US2804453A - Promoted reduction of aromatic nitrogen compounds - Google Patents

Description

United States PROMOTED REDUCTFON F AROMATIC NITRQGEN CGMPQUNDS Leigh C. Anderson, Ann Arbor, Micln, and Chester E.

Smith, Jr., Wilmington, Del., assignors to Allied Chernical & Dye Corporation, New York, N. Y., a corporation of New York No Drawing. Application August 18, 1954, Serial No. 450,784

11 Claims. (Cl. 260-143) This invention relates to improvements in the method of reducing aromatic nitrogen compounds containing nitrogen in a reducible form as a substitute of a benzene nucleus (that is, as a substituent of a hydrogen atom forming part of a benzene nucleus) and at a higher stage, of oxidation than the hydrazo stage by the action of metal alcoholates. It relates more particularly to improvements in such methods, and especially in processes in which the reducing agent is an alkali metal alcoholate, especially an alkali metal methylate and preferably methanol and sodium hydroxide, whereby the reduction is promoted.

Ordinarily, the reduction of nitrobenzene and related aromatic nitro compounds by means of alkali metal alcoholates is carried out by heating it with alcoholic caustic alkali (e. g., sodium hydroxide and a lower alcohol, usually methanol) at the boiling point of the mixture while refluxing at atmospheric pressure. Under these conditions, the alkali metal alcoholates are not sufficiently strong reducing agents to carry the reduction beyond the azoxy stage. As disclosed in U. S. Patents 2,645,636 and 2,684,358, and in application Serial No. 290,089, filed May 26, 1952, of Francis W. Cashion now U. S. Patent 2,765,301, this reduction can be promoted, so as to result in the formation of reduction products of a lower stage of oxidation than the azoxy stage, or to obtain other beneficial results, by including in the reduction reaction mixtures naphthoquinoid compounds and especially naphthoquinones and addition products thereof (for example, with bisulfites, heavy metal salts, sulfiding agents, etc.), and quinoid hydroxynaphthalene compounds.

The primary object of the present invention is to provide additional reduction promoters which, when added to reduction reaction mixtures of the type referred to above, will eliect a similar reduction promoting effect.

A further object of the present invention is to provide improvements in reductions of the type referred to above whereby the reducing power of metal alcoholate reducing agents and especially of alcoholic caustic alkali reducing agents is enhanced and other advantages are secured.

Other objects of the present invention are to provide a process for the production of aromatic azo compounds in good yields by the reduction of aromatic nitro compounds, and their reduction products up to and including azoxy compounds, with metal alcoholates under moderate reaction conditions and in simple apparatus; to provide a process for the production of aromatic hydrazo compounds by reduction of aromatic nitro compounds and other reducible aromatic nitrogen compounds with metal alcoholates under moderate conditions and in simple apparatus; and to provide improvements in the reduction of educible aromatic nitrogen compounds with metal alcoholates whereby the evolution of hydrogen gas during the reduction is suppressed.

Additional objects in part will be obvious and in part will appear hereinafter.

According to the present invention the foregoing ob- 2,84,453 Patented Aug. 27, 1957 jects are accomplished and other benefits are secured by carrying out the reduction of the reducible aromatic nitrogen compound by means of a metal alcoholate in a reaction mixture in which one or more reduction promoters of a special class have been incorporated.

