98 BENTLEY AND WEIZMANN : IX, -4- Hy d?-oxypht ha1 ic and 4 -Metkoxypk. tlmlic Acids. By \vILLIAlI HENRY BENTLEY and C'HAHLES WEIZMA". -IN connexion with some experiments which we have conducted on derivatives of naphthacenequinone and rhodamines, we had occasion to prepare considerable quantities of 4-hydroxyphthalic acid which was first investigated by Baeyer (Bey., 1877, lo, 1079), who prepared it from 4-aminophthalic acid. According to Baeyer, the acid is obtained quite pure by dissolving the sublimed anhydride in water and allow- ing to crystallise; he gives 180" (about) as the rnelt(ing point of the pure acid and 165-166' for the anhydride.4-HI'DROXYPHTHALIC AND 4-ME'J'HOXYPHTHALIC ACIDS. 99 Graebe (Ber., 1885, 18, 11 30)' who prepared 4-hydroxyphthalic acid by fusing 4-sulphophthalic acid with caustic soda, found 180-183" for the melting point of the acid, and his analysis shows more carbon and hydrogen than corresponds to hydroxyphthalic acid, indicating at once that the material was not pure, whereas Baeyer's analytical data for the acid on the contrary give no such indication.I n order to prepare 4-hy droxyphthalic acid, we fused snlphophthalic acid with caustic soda (Graebe, loc. cit. ; Rke, Annulen, 1886, 233, 232), and greatly to our surprise obtained an acid having all the properties ascribed to 4-hydroxyphthalic acid and giving good figures on analysis, but melting a t 204-205' and yielding an anhydride melting a t 171-173°. In several subsequent experiments we obtained an acid melting a t about 1 SOo, which,, after repeated crystallisations from water, melted a t 186-187" ; the mother liquors, however, on concentration yielded the acid melting a t 204-205".The acid melting a t 186-187" had also the properties ascribed to 4-hydroxyphthalic acid, but analysis, as well as the fact that its anhydride melted indefinitely between 150' and 170' even after being twice crystallised, proced i t to be impure. As we considered the subject of considerable importance we endeavoured to discover $he nature of the impurity in the acid malting at 186-187', and with this object prepared the imide, and, and dimethyl ester from each acid. These derivatives from the acid of higher melting point (204-205") mere easily obtained pure, but from the other acid (m. p. 186-1 87") repeated crystallisation was always necessary, and, finally, the derivatives obtained from each acid mere found to be identical.Moreover, the dimethyl ester from the acid of lower melting point yielded, on hydrolysis with alcoholic potash, the acid melting at the higher temperature. For some time we were unable t o discover the nature of the impurity in the acid melting a t 186-187", but when we endeavoured to prepare pure 4-methoxy- phthalic acid from each acid the results were so strikingly different that the impurity in the former was soon ascertained. 4-Nethoxy- phthalic acid, prepared from hydroxy-acid of higher melting point, was found to melt at about 170° with the formation of the anhydride melting a t 98-99O (Schall, .Bey., 1879, 12, 829, gives 138-144" and 93' respectively).When similar experiments were made with the acid of lower melting point, the product first melted at about 140' (see Schall, Zoc. cit.), and on crystallising from water yielded an acid melting at 108-109°, which on analysis gave numbers agreeing with methoxy- benzoic acid, and which yielded m-hydroxybenzoic acid (M. p. 209') on fusion with caustic potash. The impurity therefore in the acid in question and probably in samples of crude 4-hydroxyphthalic acid obtained by previous investigators is nz-hydroxybenzoic acid. Sub- H 2100 BENTLEY AND WEIZMANN : sequent experiments showed that when the fusion of 4-eulphophthalic acid with alkalis is prolonged or the temperature is too high, m-hydroxy- benzoic acid is always produced, and the crude 4-hpdroxyphthalic acid then always melts at about 180".When, however, the