The present invention relates to a process for the production of isobutylbenzene from a vinylcyclohexene. In particular the invention relates to a two stage process for producing isobutylbenzene from a vinylcyclohexene having as its first stage a dismutation reaction.

Isobutylbenzene is a high value speciality chemical used, for example, as an intermediate in the preparation of analgesics. Conventionally, isobutylbenzene is produced industrially by the side chain alkylation of toluene with propylene using an alkali metal catalyst. The alkali metal catalyst can be a liquid potassium, a liquid potassium/sodium eutectic or an alkali metal supported on a diatomaceous earth as disclosed in for example US 3,449,455. The above process has a number of disadvantages when operated commercially since the alkali metal catalyst is (a) expensive, (b) inflammable and difficult to handle and (c) short lived owing to gum formation. In addition there is formed, as a byproduct, substantial quantities of n-butylbenzene which has to be separated subsequently from the isobutylbenzene.

A two stage process has now been devised which avoids the problems associated with the alkylation route and allows isobutylbenzene to be produced selectively. An important feature of this process as described herein is that a vinycyclohexene is used as a feedstock, in place of toluene and that in the first stage of the process the vinycyclohexene undergoes dismutation with an Isoolefin to produce an isobutenylcyclohexene, for example,

which can subsequently be converted to isobutylbenzene in the second stage.

Accordingly, the present invention provides a process for the production of an isobutylbenzene from a vinylcyclohexene and an isoolefin which process comprises

(1) in a first stage contacting the vinylcyclohexene and isoolefin with a dismutation catalyst under dismutation conditions to produce an isobutenylcyclohexene and another olefin.

(2) in a second stage contacting the Isobutenylcyclohexene produced in the first stage with a dehydroisomerisation catalyst at elevated temperature to produce the isobutylbenzene.

The first stage of the process described above is a dismutation reaction between a vinylcyclohexene and an isoolefin. If-the vinylcyclohexene used is a vinylcyclohexa-mono-ene then it is preferable to use 4-vinylcyclohexene as this is the most readily available. The cyclohexene ring of the vinylcyclohexene can be substituted with alkyl or aryl groups in which case substituted isobutenylcyclohexenes and ultimately substituted isobutylbenzenes are produced. A homodismutation product of the vinylcyclohexene can be used in place of the vinylcyclohexene itself when the isoolefin 2,3-dimethylbut-2-ene is used because In this case only a single product is produced in the dismutation reaction. For example when l,2-dicyclohex-4-enylethene is used the reaction proceeds according to the equation.

It is a feature of the first stage of the process described above that although the vinylcyclohexene posses two double bonds (one cyclic In the cyclochexene ring and one exocyclic outside the ring) it is only the exocyclic double bond which undergoes dismutation. This preference of the dismutation catalyst for exocyclic double bonds means that the vinylcylohexene can be carried using any vinylcyclohexene, i.e. a vinylcyclohexa- ono-ene, a vinylcyclohexa-di-ene or a vinycyclohexa-triene (i.e. a styrene or a stilbene). As regards the isoolefin, this has a formula R CH3

C = C. R ¹ CH3 where R and R^- are independently hydrogen or hydrocarbyl radicals. The hydrocarbyl radicals are suitably C]_ to Cg alkyl groups. Preferred isoolefins are isobutene (R=R^=H), 2,3-dimeth lbut-2-ene R-R^CH _β ), and 2-me hylbut-2-ene (R=H; ^• R ¹ -^), 2-methylpent-2-ene (R=H, Rl^t^) and ^' 2,4,4-trimethylpent-2-en (R=H, R ² =C ). The first stage of the process described above is catalysed by a dismutation catalyst. The dismutation catalyst is suitably a tungsten, molybdenum or rhenium containing catalyst. Preferably the dismutation catalyst Is rhenium heptoxide supported on alumina (UK 1,054,864) or alumina phosphated by a method described in our UK patent 1,414,488. Catalysts of this type may be prepared, for example, by impregnating the alumina or phosphated alumina with ammonium perrhenate and subsequently heating the impregnated material in air to convert the perrhenate to the oxide.

The rhenium containing catalysts in the form described above can be used to catalyse the dismutation reaction between the vinylcyclohexene and all the isoolefins disclosed above with the exception of isobutene. When isobutene is used as co-feed with the vinylcyclohexene little reaction occurs with catalysts comprising only rhenium heptoxide and alumina or phosphate alumina. The isobutene/vinycyclohexene dismutation reaction may be promoted,

however, by addition of an organometallic derivative of tin, lead, aluminium or germanium. Preferred promoters are organometallic derivatives of tin e.g. tetramethyl tin CH3) Sn, tetraphenyl tin CgH5 4S and the like. Promoted catalysts can also be used with the other isoolefins to improve reaction rates.

