EP0422986A1 - Process for the preparation of dielectric fluids - Google Patents

Abstract

Simplification of the processes for the synthesis of dielectric fluids by condensation of aromatic halides and of aromatic compounds in the presence of ferric chloride. The Applicant has found that it is no longer necessary to neutralise the catalyst or to perform washings with aqueous solutions. <??>This avoids the generation of aqueous solutions contaminated with organic products, which it is difficult and costly to treat before they are discharged.

Description

The present invention relates to a process for the synthesis of dielectric fluids and more particularly to an improvement of the processes comprising a condensation of the FRIEDEL and CRAFTS type catalyzed by ferric chloride.

dans laquelle n, x, y et z ont la valeur 1 ou 2. Ces produits peuvent être préparés par condensation de :

dans lesquels n, x, y et z ont la même signification que ci-­dessus en présence d'un catalyseur de FRIEDEL et CRAFTS. Après la condensation, on procède à la destruction du catalyseur par exemple par addition d'une solution aqueuse diluée d'acide chlorhydrique suivie d'un lavage de la phase organique. La de­manderesse a découvert que si on utilise du chlorure ferrique comme catalyseur de FRIEDEL et CRAFTS, il n'est pas nécessaire de détruire le catalyseur et laver, c'est-à-dire qu'on obtient à l'issue du procédé de préparation, dans lequel on a omis l'étape de destruction et lavage du catalyseur, des liquides diélectriques ayant les mêmes propriétés que si on les avait préparés par le procédé conventionnel avec destruction et lavage.In European patent application EP 8251, dielectric liquids of the formula have been described

in which n, x, y and z have the value 1 or 2. These products can be prepared by condensation of:

in which n, x, y and z have the same meaning as above in the presence of a catalyst from FRIEDEL and CRAFTS. After the condensation, the catalyst is destroyed, for example by adding a dilute aqueous solution of hydrochloric acid followed by washing the organic phase. The Applicant has discovered that if ferric chloride is used as FRIEDEL and CRAFTS catalyst, it is not necessary to destroy the catalyst and wash, that is to say that one obtains at the end of the preparation process , in which the step of destruction and washing of the catalyst was omitted, dielectric liquids having the same properties as if they had been prepared by the conventional process with destruction and washing.

On the other hand, if other catalysts are used, for example aluminum chloride, one cannot do without this destruction and washing step. Indeed, if this step is omitted, the products obtained are unsuitable for use as a dielectric fluid. This discovery therefore makes it possible to re solve a major technical problem. In fact, the destruction of the FRIEDEL and CRAFTS condensation catalyst is most often done with an aqueous solution. An aqueous solution containing organic products is therefore obtained, and although the quantity of organic products is small, it is necessary to treat this aqueous solution before its rejection.

Patent application EP 136230 describes dielectric fluids which are polyarylalkane oligomers obtained by condensation of benzyl chloride C₆H₅CH₂Cl and benzylidene chloride C₆H₅CHCl₂ on toluene in the presence of a FRIEDEL and CRAFTS catalyst. The Applicant has made the same observation as for the process of the EP 8251 application cited above, that is to say that by using ferric chloride, it is possible to omit the washing step and yet produce a fluid capable of dielectric.

The Applicant has found a particularly simple process for synthesizing dielectric fluids by condensation of the FRIEDEL and CRAFTS type.

• a/ Condensation d'halogénures aromatiques et de compo­sés aromatiques en présence de chlorure ferrique comme cataly­seur
• b/ Elimination du catalyseur par neutralisation ou la­vage ou toute combinaison de ces moyens
• c/ Distillation éventuelle de l'excédent des réactifs
• d/ Distillation de l'ensemble des produits de conden­sation ou d'au moins l'un d'entre eux suivie de son condition­nement en fluide diélectrique,le perfectionnement consistant à supprimer l'étape b.