fusion is care- fully conducted, the formation of nz-hydroxybenzoic acid is avoided, and the 4-hydroxyphthalic acid obtained always melts directly at about ZOO". Graebe and Rke (Zoc. cit.) pointed out that m-hydroxybenzoic acid is sometimes found mixed with tho hydroxyphthalic acid produced by their fusion of sulphophthalic acid, but the material which they considered to be pure 4-hydroxyphthalic acid must have still contained m-hydroxybenzoic acid. EXPERIMENTAL. Xu Zpho nation of Ph tha Zic A nh y dy ide. I n a sealed tube or in the autoclave, phthalic anhydride is almost quantitatively sulphonated by heating with fuming sulphuric acid to 200O. I n our experiments me employed a copper autoclave in which a porcelain pot, containing a mixture of phthalic anhydride (300 grams) and fuming (73 per cent.SO,) sulphuric acid (500 grams), was placed. The autoclave was closed and heated to 200" for two to three hours; after cooling, the product, which consisted of a viscid syrup, was poured into water and neutralised with milk of lime. The soluble calcium salt mas extracted with hot water and converted into the sodium salt, the solution of which was then evaporated until crystullisation commenced. 4-Hydroxypht?~aZic Acid.-As soon as the sodium salt of sulpho- phthalic acid commenced to crystallise i t was transferred to a large nickel vessel or to the autoclave, carefully mixed with powdered caustic soda (1200 grams) and heated to 175-180O for three hours. The fused mass was then poured into a large dish, diluted with water, and acidified with hydrochloric acid.When the product contained m-hydroxybenzoic acid, this separated at once as a white precipitate while the liquid was hot, and the filtrate, on cooling, deposited a portion of the 4-hydroxyphthalic acid. After separating the latter, the liquid was extracted with ether, when a further portion of 4-hydroxyphthalicacid was obtained. The whole of the acid was then purified by crystallising from water, when, if the fusion had been conducted properly, it was obtained in warty masses melting at 204-205". If tha treatment with caustic soda had been too severe, the acid which separated after crystallibing from water was found to melt at about 180°, but by evaporating the mother liquors further quantities of 4-hydroxyphthalic acid were obtained almost pure and melting a t about 200".4-HYDROXYPHTHALTC AND 4-METHOXYPHTHALIC ACIDS.101 4-Hydroxyphthalic acid is sparingly soluble in cold water, easily so in the hot solvent; it dissolves readily in acetone, alcohol, or ether, but is almost insoluble in benzene or light petroleum. It melts at 204-205" with elimination of water and formation of the anhydride : 0.1410 gave 0.2714 CO, and 0.0427 H,O. 4Hyd~oxyphtiulic Anhydride.-The foregoing acid was fused and the beating continued until d l effervescence had ceased. On crystalli- sation from glacial acetic acid, the anhydride separated in ill-defined needles melting a t 171-173" : C = 52.49 ; H = 3-36. C8H,0, requires C = 52.7 ; H = 3.3 per cent.0.1237 gave 0.2644 and 0.0281 H,O. C8H1,0, requires C = 58.5 ; H = 2.4 per cent. It is almost insoluble in cold w$er but readily soluble in the hot solvent, and the solution on cooling deposits the free acid. It dissolves readily in alcohol or acetone ; in boiling toluene it is only sparingly soluble. 4-Hydroxyphthuli~~ide.--'l'his was prepared by heating the anhydride in a stream of dry ammonia and crystallising the product from alcohol. It separates in prismatic needles melting a t 290" [RBe gives C = 58.3 ; H= 2.5. 288-289' (~oc. ,it.)] : 0.3213 gave 24.5 C.C. nitrogen a t 20' and 756 mm. C,H50,N requires N = 8.6 per cent. 4-Hydroxyphthalimide is soluble in boiling acetone, but only very sparingly so in boiling toluene. 