DE2713277A1 - Pure hexa:methyl-phosphoro-tri:amide prodn. - by alkali treatment of crude prod. then fractional distn., used to remove acetylene from gases - Google Patents

Abstract

Prodn. of pure (>99.5%) hexamethylphosphorotriamide (I) comprises first reacting POCl3 and HN (CH3)2 in an organic solvent to give crude (I), removing salts formed as by-prods. then evaporating off the solvent. The crude (I)'s then contacted for 1-5 hr. at 60-80 degrees, esp. 110-160 degrees C, with 0.2-6, pref. 0.4-2.5 wt.% (on crude (I)) of alkali hydroxide as a >=20% aq. soln. The treated mixt. is then fractionally distilled under reduced pressure. The crude (I) may be distilled (esp. continuously) and pref. only the residue is subjected to alkali treatment. Pure (I) is used as an absorbant for removing acetylene from reaction gas streams. Less alkali hydroxide is needed compared with known processes so there is less pollution of waste water streams. Yields of pure (I) in the fractionation are improved e.g. 97.6% c.f. 91.2% calculated on cruce (I).

Description

Method of obtaining raing

Phosphoric acid tris (dimethylamide ns is known to be used in the manufacture of phosphoric acid tris (dimethylamide), (hereinafter referred to as Tris), from phosphorus oxychloride and dimethylamine in organic solvents as a by-product of dimethylammonium chloride to decompose by adding aqueous alkali metal hydroxide solutions, so as to separate the same to graze, which due to its fine-grained, voluminous nature, els also its low but significant solubility in organic solvents Causes difficulties. When phosphorus oxychloride with little more than 3 moles of dimethylamine is unset, highly concentrated alkali hydroxide solutions are required for this, otherwise the reaction only takes place up to the stage of phosphoric acid bis (dimethylamide-9 chloride leads (see. "Methods of organic chemistry", Hauben-Weyl, Vol.

Edition, 1964, page 467 and U.S. Patent 2,752,392).

The use of concentrated alkali, however, favors the formation of by-products, such as pyrophosphoric acid tetrakis (dimethylamide) or the corresponding Derivative of triphosphoric acid, which due to its toxicity from the aqueous phase must be removed by subsequent acid hydrolysis. When phosphorus oxychloride on the other hand, is reacted with at least 6 .cD dimetholamine, can be mixed with dilute Alkali hydroxide solutions can be worked, but there are extraordinarily large amounts of alkali hydroxide for J. R @ extraction it requires imins and danit red aqueous solution, so that an extractor (le- remaining in the aqueous phase large quantities of up products (see US Pat. No. 3,084,190).

After the separation of salt-like secondary products and solvents the raw tris obtained must undergo fine purification by fractionation under reduced conditions Subjected to pressure to earth. It was found, however, that when performing this Fine cleaning on the technical scale with considerable losses in yield to be expected which is 10 to 15%, based on the raw tris used for fractionation can. This is presumably due to impurities in the crude product, which have not been removed by the previously known measures and the Fraction temperature breakdown of Tris with elimination of dimethylamine catalyze, which results in the undesired formation of residues.

It is also known that pure Tris when used as an absorbent for the removal of acetylene from flowing reaction gases For a longer period of time, i.e. several days, temperatures in the range from around 1100 to 2000C is subject to thermal decomposition.

To avoid the deposits and blockages caused by this In acetylene recovery plants, therefore, according to US Pat. No. 3,002,586, basic Compounds such as oxides, hydroxides and basic salts of alkali and alkaline earth metals or aluminum as well as warm solutions thereof are used as inhibitors, which are expedient in a fixed bed between the acetylene distillation column and the storage tank from which Tris is pumped into the absorber, are arranged to have a sufficient Contacting us of Tris to ensure with the inhibitor.