The present invention is therefore in a process for the synthesis of dielectric fluids comprising the following successive steps:

• a / Condensation of aromatic halides and aromatic compounds in the presence of ferric chloride as catalyst
• b / Removal of the catalyst by neutralization or washing or any combination of these means
• c / Possible distillation of excess reagents
• d / Distillation of all of the condensation products or at least one of them followed by its conditioning in dielectric fluid, the improvement consisting in eliminating step b .

The process of steps a to d is known, it is described, for example, in patent application EP 8251. The condensation of step a is a reaction of FRIEDEL and CRAFTS.

Aromatic halides denote, for example, alkylbenzene or (polyalkyl) benzene having at least one halogen in the benzyl position on the alkyl chain, the benzated nucleus nique can, in addition to halogenated alkyl chains, be substituted by halogens, alkyls having up to three carbon atoms or nitrile or NO₂ groups.

The alkyl chains which carry at least one halogen can be identical or different and contain up to three carbon atoms.

These aromatic halides can be, for example, the products of formulas:

The foregoing aromatic halides are condensed with aromatic compounds. These aromatic compounds denote, for example, benzene which can be substituted by one or more identical or different alkyl groups and having up to 8 carbon atoms, halogens or nitrile or NO₂ groups.

These aromatic compounds can be, for example, benzene, toluene, xylene, products of formula:

The condensation of the step takes place in practice at a temperature between 50 ° C and 150 ° C. The amount of ferric chloride is usually between 50 ppm and 1% by weight of the reaction mass.

In this step , an excess of the aromatic halide or an excess of the aromatic compound can be used. Depending on the proportions of the different reactants, different condensation products are obtained, which are themselves mixtures. Most often, it may be necessary to distill the excess reagents (step c ) because these products, even in admixture with the condensation products do not have dielectric properties or cannot be used as dielectrics because of their too much volatility.

In step d , all or at least one of the condensation products is recovered. Indeed, during the condensation (step a ), a mixture of products is often obtained.

dans laquelle n₁ et n₂ valent 0, 1 ou 2 et n₁+n₂ est inférieur ou égal à 3.For example, when benzyl chloride is condensed on toluene, an oligomer A is obtained which is a mixture of isomers of formula

where n₁ and n₂ are 0, 1 or 2 and n₁ + n₂ is less than or equal to 3.

The mixture can contain the condensation product such as n₁ and n₂ = 0 which is called benzyltoluene (MBT) and the product in which n₁ + n₂ = 1 which is called dibenzyltoluene (DBT).

dans laquelle n′₁, n˝₁ et n₄ valent 0, 1 ou 2,
n′₂, n˝₂, n₃, n′₃ et n₅ valent 0 ou 1,
et sachant que la somme n′₁ +n˝₁+n′₂+n˝₂+n₃+n′₃+n₄+n₅ est infé­rieure ou égale à 2.For example, when condensing benzylidene chloride C₆H₅CHCl₂ on toluene and DBT, we obtain an oligomer B which is a mixture of isomers of formula:

where n′₁, n˝₁ and n₄ are 0, 1 or 2,
n′₂, n˝₂, n₃, n′₃ and n₅ are 0 or 1,
and knowing that the sum n′₁ + n˝₁ + n′₂ + n˝₂ + n₃ + n′₃ + n₄ + n₅ is less than or equal to 2.

When one condenses a mixture of C₆H₅CH₂Cl and C₆H₅ CHCl₂ on toluene, one obtains a mixture of oligomers A and B.

In stage d , the desired isomers or mixtures of isomers are distilled off, then they are conditioned into dielectric fluid. The packaging of products for dielectric use is known per se, it is recalled on page 4 in patent application EP 8251. It consists of a preliminary purification treatment with alkalis such as NaoH, Na₂Co₃ or compounds similar to calcium or potassium at a temperature ranging from 20 to 350 ° C. Sometimes further distillation can be advantageous. After this preliminary treatment, the next purification phase consists in using bleaching earth or activated alumina either alone or as a mixture according to the specific techniques known in the dielectric fluids sector. Likewise, it may be advantageous to add stabilizers of the epoxide or other type, such as, for example, tetraphenyltin or anthraquinone compounds.

