Organic Syntheses, Coll. Vol. 3, p.465 (1955); Vol. 21, p.56 (1941). 2-HYDROXY-1,4-NAPHTHOQUINONE [1,4-Naphthoquinone, 2-hydroxy- ] Submitted by L. F. Fieser and E. L. Martin. Checked by Reynold C. Fuson and E. A. Cleveland. 1. Procedure One liter of absolute methanol is cooled in a 3-l. round-bottomed flask to 0° in an ice-salt bath, and 80 ml. of concentrated sulfuric acid is slowly added, with good shaking, the temperature being kept at 0°. The flask is removed from the freezing mixture, and 255 g. (1 mole) of ammonium 1,2-naphthoquinone-4-sulfonate (p. 633) is added and made into an even paste by thorough shaking. After standing for 30 minutes, during which time the temperature rises to 15–20°, the flask is heated gradually on the steam bath with continuous shaking and rotating so that the solution reaches its boiling point in about 15 minutes. The solution becomes red, sulfur dioxide is evolved, and methoxynaphthoquinone begins to separate. The mixture is kept boiling very gently, with continued shaking, for 15 minutes, when the paste of separated material becomes very stiff. Two hundred and fifty milliliters of methanol is added, and the heating and rotating continued for an additional 15–20 minutes. The reaction mixture is cooled to 20–25°, water and ice are added until the flask is nearly filled, and the methoxynaphthoquinone is collected on a 15-cm. Büchner funnel and washed with cold water until the filtrate is nearly colorless; about 2–2.5 l. of water is required (Note 1) . The moist material is washed into a solution of 30 g. of sodium hydroxide in 1.5 l. of water, and the mixture is heated rapidly nearly
Submitted by L. F. Fieser and E. L. Martin.Checked by Reynold C. Fuson and E. A. Cleveland.1. ProcedureOne liter of absolute methanol is cooled in a 3-l. round-bottomed flask to 0° in an ice-salt bath, and 80 ml. of concentrated sulfuric acid is slowly added, with good shaking, the temperature being kept at 0°. The flask is removed from the freezing mixture, and 255 g. (1 mole) of ammonium 1,2-naphthoquinone-4-sulfonate (p. 633) is added and made into an even paste by thorough shaking. After standing for 30 minutes, during which time the temperature rises to 15–20°, the flask is heated gradually on the steam bath with continuous shaking and rotating so that the solution reaches its boiling point in about 15 minutes. The solution becomes red, sulfur dioxide is evolved, and methoxynaphthoquinone begins to separate. The mixture is kept boiling very gently, with continued shaking, for 15 minutes, when the paste of separated material becomes very stiff. Two hundred and fifty milliliters of methanol is added, and the heating and rotating continued for an additional 15–20 minutes. The reaction mixture is cooled to 20–25°, water and ice are added until the flask is nearly filled, and the methoxynaphthoquinone is collected on a 15-cm. Büchner funnel and washed with cold water until the filtrate is nearly colorless; about 2–2.5 l. of water is required (Note 1).The moist material is washed into a solution of 30 g. of sodium hydroxide in 1.5 l. of water, and the mixture is heated rapidly nearly to the boiling point. In about 10 minutes all the ether is hydrolyzed and a deep red solution results (Note 2). The hot solution is filtered by suction from a trace of residue, transferred to a 2-l. beaker, and acidified while still hot by adding 130 ml. of 6 N hydrochloric acid slowly, and with good stirring. The yellow suspension of hydroxynaphthoquinone thus obtained is cooled to 0° and allowed to stand for 2 hours (Note 3). The hydroxynaphthoquinone is collected, washed with 2 l. of cold water, dried overnight at room temperature, and finally to constant weight at 60–80°. The yield is 101–112 g. (58–65% based on ammonium 1,2-naphthoquinone-4-sulfonate; 99%, based on methoxynaphthoquinone) (Note 4). The hydroxynaphthoquinone thus obtained is bright yellow, is granular, and melts, with decomposition, at about 188–189° (Note 5). It is of high quality and for ordinary uses requires no further purification (Note 6).2. Notes1. The methoxynaphthoquinone weighs 111–122 g. (59–65%). It melts at 181–182° and can be further purified by crystallization from ethanol. The pure substance forms pale yellow needles, m.p. 183.5°.
