US1644483A - Reduction of nitro compounds - Google Patents

Description

I 1,644,483 1927' R. A. NELSON ET AL REDUCTION OF NITRO COMPOUNDS Filed June 22, 1920 Patented C at. 4, 1927.

U f' TE RALPH A. NELSON AND ANTON PRASIL, F BUFFALO, NEW YORK, ASSIGNORS TO NATIONAL ANILINE & CHEMICAL COMPANY, INC., OF NEW YORK, N. Y., A COR- POBATION OF NEW YORK.

nnnnc'rron on nrrno oorrr'ounns.

Application filed June 22, 1920. Serial No. 390,884,

This invention relates to improvements in the reduction of nitro compounds, and more particularly tothe reduction of nitro compounds to hydrazo compounds, by means of zinc and caustic alkali as the reducing. agents. The invention also relates to 1mprovements in the separation and isolation of the hydrazo compounds, at the end of the reduction, whereby the hydrazo compounds are obtained in an isolated state. The invention includes improvements in the reduction operation, in the extraction and isolation operation, and in the combined reduction and isolation operations.

In the reduction of nitro compounds to hydrazo compounds, it has heretofore been proposed to effect the reduction by means of zinc and caustic, all of the zinc being added' first and the alkali being gradually added, or all of the caustic alkali being added first and the zinc being gradually added. In

proceeding this way it is difficult to confine the reduction to the hydrazo stage and obtain good yields, the tendency being either for the reaction to proceed incompletely, or

to'proceed too energetically with the resulting reduction of the nitro compound to amido compounds.

In the separation of the hydrazo compound, at the end of the reduction, when alcohol has been used as the solvent, it has been proposed to separate the'zinc residue from the hydrazo compound by extraction with acid. When acid is used,'the caustic present in admixture with the hydrazo compound is neutralized so that it cannot be recovered and so that a corresponding amount of acid is used up in its'neutralization, while the zinc is similarly dissolved and converted into a-salt and requires a corresponding amount of acid for its solution. The use of acid in this way also tends to zonvert the hydrazo compound, by rearrangement, into a compound of the benzidine series, which is soluble in the acid solution.

According to the present invention objections of the character above referred to are largely overcome or minimized and the reduction and separation operations are carried out man improved and advantageous manner, with the production of hydrazo compounds with high yields.

According to the present invention, the nitro compound, in alcohol solution, is subcases, be separated mechanically, but such .esses in which the alcohol is removed b jected to reduction by means of zinc and caustic alkali, but instead of adding all of the caustic or all ofthe alkali at the outset and attempting. to regulate the reduction by the gradual addition of the other reagent, the zinc and caustic are intermittently added so that the reaction can be more readily and advantageously controlled. The intermittent addition ofthe reagents, in addition to affording better control of the reduction, avoids the accumulation of the reagents with the possibility of their sudden ly taking hold and causing the reaction tov proceed with explosive violence.

The gradual and intermittent addition of the zinc and caustic makes possible the regulation of thercduction in such away that the reduction may be stopped at the azoxy or azo stage, while it also makes possible the continuation of the reduction to the hydrazo stage, with substantial completion, and with but a relatively small amount of overreduction to the amido compounds.

At the end of the reduction, the crystals of the hydrazo compound, can, in certain mechanical separation involves a mechanical loss, and leaves a certainamount of zinc with the crystals, which zinc produces a loss in the subsequent rearrangement process, if the crystals are used in that process. It is 111016'85 advantageous, at the end ofthe reduction, to recover the alcohol by direct distillation, in a highly concentrated state so it can be used directly in a subsequent reduction. The hydrazo compound is then separated from the zinc residue by extraction with an organic solvent immiscible with water, such as benzol, for example. In the distillation of thealcohol, the use of steam or of water is avoided, so that the zinc reduction residue is left in a form particularly well adapted for extraction by means of the solvent, and the hydrazo compound can thus be extracted with substantial completion and obtained in an isolated state of high purity while the zinc oxide residue is likewise left me state adapting it for use for special p-urposes without further treatment. The present process is thus distinguished from proc- I05 steam distillation, with resulting dilution of the alcohol which prevents its further use without concentration, and also from prior in an isolated state.

proposals to distill the alcohol after dilu-.

tion of the reduction product with water, in which case the alcohol is likewise obtained in a dilute state, and the zinc residue and admixed hydrazo compound are obtained in a form preventing or making difficult the satisfactory extraction of the hydrazo compound.