The promoter can be impregnated on to the catalyst at levels of up to 20% by weight or it can be introduced into the reactor at a low level with the vinylcyclohexene and isoolefin feedstocks.

As regards the reaction conditions under which the first stage is operated, it is preferable to work at a temperature in the range 0 to 90°C and at a pressure in the range atmospheric pressure to 50 bar. The contact time of the feedstocks on the catlayst preferably lie in the range 5 mins to 60 mins.

The product of the first stage of the process consists of an isobutenylcyclohexene stage embodiments is used, together with another olefin. The other olefin will be that which is the other dismutation product of the reaction and will depend on the * particular feedstock isoolefin used in the first -stage. For example, if the feedstock isoolefin is isobutene the other olefin produced will be ethylene.

The product o^ the first stage can either be fed directly to the second stage of the process or indirectly via a separation stage, where the isobutenylcyclohexene is separated from the other olefin prior to being fed to the stage stage. The first stage of the process may be carried out either batchwise or continuously.

In the second stage of the process, the direct or indirect product of the first stage is dehydroisomerised to an isobutylbenzene. The dehydroisomerlsation reaction is effected by contacting the direct or indirect first stage product at temperatures of ambient or above with a dehydroisomerlsation catalyst. Suitable dehydroisomerlsation catalysts include supported alkali metals e.g. potassium on alumina ,or supported Group VIII metals, such as Pd, Pt, Rh, 0s or Ir, on an alumina. The dehydroisomerisation catalyst can be prepared by any conventional

technique familiar to the skilled man. The loading of alkali metal or Group VIII metal on the support should be in the range 0.01 to 20% by weight.

As regards temperature of reaction this should be ambient or above.

The invention Is illustrated by reference to the following examples.

EXAMPLES OF STAGE 1 Example 1 51 g of 8-15 BSS mesh -alumina, obtained from calcining a commercially available boehmite alumina (CATAPAL SB from Vista) at 580°C, was impregnated with a 40 ml aqueous solution of 3.6 g ammonium perrhenate, evaporated to dryness, dried in vacuo at 110°C for 6 hours, and activated for 24 hours at 580°C in a steam of air. The catalyst so prepared was found to contain 5.5% by weight Re2θγ. A "U" tube steel reactor was charged with 60 ml of the catalyst. This operation was carried out in a glove box under a nitrogen atmosphere. The charged reactor was then installed, under a rigorous nitrogen blanket, on to a unit consisting of a feed tank, a pump, a drier charged with 200 ml of 3 molecular sieve, a treater charged with 200 ml of 2% sodium on potassium carbonate, a reactor sited in a heated fluidised alumina bath, a water cooled condenser, and a product tank. A homogeneous feed, consisting of 4-vInylcyclohexene and isobutene in the molar ratio 1:3, was pumped at 120 ml/h (LHSV=2) over the catalyst bed at 30°C with an operating pressure of 23.3 bar. The products were collected and analysed at regular Intervals by standard gas chromatographlc methods. The reaction conditions and results are given in Table I. Example 2 The process of Example 1 was repeated except that the catalyst was prepared from a commercially available -alumina (ACTAL I from Laporte). The reaction conditions and results are given in Table I. Example 3

The process of Example 1 was repeated except that the reactor was heated to 70°C. The reaction conditions and results are given

in Table I.

Example 4

The process of Example 1 was repeated except that the catalyst was prepared from a commercially available -alumina as 1 mm spheres (UM 708 CB from Universal Matthey Products). The reaction conditions and results are given in Table I.

Example 5

The process of Example 1 was repeated except that the catalyst was prepared from 35 g of a commercially available -alumina as 1 mm spheres (UM 708 GB from Universal Matthey Products) and impregnated with a 50 ml aqueous solution of 5 g ammonium perrhenate. The catalyst so prepared was found to contain 10.7% by weight Re2θy.

The reaction conditions and results are given in Table I.

Example 6 The process of Example 1 was repeated except that the catalyst was impregnated with tetramethyltin before use. The catalyst so prepared contained 18.5% by weight SnMe » The reaction conditions and results are given in Table I.

Example 7 The process of Example 6 was repeated except that the feed consisted of 4-vinylcyclohexene and isobutene in the molar ratio of

1:10. The catalyst contained 16.4% Sn e4. The reaction conditions and results are given in Table I.

Example 8 The process of Example 7 was repeated except that the reactor was heated to 57°C. The catalyst contained 18.0% SnMe4« The reaction conditions and results are given in Table I.

Example 9

The process of Example 7 was repeated with a catalyst containing 5.0% SnMe4« The reaction conditions and results are given in Table I.

Example 10

The process of Example 9 was repeated except that the LHSV was increased to 4. The reaction conditions and results are given in Table I.