2. Should the sodium salt separate during the heating or filtration, it is brought into solution by adding about 1 l. of water and heating.3. By allowing the precipitate to stand for the indicated period, the final product is granular, and the filtration is rapid.4. Numerous modifications have been tried without improving the yield. The loss is probably due to a partial reduction of the quinone sulfonate by the sulfur dioxide liberated, but this was not prevented by adding manganese dioxide to the reaction mixture and no pure product could be obtained from the mother liquor.5. The temperature of decomposition varies with the rate of heating and with the nature of the glass capillary.6. Crystallization from ethanol containing a trace of acetic acid gives glistening yellow needles, melting with decomposition at about 191–192°. The red samples of hydroxynaphthoquinone often mentioned in the literature are not completely pure. Such material, or crude material of any kind, is best purified through either the sodium salt or the methyl ether.3. DiscussionOf the many reactions by which hydroxynaphthoquinone has been obtained,1,2 two have been developed into practical preparative methods, and both utilize the inexpensive β-naphthol as the primary starting material. In the first method, this is converted into β-naphthoquinone [ Org. Syntheses Coll. Vol. 2, 430 (1943)], which reacts with acetic anhydride-sulfuric acid to give 1,2,4-trihydroxynaphthalene triacetate, which is then hydrolyzed and oxidized to the desired product. The yield of the acetylation reaction is about 75%; that in the final step can be brought to 93% of the theoretical amount by hydrolyzing with ethanolic alkali in an atmosphere of nitrogen and with a trace of sodium hydrosulfite present, then diluting with water, acidifying, and adding ferric chloride. The overall yield from β-naphthol can thus be brought to 54%. The method is a good one, and it can be used to advantage for the preparation of many similar hydroxyquinones. With ordinary laboratory equipment, however, one is limited to 0.5 mole runs, and not more than about 50 g. of hydroxynaphthoquinone can be prepared at a time.The second method is that described above: β-naphthol is converted through the nitroso derivative and 1-amino-2-naphthol-4-sulfonic acid into naphthoquinone sulfonate, and this is subjected to acid hydrolysis. The sulfonate can be converted directly into hydroxynaphthoquinone by the action of concentrated sulfuric acid,3,4 but the process is not so easily controlled as when the quinone is etherified as it is formed and the ether subsequently hydrolyzed.4 The overall yield from β-naphthol is 46% of the theoretical amount, but all the reagents are inexpensive, and with ordinary apparatus, 150 g. of hydroxynaphthoquinone can be made conveniently in one run (from 300 g. of β-naphthol).The compound has also been prepared in good yield by air oxidation of 1,3-dihydroxynaphthalene,5 which in turn was obtained from ethyl γ-phenylacetoacetate.6
References and Notes
1. Beilstein-Prager-Jacobson, VIII, 300 (1925).2. Thiele and Winter, Ann., 311, 347 (1900).3. Akt.-Ges. Anilinf., Ger. pat. 100,703 [Chem. Zentr., 70, 766 (1899)].4. Fieser, J. Am. Chem. Soc., 48, 2929 (1926).5. Soliman and Latif, J. Chem. Soc., 1944, 55.6. Soliman and West, J. Chem. Soc., 1944, 53.
1,2-NAPHTHOQUINONE-4-SULFONATE, AMMONIUM AND POTASSIUM[1-Naphthalenesulfonic acid, 3,4-dihydro-3,4-dioxo, ammonium and potassium salts]
Submitted by E. L. Martin and L. F. Fieser.Checked by R. L. Shriner and Eldred Welch.1. ProcedureA mixture of 145 ml. of nitric acid (sp. gr. 1.42) and 400 ml. of water in a 2-l. beaker is cooled to 30° in a slush of ice and water, and 350 g. (1.46 moles) of pure, anhydrous 1-amino-2-naphthol-4-sulfonic acid (Note 1) is weighed into a separate 2-l. beaker. The beaker is removed from the bath; a 10-g. portion of the 1-amino-2-naphthol-4-sulfonic acid is stirred into the solution, and the liquid is then allowed to become entirely motionless. Generally, oxidation starts during this addition; if not, 2 ml. of concentrated nitric acid is poured carefully down the side of the beaker without stirring. Oxidation commences in 1–2 minutes and the mixture turns yellow (Note 2).The beaker is replaced in the ice bath, and 20–25 g. of 1-amino-2-naphthol-4-sulfonic acid is stirred into the mixture by hand. A second portion of 20–25 g. is added immediately and stirred. The mixture begins to froth and is covered with a layer of 100 ml. of ether which serves as an efficient subsident (Note 3). The remainder of the 1-amino-2-naphthol-4-sulfonic acid is added in 20–25 g. portions during the course of 3–4 minutes, the mixture being stirred well after each addition. Oxides of nitrogen are freely evolved, and a stiff yellow-orange paste is formed. The temperature is maintained between 25° and 30° by vigorous stirring and by controlling the rate of addition of the compound (Note 4). The oxidation is complete within 3–4 minutes after the last addition and gas is then no longer evolved. The thick mass is stirred until the temperature has dropped to 5–10° and then 175 ml. of saturated ammonium chloride solution (30°) is added.After the mixture has been cooled to 0°, the ammonium 1,2-naphthoquinone-4-sulfonate is collected on a 20-cm. Büchner funnel and as much of the mother liquor is removed as possible by pressing the cake with a porcelain spatula or glass stopper. The product is washed with three equal portions of a cold mixture of 150 ml. of saturated ammonium chloride solution and 100 ml. of water. The wash solution is removed as completely as possible, and the product is washed twice with 50-ml. portions of ethanol, followed by 300 ml. of ether in small portions (Note 5). The ammonium 1,2-naphthoquinone-4-sulfonate is spread out in a thin layer and dried to constant weight at 35–40°. An orange, microcrystalline product of bright appearance is thus obtained. The yield is 350–365 g. (94–98%). The ammonium salt is of good quality and is sufficiently pure for many purposes. No satisfactory method has been devised for its further purification, but it can be converted into a pure potassium salt as follows.
