2. Notes
The cooling of the reaction flask must be very efficient, a 10-15 cm. blanket of a thorough mixture of ice and salt being used. If this precaution is not employed, the time for the addition of the sulfuric acid is greatly increased, provided the temperature of the reaction mixture is still kept within the limits mentioned.
If a cork is used for the steam distillation of the reaction mixture of acetone and sulfuric acid, it should be coated well with pitch and wired into the flask. This is necessary because the vapors of the reaction mixture attack an ordinary cork very badly, and soften it so much that it is necessary to rewire it to prevent it from slipping out. A rubber stopper is satisfactory and may be used in several runs.
The evolution of gas is so vigorous that it is not possible to distil more than 2 l. of the original reaction mixture at one time in the apparatus described. The connections on the apparatus, in which the mesitylene is obtained from the crude reaction mixture, should be tight, since the fumes evolved during the heating are very irritating.
The product which distils during the initial heating and the three minutes of steam distillation is mainly satisfactory material; the rest of the steam distillation yields only a small amount of pure product. The two portions of the distillate are, therefore, kept separate, since the second distillate always contains a considerable amount of high-boiling product which tends to cause emulsification of the alkali in the purification. No recovery of acetone is made.
The mechanism of the reaction is undoubtedly as follows: when the sulfuric acid and acetone are in contact for long periods of time, several molecules of the acetone condense to form aldol condensation products. These do not break down into mesitylene until the temperature is raised in the second part of the experiment.
While the original reaction mixture is standing, the temperature gradually rises to 40'0 or 50'0 in the course of six to ten hours, and then gradually cools off again. It is probable that at the end of this time (when the flask has cooled again) the reaction mixture could be distilled with nearly as good a yield as is obtained after standing eighteen to twenty-four hours.
The wide variation in yields which are mentioned in the experimental part is probably due to a slight change in the grade of the chemicals which are used in this preparation. 3. Other Methods of Preparation
The cheapest and most convenient method by which mesitylene may be prepared is by the action of a dehydrating agent upon acetone; the agent most commonly used is sulfuric acid.[1] It has been shown also that phosphoric acid will convert acetone to mesitylene.[2] A number of other methods have also been used for the preparation of mesitylene: the action of sulfuric acid on methyl acetylene;[3] the action of sulfuric acid on mesityl oxide and phorone;[4] the action of aluminium{sic(british)} chloride on methyl chloride and benzene;[5] the action of mineral acids upon mesitoyl or benzoyl mesitylene;[6] the action of phosphoric acid upon diaceto-mesitylene;[7] the treatment of methylene-3-dimethyl-1, 5-cyclo-hexene-1 with bromine and then with alcoholic potash.[8]
[1] Ann. 141, 131 (1867); 147, 43 (1868); 278, 210 (1893); Bud. soc. chim. (2) 40, 267 (1883); J. prakt. Chem. (1) 15, 129 (1838); Am. Chem. J. 15, 256 (1893); 20, 807 (1898).
[2] J Chem. Soc. 99, 1251 (1911).
[3] Ber. 8, 17 (1875).
[4] Ber. 7, 1169 (1874); 10, 858 (1877).
[5] Ber. 12, 329 (1879); Ann. chim. phys. (6) 1, 461 (1884).
[6] Ber. 32, 1910 (1899).
[7] Ber. 32, 1563 (1899).
[8] Ber. 43, 3093 (1910).
(o)HO2CC6H>4s>NH2 + HNO2 + HCl—>(o)HO2CC6H4N2Cl + H2O (o) HO2CC6H4N2Cl + C6H5N(CH3)2—>(o)HO2CC6H4N = NC6H4N(CH3)2 + HCl
Prepared by H. T. CLARKE and W. R. KIRNER. Checked by ROGER ADAMS and J. B. DAVIS.
1. Procedure
TECHNICAL anthranilic acid (generally about 95 per cent pure) (685 g.) is dissolved in 1.5 l. of water and 500 cc. of concentrated hydrochloric acid (sp. gr. 1.17), by heating. The insoluble dark impurity present in small amounts is filtered off, and the filtrate is transferred to a 10-l. crock and chilled with stirring. It is then mixed with a mush of 2.5 kg. of ice and 750 cc. of concentrated hydrochloric acid. The crock is cooled externally with ice, and the contents stirred continuously. When the temperature reaches about 3'0, a filtered solution of 360 g. of sodium nitrite in 700 cc. of water is dropped in slowly, through a long capillary tube reaching below the surface of the liquid, until a faint but permanent reaction to starch potassium iodide paper is obtained; the temperature is kept between 3'0 and 5'0. This operation requires all but about 30 cc. of the nitrite solution and occupies one and a half to two hours. To the solution of the diazonium salt are now added 848 g. of dimethylaniline; this may be done rapidly, as the temperature does not rise appreciably. Stirring is continued for one hour, the temperature being kept at 5'0 Five hundred cc. of a filtered solution of 680 g. of crystallized sodium acetate diluted to 1200 cc. are then added, and the stirring continued for four hours. If a foamy solid rises to the surface during this time and refuses to become incorporated by the stirrer, a few drops of ethyl acetate may be added to reduce the foam. The mixture is allowed to stand overnight in an ice bath which is well insulated by several thicknesses of burlap; the temperature must be kept below 7'0 to get a good yield of product. The remainder of the sodium acetate solution is then added with stirring, and after the mixture has been stirred for an additional period of one to three hours, the temperature is allowed to rise slowly to 20-25'0 in the course of twenty-four hours. Just enough sodium hydroxide solution is then added, with stirring, to cause the mixture to have a distinct odor of dimethylaniline (about 240 cc. of a 40 per cent solution are generally required), and the mixture is allowed to stand for forty-eight hours or longer at room temperature (20-25'0).
The solid is then filtered off, washed first with water, then with 400 cc. of 10 per cent acetic acid (to remove the dimethylaniline) and finally with distilled water. The last filtrate is generally pale pink. The solid is sucked as dry as possible, spread out on a tray in order to allow most of the water to evaporate (fifteen to twenty hours) and then suspended in 4 l. of methyl alcohol in a 12-l. flask. This mixture is stirred on the steam bath under a reflux condenser for one to two hours, allowed to cool slowly, and then chilled in an ice bath and filtered. The solid product is washed with a second 4 l. of cold methyl alcohol. After being dried in air, the product varies in weight from 820 to 870 g.
The product is extracted with boiling toluene in the following manner: 150 g. are placed in a fluted filter paper of 29 cm. diameter in a 25-cm. glass funnel which passes through the cork of a 2-l. flat-bottom conical flask containing 1250 cc. of toluene (Fig. 2). The flask is heated on an electric stove, and a 12-l. round-bottom flask is placed on the funnel to act as a condenser, cold water being run through the flask. The toluene is boiled until the condensed liquid runs through almost colorless (this requires from four to ten hours). The heating is then discontinued, and, as soon as the liquid ceases to boil, the flask is removed to a bath containing water at 90-100'0; the level of the water should be slightly above the level of the liquid in the flask. This arrangement permits the temperature to fall slowly so that large crystals are obtained. In the meantime a second conical flask containing 1250 cc. of toluene is attached to the funnel, and a new charge of 150 g. of crude methyl red is placed in the paper. When extraction is complete it is found that a certain amount of black amorphous insoluble matter remains on the filter; this is discarded. The crystals of methyl red are filtered off and washed with a little toluene. The weight of pure material is 755-805 g. The mother liquors are concentrated to one-fourth of their volume, and the crystals which separate on cooling are recrystallized from fresh toluene. The recovered toluene can, of course, be employed again. The total yield of pure methyl red is 790—840 g. It melts at 181-182'0.
