IE900610L - Compositions based on polyphenylmethanes, process for their¹manufacture and their application as dielectrics - Google Patents

Abstract

Mixtures of benzyltoluene, benzylbenzene and their higher homologues, the said mixtures optionally containing triphenylmethane, ditolylphenylmethane, tolyldiphenylmethane and their higher homologues. These mixtures are prepared by chlorinating a mixture of toluene and benzene which is then subjected to the action of an inorganic halide.

Description

64075 Compositions based on polvphenvlmethanes, process for their manufacture and their application as dielectrics 4 The present invention relates to compositions based 5 on polyphenyImethanes, to a process for their manufacture and to their application as dielectrics. It relates more particularly to mixtures of mono- and dibenzvltoluanef mono- and dibensylbenzene capable of containing triphenylmethane, ditolylphenylmethane, tolyldiphenylmethane or their higher homologues.

SP - A - 259,798 describes mixtures of monobenzyltoluene, ethylbiphenvl and/or 1,1-diphenylethane with other biphenyls or other diphenylmethanes containing not more than 17 carbon atoms.

EP - A - 262,456 describes mixtures of monobenzyltoluene and of a diphenylmethane substituted by alkyl groups, the complete structure containing between 15 and 17 carbon atoms.

EP - h - 172 f 537 describes mixtures of 20 benzylbenzene isomers- EP - A - 2821083 describes mixtures of monobenzyltoluene and of ditolylmethane.

All these compositions are obtained by addition or w coupling reactions of pure reactants &?hich than require <■> difficult separations.

EP - A - 136,230 describes mixtures of monobenzvltoluene f dibensyltoluene and ditolylphenylmethane which can be employed as dielectric fluids- It also describes a process for obtaining these mixtures very simply.

Hew compositions based on polyphenvlmethanes have now been found, which have better dielectric properties than the prior art ones. Further these compositions can be employed at low temperature.

The present invention provides a composition based 10 on two oligomers A^ and A2 such that: - Ai is an isomer or a mixture of isomers of formulas _ (S)'CH2 nl i@^"2- The oligomer A2 may be, for example, meta-benzyltoluene or a mixture of two isomers of benzyltoluene or a mixture of the three isomers of benzyltoluene. It may also be a well-defined isomer with = 1 and q2 = 0, such as 3,5-dibensyltoluene or a mixture of all the isomers such that qi = 1 and ~ 0 or a fixture of isomers such that qi = 0 and q2 = 1.

A2 may also be a mixture of isomers in which qi and q2 have a number of meaningsf for example a mixture consisting of 64 % by weight of dibenzyltoluene, 22 % by weight of the mixture of isomers such that q^ + q2 = 1, 10 % by weight of the mixture of isomers such that 10 + q2 = 2 and 4 % by weight of the mixture of isomers such that qi + qj = 3 - It may also be any combination of the isomers or mixtures of isomers described above.

The same applies in the case of the oligomer Ai, which is therefore an isomer or a mixture of isomers of 15 benzvlbenaena or of its higher homologues. The composition according to the invention is such that at least one of the oligomers Ai or A2 is an isomer which has at least 3 benzene nuclei in its structure or a mixture of isomers which has 3 benzene nuclei, or a mixture comprising at 20 least one isomer or isomers having 3 benzene nuclei- The product of the invention may be a mixture of any one oligomer Jh and the oligomer Jk2 being either dibensyltoluane 4, that is to say one or more isomers in which qi = 1 and q2 = 0, or tolyl(bensylphenyl)methane, 25 that is to say one or more isomers in which = 0 and q2 = l.

