Organic Syntheses, Coll. Vol. 4, p.148 (1963); Vol. 35, p.22 (1955).
. The reduction is carried out in a 400-ml. beaker
. The anode, a cylinder of sheet lead 3 in. in height and 2.25 in. in diameter, rests on the bottom of the beaker. Clamped inside the anode and extending almost to the bottom of the beaker is the catholyte chamber, a porous cup (Note 1)
5 in. deep and 1.75 in. in diameter. Clamped securely inside the cup and about 0.25 in. above its inside bottom surface is the cathode, a cylinder of 25-gauge sheet copper 6 in. long and 1.25 in. in diameter. It is provided with a row of seven vertical slots 0.25 in. wide and 1.25 in. long, evenly spaced around its circumference; the lower ends of the slots are about 2.5 in. from the bottom of the cathode (Note 2)
. Both electrodes are provided with binding posts for connection to the circuit. A stirrer is constructed with two double propeller blades attached to the shaft, one about 1.5 in. above the other, at a pitch that will direct the flow of liquid downward. The mechanically driven stirrer
is set to run deep inside the cathode (Note 3)
The current may be drawn from a commercially available battery charger (Note 4)
or from a storage battery, each capable of operating at about 6 volts. Experiment has shown that the considerable ripple in the output of the charger has no adverse effect on the reduction. A transformer in the input to the charger, or a variable resistance in the battery circuit, and a 0–3 ampere range d.c. ammeter complete the apparatus.
B. Reduction of o-chloronitrobenzene
. The stirrer is set in position carefully inside the cathode, which is clamped in place at the top. The porous cup, previously impregnated with the electrolyte, is charged with 11.5 g. (0.073 mole) of o-chloronitrobenzene (Note 5)
and about 80 ml. of a mixture of acetic acid (70 ml.), concentrated sulfuric acid (22 ml.), and water (8 ml.) (Note 6)
. The cup is then clamped securely in position, and the beaker containing the anode is supported just clear of the bottom of the porous cup and filled with the same solution of aqueous sulfuric and acetic acids to the same level as the liquid inside the cup. The stirrer is started, the current turned on, and the system observed for a few minutes until the current has become stable. It is then adjusted at some convenient value no greater than 2 amperes.
The temperature will rise slowly and should be maintained at 30–45° throughout the reduction, with cooling as necessary. The system requires no attention while in operation except for occasional inspection and possibly the addition of a few milliliters of 90% acetic acid
to maintain the surface of the catholyte at the desired level (Note 7)
C. Oxidation of 4-amino-3-chlorophenol
. When the reduction is complete (Note 8)
, the system is disassembled, the catholyte poured into a flask, and the apparatus rinsed with hot water into the same flask. The combined catholyte and washings are extracted with ether
in a continuous-type liquid-liquid extractor
to remove the acetic acid
almost completely (Note 9)
. The residual aqueous acid solution of the aminophenol (Note 10)
is made up to 4N
in sulfuric acid
by adding 20 ml. of concentrated sulfuric acid
and diluting with water to 400 ml.
At room temperature there is added in one portion a solution of 11 g. (0.037 mole, 50% excess over the theoretical amount) of sodium dichromate dihydrate
in 20 ml. of water. A rise in temperature of some 6–7° will be observed; it is desirable to moderate the temperature by external cooling if it should rise above 35°.
After the mixture has been allowed to stand at room temperature for at least an hour (Note 11)
, a few grams of clean sand is added and the dark red mixture is filtered with suction. The filtrate is extracted with ether (100 ml., then 4–5 portions of about 30 ml. each)
, and each extract is used in turn to extract the filter cake.
extracts are combined; the ether
is removed by distillation (Note 12)
, and the dark red tarry residue subjected to steam distillation. Some 40–50 ml. of distillate is collected after solid quinone no longer appears in the condenser (total volume about 150 ml.).
There is obtained by filtration 5.0–5.5 g.
) of yellow chloro-p
-quinone of m.p. 53–55°
extraction of the filtrate yields a further 1.0 g.
, which brings the total yield to 58–63% (Note 12)
and (Note 13)
. Crystallization from a small volume of aqueous ethanol
) raises the melting point to 55–56°.
A Norton dense grade Alundum extraction thimble
has been found suitable. Deposition of silicic acid
in the interstices of the cup to decrease transfer of material is desirable. This is accomplished by soaking the cup for an hour in 20% water glass, draining off the excess, and then keeping the cup totally immersed for 3 hours in 20% aqueous sulfuric acid
Finally, the cup is stored completely immersed in the electrolyte.