It will t hus be seen that the process of the present invention, in .its entirety, involves the-reduction of the nitro compound in the presence of.alcohol by the intermittent addition of zinc and caustic alkali, the subsequent direct distillation and recovery of the alcohol, and the extraction of the hydrazocompound from the resulting reduction mass by means of an immiscible solvent so that the hydrazo compound is obtained in a state of purity and with excellent yields, while the zinc residue is likewise obtained It will also be seen that the various steps of the process, aswell as the process in lts' entirety, present features I o-nitranisol and 15 gallons of denatured.

of novelty and of advantage.

The invention will be further illustrated by the following specific examples:

Reduction of 0.-nitraxnisoZ.-15O pounds of alcohol (denatured, for example, with wood alcohol and pyridin or with benzol) are .mixed together in a steam jacketed iron-kettle, provided with a reflux condenser, and brou ht to a boil. .The mixture is maintaine in vigorous agitation and the reduction is effected by the intermittent and progressive addition of zinc dust and caustic soda, adding one or the other as needed at such a rate as to keep up a vigorous reflux action, the total amount of caustic being about 16 pounds of to B. and the totalamount of zinc dust being about 190 pounds of dust the amount of caustic soda corresponding to about 52-25% of the theoretical amount of caustic alkalinecessary. to transfer the zinc to alkali metal zincate. In the operation of the process, a part of the zinc may be firs-t added, for example, an' amount of 10 to 15 pounds thoroughly admixed with the charge, and

then about 3- pounds of caustic soda added to bring about a vigorous reaction; A further small amount of zinc and of caustic may be add'edif the reaction does not proceedat once. Once the reaction has started, it can be kept up for some time by the addition-offu'rther amounts of zincalone, further amounts of caustic-being added when required to insure, active continuation of the reaction. The intermittent addition of the zinc and caustic in this Way prevents the ac qcumulation of any large excess of reagents and resulting explosion should they take hold suddenly; and 'cau'sejfthe reaction to proceed with explosive violence. The entire period of .timerequired for the completion of the reduction; may amount to several hours, the reduction mass being heated until the reaction is complete. The

operation may thus be carried out, for'ex-' ample, over a period of from .6 to 1O hours,

' by adding about pounds of zinc dust progressively during the first 1 to 2 hours,

a further portion of 40 pounds during the next two hours, and the last portion of 40 Y above noted, the reaction may be continued for a considerable time by further additions of zinc without further additions of caustic, and with addltions of caustic only when. the

. further addition of zinc fails to' give a vigorous reaction. The caustic soda acts as an accelerator, particularly in continuing the reaction from the azoxy to the azo stage, after which further additions of caustic have :relatively little effect. The reduction can be followed, to and through-the azoxy and azo stages, and then to the hydrazo stage. During the last stage of the reduction the remaining zinc is added more slowly and-the reflux iscontinued by means of steam heat in the jacket of the kettle, the reduction as a whole appearing to progress more slowly during this stage. It is of advantage, when the hydrazo crystals begin to separate out on testing, to hasten the completion of the reduction by adding about 15 pounds of zinc dust in small portions at short intervals.

The progress of the reaction on reduction 'can be followed by taking samples of the reduction mass ,and spotting them on paper. 'As the reduction nears completion the crystals separating become larger and are more yellow in color and crystallize out rapidly. The crystals remain yellow until the reduction is complete when they suddenly become almost colorless. Upon completion of the reduction to the hydrazo stage, the mass may tend to foam somewhat, in which case the foaming may be checked by cooling of the reaction'kettle. The avoidance' of any large excess of zinc dust also tends to prevent excessivefoaming.

After complete reduction, the mixture is of a light gray 'color, and relatively thick,

so that the zinc oxide does not readily 'separate from, the solution. The alcohol is then distilled off by dlrect heating (e. g. with tlie steam jacket), and directly recovered in a highly concentrated. state so. that {itis directly available for reuse. The greater part of the alcohol ean'be recovered in this way.

The process has the advantage that a relatively small amount of alcohol is required,

"and that the alcohol can be directly recovered, without appreciable dilution, for reuse.

Furthermore, the direct distillation of the alcohol in this way leaves the residue in a That is, the reduced mass, after distillation of the alcohol, is somewhat thick and granular as distinguished from a sludge. This mass is of a steel gray color.

