HU196817B - Process for producing dialkyl-pfosphites - Google Patents

Abstract

Dialkyl phosphites are prepd. from phosphorus-trichloride and the appropriate alcohol in the absence of solvent or hydrogen chloride acceptors by working in the first step of the process with an excess of 4-13 g. mole % phosphorus trichloride above the stoichiometric ratio, and in the second step with an alcohol excess of 70-200 g. mole.%. Hydrogen chloride and alkyl chloride are eliminated from the reaction mixt. by applying 300-600 mbar vacuum and 50-180 litre per g mole inert gas or air.

Description

The present invention relates to the preparation of dialkyl phosphites by reaction of phosphorus trichloride with alcohols.

The dialkyl litholites of formula (1)

RO H \ /

RO O (l)

- in which R, a linear or branched alkyl group of 1 to 4 carbon atoms, is increasingly used as an intermediate in the manufacture of pesticides, plasticizers and oil additives. Many methods are known for their preparation, but most of them have not been industrially implemented. We aim to develop a process which is more advantageous in industrial implementation, specific material and energy use than the methods known so far.

Most commonly, dialkyl phosphites are prepared by reaction of phosphorus trichloride with the corresponding alcohol.

PCI, + 3ROH -> / P / OR / j + 3HC1 - / RO / ₂ PHO + RCI + 2HC1

The reaction is exothermic, the reaction heat of about 10 kcal being absorbed partly by the heat capacity of the reaction partners and by the (latent) heat demand of their aggregation state changes, and partly by external or internal (using volatile solvents) cooling.

The reaction is known to be carried out under atmospheric or pressure conditions, optionally in the presence or absence of a solvent, at a temperature of 40-120 ° C. The reaction mixture is degassed under atmospheric or reduced pressure.

As the carbon number of the alcohol increases, the reactivity decreases slightly and, consequently, the lower alkyl halide volatility of the by-product results in the formation of higher carbon dialkyl phosphites at higher temperatures.

In addition to the above main reaction, the occurring side-reaction of dialkyl phosphite and by-product hydrogen chloride must always be taken into account:

/ RO / ₂ PHO + HCl - »RO / OH / PHO + RCI

Degradation can continue until phosphoric acid is formed:

/ RO / OH / PHO + HCl -> P / OH / ₃ + RCI

These side reactions are greatly reduced as the temperature decreases. The same trend can be observed as the carbon number of the alkyl group increases. As the result is a smaller or greater reduction in the yield of dialkyl phosphite, the key problem in all manufacturing processes is the rapid removal of the decomposition hydrogen chloride from the reaction mixture or system and / or the rapid cooling of the reaction mixture. This applies in particular to the production of dimethylphosphite, which is readily formed but at the same time quite degradable, and to a lesser extent diethylphosphite. Many, mostly patented, techniques are known to prevent or at least mitigate yield and product quality adverse reactions. One of the known solutions is disclosed in U.S. Patent Nos. 2,570,512, 2,582,817, 2,631,161, 2,862,948 to Romanian Patent Nos. 59,706, to U.S. Patent No. 128,755, and to U.S. Patent No. 182,471. method).

Thus, the reaction is carried out in the presence of an inert organic solvent having a boiling point near the reaction temperature. (For example, lower aliphatic hydrocarbons and their chlorinated derivatives, or aromatic hydrocarbons). Such a solvent, on the one hand, reduces the reaction as a diluent and, on the other hand, removes a significant part of the reaction heat by evaporation. At the same time, large amounts of vapors contribute to the rapid elimination of hydrogen chloride from the system, which is all the more feasible since the solubility of hydrogen chloride in these solvents is low. The reaction may be carried out in batch or continuous mode - in a batch reactor (GDR Patent No. 128,755 and Hungarian Patent No. 182,471).

The disadvantage of this method is that the large amount of gas (consisting of alkyl chloride and hydrogen chloride) leaving the system can cause significant solvent losses, and the reduction of losses can only be achieved by installing larger equipment and cooling capacity. A further disadvantage is that the product is obtained in the form of a relatively dilute solution. Not only is its solvent solubilization process energy-consuming, but it also causes further deterioration in yields. Consequently, the common disadvantage of solvent-based processes is high investment costs and energy requirements, and low capacity utilization.

