TECHNICAL FIELD

The invention relates generally to the synthesis of substituted cyclopentadienes and more specifically to substantial improvements in a process for making alkyl- substituted cyclopentadienes from cyclopentenones by reacting the cyclopentenone with a Grignard reagent followed by the acidification and dehydration of the resulting tertiary alcohol with a carboxylic acid.

BACKGROUND

Alkyl-substituted cyclopentadienes are useful as monomers (e.g., for production of ethylene-propylene-diene terpolymers) and in forming metallocenes of transition metals such as titanium, zirconium and hafnium. Such metallocenes in turn are useful components of olefin polymerization catalysts, as is known in the art.

The synthesis of l-methyl-3-alkylcyclopentadienes by the reaction of 3-methyl-2- cyclopentene-1-one with alkyl Grignard reagents such as methyl, ethyl or isopropyl magnesium halides, followed by alcohol formation and dehydration using strong acids such as HC1 or p-toluene sulfonic acid is described in the literature. These processes give a 50/50 mixture of endo and exo isomers. The exo isomers are not useful in forming metallocenes. Thus when such isomer mixtures are used in making metallocenes, the yield of metallocene is less than 50% .

U. S. Pat. No. 5,434,324 describes a process which favors formation of the desired endo isomers. In the preferred mode of conducting the process, a cyclopentenone is slowly added to an alkyl magnesium halide in an inert solvent. After keeping the reaction mixture at -10° to l5°C with agitation for a suitable reaction period, the reaction mixture at ambient temperature is slowly added to an organic carboxylic acid such as acetic acid and the mixture is heated to 20-60 °C to form the alkylcyclopentadiene. As shown in the Example of the patent in which this preferred mode of operation was used, a yield of 77+4% of l-methyl-3-propylcyclopentadiene with an endo to exo isomer ratio of 2.6 was achieved.

Despite the significant improvements set forth in U. S. Pat. No. 5,434,324, the provision of a process enabling the achievement still higher yields of alkylcyclo- pentadiene with still higher ratios of endo to exo isomers would be of considerable advantage. Among the complicating factors is that when producing the cyclopentenone reactant from a 1,4-diketone as described for example in U.S. Pat. No. 4,276,199, oligomeric tarry co-products are formed and it would be advantageous if preliminary removal of such co-products could be avoided. This invention provides a process which when conducted in the proper manner has been shown capable of achieving these objectives.

THE INVENTION

Provided by this invention is a process for producing alkyl-substituted cyclopenta- diene, which process comprises:

A) feeding continuously or portionwise

1) a mixture comprising (a) in the range of 10 to 65 wt% of (a) a cyclopentenone and oligomeric tarry material in (b) 90 to 35 wt% of an anhydrous solvent/diluent therefor, into

2) a quantity of at least 15 mol% excess of alkyl Grignard reagent based on the total amount of cyclopentenone to be fed thereto, while agitating the resultant mixture and keeping the temperature of the reaction mixture in the range of -5 to 10°C to provide a first reaction mixture comprising an intermediate product and at least some remaining alkyl Grignard reagent; and then

B) concurrently feeding

1) (a) first reaction mixture and (b) an aqueous solution of at least one water- soluble carboxylic acid, into

2) a reaction vessel which preferably contains at least water or a water- soluble ether, while continuously (a) agitating the resultant mixture, (b) maintaining the pH of the resultant mixture in the range of 2 to 7, and (c) maintaining the temperature of the resultant mixture at one or more temperatures below 10°C at least until completion concurrent feed and

then, while agitating the resultant mixture, raising the temperature thereof to one or more temperatures in the range of 20 to 60 °C. Alkyl-substituted cyclopentadienes having a ratio of endo to exo isomers of 3 : 1 or more are typically formed. In preferred embodiments, the carboxylic acid is acetic acid, the pH is in the range of 3 to 6 (most preferably 4 to 5), and the cyclopentenone is at least predominately, if not substantially entirely, 3-methylcyclopent-2-en-l-one.