It would not be departing from the scope of the present invention to condense in step a mixtures of aromatic halides on mixtures of aromatic compounds.

If the aromatic halides are derived from the aromatic compounds in question, for example benzyl chloride and toluene or methyl benzyl chloride (CH₃C₆H₄CH₂Cl) and xylene, then it is possible to carry out upstream of the step to the partial halogenation of the aromatic compound. A mixture of aromatic halide and aromatic compound is thus obtained in which it suffices to add ferric chloride to carry out step a of the process.

EXAMPLE 1

In a reactor fitted with relative agitation and a condenser, 6 moles of benzyl chloride are poured in 4 hours into 30 moles of toluene containing 35 g of FeCl₃ at a temperature of 105 ° C. After the end of introduction of the benzyl chloride, the reaction mass is maintained for another 1 hour 30 minutes at 105 ° C. The whole is then subjected to a simple distillation which makes it possible to separate:
a) unreacted toluene, under a vacuum of 15 mm of mercury with a bottom temperature of 105 ° C. The toluene collected is colorless, with a purity greater than 99% according to the chromatographic analysis and contains less than 2 ppm of iron.
b) oligomer A as described above which distills at 105-263 ° C under a vacuum of 15 mm of mercury. The product obtained (900 g) which is slightly yellow has the following composition: n₁ + n₂ = 0 75% n₁ + n₂ = 1 21% n₁ + n₂ = 2 4%

The compound n₁ + n₂ = 0 consists only of a mixture of benzyltoluene isomers in the proportion 0 / m / p = 42.7 / 6.6 / 50.7.

The dielectric properties have been determined and are listed in the table of Example 7, column 7.1.

A product obtained in the same way, but by carrying out the following washes on the organic phase at the end of the reaction of the benzyl chloride:
2 X 1000 cc of 3% hydrochloric acid
3 X 1000 cc of water
leads to a product whose properties are listed in the ta leads to a product whose properties are shown in the table in Example 7, column 7.2.

It can be seen that there is no difference in the dielectric properties.

EXAMPLE 2 (not in accordance with the invention)

• a) le toluène non réagi sous un vide de 15 mm de mer­cure avec une température de pied de 105°C. Ce toluène est jaune et contient 3,2 ppm d'aluminium. L'analyse chromatogra­phique montre que ce toluène est très impur et contient notam­ment des quantités non négligeables de benzène et de xylène ;
• b) la distillation des produits plus lourds est pour­suivie en augmentant progressivement la température avec un vide plus poussé. Cette distillation est très difficile car il y a décomposition permanente avec formation de benzène, to­luène et xylène avec des difficultés pour obtenir le vide.

The same operation of condensing benzyl chloride on toluene is carried out as in Example 1, but replacing the ferric chloride with 35 g of aluminum chloride. The reaction medium at the end of the reaction of the benzyl chloride is subjected to a simple distillation as in Example 1, which leads to the following products:

• a) unreacted toluene under a vacuum of 15 mm of mercury with a bottom temperature of 105 ° C. This toluene is yellow and contains 3.2 ppm of aluminum. Chromatographic analysis shows that this toluene is very impure and contains in particular non-negligible quantities of benzene and xylene;
• b) the distillation of heavier products is continued by gradually increasing the temperature with a higher vacuum. This distillation is very difficult because there is permanent decomposition with the formation of benzene, toluene and xylene with difficulties in obtaining the vacuum.

Only 300 g of very strongly colored product containing 17 ppm of aluminum having the following composition are obtained: benzene 1.3% toluene 16.0% xylene 7.0% diphenylmethane 7.5% benzyltoluene 34.0% benzylxylene 22.0%

This product is obviously unusable in the dielectric application. In addition, a very large quantity of product remains in the distillation flask in the form of an irretrievable compact block.

In conclusion, a gross benzylation product of to luene catalyzed by aluminum chloride is not distillable without a preliminary washing making it possible to remove the catalyst.

