DD128755B1 - PROCESS FOR THE PREPARATION OF DIALKYL PHOSPHITES - Google Patents

Description

Field of application of the invention

The invention relates to a continuous process for the preparation of dialkyl phosphites from phosphorus trichloride and monohydric aliphatic alcohols having 2 to 8 carbon atoms. Dialkyl phosphites are important intermediates for the synthesis of phosphorus-containing plasticizers and pesticides.

Characteristic of the known technical solutions

Phosphorus trichloride is known to be very lively with aliphatic alcohols, according to the reaction equation

RO 0

PCl ₃ + 3 EOH- Ъ P + SCl + 2 HCl

RO H

Dialkyl phosphites are formed as main products.

To achieve high yields of the liberated during the reaction of hydrogen chloride must be removed as completely as possible before working up the reaction mixtures.

As is known, this can be done by introducing carbon dioxide or dry air during or after the reaction.

However, these methods are limited and fail in some cases, such. For example, di-n-butyl phosphite. Another disadvantage is that most of the alkyl halide formed and a part of the reactants with the purge gas lost or can be recovered only with very high technical effort.

Another way to remove the hydrogen chloride is to carry out the reaction in the presence of such solvents in which hydrogen chloride dissolves poorly.

However, these methods have the disadvantage that the solvent is enriched in the progress of the reaction of alkyl halide. Alkyl halides dissolve the hydrogen chloride to a much greater extent, which delays the removal of the hydrogen chloride. Therefore, high amounts of solvent or long reaction times are required; the space-time yield thereby deteriorates.

Furthermore, it is known to carry out the reaction in the presence of ammonia or of tertiary bases; In these cases, the separation of the resulting hydrochlorides on an industrial scale presents considerable difficulties.

Methods have also become known which replace the third mole of alcohol with water required for alkyl halide formation. As expected, it shows that this promotes the formation of by-products, thus reducing the yield of dialkyl phosphite and deteriorating its purity.

The substitution of the third mole of alcohol by the cheaper methanol brings no advantages. In this case, the reaction products contain, in addition to symmetrical dialkyl phosphites, dimethyl phosphite and methyl alkyl phosphite. Such products are generally not usable without further purification.

Furthermore, a continuous process for the preparation of dialkyl phosphites is known which operates without solvent and without cooling. The reaction is carried out in a small reactor and the liberated hydrogen chloride is removed under reduced pressure. The technical realization of this method is associated with considerable difficulties.

The necessary completely homogeneous mixing of the reactants requires a specially designed mixing nozzle whose technical dimensioning is difficult. The distilling off of the hydrogen chloride in vacuo involves great corrosion problems, and the condensation of the entrained with the hydrogen chloride gas stream alkyl halides requires considerable technical effort.

Similar difficulties occur when this process is carried out in the presence of monochloromethane as a carrier gas. Further, methods are known which perform the reaction of phosphorus trichloride and alcohols under reduced pressure in a reaction column in the gas phase. These methods require considerable expenditure on equipment and place high demands on the corrosion resistance of the system components.

Another known process, which likewise requires no solvent during the reaction, brings phosphorus trichloride with chloro-alcohol-saturated alcohols л an adiabatically operated зп circulating apparatus to the reaction. The work-up of the reaction products requires very high technical effort, since it requires a stripping column operated with an inert solvent, a plurality of separators and absorbers and is bound to certain conditions that must meet the inert solvent. The process also fails in the preparation of such dialkyl phosphites in which liquid alkyl chlorides are formed as by-products.

Object of the invention

The aim of the invention is a simple, industrially utilizable continuous process for the preparation of dialkyl phosphites by reacting stoichiometric amounts of PCI ₃ and monohydric aiiphatic alcohols having 2 to 8 carbon atoms in the presence of an inert solvent having a boiling point in the range of 30 ⁰ C to 80 ° C to develop. Explanation of the essence of the invention

This object is achieved in that PCI ₃ and alcohol in the first reactor and solvent in one of the last reactors of a multi-stage, preferably 4-stage reactor cascade are fed to the reaction mixtures kept in all reactors boiling and the solvent vapors after condensation in the respective

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upstream reactor, in the case of the I.Reaktors in this self, be recycled.