Seventeen hundred milliliters of water containing 0.3 ml. of liquid bromine is heated in a 2-l. Erlenmeyer flask to 50° on a steam bath (Note 6). The flask is removed, 50 g. of ammonium 1,2-naphthoquinone-4-sulfonate is added, and the mixture is shaken for a few minutes until solution is complete. Three grams of Norit is added, and the solution is stirred for 2–3 minutes. It is then filtered by suction and the clear orange filtrate is transferred to a 4-l. Erlenmeyer flask. Four hundred milliliters of saturated potassium chloride solution (30°) is added rapidly in one portion, and the flask is allowed to stand undisturbed. Orange crystals of potassium salt begin to separate immediately, and after standing for 30 minutes the contents of the flask are cooled to 0° in an ice-salt bath and the potassium 1,2-naphthoquinone-4-sulfonate is collected on a 15-cm. Büchner funnel. The solid is washed with 150 ml. of cold, dilute potassium chloride solution (30 ml. of saturated potassium chloride solution added to 120 ml. of water), and then with 150 ml. of ethanol in small portions followed by 300 ml. of ether. The potassium salt is dried to constant weight at 40–50°. The yield is 48–50 g. (90–92% based on the ammonium salt used). The product consists of orange needles free of colored decomposition products but still containing traces of ammonium salts. An ammonium-free compound is obtained by a second crystallization. Seventeen hundred milliliters of water containing 0.2 ml. of liquid bromine is heated to 60° in a 2-l. Erlenmeyer flask on a steam bath; the flask is removed, and 50 g. of the potassium salt is added. The salt dissolves rapidly; the solution is filtered with suction; and the clear orange filtrate is transferred to a 4-l. Erlenmeyer flask. Three hundred milliliters of saturated potassium chloride solution is added rapidly in one portion, and the flask is allowed to stand undisturbed. Orange needles of potassium salt appear in a moment or two, and after standing for 30 minutes the mixture is cooled to 0° in an ice-salt bath. The crystals are collected, washed, and dried as outlined above. The salt thus obtained weighs 45–49 g. (90–98% based on the potassium 1,2-naphthoquinone-4-sulfonate used). This product compared favorably with the sodium salt prepared by the more elaborate borax process1 with respect to color, colored decomposition products and ammonia content (Note 7) and (Note 8).2. Notes1. The 1-amino-2-naphthol-4-sulfonic acid earlier described [ Org. Syntheses Coll. Vol. 2 , 42 (1943)] is not quite pure and gives an oxidation product of somewhat inferior quality. The procedure in question yields a gray product containing water of hydration (the percentage yield reported is thus in error). On reinvestigating the matter it has been found that the darkening of the material can be minimized if not prevented entirely, and that the colored impurity can be removed completely by extraction with ethanol. The colorless, anhydrous sulfonic acid required for the present preparation is thus prepared by modifying the earlier procedure in the following respects. By stirring the mixture of nitroso-β-naphthol and sodium bisulfite solution vigorously by hand (wooden paddle), all the soluble product can be dissolved in 3–4 minutes. The solution is then filtered as rapidly as possible, using two 15-cm. Büchner funnels and changing filter papers frequently. The clear, golden-yellow filtrate is acidified immediately on completion of the filtration. The product is then light gray, whereas, if much time elapses before the bisulfite solution is acidified, the solution turns red and the aminonaphtholsulfonic acid may be deep purple-gray. After the product has been collected and washed with water, it is washed with warm ethanol until the filtrate is colorless; 1.5–2 l. of ethanol is required. The product is washed with two 100-ml. portions of ether and dried to constant weight at 60–80° in the absence of light. A pure white, dust-dry product which weighs 370–380 g. (75–78% based on the β-naphthol) is thus obtained. This product is used in the present procedure.If technical 1-amino-2-naphthol-4-sulfonic acid is used, the yield of ammonium 1,2-naphthoquinone-4-sulfonate is 313 g. (84%) of a rust-colored product. If the technical material is washed with 2 l. of warm 95% ethanol the yield is 337 g. (90%) of an orange-colored ammonium salt.
