US1396001A - Manufacture of picric acid - Google Patents

Description

0. B. MACDONALD,

MANUFACTURE opmckgc ACiD. APPLIQATIO N {ILED JULY 10, 1517- 1,396,001, I mm; Nov. 1,1921.

ATT'Y',

I UNITED STATES PATENT OFFICE.

DAVID BAIRD MACDONALD, OF LEICESTER, ENGLAND.

MANUFAC JTURE OF PICRIC ACID.

(GRANTED UNDER plications in England Dec. 15, 1915, Patent v provements in known No. 17525 of 1915; in England April 15, 191 6; in France Dec. 12, 1.916; in Russia- Jan. 13/26, 1917, and in Italy Dec. 11, 1916,) of which the following is a specification.

This invention relate to the manufacture of picric a'cid, its object being to enable pure picric acid of a high melting point and free from metallic contamination to be expeditiously and economically produced and Without danger.

To this end the invention comprises imacid manufacture and preferably also makes use of an apparatus wherein the process of manufacture may be carried out in an economic manner as Wlll be hereinafter descrlbed.

The manufacture of picric acid has been attendant with danger to -a greater or lesser extent, but more often than not to a considerable extent, and one of the important re sults broughtabout by the present invention is'the elimination of danger. Further advantages resulting from the improve- I ments constituting the present invention are volved,'falling temperature during facture of .cess of benzol has been a considerable reduction in the time inreaction, purity of picric acid produced, and economy of the extracting agents employed.

The principal improvement included in the present invention consists, in the manuplcric acid, in separating the picricric acid from the metallic impurities pres; ent in the [product of nitration by adding benzol thereto at the, end of the nitrating operation.

It is, of course;

By adding benzol 'to the product of nitration, picr'ic acid is carried into solution but the metallic bodies do not pass into solution. Then after the exdriven oil, theresidue containing a'sufiiciency of benzol is allowed to crystallize, the crystals consist- Specification of Letters Patent.

Application filed July 10, 1917.

, ing of a loosely acid processes of picric known that picric acid is soluble in benzol.

Patented Nov. 1, 1921. Serial No. 179,775.

THE PROVIS IONS OF THE ACT OF MARCH 3, 1921, 41 STAT. L, 1313.)

linked compound of picric and benzol, portion of thesaid residue (consisting of the impurities) is drained ofi'. The benzol in the crystalline compound is easily separated irernli1 the picric acid leaving the latter pure. of benzol in the manner and for the purpose just described, is applicable both in the known process which, consists in treating mercury and nitric acid with benzol, and

also in the known process which consists in first sulfonating' phenol and treating this with sodium or potassium nitrate as will be hereinafter fully set forth.

Further improvements comprised within :the present invention the nitrating process at a low temperature, and in restraining nitration and driving off the nitro-benzol by means of steam.

part of the invention as by means of same the danger hitherto present at this stage of the process is entirely eliminated. t is alo an important feature of the invention that the materials used as agents for producing the picric acid or partly recovered after use and may be used again as will be hereinafter described, thus making the process very economical.

To enable the invention to be clearly understood the same will be described with reference form and arrangement of aid of which the process cally carried out.

to a convenient apparatus byv the may bQBCOIlOl'Ill- The apparatus is illustrated diagrammati- 90 cally in the accompanying drawing and, comprises mainly, a mixing pan 1 fitted with internal movable beaters 2 and having a condenser tube 3, or other suitable cendensing means, in connection returning thecondensate to the pan by a pipe 4 and, when required, carrying it away by a pipe 5 to a receiving vessel 6. The mixing pan 1 is also provided with a gage glass 'or other known means whereby the level ofthe contents me be ascertained. Associated with the mixing pan is a erystallizing pan 7, andintermediate of, the two pans is a condensing 0r distilling app s havi g a connection by a pipe 9 and the uncrystallizable 66 e improvement consisting in the use 60 consist in carrying out 70 may be wholly more specifically therewith, capable of (not shown) ture should not however, exceed 40 Benzol (rectified) 32 parts The mercury is first dissolved in about 5 parts of the nitric acid, the solution is heated and added to the remainder of the nitric acid in the mixing: .pan 1 through the inlet 26 and mixed, the

with the mixing pan 1 and also by a pipe 10 with a storage tank 11. Means 12 and 13 for draining each pan are provided and a liquor tank drainage from the crystallizing pan ,7. Each pan is jacketed, the jackets 15 and 16 having steam and water connections 17, 18, 19, 20, a connection being provided from the mixing pan 1, to the crystallizing pan 7 by means of the pipes 21 to 25. The mixing pan and heater may be made of acid proof iron but the crystallizing pan and connections 21 to 25 and condenser 8 attached theret should be made of earthenware, aluminium or tin.