The product of the invention is advantageously a composition comprising one of the following combinations of the oligomers Ai and A2° a) A^ such that = n2 = 0 5 A2 such that qi + q2 = 1 b) A^ such that n^ + n2 = 1 A2 such that qi = q2 = 0 c) A^ such that + n2 = 1 A2 such that + q2 = 1 Although Aj_ and A2 may be in any proportion whatsoever, the quantity of A2 is advantageously greater than the quantity of A^ and is preferably from 60 to 80 % by weight of the total quantity of A^ and A2» The invention also provides a composition based on 15 the two oligomers A^ and A2f characterized in that it additionally comprises at least one oligomer chosen from the following oligomers Ble, B2 and B3s - is an isomer or a mixture of isomers of formula: _ 5 - where: n9i„ n"i_ and n4 = Of 1 and 2 n!2, n!,2, n3f n®3 and 05 = 0 and 1 such that n8^ + n'J3i + n! 2+ n?s2 + n3 + n83 + n4 + n5 is 5 smaller than or equal to 2; % and R2 denote a hydrogen; B2 is an isomer or a mixture of isomers of the same general formula as except that R1 and R2 denote methyl and the symbols n are replaced by q and have the same 10 meaning; B3 is an isomer or a mixture of isomers of the same general formula as Bi except that R^ and R2 are different and denote hydrogen or methyl and the symbols n are replaced by r and have the same meaning. 15 The oligomer may be in its simplest form triphenylmethane. It may also be a well-defined isomer of (benzylphenyl)diphenylmethane, that is to say nsi = 1 and all the other symbols having the value of zero, or a mixture of a number of isomers of this product. Bi may also 20 be a mixture of isomers in which the symbols n have & number of meanings,, for example such that 72 % by weight of consists of isomers whose sum: ns3_ + n9Bi + n*3 + n3 + n'"2 + n982 + 04 + n5 has the value 0# 21 % by weight consists of isomers whose above sum has 25 the value of 1 and the remainder consists of isomers whose above sum has the value 2. Bi may also be an isomer or a mixture of isomers denoted by a veil-defined set of symbols n. It may also be a mixture which is a combination of two or more of the abovementioned mixtures. The oligomers B2 and B3 are defined in the same way.

Particularly advantageous composition are made up of Alf h2 and B2. Among these compositions, preference is given to the following compositionss a) Ai such that ni = n2 - 0 A2 such that 50 to 90 % by weight of A2 consists 10 of isomers with n^ = n2 =0 Any B2 b) Ai such that more than 50 % by weight of Ai consists of isomers with ni + n2 = 0 A2 and B2 as in a) Among the compositions based on A^, A2 and on at least one of the oligomers Blf B2 and B3l? that comprising the 5 oligomers Alt, A2l> B2 and B3 is particularly advantageous and is unexpectedly very easy to manufacture.

The present invention also provides compositions 20 made up of the mixture A^, A2, B1(, B2.

The compositions just described can be employed as dielectric fluids, in particular in capacitors» These compositions may be purified,, for example by being brought into contact with a decolorizing earth,, a bentonite or an 25 equivalent product until a sufficiently high resistivity is obtained; they can generally be purified using the ~ 7 - conventional techniques for purifying liquids for dielectric application. Conventional additives to liquids for dielectric application may also be added to the compositions of the invention, such as epoxides or 5 antioxidants, of the di-tert-hutyl-para-cresol type, or anthraquinone derivatives. The present invention also relates to processes for the synthesis of all these compositions.

The oligomers Ai and A2 may be prepared by reaction 10 of bensyl chloride C5H5CH2CI with toluene in the case of A2 and with benzene in the case of A^. As for the oligomers Bif B2 and B3, these may be prepared by reaction of benzylidene chloride C5H5GHCI2 with benzene, toluene, benzyl chloride and the oligomers At_ and A2 -15 Benzyl chloride and benzylidene chloride are known products. For example, radical chlorination of toluene can be carried out, followed by a distillation to separate C6H5CH2C1 and CSH5CHC12.

Thenc when the various oligomers A and B have been 20 obtained, it suffices to mix them to obtain the compositions of the invention.