2. It is important that the oxidation start at this point. Should oxidation not begin, a second 1–2 ml. portion of concentrated nitric acid is added; the acid is introduced along the side of the beaker with as little disturbance as possible.3. It is necessary to add more ether from time to time to replace that which evaporates.4. The temperature must be kept within this range. At lower temperatures the oxidation is slow and not satisfactory; at higher temperatures the quinone is slightly decomposed.5. The ethanol and ether remove the small amount of decomposition products and assist in the rapid drying of the product. It is advisable to dry the preparation as rapidly as possible.6. Aqueous solutions of 1,2-naphthoquinone-4-sulfonate begin to decompose when heated to this temperature in the absence of bromine.7. Tests for the purity of the product were devised by Folin and later improved by Danielson.1 A direct comparison of the two preparations revealed no difference in the degree of purity of the product.8. This purified salt is suitable for use in the procedures of Folin and of Sullivan for the determination of amino acids.3. DiscussionSalts of 1,2-naphthoquinone-4-sulfonate have been prepared by the oxidation of 2-amino-1-naphthol-4-sulfonic acid with nitric acid,2 or by the oxidation of the more readily available 1-amino-2-naphthol-4-sulfonic acid with the same reagent.3,4,5
This preparation is referenced from:
Org. Syn. Coll. Vol. 3, 465
References and Notes
1. Danielson, J. Biol. Chem., 101, 507 (1933).2. Witt and Kaufman, Ber., 24, 3162 (1891).3. Folin, J. Biol. Chem., 51, 386 (1922).4. Böniger, Ber., 27, 24 (1894).5. Fieser, J. Am. Chem. Soc., 48, 2929 (1926).
AppendixChemical Abstracts Nomenclature (Collective Index Number);(Registry Number)
Submitted by Louis F. FieserChecked by Frank C. Whitmore and D. J. Loder.1. ProcedureThree hundred grams of β-naphthol (2.1 moles) is converted into nitroso-β-naphthol (Org. Syn. Coll. Vol. I, 1941 , 411) (Note 1), and the product is transferred to a 6-l. (1.5 gal.) crock which is wide enough to admit the Büchner funnel (30-cm.) employed. A cold solution of 600 g. (5.8 moles) of sodium bisulfite and 100 cc. of 6 N sodium hydroxide solution in 2 l. of water (Note 2) is used to rinse the material adhering to the funnel into the crock. The mixture is diluted with water to 4–4.5 l. and stirred until solution of the nitroso-β-naphthol is complete (about fifteen minutes). The dark solution is siphoned onto a large Büchner funnel and filtered by suction, thus removing a small amount of tarry material which is always present. The clear, yellowish brown filtrate is transferred to an 8- to 10-l. wide-mouthed bottle and diluted with water to 7 l. While the solution is vigorously stirred, 400 cc. of concentrated sulfuric acid is poured slowly down the walls of the bottle; the mixture is then placed in the hood and protected from the light (Note 3). The temperature rises from 20–25° to 35–40° at once and to about 50° in the course of two hours, when the reaction is nearly complete. After standing for a total of five hours or more (Note 4), the precipitate, which sets to a stiff paste in the bottle, is collected on a
filter. The residue is transferred to a 1-l. beaker and washed with 200 cc. of water. The mixture is filtered, and the residue is washed with 300 cc. of water on the filter. The moist material weighs 700–800 g. No appreciable decomposition takes place on drying the product to constant weight at 120°. A light powder of fine, gray needles is thus obtained. The yield is 410–420 g. (82–84 per cent of the theoretical amount based on the β-naphthol used) (Note 5).2. Notes1. In preparing nitroso-β-naphthol in the quantity here required it is convenient to use a 7- to 8-l. bottle, with an 8- to 10-cm. opening, equipped with a stirrer of heavy glass rod having four or five right-angle bends which extend to the top of the bottle and which are just small enough to fit the mouth. The bottle is placed in a bucket containing a salt-ice mixture which is stirred occasionally by hand. With this arrangement a temperature of 0° may be maintained without internal cooling.2. Sodium hydroxide is added to the bisulfite solution in order to neutralize any acid which has not been removed by washing, and which would liberate sulfur dioxide and thus cause some reduction of the nitroso compound before the addition product is formed. An excess of alkali, as employed above, aids in the solution of the material.3. The aminonaphtholsulfonic acid becomes rose colored on long exposure to the light, especially when moist.4. The time required for the process may be shortened somewhat by adding the sodium bisulfite-sodium hydroxide solution to the suspension of the crude nitroso compound, thus avoiding a long filtration. The amounts of water employed in the various operations should be reduced to a minimum, and enough additional sodium hydroxide solution should be used to neutralize the excess acid present. The product is of a slightly inferior quality, and the yield is 4–5 per cent lower.5. This gray material is not quite pure and contains water of crystallization so that the percentage yield reported is in error. A better product can be obtained by stirring the mixture of nitroso-β-naphthol and sodium bisulfite solution vigorously by hand with a wooden paddle thus causing all the soluble product to dissolve in three to four minutes. The suspension is then filtered as rapidly as possible using two 15-cm. Büchner funnels and changing filter papers frequently. The clear, golden-yellow filtrate is acidified immediately on completion of the filtration. The product is then light gray, whereas, if much time