79s KRISHNA AND POPE: THE ACTION OF POTASSIUM

LXXX1X.-The Action of Potassium Iodide and Iodate on some Hydroxy-acids.

By SRI KRISHNA and FRANK GEORGE POPE. DURING the course of some work, Kux's method of estimating carboxyl (2. anal. Chem., 1893, 32, 129) was applied to the case of salicylic acid and it was found that the amount of iodine liberated fell much below the quantity demanded by the equation 6R*C02H + 5KI + KIO, = GR*CO,K + 31, + 3H20, whilst a white or slightly coloured precipitate separated from the reaction mixture. The reaction was consequently further examined in the case of salicylic acid and some other aromatic hydroxy-acids.

The method of procedure adopted consisted in adding a warm (50-80") solution of the acid in small portions a t a time t o a warm aqueous solution of the iodide and iodate (in the proportions demanded by the above equation) and digesting the mixture on the water-bath for some time (usually about twenty minutes). During the addition process a considerable amount of iodine was liberated and in many cases carbon dioxide was apparently simultaneously evolved. After standing for the above time, it was found that the free iodine present had practically disappeared and that a faintly coloured precipitate had formed. This was collected, washed, recrystallised from a suitable solvent (usually benzene), and then further examined.

The reaction has been examined in the case of salicylic acid, p-hydroxybenzoic acid, 3- and 5-nitrosalicylic acids, and 3 : 5- dinitrosalicylic acid, and it has been found that in each case the carboxyl group has been eliminated and the corresponding tri- iodophenol produced ; thus bringing the reaction into agreement with known cases, for it is well known that under certain experi- mental conditions halogens can replace the acidic groups in aromatic acids. Instances of this may be seen in the work of Datta and Bhowmik ( J . Amer. Chem. Xoc., 1921, 43, 303), who have shown that chlorine replaces the sulpho-group in sulphonic acids with simultaneous formation of chloro-derivatives, whilst Pope and Wood (T., 1912, 101, 1827) showed that on brominating p-hydroxy- benzoic acid in the presence of sulphuric acid some tribromophenol was also obtained.

I n the work of Datta and Bhowmik it was found that the replace- ment of the acid group takes place with ease in the case of chlorine and bromine, but only under special conditions with iodine, further halogen atoms then entering the complex. I n this investigation

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IODIDE AND IODATE ON SOME HYDROXY-ACIDS. 799

we have found that the action of potassium iodide and iodate on the hydroxy-acids was much more rapid than that of potassium bromide and bromate, and still more so than that of potassium chloride and chlorate.

The relative positions of the hydroxyl and carboxyl groups in the simpler acids seem to have no influence on the reaction, since the same product, namely, 2 : 4 : 6-tri-iodophenol is obtained from either salicylic acid or p-hydroxybenzoic acid :

OH OH OH

and the same tri-iodonitrophenol from either 3- or 5-nitrosalicylic acid :

OH OH OH

3 : 5-Dinitrosalicylic acid yields similarly a tri-iododinitrophenol. p-Resorcylic acid apparently reacts in a normal manner, as does o-acetoxybenzoic acid,

The reaction was also extended to anthranilic acid and to acetyl- anthranilic acid, and in these cases direct substitution by iodine appears to take place without elimination of the carboxyl group.

The identity of the products was in most cases determined by observing the mixed melting points obtained with the same com- pound, prepared according to one of the already known methods.

E X P E R I M E N T AL.

Salicylic Acid.-Two grams of salicylic acid were dissolved in 25 C.C. of water, the solution warmed to 50" and added i n small quantities to an aqueous solution of 10 grams of potassium iodide and 2 grams of potassium iodate, also at 50". Iodine was liberated and carbon dioxide evolved. The mixture was kept for twenty minutes on the water-bath, the precipitate collected, kashed, dissolved in a dilute solution of sodium hydroxide, and repre- cipitated by the addition of dilute hydrochloric acid. It was again collected, washed, dried, and finally crystallised from benzene, from which it separated in long, colourless needles melting a t 158" ; it thus appears to be 2 : 4 : 6-tri-iodophenol. A specimen mixed with tri-iodophenol showed no depression of melting point (Found : I = 80.30. Calc., I = 80.72 per cent.).

F F 2

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800 THE ACTION OF POTASSIUM IODIDE AND IODATE, ETC.

p-Hydroxybenxoic acid was treated in exactly the same manner, similar quantities being used. The product obtained was identified as tri-iodophenol.

3-Nitro- and 5-nitro-salicylic acids, by the same method of treat- ment, gave a precipitate of fine, red needles of the potassium salt of a tri-iodonitrophenol. This was collected, dissolved in water, and decomposed by hydrochloric acid. The phenol obtained was recrystallised from benzene, from which it separated in shining, yellow plates melting a t 148". From the analytical data obtained it would appear to be a tri-iodonitrophenol, possibly 2 : 5 : 6-tri- iodo-3-nitrophenol (Found : I = 73.44; N = 2.92. Calc., I = 73-69; N = 2-70 per cent.).

3 : 5-Dinitrosalicylic acid, by a similar process, deposited red needles of the potassium salt of a tri-iododinitrophenol. The salt was dissolved in water, and on acidification of the solution the phenol was obtained. It was recrystallised from benzene (or toluene) and separated in glistening plates which melted at 165" (Found : I = 67-42 ; N = 4.74. Calc., I = 67-79 ; N = 4-98 per cent.).

Anthranilic Acid.-Using the same method in the case of anthranilic acid, it was found that the solution remained clear after warming, but on the addition of a few drops of hydrochloric acid a lemon-yellow precipitate was thrown down. This was collected, washed, dried, and recrystallised from benzene, separating from the solvent in needles melting a t 208". It would thus appear to be identical with (P)-3-iodo-2-aminobenzoic acid, melting at 208-209", since no depression of melting point was observed when the two compounds were mixed (Found : I = 48.03 ; N = 5-22. Calc., I = 48.28; N = 5.32 per cent.).

AcetylanthraniEic acid behaves in the same manner, a brown precipitate being obtained on warming the solution. This was collected, washed, dissolved in dilute sodium carbonate solution, and reprecipitated by the addition of hydrochloric acid. The product was collected, dried, and recrystallised from benzene, from which it separated in colourless, shining plates melting at 175". It is apparently an iodoacetylanthranilic acid (Pound : I = 41.40. C,H,O,NI requires I = 41.50 per cent.).

It is hoped to continue the work and to characterise the iodo- phenols obtained. One of us (S.K.) desires to express his thanks to the Committee of Scientific and Industrial Research for a grant that has helped to defray expenses.

(UNIVERSITY OF LONDON). EAST LONDON COLLEGE

[Received, April lst, 1922.1

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