The class of reduction promoters employed in accordance with the present invention is constituted of certain derivatives of benzoquinone, herein designated by the expression ortho-cycloalkano-benzoquinoid compounds. It consists of (1) benzoquinones in which two adjacent carbon atoms of the quinone nucleus other than those forming part of the carbonyl groups are linked respectively to the end carbon atoms of a chain of at least 3 carbon atoms, and preferably 4 carbon atoms, of which at least 2 are saturated carbon atoms and the others may be unsaturated, herein designated by the expression "ortho-cycloalkano-benzoquinones (whether free from other substituents in the benzene nucleus besides the carbonyl oxygen atoms and the cycloalkano radical, or containing additional substituents in the benzene nucleus and/ or in the cycloalkano radical, wherein one or more of the hydrogen atoms is substituted by another atom or radicalfor example, halogen, hydroxyl, nitro, mercapto, amino, cyano, sulfo, carboxyl, alkyl, alkoxy etc.); (2) addition compounds of such benzoquinones (for example, with hydroquinones, bisulfites, heavy metal salts, sulfiding agents, etc); (3) functional derivatives and tautomeric forms of such benzoquinones capable of isomerizing to such benzoquinones (for example, imides, oximes, semicarbazones and hydrazones); and (4) hydroquinones corresponding to such benzoquinones, herein designated ortho-cycloalkano-benzohydroquinones.

Thus, said class of ortho-cycloalkano-benzoquinoid compounds includes:

2,3-cyclopropano-1,4-benzoquinone (4,7-indandione) 2,3-cyclobuteno-1,4-benzoquinone (5,8-dihydro-1,4-naphthoquinone) 2,3-cyclobutano-l,4-benzoquinone (5,6,7,8-tetrahydro-1,4-

naphthoquinone) 2,3-cyclobutano-1,4-benzoquinone oxime (4-nitroso-5,6,

7,8-tetrahydro-1-naphthol) 2,3-cyclobutano-1,4-benzoquinone bis-chlorimide (5,6,7,

8-tetrahydro-1,4-naphthoquinone bis-chlorimide) 6-chloro-2,3-cyclobutano-1,4-benzoquinone 5-chloro-6-anilino2,3-cyclobutano-1,4-benzoquinone 5,6-dichlor-2,3-cyclobutano-l,4-benzoquinone 5,6-dimethyl-2,3-cyclobutano-1,4-benzoquinone 2,3-cyclobutano-1,4-benzoquinhydrone (5,6,7,8 tetrahydro-l,4-naphthoquinhydrone) Sodium bisulfite addition product of 2,3-cyclobutano-1,4- benzoquinone (cf. Example 4 of U. S. P. 2,645,636) Sodium hyd-rosulfide addition product of 2,3-cyclobutano- 1,4-benzoquinone 2,3(2-chloro-cyclobuteno)1,4benzoquinone (6-chloro- 5 ,S-dihydro-l,4-naphthoquinone) 2,3-cyclobuteno-1,4-benzohydroquinone (5,8-dihydro-1,4-

naphthalenediol) 2,3-cyclobutano-1,2-benzohydroquinone (5,6,7,8-tetrahydro-l,2-naphthalenediol) 2,3-cyclobutano-1,4-benzohydroquinone (5,6,7,8-tetrahydro1,4-naphthalenediol) 2,3-cyclobutano-1,4-benzohydroquinone diacetate diacetoxy-S,6,7,S-tetrahydronaphthalene) 6-amino 2,3 cyclobutano 1,4 benzohydroquinone (2- amino-5,6,7,8-tetrahydro-1,4-naphthalenediol) 2,3-(2'-chloro-cyclobuteno) 1,4 benzohydroquinone (6- chloro-5,8-dihydro-1,4-naphthalenediol) 6-methyl-2,3-cyclobuteno-1,4-benzohydroquinone (5,8-di

hydro-2-methyl-1,4-naphthalenediol) 2,3-(1',4'-ethano-cyclobuteno) 1,4 benzohydroquinone (5,8-dihydro-5,8-ethano-1,4-naphthalenediol) 6-methyl(2.,3'-dirnethyl-cyclobuteno) 1,4 benzohydroquinone (5,8 dihydro 2,6,7 trimethyl-1,4-naphthalenediol).

