prepared in order to characterise it. Some of the sulphonic acids described gave colour reactions with ferric chloride and characteristic salts with heavy metals. When the acid could not be satisfactorily identified it was transformed through its amino- or nitro-groups etc. into the corresponding hydroxy- or amido-compounds etc. in order to establish its constitution. I n some cases it was found convenient to extract the sulphonic acid from the sulphonated mass with alcohol (0-toluidine). The results obtained from the fusion of the products with potassium hydroxide were not taken into account unless sub-stantiated by further evidence.Sulphonation of Benzoic Acid. A mixture of 12 grams of benzoic acid 9 C.C. of sulphuric acid, and a small cryst'al of iodine' was heated a t 175-180O for aboutl six hours at the end of which time no free benzoic a,cid separated on diluting a sample,. The1 liquid after cooling was poured into watelr, when a clelar solutioln was obtaineld. T'hs solution was neutrdised with barium carbolnatel the precipitated barium sulphate filtered off, and the1 filtrate exactly iieluttraliseld with dilute sulphuric acid. After filtering the liquid was concentrated to a syrup and on keeping in a desiccator crystals were obtained which were Grained washed with a small quantity of alcohol and dried over sulphuric acid in a vacuum. The anhydrous crystals melted at 134-135O (uncorr.), and were very hygroscopic.A test experiment was conducted side by side with the above in which no iodine was used; almost the whole of the bexizoic acid was recovered unchanged. The crystals in aqueous solution gave .a reddish-brown coloration with ferric chloride but no precipitate and were identified as o-sulphobenzoic acid by the formation of salicylic acid when fused with potassium hydroxide a t a moderately low temperature (Found S=15*0. I n the above experiment about a gram of benzoic acid sublimed away and was thus not sulphonated. The following table gives a resume of the results obtained with other substances : Calc. for acid +lH,O S=14.57 per cent.) THE RESOLUTION OF THE KETO-D~LACTONE ETC. 1407 Products by known met hods. Toluene ..........o- and p-acids Benzoic acid ...... rn- and p-acids Phthalic acid . . . . . . -Catechol .......... 3-acid Quinol . . . . . . . . . . mono- and di-sulphonic acids o-Nitrophenol.. . . . . p-acid p-Nitrophenol . . . . o-acid Nitrobenzene . . . . . . m-Dinitrobenzenc . . -o-Nitrotoluene .... p-acid p-Nitrotoluene . . . . o-acid o-Nitroaniline.. . . . . p-acid p-Nitroaniline .... o-acid 3-Nitroaniline . . . . &acid o-Toluidine . . . . . . &acid p . Tolui dine . . . . . . . . Chlorobenzene .... o- and p-acid Bromobenzene . . . . o- and p-acid Subs t aiicc. --By the present, method. p-acid only o-acid no product 4-acid mono-acid p-acid o-acid no product no product p-acid o-acid p-acid o-acid 6-acid 6-acid no product p-acid p-acid Opti- Time mum of re-Yield. temper- action Per cent. ature. Hours. 90-95 100" 1 Above95 175-190 6 - - -75 60-55 1+ 73 70 4 70 50 -70 5 60 50 10 60- 65 -85 85 120 5 100-105 6 - -150 5 140 4 125 44 140 3 150 4$ 150 3 - -110 13 100 3 Summary and Conclusions. (1) Iodine acts as a positive catalyst in sulphonation. (2) Catalysis takes place smoothly when hydroxy- amin* chloro-, bromo- or carboxy-groups are contained in the molecule but with difficulty or not a t all with nitro- or sulphonic substituents. (3) There is an optimum temperature for each substance when the maximum transformation takes place. We have much pleasure in according our best thanks to Sir COLLEGE OF SCIENCE, P. C. RBy for the interest he has taken in the work. UNIVEXSXTY OF CALCUTTA. [Received January 28th 1920.