This invention relates to a process for the preparation of aromatic hydrocarbons with cyclobutene rings fused thereto.

Aromatic hydrocarbons with cyclobutene rings fused thereto are useful in the preparation of monomers, which are useful in the preparation of high performance polymers. These high performance polymers are useful as films, moldable compositions, adhesives, and in the preparation of composites.

Processes for the preparation of aromatic hydrocarbons with cyclobutene rings fused thereto suf¬ fer from two major problems. The first problem is that such synthesis involves complex multi-step sequences. Furthermore, some processes result in low yields of the desired product.

What is needed is a process for the prepara¬ tion of cyclobutene-substituted aromatic hydrocarbons

which is simple and results in high yields of said hydrocarbons.

The invention is a process for the preparation of an aromatic hydrocarbon with a cyclobutene ring fused to the aromatic hydrocarbon which comprises, dissolving an ortho al yl halomethyl aromatic hydrocarbon in an inert solvent and pyrolyzing the solution of ortho-alkyl halomethyl aromatic hydrocarbon in the inert solvent under conditions such that the ortho-alkyl and the halomethyl substituents form a cyclobutene ring thereby forming an aromatic hydrocarbon having a fused cyclobu¬ tene ring. The ortho-alkyl group having the structural formula (R' ) ₂ -CH-, where R' is separately in each occurance hydrogen or a C-._ ₂₀ alkyl, preferably hydrogen or C, - alkyl, and most preferably hydrogen.

This process results in a one-step preparation of αyclobutener-aubs.ti.tuted- aromatic hydrocarbons in which the hydrocarbons are prepared in high yields.

The starting materials for this process include any aromatic hydrocarbon which has a (R' ) ₃ -CH- alkyl group and a halomethyl group ortho to one another. Pre¬ ferred aromatic hydrocarbons include benzene, naphtha¬ lene, phenanthracene, anthracene, biphenyl, binaphthyl, or a diaryl alkane. More preferred aromatic hydrocarbons include benzene, naphthalene, biphenyl, binaphthyl, or a diphenylalkane. The most preferred aromatic hydrocarbon is benzene.

The R' substituent of the (R ¹ ) ₂ ~CH- group is preferably hydrogen or a C- ₃ alkyl and more preferably hydrogen. The halomethyl hydrocarbon is preferably bromomethyl or chloromethyl.

The aromatic hydrocarbon can be further substi¬ tuted with one or more of the following substituents: a carbonyloxyhydrocarbyl, oxycarbonylhydrocarbyl, carboxy- a ide, carboxy, carbonylhalo, cyano, nitro, hydroxy, hydrocarbyloxy, or halo group. It is preferable that the aromatic hydrocarbon be substituted with one or more of such substituents. Preferred substituents are carbonyl¬ oxyhydrocarbyl, oxycarbonylhydrocarbyl, carboxamide, car¬ boxy, carbonylhalo, nitro, or hydrocarbyloxy. More pre¬ ferred substituents are carbonyloxyhydrocarbyl, oxycar- bonylhydrocarbyl, carboxamide or oxyhydrocarbyl. Even more preferred substituents are the carbonyloxyalkyl hydrocarbons with carbonyloxymethyl being most preferred.

In one preferred embodiment wherein the aro¬ matic hydrocarbon is benzene the starting materials cor- respond to the following formula

CH

CH ₂ X

( ² ).

wherein

R is separately in each occurrence hydrogen or ^c ι- ₂ o ^alk y ^{1 ; and}

R is separately in each occurrence carbonyl- oxyhydrocarbyl, oxycarbonylhydrocarbyl, carboxamide, carboxylate, carbonylhalo, cyano, nitro, hydroxy, hydrocarbyloxy or halo;

X is chloro or bromo; and a is an integer of between 0 and 4 inclusive.

Examples of preferred starting reactants include: ortho-methylchloromethylbenzene, ortho-ethylchloromethyl- benzene, ortho-propy chloromethylbenzene, ortho- -butylchloromethylbenzene, ortho-pentylchloromethyl- benzene, ortho-hexylchloromethylbenzene, 3- or 4-methoxy ortho-methylchloromethylbenzene, 3- or 4-methoxy ortho- ethylchloromethylbenzene, 3- or 4-methoxy ortho-propyl- chloromethylbenzene, 3- or 4-methoxy ortho-butylchloro¬ methylbenzene,. 3- or__4-ethoxy. benzene, 3- or 4-ethoxy ortho-ethylchloromethylbenzene, 3- or 4-ethoxy ortho-propylchloromethylbenzene, 3- or