4-Hyd~oxypht~cc~unilic Acid, C0,H*C,H,(OH)*cO*NH*c6H~-This acid was prepared by dissolving 4-hydroxy phthalic anhydride (5.5 grams) in acetone and adding aniline (3.1 grams).The mixture became warm and, after evaporating the acetone, the residue was ground to a powder and extracted with cold aqueous sodium carbonate. From the filtered solution the aniiic mid was precipitated by the addition of acetic acid, and purified by crystallising from alcohol; it separates in pale yellow leaves : N = S.7. 0.1840 gave 9.1 C.C. nitrogen at 17' and 756 mm. Cl4Hl1O,N requires N = 5.4 per cent. The substance dissolves in cold aqueous sodium carbonate with a pale yellow colour which disappears when the solution is boiled. This is due to hydrolysis of the anilic acid, since the latter is not precipitated from the solution on acidifying with acetic acid.The anilic acid appears to melt at about 2G0°, but it is converted into the anil a t a much lower temperature, and the melting point observed is really that of the latter. 4-Hydroxyp~thaZc6niZ, C,H,(OH)(CO),:N*C6H5.-This substance was prepared by heating the anilic acid until it melted and then crystallising N = 5.7.102 BENTLEY AND WEIZMANN : the residue from alcohol, from which the a d was obtained in yellow leaves melting a t 263-264O : 0.2432 gave 12.2 C.C. nit,rogen a t 15" and 764 mm. C,,H,O,N requires N = 5.8 per cent. It is almost insoluble in cold sodium carhonate solution, but dissolves with hydrolysis on boiling. It dissolves in cold dilute caustic soda, giving a yellow solution which yields the anilic acid.This can be precipitated with acetic acid and is apparently identical with the anilic acid just described. When dissolved in an excess of cold aqueous caustic soda the anil is completely hydrolysed, the yellow colour of the solution disappearing a t the same time. Methyl 4- Hgd7*oxyphthalate, C6H3( OH) (CO,Me),. - 4 -Hy drox y ph t halic acid is esterified very readily when treated with methyl alcohol and sulphuric acid. The acid (30 grams) was dissolved in methyl alcohol (150 c.c.), mixed with concentrated sulphuric acid (100 c.c.), and warmed on the water-bath for a few hours. The cold product was poured into ice-cold water, the oil which separated extracted with ether, and the ethereal extract washed with a little sodium carbonate solution, dried, and evaporated.An oil remained which soon solidified, and after leaving in contact with porous porcelain until dry and crystallising from toluene, the methyl ester was obtained pure in minute plates melting at 107-108" [Rde, (Zoc. cit.), gives 102O]. The same substance was obtained from crude 4-hydroxyphthalic acid (m. p. 186-187'), but required s&ersl crystallisations before it was pure. On hydrolysis with alcoholic potash i t then yielded 4-hydroxyphtbalic acid melting a t once at 204-205' (see p. 100) : N=5.9. 0.1 934 gave 0,4022 CO, and 0.0844 H,O. C1,H1,O, requires C: = 57.1 ; H = 4.7 per cent. Methyl 4-hydroxyphthalate is readily soluble in alcohol or ether, sparingly so in cold water, but more easily in the hot solvent o r toluene ; it dissolves readily in cold aqueous sodium carbonate, from which solution it can be extracted by ether.Owing to this property, a further quantity of the dimethyl ester was obtained when the extract, obtained by shaking the ethereal solution with sodium carbonate (see above), was acidified. Methyl 4-Metl~oxyphtha2te, C6H3( OMe)( CO,Me),.-Pure 4-hydroxy - phthnlic lacid (50 grams) was dissolved in aqueous caustic soda, and dimethyl sulphate (200 grams) added in small portions a t a time, the mixture being constantly shaken and kept alkaline. At the end of the operation the product was heated for a short time on the water-bath, cooled, acidified, and extracted with ether. The ethereal solution was dried, evaporated, and the residue dissolved in methyl alcohol (250 c.c.), mixed with concentrated sulphuric acid C = 56 7 ; H = 4.8.4-HYDROXYPHTEIALIC AND 4-METHOXYPHTHALIC ACIDS. 