Methods are also known (U.S. Patent No. 2,864,847, British Patent No. 853,982) which chemically remove the last traces of hydrogen chloride by administering ammonia or tertiary amines. In this case, the stoichiometric ratios are strictly observed! and removal of the resulting amine hydrochloride complicates industrial scale implementation.

In an interesting variant of this solution (Hungarian Patent No. 169,143), the by-product hydrogen chloride is reacted with a trialkyl-rosilyl to convert the latter compound to a dialkyl-phosphite. The process seems to be advantageous, but industrial implementation has not been achieved mainly for economic reasons. In order to avoid the disadvantages of solvent processes, several methods have been developed which, bypassing the solvent, produce the dialkyl phosphites by direct reaction of the reagents. (U.S. Pat. No. 2,582,817, Czechoslovakian Patent No. 148,569). The main problem here is the perfect mixing of the reagents, removal of the heat of reaction, rapid removal of hydrogen chloride and corrosive properties of the reaction mixture.

Problems in the field have been solved by developing different methods for introducing reagents. Special reactors have been used, reducing the occurrence of hydrogen chloride side reactions by reducing residence time in the reactor and by rapidly cooling the reaction mixture. The remaining hydrogen chloride in the reaction mixture,

196,817 utilize heat stripping to remove by-product alkyl halide and unreacted alcohol.

The disadvantages of these processes are the need to cool the reactor and the reaction mixture, the relatively high vacuum requirement of 10 30 mbar for stripping, and the need for significant cooling capacity to reduce material losses. In addition, it requires a relatively sophisticated technique to accurately maintain the reagent feed ratio, to separate atmospheric and vacuum spaces, and to control the closing fluid level. Further industrial scale implementation is further complicated by corrosion problems / Both solvent and solvent-free processes can be batch or continuous, while the advantages of the latter mode are obvious. In this case, the reagents are added continuously and simultaneously to the reactor tube reactor or to the cascade series tank reactor. A common feature of prior art processes is the use of an alcoholic excess of 2-20 gtnol (i.e. 1: 3.06-3.6 / mol) in relation to the stoichiometric ratio. In this case, the product naturally contains more or less unreacted alcohol, thus retaining more hydrochloric acid in its dissolved state, which inevitably leads to a greater decomposition of the dialkyl phosphite and thus to a deterioration of the yield.

In the case of excess phosphorus trichloride, the references cited therein (Ch. H. Campbell, DH. Chadwick, S. Kaufmann, Ind. Eng. Chem. 59, No. 11, 1871-74 (1957), V. Sauli, Chem. Prum 23/48). 554-556 (1973) states that the yields of dialkyl phosphite are rapidly decreasing and at the same time the formation of a poorly soluble, yellow flammable phosphorous compound is observed.

In our experience, the reaction is carried out in a reactor equipped with an atomiser having an adjustable orifice orifice which injects gas from the gas distribution chambers through an intermediate manifold provided with holes, wherein the gas is formed so that the gas entering the orifice , the liquid entering the atomizer in the direction of the gas stream is transformed into a fine mist in the reactor, where the gas also provides intensive mixing of the liquid peaks. Thus, setting an excess of 4-13 gmol% phosphorus trichloride, i.e. a molar ratio of PCI ₃ : ROH = 1: (2.6-2.9), will not lead to the formation of said unpleasant byproduct, and if unreacted phosphorus chloride In an in-line column reactor (Figure 1), an excess of alcohol is reacted, and the combined crude product is distilled to give dialkyl phosphites at a favorable yield which is superior to those known in the art.

This recognition is the basis of the process of the present invention, which involves the reaction of phosphorus trichloride with an aliphatic alcohol in two steps. In the first stage, 85-98% of the phosphorus trichloride feed is reacted in the intensive reactor 2 equipped with the atomizer 1, and in the second stage the reaction in the continuous column reactor 3 is completed with an excess of alcohol (70-200 gmol%) and finally the crude dialk purified by distillation.