Ewtractz'on of hydrazamisolr-After the removal of the alcohol by distillation, the residue, consisting mainly of the hydrazanisol with some small amounts of anisidine, and of the zinc oxide residue-admixed with some caustic soda or sodium zincate, is cooled to about C., and about 40 gallons of benzene added, and the mixture agitated until a strong solution of the hydrazanisol 'in benzene is obtained, for example, for a period of about 1 hour. The mixture is then transferred to a settling tank, the zinc permitted to settle, and the benzene solution decanted. The zinc residue is further extracted by the addition of further amounts of benzene until all of the h drazanisol has been extracted, leaving the zinc residue in a relatively pure state. The total amount of benzene used may amount to 80 gallons or more. It will be evident that the particular mode of effecting the extraction of the hydrazanisol from the zinc residue is capable of considerable variation. The benzene used for the subsequent extraction or washing of the residue, and containing relatively less hydrazanisol, can with advantage be used in extracting hydrazanisol from subsequent reduction products. After the completionof the 'extraction, the remaining benzene held by the zinc residue canbe' recovered by distillation. The zinc oxide residue is substantially free from organic matter and of suflicient purity so that it can be directly disposed of, without previous incineration,

, for special purposes. Similarly the hydrazo compound, although produced by the action of zinc, is nevertheless free from zinc. That is, the process of the present invention enables a substantially complete recovery of both the zinc residue and of the hydrazo compounds to be obtained. Q L

The hydrazo compound is moreover obtained in solution in the non-iniscibie solvent, from which it can be separated by crystallization, or by distilling ofi' the solvent, either directly, or by means of steam or an inert gas. By crystallization from the solvent, or by distillation of the solvent, the hydrazo compound can obtained in an isolated state well adapted for further treatment or use. The solution of the hydrazo compound is also available for use directly for the conversion ofthe hydrazanisol, by rearrangement with acid, to dianisidine; and solutions of other hydrazo compounds can similarly be produced and treated for the conversion of the hydrazo compound to the corresponding 'compound of the bensidine series, for example, as set forth in application Serial No. 390886, filed J une' 22, 1920.

Instead of using benzene for the extraction of the hydrazo compound from the Zinc residue, other non-miscible solvents, such as toluene, may be similarly used. I

So also, instead of reducing o-nitranisol to hydrazanisol, other nitro compounds can be reduced to the corresponding hydrazo compounds in. a similar manner; for example, nitro-benzene can be similarly reduced to hydrazo-benzene and o-nitro-toluene can be similarly reduced to tolidine, the reduction in each case passing from the nitro, through the azoxy and azo stages, to the hydrazo stage.

A suitable apparatus for the practice of the invention isillustrated, in a somewhat conventional and diagrammatic manner, in the accompanying drawings. The appara .tus illustrated comprises a jacketed cast iron kettle 1 having a cover 2 and heating or cooling jacket 3 and having a'relatively large upwardly extending reflux pipe 4 leading to the condenser 5 from which the return pipe 6 returns the condensate either to the kettle or through thebranch pipe 9 to a storage tank. The return pipe 6 has lass sights 7 and 8 therein by means of which the flow of the condensate can be observed.

i The kettle is provided with feeding means for feeding the powdered zinc which includes the hopper 10 and the connecting pipe 11 having two quick acting valves 12 and l3 therein. The return pipe 6 from the condenser enters the pipe 11' between thevvalves 12 and 13, the arrangement being such that the valve 12 can be opened to ermit the powdered zinc to enter from the opper 10, and the valve 12' can then be closed and the valve 13 opened to permit the zinc to enter the kettle. The returning condensate assists in washing the zinc ,down into the kettle. Storage tanks 14, 15 and 16 are provlded for the alcohol, for the benzene or other immiscible solvent, and for the ortho-nitranisol or other nitrocompound. These storage tanks .connect with the reduction kettle through the pipe 17 and the reflux pipe 4. A storage tank for the caustic alkali is indicated at 18 connecting with the kettlethrough the pipe 19 and reflux pipe 4.

The heating and cooling jacket is provided with suitable steam and water connections,

the steam inlet pipe being indicated at 20,

an outlet pipe at 21, the water supply pipe at 22 and drain pipe at 26. Branch pipes for water are indicated at 23 and 24, the pipe 24 permitting water to flow upon the outside of the kettle, stythat this contents of the kettle.

can be blown out by the application of air pressure above the liquid contents thereof,

a 'air presure'being introduced through pipe 29. The reflux pipe 4 is provided with a glass sight 28 for observing the flow of liquid and vapor therethrough. The pressure indicator 30 is also proyided, and the cover has a suitable manhole, not shown, for gainaccess to the interior of the kettle.

in Tn the operation of the aparatu's, for example, the nitro compound and-the .alcohol are introduced from the respective storage tanks into the kettle, and heated, with agitation, to a refluxing temperature, a part of. the zinc dustthen added from the hopper 10 by closing the lower 'valve 13, opening up er valve 12, permitting the zinc to pour in tween the valves, then closing the upper valve and opening the lower one, so that the zinc drops into the kettle and is washed down by the refluxing alcohol. After thorough agitation and continued refluxing the caustic sodais added with resulting vigorous reaction. The rate. of reaction can be followed by means of the sight glasses in the vapor line 4 and in the return pipe 6.