This cathode design, with the stirring described, is regarded as preferable to the combination used by Lukens3
and much simpler in construction. It provides better dispersion of the organic material, a feature which is particularly necessary if these reductions are carried out in aqueous solution (Note 6)
A Battery Booster, type 6-AC-4, manufactured by P. R.
Mallory and Company, Inc., Indianapolis, Indiana, gave good service.
Material equivalent to Eastman Kodak Company white label grade was used. It has been found that the same results are obtained using m-chloronitrobenzene
. Likewise, either o- or m-nitrotoluene
may be used in the preparation of toluquinone (Note 13)
The submitter states that lower yields of quinones (50–65%) are obtained by using as the electrolyte 75% by weight aqueous sulfuric acid
. The catholyte at the end of the reduction is diluted to about 500 ml. (4N
in sulfuric acid
) and oxidized directly. The low solubility of the nitro compounds in the aqueous acid makes exceedingly efficient stirring a necessity, and the cell must be maintained at 50–60° during the reduction to keep the nitro compound molten and so promote the formation of a fine emulsion. Solid aminophenol sulfate
sometimes crystallizes near the end of the reduction, and evolution of hydrogen
near the end of the run may force the pasty material out the top of the porous cup. In general, these difficulties are more troublesome than the continuous extraction necessitated by the use of acetic acid
in the catholyte.
In operation, a flood of electrolyte should be observable pouring over the lower ends of the slots in the cathode.
Complete reduction of the nitro compound is assured by the use of about 1.2 equivalents of current (9.4 ampere-hours), but a larger excess of current is no disadvantage.
It has been found satisfactory to continue the extraction for 30 minutes after the volume of the aqueous phase no longer decreases visibly. Saturated aqueous sodium bicarbonate
washes may be used to effect removal of the acetic acid
solutions of alkyl quinones. The cascade distribution apparatus devised by Kies and Davis4
is useful for this purpose. As halogenated quinones have been found to be unstable to bicarbonate, the acetic acid
must be removed before oxidation of the corresponding aminophenols.
It has been found that the sulfates of the aminophenols may be obtained in yields about the same as those recorded for the quinones by concentrating the aqueous catholytes under reduced pressure after removal of the acetic acid
It is recommended that the oxidation mixture be stored in a refrigerator if more than 6–8 hours must elapse before the work-up is completed.
Prolonged heating after removal of the ether
may lead to sublimation of the product, with resulting lower yield.
Essentially the same procedure, with alteration only in the temperature during the oxidation, is stated by the submitter to be satisfactory for the preparation of several other p
-benzoquinones. For p-benzoquinone
itself and for toluquinone
(both in 80%
yield) the oxidation is best carried out at 5–10°; for 3-chlorotoluquinone
yield), at 15–20°; for 2,5-dichloroquinone
yield), at 55–60°. In the last case, some of the weakly basic aminophenol is ether
extracted along with the acetic acid
; it may be recovered by distilling most of the ether
and acetic acid
under reduced pressure, extracting the dark residue with two 25-ml. portions of 1N sodium hydroxide
, and making the alkaline extract neutral or slightly acid with sulfuric acid
. Normal oxidation is carried out after combining this suspension of aminophenol with the original aqueous solution.
The low vapor pressure of 2,5-dichloroquinone
precludes the use of steam distillation; however, the quinone precipitates directly from the oxidation mixture as a tan solid and may be purified readily by sublimation, followed by crystallization from ethanol
. An excellent sublimation apparatus that will easily handle 10-g. quantities of this quinone has been described.5
This method has given only 25%
yield of methoxyquinone
which is highly sensitive to acid and requires a special isolation procedure.6
The present method is the result of a study by Cason, Harman, Goodwin, and Allen.6,7
The sequence of electrolytic reduction followed by oxidation has been used for the preparation of 5-bromotoluquinone
The preparation of an intermediate p-aminophenol
from the corresponding aromatic nitro compound by electrolytic reduction is a useful general method.11,12,13,14,15,16,17,18
-quinone has been prepared by acid dichromate oxidation of chlorohydroquinone19,20,21,22
It has been shown that pure chloro-p
-quinone is obtained only with some difficulty when chlorohydroquinone
is used.7 Potassium bromate
also has been used to oxidize chlorohydroquinine
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