The watery mother liquors from the crude methyl red are rendered alkaline with sodium hydroxide and distilled until no more dimethylaniline passes over. In this way 250 to 400 g. of moist dimethylaniline are recovered.
2. Notes
The amount of hydrochloric acid indicated must not be reduced; otherwise, diazoamino compounds are formed.
It is essential to keep the temperature low while unreacted diazobenzoic acid remains in solution, in order to avoid decomposition. If this precaution is not taken, the yields are considerably diminished, through the formation of tarry by-products.
The use of a capillary tube for the addition of sodium nitrite prevents loss of nitrous acid by local reaction at the surface of the acid solution. The tube should not be tightly connected to the dropping funnel, but should be so arranged that air is sucked through with every drop. In this way, the entrance of the acid liquor into the capillary is prevented.
The formation of the azo compound takes place slowly on the addition of the dimethylaniline, but the speed of the reaction is greatly increased when the hydrogen ion concentration is lowered by the addition of the sodium acetate. It is nevertheless necessary to allow the reaction mixture to stand a long time; if the product be filtered off after only twenty-four hours, a further quantity of dye will separate from the filtrate on standing. The hydrochloride of methyl red is only sparingly soluble in cold water, and is apt to separate in blue needles if the acidity is not sufficiently reduced.
The alcoholic filtrate, obtained on digesting and washing the crude methyl red, contains a more soluble red by-product which gives a brownish-yellow solution in alkali. The methyl alcohol may be recovered with very little loss by distillation; it is, however, impracticable to attempt to recover any methyl red from the residue, owing to the tarry nature of the by-product. The proportion of this by-product is greatly increased if the temperature of the mixture is allowed to rise too soon after the addition of the sodium acetate.
Methyl red is described as crystallizing in needles from glacial acetic acid; on recrystallization from toluene it separates in plates.
When the methyl red is crystallized from toluene, it sometimes separates in the form of bright-red lumps, probably on account of too rapid crystallization. Under these conditions it is advisable to crystallize again, using a somewhat larger amount of toluene.
It is advisable to titrate the crude anthranilic acid with standard alkali and phenolphthalein before starting the experiment. In checking these directions, an 80 per cent anthranilic acid was used; it gave a correspondingly lower yield of methyl red (650-700 g.). The yield of methyl red is about 65 to 70 per cent based on the dimethylaniline actually used up, but only 58-63 per cent based on the anthranilic acid actually present in the technical anthranilic acid employed.
3. Other Methods of Preparation
Methyl red was first prepared[1] by diazotization of anthranilic acid in alcoholic solution, the product being allowed to react with dimethylaniline in the same solvent. It has been stated[2] that this process does not work satisfactorily and yields a different product, of brownish-red color.
The preparation of methyl red in aqueous solution has been described by two workers, one of whom[3] gives but few details and claims a nearly quantitative yield; the other[4] gives fuller details and states the yield to be 43.1 per cent of the theory. The recrystallization of methyl red from toluene is stated[5] to yield a product melting at 183'0.
[1] Ber. 41, 3905 (1908).
[2] Chem. Zentr. 1910, (1), 960; 1910, (11), 1561.
[3] J. Chem. Soc. 97, 2485 (1910).
[5] J. Chem. Soc. 99, 1334 (1911).
p-NITROBENZOIC ACID
(p)NO2C6H4CH>3s> + 3O(Na2Cr2O7 + H2SO4)—> (p)NO2C6H4CO2H + 3H2O
Prepared by O. KAMM and A. O. MATTHEWS. Checked by H. T. CLARKE and W. W. HARTMAN.
1. Procedure
IN a 5-l. round-bottom flask, fitted with a mechanical stirrer, are placed 680 g. of sodium dichromate, 1500 cc. of water, and 230 g. ofp-nitrotoluene. Stirring is started, and 1700 g. of concentrated sulfuric acid are allowed to flow in during about thirty minutes. The heat of dilution of the sulfuric acid will cause the nitrotoluene to melt, and rapid oxidation will soon take place. The last half of the sulfuric acid must be added gradually, in order to prevent too violent a reaction. Since a small amount of nitrotoluene is volatilized, it is advisable to carry on this work under a hood.
After the sulfuric acid has been added and the spontaneous heating of the reaction mixture has subsided, the mixture is heated to gentle boiling for about half an hour. After the reaction mixture has cooled, 2 l. of water are added, the cooled solution is filtered through a cloth filter, and the product washed with about 1 l. of water. In order to remove the chromium salts as completely as possible, the crude nitrobenzoic acid is warmed on the water bath and agitated with 1 l. of dilute (5 per cent) sulfuric acid solution. After cooling, the product is again filtered. It is then dissolved in 5 per cent sodium hydroxide solution, filtered from any chromium hydroxide remaining, and also from unchanged nitrotoluene. The filtrate, which should be light yellow or greenish in color, is acidified with dilute sulfuric acid, with stirring. It is usually preferable to run the alkaline solution into the dilute sulfuric acid, rather than to use the reverse procedure, for the precipitation of the nitro acid. The precipitated product is filtered with suction, washed thoroughly, and dried. The product should possess only a light-lemon color. The yield should be 230-240 g. (80-85 per cent of the theoretical amount).
For a product of special purity, crystallization from benzene is advisable. For most purposes, however, the nitrobenzoic acid may be used without crystallization, since its melting point is found to be within 2'0 of the correct value of 238'0.
2. Notes
The above procedure differs from that recorded in the literature, mainly in the use of a fairly large excess of sulfuric acid. This shortens the reaction time from forty hours to about one hour, which is especially convenient in the preparation of the acid on a laboratory scale. Because of the use of this large excess of sulfuric acid, the reaction is apt to be rather violent if the directions given are not carefully followed. The oxidation should be carried out under a hood. Small amounts of nitrotoluene are lost by volatilization, but this loss is not serious, as can be seen from the yield of product obtained.
Ten or 20 g. of unchanged nitrotoluene can be recovered from the reaction mixture by steam distillation, but the value of the by-product would not pay for the time spent in recovery.
The washing of the crude reaction product with dilute sulfuric acid is advisable, if good material is to be obtained. If an efficient centrifuge is available for use at this stage of the operation, this separate washing may prove to be less essential.
