CA1245672A - Process for producing aminophenols - Google Patents

Abstract

Abstract of the Disclosure:

A process for producing an aminophenol, which comprises (A) a step of reacting a dihydric phenol with an aminating reagent in the liquid state under heat in the presence of water and a water-soluble catalyst, (B) a step of removing the unreacted aminating reagent from the reaction mixture, and then precipitating the crude aminophenol from the reaction mixture from which the aminating reagent has been removed, thereby to obtain a crystallization mixture containing the crude aminophenol, (C) a step of separating the crystallization mixture into crystals of the crude aminophenol and the reaction mother liquor containing the catalyst, (D) a step of circulating part or the whole of the reaction mother liquor to the aminating step, and (E) a step of washing the crude aminophenol crystals with a washing liquor to obtain the washed crude aminophenol crystals and the washing mother liquor, and thereafter separating the aminophenol from the washed crude aminophenol crystals and purifying it.

Description

~ 1 --This invention relates to a process for producing aminophenols from dihydric phenols. More specifically, it relate~ to a process for producing aminophenols, which comprises reacting dihydric phenols with aminating reagen~s in the liquid state in the presence of water and a wa~er-soluble catalyst, separating and recovering the amino-phenols and the catalyst efficiently from the resulting mixture, and recycling the c~talyst to the reaction system.
Aminophenols are useful as intermediates for the productiQn of medicines, agricultural chemicals, dyes, rubber chemicals, additives for synthetic resins, etc. For the production of aminophenols by reacting dihydric phenols with aminating reagents such as ammonia or amines, methods have heretofore been proposed which i~volve using as a catalys~ ammonium sal~ of arsenic or phosphoric acid (U. S.
Patent No. 2~376,112)~ a catalyst co~posed of an ammonium halide of copper, cobalt or nickel (Japanese Laid-Open Patent Public~tion No. 42829/1977), stannous chloride (Japanese Laid-Open Patent Publication No. 100427/1977), a catalyst composed of stannous chloride and am~onium chloride (Japanese Laid-Open Patent Publication No.
1004~8/1977), and a molybdic acid-type catalyst which gives aminophenols in higher yields and selectivities than the preceding mcthods (Japanese Laid-Open Patent Publication No. 108841/1980). Since, however, all of these methods use large amounts of catalysts, the economical industrial production of aminophenol by these methods requires es-tablishment of techniques of efficiently separating the catalyst and aminophenol from the reaction mixture and recycling the recovered catalyst to the reaction system.
Investigvations of the present inventors, how-ever, have led to the discovery that the technique gen-erally used in ~his field for separatin~ ~he catalyst from ~ ~ ~ 5 ~ ~

the re~ction mixt~re after the reac~ion has the following defects.
When a method is employed in which the reaction mixture is directly distilled to distill off the amino-phenol and the catalyst is recovered as a distillationbottom, a considerable amount of the aminophenol remains in the distillation bottom, and the aminophenol cannot be separated with good efficiency. If one attempts to distill off the aminophenol completely, the aminophenol changes to a high-boiling compound by polycondensation reaction.
Consequently, the distillation bottom becomes tarry, and it is substantially impossible to recover and re-use the catalyst.
On the other hand, when a method is employed in which ~he catalyst is separated from the aminophenol and recovered by extracting the reaction mixture with a solvent which does not dissolve the catalyst, the aminophenol con-tains high-boiling by-products which have strong colora-tion, and the separation of the catalyst is not always carried out with good efficiency.
The present inventors have found through the aforesaid experimental studi~s that these ordinary methods cannot be applied to the industrial produc~ion of amino-phenol. With this background, the present inventors have extensively studied a process for industrially producing an aminophenol in which the aminophenol and the catalyst are separated from the reaction mixture with good efficiency, and the recovered catalyst is recycled to the reaction system. These investigations have led to the present invention.
It is an object of this invention to provide a process for producing aminophenols on an industrial scale.
Another object of this invention is to provide a process for producing aminophenols industrially advanage-ously, in which the desired aminophenols can be recoveredin high yields from the reac~ion mixture, and the catalyst '7~

