Nitration processes

Abstract

The present invention relates to improvements in processes of preparing dinitrated aromatic compounds, particularly dinitrated aniline and dinitrated substituted aniline compounds, employing relatively dilute and then more concentrated nitric acid as the nitrating agent aniline and substituted phenol compounds in a two-step process, employing, in the first or mononitration step the spent nitric acid from the second of dinitration step.

Description

TECHNICAL FIELD

The present invention relates to improvements in processes for preparing dinitrated aromatic compounds, particularly aromatic compounds such as aniline and substituted aniline compounds, employing relatively dilute and then more concentrated nitric acid as the nitrating agent. Moderate reaction temperatures are used. In these processes two nitro groups are introduced in the benzene or aromatic ring of the compound to be nitrated.

BACKGROUND ART

It has been common practice in the past in the preparation of dinitro aromatic compounds to use concentrated nitric acid containing sulfuric acid as a catalyst, as the nitrating medium. This is as exemplified, in U.S. Pat. No. 4,136,117 to Robert E. Diehl and Stephen D. Levy, issued Jan. 23, 1979. Also it is known from the same patent (col. 1, lines 52-60) that Belgium Pat. No. 762,232 discloses a method for the preparation of 2, 6-dinitro-tertiary anilines, wherein both N-substituents are haloalkyl, by nitration with at least a five fold excess of nitric acid, which is present at the start of the reaction in a concentration of 50% to 90% and in an amount to leave an acid concentration of 50% at the end of the reaction, in the presence of a catalytic amount of nitrous acid or nitrite ion generating material.

Each of the above processes have disadvantages from an economical and environmental standpoint. The processes utilizing mixtures of nitric acid and sulfuric acid generate spent acids containing 40% or more acid, including some nitric acid. This spent acid either has to be neutralized prior to disposal--resulting in the generation of considerable amounts of mixtures of sodium nitrate and sodium sulfate which must be disposed of in the environment--or the spent acid must be concentrated by evaporation of water (with expenditure of energy) to a concentration which can be used for subsequent nitration reactions.

In the other process, referred to above, in which a five fold excess of concentrated nitric acid is utilized along with a nitrous acid or nitrite ion generating material, the spent acid from the dinitration process contains 50% or more of nitric acid. This spent acid, like that containing sulfuric acid, must either be concentrated prior to use in the dinitration process or must be neutralized, for example, to form sodium nitrate, and then disposed of in the environment.

DISCLOSURE OF THE INVENTION

The present invention has, as one object, the elimination or minimizing of the above described disadvantages. In accordance with the present invention, the first nitro group is introduced into the aromatic compound, for example, aniline or phenol, by reacting such compound at moderate temperature and pressure conditions, for example, about 40°-65°C and atmospheric pressure, with a relatively dilute aqueous nitric acid of the order of 10%-50% by weight HNO₃ concentration in the presence of a suitable liquid, water-immiscible organic solvent for the nitratable compound; for example, a solvent such as dichloroethane. In the case of aniline, the compound formed is either mononitroaniline or a reaction product of aniline and nitric acid which is believed to be a salt of aniline and nitric acid. In the case of phenol, the compound formed is mononitro phenol. The resulting mixture is then allowed to separate into an organic phase containing such solvent and the nitrated aromatic compound and a water phase which contains 10% by weight or less of HNO₃.

Next the nitratable aromatic compound in the organic phase is reacted with a relatively concentrated aqueous nitric acid of about 60%-100% by weight HNO₃ concentration at moderate temperature and pressure conditions, for example, of the order of 40°-70°C and atmospheric pressure. In this reaction the aromatic compound is dinitrated, that is, two nitro groups are introduced into the aromatic ring of the compound. In the case of phenol, a dinitro phenol is formed and in the case of aniline, the reaction results in the formation of the dinitroaniline. The spent (more dilute) acid from this step can then be reacted with aniline as described in the first step above.

Although reference has been made above to the reaction of nitric acid and aniline, the processes of this invention are also applicable to the dinitration of nitratable aromatic compounds in general, and to substituted anilines, phenol and substituted phenols in particular, as will be described in greater detail hereafter.

The processes of this invention are carried out using nitric acid which is substantially free of sulfuric acid, but which may be free of or may contain catalytic amounts on nitrous acid or nitrite ion generating material. It is preferred to use pure or technical grade nitric acid as made and sold commercially as the nitrating agent in the second step, and free from additives or catalytic additives.

