US2804452A

US2804452A - Reduction of aromatic nitrogen compounds

Info

Publication number: US2804452A
Application number: US448378A
Authority: US
Inventors: Erkkila Armas Victor
Original assignee: Allied Chemical and Dye Corp
Current assignee: Allied Corp
Priority date: 1954-08-06
Filing date: 1954-08-06
Publication date: 1957-08-27
Anticipated expiration: 1974-08-27
Also published as: DE1022235C2; DE1022235B

Description

United States Patent REDUCTIONOF AROMATIC NITROGEN COMPGUNDS Armas Victor-Erkkila, Attica, N. Y., assignor to Allied Chemical &.Dye Corporation, New York, N. Y., a corporation of New York No Drawing. Application August 6,1954, Serial No. 448,378

13 Claims. (Cl. 260-143) This inventionv relates to improvements in the method oi reducing aromatic nitrogen compounds containing mtrogen inza reduci-ble form as a substituent of a benzenenucleus' (that is, as a substituent of a hydrogen atom forming part of a benzene nucleus) and at 'a'higher stage, ofoxi-dation than the hydrazo stage by the action vof metal alcoholates. It relatesmore particularly to improvements in'such methods, andespecially in processes in which the reducingsagent is an alkali metal alcoholate, especially anallcali metal methyl'ate and prefera'blymethanol and sodiumv hydroxide, whereby the reduction is promoted.

Ordinarily, thereduction 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 sufiiciently .strong reducing agents to carry the reduction beyond the 'azoxy stage. As disclosed in U. S. Patents 2,645,636 and 2,684,358, this reduction can bepromoted, so as to result in the formation of reduction products of a lower stage of oxidation than the azoxy stage, orJto obtain other beneficial results, by including in the reduction reaction mixtures naphthoquinoid 'compounds 'an-d especially naphthoquinones. and addition products thereof (for example, with bisulfites, heavy metal salts, etc.) and quinoid hydroxynaphthalene compounds.

The primary object of the present-invention is to:provide additional reduction promoterswhich, when added to reduction reaction mixtures of the type referredto above, will eifect a similar reduction promoting effect.

A further object of the present invention is to provide improvementsin 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'inclu'ding azoxy compounds, with metal alcoholates undermoderate 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 wit-h metal alcoholates under moderate conditionsandin simple apparatus; and to provide improvements in/thereduction of reducible 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 ,inpart will appear hereinafter.

According to thepresent invention the foregoing objects areaccomplishedand other benefits are secured by carrying out thev reduction of the reducible aromatic radical has. as hydrogen substituents more than one elec- Patented Aug. :27, .1957

nitrogen compound by means-of a metal alcoholate in av reaction mixture in which one or morereduction promoters of a special class have been incorporated.

The class of reduction promoters employed in accordance with the present invention is constituted of certain ice condensed polynuclear dioxy compounds which contain at least 10 nuclear carbon atoms, namely, thosein which one of the nuclei consists of an alicyclic dioxy radical having 6 nuclear carbon atoms and having the oxy substituents in quinoid relation to each other, at 1east'2 of the nuclear carbon. atoms. of said alicyclic dioxy radical other than those to which the oxy substituents are joined being saturated ,carbon atoms and preferably at least 4 of the 6 nuclear carbon atoms of said alicyclic dioxy radicalbeingsaturatedcarbon atoms. Said class comprises 1) condensed polynuclear diketones, such as the condensed nuclear derivatives of cyclohexandione and ,cyclohexendione in which the carbonyl groups are in quinoid relation, and particularly in 1,2- and 1,4-relation (whether freefrom other substituents besides the oxy substituents, or containing additional substituents wherein one or-m-ore of the hydrogen atoms is substituted by .anotheratom or radicalfor example, halogen, hydroxyl,