or the unreacted phenols are recovered and recycled to the reaction system.
Further objects of this iinvention and advantages will become apparent from the following description.
According ~o ~his invention, the above objects and advantages are achieved by a process for producing an aminophenol, which comprises tA~ a step of reacting a dihydric phenol with an aminating reagent in the liquid state under heat in the presence of water and a water-soluble catalyst, ~ B) a step of removing the unreacted aminating reagent rom the reactior. mixture, and then precipitating the crude aminophenol from the reaction mi~ture from which the aminating reagent has been removed, tbereby to obtain a crystallization mixture containing the crude aminophenol, (C) a step of separating the crystallization mixture into crystals of the crude aminophenol and the reaction mother liquor containing the catalyst, (D) a step of recycling part or the whole of the reaction mother liquor to the aminating step, and, (E) a step of wa~hing thP crude a~inophenol crys~als with a washing liquor to obtain the washed crude aminophenol crystals and the washing mother liquor, and thereaf~er separating the aminophenol from the washed crude aminophenol crystals and purifying it.
The accompanying drawing, ~igure 1, is a flow chart illustrating the continuous production of amino phenols, which is suitable for the practice of the process of this invention for producing aminophenols.
Examples of the dihydric phenol used as a reac-tion material in step ~A) of the process of thi~ invention include dihydric phenols having no substituent such as hydroquinone, resorcinol and cate~hol; and dihydric phenols havins hydrocarbon groups such as ~-methylhydroguinone, 4 me~hylresorcinol, 5-methylresorcinol, 5-ethylresorcinol, S-isopropylresorcinol, 5 n-butylresorcinol, 5~sec-butyl-5~2 r~sorcinol, 5-tert-butylresorcinol, 3-methylcatechol, 4-methylcatechol, 4-ethylcatechol, 4-n-propylcatechol, 4-isopropylcatechol, 4-n-butylcatechol, and 4-tert-butyl-catechsl. Among these dihydric phenols, the use of the dihydric phenols having no substitLent is preferred. It is especially preferred to apply resorcinol or hydroquinone to the process of this invention.
Examples of the aminatiny reagent used in step (A) of the process of this invention include ammonia and aqueous ammonia in various concentrations; primary amines such as methylamine, ethylamine, n-propylamine, isopropyl-amine, n-butylamine, sec-butylamine, tert-butylamine, amylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, dodecylamine and benzylamine, and secondary i5 amines such as dimethylamine, diethylamine~ di-n-propyl-amine, diisopropylamine, di-tert-butylamine, diamylamine, dihexylamine, diheptylamine, dioctylamine and didodecyl-amine. Of these aminating reagents, ammonia i5 preferred.
The ammonia may be used as ammonia gas or aqueous ammonia as required. The agueous ammonia preferably has a concen-tration of 10 to 60% by weight.
The proportion of the aminating reagent is usu-ally at least 1 mole, preferably 1 to 5 moles, per mole of the dihydric phenol. When the aminating reagent is used in an amount exceeding the theoretical amount, the excess of it is recovered after the reaction and reused~
In the present invention, the reaction of the dihydric phenol with the amina~ing reagent should be car-ried out in the presence of a catalyst. The catalyst may be a known water-soluble catalyst. Examples include vari-ous metal compounds such as oxides, ammonium compounds, sulfates and a~monium salts of molybdenum, copper, antimony, vanadium, iron and nickel; and various ammonium compounds such as ammonium salts, primary amine salts, secondary amine salts, ~ertiary amine salts and quaternary ammonium salts, and compounds capable of forming ammonium compounds in the reac~ion sys~em. C,peciic examples of the ammonium salts are ammonium hali.des such as ammonium chloride, ammoniu~ bromide and ammorlium iodide~ ammonium nitrate~ ammonium sulfatte, ammonium phosphate and hete{o-polyacid or isopolyacid ammonium sal.ts such as ammoniummolybdate or ammonium tungstate. Examples of the primary amine salts or secondary amine salts are salts of the primary amines or secondary amines exemplifiecl above as the reaction material with various acidic compounds~ such as hydrofluorides9 hydrochlorides, hybrobromides, hydro-iodides, sulfates, nitrates, phosphates, organic acid salts, and heteropolyacid sal~s. Examples of the compounds capable of forming ammonium compounds in the reaction system are acidic compounds such as hydrochloric acid, hydrobromides, and heteropslyacids or isopolyacids con-taining molybdenum or tungsten as a component~ These acidic compounds c~ange to a~monium compounds by reaction with the aminating re2gent such as ammonia, the primary amine or the secondary amine.
~0 ~hen an a~monium compound is used as a atalyst component, it is preferably an ammoniating reagent corres-ponding ~o the aminatins reagent for the reaction sub-strate. For example, when am~onia is used as the aminating reagen~, it is preferred to use an ammonium salt. When the primary or secondary amine is used as the aminating re~
agent, it is preferred to use an amine salt corresponding to it as ~he a~monium compound used as the catalyst com-ponent.
The particularly preerred proportion of the catalyst is usually 0.01 to 2 moles, preferably 0.05 to 1 mole, per mole of the dihydric phenol.
In s~ep (~ of the process of this invention, water is used in an amoun~ of usually 10 to 1000 parts by ~eight9 preferab1y 10 ~o 500 parts by weight, per 100 parts 3~ ~y weight o the dihydric phenol.
~he reaction of s~ep (A~ is carried out usually in an atmospherQ of nitrogen. I~ is also possible to ~arry it out in an atmosphere of an inert 92~ suoh as argon and helium. The reaction temperature may vary ~epending upon the type o the reaotion ~ubstrate~ its concentration and the type and concentration of the c:atalyst, but is us~ally in the range of 17~ to 350C, preferably in the r~nge of 180 to 300C~ The reaction is usually carried out under el~vated pressures. The pressure, including the autogenous pressure attributed to the charged starting materi~ls during the reaction and the pressuri%ation with an inert ga~ which is carried out as desired before the reaction~ is usually in the range of S to 150 kg/cm2-~, preferably in the range of 10 to 50 kg/cm2-GO The aminating reaction can be carried out batchwise~ semicontinuously, or continu-ously.
The reaction mix~uee obtained after the aminatingreaction in step (A) contains the desired aminophenol, a by-product phenylenediamine, and a trace o a coloring high-boiling material. Usuallyv it al~o contains small amounts of the unreacted dihydric phenol and the aminating reag~nt~ and water a~d the catalyst.
In the next step (B) of the process of this inven~ion, ~he unreacted a~inating reagent is removed from the reaction mixture formed in step (A), and the crude aminophenol is precipitated to obtain a crystalliæation mixture of the crude aminophenol.
It iB especially preferred in this invention to add the washing mother liquor obtained in step ~E) to the reaction mixture from which the unreacted aminating reagent has been xemoved as aboYe. A required, however, the aforesaid washing mother liquor may be add~d to the reaction mixture a~ other stages in the processy and it is also within ~he process o ~his invention that the washing mother liquor is not ~ecycled for re-use. The advantage of adding the washing mother liquor to the reaction mixture oDtained in s~ep ~A3 from which ~he aminating reagent has ~i7,~

