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 pa.s.sing over the receiver. It is, therefore, necessary that the stream pa.s.sing 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 pa.s.sing through it would be so rapid as to prevent small quant.i.ties 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 quant.i.ties 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 pa.s.sing 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 and _o_-toluidine with alkali;[2] by treating a solution of _o_-amin.o.benzaldehyde 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 a.r.s.enic 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 h.o.m.ologues of quinoline, the use of a.r.s.enic 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).

XXII

QUINONE

(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 ma.s.s 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