nitro, mercapto, amino, cyano, sulfo, carboxyl, alkyl, alkoxy, etc., but no carbon atom of said alicyclic dioxy tronegative radical); (2) corresponding hydroxy compounds in which one or both of the carbonyl groups of the, above diketones are replaced by one or two groups (whet-her free from other substituents besides the hydroxylgroups or containing additional substituents. as above), such as the condensed nuclear derivatives of cyclohex-andiol and cyclohexendio'l (condensed polynuclear secondary alc0h0ls);-and condensed nuclear derivatives of cyclohexadiendiol, in which the hydroxyl groups are in quinoid relation, and particularly in 1,2-

or 1,4-relation; '(3) addition compounds of such diketones and hydroxy-ketones (for example, with bisulfites, such as those disclosed in U.-S. P. 2,645,636); (4) functional derivatives of such dik-etones, hydroxy-ketones and dihydroxy compounds (for example, imides, oximes, semicarbazones, hydrazones, and esters which are saponifiable jby caustic alkalis); and :(5) ,ta-utomeric forms of. such .diketones; and hydroxy-ketones capable of isomerizing to suchketones.

Preferred-reduction promoters for use in accordance with the present invention arethe 1,2- and 1*,4diOXY- .,naphthanes (diones, diolsand ol-ones) and especially the V 1,4-naphthandi0nes and 1,4-naphthandiols.

Thus, saidclass of-condensedpolynuclear dioxy-compounds includes A -naphthantriene-1,4-dione (.2,3-dihydro-1,4-naphthoquinone) A -naphthandiene 1,4 dione (4a,5,8,8a-tetrahydro-1,4-

naphthoquinone) Z-methyl A -naphthandienel ,4-dione-4-oxime (Z-methyldimethyl 2 phenyl 4a,5,8,8a-tetrahydro-1,4-naphth0- quinone) 2,3 dimethyl 2 phenylA -naphthantriene-1,4-dione (2,3 dimethyl-Z-phenyl 2,3-dihydro -1,4-naphtho-quinone) 5,8 endomethylene-A naphthandiene -1, 4 dione (5,8-

methano-4a,5,8,8a-tetrahydro-1,4-naphthoquinone) I 5,8 endoethylene -A naphthandiene 1,4 dione (5,8-

ethano-4a,5,8,8a-tetrahydro-1,4-naphthoquinone) 6-methoxy-A -naphthandiene-1,4-dione (6-methoxy-4a,5,

8,8a-tetrahydro-1,4-naphthquinone) 2,3,4a,8a-tetrachloro -A naphthandiene -1,4- dione (2,3,

4a,8a tetrachloro 4a,5,8,8a tetrahydro -1,4-naphthoquinone) A naphthantriene -1,4 diol l,2,3,4 tetrahydro-l,4-

naphthalenediol) 2-methyl-4-hydroxy -A naphthantriene -I- one (l-hydroxy-4-keto-2-methyl-1,2,3,4-tetrahydonaphthalene) A naphthantetrene -l,4 diol (2,3-dihydro-1,4-dihydroxynaphthalene) Compounds of this class can be prepared in various Ways. One group of compounds particularly useful in accordance with the present invention can be obtained by the Diels-Alder reaction of a conjugated diene with a 1,4-benzoquinone or 1,4-naphthoquinone. Suitable conjugated dienes include 1,3-butadiene, 2-methyl-l,3-butadiene, 2-3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene,

2-bromo-l,3-butadiene, 2-phenyl-l,3-butadiene, Z-methyl- 2-chloro-l,3-butadiene, 1,3-cyclopentadiene, 2-methyl-1,3- pentadiene, 3-chloro-4-methyl-1,3-pentadiene, 1,3-cyclohexadiene and 3-chloro-4-methyl-l,3-hexadiene. Those derived from 1,4-benzoquinone and its substitution prodnets are of particular value in view of their superior promotor activity.

I have discovered that said condensed polynuclear dioxy compounds constitute highly effective reduction promoters in the reduction of aromatic nitrogen compounds of the type referred to above by metal alcoholates and especially alkali metal alcoholates.