THE DRAWINGS

The accompanying drawing, FIG. 1, is a flow diagram which is a schematic representation of equipment which can be used to carry out one of the preferred embodiments of the processes of this invention involving the dinitration of substituted aniline compounds.

BEST MODE FOR CARRYING OUT THE INVENTION

In FIG. 1, numerals 10, 11 and 12 represent, respectively, storage tanks for the liquid organic solvent, liquid nitric acid, and the liquid substituted aniline compound to be dinitrated in the process. By means of one of the pumps 9, pipe line 13, connected to tank 10, conveys solvent from storage tank 10 to solvent extractor 14. Pipe line 15, connected to tank 12, similarly conveys the substituted aniline from storage tank 12 to the reactor 16, for reaction with a dilute or spent nitric acid from a source to be described below. The reaction mixture overflow from reactor 16 flows via pipe line 17 to a separator 18 in which the substituted aniline-nitric acid reaction product (also referred to as aniline salt) is separated from the aqueous phase of the reaction mixture as a lower layer which can flow via pipe 19 to a reaction vessel 20 (designated Reactor I). Concentrated nitric acid is conveyed to vessel 20 via pipe 21 from storage tank 11. Dinitration is carried out in vessel 20 and vessel 22 (designated Reactor II) which provide sufficient dwell time to insure that a dinitrated product is obtained; the reaction mixture in vessel 20 overflows from that vessel through pipe 23 to vessel 22 where additional dwell time is provided. The overflow from vessel 22 flows through pipe line 24 to separator 25 in which the dinitrated product is allowed to separate from the aqueous spent nitric acid. This spent acid is then pumped through pipe 26 to reactor 16 for reaction with additional substituted aniline.

The upper layer (aqueous phase) in separator 18 flows via pipe 27 to the solvent extractor 14 and the overflow from this extractor flows via pipe 28 to separator 29 wherein the solvent and aqueous phase are allowed to separate into an upper aqueous phase, which is waste, and a solvent lower phase which solvent phase is pumped via pipe line 30 to reactor 16.

There is also provided, in FIG. 1, pipe line 31 which is connected to organic solvent pipe line 13 and permits solvent to be pumped from storage tank 10 to reactor 22 (Reactor II), if required. In addition, pipe line 32 is provided to convey nitric acid, if required, from pipe line 21 (connected to storage vessel 11) to reactor 16.

As is indicated in FIG. 1 alll reaction vessels 16, 20 and 22 are provided with cooling coils and agitators to provide temperature control and intimate mixing of the vessel contents, and also with condensers to condense vapors back into the reactors. Conventional valves are used as shown in the drawing.

As noted above, the present invention is practiced in several steps, one of which comprises reacting a dinitratable aromatic compound, for example, aniline or a substituted aniline, with an aqueous dilute or spent nitric acid (from another step as described hereinafer) of about 20%-50% by weight aniline'381,83 1.83 moles) of spent aqueous 35% HNO₃.

The product (organic phase) obtained from separator 25 during the 60 minute collection period consisted of 1,068 grams of solution containing 438 grams (1.5 moles) of N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitro aniline and 78.4 grams (0.24 mole) of N-nitroso-N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitro aniline along with dichloroethane. The total yield of the desired aniline was 95%. There was collected from the lower aqueous layer in separator 25 333 grams of spent aqueous nitric acid of 35% HNO₃ concentration, and from the upper aqueous layer in separator 29 there was collected 175 grams of aqueous waste of about 1% HNO₃ concentration. Denitrosation of the N-nitroso compound in the organic layer product from separator 25 was effected in the manner described in the last paragraph of Example 1 to give a yield of the desired product N-(1-ethylpropyl)-3, 4-dimethyl-2, 6-dinitro aniline of 533.7 grams.

It is apparent from this Example that the present process can be operated continuously to produce a dinitrated product in high yields, and with the generation of very low concentrations of nitric acid waste which can be disposed of cheaply and readily.