4-ethoxy ortho-butylchloromethylbenzene, 3- or 4-propoxy ortho-methylchloromethylbenzene, 3- or 4-propoxy ortho- -ethylchloromethylbenzene, 3- or 4-propoxy ortho- -propylchloromethylbenzene, 3- or 4-propoxy ortho-butyl- chloromethylbenzene, 3- or 4-butoxy ortho-methylchloro- methylbenzene, 3- or 4-butoxy ortho-ethylchloromethyl¬ benzene, 3- or 4-butoxy ortho-propylchloromethylbenzene, 3- or 4-butoxy ortho-butylchloromethylbenzene, 3- or 4-pentoxy ortho-methylchloromethylbenzene, 3- or 4-pen- toxy ortho-ethylchloromethylbenzene, 3- or 4-pentoxy

ortho-propylchloromethylbenzene, 3- or 4-hexoxy ortho- methylchloromethylbenzene, 3- or 4-hexoxy ortho-ethyl¬ chloromethylbenzene, 3- or 4-hexoxy ortho-propylchloro- methylbenzene, 3- or 4-hexoxy ortho-butylchloromethyl- benzene, methyl 3,4-ortho-methylchloromethylbenzoate, methyl 3,4-ortho-ethylchloromethylbenzoate, methyl 3,4- ortho-propylchloromethylbenzoate, methyl 3,4-ortho- butylchloromethylbenzoate, ethyl 3,4-ortho-methylchlo- romethylbenzoate, ethyl 3,4-ortho-ethylchloromethylben- zoate, ethyl 3,4-ortho-propylchloromethylbenzoate, ethyl 3,4-ortho-butylchloromethylbenzoate, propyl 3,4-ortho- methylchloromethylbenzoate, propyl 3,4-ortho-ethylchlo- romethylbenzo te, propyl 3,4-ortho-propylchloromethyl- benzoate, propyl 3,4-ortho-butylchloromethylbenzoate, butyl 3,4-ortho-methylchloromethylbenzoate, butyl 3,4- ortho-ethylchloromethylbenzoate, butyl 3,4-ortho-pro- pylchloromethylbenzoate, butyl 3,4-ortho-butylchloro- methylbenzoate, pentyl 3,4-ortho-methylchloromethylben- zoate, pentyl 3,4-ortho-ethylchloromethylbenzoate, pentyl 3,-4-orthQ-pr.αμylchloromethylbenzoate _r pentyl 3,4-ortho— -butylchloromethylbenzoate, hexyl 3,4-ortho- -methylchloromethylbenzoate, hexyl 3,4-ortho-ethylchloro- methylbenzoate, hexyl 3,4-ortho-propylchlorome hylbenzoate, hexyl 3,4-ortho-butylchloromethylbenzoate, benzyl 3,4- ortho-methylchloromethylbenzoate, benzyl 3,4-ortho-

-ethylchloromethylbenzoate, benzyl 3,4-ortho-propylchloro- methylbenzoate, benzyl 3,4-ortho-butylchloromethylbenzo- ate, phenyl 3,4-ortho-methylchloromethylbenzoate, phenyl 3,4-ortho-ethylchloromethylbenzoate, phenyl 3,4-ortho- propylchloromethylbenzoate, and phenyl 3,4-ortho-butyl- chloromethylbenzoate. For the preferred starting reactants, the butyl groups are selected from normal, iso or secondary butyl groups, but not tertiary butyl groups.

In one even more preferred embodiment, the starting material is methyl 3,4-ortho-methylchlorometh- ylbenzoate.

The product prepared by the process of this invention is an aromatic hydrocarbon with a cyclobutene ring fused to one of the rings of the aromatic hydrocar¬ bon. The preferred aromatic hydrocarbons are described hereinbefore. The product can be substituted as described hereinbefore.

In one preferred embodiment, wherein the aromatic hydrocarbon is benzene the products correspond generally to the formula

(R ¹ ) ₂

(R ² )

wherein R 1, R2 and a are as defi.ned hereinbefore.