This Estentschrift, the view with the prevention of thermal Decomposition tendency of pure Tris when used as acetylene absorbent in the Concerning gas flow, stones could meanwhile be removed for the invention The problem to be solved is to provide a method for the treatment of raw tris for use, with the help of which it is possible, by subsequent fractional distillation, under Highly pure Tris under reduced pressure, i.e. with a degree of purity of over 99.5 % to gain practically without residue formation, which results in improved exploitation, based on the raw tris used.

The method according to the invention for the recovery of Tris with a degree of purity of over 99.5% from raw tris, which is obtained by reacting phosphorus oxychloride and dimethylamine has been prepared in organic solvents by treatment with aqueous Alkali hydroxide and subsequent fractional distillation under reduced Druclr, is marked by the fact that the raw tris after the separation of the salt-like By-products and after the solvent has been distilled off, but before fractionation with 0.2 to 6.0, ó alkali hydroxide, based on the weight of the raw tris used, in the form of an at least 20% aqueous solution at temperatures from 600 to 1800C is brought into contact for 1 to 5 hours.

It is more critical in carrying out the method of the invention Meaning that the contact with the aqueous alkali hydroxide solution only after the removal of the salt-like by-products, including in particular dimethylammonium chloride is to be understood and is carried out after the solvent has been distilled off, to make sure that the unwanted by-products don't get through in Use the organic solvent to remove the influence of the alkali hydroxide. It could be proven that in the treatment according to the invention after E @ eration of the water contained in the lye by Desti. ation, a voluminous Solid forms that dissolve in water or water-containing Tris, not chlorine contains and reacts only slightly alkaline in aqueous solution. It is therefore assumed that this solid is formed from a by-product under the action of the alkali metal hydroxide in Rohtris forms, the two previously known methods of partial decomposition of Tris is involved in fractionation with residue formation.

The alkali hydroxide is advantageously in a range of 0.4 to 2.5 %, based on the weight of the Rohrtris, used, with 20% to saturated aqueous solutions. have proven. Because they are more readily available, they are more than alkali hydroxides Sodium hydroxide and potassium hydroxide are preferred. Contacting is preferred made at temperatures from 1100 to 1600C, whereby by mechanical movement good mixing in the reaction vessel can be ensured. The one for making contact The time required depends on the amount of Pohtris used and the amount available standing Xeaktionsbehältern. In the case of approaches on the 10,000 kg scale, Contact times of 1.5 to 2 hours have proven particularly useful.

However, it is not absolutely necessary to use the entire amount of raw tris to treat with the aqueous alkali hydroxide solution.

According to a further embodiment of the method according to the invention the raw tris can also first be subjected to a gentle distillation and only that Residue with the aqueous Brought into contact with alkali hydroxide solution will. With gentle distillation, a simple distillation is possible without Understand fractionation with a short dwell time in the heated part of the apparatus, as in a continuously operated circulation evaporator or a so-called short-path distillation in a thin film or falling film evaporator.

The resulting distillation residue or the bottom drain is then treated with permanent alkali hydroxide under the specified conditions subjected.

According to both embodiments of the method according to the invention can the raw tris directly after contact with the aqueous alkali metal hydroxide solution subjected to fractional distillation without separating the above Solid, since it does not interfere with the fractionation, does not cause corrosion and remains in the residue as a fluffy cake. However, the solid can also precipitated and separated by distilling off the water prior to fractionation will. It falls in a voluminous, poorly sedimenting form and exchanges large ones Quantities before. The actual amount of solids is generally only about 1 to 2%, based on the weight of the amount of raw tris. He can take the usual measures, such as filtration or centrifugation.

The inventive method for the production of Reintris in technical scale is characterized by its economic efficiency and environmental friendliness, since this considerably smaller amounts of aqueous alkali metal hydroxide than in the previously known methods are required. whereby in particular a waste water pollution is avoided. In addition, there are better yields of pure tris in the fractionation achieved, which adversely affects b @ through undesirable residue formation became.