elapses before the bisulfite solution is acidified, the solution turns red and the aminonaphtholsulfonic acid may be deep purple-gray in color. After the product has been collected and washed with water, it is washed with warm alcohol until the filtrate is colorless, 1.5–2 l. being required. The product is washed with two 100-cc. portions of ether and dried to constant weight at 60–80° in the absence of light. A pure white, dust-dry product is thus obtained, weighing 370–380 g. (75–78 per cent of the theoretical amount based on the β-naphthol). The wash alcohol does not dissolve an appreciable amount of the aminonaphtholsulfonic acid since evaporation of the deep red wash liquor gives a dark residue weighing only 3–4 g. (E. L. Martin and Louis F. Fieser, private communication.)3. Discussion1-Amino-2-naphthol-4-sulfonic acid has been prepared by warming 2-naphthoquinone-1-chloroimide with sodium bisulfite solution;1 by reduction of 1-benzeneazo-2-naphthol-4-sulfonic acid with stannous chloride and hydrochloric acid;2 by treatment of 1-amino-2-naphthol hydrochloride with sodium sulfite;3
and by treatment of nitroso-β-naphthol with sodium bisulfite and hydrochloric acid.4
In a 12-l. round-bottomed flask (Note 1) fitted with a mechanical stirrer is placed 500 g. (3.5 moles) of technical β-naphthol dissolved in a warm solution of 140 g. (3.5 moles) of sodium hydroxide in 6 l. of water. The solution is cooled to 0° in an ice and salt bath, and 250 g. (3.5 moles) of powdered technical sodium nitrite is added. Stirring is started, and 1100 g. (833 cc., 4.6 moles) of sulfuric acid (sp. gr. 1.32) is added from a dropping funnel at such a rate that the whole is added in one to one and one-half hours, the temperature being kept at 0°. During the reaction, crushed ice is added from time to time to maintain the temperature at 0°; about 1 kg. is generally used (Note 2). After all the sulfuric acid has been added, the solution should react acid to Congo red paper. The mixture is stirred one hour longer at the low temperature, and then the nitroso-β-naphthol, which has gradually separated during the reaction, is filtered with suction and washed thoroughly with water. The product is at first light yellow in color, but after three to four days it gradually changes to a dark brown. The moisture content seems to have some effect on the color.
After the product has been air-dried for about four days, the yield is about 665 g.; it melts at 97°. A sample of this partially dried product, on drying in a vacuum desiccator over sulfuric acid for twenty hours, loses about 10 per cent of its weight, and the melting point is 106°. By longer drying under ordinary conditions, the melting point of 106° is reached (Note 3). The total yield of dry product is about 595 g. (99 per cent of the theoretical amount).
This product is satisfactory for most purposes. It may be obtained in a crystalline condition, however, by recrystallizing from hot ligroin (b.p. 60–90°). About 2 g. of nitroso-β-naphthol will dissolve in 15 cc. of boiling ligroin. The product is not very soluble in cold ligroin, so that nearly all is recovered.
2. Notes
1. A large vessel is needed for the reaction, as the nitroso-β-naphthol separates in a finely divided condition and there is some tendency to foam.
It has been suggested that instead of a flask there be used a 13–14 l. bottle or crock with an opening of 20–22 cm. and equipped with a stirrer of heavy glass rod having four or five right-angle bends which extend to the top of the bottle and which are just small enough to fit the mouth. If the salt-ice mixture in the cooling bath is stirred well, a temperature of 0° may be maintained without internal cooling (L.F. Fieser, private communication).
2. It is very necessary to keep the temperature near 0° while adding the sulfuric acid, or a tarry product will be obtained. Vigorous stirring and the addition of the sulfuric acid at the proper rate are essential for a good product. Instead of the 1100 g. of sulfuric acid (sp. gr. 1.32) there can, of course, be added an equivalent amount of concentrated acid and sufficient ice to give a cold solution.
3. The final air-dried product is pure except for its moisture content, as is shown by the fact that on drying in a vacuum desiccator it has a very good melting point.
3. Discussion
Nitroso-β-naphthol can be prepared by the action of sulfuric acid upon a solution of potassium or sodium nitrite and the sodium salt of β-naphthol;1 by the action of sodium nitrite upon an alcoholic solution of zinc chloride and β-naphthol;2 by the action of sodium nitrite upon β-naphthol suspended in zinc sulfate solution;3 and electrolytically from β-naphthol.4
In an 8-l. (2-gal.) earthenware crock, equipped with a mechanical stirrer and a tube for introducing steam, are placed 240 g. (1.39 moles) of nitroso-β-naphthol (from 200 g. of β-naphthol, Org. Syn. Coll. Vol. I, 1941 , 411 ) (Note 1), 1.5 l. of water, and 300 cc. of 5 N sodium hydroxide. The lumps are broken up with a rod, and the mixture is stirred for about thirty minutes. At the end of this time, practically all the nitroso compound is dissolved and 1.2 l. of 5 N sodium hydroxide is added. Steam is passed in until the temperature of the mixture is 35°, and then the steam is shut off and 600 g. of technical sodium hydrosulfite (at least 85 per cent pure) is added while the solution is being stirred. The solution is stirred continuously for five minutes while the temperature rises to 60–65°, and then for one minute at five-minute intervals during one-half hour. At the end of about fifteen minutes the solution becomes clear and light yellow in color. A small amount of black scum floats on the surface.