A particularly convenient process for obtaining the mixture of the oligomers A2 and B2 is described in IP - h - 135230 and consists? in a first stage£, in 25 reacting chlorine with toluene by a radical reaction in the presence of a free radical generator and, in a second ~ 8 - stage, in subjecting the product of reaction of this first stags to the action of an inorganic halide or of an inorganic acid.

A suitable process for preparing Aj + is characterised in that: a) chlorine is reacted with a mixture of bensens and toluene by a radical reaction in the presence of a free radical generator, b) the unreacted toluene is removed, c) the product obtained is subjected to the action of an inorganic halide or of an inorganic acid.

The radical chlorination of the mixture of benzene and toluene is usually carried out at a temperature of, say, 50 to 110°C and better at 70 to 100°C. It is 15 preferably conducted so that only 10 to 40 % of the toluene introduced, expressed as a molar percentage, is converted into the corresponding chlorinated derivative. Either a photochemical initiation or a chemical initiator may be employed as a free radical generator; among the chemical 20 initiators there may be mentioned aso compounds like asodiisobutyronitrile or asodivaleronitrile and peroxides, such as lauroyl peroxide. The quantity of chemical initiator employed is generally from 0.05 to 3 %, and preferably 0.1 to 1.5 %, by weight relative to the toluene 25 introduced.

We have found to our surprise that if the benzene-toluene mixture contains at least 15 mol%, and preferably 20 to 30 %e of toluene there is no chlorination of benzene. The toluene is then removed,, for example by distillation 5 with the aid of one or more columns and with the benzene, which might leave with the unchlorinatad toluene s being returned to the reaction mixture which contains the chlorinated toluene.

The reaction mixture obtained during the preceding 10 stage, that is to say a mixture of C5H5e CgHgCH^Cl and C5H5CHCI2 is next subjected to the action of an inorganic halide or of an inorganic acid. In practice this reaction takes place at a temperature oft, say, 30 to 1100C and preferably 50 to 100°C. Among the inorganic halides, it is 15 preferable to employ ferric chloride,, antimony trichloride, titanium tetrachloride or aluminium chloride in weight proportions relative to the reaction mixture which are usually from 50 ppm to 1 % and preferably from 100 ppm to 0.5 %. Inorganic acids may also be employed: for example 20 sulphuric acid at a weight concentration of 70 to 95 %» It is also possible to employ seolites or certain inorganic oxides.

An alternative form of the process in respect of this second stage consists in pouring the reaction mixture 25 from the first stage into a heel of benzene or of benzene and of the mixture of oligomers according to the invention, containing the inorganic halide or acid in solution or dispersion; this altarnative form is of particular interest where such a process is run continuously (it is obvious that this synthesis can he performed noncontinuously or 5 continuously)- After distillation of the excess benzene it is recommended to carry out the removal of the inorganic halide or of the inorganic acid by any known method,, such as washing with water, neutralizing and drying. 10 A^ + Bi can also be prepared according to an alternative form of the above process in which benzene is introduced after the chlorination of toluene.

The process is characterised in that: a) chlorine is reacted with toluene by a radical 15 reaction in the presence of a free radical generator, b) the unreacted toluene is removed, c) benzene is added and the product obtained is subjected to the action of an inorganic halide or of an « inorganic acid.

The implementation of the process is the same as in the preceding case where a mixture of toluene and benzene is chlorinated? on the other hand, the removal of toluene is much easier because it is the most volatile compound.

It is also possible to replace the stages a) and b) 25 with a synthesis of a mixture of C5H5CH2CI and CgHgCHC^.

The invention also provides a process for preparing the mixture of oligomers A^ + A 2, characterised in that benzyl chloride is brought into contact with benzene and toluene in the presence of an inorganic halide or of an 5 inorganic acid.

This reaction can be carried out under the same conditions as those described above in stage c) of the processes for preparing Ai + .

It is also possible to prepare Ai + A2 using an 10 alternative form of the above process, characterised in that: a) chlorine is reacted with toluene and benzene in the presence of a free radical generator, b) benzylidene chloride is removed, c) the product obtained is subjected to the action of an inorganic halide or of an inorganic acid.

