ISOMERIC SULPHONIC ACIDS OF P-NAPHTHTLAMINE. 33 IV.-The Isomeric Sulp phonic Acids of P-Naphthylanaine. By ARTHUR G. GREEN. BY the sulphonation of 6-mphthylamirre under different conditions, four isomeric monosulphonic acids have been obtained [a (Badische), /? (Bronner’s) y (Dahl’s) and d (Bayer’s)] but our knowledge con-cerning them is still very incomplete. It therefore seemed of interest t o communicate a few results which I have obtained in their investi-gat ion. By heating P-naphthylamine with 3 to 114 times its weight of ordinary sulphuric acid at 100-105” a mixture is obtained which * With Br it is for instance less than 8000 cal. and supposing i t were as much as this with H, this would give the afinity of H + Br2 as 16,000 only whereas we know they combine to form 2HBr with an evolution of 17,000 cal.and that this compound so f0md is far from being saturated as is shown by its heat of dissolution. T’OL. LV. 34 GREEN THE ISOMERIC SCLPHONIC ACIDS consists according to Dahl (Germ. Pat. No. 29084 32271 32276),of the a- @- and y-acidsin the proportion of about 50 per cent. of a 10 per cent. of /I and 40 per cent. of y. These can be separat'ed by means of the difference in the solubilities or" the sodium salts in spirit and of the barium salts in water. The proportion of the several isomerides varies greatly with the temperature at which the reaction takes place ; thus by heating the above melt for some time at 120' the quantity of a-acid is greatly diminished whilst that of the p-acid is increased. On the other hand by sulphonation with three parts of fuming aulphuric acid (20 per cent.anhydride) a t 70-80" for a short time about 70 per cent. of the y- and 30 per cent. of the a-acid is formed but scarcely any of the @-acid. A similar mixture is obtained (Dahl Germ. Pat., No. 32276) by agitating P-naphthylamine sulphate with ordinary sulphuric acid for two or three days at a temperature of 15-20'. 13s heating p-naphthylamine hydric sulphate at 200-210" EL product is obtained which oonsists chiefly of the @-acid (Liebmann Monit. Sci., 1885 1043). By heating /I-naphthylamine snlphate (1 part) with 3 parts of ordinary sulphuric acid at 160-170" for one hour a mixture of about equal quantities of the P- and &acids is formed (Bayer and Dnisberg Rer. 20 1426 ; C . Schultz Ber.20 1358). The &acid is also obtaiued from a-naphthalenedisulphonic acid by heating it under pressure a t 250" with aqueous sodium hydrate and then with tmmonium chloride (A. Weinberg Ber. 20 2906 3353). The 6-naphthylamine-P-snlphonic acid is obtained from @-naphthol-P-sulphonic acid (Schaeff er's acid) by heating with ammonia under pressure (Farbfabrik vorm. Bronner Germ. Pat. No. 22547). The constitution of these four acids is probably represented by the formuh-a B Y 6 In these formuls it will be seen that the a- and y-acids contain the HSO group in an a-position whilst in the p- and &acids the HSOJ gronp is in the P-position. This explains the influence of temperature on the formation of the several acids for like the a- and P-sulphonic acids of naphthalene, the acids with the HSO gronp in the a-position (the a- and y-acids) are formed at low temperatures whilst those with the HSO group in the P-position (the p- and &-acids) are formed at higher temperatures, Also just as a-naphthalenesulphonic acid is converted into P-naph-thalenesulphonic acid by heating with HzSOa to a higher temperature OF 6-NAPHTHYLAMINE.35 so each of the a-acids of p-naphthylamine (the m- or ./-acid) is converted into a mixture of the two @acids (the p- and &-acids) by the same treatment. Products of the Sulphonation of /3-Naphthylamirte at 100-105". P-Naphthylamine was heated for five or six hours with 3-34 times its weight of ordinary concentrated sulphiiric acid at a tem-perature of 100-105" ; the melt was poured into water and the pre-cipitate washed pressed and dried.For the separation of the isomeric acids the method given in Dahl and Co's. patent was employed and found to serve very satisfactorily. The acids were converted into the sodium salts and boiled for an hour with six or seven times their weight of 90 per cent. spirit. The insoluble residue after pressing and a final extraction is the pure sodium salt of the or-acid. From the sodium salt the pure a-acid