FR2649696A1 - PROCESS FOR THE PREPARATION OF PENTACHLOROPHENOL - Google Patents

Abstract

The present invention relates to a process for preparing pentachlorophenol by chlorinating other chlorophenols, in particular dichlorophenols and trichlorophenols. More specifically, the present invention relates to a process for chlorinating with gaseous chlorine, dichlorophenols and / or trichlorophenols, optionally mixed with monochlorophenols, in pentachlorophenol, characterized in that the reaction is carried out: - in the presence of a quantity effective halide of zirconium, hafnium, tellurium, antimony, nobium or aluminum or one of their precursors, until approximately the tetrachlorophenol stage is reached, then in adding an effective amount of aluminum halide to obtain pentachlorophenol. Pentachlorophenol is a compound used as a fungicide and wood preservative.

Description

PROCESS FOR THE PREPARATION OF PENTACHLOROPHENOL

  The present invention relates to a process for preparing pentachlorophenol by chlorinating other chlorophenols, especially

  dichlorophenols and trichlorophenols.

  More precisely, the process of the invention makes it possible to prepare pentachlorophenol of purity that is still improved compared to current processes. Pentachlorophenol is a compound used as a fungicide and

wood preservative.

  The technical pentachlorophenol appeared, twenty years ago, in the appearance of a solid of very dark color,

  containing tarry impurities.

  Overall there are 2 essential routes for the preparation of pentachlorophenol. A first type of process consists in chlorinating benzene to hexachlorobenzene and then hydrolyzing one of the C-Cl bonds in

  C-OH to form pentachlorophenol.

  A second type of process involves chlorinating the phenol.

  In general, processes involving the hydrolysis of hexachlorobenzene in alkaline medium and at high temperature, lead to the formation of more polychlorinated dibenzo-p-dioxins as

  by-products, as chlorination processes of phenol.

  It has been discovered for some years that polychlorinated dibenzo-p-dioxins have toxic properties, at varying levels, depending on the number of chlorine atoms they

  include and position these chlorine atoms.

  Although the polychlorinated dibenzo-p-dioxins that are likely to be formed in phenol chlorination processes are not those that are recognized as very toxic in animals, various means have been sought to eliminate these by-products as much as possible.

  or to prevent as much as possible their formation.

  Thus, it has been proposed in US Pat. No. 4,016,047 to eliminate polychlorinated dibenzo-p-dioxins up to less than 25 parts per million (0.0025% by weight) by adding impure pentachlorophenol to phenolic compound or an organic phosphite,

  then distilling said pentachlorophenol.

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  This document indicates that the levels of polychlorinated

  benzo-p-dioxins impure pentachlorophenol are of the order of 0.2%.

  These contents are very high and, even if separated from pentachlorophenol, polychlorinated dibenzo-p-dioxins nevertheless pose the problem of their

os05 destruction.

  Thus, it has been sought to limit as much as possible the amount of polychlorinated dibenzo-p-dioxins which are formed during the chlorination of chlorophenols to pentachlorophenol, so as to obtain polychlorinated dibenzo-p-dioxin levels which are much lower than

  is generally considered acceptable.

  Thus the industrial process that the applicant company operates allows to obtain a pentachlorophenol having the angle

  polychlorinated dibenzo-p-dioxins excellent quality.

  However, in pursuing its research effort in the field of chlorophenols, the plaintiff company has found a new process for the chlorophenol chlorination which leads to a

  pentachlorophenol containing even less polychlorinated dibenzoparan

  dioxins. More specifically, the present invention relates to a chlorination process with gaseous chlorine, dichlorophenols and / or trichlorophenols, optionally mixed with monochlorophenols, pentachlorophenol, characterized in that the reaction is conducted - in the presence of an effective amount a halide of zirconium, hafnium, tellurium, antimony, nobium or aluminum or one of their precursors, until the tetrachlorophenol stage is reached, and then adding an effective amount of aluminum halide or one of the precursors to obtain pentachlorophenol. The halides which can serve as catalysts for the first part of the chlorination are chlorides, bromides, iodides and fluorides of zirconium, hafnium, tellurium, antimony,

nobium and aluminum.