As the inert solvent dichloromethane, trichloromethane, carbon tetrachloride, n-pentane or hydrocarbon fractions of boiling ranges can be used from 30 to 6O ⁰ C.

In the reaction of phosphorus chloride can be used as monohydric aliphatic alcohols, for example, ethanol, n-propanol, i-propanol, n-butanol, i-butanol, i-amyl alcohol, 2-ethylbutanol or 2-ethylhexanol. In the first reactor of the reactor cascade phosphorus trichloride and monohydric aliphatic alcohol in the stoichiometric molar ratio (1: 3) are continuously metered below level, with care being taken by a stirrer or the vigorously boiling mixture itself for good mixing. The solvent used as an entraining agent for hydrogen chloride is fed into a rear reactor of the cascade. It passes through these in the opposite direction, that is, the vapors of a reactor are cooled and the condensate introduced into the respective upstream reactor. The condensed vapors of the first reactor are returned to themselves. The reaction mixture passes in the usual way via the overflows of the reactors in the respective downstream reactor. From the last reactor, the mixture of dialkyl phosphite, alkyl halide and solvent runs off and can be worked up by distillation in a known manner. The uncondensed portion of the vapors, which consists predominantly of hydrogen chloride, is removed from the reaction system. It can be worked up in a known manner to aqueous hydrochloric acid, wherein most of the remaining alkyl halides and the solvent are separated and the solvent can be recycled to the process. The inventive embodiment of the process makes it possible to produce dialkyl phosphites in almost theoretical yield in such good purity that their purification by distillation overhead can be omitted for most uses. By the opposite direction of the inert solvent used as HCI entraining agent succeeds, side reactions of the hydrogen chloride with dialkyl phosphite, which in discontinuous process control or recycling of the condensate in the same reactor after Reaktionsgieichung

RO 0 EO 0

p '+ HCl> P ^ + RCl

^ ⁴ H HO ^ H

Reduce product quality and yield, significantly reduce it. For the same reason, the solvent requirement is lowered and the space-time yield is increased compared to the abovementioned process variants.

The reaction mixture contains after leaving the reactor system virtually no more hydrogen chloride. The subsequent work-up by distillation therefore makes no high demands on the corrosion resistance of the apparatus.

The design of the reactor system also makes it possible to facilitate subsequent separation of the alkyl chloride without substantial equipment changes by adaptation of the solvent.

embodiments Example 1:

Di-n-butyl

C ₄ H ₉ O ⁴ H

In the first reactor of a cascade, which consists of four side by side vertically offset enameled stirring apparatus with heating mantle, hourly continuously below level 17.51 phosphorus trichloride and 551 n-butanol are dosed; in the third reactor 501 dichloromethane are fed simultaneously. The reaction mixture is kept vigorously boiling by heating over the jacket of the reactors.

The vapors pass through coolers powered by cooling water into an absorption apparatus for hydrogen chloride. The condensed from the vapors fraction containing dichloromethane and a portion of the butyl chloride formed is separated and fed via a dip tube in the respective upstream reactor. The condensate from the vapors of the first reactor is fed back to this via a dip tube. The reaction mixture passes through the apparatus via overflows. From the fourth reactor run during this period from 89.21 reaction mixture. From 500 ml of this mixture, the solvent is removed by distillation. This gives 225 g of di-n-butyl phosphite in a purity of 94.7%; the yield is 97.8% of theory.

Example 2:

Di-iso-butyl phosphite

Uli - UMpU

CH ^ / ^ TT

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In the first reactor of a cascade, consisting of four successively connected vertically displaced glass flask, hourly continuously below level 240ml phosphorus trichloride and 764ml iso-butanol are added. In the third reactor at the same time 700ml of n-pentane are fed. The reaction mixture is kept vigorously with heating baths. The vapors pass through a cooler in an absorption system for hydrogen chloride. The condensed from the vapors fraction containing n-pentane and a portion of iso-butyl chloride formed is separated and introduced via dipping in the respective upstream reactor. The condensate of the vapors of the first reactor is fed back to this directly by dipping. The reaction mixture passes through the apparatus via overflows. After distilling off the reaction mixture, di-iso-butyl phosphite is obtained in 98.4% yield with a purity of 95.7%.