The solution is now cooled to 20° by the addition of about 1 kg. of ice and 500 cc. of technical concentrated hydrochloric acid (sp. gr. 1.16) is added with stirring. This precipitates the aminonaphthol as a voluminous, almost white precipitate (Note 2) which is collected on two 20-cm. Büchner funnels. It is rapidly pressed as free from mother liquor as possible and transferred quickly (Note 3) to an 8-l. (2-gal.) crock containing 2.5 l. of water and 250 cc. of technical concentrated hydrochloric acid. The large lumps are broken up with a rod, steam is passed in, and the stirrer is started. Steam is introduced at such a rate that a temperature of 85–90° is reached within ten minutes; the mixture is stirred at this temperature for one hour longer. The hot mixture is then filtered through a 15-cm. Büchner funnel, and the filtrate is cooled to 35–40° in an ice bath.
The claret-colored solution (5.2–5.8 l.) is filtered through a fluted filter paper in a 15-cm. funnel into 1.2 l. of concentrated hydrochloric acid in an 8-l. bottle. The aminonaphthol hydrochloride starts to precipitate immediately. The mixture is allowed to stand for at least two hours with occasional agitation to ensure complete precipitation. The hydrochloride is collected on a 15-cm. Büchner funnel and washed successively with three small portions of 20 per cent hydrochloric acid and three 50-cc. portions of ether (Note 4). It is then dried in the air in thin layers on filter paper. The yield is 180–200 g. of anhydrous material (Note 5) (66–74 per cent of the theoretical amount based on 200 g. of β-naphthol). The hydrochloride is unstable; in solution it decomposes rapidly, but this decomposition can largely be prevented by the addition of sodium bisulfite. The dry solid slowly changes and should be used within a few weeks of its preparation (Note 6).
2. Notes
1. It is usually not convenient to dry the nitroso-β-naphthol. The amount given in these directions corresponds to 200 g. of β-naphthol, and the yield is calculated on this basis. The nitroso-β-naphthol dissolves in one mole of sodium hydroxide, forming a green solution. There is left in suspension a small amount of amorphous brown material which need not be removed.
2. The amounts of sodium hydroxide, sodium hydrosulfite, and hydrochloric acid used are such that complete precipitation of the aminonaphthol results at this point. It is well to test for complete precipitation, however, by adding a few drops of alkali to one portion of the filtrate and a little acid to another.
3. The aminonaphthol is very sensitive to atmospheric oxidation. When first precipitated it is white, but it becomes purple in the air and therefore should be handled rapidly. A small amount of sodium bisulfite may be added at this point to decrease the oxidation, but this is usually unnecessary since some bisulfite from the reduction adheres to the precipitate and is carried through to the final precipitation.
4. Washing with ether greatly facilitates the drying of the product and also lightens its color somewhat. If the material is to be used without being dried, the washing with ether may be omitted.
5. Air-dried material, when apparently completely dry, contains 10–15 per cent of moisture. In order to obtain the true weight of the material an aliquot sample should be dried over sodium hydroxide under reduced pressure.
6. The product, as first formed, is a very light purple but darkens on long standing. It may be purified by dissolving in hot water containing sodium bisulfite, filtering, and reprecipitating with hydrochloric acid.
(A) Diazotization of Sulfanilic Acid.—A mixture of 105 g. (0.5 mole) of sulfanilic acid dihydrate, 26.5 g. (0.25 mole) of anhydrous sodium carbonate, and 500 cc. of water is heated and stirred until all the sulfanilic acid has dissolved, and the solution is then cooled in an ice bath to 15° (sodium sulfanilate begins to crystallize at this temperature). A solution of 37 g. (0.54 mole) of sodium nitrite in 100 cc. of water is added and the resulting solution is poured at once onto a mixture of 106 cc. (1.25 moles) (Note 1) of concentrated hydrochloric acid (sp. gr. 1.18) and 600 g. of ice contained in a 2-l. beaker. The solution, from which p -benzenediazonium sulfonate separates on stirring, is allowed to stand in an ice bath for fifteen to twenty-five minutes, during which time the naphthoxide solution is prepared.
(B) Coupling: Orange II.—Seventy-two grams of β-naphthol (0.5 mole) is dissolved in the warm solution obtained by dissolving 110 g. (2.75 moles) (Note 2) of sodium hydroxide in 600 cc. of water in a 5-l. flask, and the solution is cooled to about 5° by the addition of 400 g. of ice. The suspension of the diazonium salt then is added and the mixture is stirred well and allowed to stand without external cooling for one hour (Note 3). The azo compound soon separates from the red solution and eventually forms a stiff paste.