I have found that the inclusion in the reaction mixture of merely a small amount of a condensed polynuclear dioxy compound of said type and especially of a 1,4-naphthadione 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 larly, 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 operating conditions. 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 inclusion 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 condensed polynuclear dioxy compounds employed in accordance with the present invention are not quinones but cycloaliphatic compounds.

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 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 to be reduced is added to the heated mixture. The reduction 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 the condensed polynuclear dioxy compounds are effective as reduction promoters even when employed in small amounts. Thus, amounts lying within the range %()0 to & mol of such dioxy compounds per mol of reducible aromatic nitrogen compound are ordinarily employed. The minimum amount required to produce a significant reduction-promoting effect varies with the individual promoter employed, the nature of the reducible aromatic nitrogen compound, and the reaction conditions. In gen- -eral, 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.

M Amounts greater than ,4 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 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. 2,3,4a,5,8,8a hexahydro 1,4 naphthoquinone (A naphthanene-l,4-dione) B. 2,3-dihydro-1,4 naphthoquinone (A -naphthantricne-1,4-dione) C. 4a,5,8,8a-tetrahydro-1,4 naphthoquinone (A -naphthandiene-1,4-dione) D. 1,4,4a,9a-tetrahydro-anthraquinone (1,3-butadiene reacted with 1,4-naphthoquinone) E. 1,4-naphthoquinone Fifty-six parts of solid sodium hydroxide were then added Table 2 Percent of Theoretical Yield Based on Nitrobenzene Charged Promoter Hydrazo- Azobenzene Aniline benzene Azoxybenzene None (Control) A EXAMPLE 2 Percent Hydrazobenzene 63 Azobenzene 36.4 Azoxybenzene Aniline 0.6

EXAMPLE 3 Part 1.-The procedure of Example 2 was repeated using 63 parts of azobenzene (S. P. 67.6") as the starting material in place of the azoxybenzene. The yields of reduction products, expressed as percent of theory based on the azobenzene charged, were as follows:

Percent Hydrazobenzene 99.9 Azobenzene 0 Aniline 0.1

Part 2.By way of comparison the following results were obtained when employing 1 part of 1,4-naphthoquinone in place of the 4a,5,8,8a-tetrahydro-1,4-naphthoquinone under otherwise identical conditions:

Percent Hydroazobenzene 90 Azobenzene 9.8 Aniline 0.2

As noted above, the invention is not limited to the details of the foregoing illustrative examples, and changes 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 in 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 o,0-dichlorohydrazobenzene, o,o-'hydrazotoluene, 0,0- hydrazoanisole, 0,0-diethoxyhydrazobenzene, 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 cor- 6, responding 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) proceed-s according to the following equations, in which R is an aromatic nucleus:

4RNO 30113011 3NaOH 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 reduction promoter employed. Thus, it is possible to reduce nitrobenezene to hydrazobenzene in a single reaction mixture. However, it is possible to reduce nitrobenzene 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 tohydrazobenzene 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 preferred 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 sufiicient 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 operations, 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 effect 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, potassium hydroxide) and other alcohols (for example, ethyl alcohol and the various propyl, butyl and higher alcohols) may be employed, if desired.

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.

If desired, the reaction mixture can be steam distilled to remove the methanol (and the aqueous methanol thus obtained can be dehydrated by fractional distillation for reuse in subsequent reactions), and the remaining hot aqueous mass can then be cooled to crystallize the reduction product, which can be separated and washed with water as usual; or, where the product is present in molten form in the hot aqueous mixture, as in the case of azoxyand azobenzenes, the mass can be stratified into an aqueous phase and an oil phase, whereupon the latter can be readily separated. 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 pro moter 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.