been removed is ~hat the ratio of recovery of the desired aminophenol can be increased, and the temperature and concentration of the reaction mixture to be subjected to crystalliza~ion can be adjusted~ The above reaction mix-ture contains wa~er and a small amount of the unreactedaminating reagent which remains unremoved. In step ~B) of this invention, water is sometimes entrained in the un-reacted aminating reagen~ during the course of its removal, and the liquid can be removed. Thig liquid will be refer-red to hereinafter ~s the recovered liquid.
~ccording to one specific procedure of the opera~
tion of removing the unreacted aminating reagent~ the temperature of the reaction mixture from which the un-reacted aminating reagent ha~ been remoYed is adjusted ~5 usually to 80 to 250C, preferably 100 to 200C, namely to a point egual to the reac~ion temperature or lower than it, and ~he pressure of the reaction system including the reaction mixture is released to thereby remove a greater portion of the unreacted aminating reagent. The pressure of the reaction system upon the termination of the pressure releasing operation can u~ually be set at 0 to 10 kg~cm2-G.
In the process of this invention, the pressure is prefer-ably set at 0 to 5 kg/cm2-G in view of the subsequeDt operationO
The mixture composed of the unreacted aminating reagent removed from the reaction mixture by the above opera~ion and water entrained in it can then be conducted to a stripper. At this time, the mixture i cooled to a temperature of usually 30 ~o 100C, preferably S0 to 98C, and the recovered aminating reagent is separated as a vapor phase and the recovered liquid, as a liquid phase~ The recovered liquid may sometimes con~ain some amount of the aminating reagent dissolved therein, but it is not par-ticularly detrimental. This gas-liquid separating opera-tion i~ usually carried out under atmospheric pressure, butas required, under suitable eleYated pressures. The recovered aminating reagent ~ay be lecycled to the aminat~
ing step (A) and can be re-used as ~he starting ~aterial.
In ~tep ~B~, the reaction mix~ure from which the aminating reagent has been removed is then cooled to ex tract the crude aminophenol. At this time~ it is espe-cially preferred to add the washin~3 mother liquor obtained in step (E) to the reaction mixture. This brings about the advantage that the ratio o the desired aminophenol to be recovered can be increased, and the temperature and con-centration of the reaction mixture ~o be subjected ~ocryskallization can be v ery easily adjusted.
Specifically, the washing mother liquor obtained in step (E) and kept at a low tempeeature is added to the aforesaid aminating ayent-removed reac~ion miacture having 15 substantially the same temperature as the reaction mixture, and the temperature of the tesulting reaction mixture to be subjected to crystallization is set usually at 5Q to 100C, preferably at 65 to 90C. The amount of the washing mother liquor added at this time is usuallly 10 to SOO parts by ~0 wei~ht, preferably 10 to 50 parts by weight, per 100 par~s by weight of the aminating reagent removed reactivn mix-ture. If required, the temperature of the mixture can be forcibly lowered to the aforesaid set temperature by, for example, blowing an inert gas into the reac~ion mixture ~o be subjected to crystallization. If required in the above operation, a suitable amount of water may be added to the aminating reagent-removed reaction mixture to be subjected to crystallization. Thereafker, the reaction mixture to be ~ubjected to crystallization which has been made uniform by 3~ thorough stirring is cooled at a cooling rate of usually 0.001 to 1C/min., preerably 0.01 to 0.5C/min~, and finally to 0 to 50C usually, preferably 25 to 45C.
Consequently, the mi~ture turns to a crystallization mix-ture con~aining the precipitated crude aminophenol.
In s~ep (C) of the proce~s of ~his invention, the crystalliza~ion mixture is sep2rated into the crude amino-- 9 ~~
phenol rystal~ and the reaction mother liquor containing the ca~alyst dissolved therein. The separation may be carried out, for example, ~y decantatiQn, usually filtra-tion through a filtec made of a plastic or metallic mesh, or centrifugal filtration. The temperature at the time of separating operation is usually 0 to 40C, preferably 10 to 35C.
In step (D) of the process of this invention, the reaction mother liquor obtained in step ~C~ is partly or wholl~ recycled to the aminating reaction step ~A)~ As a result, the recovered catalyst contained in the reac~ion mother liguor, which sometimes al50 contains small amount cf unconverted dihydric phenol, can be recycled to the ~eaction for re-use.