EXAMPLE 3

• a) le toluène non réagi avec une pureté supérieure à 99 %, directement utilisable dans une nouvelle opération de synthèse ;
• b) un mélange d'oligomère A et d'oligomère B comme dé­crit précédemment dans la proportion pondérale 97,5/2,5.

The procedure is as in Example 1 of the patent, except that instead of using pure benzyl chloride, a crude product of photochlorination of toluene is used. For this, 6 moles of chlorine are introduced into 24 moles of toluene under photochemical irradiation at a temperature of 90 ° C. The reaction product is gradually introduced into 12 moles of toluene containing 35 g of FeCl₃ at 105 ° C. After the end of the reaction, the medium is distilled as in Example 1, making it possible to separate:

• a) unreacted toluene with a purity greater than 99%, directly usable in a new synthesis operation;
• b) a mixture of oligomer A and oligomer B as described above in the weight proportion 97.5 / 2.5.

The dielectric properties have been determined and appear in the table of Example 7, column 7.3.

A product obtained in the same way but by washing with hydrochloric acid and water on the organic phase after the end of the Friedel and Crafts reaction leads to a product whose dielectric properties are shown in the table of l 'example 7, column 7.4. It can be seen that there is no difference in the dielectric properties.

EXAMPLE 4

Example 3 is repeated, but replacing the ferric chloride with 35 g of aluminum chloride at the Friedel and Crafts reaction. The reaction medium is then subjected to distillation. The same difficulties are encountered as those observed in Example 2, which leads to a product unsuitable for dielectric application.

EXAMPLE 5

• a) les dichlorotoluènes non réagis, sous un vide de 15 mm de mercure avec une température de pied de 150°C. Le distillat obtenu est incolore et contient moins de 1 ppm de fer. L'analyse chromatographique montre que la teneur en di­chlorotoluènes est supérieure à 99 % ;
• b) les produits de formule :
  

The procedure is as in Example 3 of the patent, except that a mixture of dichlorotoluene isomers (33% of 2-4, 26.5% of 2-5, 18.8% of 2-6, 11.6% of 2-3, 8.1% of 3-4). The photochemical reaction of 6 moles of chlorine is carried out with 24 moles of dichlorotoluenes at 120 ° C. The Friedel and Crafts reaction is then carried out by reacting the photochlorination reaction medium with 12 moles of dichlorotoluenes in the presence of 20 g of FeCl₃ at a temperature of 140 ° C. The introduction takes place in 4 h 30 with regular addition of small amounts of FeCl₃. The reaction mass is kept for another 1 h 30 with stirring at 140 ° C., then subjected to simple distillation under vacuum which makes it possible to separate:

• a) unreacted dichlorotoluenes, under a vacuum of 15 mm of mercury with a bottom temperature of 150 ° C. The distillate obtained is colorless and contains less than 1 ppm of iron. Chromatographic analysis shows that the dichlorotoluene content is greater than 99%;
• b) the products of formula:
  

1500 g are obtained under a vacuum of 15 mm of mercury vacuum with a vapor temperature of 260 to 280 ° C. It is a slightly yellow liquid containing less than 1 ppm of iron. This product is ideal for dielectric application.

A product obtained in the same way but with washing of the organic phase resulting from the Friedel and Crafts reaction with aqueous hydrochloric acid and then with water leads to a product identical to that obtained without washing the catalyst.

The dielectric properties of these two products were measured (with washing and without washing) as in Example 7, there is no difference, the two products are suitable as dielectric.

EXAMPLE 6 (not in accordance with the invention)

• a) les dichlorotoluènes non réagis sous vide de 15 mm de mercure avec une température de pied de 150°C. La distilla­tion est très difficile à conduire à cause de la formation de mousses dues à des réactions de décomposition. Les dichloroto­luènes obtenus sont très colorés et contiennent 95 ppm d'aluminium. La pureté d'après l'analyse CPG est de 85 % seu­lement (contiennent 10 % de produits légers et 5 % de produits lourds).
• b) les produits plus lourds : en augmentant progressi­vement la température pour atteindre 240-280°C, il y a des dépôts blanchâtres, le distillat très coloré s'épaissit on n'obtient que 1200 g du produit contenant au moins 10 % de plus légers (dichlorobenzènes et dichlorotoluènes générées par décomposition) et 170 ppm d'aluminium.