was obtained well crystallised in the form of prismatic tables. For this purpose i t was dissolved in boiling water some ammonia added and then acetic acid just short of pre-cipitation ; on cooling the acid crystallises out. Precipitation with acetic acid from an ammoniacal solution was found to be a very con-venient way of obtaining all these isomeric acids in a well-crystallised form.From the alcoholic filtrate containing the p- and 7-acids the spirit was distilled off the residue dissolved in water and precipitated with hydrochloric acid. The precipitated sulphonic acids were neutralised with barium hydrate and left to crystallise. A sparingly soluble barium salt crpta,llised out whilst the mother-liquor contained the easily soluble barium salt of the y-acid. From this the y-acid wm set free by hydrochloric acid and obtained pure in the form of small plates by precipitation with acetic acid. The sparingly soluble barium salt was purified by recrystallisation from water. According to Dahl id consists of the salt of the P-acid only but my experiments prove that it is a mixture of about equal parts of the p- and 8-acids.By repeated fractional crystallisations from hot water the two acids were separated. The more soluble one was found to be identical in appearance properties and in its sodium and ammonium salts with the &acid obtained by Bayer's method of sulphonating at 170". The &-acid was also obtained from the Yodium last which crystallised out on cooling the hot alcoholic solution of the mixed sodium salts (see above). This according to Dahl is the sodium salt of the P-acid but from my experiments it appears tb consist almost entirely of the salt of the &acid. The presence of the &acid as well as the p-acid amongst the products of the sulphonation at 100" might certainly be expected since as bas already been men-tioned both the a- and y-acids which are probably the primar 36 GREEN THE ISOMERIC SULPHONIC ACIDS products are converted into mixtures of p- and &acids on further heating with snlphuric acid.The proportion in which the four isomerides are formed a t 100" may be roughly estimated as about 50 per cent. of s,40 per cent. of 7, 5 per cenlt. .of @ and 5 per cent. of 6. Properties of the four Isomeric Acids. I n the formulae given above it will be seen that the a-acid differs greatly from the p- y- and &acids in being a homonucleal compound, whilst the other three are heteronucleal. This is fully borne out in their properties. Thus the a-acid is the only one whose sodium salt is insoluble in spirit. The azo-compounds also show characteristic differences.For instance the scarlets obtained by combining the diiizotised acids with p-naphthol are very similar in shade and readily soluble in water whether the 13- y or &acid is employed but that from the a-acid is almost insoluble. Again by combining diazotised primuline or benzidine with either the (3- y- or &acids scarlets of almost the same shade are obtained but the a-acid gives an orange. By diazotising and boiling with dilute sulphuric acid the a-acid was converted i.nto the corresponding a-sulphonic acid of @naphthol (Bayer's) whose sodium salt was soluble in alcohol and crystallised from it in silky plates exceedingly soluble in water. It is to be observed that the aaphkhylaminesulphonic acid insoluble in spirit, correspon\ds to the naphtholsnlp honic acid soluble in spirit.The ammonium salt of the a-acid forms very soluble large solid prisms; that of the y-acid exceedingly soluble tables; the &salt tolerably soluble small plates ; whilst the ,@salt which is the least soluble of ali crystallises in beautiful large thin plates often 1 or 2 inches long and having a violet fluorvscence. The ammonium salt of the p-acid serves very conveniently for its identification and separation from the 6-acid. The sodium salt of the @-acid crystallises in flat needles which when air-dried contain 2H20 (as given by Forsling Ber. 20 77). The sodium salt of the &acid crystallises in plates (according Bayer in needles). In regard to the crystalline forms of the free acids it has already been mentioned that the a-acid crystallises in large tables the ./-acid in plates.The &acid from whatever source it was obtained always formed very fiue voluminous needles (as stated by Bayer and others). When quite free from acid it is tolerably soluble in water. Since the occur-rence of the &acid together with the @-acid (whether obtained by sulphonation a t 100" or from the sulphonic acid of @naphthol) has hitherto not been suspected it appears probable that the @acid has scarcely ever been obtained quite pure. That this is indeed the case The ammonium salts of the four acids are very characteristic OF P-KAPHTHTLAMINE. 