With reference to the recycles, the step (A~ will again be de~cribed. In the aminating reaction step ~A) in this invention, the dihydric phenol and the aminating reagent are heated in the presence of water and the water-soluble catalyst to perform amination~ At this ti~e~ the unreacted aminating reagent removed in step (B) may some-times be recycled to step (A), and the mother liguor con-taining the catalyst and the unreacted dihydric phenol separated in step (C) is sent to step (~ by step ~D3v Accordingly, the amounts of the dihydric phenol, aminating reagent and catal~st to be charged in step ~A) are prescribed so as to atisfy the aoresaid conditions by csnsi~ering the amounts of the recycles. With regard to the ca~alyst, the catalyst is sometime~ lost during the opera~ions in all of the st~ps of the process of this 3~ invention. Accoridngly, even if all the reactio~ mother liquor separated in step (C~ is recycled to step (A) t not all of the catalyst used in the reaction i5 re overed and recycled to the aminating reaction step. The loss of the catalys~ in this case is usually very lit le, but general-33 ly~ the catalyst is additionally supplied in an amountcorresp3ndinq to the loss, and as required, the amount of the additional ca~alyst can be properly selec~ed within a range which meets the charging conditions. With regard to the ami~ating reagent, a greater portion o the unreacted aminating reagent is recovered by step (B), and recycled to the aminatirag step (A). A part of the unreacted aminating agent is also recycled to the aminating reacJion step IA) as dissolved in the reaction mother liquor via 5tep (D).
Hence, a high recovery ratio of the unreac~ed aminating reagen~ can be achieved.
lD The amount of the aminating reage~t to be addi~
tionally supplied in the aminating reaction is selected so as to ~atisfy the aforesaid char~ing conditions as in the case of ~he catalyst. Although the unreacted dihydric phenol remaining in the reaction mixture is usually little, is it is recovered 2S dissolved in the reactisn mother liquor by step (D) and recycled to step ~Al. In performing the next aminating reaction, tberefore, the dihydric phenol is additionally supplied in an amoun~ corresponding to the consumption as prescribed as în the case of the aminating ~ea9ent. The solvent may be added, as required, in amounts which satisfy the aforesaid charging conditions.
In step ~E) of the process of ~his invention, the crude arninophenol crystals obtained in step (C~ are washed with a wa~hing liquor to obtain washed crude aminophenol crystals and a washing mother liquor, and thereafter, the aminophenol is separated from the washed crude aminophenol crystals and purified. Preferably but not essentially, the washing mother liquor is sent to s~ep (B) and added to the aminating reagent-removed reaction mixture, as stated hereinabove~
Step IE) will now be described i~ detail. In performing the operation of washing the crude aminophenol crystals, the tempera~ure o the washing system including ~he washing liquor is prescribed usually at 0 to 50C, preferably at 25 to 45C. As required, the pressure may be prescribed at an elevated or reduced pressure~ Desirably, the washing opera-ion is carried out in an a'cmosphere of an inert gas ~uch as nitrogen. Pr,eferably, the reaction solvent recovered in s'cep (B~ is used as 'che washing liquor in this invention. As reguiredr f resh water or a liquor 5 prepared by addillg a suitable amoun4 of f resh water to the recovered 1 iquid can be u5ed as the washing 1 iquor .
Specif ically, 'che washing operation is carried out as follows in ~ccordar~s~e with the prvcess of this invent:ion. First, the crude aminophenol crystals are 10 washed with the washing liq~aor~ This can ~e carried out, for e;~eample, by holding the crude aminophenol crystal~ on a filter and sprinkling the washing liquor onto them~ or by addin~ the crude aminophenol crystals to the washing liquort stirring the mixture for a suitable period of time"
and then separating the crystals by filtration or the like.
The washed crude aminophenols may, as required, be washed further wi~h a suitable amount of water or a mixture of the recovered liquid with water. The washing operation in this case is de~irably carried out after washing the crude aminophenol crystal6 with the recovered liquid.
~he amount of the washing 1 iquid to bc used in the washing operation is usually lQ to lOQO parts by weight, preferably 10 to 1000 parts by weight, per 100 parts by weight o~ the crude aminophenol crystals.
After the washing of the crude aminophenol cry-s~als i5 over, a greater portion of the washing mother liquor adhering to the washed crude aminophenol crystals is r~moved by an ordinary method, for example by shaking it off using a centrifugal separator to give a cake of the washed crude aminophenol crystals. The ~reatment of re-moving the adhering washing mother liquor is not limited to the case mentioned, but can be carried out at any time a required numbers of times duriny the washing of the crude aminophenol crystals with the washing liquor. The washing mother li~uor obtained by the washing operation may be recycled to step (B) for re-use.