This process resembles the preceding preparations. In the case of stage b) it is advantageous to employ distillation, for example by collecting the light fraction 20 of the mixture obtained in a). This light fraction consists of benzene, toluene and benzyl chloride; it then suffices to add to it (i) an inorganic halide or an inorganic acid or (ii) a product containing this halide or this acicL It is also possible to perform stage a) without 25 benzene and to add it at stage c). Toluene also may be added at stage c).

The invention also provides a process for preparing the mixture of the oligomers Ai, h2, Bi, B2 and B3e characterised in that: a) chlorine is reacted with a mixture of benzene and toluene by a radical reaction in the presence of a free radical generator, b) the above reaction product is then subjected to the action of an inorganic halide or of an inorganic acid. As before, provided the benzene-toluene mixture contains at least, say, 15 mol% of toluene, there is no chlorination of benzene. This process can be carried out in a similar manner to that of the preceding processes.

The following Examples further illustrate the present invention.

EXAMPLE 1 The tests consist in subjecting models of capacitors to accelerated aging at elevated voltage and temperature» The chief criterion in the tests is the number of capacitors which fail. In some tests the aging period is short and the measurement of the dielectric strength of the capacitors which have not failed during the test yields additional information on the deterioration of the insulation.

I- TEST ON MIXED CAPACITORS Two series of ten capacitors were manufactured for this testf comprising two layers of smooth polypropylene film 12 ;j,m thick and a layer of paper of relative density 5 1.0 and 12 thick.

These two series of capacitors were impregnated, one with an oligomer A2 such that 75 % by weight is henzyltoluene (q-^ = q2 = 0) and 25 % by weight isomers such that qi + q2 = 1 and containing bisphenol A diglycidyl 10 ether in the proportion of 1 part to 100 parts of A2, the other with a mixture of A^ and A2 such that; a) A2 represents 70 % by weight of Ai + A2, b) A^ is made up of 70 % by weight of isomers such that ni_ = n2 = 0 and 30 % by weight of isomers such that "v Tip ~ 1. 1.1. Endurance After impregnation and heat forming the capacitors were subjected to aging at 85°C under 2700 V (75 V/>sxm) for 535 h. After this first aging, no failure having been 20 observed,, the test was continued under 3000 ¥ (83.8 V/^m) in order to increase its severity- - 14 ~ After 4400 h of agingf the following results have been obtained.

Number of surviving capacitors Time under voltage 5s* to Ai + A? 0 695 Q 1056 8 1458 7 3290 3450 9 3915 8 3990 7 4400 7 These results are in favour of the mixture Aj_ + A2 1.2 Changes in tan 5 The tan S of the capacitors was measured after 535 20 1450 and 4400 hours5 aging.

The following results were obtained: Tan 6 x ~4 (85 ° C) Aging period Measurement voltage (volts) . A2 A1 + a2 500 .S .7 1000 6.1 .6 535 2000 6.4 .9 3000 7.9 7.0 500 9.0 6.4 1000 9.4 6.5 1460 2000 .3 6.8 3000 12.5 8.1 500 4«6 4.1 1000 4 . 5 4.2 4400 2000 4.9 4.4 3000 | 5.9 i i i 4.9 The tan £ of the capacitors impregnated with the mixture Ajt + is significantly lover than that of the capacitors impregnated with A2» showing that the deterioration is less pronounced.

II. TESTS OH ALL-FILM CAPACITORS Three series of ten capacitors were manufactured for this test, comprising two layers of rough polypropylene 5 film with a weight thickness of 13.5 /m.

Two series were impregnated with the above oligomer &2i and one series was impregnated with the above mixture A1 + h2-2.1. Endurance After impregnation and heat forming, these capacitors were subjected to aging at 90°C under 2400 V (88.9 V//am) for 500 hours.