These and still other embodiments and features of this invention will be apparent from the ensuing description and appended claims. Cyclopentenones for use in the process of the invention can be prepared from

1 ,4-diketones by the process described in U.S. Pat. No. 4,276,199, the entire disclosure of which is incorporated herein by reference. Such diketones have the formula

CH ₃ COCH ₂ CH ₂ COCH ₂ R where R is hydrogen or a hydrocarbyl group which contains 1 to 15 carbon atoms. Non- limiting examples of hydrocarbon groups include alkyl, substituted alkyl, aryl, substituted aryl, alkenyl, or substituted alkenyl, such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, hexyl, heptyl, octyl, 2-ethylhexyl, dodecyl, pentadecyl, cyclopentyl, cyclohexyl, pentenyl, benzyl, phenyl, tolyl, tetrahydronaphthyl, and naphthyl. Preferred cyclopentenones for use in the process are 3-alkylcyclopent-2-en-l- ones such as 3-methylcyclopent-2-en-l-one.

The initial mixture comprising a cyclopentenone and oligomeric tarry material can contain other materials such as other impurities formed during the synthesis of the cyclopentenone, residual solvents and/or diluents used in such synthesis. Typically such initial mixtures contain 50 wt% or more of the combination of a cyclopentenone and oligomeric tarry material.

Among suitable inert solvents for use with the mixture of cyclopentenone and oligomeric tarry material in the practice of this invention are paraffinic, cycloparaffinic and aromatic hydrocarbons, halohydrocarbons, halocarbons and ethers, all of which should of course be liquids at ambient room temperatures. Particularly preferred solvents are liquid cyclic ethers, especially tetrahydrofuran, and liquid aromatic hydrocarbons, especially toluene. Other suitable aromatic hydrocarbons include xylenes, trimethyl-

benzenes, tetrahydronaphthalene, ethylbenzene, diethylbenzenes, and mixture such as benzene-toluene-xylene mixtures. Other ether solvents include diethyl ether, dioxane, and mixture such as tetrahydrofuran-diethyl ether-dioxane mixtures.

Non-limiting examples of alkyl magnesium halides (Grignard reagents) include C, to o alkyl magnesium chlorides and bromides. Non-limiting examples of alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, isobutyl, pentyl, or hexyl.

Usually the Grignard reagent is formed and often used in an ethereal medium, but the medium can be a suitable liquid hydrocarbon.

One of the important features of this invention is the addition of a dilute mixture of the cyclopentenone and oligomeric tarry material in an anhydrous solvent/diluent therefor to the Grignard reagent. As noted above the dilute mixture will comprise in the range of 10 to 65 wt% of the cyclopentenone plus oligomeric tarry material with the balance (i.e. 90 to 35 wt%) being the anhydrous solvent/diluent. Insignificant amounts of other incidental impurities may be present, provided of course that the mixture is substantially anhydrous and does not contain excessive amounts of components which are reactive with Grignard reagents or which would otherwise interfere with the desired reaction. In this connection, the oligomeric tarry material which is present is typically formed as a co-product during the synthesis of the cyclopentenone, especially when prepared from 1,4-diketones. As used herein and in the claims hereof, the term "oligomeric" to describe the tarry material does not mean or imply that the material has actually been analyzed to the extent necessary to fully determine its chemical structure or molecular weight. Rather, the term is used merely as a convenient way of indicating that the material behaves more like a sticky or tarry substance which presumably is of lower molecular weight, than a high polymer which normally is not a sticky or tarry material.

Another important feature of the invention is that the proportions of the cyclopentenone-tarry material mixture and of the Grignard reagent are such that there is at least 15 mol percent excess of the Grignard reagent based on the total amount of the cyclopentenone to be fed thereto. Preferably this excess is at least 20 mol % and most preferably over 25 mol% . Ordinarily an excess of over 50 mol % is not required.

Moreover, the proportions are such that upon completion of the addition of the cyclopen-

tenone-tarry material mixture to the Grignard reagent, the resultant mixture contains at least some (e.g., at least 1-3 mol %) residual or unreacted Grignard reagent in order to ensure a complete conversion of the cyclopentenone.