In step ~E) o the process of this invention, the washed crude aminophenol crystals can be purified by treat-ing them by a method of distillation followed by recrystal-lization. The procedure o these treatments will be de-scribed below. The ~ashed crude aminophenol crystalsobtained in step IE~ are distilled under reduced pressure in an atmopshere of an inert gas such as nitroge~ to remove traces of the catalyst and high-boiling condensation pro ducts remaining therein. The distillation usually give~ an io aminophenol having an aminophenol content of at least 90%
by weight~ The aminophenol may sometimes contain small amounts of phenylenediamines and at times a trace of the unreac~ed dihydric phenol a~ impurities. The amount of other impuri~ie~ .is only trace and can actually be ignored.
The distillation is desirably carried out at a pressure of 0.1 to 600 mm~g, preferably 1 to 500 mmHg, and a tempera-ture of usually 120 to 250C, preferably 140 to ~20C. The distillation can be carried out batchwise or continuously.
The distilla~ion bo~tom obtained by the distillation con-tains a small amount of the catalyst in addition to high-boiling condensation products~ When the catalyst con ains a me~al component, the distillation bottom is burnt ts remove the organic matter, and the catalyst can be re-covered as metal oxide. For example, when the catalyst used is of a molybdic acid type, it may be recovered as molybdenum oxide and can be directly used as an additional supply of catalyst in the aminating step (A).
Recrystallization of ~he crude aminophenol ob-tained by distillation in the present invention gives high purity aminophenols. ~esirably, the recrystallization opera~ion in the process of this invention is carried out in an atmospher~ of an inert gas such as nitrogen. Ex-amples of a recrystallization solvent tha~ can be used in the recrystallization operation include water, methanol t ethanol, methyl isohutyl carbinol and ethyl acetate. The use of water is preferred in view of the purity of the ,'RL~ P.