When a sparingly soluble organic acid is precipitated from fairly concentrated solution, the precipitate is liable to carry down with it some of the salt of the organic acid. Addition of the salt solution to the mineral acid, with stirring, avoids this difficulty. 3. Other Methods of Preparation
The nitration of benzoic acid produces only very small yields of thep-nitro product.[1] The only practical method for the preparation consists in the oxidation ofp-nitrotoluene, although for this purpose various oxidizing agents are used. In addition to nitrotoluene,p-nitrobenzyl alcohol,p-nitrocinnamic acid and similar compounds may be oxidized, but their cost is prohibitive in comparison with that of the cheaper nitro hydrocarbon.
p-Nitrotoluene may be oxidized by means of strong nitric acid,[2] chromic acid mixture,[3] or permanganates.[4] Electrolytic oxidation[5] has also been proposed. The procedure given above involves the use of chromic acid mixture, but, owing to a change in the concentration of sulfuric acid, the time of reaction is greatly shortened and the preparation is thus considerably improved.
[1] Ber. 8, 528, 536 (1875)
[2] Ann. 127, 137 (1863); 128, 257 (1863)
[3] Ann. 139, 335 (1866).
[4] J. Am. Chem. Soc. 41, 1575 (1919).
[5] R. P. 117, 129; Frdl. 6, 112.
XIVp-NITROBENZYL CYANIDE
C6H5CH2CN + HNO3—> (p)NO2C6H4CH2CN + H2O
Prepared by G. R. ROBERTSON. Checked by ROGER ADAMS and H. O. CALVERY.
1. Procedure
IN a 2-l. round-bottom flask, fitted with a stopper holding a dropping funnel and a mechanical stirrer, is placed a mixture of 275 cc. of concentrated nitric acid (sp. gr. 1.42) and 275 cc. of concentrated sulfuric acid (sp. gr. 1.84). This is cooled to 10'0 in a freezing mixture, and 100 g. of benzyl cyanide (free from alcohol and water) are run in slowly, at such a rate that the temperature remains at about 10'0 and does not exceed 20'0. After all the benzyl cyanide has been added (about one hour), the ice bath is removed, the mixture is stirred for an hour and then poured on to 1200 g. of crushed ice. A pasty mass slowly separates; more than half of this mass isp-nitrobenzyl cyanide, the other constituents beingo-nitrobenzyl cyanide, and a variable amount of an oil which resists hydrolysis; apparently no dinitro compounds are formed. The mass is filtered on a porcelain funnel with suction, pressed well to remove as much oil as possible, and dissolved in 500 cc. of boiling alcohol (95 per cent). On cooling,p-nitrobenzyl cyanide crystallizes; the mother liquor, on distillation, gives an impure alcohol which can be used for the next run. Recrystallization from 550 cc. of 80 per cent alcohol (sp. gr. 0.86 to 0.87) yields 70 to 75 g. (50-54 per cent) of a product which melts at 115-116'0.
This product is satisfactory for most purposes, and incidentally for the preparation ofp-nitrophenylacetic acid. Occasionally it must be free even from traces of the ortho compound, and in this case should be crystallized again from 80 per cent alcohol; it then melts at 116-117'0.
2. Notes
Fuming nitric acid may be used in nitrating benzyl cyanide, but the method here described is cheaper.
The yield of 70 g. is obtained from benzyl cyanide, which boils over a 5'0 range prepared as described in preparation III (p. 9). Very pure benzyl cyanide will give a slightly higher yield, while commercial grades may give only 50 g. ofp-nitrobenzyl cyanide and much oil.
The reaction has been also carried out with 500 g. of benzyl cyanide. Under these conditions a 5-l. flask was used, and it required two and a half hours to add the benzyl cyanide. The yield of product was 325 to 370 g.
3. Other Methods of Preparation
Nitrobenzyl cyanide has hitherto been prepared by the action of fuming nitric acid[1] on benzyl cyanide.
[1] Ber. 17, 505 (1884); 33, 170 (1900); J. Biol. Chem. 39, 585 (1919); J. Am. Chem. Soc. 43, 180 (1921).
p-NITROPHENYLACETIC ACID
(p)NO2C6H4CN + H2SO4 + 2H2O—> (p)NO2C6H4CH2CO2H + NH4HSO4
Prepared by G. R. ROBERTSON. Checked by ROGER ADAMS and H. O. CALVERY.
1. Procedure
IN a 1-l. round-bottom flask are placed 100 g. ofp-nitrobenzyl cyanide. A solution of 300 cc. of concentrated sulfuric acid (sp. gr. 1.84) in 280 cc. of water is prepared, and two-thirds of this solution is poured on to thep-nitrobenzyl cyanide. The mixture is shaken well, until the solid is all moistened with the acid. Any solid material sticking to the walls of the vessel is now washed down into the liquid with the remainder of the acid, the flask is attached to a reflux condenser, then set, without shaking, over a 10-cm. hole in a large sheet of asbestos board which rests on a tripod, and heated until the mixture boils. The boiling is continued for fifteen minutes.
The reaction mixture, which becomes rather dark, is diluted with an equal volume of cold water and cooled to 0'0 or below. The solution is filtered, the precipitate is washed several times with ice water and then dissolved in 1600 cc. of boiling water. (A few grams of animal charcoal are added in dissolving the precipitate, if a technicalp-nitrobenzyl cyanide has been used.) This solution is filtered as rapidly as possible through a large folded filter, preferably with a steam funnel. In spite of all precautions, however, some solid usually separates on the filter. This must be redissolved in a minimum quantity of boiling water, and this solution then filtered into the main solution. Thep-nitrophenylacetic acid separates in long, pale-yellow needles, which melt at 151-152'0. The yield is 103 to 106 g. (92- 3 per cent of the theoretical amount).
2. Notes
If the flask is not protected with an asbestos board or the equivalent, decomposition occurs where the substance is super-heated on the side walls of the flask. If crystals of the cyanide are allowed to remain on the upper walls of the flask, they are not easily washed down and so are not hydrolyzed.
The solubility curve ofp-nitrophenylacetic acid is very steep at temperatures near 100'0, so that the filtering of the boiling solution should be rapid.
If a good grade of cyanide be used, it is not necessary to add bone-black in order to obtain the acid in a pure state.
In making experiments with 500 g. ofp-nitrobenzyl cyanide, it was found that the time for hydrolysis was about the same as when smaller amounts were used.
3. Other Methods of Preparation
p-Nitrophenylacetic acid has been formed by the nitration of phenylacetic acid;[1] by the hydrolysis of its ester[2] or its amid,[3] and by the hydrolysis of its nitrile with hydrochloric acid.[4]
[1] Ber. 42, 3596 (1909).
[2] Ber. 12, 1765 (1879).
[3] Ber. 14, 2342 (1881).
[4] Ber. 15, 834 (1882).
NITROSO-b-NAPHTHOL
C10H7OH(b) + HNO2—> C10H6(OH)NO(1,2) + H2O
Prepared by C. S. MARVEL and P. K. PORTER. Checked by H. T. CLARKE and W. W. HARTMAN.