Another important feature of the process of the present invention is the reduced pressure in the reactor 2

- 300-700 mbart - and a stream of nitrogen gas or air

50-140 liters / gmol dipalkylphosphite are used to facilitate removal of hydrogen chloride from the system. It also performs a liquid or atomizing function of nitrogen or air sucked into the nozzle slot. By varying the amount of nitrogen gas or air aspirated, the reactor and material flow temperature (temperature profile) can be controlled. The feed rate of the components and the amount of nitrogen or air in the nebulizer or purge are chosen such that the temperature in the nebulizer space is preferably 40-120 ° C, preferably 50-90 ° C in the collector, preferably 20-40 ° C. be. In addition, the beneficial cooling effect of desorption processes should be considered.

Thus, in order to demonstrate the advantages of the process of the present invention, the process of desorption of volatile by-products, in particular hydrogen chloride, which degrades the yield of dialkylphosphite, from the reaction medium must be investigated in more detail. The solubility equilibrium is determined by the chemical composition of the reaction mixture, the partial pressure of the hydrochloric acid in the gas phase in contact with it, and the temperature. The possibilities for changing the temperature are limited. This is determined, on the one hand, by the required and optimum reaction temperature and, on the other hand, by the increase in undesirable reactions. The solubility equilibrium can be more effectively influenced by changing the composition of the reaction mixture. It has been observed that the reaction mixture contains a small amount of unreacted phosphorus trichloride

- retains less hydrogen chloride under dissolved conditions. That is, if a slight excess of phosphorus trichloride is used in the addition of the reagents, a more soluble equilibrium equilibrium may be used for the removal of the reaction mixture. This embodiment of the process according to the invention is novel.

A favorable desorption equilibrium can only be utilized in practice if the desorption process occurs rapidly in time, i.e., if not only the thermodynamic but also the kinetic conditions of the process are assured. This condition is fulfilled in the process according to the invention by the atomization device 1 integrated in the reactor 2 to spray the reactants and / or the product into fine mist drops. The large contact surface thus formed is favorable both for the chemical reaction and for the transfer of dissolved hydrogen chloride across the phase boundary. Due to the intensive nitrogen gas or air purge and the vacuum, the surface hydrogen chloride concentration is practically zero, so that the driving force of the material is maximal at the given temperature. As a result, the apparatus and process provide particularly advantageous conditions for the desirable removal of hydrogen chloride, while avoiding the destruction of the mcllcrcrcc. This effect is exacerbated by the fact that the droplets of liquid leaving the atomizer 1 form a curtain on the wall of the reactor 2 and, due to condensation from the vapor phase to the liquid phase, there is further heat release. As a result of the condensation peak, the likelihood of HCl dissolution is also reduced.

196,817 δ

The vapors leaving the atomization reactor 2 are introduced into a continuous column reactor 3, where, in a one-way operation with continuously fed alcohol, the conversion of unreacted phosphorus trichloride in the first stage is complete. The excess alcohol absorbs the product discharged with the gases, thereby ensuring a reduction in delivery losses that would otherwise be achieved only with significant cold energy input. The column is provided with a jacket so that the most favorable temperature distribution within the reactor can be set by heat-drying. Thus, the main advantage of the process according to the invention over the methods known hitherto is that by choosing an unconventional route the use of a simple and easy-to-prepare apparatus, with a favorable energy input, results in a higher yield of dialkyl phosphite.

Accordingly, the present invention relates to a process for the preparation of dialkyl phosphites, e.g. for the preparation of dimethyl, diethyl, dipropyl, diisopropyl, dibutyl phosphates by direct reaction of phosphorus trichloride with the corresponding alcohol, with the exclusion of a solvent or hydrogen chloride acceptor. The reaction is carried out in the apparatus of Figure I in two steps such that in the first step, 4-13 gmol% of phosphorus trichloride relative to the stoichiometric ratio of reactants, and in the second step, 70-200 gmol% of excess phosphorus trichloride. we work with alcohol. The reaction mixture is stripped of hydrogen chloride and alkyl chloride at a vacuum of 300-600 mbar and 50-180 l / gmol, preferably 70-140 l / gmol of nitrogen gas or air, per phosphorus trichloride. According to the invention, the following procedures are employed for the preparation of dialkyl phosphites by reaction of phosphorus trichloride with the corresponding alcohol.