aminophenol and economy. The recLystallization solvent may be a mixture of~ for example, the above-exemplified com-poundsO The amount of the recrys~allization solvent used i5 usually 50 to 1~00 parts by weight, prefeeably 100 to 500 parts by weight, per 100 parts by weight of the amino phenol to be recrystallizedO According to the process of this invention, the aminophenol to be recrystalli2ed is dissolved uniformly in the recrystallization solvent, and then the temperature of the solution is lowered to pre-cipitat~ the aminophenol. The temperature conditions inthis procedure are such that prior to the precipitatîon of tbe crystals, the solution of the aminophenol in the re-cryst~lliza ion solvent is maintained usually at 60 to 100C, preferably 70 to 90C, and then cooled at a rate of usually OoOl to 1C/min~, preferably 0.01 to 0.5C, and finally kept usually at 0 to 50C, preferably at 25 to 45C~ The aminophenol crystals precipitated ~y the above procedure are separated from the recrystallization mother liquor by an ordinary method such as filtration. As re-quired, the collected recrystallization mother liquor is re~oved, and the aminophenol crystals may further be washed with a suitable amount of a fresh supply of the recrystal-lization solvent. The wet aminophenol crystals haYing the recrystallization solvent adhering thereto are, for ex-ample, dried under reduced pressure to remove the recrys~al-lization solvent to give a highly pure aminophenol 2S a final product.
Th~ recrystalliz~tion mother liquor is usually concentrated and filtered to separate it ints a filtrate 3~ and secondary crystals. The crystals may be sent to the distiliation step and distilled together with the washed crude ami~ophenol crystalsO On the other hand, the fil-trate is discarded, or as required may be sent in a suit-able amount to the distillation step and treated in tne 3~ same manner as in the case of the cry tals. Alternatively, a suitable amoun~ of the recrystallization mother liquor may be removed ou~ of the syste~, and ~he remainder may be distilled in ~he distillation step~ On the other hand, ~he recrystalli~ation washing liquor left after washing the precipitated aminophenol is recycled and re-used as the recrystallization solvent for preparing the recrystalliza-tion solution. When the reaction solvent used in this i.nvention is water and the recrystallization solvent i8 also water, water which distills o~t from the top during the distillation in the distillation step may be used as a lo fresh recrystallization solvent or a washing liquor for the precipitated aminophnenol~
In the recrystallization operation in step (E~ of the present invention, a very small amount of -~uch an additive as sodium thiosulfate, sodium dithionite~ sodium is sulfite, sodium hydrogen sulfite or sodium sulfide may be added to the recrystallization solution in order to stabi-lize the aminophenol. The amount of the additive is usu-ally 0~001 to 5 parts by weight, preferably 0.05 to 1 part by weight, per 100 parts by weight of the recrystallization solution.
The aminophenol crys~als as washed are wet with the adhering recrystalization solvent. upon removal of ~he solYent by drying~ an aminophenol having a purity of at lea~. 99.5% can be obtained.
The process for producing the aminophenol in accordance wi~h this invention is specifically des~ribed by way of example with refere:lcQ to the accompanying drawing, ~igure lr ~hich illustrates the process for producing an a~inophenol by a continuous method. The aminating step ~A) is carried out in a reactor 1. The reaction mixture ob-tained in the aminating step tA3 is sent to a flash tower