Among preferred classes of aromatic hydrocar¬ bons with, cyclobutene rings fused thereto include cyclo- butabenzene (bicyclo(4.2.0)octa-l ₇ 3,5,7-tetraene) 1-alkyl- cyclobutabeπzenes, hydrocarbyl cyclobutabenzoate, hydro- carbyl 1-alkylcyclobutabenzoate, hydrocarboxy cyclobuta- benzene, hydrocarboxy 1-alkylcyclobutabenzene, cyclobuta- benzamides, and 1-alkylcyclobutabenzamides. Even more preferred classes include alkyl cyclobutabenzoates, cyclo- butabenzamides, and alkoxy cyclobutabenzenes♦

Examples of some preferred aromatic hydrocar¬ bons with fused cyclobutene rings include methylcyclobu- tabenzene, ethylcyclobutabenzene, propylcyclobutabenzene, butylcyclobutabenzene, pentylcyclobutabenzene, hexylcyclo- butabenzene, benzylcyclobutabenzene, phenylcyclobutaben¬ zene, methyl cyclobutabenzoate, ethyl cyclobutabenzoate, propyl cyclobutabenzoate, butyl cyclobutabenzoate, pentyl cyclobutabenzoate, hexyl cyclobutabenzoate, benzyl cyclo¬ butabenzoate, phenyl cyclobutabenzoate, methoxycyclobuta- benzene, ethoxycyclobutabenzene, propoxycyclobutabenzene, butoxycyclobutabenzene, pentoxycyclobutabenzene, hexoxy- cyclobutabenzene, benzoxycyclobutabenzene, phenoxycyclo- butabenzene, N-methylcyclobutabenzamide, N-ethylcyclobu- tabenzamide, N-propylcyclobutabenzamide, N-butylcyclobu- tabenzamide, N-pentylcyclobutabenzamide, N-hexylcyclobu- tabenzamide, N-benzylcyclobutabenzamide, and N-phenylcy- clobutabenzamide.

Examples of even more preferred aromatic hydro¬ carbons.,with cyclobenzene rings, fused,thereto, are methyl cyclobutabenzoate, ethyl cyclobutabenzoate, propyl cyclo¬ butabenzoate, pentyl cyclobutabenzoate, and hexyl cyclo¬ butabenzoate.

In one of the most preferred embodiments the aromatic hydrocarbon with a cyclobutene ring fused thereto is methyl cyclobutabenzoate.

Hydrocarbyl means herein an organic moiety containing carbon and hydrogen atoms. The term hydro¬ carbyl includes the following organic moieties: alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, ali- phatic and cycloaliphatic aralkyl and alkaryl. Ali¬ phatic refers herein to straight- and branched-, and

saturated and unsaturated, hydrocarbon chains, that is, alkyl, alkenyl or alkynyl. Cycloaliphatic refers herein to saturated and unsaturated cyclic hydrocarbons, that is cycloalkenyl and cycloalkyl. The term aryl refers herein to biaryl, biphenylyl, phenyl, naphthyl, phenanthranyl, anthranyl and two aryl groups bridged by an alkylene group. Alkaryl refers herein to an .alkyl-, alkenyl- or alkynyl-substituted aryl substituent wherein aryl is as defined hereinbefore. Aralkyl means herein an alkyl, alkenyl or alkynyl group substituted with an aryl group, wherein aryl is as defined hereinbefore. ^c _ι _2o ^a lkyl includes straight- and branched-chain methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, penta- decyl, hexadecyl, heptadecyl, octadecyl, nonadecyl and eicosyl groups.

Cycloalkyl refers to alkyl groups contain¬ ing one, two, three or more cyclic rings. Cycloalkenyl refers,,to mono-, di.--and...polycyclic.-groups containing one or more double bonds. Cycloalkenyl also refers to cycloalkenyl groups wherein two or more double bonds are present.

Hydrocarbylcarbonyloxy refers to a substitu¬ ent in which a hydrocarbyl moiety is bonded to a carbonyl moiety which is further bonded to an oxygen atom and includes substituents which, correspond to the formula

R 2^C"O-

Hydrocarbylcarbonyl refers herein to a substi- tuent which is a hydrocarbyl moiety bonded to a carbonyl moiety and includes substituents which correspond to the formula

Hydrocarbyloxycarbonyl refers herein to a substituent in which a hydrocarbyl moiety is bonded to an oxygen atom which is further bonded to a carbonyl moiety and includes substituents which correspond to the formula

2 "

R 0C-

The term carboxamide refers to a substitu- enr which corresponds ^' to the formula

O

¹¹ 2 -CN(R^).

2 wherein R is a hydrocarbyl moiety.

The term carbonylhalo refers to a substituent which corresponds to the formula

0 tr

-CX

wherein X is a halogen.

The term carboxy refers herein to a substi¬ tuent which corresponds to the formula

O

II

-COH

The term hydrocarbyloxy refers herein to a substituent which corresponds to the formula

R ² -0-

₂ wherein R is a hydrocarbyl moiety...,., . ..._.