1, a precisely measured amount of phosphorus trichloride is injected into the reactor 2 with the atomizer 1 at a vacuum of 500 to 600 mbar at a flow rate of 10 to 100 gmol / h. (2.6-2.9) gmol of C 1-4 aliphatic alcohol and 50-60 liters / gmol of dried air (or nitrogen) (500-6000 l / h) for the reactants or the reaction mixture, based on phosphorus trichloride ). As a result of the effective atomization, the reagents are perfectly mixed and the reaction proceeds rapidly. The main product in the form of fine droplets is freed from the bulk of the hydrogen chloride content in the reactor outwardly and then merges into large droplets in the lower part of the reactor 2 due to cooling and flow rate reduction.

The amount of air or nitrogen aspirated here, at 100,000 to 5,000 l / ό, which corresponds to 10-50 liters per gmol of dialkyl phosphite, after bubbling through the reactor from the bottom up, that is, countercurrent with dialkyl phosphite, promotes hydrogen chloride and rapid cooling. This effect is complemented by the air or nitrogen drawn in by the atomiser 1, which flows in the same direction as the product stream. Together, these two gas streams provide the desired reaction temperature or reactor temperature profile. The reaction zone temperature T = 50 to 90 ° C, collected in the lower portion of the reactor product temperature T _z = 20-40 ° C;

The by-products of the reaction, the unreacted phosphorus chloride c1, the dialkyl phosphite discharged with the gas stream, and the combined gas stream exit at the upper outlet of reactor 2 and enter the continuous column 3 reactor where 4-70 gmol / h is fed at the top of the column. complete conversion of the phosphorus trichloride with the direct flow of alcohol and absorption of the dialkyl phosphite from the gas stream. The liquid mixture gradually cools down into the bed 5 as it flows down the reactor. The dialkyl phosphite formed in the atomiser 2 also flows through the condenser 6. From here, the liquid T ₃ = 15-35 ° C - through which the dry air or nitrogen is bubbled again through the 4 coolers at a rate of 10-50 l / g dialkyl phosphite (100 5000 l / h) to homogenize and bend the volatile components - preferably, it is sucked directly into a continuous distillation apparatus (possibly into a deep-frozen container of sufficient capacity).

The invention is illustrated by the following examples:

Example 1: Preparation of Dhnelil phosphite

5 gmol (687 g) of phosphorus trichloride were sprayed in a spray reactor at 600 mbar at a pressure of 750 l / h at a flow rate of 15 gmol / h, while 13.5 gmol (433 g) of methanol was simultaneously sprayed at the bottom of reactor 2 Dried air is introduced at a rate of 450 liters / hour (1501).

T _t = 54 'C, T ₂ = 23' C. A stream of gas containing unreacted phosphorus trichloride and captured dimethyl phosphite is fed to a continuous column reactor, where 3.66 gm (117 g) of methanol fed at the top of the column at a flow rate of 11 gmol / h is complete and complete. goes to 5 product collectors. Dimethylphosphite formed in the atomization reactor 2 also flows through the condenser 6. Dry air is aspirated at 300 L / hr (100 L) through a 5 hopper (T ₃ = 20 ° C) to remove and homogenize hydrochloric acid and methyl chloride. The aeration reaction mixture is distilled in a continuous distillation plant. The amount of pure dimethyl phosphite obtained was 471 g (4.28 gmol), which corresponds to a yield of 85.64% based on phosphorus trichloride.

Example 2: Preparation of diethyl phosphite

5 gmol (687 g) of phosphorus trichloride and 14 gmol (645 g) of ethanol were sprayed at 600 mbar at 600 lbar at a spray air rate of 800 l / h and phosphorus trichloride and at the bottom of reactor 2 at 300 l / h. (150 L) of air. T, = 66 'C, T ₂ = 28' C. At the same time, the gas stream containing unreacted phosphorus trichloride and the captured diethylphosphite is fed to a continuous column reactor 3 where the complete reaction proceeds at a flow rate of 8 gmol / h, 4 gmol (184 g) of alcohol at the top of the column. The reaction mixture is introduced into the product pool 5. Diethylphosphite formed in the 2 atomization reactor also flows here. Hydrochloric acid and ethyl chloride discharge and homo4

Ί

For 196,817 g / l, dry air is sucked through the product 5 at a rate of 500 liters / hour (250 L). (T ₃ = 24 ° C). After aeration, the product is subjected to continuous distillation. The yield of pure diethyl phosphite was 4.68 gmol (646 g), which corresponds to a yield of 93.5% based on phosphorus trichloride.