2. From the top of th~ ~ower~ the unreacted aninating reagen~ and water entrained in it are withdrawn, and the aminating reagent-removed reactisn mixt.ure is withdrawn from its bo~tom. The materials withdrawn from the top of the tower are introduced into a gas-liquid separator 3, and ~q the gas separated t.here is returned as the unreacted amina~ing reagent a to the aminating step (A). The sep-arated liquid is sent. as ~ne recoYered liquid b to a filtration-washing devi~e 5. At this time, a suitable amount of water may be a~ded to the r~co~red liquid b.
On the other hand, the aminating reagent-removed reaction mixture withdrawn from tne bottom of the flash tower 2 is sent to a crystallization tank 4. At this time, it is preferred that the washing mother liquid d formed in the step of the filtration-washing device 5 be sent to the flash tower 2, and the aminating reagent-remove~ reaction mixture be conveyed to the crystallization tank 4 while heing washed with ~he mother liquor d. ~s requi.red, a part of the washing mother liquor d may be directly sent to the i5 crystallization tank 4. The reaction mother liquor c containing the catalyst which is formed in the iltration-washing device 5 is returned to the reactor 1 for the amination step, and supplemented with required amounts of the dihydric phenol k, the aminating reagent ~, and the additional catalyst m. The amination reaction is again carried out.
The washed crude a~inophenol crystals from the filtra~ion-washing device 5 are sent to a distillation column 6, withdrawn as a crude aminophenol from the ~op of the column, and fed to a recrystallization tank 7. Water is withdrawn from the top of the column 6, and the dis-tillation bottom i is withdrawn from its bottom. The aminophenol crystals obtained in the recrystallization ~ank are fed into a filtration-washing device 8, and dried in a dryer 10 to giv2 an ~minophenol as a final product n. In the filtra~ion-washing device 8, a recrystallization sol-vent ~ is added~ and the recrystallization washing liquor f formed in the washing device 8 is recycled to the recry-stallization tank 7. The recrystalliza~ion mGther liquor e formQd in the washing device 8 is sent to a secondary recrys~allization tank 9. ~ suitable amount of the secondary recrystallization mother liquor obtained here is removed as a waste liguor i, an~ the remainder is recycled to the distill2tion columr, 6. If desired, the re~rystal-lizatlon mother liquor e may be partly discharged as the waste 'iquor l, and the remain~er may be recycled to the distillation column 6 without going through the secondary recrystallization tank 9.
As is clear from the foregoing statement~ when the process of this invention is applied to the industrial production of ami.nophenols, highly pure aminophenols can be produced economically advantageously without any signifi-cant losses of the catalyst and the unreactQd aminating agent by simpler process steps than in a conventional process.
1~ The following Examples illustrate the process of this in~ention in greater detail. All parts and percent~
ages in these examples are by weight unless otherwise specified.