In the process of this invention the ortho alkyl halomethyl aromatic hydrocarbon is dissolved in an inert solvent, and thereafter pyrolyzed to form a cyclobutene ring. Dissolving the aromatic hydrocarbon in a suitable solvent is critical to the invention, as this allows the preparation of the aromatic hydrocarbon with the cyclobutene ring fused thereto in high yields.

In general suitable solvents are those which dissolve the ortho alkyl halomethyl aromatic hydrocarbons and which are stable at pyrolysis conditions. Preferable

solvents include benzene, substituted benzenes, biphenyl or substituted biphenyls. Preferred solvents are benzene, toluene, xylene, chlorobenzenes, nitrobenzenes, alkylben- zoates, phenylacetates, or diphenyl cetates. The most preferred solvent is xylene.

In general the ratio of solvent to the starting material, the ortho-alkyl halomethyl aromatic hydro¬ carbon, is such that the starting material is dissolved and results in an acceptable yield of products. It is preferable that the ratio of solvents to starting mate¬ rial be at least 2:1. Preferable solvent to starting material ratios are between 2:1 and 10:1; and more preferred, between 3:1 and 4:1.

During the pyrolysis the starting material dissolved in solvent is exposed to temperatures at which the ortho-alkyl halomethyl aromatic hydrocarbon eliminates a hydrogen halide and forms a cyclobutene ring. Suitable temperatures are.-those at. which -this takes- place. Preferable temperatures are 550°C or greater. More preferred temperatures are between 550°C and 750°C, with between 700°C and 750°C being most preferred.

The pyrolysis can take place at any pressure at which good yields of the aromatic hydrocarbons with cyclobutene rings fused thereto are prepared. Preferable pressures are between 760 mm and 10 mm of mercury (101.3 and 1.3 kPa). More preferred pressures are between 25 mm and 75 mm of mercury (3.3 and 10.0 kPa), with between 25 mm and 35 mm of mercury (13.3 and 4.7 kPa) being most preferred.

In one preferred embodiment the pyrolysis takes place by flowing a solution of the ortho alkyl halomethyl aromatic hydrocarbon through a hot tube reac¬ tor at the pyrolysis temperatures. In this embodiment is preferred to pack the hot tube with a packing material. Any packing material which is inert to the reactants and stable to the reaction conditions is suitable, examples include quartz chips and stainless steel helices.

The product can be recovered by distillation of the materials after pyrolysis. In the embodiment wherein a low boiling solvent is used, the solvent comes off in the first cut of a distillation while the product comes off in the second cut. The starting material is usually left as a residual material in the distillation pot and can thereafter be recycled. When high boiling solvents such as biphenyl, substituted biphenyls or dipJaenylacetates are used, the product is distilled out and the starting material left in the solvent is recycled.,

This process generally results in the prepa¬ ration of cyclobutene fused aromatic hydrocarbons with a yield of about 40 percent, in more preferred embodi¬ ments the yield is about 50 percent.

The following examples are included for illus- trative purposes only, and do not limit the scope of the claims or the invention.

Example 1 - Pyrolysis of methyl 3-(chloromethyl)- -4-methylbenzoate

The experimental setup is a quartz tube packed with quartz chips. The central portion of the. tube is placed in a furnace. A 250 millimeter portion of the tube above the furnace serves as a preheating zone and the temperature in the middle of such preheating zone is between 250°C and 300°C. Attached to the top of the tube is an addition funnel. Attached to the bottom portion of the tube are cold traps and a means for pulling a vacuum on the tube. Methyl 3-(chloromethyl)-4-methylbenzoate (50 g) is dissolved in 200 g of ortho xylene and placed in the addition funnel. The furnace is heated up to 730°C. A vacuum pump is turned on and pressure is adjusted to- 25 mm of mercury (3.3 kPa). The solution of methyl 3-(chloromethyl)-4-methylbenzoate is added drop- wise for a period of 1 hour and 15 minutes. Product and unreacted starting material are collected in cold traps. The pyrolytic tube is flushed with 200 ml of acetone after a cooling down period. The acetone solution is combined with the ortho-xylene solution collected in the cold traps. Acetone and ortho-xylene are distilled off with a 16-inch Vigreaux column under normal pressure. When most of the ortho-xylene is distilled, the system is brought to 0.5 mm mercury (67 Pa) and 15.5 g of pure methyl 3,4-cyclobutabenzoate is collected at 61°C. The residue left in the distillation pot is methyl 3-(chloromethyl)-4-methylbenzoate, 23 g.