  The aluminum halide added in the second part of the chlorination is aluminum chloride, aluminum bromide, iodide 3-

  of aluminum and aluminum fluoride.

  Of these halides, chlorides are preferred.

  It is also possible to use precursors of these chlorides, that is to say generally the metals themselves, or some of their derivatives, such as oxides, which are transformed at least once.

  partially corresponding chlorides in the reaction medium.

  In the present text, when it comes to the halides of the aforementioned metals, this will also include the chlorides formed

  in-situ from their precursors.

  The preferred variant of the present process consists in carrying out the first part of the chlorination in the presence of zirconium chloride, hafnium chloride, tellurium chloride, antimony chloride, nobium chloride or aluminum chloride. then to introduce aluminum chloride for the second part of the

  chlorination leading to pentachlorophenol.

  As previously indicated, the first part of the chlorination leads the chlorophenol (s) involved at approximately

2,3,4,6-tetrachloro phenol.

  This means that a majority of the

  engaged chlorophenols is at this stage tetrachlorophenol.

  Generally the aluminum halide necessary for the second part of the chlorination will be introduced when at least 60% and preferably at

  less than 70% of the chlorophenols will be converted to tetrachlorophenol.

  The dichlorophenols and trichlorophenols, which represent the bulk of the phenolic compounds used in the process of the invention, are more particularly 2,4-dichlorophenol,

  2,6-dichlorophenol and 2,4,6-trichlorophenol.

  Most often the process will therefore be applied to 2,4-dichlorophenol, 2,6-dichlorophenol, 2,4,6-trichlorophenol and their

mixtures.

  It is very interesting to use the industrial mixtures, obtained from the chlorination of phenol or monochlorophenols and consisting essentially of 2,4,6-trichlorophenol, 2,4-dichlorophenol and 2,6-dichlorophenol, and that small amounts of 2-chlorophenol,

  4-chlorophenol and 2,3,4,6-tetrachlorophenol.

  In fact, these industrial mixtures are very suitable in the context of the present process and are much more economical than the

  pure dichlorophenols or trichlorophenols.

  Chlorination of chlorophenols defined above is carried out

  without solvent, that is to say in the molten state.

  The first phase of the chlorination is carried out at a temperature between the melting point of the chlorophenol (s)

  implemented, that is to say about 70 to 80 C, and about 100 0C.

  The second phase of the chlorination is carried out at a temperature between the melting point of the reaction mixture at

  the end of the first phase and 180 C approximately.

  As the chlorination progresses, the temperature must be high to maintain the reaction mixture at

the liquid state.

  Preferably, the temperature of the reaction mixture at each instant of the chlorination will be that which makes it possible to maintain the mixture at

  the liquid state while being the lowest possible.

  The quantity of zirconium, hafnium, tellurium, antimony, nobium or aluminum halide used for the first phase of the

chlorination can vary widely.

  Generally, from 0.01% to 10% by weight of halide of these metals relative to the weight of the chlorophenol (s) employed will be used. Preferably this weight ratio halide

  metal / chlorophenols will be from 0.1% to 5% by weight.

  The amount of aluminum halide used for the second phase of the chlorination can also vary within wide limits. Generally, from 0.05% to 10% by weight will be used

  of aluminum halide relative to the weight of the chlorophenols employed.

  Preferably the weight ratio of aluminum halide / chlorophenols

will be from 0.1% to 5% by weight.

  The amount of chlorine used is essentially a function of the chlorophenol (s) involved, as well as the desired degree of conversion. One of the advantages of implementing the process of the invention lies in the excellent rate of fixation of the chlorine by

compared to committed chlorine.