The following results were obtained: Number of surviving capacitors Time under voltage A2 A-) + A2 0 160 19 188 18 259 17 418 17 a 479 16 9 500 16 G These results show a slight difference in favour of the mixture A^ + A2. 2.2 Change in the breakdown voltage To confirm these results, the breakdown voltage of 5 the capacitors which still survived at the end of the aging test was measured.

The same measurement, performed on new capacitors, gives a value of 11,5 kV. Any deterioration in the insulation during the aging is reflected in a drop in the 10 dielectric strength.

The following results were obtained: - capacitors impregnated with A2 : 6.6 kV - capacitors impregnated with + A2 : S.4 kV These results show significantly that the deterioration of the capacitors impregnated with + A2 is much smaller.

EXAMPLE 2 - Synthesis of an oligomer 54 moles of benzene (4212 g) and 1 g of FeCl3 are charged into a S-litre reactor fitted with a rotary 20 stirrer, a reflux condenser, a nitrogen injector and a dropping funnel. The mass in the reactort, blanketed with nitrogen, is heated to 65*C. 5 moles of benzyl chloride (759 g) are introduced via the dropping funnel over 4 h. The reaction mixture is kept stirred for another 1 h and 25 0,25 g of FeCl3 are added. The reaction mixture is kept at 700C for another 2 h under a stream of nitrogen. The quantity of hydrochloric acid released is 5.95 moles, The unreacted ban sen e is then removed by a sixnpla distillation. The crude polyphenylmethane (873 g) is then treated with 1 % of anhydrous Na2CC>3 for 3 h at "275°C with stirring.

After treatment, the product is subjected to a distillation with a column 30 cm in height„ filled with a packing consisting of glass helices, under a vacuum of 1 mm of mercury„ The fraction of compounds containing two aromatic 10 rings comes over at about 85-95°C.

The fraction of compounds containing three aromatic rings comes over at about 170-200*C.

The fraction of compounds containing four aromatic rings comes over at about 260-280°C (after the distillation 15 column has been removed).

The residue represents 5.8 % of the material introduced. The distillation fractions are mixed and represent 94 % of the material introduced. An oligomer is obtainedj. whose weight composition is the following: 20 and ~ 0 66.5 % nx = l,n2 =0 27 % nj and n2 ~ 1 6.5% The characteristics are as follows: crystallisation point = + 3*C 25 viscosity at 40°C - 3.4 cP viscosity at 20°C = 5.8 c? relative density at 40°C = 1.001 relative density at 20 °C = 1.012 EXAMPLE 3: Synthesis of the mixture A^ + Bi 9„61 moles of benzyl chloride (1266 g) and 5 0B 306 moles of benzvlidene chloride (1266 g), which is obtained by photochlorination of toluene (toluene/chlorine molar ratio = 4) and separation of the unreacted toluene by distillation, are placed in the dropping funnel in an apparatus identical with that of Example 2„ This material is reacted in the same conditions as in Example 2 with 50 moles of benzene (3900 g) and 1 g of F&Clj. The hydrochloric acid collected is 9-99 moles. The product obtained after distillation of the unreacted benzene represents 1304 g. It is treated with sodium 15 carbonate as in Example 2 and is then subjected to the same distillation. The distillation residue represents 14.2 % of the material introduced. The fractions are mixed and represent 85 % of the material introduced. The product thus obtained is a mixture of oligomers Ai_ and Bi. 20 It consists, on a weight basis, of - 53 %: of oligomers Ai «i and n2 ~ 0 - 31 %: of oligomers ni = 1, - 0 25 of oligomers Bi n']_ ~ n2 = nMi = n"2 =n3 = n«3 = n4 = 115 = 0 ~ 20 - - 16 %: of oligomers Ai_ ~ n2 = 1 of oligomers Bi n® ^ + n'2 + n"1! + n"2 + n3 + n'3 + n4 + ns = 1 The characteristics are as follows" crystallisation point : -15 °C viscosity at 20*C : 8.1 cP relative density at 20°C : 1.019 EXAMPLE 4: Preparation of A]_ + A2 + + B2 + B3 10 5 moles of benzene (390 g) and 5 moles of toluene (460 g) are placed in a 1-1 reactor fitted with a stirrer, a condenser, a chlorine feed tube and a 30-watt Philips TLADK lamp arranged externally,* 1.25 moles of chlorine (78.1 g) are then introduced while the temperature is 15 maintained at 85°C for 1 h» The quantity of hydrochloric acid released is 1.15 moles. Chromatographic analysis shows that the benzene is perfectly inert during the chlorination. The mixture contains 16 % of benzyl chloride and 0.52 % of benzylidene chloride by weight. 20 The reaction mixture is placed in a dropping funnel and is introduced over 1 h into a 1-1 reactor fitted with a rotary stirrer? containing 0.166 moles of toluene (15.3 g), 0.166 moles of benzene (12.95 g) and 0.15 g of FaCl3 at a temperature of 80°C. The whole is maintained at 80°C for 25 another 1 h with nitrogen purging. The quantity of hydrochloric acid released is i.i moles.