Preferred ortho-cycloalkano-benzoquinoid compounds.

employed in accordance with the present invention are those in which the benzoquinone and benzohydroquinone contain the carbonyl or hydroxyl radicals in para relation (2,3-cycloalkano 1,4 benzoquinones and benzohydroquinones). Those in which the cycloalkyl radical contains 4 carbon atoms and the quinone nucleus is otherwise unsubstituted are especially preferred. We have discovered that the ortho-cycloalkano-benzoquinoid compounds constitute highly etfectivereduction promoters in the reduction of aromatic nitrogen compounds of the type referred to above by metal alcoholates and especially alkali metal alcoholates. We have found that the inclusion in the reaction mixture of even a small amount of a benzoquinoid compound of said type and especially of a 2,3-cyclo-alkano4,4-benzoquinone or corresponding hydroquinone has a modifying effect upon the reaction as a result of which a number of benefits may be secured.

Thus, as compared with a reduction carried out under the same conditions but in the absence of such reduction promoter, the speed of the reduction is increased and/or products of a higher stage of reduction are obtained, without substantial sacrifice of the total yield of reduction products secured from the starting material. In the reduction of aromatic nitro compounds, the inclusion of a reduction promoter of the above type in the metal alcoholate reaction mixture makes possible the obtainment of azo compounds directly, without requiring the use of drastic operating conditions, such as high temperatures and pressures of 10 or more atmospheres. Similarly, the inclusion of a reduction promoter of the above type in the reaction mixture makes possible the production of hydrazo compounds from nitro, azoxy and azo compounds by means of metal alcoholate reducing agents Without requiring the use of drastic operatingconditions. By their presence, .the reduction promoters suppress almost completely side reactions leading to the evolution of hydrogen gas during the reduction, thereby greatly increasing the safety of the reduction process and minimizing waste of the reducing agent.

When no substantial change in the degree of reduction is desired, the inclusion of a reduction promoter of the above type in the reduction reaction medium makes possible the use of milder reaction conditions or the use of decreased amounts of reducing agent. Thus, in the reduction of an aromatic nitro compound with sodium hydroxide and methyl alcohol, the presence of a reduction promoter of the above type in the reaction mixture makes possible the use of a lesser amount of sodium hydroxide, thereby decreasing the cost of the operation. This result is surprising because the related alkyl-substituted benzoquinones do not display a similar reduction-promoting eifect. For example, duroquinone (2,3,5,6-tetramethyl- 1,4-benzoquinone) and 2,3-dimethyl 1,4-benzoquinone which might be expected to have a reduction-promoting eifect similar to that of 1,4-naphthoquinone, not only because of their similar chemical composition to 1,4-naphthoquinone but the similarity of their oxidation-reduction potentials to that of 1,4-naphthoquinone, have very little ,elfect upon the reduction reaction.

In the practice of the present invention, the reducible aromatic nitrogen compound is subjected to the reducing action of a metal alcoholate reducing agent in a reaction mixture in which one or more of the promoters referred calcium chloride in an oven at about 100.

to above have been incorporated. In the preferred practice of the invention, wherein the reducible aromatic nitrogen compound is heated with a caustic alkali and an alcohol (preferably sodium hydroxide and methanol) at the boiling point of the reaction mixture, the reduction promoter is preferably mixed with the alcohol and, after adding the caustic alkali" and heating, the nitrogen compound tion promoter may be added to the reaction mixture in.

various ways and at various times, however, without departing from the scope of the invention.

The reduction promoter can be employed in various amounts. It is a feature of the present invention that merely small amounts of the ortho-cycloalkano-benzoquinoid compounds are effective as reduction promoters. Thus, amounts lying within the range 10, to & mol of such benzoquinoid compounds per mol of reducible aromatic nitrogen compound are ordinarily employed. The minimum amount required to produce a significant reduction-promoting etfect varies with the individual benzoquinoid compound employed, the nature of the reducible aromatic nitrogen compound, and the reaction conditions. In general, a greater reduction-promoting effect is secured by increasing the amount of reduction promoter employed and a lesser effect results from decreasing the amount employed, other reaction conditions being constant. Amounts greater than V mol of reduction promoter per mol of reducible aromatic nitrogen compound usually are not advantageous, although they may be used if desired, since the additional benefits derived therefrom are not of sufficient commercial importance .to compensate for the increased cost of the extra amount of reduction promoter.