1. Procedure
IN a 12-l. round-bottom flask fitted with a mechanical stirrer are placed 500 g. of technical b-naphthol dissolved in a warm solution of 140 g. of sodium hydroxide in 6 l. of water. The solution is cooled to 0'0 in an ice-and-salt bath, and 250 g. of powdered technical sodium nitrite is added. Stirring is started and 1100 g. of sulfuric acid (sp. gr. 1.32) are added from a dropping funnel, at such a rate that the whole is added in one to one and a half hours, the temperature being kept at 0'0. During the reaction crushed ice is added from time to time to maintain the temperature at 0'0; about 1 kg. is usually used. After all of the sulfuric acid has been added, the solution should react acid to Congo paper. The mixture is stirred one hour longer at the low temperature and then the nitroso-b-naphthol, which has gradually separated out 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 97'0. A sample of this partially dried product, on dryingin vacuoover sulfuric acid for twenty hours, loses about 10 per cent of its weight and the melting point is 106'0. By longer drying under ordinary conditions, the melting point of 106'0 is reached. The total yield of dry product is about 595 g. (99 per cent of the theoretical amount).
This product is satisfactory for all purposes. It may be obtained in a crystalline condition, however, by recrystallizing from hot ligroin (sp. gr. 0.71-0.72). About 2 g. of nitroso-b-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
It is very necessary to keep the temperature near 0'0 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.
A large vessel is needed for the reaction, as the nitroso-b-naphthol separates in a finely divided condition and there is some tendency to foam.
The final air-dried product is pure except for its moisture content, as is shown by the fact that on dryingin vacuoit has a very good melting point. A sample of Kahlbaum's nitroso-b-naphthol melted at 101—105.
3. Other Methods of Preparation
Nitroso-b-naphthol has been made by the action of hydroxylamine hydrochloride on b-naphtho-quinone-chlorimide;[1] by the action of sulfuric acid upon a solution of potassium or sodium nitrite and the sodium salt of b-naphthol;[2] by the action of sodium nitrite upon an alcoholic solution of zinc chloride and b-naphthol;[3] by the action of sodium nitrite upon b-naphthol suspended in zinc sulfate solution;[4] by the action of nitrous acid on b-dinaphthol methane;[5] and by the action of nitrosyl sulfate upon the sodium salt of b-naphthol.[6]
[1] Ber. 27, 241 (1894).
[2] Ber. 8, 1026 (1875); 27, 3076 (1894); J. Chem. Soc. 45, 295 (1884).
[3] Ber. 18, 705 (1885).
[4] D. R. P. 25,469; Frdl. 1, 335 (1883).
[5] Ber. 33, 806 (1900).
[6] J Chem. Soc. 32, 47 (1877); Ann. 189, 146 (1877).
C6H5CH2CN + 2H2O + H2SO4—> C6H5CH2CO2H + NH4HSO4
Prepared by ROGER ADAMS and A. F. THAL. Checked by O. KAMM and A. O. MATTHEWS.
1. Procedure
IN a 5-l. round-bottom flask, fitted with a mechanical stirrer and reflux condenser, are mixed 1150 cc. of water, 840 cc. of commercial sulfuric acid and 700 g. of benzyl cyanide (preparation III, p. 9). The mixture is heated under a reflux condenser and stirred for three hours, cooled slightly and then poured into 2 l. of cold water. The mixture should be stirred so that a solid cake is not formed; the phenylacetic acid is then filtered off. This crude material should be melted under water and washed by decantation several times with hot water. These washings, on cooling, deposit a small amount of phenylacetic acid which is filtered off and added to the main portion of material. The last of the hot water is poured off from the material while it is still molten and it is then transferred to a 2-l. Claisen distilling flask and distilledin vacuo. A small amount of water comes over first and is rejected; about 20 cc., containing an appreciable amount of benzyl cyanide, then distils. This fraction is used in the next run. The distillate boiling 176-189'0/50 mm. is collected separately and solidifies on standing. It is practically pure phenylacetic acid, m. p. 76-76.5'0; it amounts to 630 g. (77.5 per cent of the theoretical amount). As the fraction which is returned to the second run of material contains a considerable portion of phenylacetic acid, the yield actually amounts to at least 80 per cent.
For the preparation of small quantities of phenylacetic acid, it is convenient to use the modified method given in the Notes.
2. Notes
The standard directions for the preparation of phenylacetic acid specify that the benzyl cyanide is to be treated with dilute sulfuric acid prepared by adding three volumes of sulfuric acid to two volumes of water. There action, however, goes so vigorously that it is always necessary to have a trap for collecting the benzyl cyanide which is blown out of the apparatus. The use of the more dilute acid, as described in the above directions, is more satisfactory.
The phenylacetic acid may also be made by boiling under a reflux condenser for eight to fifteen hours, without a stirrer, but this method is not nearly so satisfactory as that described in the procedure.
When only small quantities of the acid are required, the following modified procedure is of value. One hundred grams of benzyl cyanide are added to a mixture containing 100 cc. of water, 100 cc. of concentrated sulfuric acid, and 100 cc. of glacial acetic acid. After this has been heated for forty-five minutes under a reflux condenser, the hydrolysis is practically complete. The reaction mixture is then poured into water, and the phenylacetic acid isolated in the usual manner.
The odor of phenylacetic acid is disagreeable and persistent.
3. Other Methods of Preparation
The standard method of preparation of phenylacetic acid is by the hydrolysis of benzyl cyanide with either alkali[1a] or acid.[2a] The acid hydrolysis runs by far the more smoothly and so was the only one studied. There are numerous other ways in which phenylacetic acid has been formed, but none of them is of practical importance for its preparation. These methods include the following: the action of water on phenyl ketene;[3a] the hydrolysis and subsequent oxidation of the product between benzaldehyde and hippuric acid;[1] the reduction of mandelic acid;[2] the reduction of benzoylformic acid with hydriodic acid and phosphorus;[3] the hydrolysis of benzyl glyoxalidone;[4] the fusion of atropic acid with potassium hydroxide;[5] the action of alcoholic potash upon chlorophenylacetylene;[6] the action of benzoyl peroxide upon phenylacetylene;[7] the alkaline hydrolysis of triphenylphloroglucinol;[8] the action of ammonium sulfide upon acetophenone;[9] the heating of phenylmalonic acid;[10] the hydrolysis of phenylacetoacetic ester;[11] the action of hydriodic acid upon mandelonitrile.[12]
[1a] Ann. 96, 247 (1855); Ber. 14, 1645 (1881); Compt. rend. 151, 236 (1910).
[2a] Ber. 19, 1950 (1886).
[3a] Ber. 44, 537 (1911).
[1] Ann. 370, 371 (1909)a
[2] Chem. (2) 1, 443 (1865); Ber. 14, 239 (1881).
[3] Ber. 10, 847 (1877)
[4] J. prakt. Chem. (2) 82, 52, 58 (1910).
[5] Ann. 148, 242 (1868).
[6] Ann. 308, 318 (1899).
[7] J. Russ. Phys. Chem. Soc. 42, 1387 (1910); Chem. Zentr. 1911 (I) 1279.
[8] Ann. 378, 263 (1911).
[9 Ber. 21, 534 (1888); J. prakt. Chem. (2) 81, 384 (1910).
[10] Ber. 27, (1894).
[11] Ber. 31, 3163 (1898)
[12] Inaugural Dissertation of A. Kohler (1909), Univ. of Bern.