The product obtained after distillation of the benzene and of the unreacted toluene represents 180 g. It treated «rith sodium carbonate as in Example 1 and is subjected to the same distillation. The distillation 5 residue represents 2.76 % of the material introduced. The distillation fractions are mixed and represent 97„1 % of the material introduced. The product thus obtained is a mixture of oligomers Alf, A2 f Blf, B2 and B3. - 71.1 % of oligomer A^ + A2 and n2 = 0 and q2 = 0 24.3 % of oligomer A^ + A2 = 1 and n2 = 0 qx = 1 and q2 = 0 of oligomers Bi + B2 + B3 such that all the coefficients n„ p and r are zero 4.6 % of oligomers + A2 nl = n2 = 1 gi = g2 = 1 of oligomers + B2 + B3 such that the sum of all the coefficients n is equal to 1£, the sum of all the coefficients q is equal to 1, the sum of all the coefficients r is equal to 1.

In the oligomer A^ + A2f the weight distribution between A2 is 85/15 (determined by gas phase chromatography) for the value and n2 = 0. The characteristics are as follows: crystallisation at < -32 "C viscosity at 20*C = 6.7 cP 5 relative density at 20°C = 0.998 EXAMPLE 5 We made up a few mixtures of product from Example 2 with a product A2 + B2 prepared according to the technique described in EP - A - 135 f 230 and whose 10 composition by weight relative to the general formula is the following: ~ 75 % of oligomer A2 qi and q2 = 0 - 23 %: of oligomer A2 =1 and n2 = 0 of oligomers B2 q'i = a"2 = q"i = q°B2 = qi = <3*3 = ^4 = ^5 = 0 - 2% of oligomers A2 q^ = q2 = 1 of oligomers B2 q' ^ + q»2 -r qasi + qs,2 + q3 + 20 q'3 + q4 + q5 = 1 The content of oligomers B2: <3e 1 53 q'2 *= qnl = <3"2 = 53 = q'3 = 94 = <35 = 0 is 2.5 %f determined by chromatographic analysis.

The crystallisation point is below -400 c. The 25 viscosity at 20°C is 6.5 cP and the relative density 1.006.

Weight composition Start of crystallization Product A^ 100 +3°C Product Ai 90 -5*C Product A 2 + B2 10 Product A^ 80 -10°C Product A2 + B2 20 Product hi Product A2 + 2>2 50 50 -30 0 C

Claims (17)

1. A composition comprising two oligomers and A2 such that: A^ is an isomer or a mixture of isomers of 5 formula: 0 O )-CH. 0~ch2-—(3f CH r® n2 with ni and n2 = 0, 1 ~t such that «i + n2 is no greater than 3 and R denotes hydrogen? and A2 is an isomer or a mixture of isomers of the 10 same general formula as Ai except that R denotes methyl and n^ and n2 are replaced by qi and q2 which have the same meaning, as ni and n2 respectively, at least one of the oligomers A]_ and A2 comprising an isomer which has three benzene rings. 15