A SU~ 316 stainless steel autoclave was charged with 110 p~rts of resorcinol, 194 parts of 27.5% aqueous a~monia and 35 parts of ammonium paramolybdate l~N~4)6Mo7O24.4H2O~ as a catalyst under a nitrogen atmos-pheret and the reaction was carried out at 200C for 6 hours ~ith stirring. A this time, the pressure decreased to 22 kg/cm~-G from 33 kg/cm2-G.
After the reaction, the reaction mixture was transferred to a flash tower, and its ~emperature was lowered to 140C. While the reaction mixture was main-tained at this temperature, the pressure was releasedto remove ammonia from the reaction mixture. By this operation, 93O7 parts of a mixture of ammonia and water entrained was re~oved. The mixture flash-removed was conduct2d to a stripper and separated at 95C into 32.2 parts of ammonia gas and 61.4 part~ of an aqueous solution eontaining small amoun~ of ammonia (to be referred to as

3~

the recovered solution) which were respectively recovered.
The reac~ion mi~ture left after the ammonia removing operation was transferred to a crystalliæation tank while being washed with 66 parts of water~ and then kept at a temperature of 65C. The mixture was suffici-ently stirred so as to form a unifc)rm solution~ By cooling the solution to 30C over 4 hours, a crystallization mix-ture containing precipitated meta-aminophenol crystals was obtained. The crystallization mixture was centrifugally filtered by using a lO0-mesh basket to separate it into crude meta-aminophenol crystal~ and the reaction mother liquor. The amount of the resulting re~ction mother liquor was 192.3 parts. The crude meta-aminophenol crystals obtained were further washed under centrifugation with all i5 4f the eecovered solution mentioned above to obtain 91.3 parts of washed crude meta-aminophenol crystals in the form of a wet cake and 54.~ parts of the washing mother liquor.
The washed meta-aminophenol crystals were sub-jected to simple distillation at 160C and 7 mm~g to give 7B.9 parts of crude meta-aminophenol as a distillate. The amount of the distillation residue was 2.4 parts~ and the amount of the difitillate was 8.0 parts.
To the meta-aminophenol obtained by distillatioon w~s added 94.7 parts of water containing 0~4~ of sodium dithionite, and the mixture was heated at 80 to 85C to prepare a recrystallization aqueous solution of meta-amino-phenol. The aqueous solution was cooled with stiriny to 40C over 4 hours, and the resulting crystallization mix-ture was centrifugally filtered through a 100-mesh haske~
to give meta-aminophenol crystals and 98.5 parts of the recrystallization mother liquor. The meta-aminophenol crys~als were washed under centrifugation with 36.8 parts of wa~er 7 and dried to give 68.9 parts of meta-aminophenol having a purifty of 9S.~%.
In the reaction of this example, the conversion of resorcinol was 93.8 mole%, and the selectivity of meta-aminophenol was 90.5 mole~

.~s~ s~J

80.9 parts of resorcinol, 0.75 part of ammoni~m paramolybdate~ the recovered ammonia gas obtained in Example 1, and 15.9 parts of a fresh supply of ammonia gas were added ~o 15G.7 parts of the reaction mother liquor obtained in Example 1, and the mi~ture W2S reacted~ In the aminophenol distillation step, the secondary crystals obtained from the recrystallization mother liquor in Example 1 were added to the washed meta-aminophenol cry-stals obtained in this example and distilled ~ogether.Furthermore, in the preparation of the recrystallization aqueous solution, the recrystallization washing mother liquor and the distillate obtained in Example 1 were used instesad of water.
1~ Otherwise, the reaction and work-up were carried out under the same conditions and by the same method as in Example 1 to give 69 parts of meta-aminophenol having a purity of 99.8~.
In the reaction of Example 2, the conversion of resorcinol was 99.1 mole~ and the selectivity of meta-aminophenol was gl.2 mole~, as calculated on the basis of the resorcinol that was added as a supplement. The total yield of met~-a~inophenol at this time was 86 mole~ based on the charged resorcinol.

Claims (5)

What is claimed is:

1. A process for producing an aminophenol, which comprises (A) a step of reacting a dihydric phenol with an aminating reagent in the liquid state under heat in the presence of water and a water-soluble catalyst, (B) a step of removing the unreacted aminating reagent from the reaction mixture, and then precipitating the crude aminophenol from the reaction mixture from which the aminating reagent has been removed, thereby to obtain a crystallization mixture containing the crude aminophenol, (C) a step of separating the crystallization mixture into crystals of the crude aminophenol and the reaction mother liquor containing the catalyst, (D) a step of circulating part or the whole of the reaction mother liquor to the aminating step, and (E) a step of washing the crude aminophenol crystals with a washing liquor to obtain the washed crude aminophenol crystals and the washing mother liquor, and thereafter separating the aminophenol from the washed crude aminophenol crystals and purifying it.

2. The process of claim 1 wherein the solution containing water which is entrained in the unreacted aminating reagent when the unreacted aminating reagent is removed from the reaction mixture in step (B) is used as the washing liquor for the crude aminophenol crystals in step (E).

3. The process of claim 1 wherein the washing mother liquor obtained in step (E) is added to the aminating agent-removed reaction mixture in step (B), and thereafter the crude aminophenol is precipitated in step (B).

4. The process of claim 1 wherein the unreacted aminating reagent removed and recovered from the reaction mixture in step (B) is recycled to step (A) as part of the starting material.

5. The process of claim 1 wherein in separating the aminophenol from the washed aminophenol crystals and puri-fying it in step (E), the washed aminophenol crystals are distilled to give a crude aminophenol, and the crude amino-phenol is recrystallized to give a pure aminophenol.