37 seems to be shown by the fact that the p-acid is always described as crgstallising in lustrous plates (which are even regarded as very characteristic) whereas I found that when obtained from the pure ammonium salt it invariably crystallises in compact prismatic needles.In order to prove that this difference of crystalline form is due t o a trace of &acid a small quantity of &acid was added to an alkaline solution of pure P-acid (needles) on precipitating from the hot solution with an acid the whole then came out in silky plates. S-Na~hthylaminesu~honic Acids from P-Na~lLtholsulpl2onic Acids. It is usually considered thatl two monosulphonic acids only are formed by salphonating P-naphthol under varying conditions viz., Bayer's acid and Schaffer's acid ; the former being the chief product at a low temperature the latter at a high temperature. Considering the analogous reactions of hydroxy- and amido-compounds it seemed t o me probable that corresponding t o the behaviour of P-naphthyl-amine p-naphthol should give on sulphonation at a low tempewture, a mixture of two a-sulphonic acids ( a and 7 ) which by heating to a higher temperature would be converted into two P-sulphonic acids ( p and 8).The different behaviour of Schaffer's acid so called when obtained under different conditions strengthened this assumption, and led me to attempt to prove the presence of another acid associ-ated with the P-acid. The product taken f o r invzstigation was the p-naplltholsulphonic acid obtained according to Armstrong's method, by heating molecular proportions of p-naphthol and 100 per cent. sulphuric acid a t 100". The sulphonic acid so obtained is usually assumed to be identical with Schaffer's acid.As the separation of the p-naphtholsulphonic acids is very difficult whereas that of bhe P-naph-thylaminesulphonic acids is comparatively easy the method which was employed consisted in converting the naphtholsulphonic acids into naph thylaminesulphonic acids by treatment with ammonia and separating these. 100 grams of ,%naphthol was heated with 70 grams of 100 per cent. HzSOa for 2 or 3 hours at 100-105" till the reaction was complete when the melt solidified t o a hard mass of the sulphonic acids. This was dissolved in water neutralised with sodium carbonate (filtering from a little tar which remains insoluble) and the sodium s d t precipitated with sodium chloride. Or else the hot solution was neutralised with ammonia when the sparingly solu-ble salt ci-ystallised out on cooling The yield of the ammonium salt is about 110 grams.The conversion into p-naphthylaminesulphon ic acid was performed by heat'ing with aqueous ammonia under pressure at 250-280" or by passing dry gaseous ammonia over the dry sodinnr salt heated to about 280-290". The product was precipitated wit 38 MATTHEWS ON ETHTLIC CINNAMTLDlETHACETATE. sulphuric acid and submitted to a careful series of fractional preci-pitations and crystallisations of the ammonium salt. By this means pure /?- and 8-sulphonic acids were isolated from it and had all the properties pyeviously described. The P-acid crystallised in prismatic needles its ammonium salt in large thin plates and its sodium salt in flat needles. The &acid crystallised in very fine matted needles its ammonium salt in small plates and its sodium salt in small plates. It is thus proved that the P-naphtholsulphonic acid obtained by Armstrong’s method is a mixture of the 6- and 8-sulphonic acids, whose constitution is probably represented by the formula-Whether the yacid occurs along with the a-acid amongst the pro-ducts of the sulphonation of @naphthol a t a low temperature I have not yet been able t o determine but hope to be able t o do so before long. In conclusion I desire to express my thanks to Messrs. Brooke, Simpson and Spiller in whose laboratory the above research was carried out