The invention will be illustrated by the following specific examples, but it is to be understood that it is not limited to the details thereof and that changes may be made without departing from the scope of the invention. The temperatures are in degrees centigrade and the parts are by weight, unless designated as parts by volume in which case the amount signifies the volume occupied by the same number of parts by weight of water at 4 C.

Example 1 Part 1.Sixty parts of methanol and 0.95 part of 5,6,7,8-tetrahydro-1,4-naphthoquinone were charged to a flask equipped with a reflux condenser, agitator, dropping funnel and thermometer; then 74.5 parts of solid sodium hydroxide were added, and the mixture was heated to refluxing. To the resulting heated mixture, 123 parts of nitrobenzene were added over the course of an hour, and the reaction mass was then boiled under reflux for 22 hours under atmospheric pressure. A negligible amount of gaseous hydrogen was evolved during the addition of nitrobenzene and the subsequent reflux period. The mixture was then diluted with 300 parts of water and distilled (to remove unreacted methanol) until its temperature reached 110. The residue was allowed to stand and separate into an upper oil phase containing the reduction product and a lower aqueous phase. The aqueous phase, consisting essentially of sodium hydroxide and sodium formate in solution, was drawn off at about The oil phase was boiled with dilute hydrochloric acid, and then allowed to stand. The oil phase which separated was drawn off, filtered hot, and dried over The yield of product, which consisted essentially of a mixture of about 97% of azobenzene and about 3% of azoxybenzene and had a setting point of 65.1, was about 98% of the theoretical based on the nitrobenzene charged.

Part 2.-The process of part 1 of this example was repeated without the addition of 5,6,7,8-tetrahydro-l,4- naphthoquinonebut in otherwise the same manner. A large amount of hydrogen was evolved and the product consisted essentially of azoxybenzene (it had a setting point of 33.5"). The yield was about 98% of. the theoretical.

Part 3.The process of part 1 of this example was repeated with 1.0 part of duroquinone (2,3,5,6-tetramethyl-1,4-benzoqu-inone) in place of the 5,6,7,8-tetrahydro-lA-naphthoquinone, but in. otherwise the same manner. The product consisted essentially of a mixture of about 92% azoxybenzene and about 8% azobenzene (it had a setting point of 312). The yield was about 98% of the theoretical.

Part 4.-The process of part 1 of this example was repeated with 1.0 part of 1,2,3,4,5,6,7,8-octahydro-9,10- anthraquinone in place of the 5,6,7,8-tetrahydro-1,4- naphthoquinone, but in otherwise the same manner. The product consisted essentially of a mixture of about 86% azoxybenzene and about 14% azobenzene. The yield was about 98% of the theoretical.

Example 2 The procedure described in Example 1, part 1, was repeated, except that 0.9 part of sodium bisulfite was added to the flask in addition to the 5,6,7,8-tetrahydro- 1,4-naphthoquinone and methanol, and the mixture was refluxed for a half hour (to form the sodium bisulfite addition product of 5,6,7,8-tetrahydro-1,4-naphthoquinone) and then cooled to room temperature, before adding the sodium hydroxide. The product consisted essentially of a mixture of about 82% azobenzene and 18% azoxybenzene (it had a setting point of 594). The yield was about 98% of the theoretical.

Example 3 The procedure described in Example 1, part 1, was repeated, except that 2.0 parts of 5,6,7,8-tetrahydro1,4- naphthoquinone were employed. The isolated oil phase was agitated with hot Water, after which the aqueous mixture was cooled to room temperature and filtered, and the filter cake was dried. It consisted essentially of a mixture of about 80% of azobenzene and about 20% of hydrazobenzene. The yield of product was 98% of the theoretical.