Example 3: Preparation of diisopropyl phosphite

5 gmol (687 g) of phosphorus trichloride and 13 gmol (78 g) of isopropyl alcohol were atomized in a spray reactor 2 at 600 mbar at a spray air rate of 800 l / h and phosphorus trichloride (15 gmol / h). at a rate of 75 l / h dry air is aspirated. T, = 72 'C, T ₂ = 32' C.

At the same time, the gas stream containing unreacted phosphorus trichloride and the captured diisopropylphosphite is fed to a continuously operating 3 column reactor where the top of the column is fed with 3.33 gmol (200 g) of isopropyl alcohol at a rate of the reaction mixture goes to the product manifold 5. The diisopropyl phosphite formed in the atomization reactor 2 also flows there. Dry air is sucked into the desiccator at a rate of 500 liters / hour (166 L) for de-hydrochloric acid and de-isopropyl chloride homogenization. (T ₃ = 27 ° C). The pelleted phosytol is subjected to continuous distillation. The amount of pure diisopropyl phosphite was 262 g (4.59 gmol), which corresponds to a yield of 91.8% based on phosphorus trichloride. a.

Example 4: Preparation of Dibutylphosphite

5 gmol (687 g) of phosphorus trichloride and 13 gmol (964 g) of butyl alcohol were sprayed at 500 lbar at 500 mbar at a spray rate of 600 l / h and nitrogen phosphorus at a rate of 400 liters / h. I) introducing dried nitrogen, T 1 = 73 ° C, T ₂ = 30 ° C. At the same time, the gas stream containing unreacted phosphorus trichloride and the captured dibutyl phosphite is introduced into a continuously operating column of 3 columns, where the top of the column is reacted with 4 gmol (296.5 g) of butanol in a complete stream. The reaction mixture is fed to the product manifold 5 and the dibutylphosphite from the atomizer 2 is removed. For the purpose of homogenization and desulphurisation, dry nitrogen is passed through the 5 manifolds (T ₃ = 25 ° C) at a rate of 400 L / h (133 L). The dibutyl phosphite thus obtained is subjected to continuous distillation. The amount of pure dibutyl phosphite was 896 g (4.62 gmol), corresponding to a yield of 92.3% based on phosphorus trichloride.

Claims (1)

A patent claim A process for the continuous preparation of (RO) ₂ P (O) H of formula (I) wherein R is a linear or branched C 1 -C 4 alkyl dialkyl phosphite from phosphorus trichloride and a C 1 -C 4 aliphatic alcohol, characterized in that the reaction is in a first stage into a reactor (2) equipped with an atomiser (1) at a pressure of 300-700 mbar, preferably 500-600 mbar, 50-601 / gmol phosphorus trichloride · hour with dried air or nitrogen, 10-100 gmol of phosphorus trichloride / hour at a rate of 1: (2.6-2.9) gmol of phosphorus trichloride and C 1-4 aliphatic alcohol at a rate of 10-50 l / gpiol of phosphorus per g trichloride · hourly dried air or nitrogen, whereby 85-98% of the phosphorus trichloride is reacted at 50-90 ° C, and in the second step, unreacted phosphorus trichloride and the gas flowed dialkyl phosphite is fed to the column reactor (3) connected to the reactor (I) provided with the atomizer (2), where it is simultaneously reacted with 70-200 gmol% of phosphorus trichloride to react with excess phosphorus trichloride. aliphatic alcohol is added and the product formed in the reactors (2) (3) is introduced into the product collection tank (5), into which the product is supplied with 10-50 l / g of phosphorus trichloride · hourly dried air or nitrogen to purify hydrogen chloride and alkyl chloride.