Still another important feature of the invention is that the reaction mixture formed upon completion of the Grignard reaction and an aqueous solution of at least one water- soluble carboxylic acid are concurrently fed to a reaction zone while maintaining the pH of the resultant mixture within the range of 2 to 7, preferably 3 to 6 and most preferably 4 to 5. The temperature of the mixture is kept below 10°C at least until the completion of the concurrent feed. Then, while agitating the reaction mixture, the temperature of the mixture is maintained within the range of 20 to 60°C. When the process is conducted in the proper manner (e.g. in the absence of hot spots or over-acidification in a suitable inert atmosphere such as under a blanket of nitrogen), a good yield of alkyl-substituted cyclopentadiene having a ratio of endo to exo isomers of 3: 1 or more can be formed. The concurrent separate feeds can be continuous feeds or they can occur in increments and if conducted in increments, the increments need not be fed simultaneously. The rates of these concurrent feeds should be such that substantially at all times the pH in the reaction mixture remains within the range of 2 to 7 and preferably in the range of 3 to 6. The concurrent feeds may be made into an initially empty reaction vessel or, alternatively, the vessel may initially contain a suitable liquid medium such as water or an ether having high water solubility, such as tetrahydrofuran, to facilitate agitation and pH control.

Non-limiting examples of organic carboxylic acids include formic acid, acetic acid, trifluoroacetic acid, trimethylacetic acid, propionic acid, butyric acid, benzoic acid, oxalic acid, or tartaric acid. Preferred are C, to Q alkyl carboxylic acids. Most preferred is acetic acid.

The following example is presented for the purpose of illustration, and not limitation.

EXAMPLE Preparation of l-Butyl-3-Methylcyclopentadiene To a solution of 3-methylcyclopentenone (0.96 gram, 10.0 mmol, 47 wt%) and oligomeric tarry material (0.29 gram, 14 wt%), and toluene (0.80 gram, 39 wt%) is

added an additional 2.00 grams of toluene. The resultant mixture is added portionwise over a period of 25 minutes to a stirred 2.0 molar tetrahydrofiiran solution of butylmagnesium chloride (6.6 mL of solution, 13.2 mmol of butylmagnesium chloride) under nitrogen atmosphere at 5°C. The resultant mixture is then stirred at 22 °C for one hour. This mixture and an aqueous mixture of acetic acid (1.5 grams, 25 mmol) in 10.5 grams of distilled water are both added separately but concurrently to a vessel containing a heel of continuously stirred distilled water (3.00 grams), the additions being made dropwise over a period of 45 minutes while keeping the temperature at 5°C by external cooling. The pH of this reaction mixture remains between 4 to 5 at all times, and the final pH is 4.5. The product mixture is then warmed to 40-60 °C for 1-2 hours in order to complete the dehydration reaction. The yields of l-butyl-3-methylcyclopentadiene are in the range of 83 +4% with an endo- to exo- isomer ratios in the range of 76+3% to 24 +3 % . The best ratio of endo-isomer to exo-isomer achieved to date in an operation conducted in this manner is 3.8 to 1 and the highest product yield achieved to date in such operation is 87% .

Additional advantages of this invention include the following: a) The process enables use of crude cyclopentenones containing associated tarry material, and thus eliminates special cyclopentenone purification procedures such as distillation, and also eliminates attendant losses of cyclopentenone during such purification. b) Elimination of cyclopentenone purification procedures reduces overall processing time. c) Use of the crude cyclopentenone in diluted form reduces heat-kick on addition to the Grignard reagent and thus facilitates the addition especially in cases of large scale plant operation. d) Hot spots and over-acidification during the dehydration step are eliminated by use of the concurrent feed. e) The concurrent feed enables reduction in reactor loading during the dehydration reaction. The materials referred to by chemical name or formula anywhere in the specifica¬ tion or claims hereof are identified as ingredients to be brought together in connection

with perfoπning a desired operation or in forming a mixture to be used in conducting a desired operation. Accordingly, even though the claims hereinafter may refer to substances in the present tense ("comprises", and "is" ), the reference is to the substance, as it existed at the time just before it was first contacted, blended or mixed with one or more other substances in accordance with the present disclosure. The fact that a substance may lose its original identity through a chemical reaction, complex formation, solvation, ionization, or other transformation during the course of contacting, blending or mixing operations, if done in accordance with the disclosure hereof, is within the purview and scope of this invention.