.Near the completion of the reduction, the mass tends to foam somewhat. When foaming is indicated in the sight glass in the vapor line, water can be run on to the surface of the kettle and into the 1acketto cool the reacting mass and check the foaming. The avoidance of any considerable excess of zinc likewise tends to decrease the foaming tendency.

a Any pressure developed during the operation of the apparatus is taken care 'of by the pipe 9 which acts as a vent. A too vigorous] reaction can be checked by running cooling water on to the -surface of the kettle and through the jacket. When the reduction is complete, the alcohol can be distilled off throu h the condenser and the branch pipe 9 an ,thereby recovered in a concentrated p 'poundsby reduction of nitro compounds by 7 state available for reuse. After cooling the residue, the benzene or other immisc ble solvent is added and thoroughly agitated and then blown into, settling tanks (not shown) through the blow-out pipe 27 by means of air pressure applied above the contents of the kettle, or discharged by gravity through the outlet- 27.

of alcohol, directly distilling oil the alcohol at the end'of the reduction, and extracting the hydrazo compound from the zinc residue by a solvent immiscible with water.

distilling oil the alcohol, and extracting the hydrazo compound from the zinc residue by means of an organic solvent immiscible with water.

3. The method of reducing nitro compounds to hydrazocompounds and of separating the resulting hyrazo compounds, which comprises su'bJecting the nitro compounds to reduction with zinc and caustic alkali in the presence of alcohol, the reduction being carried out with the use of a small amount of caustic alkali, and with intermittent addition of the zinc and alkali, dis.- tilling off the alcohol from the reduction mass and thereby obtaining the reduction mass ina 'form well adap-ted for extraction, and extracting the hydra-Z0 compound from thezinc residue by means of an organic solvent immiscible with water. i

4. The method of producing and isolating hydrazanisol, which comprises subjecting o-nitranisol to reductionwith zinc and caustic alkali in the presence of alcohol, d is 5. The method of separating hydrazani'sol from admixture with zinc oxide residues and alcohol, which comprisesdistilling off the alcohol, and extracting the hydrazanisol from the. zinc residue with a low boiling solvent of the benzene series.

6. ln the production of hydrazo comounds by reduction of nitro compounds y means of zinc and caustic alkali in the presence of. alcohol, the steps comprising the removal of the alcohol by distillation and extracting the hydrazo coin-pounds from the residues by means of a liquid hydrocarbon solvent. i

7. In the. production of hydrazo com-.

means of zinc and caustic alkali in the presence of alcohol, the steps comprising the removal and recovery of the alcohol by direct distillation and extracting the hydrazo compounds from the res'dues by meansof an aromatic hydrocarbon solvent.

8. In the production of hydraz'o com- .pounds by reduction of nitro compounds by meansot' zinc and caustic alkali in the presence of alcohol, the steps comprising the re moval of the alcohol by distillation and extracting the hydrazo compounds from the residue with benzene.

9. The method of separating hydrazanisol from admixture with alkaline zinc residues and alcohol, which comprises the removal of I the alcohol by the hydrazanlsol from the residue with benzene.

10. The method of producing and isolating hydrazo compounds, which comprises subjecting a nitro compound, in the presence of alcohol, to reduction with zinc and about 2 to 2.6% of the amount of caustic alkali necessary to transform the zinc into alkali zincate, directly distilling ofi' the alcohol at the end of the reduction and extracting the hydrazocompounds from the zinc residue by a solvent immiscible with water.

11. The method of producing and isolating hydrazo compounds, which comprises subjecting a nitro compound, in the presence of alcohol, to reduction With zinc and about 2 to 2.6% of the amount of caustic alkali necessary to transform the zinc into alkali zincate, directly distilling oil the alcohol at the end of the reduction, and extracting the hydrazo compounds from thezinc residue by an aromatic hydrocarbon solvent.

12. The method of producing and isolatdistillation and extracting ing hydrazanisol, which comprises subjecting nitranisol, in the presence of alcohol, to reduction with zinc and about 2 to 2.6% of the amount of caustic alkali necessary totransform the zinc into alkali zincate, directly distilling oil the alcohol at the end of the reduction and extracting the hydrazanis01 from the zinc residue by a solvent immiscible with water.

13. The method of producing and isolating hydrazanisol, which comprises sub'ecting nitranisol, in the presence of alcoho to reduction with zinc and about 2 to 2.6% of y the amount of caustic alkali necessary to transform the zinc into alkali zincate, directly distilling oil the alcohol at the end of the reduction and extracting the hydrazanisol from the zinc residue by an aromatic hydrocarbon solvent.

In testimony whereof we aflix our signatures.

RALPH A. NELSON. ANTON PRASIL.

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