  The quantity of total chlorine introduced will therefore generally be equal to or greater than the stoichiometric quantity required for

  transformation of chlorophenols or chlorophenols into pentachlorophenol.

  The excess of chlorine committed to obtain a total or almost total conversion of chlorophenols to pentachlorophenol will be less important than in the processes where all the catalyst is used

at the beginning of the chlorination.

  In practice, it will be convenient to determine the end of the first phase of chlorination by measuring the amount of chlorine introduced. When this amount is equal to about 1 to 1.5 times the theoretical amount to convert the chlorophenol (s) to tetrachlorophenol, the halide may be considered

  of aluminum for the second phase of chlorination.

  Most often, although it is not imperative, the chlorine is introduced by bubbling into the reaction medium and the part that may not react immediately emerges from the apparatus o

the reaction is carried out.

  The pressure in the reactor is therefore usually equal or

  slightly above atmospheric pressure.

  Chlorine can be used alone or diluted with an inert gas, such as nitrogen for example. The presence of an inert gas makes it possible, if necessary, to increase the gas flow without increasing

  correspondingly the amount of chlorine introduced in a given time.

  Chlorine can also be formed in situ from hydrochloric acid by the addition of an oxidizing compound such as

hydrogen peroxide for example.

  The pentachlorophenol obtained can be optionally purified by any known method, for example by treatment in solution with

using carbon black.

  The following examples illustrate the invention.

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EXAMPLES 1 & 5

  In a 150 cm3 glass reactor comprising a mechanical stirrer and counter-blades, a thermometric probe, a chlorine inlet tube, immersed in the reaction medium, a condenser connected to a washing column and a flask containing a aqueous solution of sodium hydroxide, 49.4 g of 2,4,6-trichlorophenol (0.25 mol) are charged.

  a first catalyst (indicated in the attached table).

  The mixture is heated to 80.degree. C. and 0.35 moles are then introduced with stirring.

  chlorine with a flow rate of 5 liters / hour.

  After purging with nitrogen, 0.89 g (1.8% by weight relative to the 2,4,6-trichlorophenol employed) of aluminum chloride is introduced, and the chlorination is continued at 80 ° C. is necessary to increase

  gradually the temperature of the reaction mixture (up to 170 -

  180oc) to keep it in the liquid state.

  The final reaction mixture is chromatographically deposition

  high pressure liquid (HPLC) after purging the unit with nitrogen.

  The polychlorinated dibenzoparadioxins are assayed by HPLC or GPC (gas phase chromatography) in the final reaction mixture: the

  result is expressed in hexachlorodibenzoparadioxins (HCDD).

  The table below gives the various indications concerning the catalysts used, the final temperature of the reaction mixture, the total amount of chlorine involved, as well as the

results obtained.

  The following abbreviations are used: - TCP TT = conversion rate of 2,4,6-trichlorophenol; RR RRP = real yield of 2,3,4,6-tetrachlorophenol; - RR in PCP = actual yield of pentachlorophenol;

  - T C = final temperature of the C test.

  The 100% complement of the RR sum of tetrachlorophenol -

  and pentachlorophenol-corresponds (to accuracy of assay results) to heavy byproducts, which are not polychlorinated dibenzoparadioxins. Catalysts C12 TT% RR% RR% HCDD EXAMPLES (% relative to TCP) TC engaged in en% in (mol) TCP TTCP PCP weight Example 1 1% AlCl3 + 1.8% A1C13 172 0.61 100 8.9 81.2 0.00016 Example 2 1% ZrCl4 + 1.8% AlCl3 170 0.61 100 12.1 82.2 0.00024 Example 3 1.8% ZrCl4 + 1.8% AlCl3 171 0.61 100 12 77.9.0.00019 Example 4 1% SbCl3 + 1.8% AlCl3 170 0.61 100 6.3 81.4 0.00011 Example 5 1% TeCl4 + 1.8% AlCl3 175 0.61 100 5, 8 85.5 0.00030 -8-

COMPARATIVE TEST A

  Example 1 is repeated under the same conditions, but in

charging 2.8% AlCl3.