I claim:

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 a condensed polynuclear dioxy compound containing at least nuclear carbon atoms has been incorporated, one of the nuclei of said condensed polynuclear dioxy compound consisting of an alicyclic dioxy radical having 6 nuclear carbon atoms and having the oxy substituents in quinoid relation to each other, at least 2 of the nuclear carbon atoms of said alicyclic dioxy radical other than those to which the oxy substituents are joined being saturated carbon atoms, whereby the reduction of the aromatic nitrogen compound is promoted.

2. A method as defined in claim 1, wherein the aromatic nitrogen compound is reduced to a lower stage of oxidation than the azoxy stage, the alcoholate is sodium methylate and the condensed polynuclear dioxy compound is a condensed dinuclear 1,4-diketone.

3. A method as defined in claim 2, wherein the condensed polynuclear dioxy compound is a naphthan-1,4- dione. Y

4. A method as defined in claim 2, wherein the condensed polynuclear dioxy compound is a Diels-Alder reaction product of a conjugated diene with a 1,4-quinone.

5. A method as defined in claim 2, wherein the condensed polynuclear dioxy compound is a bisulfite addition compound of a condensed dinuclear diketone.

6. 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 sodium methylate in a reaction mixture to which a condensed dinuclear diketone having 10 nuclear carbon atoms has been added in an amount at least mol per mol of aromatic nitrogen compound, one of the nuclei of said condensed dinuclear diketone consisting of an alicyclic diketone radical having 6 nuclear carbon atoms of which at least 4 are saturated carbon atoms and having the carbonyl groups in quinoid relation to each other, whereby, the reduction of the aromatic nitrogen compound is promoted.

7. A method as defined in claim 6, which comprises reacting the aromatic nitrogen compound with a reducing mixture of sodium hydroxide and methanol in a reaction mixture in which a dioxynaphthane having the oxy groups in quinoid relation to each other has been incorporated.

8. A method as defined in claim 7, wherein the dioxynaphthane is a 1,4-dioxynaphthane in which the carbon atoms in the 2,3 positions are unsaturated.

9. A method as defined in claim 8, wherein the 1,4-dioxynaphthane is a Diels-Adler reaction product of a 1,3- butadiene with a 1,4-benzoquinone.

10. A method as defined in claim 9, wherein the 1,4- dioxynaphthane is A -naphthandiene-1,4-dione.

11. A method as defined in claim 7, wherein the dioxynaphthane is A -naphthantriene-1,4-dione.

12. A method as defined in claim 7, wherein the condensed polynuclear dioxy compound is M-naphthanene- 1,4-dione.

13. A method as defined in claim 1 wherein the aromatic nitrogen compound is reduced to a lower stage of oxidation than the azoxy stage, the alcoholate is sodium methylate and the condensed polynuclear dioxy compound is a naphthandiol.

References Cited in the file of this patent UNITED STATES PATENTS 2,645,636 Sogn July 14, 1953 2,684,358 Sogn July 20, 1954 2,684,359 Sogn July 20, 1954

Claims

1. THE IMPROVEMENT IN THE METHOD OF REDUCING AN AROMATIC NITROGEN COMPOUND CONTAINING NITROGEN IN A REDUCIBLE FORM AS 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 A CONDENSED POLYNUCLEAR DIOXY COMPOUND CONTAINING AT LEAST 10 NUCLEAR CARBON ATOMS HAS BEEN INCORPORATED, ONE OF THE NUCLEI OF SAID CONDENSED POLYNUCLEAR DIOXY COMPOUND CONSISTING OF AN ALICYCLIC DIOXY RADICAL HAVING 6 NUCLEAR CARBON ATOMS AND HAVING THE OXY SUBSTITUENTS IN QUINOID RELATION TO EACH OTHER, AT LEAST 2 OF THE NUCLEAR CARBON ATOMS OF SAID ALICYCLIC DIOXY RADICAL OTHER THAN THOSE TO WHICH THE OXY SUBSTITUENTS ARE JOINED BEING SATURATED CARBON ATOMS, WHEREBY THE REDUCTION OF THE AROMATIC NITROGEN COMPOUND IS PROMOTED.