Example 4 Forty-three parts of methanol and 1 part of one of the reduction promoters set out in the following Table 1 were charged to a flask equipped with a reflux condenser, stirrer, dropping funnel and thermometer.

TABLE 1 A. 2,3-cyclobuteno-1,4-benzohydroquinone (5,8-dihydro- 1,4-naphthalenediol) B. 2,3-cyclobutano-1,4-benzohydroquinone (5,6,7,8-tetrahydrol,4-naphthalenediol) C. 1,4-naphthohydroquinone (1,4-naphthalenediol) Fifty-six parts of solid sodium hydroxide were then added with cooling and the resulting mixture was heated to refluxing. Then 85 parts of nitrobenzene were introduced over the course of a half hour while maintaining the mass at 95, and the reaction mass was boiled, and refluxed under atmospheric pressure (about 90 to 100) for 22 hours (including the period of nitrobenzene addition). The mixture was then diluted with water to, 3000 parts by volume, cooled to about 10, and filtered, and the filter cake was dried (either in a vacuum drier at a temperature not exceeding 50 or by standing in the atmosphere at room temperature-2530).

The proportions of hydrazobenzene, azobenzene, azoxybenzene, and aniline thus produced are set out in Table 2.

TABLE 2 Percent of Theoretical Yield Based on Nitrobenzene Charged Promoter Azobenzene Hydrazo- Aniline Azoxybenzene benzene None (Control) A 5 7 can be made without departing from the scope of the invention.

Thus, the process is applicable to the reduction of other aromatic nitrogen compounds containing nitrogen in a reducible form as a substituent of a benzene nucleus, as for example, o-nitrotoluene, m-nitrotoluene, o-nitrochlorobenzene, m-nitrochlorobenzene, p-nitrophenetole, p-nitrobenzoic acid, o-nitrobenzene sulfonic acid, and their reduction products. In view of the extensive use of hydrazobenzene and its o-substituted derivatives (such as 0,0-dichlorohydrazobenzene, o,o-hydrazotoluene, o,o-hydrazoanis0le, o,o'-diethoxy-hydrazobenzene, etc.) as intermediates for the manufacture of benzidine and related derivatives of benzidine, the process of the present invention is of special value as a means for reducing the cost of manufacturing such hydrazo compounds from the corresponding reducible aromatic nitrogen compounds (such as, nitrobenzene and its o-substituted derivatives and reduction products thereof) in which the nitrogen is at a higher stage of oxidation than the hydrazo stage.

The reduction of aromatic nitro compounds to azoxy compounds (1), of azoxy compounds to azo compounds (2), and of azo compounds to hydrazo compounds (3) proceeds according to the following equations, in which R is an aromatic nucleus:

In carrying out the reduction by means of sodium hydroxide and methanol, it is preferable to employ these reagents in amounts in excess of those theoretically required. Extra methanol over that theoretically required is generally desirable for use as a solvent, and an additional excess is desirable to counteract the diluting effect of the water generated in accordance with above Equations 1 and 2, which would otherwise tend to retard the reaction. An excess of sodium hydroxide also is desirable since it tends to increase the rate of reaction.

It is possible to carry the reduction of a particular reducible aromatic nitrogen compound to various stages, depending upon the amounts of sodium hydroxide and methanol employed, as well as the nature and amount of the particular promoter employed. Thus, it is possible to reduce nitrobenzene to hydrazobenzene in a single reaction mixture. However, it is possible to reduce nitro benzene to azoxyand%or azobenzene in one reaction mixture, as illustrated in the above examples, and then to isolate and reduce the resulting azoxybenzene and/or azobenzene to hydrazobenzene with a fresh charge of sodium hydroxide and methanol.