Example 3:

Diethyl phosphite C ₂ H ₅ O о ^P 4

C ₂ H ₅ O ^ H Analogously to Example 2 per hour 288 ml of PCI ₃ and 577 ml of ethanol in the presence of 840 ml of a technical hydrocarbon fraction of the boiling range 30 to 6O ⁰ C implemented.

After work-up, diethyl phosphite is obtained in 95.3% yield with a purity of 92.1%.

Example 4:

Di-n-propyl phosphite

CJi ₇ O 0

^{3 7} \ _p ^

C ₃ H ₇ O ^ ⁴ H Analogously to Example 2, 263 ml of PCI ₃ and 677 ml of n-propanol are reacted every hour in the presence of 765 ml of n-pentane. After work-up, di-n-propyl phosphite is obtained in 98.0% yield with a purity of 94.8%.

Example 5:

Di-iso-propyl phosphite

As in Example 2, 260 ml of PCI ₃ and 683 ml of isopropanol are reacted in the presence of 760 ml of dichloromethane per hour. After workup, di-iso-propyl phosphite is obtained in a yield of 92.1% with 91.7% purity.

Example 6:

Di-iso-amylphosphit

CH-CH ₂ -CH ₂ O

CH ₃ у \ _н

⁴⁴ CH-CH ₂ -CH ₂ O

As in Example 2, 222 ml of PCI ₃ and 834 ml of isoamyl alcohol are reacted in the presence of 650 ml of dichloromethane per hour.

After work-up, di-iso-amyl phosphite is obtained in 97.3% yield with a purity of 94.3%.

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Example 7:

Di-2-athylbutyl phosphite

C ₃ H ₅ --CH - CH ₂ O

C ₂ H ₅

O ₃ H ₅ -OH-CH ₂ OO ₂ H ₅

Analogously to Example 2, 182 ml of PCI3 and 995 ml of technical 2-ethylbutanol (purity 77%) are reacted every hour in the presence of 530 ml of chloroform.

After workup, di-2-ethylbutyl phosphite is obtained in 96.9% yield with a purity of 77.1%.

Example 8:

Di-2-athylhexyl phosphite

с, .н _л - си -

₄ H ₉ - c

CpH, P ^ f

^25/4 H

C ₄ H ₉ --CH - CH ₂ O

C ₂ H ₅

As in Example 2, 183 ml of PCI ₃ and 988 ml of 2-ethylhexanol are reacted every hour in the presence of 535 ml of carbon tetrachloride.

After work-up, di-2-ethylhexylphosphite is obtained in 95.2% yield with a purity of 93.4%.

Example 9: (Comparative Example)

Batch production of di-n-butyl phosphite

In a provided with stirrer, thermometer, dropping funnel and Intensivruckflußkuhler 1-liter multi-necked flask 3 moles of n-butanol are placed in 250 ml of methylene chloride. With stirring and vigorous reflux, 1 ml of PCI _{3 is} added dropwise to the mixture prepared within 30 minutes. The flask contents are then heated for 4.5 hours while stirring and refluxing. After completion of the reaction, methylene chloride and the n-butyl chloride formed in the reaction are distilled off under reduced pressure.

Content of di-n-butyl phosphite in the crude product after distillation: 84%.

Yield of di-n-butyiphosphite bez. on PCI ₃ : 85%.

Claims (1)

-1- 196 Invention claim: A process for the continuous production of dialkyl phosphite by reacting stoichiometric amounts of PCI ₃ and monohydric aliphatic alcohols having 2 to 8 carbon atoms in the presence of an inert solvent having a boiling point in the range of 30 ° C to 80 ° C, characterized in that PCI ₃ and alcohol are fed into the first reactor and solvent in one of the last reactors of a multi-stage, preferably four-stage reactor cascade, wherein the reaction mixtures in all reactors kept boiling and the solvent vapors after condensation in the respective upstream reactor, in the case of the first reactor in these themselves , to be led back.