C6H5CH=CHBr + KOH—> C6H5CTBCH + KBr + H2O
Prepared by JOHN C. HESSLER. Checked by J. B. CONANT and E. R. BARRETT.
1. Procedure
IN a 500-cc. Pyrex distilling flask are placed 150 g. of potassium hydroxide. The mouth of the flask is provided with a one-hole stopper holding a dropping funnel; the side tube of the flask is connected with a condenser set for downward distillation. The b-bromostyrene (100 g.) is placed in the dropping funnel.
The distilling flask is gradually heated in an oil bath until the temperature of the bath is 200'0, and the bromostyrene is then dropped in upon the molten potassium hydroxide, at the rate of somewhat less than a drop a second. Since the boiling point of phenylacetylene is 142-143'0, and that of bromostyrene is 218-220'0, the phenylacetylene distils away from the unchanged bromostyrene.
While the bromostyrene is being dropped in, the temperature of the oil bath is raised very gradually to 215-220'0, and is kept at this temperature until all the bromostyrene has been added. Finally the temperature is raised to 230'0, and is held there until no more distillate comes over. The distillate is colorless; it consists of two layers, the lower one being water. The upper layer is separated and dried with solid potassium hydroxide. It is then distilled. The yield of the distilled phenylacetylene, boiling at 142-144'0, is 37 g. (67 per cent of the theoretical amount). 2. Notes
Toward the end of the reaction, a crust of potassium bromide may tend to cover the melted potassium hydroxide. One can break the crust by shaking the distilling flask gently, or by using a glass rod inserted through a second hole in the stopper holding the dropping funnel.
It is convenient to have such a rod or stirrer passing through a mercury seal in the stopper of the flask. An occasional turn of this stirrer breaks the crust and facilitates the operation. Mechanical stirring should not be employed, as it reduces the yield tremendously. Apparently this is because it facilitates the solution of bromostyrene in the tarry by-products and thus causes it to polymerize instead of reacting with the potassium hydroxide. A single Pyrex flask can be used for only three or four runs. The flask should be emptied while still very hot.
The yield of material can be somewhat increased by working with small lots (25 g. of bromostyrene).
The use of steel or copper vessels in place of a glass flask seems to diminish the yield slightly.
3. Other Methods of Preparation
Phenylacetylene has been prepared by the elimination of carbon dioxide from phenylpropiolic acid by means of phenol[1] or aniline[2] or by heating with barium hydroxide;[3] from styrene dibromide, by heating with potassium hydroxide in alcohol;[4] by heating b-bromo or chloro styrene with sodium ethylate or potassium hydroxide in alcohol;[5] by passing the vapors of a-dichloroethylbenzene over hot soda lime;[6] by the action of alcoholic potassium hydroxide on dibenzal-acetone tetra-bromide;[1b] by the action of aqueous potassium hydroxide on phenyl propargylaldehyde;[2b] by the action of molten potassium hydroxide on b-bromo-styrene.[3b]
[1] Ber. 20, 3081 (1887).
[2] Rec. trav. chim. 16, 157 (1896).
[3] Arm. 221, 70 (1883).
[4] Ann. 154, 155 (1870); 235, 13 (1886); Bull. soc. chim. 35, 55 (1881); (3) 25, 309 (1901).
[5] Ann. 308, 265 (1899); 342, 220 (1905).
[6] Jahresb. 1876, 308; Gazz. chim. ital. 22 (2), 67 (1892); Bull. soc. chim. (3) 25, 309 (1901).
[1b] Ber. 39, 4146 (1900).
[2b] Ber. 31, 1023 (1898).
[3b] J. Am. Chem. Soc. 44, 425 (1922).
C6H5NH2<.>HCl + NaNO2 + HCl—> C6H5N2Cl + NaCl + 2H2O C6H5N2Cl + 4H(Na2SO3)—> C6H5NHNH2<.>HCl
Prepared by G. H. COLEMAN. Checked by J. B. CONANT and H. R. THOMPSON.
1. Procedure
IN a 12-l. round-bottom flask, fitted with a mechanical stirrer, are placed 1045 cc. of concentrated commercial hydrochloric acid (sp. gr. 1.138). The flask is surrounded with a freezing mixture of ice and salt, and when the contents are at 0'0, stirring is started and 500 g. of cracked ice are added; then 372 g. of aniline, also cooled to 0'0, are run in during five minutes. The mixture is treated with 500 g. more of cracked ice, and a cold solution (0'0) of 290 g. of technical sodium nitrite dissolved in 600 cc. of water are allowed to run in slowly (twenty to thirty minutes) from a dropping funnel, the end of which is drawn to a small tip, and reaches nearly to the bottom of the flask. During this addition, the stirrer is operated rather vigorously, and the temperature is kept as near 0'0 as possible by the frequent addition of cracked ice (about 1 kg).
In the meantime, a sodium sulfite solution is prepared by dissolving 890 g. of sodium hydroxide, of about 90 per cent purity, in about 1 l. of water and then diluting to 6 l. A few drops of phenolphthalein solution are added and sulfur dioxide passed in, first until an acid reaction is indicated and then for two or three minutes longer. During the addition of the sulfur dioxide, the solution is cooled with running water. On account of the strong alkaline solution, the original color produced by the phenolphthalein is very faint, but this slowly increases until it becomes deep just before the acid point is reached. It is best to remove a small sample of the liquid from time to time, dilute with three or four volumes of water and add a drop more of phenolphthalein.
The sodium sulfite solution is placed in a 12-l. flask and cooled to about 5'0. Approximately 500 g. of cracked ice are added, and then, with mechanical stirring, the diazonium salt solution is run in as rapidly as possible. The mixture becomes a bright orange-red. The flask is now warmed to about 20'0 on a steam bath, until the solid sodium sulfite, which has separated while cooling, redissolves. The total amount of liquid is now about 10 l. One-half of this is poured into another 12-l. flask, and both halves are warmed on the steam bath to 60-70'0, until the color becomes quite dark (thirty to sixty minutes). Sufficient hydrochloric acid (300-400 cc.) is now added to each flask to make the solutions acid to litmus. The heating is continued and the color gradually becomes lighter until, after four to six hours, the solutions have become nearly colorless; they may be heated overnight, if desired.
To the hot solutions are now added about one-third of their volume of concentrated hydrochloric acid (2 l. to each portion) and the mixtures cooled, first in running water, then in a freezing mixture, to 0'0. The phenylhydrazine hydrochloride precipitates in the form of slightly yellowish or pinkish crystals which may be filtered off and dried.
The free base is liberated by adding to the phenylhydrazine hydrochloride 1 l. of a 25 per cent solution of sodium hydroxide. The phenylhydrazine separates and is taken up with benzene (two 300-cc. portions). The combined extractions are well dried with 200 g. of solid sodium hydroxide, poured off, and distilled. Most of the benzene may be distilled under ordinary pressure, and the remainder, and any low-boiling impurities, under diminished pressure. The pure phenylhydrazine boils at 137-138'0/18 mm., and is obtained as a pale-yellow liquid. It can be crystallized on cooling in an ice bath; the crystals melt at 230. The crude phenylhydrazine from two lots of aniline (744 g.) is best distilled at one time and gives 695-725 g. of pure product (80-84 per cent of the theoretical amount).