(C) Reduction: 1,2-Aminonaphthol Hydrochloride.—The suspension of Orange II is heated to 45–50°, when all the material dissolves with slight evolution of gas. About one-tenth of 230 g. (about 1.1 moles) of technical sodium hydrosulfite (Note 4) is added cautiously and the mixture is stirred until the froth subsides; the remainder is then added without delay. The yellow material which first separates (probably the hydrazo compound) soon is converted into the nearly colorless aminonaphthol. In order to complete the reduction and to give an easily filterable product the mixture is heated strongly until it begins to froth; it is then cooled to 25° by stirring in an ice bath, and the pink or cream-colored product is collected and washed free from the slightly yellow mother liquor with water.
The crude aminonaphthol is washed into a beaker containing a solution at 30° of 2 g. of stannous chloride dihydrate and 53 cc. (0.63 mole) of concentrated hydrochloric acid in 1 l. of water. When the mixture is stirred the amine soon dissolves, leaving in suspension a small amount of fluffy material which is easily distinguishable from the original lumps (Note 5). The solution is clarified by stirring (without heating) for five minutes with 10 g. of decolorizing carbon, and it is then filtered by suction. The pale yellow solution is treated with 50 cc. of concentrated hydrochloric acid and heated to the boiling point, a second 50 cc. of the acid being added as the heating progresses. The color becomes somewhat fainter during this process. The vessel containing the hot solution is transferred to an ice bath and allowed to cool undisturbed, and the 1-amino-2-naphthol hydrochloride soon separates in the form of large, perfectly colorless needles. When fairly cold, 100 cc. of concentrated hydrochloric acid is added and the solution is cooled to 0° before collecting the product (Note 6). The hydrochloride is washed with a cold solution of 50 cc. of concentrated hydrochloric acid in 200 cc. of water and dried on a filter paper at a temperature not above 30–35°. The yield is 70–83 g. (72–85 per cent of the theoretical amount). The material will remain colorless, or very nearly so, if protected from the light in storage. The fresh solution in water is only faintly colored and leaves but a trace of residue on filtration.
Although this material is suitable for most purposes, it may be purified further in the following manner. It is dissolved by heating in a solution of 2 g. of stannous chloride and 2 cc. of concentrated hydrochloric acid in 1 l. of water, and the hot solution is clarified by filtration through a 5-mm. mat of decolorizing carbon (Note 7). The yellow or red color which may develop disappears on reheating to the boiling point. After the addition of 100 cc. of concentrated hydrochloric acid the solution is allowed to cool in an ice bath, treated with a second 100 cc. of acid, cooled to 0°, and collected and washed as before. The crystalline product is colorless, ash-free, and of analytical purity. The loss in the crystallization of an 80-g. lot amounts to 5–10 g. (6–12 per cent).
2. Notes
1. Diazotization can be accomplished by the use of just one equivalent of acid (0.5 mole), but the solution of the diazoic acid, NaO3SC6H4N=NOH, so formed is much less stable than the suspension of the inner salt which results from the use of more acid.
2. The excess alkali is not required for the process of coupling, but rather to provide conditions suitable for the reduction.
3. The yield is not improved by allowing a longer period for the reaction. Under the conditions specified, the mixture during the coupling remains at a temperature of 5–10°.
4. If the hydrosulfite is of poor quality more will be needed, and an additional amount of sodium hydroxide should also be added.
5. The solution is highly supersaturated, but it will remain so unless allowed to stand for an undue amount of time. It is also a mistake to add the quantity of concentrated hydrochloric acid specified to a suspension of the aminonaphthol, for this may initiate crystallization.
6. An alternative method of crystallization is to add all the hydrochloric acid (200 cc.) to the boiling solution and to allow this to cool slowly; very large, thick needles result. In the presence of stannous chloride there is no danger of a darkening of the solution as the result of oxidation.
7. This method is preferable to the usual one when dealing with a substance sensitive to air oxidation.
3. Discussion
1-Amino-2-naphthol has been obtained from β-naphthylamine 1 and, more practically, from β-naphthol through the nitroso compound or an azo compound. Nitroso-β-naphthol has been reduced in alkaline solution with hydrogen sulfide 2 , 3 or sodium hydrosulfite,4 but early workers encountered difficulty in converting the amine into its hydrochloride without undue oxidation. Sulfur dioxide was employed as an anti-oxidant, but it is wholly inadequate. Reduction in an acidic medium, usually with stannous chloride, has been more satisfactory. The isolalation of the amine stannochloride and its tedious decomposition with hydrogen sulfide 5 are unnecessary, for the amine hydrochloride can be caused to crystallize essentially free from tin by avoiding an excess of the reducing agent.2, 6, 7 Nitroso-β-naphthol has been reduced also with zinc dust and sulfuric acid,8 but the quality of the material, used for conversion to the quinone, is in some doubt.