103 (160 c.c.), and heated a few hours on the water-bath.The cold product was then poured into ice-cold water, the oil which separated extracted with ether, the ethereal solution washed with dilute caustic soda, dried, and evaporated, when an oil remained which was pur;L%ed by distillation under reduced pressure. Methyl 4-methoxgpl~thaZate is an oil which distils a t 195-197"/20 mm. and does not solidify a t - 10" : 0.1466 gave 0,3144 CO, and nJ37i2 H,O. C=58*5 ; H=5.4. c~,H,*,o, requi-ies C = 58.9 ; H = 5.3 per cent. 4-Jfet?~oxgphtitaZic Acid, C,H,(OMe)(CO,H),.-This acid was prepared horn the foregoing ester by hydrolysis with alcoholic potash on the water-bath ; after diluting with water and evaporating until the alcohol had been removed, the solution was acidified with hydro- chloric acid, when the aJid was precipitated.It was collected and purified by recrystallisirlg from water, from which i t was obtained in glistening needles : 0.1110 gave 0.2253 CO, and 0.0411 H,O. 4-nfethox~pl~thaZic acid is readily soluble in alcohol, acetone, or ether. When rapidly heated i t melts a t about 178" with effervescence. Slowly heated, it melts a t about 170". As stated in the introduction, when we attempted to prepare 4-methoxyphthalic acid from the crude 4-hydroxjphthalic acid (m. p. lS6-187") we obtained first zn acid melting a t about 140° with effervescence, which on recrystallising from water melted a t 108--10V', and proved on examination to be m-methoxybenzoic mid : 0.1 137 gave 0.2620 CO, and 0.0533 H,O.C8H803 requires C = 63.1 ; H = 5.3 per cent. 4-~Methoxyp?~t?~aZic Anhydride, C,H,( ONe)( CO),O.-This substance was prepared by heating the corresponding acid until it melted, and crystallising tho product from glacial acetic acid, from which it separ- ated in glistening leaflets melting a t 98-99' [Schall (Bey., 1879, 12, 829) gives 93'1 : C=54*9; H=4*1. C,H,C, requires C = 55.1 ; H = 4.1 per cent. C = 62.8 ; H = 5.2. 0.1 182 gave 0,2625 CO, and 0,0363 H20. C,H,O, requires C = 60.7 ; H = 3.4 per cent. It is readily soluble in alcohol, acetane or warm benzene ; in cold water it is almost insoluble, bat melts in boiling water and gradually passes into solution, from which the freJ acid separates on cooling.4-iClethoxgpl~t?~cdinzide, C,H,(OMe)(CO),NH.-This imide was ob- tained by heating the anhydride in a stream of dry ammonia gas and crystallising the product from alcohol, when i t separates in prismatic plates melting at 224-225" : C = 60.6 ; H = 3.4.104 BENTLEY, ROBINSON, AND WEJZMANN : ~-HYDROXYYHTHALIC 0.1711 gave 11-8 C.C. nitrogen a t 16" and 764 mm. C,H70,N requires N = 7.9 per cent Tf, is soluble in acetone, sparingly soluble in Cold toluene, but more 4 - Methoab,l .' q,lUniJic Acid, C,H,(OMe)(CO,H)CO*NH*CGH,.-In 08. reaulAe derivative, the anhydride (10 grams) W a s dis- order t o prepare c_ -1 mixed with aniline (4.7 grams). The solved in warm benzene temperature of the mixture rose ray.,, s- and the unilic acid suddenly separated as a white, amorphous powder, which, frf+dA buxbb;;,,g by the aid of the pump and washing with benzene, was quite pure and melted at 148-149" with effervescence : the boiling solvent. 0.2727 gave 13.2 C.C. nitrogen at 17" and 764 mm. It is readily soluble in alcohol or acetone and separates from dilute alcohol in leaflets, 4-Methox~~l,,tl~alaniZ, C,H,(O~le)(CO),:N~C,H,.-This was prepared by heating the anilic acid a t its melting point u r t i l effervescence had ceased. On crystallising the residue from alcohol, the anil separated in colourless needles melting at 1 7 9 O : N=5*2. C,,H,,O,N requires N == 5.2. 0.2928 gave 13.S C.C. nitrogen at 17" and 764 mm. C,,H,,O,N requires N = 5.5 per cent. 4-MetJ~ox?/;u?~tl~aZaniZ dissolves in hot dilute aqueous caustic soda, from which solution acetic acid precipitates an anilic acid, This, when purified by dissolving iii sodium carbonate and reprecipitating with acetic acid, melts at 148-149", and is probably identical with the anilic acid described above. N=5.5. THE UNIVERSITY, MANCHEWER.