Experimental Procedure Examples 2-12 A quartz tube packed with quartz chips is placed in an electric furnace such that a 120 mm portion

above the furnace serves as a preheating zone, the tem¬ perature of which is 250°C. At the top of the quartz tube is inserted an addition funnel. The quartz tube is connected at the bottom to cold traps and a vacuum pump or water aspirator.

A furnace is heated to the desired temperature as indicated by the thermal couple inside a thermal well extended to the middle of the heated zone. Vacuum is then applied. The solution in the addition funnel is then added. The products and unreacted starting material are collected by the cold traps. Product yields are determined by gas chromatography. The material in the addition funnel is the starting material dissolved in ortho-xylene or toluene.

Examples 2-5

In Examples 2-5 the ratio of solvent to starting material,. s.varied—-The.. esults..are...Gontai-ned--in. Table I. Table I shows that the pyrolysis of methyl 3-(chloromethyl)- -4-methylbenzoate using a solvent to starting material ratio of between 21 and 4 results in good selectivity and yield. The selectivity and material balance goes down when the ratio of solvent to starting material is only 2.

TABLE I

Addition ²

Temp Diluent ¹ Rate Materia

Experiment <°C) Substrate ml/min. Conversion ³ Selectivity ⁴ Yield ⁵ Balance

2 730 21.0 2.5 57 79 45 89

3 725 5.5 3.0 46 70 32 86

4 725 4.0 3.0 45 69 31 88

5 730 2.0 2,5 66 55 37 71

¹ Ratio of diluent (solvent) to substrate.

² Addition rate of diluent and substrate to the pyrolysis tube.

³ Conversion refers to the mole percent of reactants converted to products and by-products

⁴ Selectivity refers to the mole percent of the desired product recovered compared to the total products and by-products.

⁵ Yield refers herein to mole percent of the desired product compared to the total reac¬ tants fed.

⁶ Material balance is the mole percent of the unreacted reactant and desired product com¬ pared to the total reactants fed to the reactor.

Examples 6-8

The pressures were varied for the pyrolysis of methyl 3-(chloromethyl)-4-methylbenzoate. The results are contained in Table II. Table II demonstrates that lower reaction pressures result in better yields of product... '

TABLE II

Addition ²

Pressure Temp Diluent ¹ Rate Materia

Experiment mmHg (kPa) (°C) Substrate ml/min. Conversion ³ Selectivity ⁴ Yield ⁵ Balance

6 25 (3.3) 730 21 2.5 57 79 45.0 89.0

7 150 (20.0) 700 24 2,5 51 46 23.5 72.0

8 150 (20.0) 715 90 2.5 70 40 28.0 58.5

¹ Ratio of diluent (solvent) to substrate.

² Addition rate of diluent and substrate to the pyrolysis tube.

³ Conversion refers to the mole percent of reactants converted to products and by-product

⁴ Selectivity refers to the mole percent of the desired product recovered compared to the total products and by-products.

⁵ Yield refers herein to mole percent of the desired product compared to the total reac¬ tants fed.

⁶ Material balance is the mole percent of the unreacted reactant and desired product com¬ pared to the total reactants fed to t e reactor.

Examples 9-12 - Pyrolysis of 2-chloromethyl-l-methyl- benzene and methyl 3-(halomethyl)-4- -methylbenzoate

In Examples 9-12, 2-chloromethyl-l-methylben- zene and methyl 3-(chloromethyl)-4-methylbenzoate are pyrolyzed. The results are contained in Table III.

TABLE III

Temp ^Pr f i!g ^re Materia

Experiment Reactant °C (kPa) Conversion ¹ Selectivity ² Yield ³ Balance

Cl 9 710 25-35 57 65 37.0 80

(3.3-4.7)

Cl 10 710 25-35 42 63 26.5 85

(3.β-4.7)

C0 ₂ CH ₃

Cl

11 700 15Q-175 89 34 30.0 41

(20.p-23.3)

Cl

12 700 150-175 51 46 23.5 72

(20.P-23.3)

C0 ₂ CH ₃

¹ Conversion refers to the mole percent of reactants converted to products and by-products

² Selectivity refers to the mole percent of the desired product recovered compared to the total products and by-products.

³ Yield refers herein to mole percent of the desired product compared to the total reac- tants fed.

Λ

⁴ Materιal balance is the mole percent of the unreacted reactant and desired product com- pared to the total reactants fed to the reactor.