2. Notes
If the sodium sulfite solution contains an excess of alkali, a black tar tends to form when the solution is warmed, and very little phenylhydrazine is obtained. Great care must be taken in determining the end point in the neutralization of the sodium hydroxide by the sulfur dioxide.
If the sodium sulfite-diazonium salt mixture is acidified before warming or before becoming dark, the red color of the solution does not disappear on heating, and the precipitated phenylhydrazine hydrochloride obtained is colored red.
The benzene solution of phenylhydrazine should be well dried before distilling, since the presence of moisture causes an increased amount of foaming to take place just after the benzene has distilled off. When the distillation is carried out carefully, practically no phenylhydrazine distils with the benzene or other low-boiling impurities.
In order to obtain the maximum yield, it is necessary to cool the hydrochloric acid solution of the phenylhydrazine hydrochloride from 20'0 to 0'0, before filtration. From 5 to 10 per cent of product separates between these two temperatures. When this is done, no more phenylhydrazine hydrochloride is obtained by concentration of the mother liquor. An increase in the amount of hydrochloric acid above 2 l. for the precipitation of the hydrochloride produces no increase in yield of product.
Most published directions for the preparation of phenylhydrazine specify the use of zinc dust and acetic acid following the reduction with sodium sulfite. No improvement in the quality or quantity of the product was obtained by using zinc and acetic acid.
It is best to use freshly prepared sodium sulfite for the reduction, since the commercial quality is poor and gives a lower yield of phenylhydrazine. A cylinder of liquid sulfur dioxide should, of course, be available.
The rapid addition of the diazonium salt solution to the sodium sulfite seems to be advantageous.
Pure phenylhydrazine dissolves in dilute acetic acid to yield a perfectly clear solution.
The phenylhydrazine hydrochloride may be purified by crystallizing from water. A 600-cc. portion of water is used for 100 g. of crude hydrochloride, and the solution boiled a short time with a few grams of animal charcoal. After filtering, 200 cc. of concentrated hydrochloric acid are added, and the mixture cooled to 0'0. Pure white crystals in a yield of 85-90 g. are obtained.
Rubber gloves should be worn when working with large quantities of phenylhydrazine, since the product may cause serious injury to the skin. The vapors of phenylhydrazine should not be inhaled.
3. Other Methods of Preparation
Phenylhydrazine has been prepared by the reduction of benzene diazonium salts with sulfites;[1] by the reduction of benzene diazonium chloride with stannous chloride;[2] by the reduction of benzene diazonium hydrate with zinc or sulfur dioxide;[3] by the reduction of sodium benzene diazotate with sodium stannite;[4] by the reduction of diazoamino benzene;[5] by the reduction of nitrosophenyl hydroxylamine or its methyl ether;[6] and by the action of hydrazine hydrate on phenol.[7]
[1] Ann. 190, 79 (3878); Ber. 20, 2463, (1887).
[2] Ber. 16, 2976 (1883); 17, 572, footnote (1884).
[3] Ber. 31, 346 (1898).
[4] Ber. 36, 816 (1903).
[5] Ber. 31, 582 (1898).
[6] Ann. 190, 77 (1878).
[7] Ber. 31, 2910 (1898).
The most feasible method consists in the reduction of diazonium salts with sodium sulfite. Although this method is given in several laboratory manuals, the results were not found entirely satisfactory. The present directions provide for a lengthy but essential heating of the diazonium-sulfite mixture, omit the useless zinc dust reduction, and supply exact details for preparation on a fairly large laboratory scale.
PHTHALIMIDE CO CO C6H4< >O + NH4OH—> C6H4< >NH + 2H2OCO COCO CO2C<6s
Prepared by W. A. NOYES and P. K. PORTER. Checked by H. T. CLARKE and J. H. BISHOP.
1. Procedure
IN a 5-l. round-bottom flask (Pyrex) is placed a mixture of 500 g. of phthalic anhydride and 400 g. of 28 per cent ammonium hydroxide. The flask is fitted with an air condenser not less than 10 mm. in diameter and is then slowly heated with a free flame until the mixture is in a state of quiet fusion at a temperature of about 300'0. It requires about one hour before all the water has gone and about one and a half to two hours before the temperature of the reaction mixture reaches 300'0 and the mixture is a homogeneous melt. It is advisable, during the heating, to shake the flask occasionally; some material sublimes into the condenser and must be pushed down with a glass rod. The hot reaction mixture is now poured out into a crock, covered with a paper to prevent loss by sublimation, and allowed to cool. The product is practically pure without further treatment, and melts at 232-235'0. The yield is 470-480 g. (94-95 per cent of the theoretical amount).
Phthalimide may also be made by using 500 g. of phthalic anhydride and 500 g. of ammonium carbonate which has been previously ground in a mortar. The subsequent procedure is the same as when aqueous ammonia is used. Frequent shaking is necessary, and the sublimed material must be occasionally pushed back into the reaction flask. About two hours are required for completion.
2. Notes
Several smaller runs of 25 g. of phthalic anhydride gave the same percentage yield.
Phthalimide may be recrystallized from water, but only about 4 g. of phthalimide will dissolve in a liter of boiling water. It may also be crystallized from alcohol, in which solvent it dissolves to the extent of five parts in a hundred at boiling temperature.
On a large scale, it would be advisable to collect the small amount of ammonia given off during the reaction.
If desired, the product obtained by pouring the reaction mass into the crock may be treated with hot water to soften the cake, broken up with a glass rod, transferred to a flask and boiled with water for a few minutes. This treatment, however, is quite unnecessary; for all practical purposes, the crude cake, as it is obtained, may be ground up and used directly.
3. Other Methods of Preparation
Phthalimide has been formed by heating ammonium phthalate;[1] by heating acid ammonium phthalate;[2] by passing dry ammonia over heated phthalic anhydride;[3] by treating phthalyl chloride with dry ammonia;[4] by heating phthalamide;[5] by heating phthalic anhydride with ammonium thiocyanate;[6] by heating phthalic anhydride with urea;[7] by heating phthalic anhydride with ammonium carbonate;[1b] by heating phthalic acid with nitriles;[2b] by fusingo-cyanobenzoic acid;[3b] and by the action of potash ono-cyanobenzaldehyde.[4b]
[1] Jahresb. 1868, 549; Ann. 19, 47 (1836); 41, 110 (1842); 42, 220 (1842); 205, 300 (1880); 215, 181 (1882).
[2] Jahresb. 1847-1848, 590.
[3] Am. Chem. J. 3, 29 (1881).
[4] Am. Chem. J. 3, 28 (1881).
[5] Ber. 39, 2278 (1906).
[6] Ber. 19, 1398 (1886),
[7] Ber. 10, 1166 (1877); Am. Chem. J. 18, 333 (1896); J. Am. Chem. Soc. 32, 116 (1910); Z. angew. Chem. 32, I, 301 (1919).
[1b] J. Am. Chem. Soc. 42, 1282 (1920).