At the commencement of the process the materials may, for example, be used in the following proportions viz 4 parts (by weight) (by weight) (by weight) Mercury (metal) Nitric acid (s. g. l. 42) 100 parts preferably to boiling point benzol being. then added in a slow stream over about three hours, maybe added in three separate portions during this period.

the heaters 2 and as the temperature has a the process, the pan water in the jacket 15 to maintain the temperature of the mixture at approximately 35 C. The purpose of this low temperatureis to produce largely, during the reaction, dinitrophenol in the first instance which later on, when the temperature is raised, is converted into tri-nitrophenol. The tempera- C. since at a higher temperature than this a basic mercuric picrate is liable to form, the yield of picric acid being thereby reduced. At a higher temperature than 40 C. picric acid would be formed, but since the reaction process extends over a period of 8 to '10 hours if the higher temperature is maintained, the picric acid formed will be largely split up 'into oxalic acid and various other bodies.

By carrying out the reaction during nitration at the comparatively low temperature specified the formation of basic mercuric picrate is obviated and consequently the anger of explosion at this stage is eliminated.- A thermometer of suitable type is ture.

After a period of about ten hours has been allowed for the, reaction to take place-during which the nitro-benzol and nitric acid which volatlhze 'are collected through the 14: is arranged to receive theor alternatively it I 1 is heated by warm condenser tube 3, condensed and returned by the tube 4.to the pan-the temperature of the liquid is raised to boiling point and maintained thereat for a period of about one hour. The nitro-benzol and nitric acid driven off during ebullition is collected through the condenser tube 3 and directed by the pipe 5 into the receiving vessel 6 and reserved for further use as will be explained later herein.

A jetof steam (preferably dry) is now blown through the liquid conveniently by a pipe 28 (or the spindle 29 ofthe heaters may be hollow to admit the steam) during which operation also the volatilized nitrobenzol is collected through the condenser tube 3 and carried off to the receiving vessel 6 just referred to. Preferably the steam is blown through the liquid at or about the same time that the temperature of the latter is raised as aforesaid but it may be intro duced at an earlier or later stage if desired.

The use of steam forms an important paiit of this invention seeing that it is one of the contributory features to the danger from the process. By introducing steam into the mass at that stage in the'nitration process when it is desirable that -further nitration should be prevented, the extreme oxidation of the phenolic bodies into oxalic acid and the like which will take place During the period of reaction the mixture unless the'strong nitrating agent is diluted, is obviated. The steam therefore constitutes a diluting or restraining agent and at the same time carries off the nitro-benzol and an mono-nitro-phenol which may be volatile at the temperature employed, thus facilitating the purification and final crystallization of the picric acid.

When practically all the nitro-benzolhas been removed from the mixture and collected in the manner described, the steam is shut off. Fresh benzol (about 60 parts) is then added to the mixing pan, and after the contents have been thoroughly mixed for about fifteen minutes the mixture is allowed to settle, whereupon the benzol portion containing crude picric acid is tapped off at 21 and run into the crystallizing pan 7. I

The crystallizing pan is then steam heated by the jacket 16 whereby the benzol is volatilized and by passing through the condensing coil 8 is distilled back through the pipe 9 into the mixing pan 1.

The contents of this pan 1 are again thoroughly mixed, allowed to settle, and the benzol again tapped off at 22 and run into the cry stallizing, pan 7. The crystallizing pan is then heated to drive off about half the benzol which is distilled by the condenser 8' and carried by the pipe 10 to the storage tank 11 and reserved for further use, and then the said pan .is waiter cooled by the jacket 16 to cause crystallization of the contents, The mother liquor is drained off from the crysta llizing pan by the connection 13 and collected in the. liquor tank 14 the said liquor containing some picric acid, orthomononitrophenol, nitro-benzol and benzol.

About-3O parts of fresh benzol are now added to the contents of the crystallizing pan 7 by means of the inlet 7, the pan is heated, to dissolve the contents after which it is cooled to cause crystallization. When crystallization has taken place the liquor is drained off at 13 and collected in the liquor tank 14.

Samples of crystals (which contain combined benzol) are now taken from the crystallizing pan, and the benzol is dissipated with heat of say a water-bath. The residue consisting of picric acid is tested for melting point, which, with two crystallizations as described, should be 122 C. sharp.

Upon the melting point being found correct the crystallizing pan is again heated by a gradually increasing temperature up to about 100 C., to drive off the last traces of the benzol, ,the remaining contents of the pan being purepicric acid. The crystallizing pan is fitted with an observation glass 30 which may be removed for sampling the crystals.