Example 11

The process of Example 9 was repeated except that the LHSV was increased to 10. The reaction conditions and results are given in

Table I. Example 12

The process of Example 7 was repeated with a catalyst containing 3.0% SnMe4» The reaction conditions and results are given in Table I.

Example 13 The process of Example 7 was repeated with a catalyst containing 1.0% SnMe4« The reaction conditions and resuts are given in Table I.

TABLE I

VCH = 4- d.nlycyclohexene IBCH = 4-isobutenylcyclohe_ene DCHE = l,2-dicyclohex 4-enylethene

Example 14

70 g of a commercially available alumina (PURALOX SG from Condea) was digested for 6 hours at 80°C in 250 ml of an aqueous solution containing 5 g of ammonium phosphate dibasic [(NH )2HPO4] . Distilled water was added as necessary to keep the alumina covered. The resultant slurry was filtered and washed with 2 litres of distilled water. This material was dried at 110°C overnight and then calcined at 580°C for 16 hours in a current of air.

38 g of the phosphated alumina was subsequently impregnated with a 50 ml aqueous solution of 1.30 g ammonium perrhenate, evaporated to dryness, dried in vacuo at 120°C for 6 hours, and activated for 24 hours at 580°C in a stream of dry air. The catalyst so prepared was kept at ambient temperature under an inert atmosphere. 5.9 g of the catalyst was charged into a glass reactor under a blanket cover of nitrogen. To this was added 17 g of feed and the reactor was sealed. The feed consisted of 4-vinylcyclohexene and 2-me hyl-2-pentene in the molar ratio of 1:4. After 120 minutes, at ambient temperature, the products were analysed by standard gas chromatographic methods. The results indicated that 82.2% of the

4-vinylcyclohexene was converted affording dismutation products with the following selectivities 3.8% cis-4-n-butenylcyclohexene 33.0% 4-isobutenylcyclohexene, 58.8% trans-4-n-butenylcyclohexene, and 4.4% 1,2-dicyclohex-4-enylethene. Example 15

3.1 g of the catalyst prepared in Example 14 was charged into the reactor. 10.3 g of a feed, consisting of 4-vinylcyclohexene and 2-methyl-2-butene in the molar ratio of 1:4, was added and the reactor sealed. After 90 minutes, at ambient temperature, the products were analysed and the results were as follows; 91.2% of the 4-vinylcyclohexene was converted affording dismutation products with the following selectivities 2.2% iso-4-propenylcyclohexene, 75.0% trans-4-propenyl cyclohexene, 17.3% 4-isobute ylcyclohexene and 5.7% 1,2-dicyclohex-4-enylethene. Example 16

10

58 g of 1/16" extrudate -alumina, obtained from calcining the commercially available boehmite alumina (PURAL NG from Condea) at 580°C, was impregnated with a 80 ml aqueous solution of 8.64 g ammonium perrhenate, evaporated to dryness, dried in vacuo at 110°C for 6 hours at 580°C in a stream of dry air. The catalyst so prepared was found to contain 10.4% by weight Re2θy.

14.5 g of the catalyst was charged into the reactor with 29 g of a feed consisting of styrene and 2-methyl-2-pentene In the molar ratio of 1:25. The reactor was sealed, and after 90 minutes, at ambient temperature, the products were analysed. The results were as follows; 69.9% of the styrene was converted affording dismutation products with the following selectivities 7.5% cis-n-butenylbenzene, 3.3% isobutenylbenzene, 80.3% trans-n-butenylbenzene, 0.9% cis-stilbene, and 7.9% trans-stilbene. Example 17

35 g of a commercially available -alumina as 1 mm spheres (UM 708 CB from Universal Matthey Products) was Impregnated with a • 50 ml aqueous solution of 5 g ammonium perrhenate, evaporated to dryness, dried in vacuo at 110°C for 6 hours, and activated for 24 hours at 580°C in a stream of air. The catalyst so prepared was found to contain 10.7% by weight Re2θy.

6 g of the catalyst was charged into the reactor with 22.8 g of a feed consisting of 4-vinylcyclohexene and 2,4,4-trimethyl-2-ρen- tene In the oalr ratio of 1:2. The reactor was sealed, and after 90 minutes, at ambient temperature, the products were analysed. The results were as follows, 27% of the 4-vlnylcyclohexene was converted affording dismutation products with the following selectivity 16.1% 4-isobu enylcyclohexene, 5.4% 2-cyclohex-4-enyl-3,3-dimethylbut-1- ene, 78.4% l,2-dicyclohex-4-enylethene. Example 18

51 g of 8-15 BSS ech -alumina, obtained from calcining a commercially available boehmite alumina (CATAPAL SB from Vista) at 580°C, was Impregnated with a 40 ml aqueous solution of 3.6 g ammonium perrhenate, evaporated to dryness, dried in vacuo at 110°C for 6 hours, and activated for 24 hours at 580°C in a stream of

11

air. The catalyst so prepared was found to contain 5.5% by weight

R ^β 2θ7.