2. A composition according to Claim 1, in which nl ~ n2 ~ 0 an(^ q^ + q2 = 1.

3. A composition according to Claim 1, in which nl +"2=1 and qi - q2 = 0.

4. A composition according to Claim 1, in which 20 ni + n2 ~ 1 and + q2 = 1.

5. - A composition according to any one of the preceding claims which additionally comprises at least one oligomer Blf, B2 and B3 such that - 25 - is an isomer or a mixture of isomers of formula; where: n8l» nJ!,l anc^ n4 = 1 and 2 5 n~2' n^2' n3' n"3 arx<^ n5 ~ 0 an(^ 1 such that n'j + n*S + ng2 * n"#2 + n3 + n'3 + n4 + n5 no greater than 2; Ri^ and R2 denote hydrogen; B2 is an isomer or a mixture of isomers of the 10 same general formula as except that Ri and R2 denote methyl and the symbols n are replaced by symbols q which have the same meaning as the respective symbols n, B3 is an isomer or a mixture of isomers of the same general formula as except that Ri and R2 are 15 different and denote hydrogen or methyl and the symbols n are replaced by syrabols r ?*°hich have the same meaning as the respective symbols n. - 26 -

6. A composition according to Claim 5, which comprises the oligomers A2 and 83 -

7. A composition according to Claim 5, which comprises the oligomers A]_, Ajf B^, B2 and B3. 5

8. A composition according to Claim 1 substantially as described in Example 1 or 5.

9. Process for preparing the mixture of A^_ as defined in Claim 1 and Bl as defined in Claim 5 in which1 a) chlorine is reacted with a mixture of benzene 10 and toluene by a radical reaction in the presence of a free radical generator, b) the unreacted toluene is removed, c) the product obtained is subjected to the action of an inorganic halide or of an inorganic acid. 15

10. Process for preparing a mixture of A-j_ as defined in Claim 1 and B2 as defined in Claim 5 in which: a) chlorine is reacted with toluene by a radical reaction in the presence of a free radical generator, b) the unreacted toluene is removed, 20 c) bensene is added and the product obtained is subjected to the action of an inorganic halide or of an inorganic acid.

11. Process for preparing a composition as claimed in any one of Claims 1 to 8 in which benzyl chloride is 25 brought into contact with benzene and toluene in the presence of an inorganic halide or of an inorganic acid. - 27 -

12. Process for preparing a composition as claimed in any one of Claims 1 to 8 in which: a) chlorine is reacted with toluene and benzene ( in the presence of a free radical generator, 5 b) benzylidene chloride is removed, c) the product obtained is subjected to the action of an inorganic halide or of an organic acid.

13. Process for preparing a composition as claimed in any one of Claims 1 to 8 in which; 10 a) chlorine is reacted with toluene in the presence of a free radical generator, b) benzylidene chloride is removed, c) benzene is added and the product obtained is subjected to the action of an inorganic halide or of an 15 inorganic acid

14. Process for preparing a composition as claimed in Claim 7 in which: a) chlorine is reacted with a mixture of benzene and toluene by a radical reaction in the presence of a free 20 radical generator, b) the above reaction product is then subjected to the action of an inorganic halide or of an inorganic acid. n

15. Process acceding to any one of Claims 9 to 14 25 substantially as hereinbefore described. - 28 -

16. IS. A mixture wherever prepared by a process as claimed in any one of Claims 9 to 15.

17. The use of a composition as claimed in any one of Claims X to 8 and 16 as a dielectric fluid. Dated this the 19th day of February, 1990 F. R. K2LLY & GO. <• 1.1 »WUM, MWAAeitf,, 4 AGSNTS FOR THE JkPPJLICJyMTS