  49.4 g of 2,4,6-trichlorophenol (0.25 mol) are charged.

1.40 g of aluminum chloride.

  The mixture is heated to 80 ° C. and then, with stirring, 0.60 mol is introduced.

  chlorine with a flow rate of 5 liters / hour.

  It is necessary to gradually increase the temperature of the reaction mixture to 167 C in order to maintain it in the liquid state. After 2 h 40 of chlorination, the apparatus is purged with nitrogen and the final reaction mixture is assayed by high pressure liquid chromatography. (HPLC). The polychlorinated dibenzoparadioxins are assayed by HPLC or GPC (gas phase chromatography) in the final reaction mixture: the

  result is expressed in hexachlorodibenzoparadioxins (HCDD).

  The following results are obtained: TT of TCP: 100% RR in PCP: 81.5% RR in TTCP: 7.4% - HCDD% by weight: 0.0006

2649696.

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Claims (10)

  Process for chlorinating gaseous chlorine, dichlorophenols and / or tiichlorophenols, optionally in admixture with monochlorophenols, to pentachlorophenol, characterized in that the reaction is carried out in the presence of an effective amount of a zirconium halide , of hafnium, tellurium, antimony, nobium or aluminum or of one of their precursors, until the tetrachlorophenol stage is reached, and then adding an effective amount of aluminum halide or one of the precursors to obtain pentachlorophenol. 2. Process according to claim 1, characterized in that the halides which can serve as catalysts for the first part of the chlorination are chlorides, bromides, iodides and fluorides of zirconium, hafnium, tellurium and antimony. , nobium and aluminum. 3. Method according to claim 1, characterized in that the aluminum halide added in the second part of the chlorination is aluminum chloride, aluminum bromide, iodide   of aluminum and aluminum fluoride.   4. Method according to one of claims i to 3, characterized   in that the first part of the chlorination is carried out in the presence of zirconium chloride, hafnium chloride, tellurium chloride, antimony chloride, nobium chloride or aluminum chloride, and then at introduce aluminum chloride for the second   part of the chlorination leading to pentachlorophenol.   5. Method according to one of claims 1 to 4, characterized   in that the aluminum halide required for the second part of the chlorination will be introduced when at least 60% and preferably at least   70% of chlorophenols will be converted to tetrachlorophenol. - 10 -   6. Method according to one of claims 1 to 5, characterized   in that it applies to 2,4-dichlorophenol, 2,6-dichlorophenol,   2,4,6-trichlorophenol and mixtures thereof.   7. Method according to one of claims 1 to 6, characterized   in that it applies to industrial mixtures resulting from the chlorination of phenol or monochlorophenols and consisting essentially of 2,4,6-trichlorophenol, 2,4-dichlorophenol and 2,6-dichlorophenol.   8. Method according to one of claims 1 to 7, characterized   in that the first phase of the chlorination is carried out at a temperature between the melting point of the chlorophenol (s) used, that is to say about 70 ° C. and about 100 ° C. The second phase chlorination takes place at a temperature between the melting point of the reaction mixture at the end of the first phase and about 180 C.   9. Method according to one of claims 1 to 7, characterized   in that the amount of zirconium, hafnium, tellurium, antimony, nobium or aluminum halide used for the first phase of the chlorination is from 0.01% to 10% by weight of halide of these metals with respect to the weight of the chlorophenol (s) involved. Preferably this weight ratio metal halide / chlorophenols will be from 0.1% to 5% in weight.   10. Method according to one of claims 1 to 9, characterized   in that the amount of aluminum halide used for the 2nd stage of the chlorination is from 0.05% to 10% by weight   of aluminum halide relative to the weight of the chlorophenols employed.   Preferably the weight ratio of aluminum halide / chlorophenols will be from 0.1% to 5% by weight.