The temperature at which the reaction is carried out also may be varied although, in the reduction performed with the aid of alcoholic caustic alkali, temperatures at or near the boiling point of the reaction mixture at atmospheric pressure (ordinarily about to are preferred. At lower temperatures, the reaction is slower, under otherwise similar conditions, and may require an excessively long time to produce the same results as the preferred temperatures. Conversely, higher reaction temperatures result in a short time cycle but require the use of closed reaction vessels. However, temperatures greatly exceeding though not precluded, are less desirable; since even in the presence of the reduction promoters they lead to evolution of considerable amounts of hydrogen gas and formation of primary amines, with consequent loss of yield of the desired reduction products.

While for economical and simple operation it is pre- 75 ferred to use, as a solvent or diluent of the reaction mixture, an excess of the alcohol employed for the alcoholate, the invention is not limited thereto. Thus, other solvents and diluents can be employed; for example, the process may be carried out with amounts of sodium hydroxide and methanol only slightly in excess over the amounts theoretically required for the reduction, in a reaction medium containing a suflicient amount of xylene or other inert solvent or diluent (such as, benzene, toluene, monoand dichloro-benzenes) to provide a stirrable reaction mass. Further, while it is simpler to employ as the solvent or diluent an excess of the alcohol functioning as a reducing agent, other alcohols can be employed; also mixtures of alcohols can be used, especially where it is desired to modify the boiling temperature of the reaction mixture' As a matter of convenience and for economical opera tion, the process is generally carried out by forming a metal alcoholate in the reaction mixture; for example, by reacting caustic alkali with the alcohol. If desired, however, preformed metal alcoholates may be employed as reducing agents, thereby avoiding the diluting eflfect of the water formed as a by-product of the reaction of caustic alkali with the alcohol.

Sodium hydroxide and methanol are employed in the specific examples in view of their relatively lower cost and ready availability. The invention is not limited thereto, however, and other alkalis (for example, potas sium hydroxide) and other alcohols (for example, ethyl alcohol and the various propyl, butyl and higher alcohols) may be employed, if desired.

Other compounds may be substituted forthe sodium bisulfite employed in Example 2 to form addition products with the ortho-cycloalkano-benzoquinone. Thus, corresponding amounts of the various other bisulfites and other compounds disclosed in U. S. P. 2,645,636, or of sodium hydrosulfide or the other sulfiding agents disclosed in application Serial No. 290,089, referred to above, may be employed. The products of the reduction can be isolated from the reaction mixtures in any suitable manner. Aside from those cases in which the reaction mixture contains an insoluble residue resulting from the presence of the reduction promoter in the reaction mixture, the isolation of the reduction products can be carried out in the usual manner. Thus, for example, the reaction mixture may be cooled to crystallize the reduction product and filtered, and the cake washed with water to remove alcohol, sodium formate formed as a by-product of the reduction, and sodium hydroxide. Generally, it is preferred to steam distill the methanol (and dehydrate the aqueous methanol thus obtained by fractional distillation for reuse in subsequent reactions), and then cool the remaining hot aqueous mass to crystallize the reduction product, which may be separated and washed with water as usual. Where the product is molten in the hot mixture, as in the case of azoxyand azobenzenes, it is simpler to stratify the mass into an aqueous phase and an oil phase, whereupon the latter can be readily separated, as illustrated in the examples.

Ordinarily, the reduction promoters of the above type are soluble in the aqueous and/or alcoholic layer and are removed therewith from the reduction product, When the use of the reduction promoter produces a small amount of insoluble by-product, it may be removed by filtering the hot mixture prior to the phase-separation, or in any other suitable manner.

We claim:

l. The improvement in the method of reducing an aromatic nitrogen compound containing nitrogen in a reducible form as a substituent of a benzene nucleus at a higher stage-of oxidation than the hydrazo stage-by the action of a metal alcoholate, which comprises carrying out the reduction in a reaction mixturein which an orthocycloalkano-benzoquinoid compound has been incorporated, whereby the reduction of the aromatic nitrogen compound is promoted.