4.4 g of the catalyst was charged into the reactor with 4.6 g of a feed consisting of 4-vinylcyclohexene and 2,3-dimethyl-2-butene in the molar ratio of 1:3. The reactor was sealed, and after

60 minutes, at ambient temperature, the products were analysed. The results were as follows, 81.7% of the 4-vinylcyclohexene was converted affording dismutation products with the following selectivity 78.9% of 4-isobutenylcyclohexene and 21.1% 1,2-dicyclo- hene-4-enylethene. Example 19

The reaction apparatus comprised a feed tank, a pump, a feed treater containing 2% by weight sodium on potassium carbonate tablets, a cylindrical vertical reactor fitted with a water cooled jacket and centrally situated thermocouple and a product tank. P ^' rior to use the apparatus was flushed with nitrogen .

The reactor was charged with 5 ml of catalyst. The catalyst used was prepared in the following way: 30 g of 8-15 mesh -alumina obtained from calcining Condea SB boehmite alumina at 580°C was -impregnated with a 30 ml aqueous solution of 2.1 g of ammonium perrhenate, evaporated to dryness, dried in vacuo at 110°C for 6 hours and activated for 24 hours at 580°C in a stream of dry air. The catalyst so prepared was found to contain 6.2% by weight Re2θy. The feed tank was charged with dry 4-vinylcyclohexene (49.5% purity; 71 ml) and dry 2-methylρentene-2 ( 98.5% purity; 200 ml). The feed was pumped at 30 ml/hour over the catalyst bed at 14°C, with an operating pressure of 1.2 barg.

Analysis of the collected products for the period 4 hours to 5 hours showed a 4-VCH conversion of 86.4%, a ratio of IBCJ/NBCH=0.65 and a ratio of hexene 3/IBCH=0.82. Example 20

The reaction apparatus was as previously. The catalyst was prepared as In Example 1.

The reactor was charged with 11.3 mis of catalyst. The feed tank was charged wtih dry 4-vinylcyclohexene and dry

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2,4,4-trimethylpentene-2 in a molar ratio of 1:10. The feed was pumped at 20-25 ml/hour over the catalyst bed, initially at 17°C, after 19 hours the temperature was raised to 50°C.

Analysis of the collected products for the period 1-2 hours to 15-16 hours and 19-20 hours are shown in Table 2. Example 21

The reaction apparatus used was as previously. The catalyst was prepared as in Example 1 and then impregnated with 5% w/w tetramethyltin. a The reactor was charged with 20 ml of the tetramethyltin

Impregnated catalyst. The feed tank was charged with dry 4-vinyl- cyclohexene (35 ml) and dry 2,4,4-trimethylpentene-2 (420 ml). The feed was pumped over the catalyst bed at a rate of 40 ml/hour at 50°C at an operating pressure of 0.4 barg. Analysis of collected products for the periods 1-2 hours and 4-5 hours are shown in Table 2.

TABLE 2

14

Example 22

The process of Example 18 was repeated except that the catalyst was impregnated with tetramethyltin before use and the feed was 27 g of isobutene and 9.6 g of l,2-dicyclohex-4-enylethene. The catalyst so prepared contained 6.4% by weight SnMe4» After 30 minutes reaction the products were analysed. 13.7% of the l,2-dicyclohex-4-enylethylene was converted affording dismutation products with the following seectivities 54% 4-isobutenylcyclohexene and 4.6% 4-vinylcyclohenene. Example 23

13.1 g of the catayst prepared in Example 17 was charged into a steel reactor under a blanket of nitrogen. To this was added 8.4 g of l,2-dicyclohex-4-enyl ethylene and 27 g of isobutene. The reactor was sealed and rocked. After 1 hour at ambient temperature, the products were analysed. 3.7% of the l,2-dicyclohex-4-vinyl ethylene was converted affording dismutation products with the following selectivities 31.3% 4-iso'buten ϊcyclohexene and 69.% 4-vinylcyclohexe'ne. Example 24 EXAMPLE OF SECOND STAGE

A palladium on alumina catalyst (0.5% wt Pd) was packed Into a quartz tube in a vertically mounted furnace equipped with a temperature controller. The catalyst was heated from room temperature to 550°C under a stream of nitrogen (10 litres/hour) and maintained at this temperature for 12 hours. The catalyst was then cooled to 350°C. The nitrogen flow was reduced to 0.98 litres/hour, and degassed 4-isobutenylcyclohexene passed over the catalyst in vapour form. After contact with the catalyst, the vapour/nitrogen mixture was cooled and any condensable products trapped by means of a water condenser. Analysis of the condensed product obtained after 1 hour (using GLC techniques) showed a 100% conversion of 4-isobutenylcyclohexene with a 95% seectivity to isobutylbenzene.