Example 5 is reproduced, but replacing the ferric chloride with 35 g of aluminum chloride. The product after the end of the Friedel and Crafts reaction is subjected to a simple distillation to separate:

• a) the unreacted dichlorotoluenes under vacuum of 15 mm of mercury with a bottom temperature of 150 ° C. Distillation is very difficult to conduct due to the formation of foams due to decomposition reactions. The dichlorotoluenes obtained are very colored and contain 95 ppm of aluminum. The purity according to the CPG analysis is only 85% (contains 10% of light products and 5% of heavy products).
• b) heavier products : gradually increasing the temperature to reach 240-280 ° C, there are whitish deposits, the very colored distillate thickens, only 1200 g of the product containing at least 10% more are obtained light (dichlorobenzenes and dichlorotoluenes generated by decomposition) and 170 ppm of aluminum.

This product is obviously unsuitable for use as a dielectric.

There is only a large quantity of product left in the bottom of the flask in the form of an irretrievable black compact block.

In conclusion, the desired products cannot be obtained without a prior washing of the reaction medium to remove the aluminum chloride.

EXAMPLE 7 Dielectric properties

They are measured by cell aging tests at 100 ° C.

The samples were treated overnight at room temperature with 3% of activated TONSIL 13, after addition of 1% of DGEBA epoxy (diglycidil ether of bisphenol A).

The filtered samples were placed in tanδ measuring cells (2 cells per sample). These cells were placed in an oven at 100 ° C and the tanδ was followed for 500 hours.

The results obtained, given in the table below, show that the four products have equivalent stability. tanδ x 10⁻⁴ (100 ° C) 7.1 7.2 7.3 7.4 Time 1 2 1 2 1 2 1 2 0 1.4 2.1 2.0 1.7 1.9 1.9 1.6 2.1 30' 1.2 1.9 1.9 1.5 1.8 1.7 1.5 1.9 6 p.m. 1.5 1.8 1.9 1.7 1.7 1.7 1.6 1.8 41 h 1.8 2.4 2.1 2.0 2.0 2.2 1.9 2.3 140 hrs 2.3 2.7 2.0 2.4 3.0 1.9 2.4 2.9 210 h 2.4 3.0 2.5 2.7 2.9 3.0 2.8 3.0 260 h 2.6 3.3 3.0 3.5 3.6 5.0 3.1 4.2 310 h 3.4 3.9 4.1 4.0 4.9 5.5 3.9 5.0 370 h 4.2 5.0 4.6 4.9 5.5 5.7 4.8 5.9 440 h 5.6 6.0 6.1 5.9 6.5 6.0 5.9 6.6 510 h Stop 9.3 10.6 9.0 10.9 8.5 9.6 7.7 11.0

Claims (4)

1. In a process for the synthesis of dielectric fluids comprising the following successive steps: a / condensation of aromatic halides and aromatic compounds in the presence of ferric chloride, as catalyst, b / elimination of the catalyst by neutralization or washing or any combination of these means, c / possible distillation of the excess reagents, d / distillation of all of the condensation products or of at least one of them followed by its conditioning in dielectric fluid, the improvement consisting in eliminating step b . 2. Method according to claim 1 characterized in that the aromatic halide is benzyl chloride and that the aromatic compound is toluene. 3. Method according to claim 2 characterized in that the aromatic halide is a mixture of benzyl chloride (C₆H₅CH₂Cl) and benzylidene chloride (C₆H₅CHCl₂). 4. Method according to claim 1 characterized in that the aromatic halide is a product of formula

and that the aromatic compound is dichlorotoluene