2. A method as defined in claim 1, wherein the alcoholate'is sodium methylate, the aromatic nitrogen compound is reduced to a lower stage of oxidation than the azoxy stage and the ortho-cycloalkano-benzoquinoid compound is selected from the group consisting of,2,3- cycloalkano-1,4-benzoquinones having a hydrocarbon chainof 4 carbon atoms in the cycloalkano radical and the corresponding benzohydroquinones.

3. A method as defined in claim 1 wherein the metal alcoholate is sodium methylate, the aromatic nitrogen compound is reduced to a lower stage of oxidation than the azoxy stage, and the ortho-cycloalkano-benzoquinoid compound is an addition product of a 2,3-cycloa1kano-l,4- benzoquinone having a chain of 4 carbon atoms in the cycloalkano radical.

4. The improvement in the method of reducing a reducible aromatic nitrogen compound selected from the group consisting of nitrobenzene, its ortho-methyl, halogen, methoxy, ethoxy, carboxy and sulfo derivatives, and their reduction products in which the nitrogen is at a higher stage of oxidation than the hydrazo stage, by the action of a metal alcoholate, which comprises reducing the aromatic nitrogen compound to a lower stage of oxidation than the azoxy stage by reacting the aromatic nitrogen compound with a reducing mixture of an alkali metal hydroxide and a lower alcohol in a reaction mixture in which a small amount of an ortho-cycloalkanobenzoquinoid compound has been incorporated.

5. A method as defined in claim 4, which comprises heating the aromatic nitrogen compound with a reducing mixture of sodium hydroxide and methanol in a reaction mixture in which a 2,3-cycloalkano-1,4-benzoquinone having a chain of 4 carbon atoms in the cycloalkyl radical has been incorporated.

6. A method as defined in claim 5, wherein a small amount of a 2,3-cycloalkano-1,4-benzoquinone having a chain of 4 carbon atoms in the cycloalkyl radical is incorporated with the methanol, sodium hydroxide is added, and the aromatic nitrogen compound is heated with the resulting reaction. mixture.

7. A method as defined in claim 5, wherein the cycloalkano-benzoquinone is 2,3-cyclobuteno-1,4-benzoquinone.

- 8. A method as defined in claim 5, wherein the cycloalkano-benzoquinone is 2,3-cyclobutano-l,4-benzoquinone.

9. A method as defined in claim 4, which comprises heating the aromatic nitrogen compound with a reducing mixture of sodium hydroxide and methanol in a reaction mixture in which a 2,3-cycl'oalkano-1,4-benzohydroquinone having a chain of 4 carbon atoms in the cycloalkyl radical has been incorporated.

10. A method as defined in claim 9, wherein the cycloalkano-benzohydroquinone is 2,3-cyclobuteno-1,4-benzohydroquinone.

11. A method as defined in claim 9, wherein the cycloalkano-benzohydroquinone is 2,3-cyclobutano-1,4-benzohydroquinone.

References Cited in the file of this patent UNITED STATES PATENTS Sogn July 20, 1954'

Claims (1)

1. THE IMPROVEMENT IN THE METHOD OF REDUCING AN AROMATIC NITROGEN COMPOUND CONTAINING NITROGEN IN A REDUCIBLE FORM AS A SUBSTITUENT OF A BENZENE NUCLEUS AT A HIGHER STAGE OF OXIDATION THAN THE HYDRAZO STAGE BY THE ACTION OF A METAL ALCOHOLATE, WHICH COMPRISES CARRYING OUT THE REDUCTION IN A REACTION MIXTURE IN WHICH AN ORTHOCYCLOALKANO-BENZOQUINOID COMPOUND HAS BEEN INCORPORATED, WHEREBY THE REDUCTION OF THE AROMATIC NITROGEN COMPOUND IS PROMOTED.