It will be noted from Example 7 that the continuous processes of this invention can be carried out in the following manner. A dinitratable aromatic compound dissolved in an inert organic solvent and dilute aqueous nitric acid of 20%-50% HNO₃ concentration are continuously supplied to a reaction zone with agitation and temperature control, as previously described above, and in a mole ratio of about 1:1 to about 1:1.5 of aromatic compound to HNO₃. The overflow from such zone is then conveyed continuously to a separation zone to allow the reaction mixture to separate into an organic phase and an aqueous phase. The organic phase, which contains the organic solvent and reaction product of the aromatic compound and nitric acid, is then supplied continuously to another reaction zone along with concentrated aqueous nitric acid of about 65% to about 80% by weight of HNO₃, with agitation and temperature control, as previously described above, with sufficient residence time to complete dinitration of the aromatic compound. In this step, the mole ratio of compound to acid suitable for batch operation, as described above, is employed in the continuous operation. The reaction mixture from this reaction zone is continuously supplied to the separation zone where the reaction mixture is allowed to separate into an organic phase containing the desired dinitrated aromatic compound and the organic solvent and an aqueous phase of spent nitric acid containing about 20%-50% by weight HNO₃. This aqueous phase is continuously returned to the first reaction zone for reaction with additional dinitratable aromatic compound. The organic phase is continuously removed from the separation zone and the organic solvent can be stripped from the desired dinitrated product by vacuum distillation, if desired.

The denitrosation step described in the last paragraph of Example 1, and as referred to in Examples 2, 3, 6 and 7, can be carried out under different and varied conditions as described in the aforementioned U.S. Pat. No. 4,136,117, column 3, lines 47-67; column 4, lines 1-13; column 7, Example 16; and column 8, lines 1-23 and Examples 17-24, the subject matter of which is hereby incorporated herein by reference.

In the dinitration of anilines, the spent acid resulting from the dinitration step is normally about 35%-40% or from 10%-50% HNO₃. In the processing of phenols, the spent acid from the dinitration may be as great as 50% HNO₃. To use these acids in the first step of the processes described, they may be substantially diluted, say to 10% concentration.

INDUSTRIAL APPLICABILITY

The present process has wide applicability to commercial processes for preparation of dinitrated aromatic compounds, including agricultural herbicides.

Claims

1. A continuous process of dinitrating a dinitratable substituted aniline compound which comprises continously supplying (1) an aqueous nitric acid of about 10-40% hno₃ by weight and substantially free of sulfuric acid, (2) a substituted aniline compound and (3) a liquid, inert, water-immiscible organic solvent for said aniline compound, in a mole ratio of about 1:1 to about 1:1.3 of hno₃ to said aniline compound, to a reaction zone at a temperature of about 40° to about 70°C and atmospheric pressure, thereby forming in said zone an emulsion containing a salt of said nitric acid and aniline compound, continuously conveying the overflow emulsion from said zone to a separation zone to allow continuous separation of said emulsion into an aqueous phase and an organic phase containing said salt and solvent, continuously conveying said organic phase to a second and third reaction zone and reacting said salt in the organic phase in said zones with an aqueous nitric acid of 65%-80% by weight hno₃ and substantially free of sulfuric acid at a temperature of about 40°C to about 70°C at atmospheric pressure, in a mole ratio of hno₃ to salt of about 1.9:1 to about 2.5:1, until the dinitro derivative of said aniline compound is formed and continuously removing said derivative in said organic solvent from the third reaction zone, said substituted aniline compound having the structural formula: ##STR4## wherein:

R₇ is CH₃, C₂ H₅, C₃ H₇ --n, C₃ H₇ --i, C₄ H₉ 13 i C₄ H₉ --i, CF₃ or Cl;

X is CH₃, --CH₂ --O--CH₃ or --CH(CH₃)O--CH₃ --CH(CH₃)--O--CH₃ ; and

R₅ is C₃ -C₇ secondary alkyl, or monochloralkyl C₃ -C₄.

2. A process according to claim 1, wherein said aniline compound is n-sec. butyl-3, 4-xylidine, N-(1-ethylpropyl)-3, 4-xylidine or N-(1-methylbutyl)-3, 4-xylidine.

3. The continuous process defined in claim 1, wherein, in the step in which the said dinitro derivative is formed, a spent nitric acid is yielded in a concentration of about 10%-50% hno₃ by weight, characterized in that the said spent acid so yielded is thereafter used in the first defined supplying step of said continuous process.