Example 10,000 raw tris, resulting from a L ^ slm ,. in chloroform The solvent is distilled off at normal pressure and the amine salt is suctioned off were stirred with 75 kg of 20% sodium hydroxide solution at 140 ° C. for 2 hours and then fractionated at 95 ° C / 5 mm Hg. The distillation lasted a whole 20 hours, during which the bubble temperature was finally reached at 1200C. As the main fraction 8,460 kg of Tris with a purity of 99.7 ° C. were obtained and 165 kg of a solid one porous, water-soluble residue. The tris contained in the flow, the water and contained solvent residues, was completely recovered in further distillations. The yield of pure tris, based on the raw tris used, was 97.6%.

Comparative example: The procedure was as in Example 1, the alkali treatment did not take place, however.

After the forerun, 8.v20 kg of pure tris (99.7%) were obtained and 730 kg of black tar as residue, which solidified asphalt-like on cooling and contained practically no tris. The yield of pure tris, based on the amount used Raw tris, was 91.2%.

Example 2 10,000 kg of raw tris obtained from solution in toluene after centrifugation of the amine salt and distilling off the solvent have been obtained stirred with 270 kg of about 50% sodium hydroxide solution for 1.5 hours at 1600C, with through Applying a vacuum, water and solvent residues were largely removed. the The resulting thin suspension was clarified using the amine salt centrifuge and then at ei - pressure to distilled from 5 mm Hg, the bubble temperature Did not exceed 1340C. There were 840 kg of 98.5% forerun, 8,180 kg of 99.9% Main fraction and 750 kg of Rücl stood, the one carried out on a laboratory scale Trial distillation still consisted of up to 88 4 Tris.

The plague was a thick, water-soluble oil. So it was a total of 9,660 kg of Tris obtained, corresponding to a yield of 96.6%, based on on inserted raw tris.

Example 3 Crude tris, obtained from POCl3 and dimethylamine in toluene Centrifuging off the amine salt and distilling off the toluene has been obtained, was in a continuous circulation evaporator at 1200C bottom temperature and one Vacuum of 15 mm Hg without a column distilled so that 85% of the amount used were obtained as a distillate. The proportion that is not exaggerated was 10% by weight a 25% sodium hydroxide solution for 4 hours at 130.degree. C., finally by applying Underpressure the water was largely removed.

The mixture was then centrifuged. The solid became processed together with'den amine salt from the Rohtris production, from the amine was recovered by alkali treatment. The filtrate and that from the continuous Distillate originating from distillation were together discontinuously at 95 ° C mm Hg fractionated, 1.2% by weight of the deposit being obtained as an oily residue. Several fractionations can be carried out one after the other, without each to remove the residue. The yield of Tris after fractionation was 97.2% of the amount of raw tris introduced into the continuous distillation.

88% of this was obtained as pure tris, 99.8%, the remainder as 98.5 % lead.

Claims (5)

1 a t e n t a n s p r i c n c 1. Process for the production of phosphoric acid tris (dimethylamide) with a degree of purity of more than 99.5% from the pipe product, which is processed by made of phosphoro-ychrorid and dimethylamine in organic solvents has been, by treatment with aqueous alkali hydroxide and subsequent fractionation Distillation under reduced pressure t, dcffi the, crude product after the separation of the salt-like by-products and after distilling off the solvent, but before fractionation with 0.2 to 6.0% alkali hydroxide, based on the weight of the pipe product used, in form an at least 20% aqueous solution at temperatures of 600 to 180 0C is brought into contact for 1 to 5 hours. 2. The method according to claim 1, d a d u r c h g e k e n n -z e i c Not that the crude product is subjected to a gentle distillation and the residue thereof is brought into contact with the aqueous alkali hydroxide solution. 3. The method according to claim 2, d a d u r c h g e k e n n -z e i c Note that the crude product is subjected to continuous distillation. 4. Before @ according to claim 1 to, d a d u r c h g e -n z e i c h n e t that 0.4 to 2.5% of the alkali, based on the weight of the act used, be used. 5. The method according to claim 1 to 4, d a d u r c h g c -g e k e n n notices that the alkali hydroxide treatment is carried out at a temperature of 110 ° to 160 ° C is made.