[2b] J Am. Chem. Soc. 18, 680 (1896); 20, 654 (1898).
[3b] Rec. trav. chim. (I) 11, 93 (1892).
[4b] Ber. 30, 1698 (1897).
Of these, the first three are the only ones which need be considered as methods for the preparation of phthalimide. It was found that the third was by no means easy to bring about: dry phthalic anhydride is apparently only superficially affected by the dry ammonia, and it was difficult to introduce sufficient heat into the loose mass of crystals to cause the reaction to start.
/ \ / \ C3H5(OH)3 + C6H5NH2 + 4O(C6H5NO2)—> | | | + 4H2O \ / \n/
Prepared by H. T. CLARKE and ANNE W. DAVIS. Checked by ROGER ADAMS and A. W. SLOAN.
1. Procedure
IN a 5-l. round-bottom flask, fitted with an efficient reflux condenser of wide bore, are placed, in the following order, 80 g. of powdered crystalline ferrous sulfate, 865 g. of glycerol (c. p.), 218 g. of aniline, 170 g. of nitrobenzene, and 400 cc. of concentrated sulfuric acid (sp. gr. 1.84). The contents of the flask are well mixed and the mixture heated gently over a free flame. As soon as the liquid begins to boil, the flame is removed, since the heat evolved by the reaction is sufficient to keep the mixture boiling for one-half to one hour. If the reaction proceeds too violently at the beginning, the reflux condenser may be assisted by placing a wet towel over the upper part of the flask. When the boiling has ceased the heat is again applied and the mixture boiled for five hours. It is then allowed to cool to about 100'0 and transferred to a 12-l. flask; the 5-l. flask is rinsed out with a small quantity-of water. The 12-l. flask is then connected with the steam-distillation apparatus shown in Fig. 3, a 12-l. flask being used as a receiver; steam is passed in (without external heat) until 1500 cc. have distilled (ten to thirty minutes). This removes all the unchanged nitrobenzene (10-20 cc.). The current of steam is then interrupted, the receiver is changed, and 1500 g. of 40 per cent sodium hydroxide solution are added cautiously through the steam inlet. The heat of neutralization is sufficient to cause the liquids to boil and thus become thoroughly mixed. Steam is then passed in as rapidly as possible until all the quinoline has distilled. In this process, 6-8 l. of distillate are collected (two and a half to three and a half hours are required, unless a very efficient condensing apparatus is used, under which conditions the distillation may be complete in one-half to one and a half hours). The distillate is allowed to cool, and the crude quinoline separated. The aqueous layer of the distillate is again distilled with steam until all the quinoline has been volatilized and collected in about 3 l. of distillate.
These 3 l. of distillate are then mixed with the first yield of quinoline and 280 g. (150 cc.) of concentrated sulfuric acid are added. The solution is cooled to 0-5'0, and a saturated solution of sodium nitrite added until a distinct excess of nitrous acid is present (as shown either by starch-potassium iodide paper or by the odor). This generally requires 50 to 70 g. of sodium nitrite. The mixture is then warmed on a steam bath for an hour, or until active evolution of gas ceases, and is then distilled with steam until all the volatile material has been expelled (41. of distillate will result) The receiver is then changed and the mixture in the distillation flask is neutralized, as before, with 700 g. of 40 per cent sodium hydroxide solution. The quinoline is distilled exactly as described above, the aqueous portions of the distillate being distilled with steam until all the quinoline has been isolated. The crude product is then distilled under reduced pressure, and the fraction which boils at 110-114'0/14 mm. is collected. The foreruns are separated from any water which may be present, dried with a little solid alkali, and redistilled. The total yield is 255-275 g. (84-91 per cent of the theoretical amount based on the aniline taken).
2. Notes
Although these directions have been used many times with results exactly as described, in a few cases the yields have dropped to 60-65 per cent without any apparent reason. At present no explanation can be given for this.
In the Skraup synthesis of quinoline the principal difficulty has always been the violence with which the reaction generally takes place; it occasionally proceeds relatively smoothly, but in the majority of cases gets beyond control, with consequent loss of material through the condenser. By the addition of ferrous sulfate, which undoubtedly functions as an oxygen carrier, the reaction is extended over a longer period of time. It is thus possible to work with much larger quantities of material when ferrous sulfate is employed.
It is important that the materials should be added in the correct order; should the sulfuric acid be added before the ferrous sulfate, the reaction may start at once. It is also important to mix the materials well before applying heat; the aniline sulfate should have dissolved almost completely and the ferrous sulfate should be distributed throughout the solution. To avoid danger of overheating, it is well to apply the flame away from the center of the flask where any solids would be liable to congregate.
In the apparatus for steam distillation, the greater portion of the condensation is effected by the stream of water passing over the receiver. It is, therefore, necessary that the stream passing through the condenser should be sufficiently rapid to cause it to form a uniform film over the receiving flask. A 12-l. flask is even more efficient as a condenser than the 5-l. flask. It is important that the tube through which the vapors leave the distillation flask should be neither too short nor, especially, too narrow. Where the external diameter of the steam inlet tube is 5-8 mm., the internal diameter of this steam head should be not less than 28 mm. Were it less, the current of steam passing through it would be so rapid as to prevent small quantities of liquid from returning to the flask, and these would be driven over into the receiver.
Much time can be saved by the use of the steam distillation apparatus described, especially when large quantities have to be handled. The above directions avoid the use of extraction methods, which not only consume more time but may lead to appreciable losses of material. If the downward condenser is of iron, the apparatus is even more efficient and the time for the steam distillation is halved.
The percentage yields have been based on the amount of aniline taken. It would probably be more legitimate to base the calculation on the amounts of aniline taken and of nitrobenzene not recovered, since undoubtedly the latter is reduced to aniline during the course of the reaction. If this be done, the yield is found to be only 55 to 60 per cent of the calculated amount.
In a number of experiments, the glycerol used contained an appreciable amount of water. Under these conditions, the yield of product is much lower. "Dynamite" glycerol containing less than half a per cent of water is best employed; U. S. P. glycerol contains 5 per cent of water and usually gives lower yields.
3. Other Methods of Preparation
Quinoline has been produced by passing the vapor of allylaniline over red-hot lead oxide;[1a] by heating acrylideneaniline, or better, a mixture of aniline, glycerol and sulfuric acid;[2a] by heating aniline with glycerol and sulfuric acid, using nitrobenzene as an oxidizing agent;[1] by treating a mixture of glyoxal ando-toluidine with alkali;[2] by treating a solution ofo-aminobenzaldehyde with acetaldehyde and alkali;[3] by heating methylacetanilide with zinc chloride;[4] by heating aminoazobenzene with glycerol and sulfuric acid;[5] by heating a mixture of aniline, glycerol and sulfuric acid with arsenic acid.[6]
[1a] Ber. 12, 453 (1879).
[2a] Ber. 13, 911 (1880); Monatsh. 1, 316 (1880).
[1] Monatsh. 2, 141 (1881); J. prakt. Chem. (2) 49, 549 (1894),
[2] Monatsh. 15, 277 (1894).
[3] Ber. 15, 2574 (1882); 16, 1833 (1883).