4. A process of dinitrating a dinitratable substituted aniline compound which comprises reacting (1) an aqueous nitric acid of about 10-40% hno₃ by weight and substantially free of sulphuric acid with (2) a substituted aniline compound in the presence of a liquid, inert, water-immiscible organic solvent for said aniline compound, in a mole ratio of about 1:1 to about 1:1.3 of hno₃ to said aniline compound and at a temperature of about 40° to about 70°C and atmospheric pressure, thereby forming an emulsion containing a salt of said nitric acid and aniline compound dissolved in said solvent, separating said emulsion into an aqueous phase and an organic phase containing said salt, separating the organic phase from the aqueous phase and reacting said salt in the organic phase with an aqueous nitric acid of 65-80% by weight hno₃ and substantially free of sulphuric acid in a mole ratio of hno₃ to said salt of about 1.9:1 to about 2.5:1 and at a temperature of about 40° C. to about 70°C and at atmospheric pressures until a reactive mixture containing the dinitro derivative of said compound is formed, said substituted aniline compound having the structural formula: ##STR5## wherein: R₅ is C₃ -C₇ secondary alkyl or monochloralkyl C₃ -C₄ ;

X is CH₃, --CH₂ --O--CH₃ or --CH(CH₃)--O--CH₃ ; and

R₇ is CH₃, C₂ H₅, C₃ H₇ --n, C₃ H₇ --i, C₄ H₉ --i, CF₃ or Cl.

5. A process according to claim 4, wherein said aniline compound is n-sec. butyl-3, 4-xylidine N-(1-ethylpropyl)-3, 4-xylidine, or N-(1-methylbutyl)-3, 4-xylidine.

6. The process defined in claim 4 wherein the reaction mixture containing said dinitro derivative also contains spent nitric acid in a concentration of 10%-50% hno₃ by weight, together with the subsequent step of repeating said process utilizing the said spent nitric acid in the said first-defined reacting step.

7. The process of dinitrating a dinitratable substituted phenol compound without use of sulfuric acid which comprises the steps of:

(A) supplying the following ingredients: an aqueous nitric acid of about 10% to 50% hno₃ by weight and substantially free of sulfuric acid; a dinitratable substituted phenol compound; and a liquid, inert, water-immiscible organic solvent for said substituted phenol compound;

(B) reacting said ingredients, thereby forming an emulsion containing a mononitrated derivative of the said compound;

(C) permitting the separation of said emulsion into an organic phase containing the mononitrated derivative of said compound, and an aqueous phase containing aqueous spent nitric acid as a waste;

(D) reacting said separated organic phase with aqueous nitric acid of 60% to 100% by weight hno₃ and substantially free of sulfuric acid, thereby forming a second mixture;

(E) permitting the separation of said second mixture into an aqueous phase consisting of spent nitric acid of 10% to 50% by weight, and an organic phase containing the dinitrated derivative of said substituted phenol compound;

(F) removing said organic phase containing the dinitrated derivative, thus leaving the said spent nitric acid of step (E), and

(G) repeating the foregoing steps (A) to (F), inclusive, utilizing as the acid in step (A) the said spent nitric acid of step (E),

whereby the aqueous waste of step (C) is the only waste generated in the process. 8. The process as defined in claim 7, wherein the said spent nitric acid of step (E) is diluted to substantially 10% concentration prior to its utilization as the acid in step (A). 9. The process of dinitrating a dinitratable aniline compound without the use of sulfuric acid, which comprises the steps of:

(A) supplying the following ingredients: an aqueous nitric acid of about 10% to 50% hno₃ by weight and substantially free of sulfuric acid; a dinitratable aniline compound; and a liquid, inert, water-immiscible organic solvent for said aniline compound;

(B) reacting said ingredients thereby forming an emulsion containing a mononitrated derivative of the said compound;

(C) permitting the separation of said emulsion into an organic phase containing the mononitrated derivative of said compound and an aqueous phase containing aqueous spent nitric acid as a waste;

(D) reacting said separated organic phase with aqueous nitric acid of 60% to 100% by weight hno₃ and substantially free of sulfuric acid, thereby forming a second mixture;

(E) permitting the separation of said second mixture into an aqueous phase consisting of spent nitric acid of 10% to 50% by weight, and an organic phase containing the dinitrated derivative of said aniline compound;

(F) removing said organic phase containing the dinitrated derivative, thus leaving the said spent nitric acid, and

(G) repeating the foregoing steps (A) to (F), inclusive utilizing as the acid in step (A) the said spent nitric acid of step (E),

whereby the aqueous waste of step (C) is the only waste generated in the process. 10. The process as defined in claim 9, wherein the residual nitric acid of the aqueous phase of said step (C) is substantially 10% by weight nitric acid or less.