The nitroso derivative has disadvantages as an intermediate in that it involves handling either a voluminous precipitate or a large volume of solution, and in that some tar is likely to form; hence an azo compound is preferable. Technical Orange II has been reduced in a neutral or alkaline medium with sodium sulfide 2 or sodium hydrosulfite,9 the sulfanilic acid being eliminated as the soluble sodium salt. With stannous chloride, the necessity of isolating the amine stannochloride1 can be avoided by using just the calculated amount of reagent, the resulting mixture of amine hydrochloride and sulfanilic acid being separated with an alkaline buffer.2 Witt10 found that the sulfanilic acid can be kept in solution if this is sufficiently acidic, and with this improvement Russig11 worked out a procedure for the preparation and reduction of Orange II which was reported to give excellent yields but which, judging from the results of conversion to the quinone, affords a poor product.
Orange II also has been reduced with zinc dust and hydrochloric acid,12 by electrolysis,13 and by catalytic hydrogenation,14 while a number of other azo dyes derived from β-naphthol have been reduced to 1,2-aminonaphthol with hydrogen and Raney nickel.15
The method described above is novel chiefly in that it makes use of stannous chloride as an antioxidant in preparing and crystallizing the amine hydrochloride. The method is applicable with slight modifications to the preparation of many other aminophenols.16
Submitted by W. W. Hartman, J. R. Byers, and J. B. Dickey.
Checked by Louis F. Fieser and J. T. Walker.
1. Procedure
In a 3-l. round-bottomed flask, fitted with a reflux condenser, are placed 100 g. (0.435 mole) of 1-nitro-2-acetylaminonaphthalene (p. 438) and a solution of 112 g. (2.8 moles) of sodium hydroxide in 2.7 l. of water (Note 1). The mixture is boiled until ammonia is no longer evolved (six to seven hours). The solution becomes deep red in color. It contains suspended crystals of sodium nitronaphthoxide; these are dissolved by the addition of 1 l. of hot water. The small amount of insoluble material is removed by filtration, washed with hot water until the washings are colorless, and then discarded although it contains a little nitronaphthylamine. The combined
washings and filtrate are made acid by adding 500 cc. of glacial acetic acid. The nitronaphthol precipitates as small, bright yellow crystals which are filtered on a 10-cm. Büchner funnel, washed with water, and dried. The yield of material melting at 101–103° is 76–81 g. (92–98 per cent of the theoretical amount).
The product is purified by recrystallization from 500 cc. of methyl alcohol containing 5 cc. of concentrated hydrochloric acid. The first crop of crystals amounts to 60 g. and melts at 103–104°. The mother liquors are concentrated to 150 cc., and a second crop weighing 12–13 g. is collected. The total yield of recrystallized material is 72–73 g. (88–89 per cent of the theoretical amount).
2. Notes
1. This concentration of alkali was found to be very satisfactory. The hydrolysis takes place rather rapidly at first when stronger alkali is used, with the precipitation of the sodium salt which forms a thick paste and causes bumping. When more dilute alkali is used, much more time is required to complete the hydrolysis.
3. Discussion
1-Nitro-2-naphthol has been prepared by the nitration of β-naphthyl ethyl ether;1, 2 by the oxidation of 1-nitroso-2-naphthol;3 and by the treatment of β-naphthol with diacetylnitric acid.4 It has also been prepared by the treatment of β-naphthylamine with three moles of sodium nitrite in the presence of an excess of acid;5 by the decomposition of benzeneazo-β-naphthol with nitric acid;6 by heating the nitrate of pseudocumeneazo-β-naphthol under reduced pressure;6 by the treatment of 1-bromo-2-naphthol in acetic acid with nitric acid;7 and by the reaction of nitrogen dioxide with β-naphthol.7 It has been prepared from 1-nitro-1-bromo-2-ketodihydronaphthalene by treatment with caustic alkali,8 and by the fusion of α-nitronaphthalene with sodium hydroxide.9
The method on which this procedure is based has been described by Andreoni and Biedermann and by others.10
References and Notes
1. Wittkampf, Ber. 17, 393 (1884).2. Gaess, J. prakt. Chem. (2) 43, 22 (1891).3. Stenhouse and Groves, Ann. 189, 151 (1877); Fierz-David and Ischer, Helv. Chim. Acta 21, 680 (1938).4. Pictet and Krijanowski, Arch. sci. phys. nat. Genève (4) 16, 191 (1903) (Chem. Zentr. 1903, II, 1109).5. Deninger, J. prakt. Chem. (2) 40, 300 (1889).6. Charrier and Ferreri, Gazz. chim. ital. 44 (I) 176 (1914).7. Armstrong and Rossiter, Ber. 24 (R), 720 (1891); J. Chem. Soc. Proc. 1891, 87, 89.8. Fries, Ann. 389, 317 (1912).9. Wohl, Ger. pat. 116,790 [Frdl. 6, 114 (1900–02)].10. Andreoni and Biedermann, Ber. 6, 342 (1873); Jacobson, ibid. 14, 806 (1881); Liebermann and Jacobson,