Y The remaining contents of the mixing pan '1 are now heated until-- all the nitric acid and moisture are driven off and collected by the condenser tube 3 into the receiving vessel 6; leaving practically dry mercury salt in the pan. It is preferable to carry out this evaporation at a low temperature by means of a vacuum.

When starting a fresh batch, a portion of the nitric acid charge is added to the mercury salt and warmed in the mixing pan 1 until solution is effected, then the remainder of the nitric acid is added and the process is continued as before, no further mercury being required, although it may have to be renewed from time to time on account of accumulating iron salts. v

The time occupied bythe complete process is approximately 24 hours although it may be less of course when one of the crystallizations is omitted.

The picric acid left in the mother liquor may, if desired,be recovered from this by prolonged crystallization and if the residual liquor is treated with a jet of dry steam, which removes the nitro-benzol and benzol, the orthomononitro-phenol will be left in a condition suitable fin dye manufacture.

This nitric acid and nitro-benzol (.Olllvttd in the receiving vessel 6 may be separated in any known manner and collected in tanks 31, 32 and the nitric acid may be revivified or concentrated and used again in this process.

The benzol distilled into the storage tank 11 may also be used again.

Therefore, in so far as the materials emtilling and collecting or returning to the mixing pan the benzol from the crystallizing pan 7, and separating from the remaining contents in the mixing pan the dry mercury salt, be recovered and used again the process may be said to be economical.

As the process is carried out in a closed apparatus and the temperature during the process has a natural tendency to fall all danger is eliminated, in addition to which the necessity for personal attention is considerably reduced.

Obviously it will depend upon the quantity orlevel of the solution in the mixing pan as to which of the outlets 21 22 or 23 is used for tapping off at each operation. A branch 3" on the condenser tube 3 may lead to a suitable acid tower so that any nitrous fumes given oil may be oxidized and returned to the mixing pan 1.

-Hitherto, therehas been attendant with the process of producing picric acid which consists in first sulfonating phenol and then treating this with sodium or potassium nitrate in such a manner that picric acid is formed together with considerable quantities of sodium or potassium sulfate or acidsulfate or mixture of same, great difficulty in extracting the picric acid; also considerable waste of same in the process of'washing as usually carried out. These disadvantages have been so pronounced as to retard somewhat the development of processes of making picric acid with, nitrates of the alkalis.

' By the use of benzol according to the present invention the aforesaid disadvantages are overcome. This is achieved by treating the mixture of picric acid and sulfate, or .the acid-sulfate of the alkalis, according to the process used, with benzol.

By treating the aforesaid mixture with benzol in a suitable a )paratus in the presence of mineral acid, such as sulfuric acid) and with or without added waterat a suitable temperature above the freezing point of benzol, the picric acid together with any organic byproducts passes into solution.

According to an example of the process, 100 parts of phenol may be heated with say 1000 parts of concentrated sulfuric acid for say two hours at a temperature of 170 this producing phenol-di'sulfonic acid.

To this 96 parts of dry powdered hile saltpcter are added and heated at 140 (7. pro ducing nitro-phcnol-di-sulfonic acid. This is diluted with 320 parts of water and heated to 8090 with 244 parts of (bile saltpeter, the temperature being allowed to reach 40 C., approximately 400 parts of benzol.

are added thereto and the solution of pie- 'ric acid in benzol is tapped off and run into the crystallization pan and then treatedin the manner previously mentioned, the benzol being driven offand condensed and returned to the mixing pan or collected in the storage tank leaving the picric acid in the pan 7.

If other organic bodies are present at this stage a suitable quantity of benzol is left in the picric acid in the crystallizing pan. This pan is cooled and the contents allowed to crystallize in the form of a loose compound of picric acid and benzol from which is subsequently drained the uncombined benzol together with such impurities as may be present. The picric acid may be recrystalized from further benzol if desired.

In the process just described, instead of the sodium nitrate the calculated quantity of potassium nitrate may be used.

The invention is-not to be confined to. the hereindnentioned quantities and details as these are given only as examples and may be varied if found necessary or desirable.

In the apparatus employed instead of tapping into solution off from' the mixing pan it may be separated by decantation or siphoning and the invention is not to be restricted to the. precise construction. and arran ement dation and driving off the nitro-benzol by means of steam substantially as and for the purpose herein described.

In testimony whereof I have signed my name to this specification in the presence of two subscribing Witnesses.

DAVID BAIRD MACDONALD. ,Witnesses R. W. C. TAYLOR,

GEORGE LESTER.

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