[4] Ber. 23, 1903 (1890).
[5] Ber. 24, 2623 (1891)
[6] Ber. 29, 704 (1896)
Of the above methods, the only ones which need be considered are those in which a mixture of aniline, glycerol and sulfuric acid is heated with an oxidizing agent. With the use of nitrobenzene, the reaction, according to the original method, takes place with extreme violence.
The method above described is the most satisfactory for the preparation of quinoline itself, but for the preparation of homologues of quinoline, the use of arsenic acid is preferable, since the yields are somewhat greater.
Since the work was carried out, a method has been published[7] in which aniline, glycerol and sulfuric acid are treated with ferric oxide. By this method Adams and Parks were unable to obtain yields comparable with those resulting from the above directions.
[7] Chem. News 121, 205 (1920).
(1)HOC6H4OH(4) + O(Na2Cr2O7 + H2SO4)—> O=C6H4=O + H2O Prepared by E. B. VLIET. Checked by ROGER ADAMS and E. E. DREGER.
1. Procedure
IN a 2.5-l. beaker, 100 g. of hydroquinone are dissolved in 2000 cc. of water heated to about 50'0. After the solid is completely dissolved, the solution is cooled to 20'0, 100 g. of concentrated sulfuric acid are slowly poured in, and the mixture is again cooled to 20'0. A concentrated solution of technical sodium dichromate is prepared by dissolving 140 g. in 65 cc. of water. This solution is then added gradually to the hydroquinone solution, with the use of a mechanical stirrer (see notes), the mixture being cooled so that the temperature never rises above 30'0. At first a greenish-black precipitate forms, but upon further addition of the sodium dichromate solution, the color changes to yellowish green. As soon as this color remains permanent (a slight excess of sodium dichromate does no harm) the reaction is complete. This requires about one-half to three-quarters of an hour; 90 to 110 cc. of sodium dichromate solution is necessary. The mixture is then cooled to about 10'0 and filtered with suction. As much water as possible is pressed out of the crystals.
The filtrate is extracted twice, 150 cc. of benzene being used for each extraction. The precipitate of quinone is transferred to a 1-l. beaker, and 500 cc. of benzene, including the 300 cc. used to extract the filtrate, are added, The mixture is now heated with stirring on a steam-bath, and as soon as most of the quinone has dissolved the benzene layer is decanted into another beaker. It is dried while hot by stirring a short time with a little calcium chloride, and then filtered through an ordinary funnel into a 1-l. distilling flask before it cools. There is a certain amount of quinone which does not go into the 500 cc. of benzene, so that the residue is extracted a second time with about 100 cc. of benzene, which is dried and filtered with the first extract. During these extractions, the benzene should not be at the boiling point, as this will cause a considerable volatilization of the quinone.
The distilling flask is now attached to a condenser set for downward distillation, and the benzene is distilled. As soon as the quinone starts to separate, the residue in the flask is transferred to a beaker and cooled in an ice bath. The precipitate is filtered off with suction and the product spread out for a short time to dry. The product is yellow in color and weighs 75 to 80 g. (76-81 per cent of the theoretical amount). Material made in this way will hold its yellow color over long periods of time, provided it is protected from light.
The benzene distillate is yellow and contains some quinone. This, as well as the benzene from the final filtration of the quinone crystals, may be used in a subsequent run and thus raises the yield of the subsequent runs to about 85-90 g. (85-90 per cent of the theoretical amount).
2. Notes
As the mixture becomes thick during the oxidation, it is very necessary to use a stirrer which will keep the whole mass agitated by reaching to the sides and bottom of the beaker.
If impure hydroquinone is used, a black, sticky precipitate will usually appear after the addition of the sulfuric acid to the hydroquinone solution. This should be removed, before the oxidation is started, by filtration without suction through a fluted filter.
When technical sodium dichromate is used, the solution should be filtered with suction, before it is added to the hydroquinone, in order to remove any insoluble impurities.
In the laboratory it is convenient to make several small runs of the size indicated, as far as the oxidation is concerned; but the benzene extractions can be combined.
It is also possible to obtain good yields of quinone in the following manner: 1500 cc. of water, 465 g. of concentrated sulfuric acid and 300 g. of hydroquinone are mixed in a 3-l. beaker. The mixture is cooled to 0'0, and 330 g. of sodium dichromate are added in powdered form, the temperature being kept below 5'0 at all times. This procedure requires a longer time and much more care in the control of conditions than the method described above.
3. Other Methods of Preparation
Quinone may be prepared by the oxidation of aniline with dichromate or manganese dioxide and sulfuric acid.[1] This is a more feasible commercial method than the one given. However, the oxidation of hydroquinone is more rapid and convenient and, hence is more desirable for use in the laboratory. Various materials have been oxidized by chemical means to give quinone: they are quinic-acid,[2] hydroquinone,[3] benzidine,[4]p-phenylenediamine,[5] sulfanilic acid,[6]p-phenolsulfonic acid,[7] arbutin,[8] aniline black,[9] and the leaves of various plants.[10] Quinone is also formed by several other methods: by the fermentation of fresh grass;[11] by the action of iodine on the lead salt of hydroquinone;[1b] by the decomposition of the compound, C6H4<.>2CrO2Cl with water;[2b] by the action of sulfuric acid on phenol blue;[3b] by the electrochemical oxidation of aniline,[4b] hydroquinone[5b] or benzene;[6b] by the catalytic oxidation of benzene.[7b]
[1] Jahresb. 1863, 415; Ber. 10, 1934, 2005 (1877); 16, 687 (1883); 19, 1468 (1886); 20, 2283 (1887); 31, 1524 (1898); Ann. 200, 240 (1880); 215, 127 (1882).
[2] Ann. 27, 268 (1838).
[3] Ann. 51, 152 (1844) j Am. Chem. J. 14, 555 (1892).
[4] Jahresb. 1863, 415.
5 Jahresb. 1863, 422.
6 Ann. 159, 7 (1871); Ber. 8, 760 (1875).
[7] Ber. 8, 760 (1875).
[8] Ann. 107, 233 (1858).
[9] Ber. 10, 1934 (1877); 34, 1285 (1901).
[10] Ann. 89, 247 (1854); Ber. 34, 1162 (1901).
[11] Ber. 30, 1870 (1897).
[1b] Ber. 31, 1458 (1898); Am. Chem. J. 26, 20 (1901).
[2b] Ann. chim. phys. (5) 22, 270 (1881).
[3b] Ber. 18, 2915 (1885); 21, 889 (1888).
[4b] D. R. P. 109,012; Frdl. 5, 664 (1900); D. R. P. 117,129; Frdl. 6, 112 (1901); J. Soc. Dyers and Colourists, 36, 138 (1920).
[5b] D. R P. 117,129; Frdl. 6, 112 (1901).
[6b] D. R. P. 117,251; Frdl. 6, 109 (1901); U. S. Pat. 1,322,580 (1919); C. A. 14, 287 (1920); Rev. produits chim. 21, 219 (1918); 21, 288 (1918).
[7b] U. S. Pat. 1,318,631 (1919); C. A. 14, 70 (1920).