PROCESS FOR THE PREPARATION OF (2,2)-PARACYCLOPHANE AND DERIVATIVES THEREOF

Abstract: Process for the preparation of (2,2)-paracyclopha­ ne or derivatives thereof by the Hofmann elimination of p-methyl-benzyl-trimethylammonium hydroxide or deriva­ tives thereof, in an aqueous solution of an alkali metal hydroxide, wherein said elimination is carried out in the presence of a compound of the formula (I): (R) m - A - (X) n (I) wherein A represents an aromatic group, X an electron donor group, R hydrogen or an alkyl group containing from 1 to 4 carbon atoms, n is an integer comprised between 1 and 6 and m is zero or an integer comprised between 1 and a value such that the sum m+n be equal to the number of substi­ tuable positions in the aromatic group.

Description: The present invention relates to a process for the preparation of (2,2)-paracyclophane and derivatives thereof having the formula: wherein B may be a halogen, an alkyl, an aralkyl, or a halogenaralkyl radical having from 1 to 20 carbon atoms, and p is zero or an integer comprised between 1 and 4, that is zero or the integer 1, 2, 3 or 4. In particular B may be halogen like chlorine, bromine, iodine and fluorine, preferably chlorine; an alkyl, aralkyl or halogen-aralkyl radical with up to 20 carbon atoms, preferably an alkyl radical from 1 to 6 carbon atoms and an aralkyl or halogen-aralkyl radical from 7 to 10 carbon atoms; the halogen in the halogen-aralkyl radical may be fluorine, chlorine and bromine, preferably chlorine and bromine. More particularly, the present invention relates to a process for preparing (2,2)-paracyclophane and its derivatives having the formula (II), starting from a p-methylbenzyltrimethylammonium derivative having the formula: wherein B and p are the same as defined above and Y is a hydroxy radical or a halogen, by the Hofmann elimination. (2,2)-paracyclophane and its derivatives such as dichloro-(2,2)-paracyclophane, tetrachloro-(2,2)-paracyclophane, tetramethyl-(2,2)-paracyclophane, dimethyl-dichloro-(2,2)-paracyclophane, diethyl-(2,2) paracyclophane, dibromo-(2,2)-paracyclophane, are products well known in the literature and are generally utilized as intermediates in the preparation of the corresponding poly-p-xylylenes. Said polymers, and in particular poly-p-xylylene and its chlorinated derivatives, are advantageously utilized in the form of coating films in the field of the conformal coating, obtained by application according to the vacuum vapor deposition technique, in the electronic field. Various processes have been proposed for preparing (2,2)-paracyclophane and its derivatives (II). However such known processes are not fully satisfactory and are not suitable for being adopted on an industrial scale, mainly due to the low productivity of the process and to the difficulty in recovering the product from the reaction mixture. Thus, for example, Organic Syntheses, Collective Vol. 5, John Wiley & Sons, Inc., New York-London - Sydney - Toronto, 1973, pages 883-886, describes a process for preparing (2,2)-paracyclophane by the Hofmann elimination starting from p-methylbenzyltrimethylammonium hydroxide obtained by reacting the corresponding bromide with silver oxide. The elimination is carried out in the presence of an alkaline medium and an inert organic solvent (e.g., toluene) and a yield of about 10% is attained. According to European patent application No 108, 297, it is possible to increase the reaction yield by carrying out the Hofmann elimination in an alkaline medium and in the presence of large amounts of dimethylsulphoxide. The large volumes and the long reaction times, generally exceeding 50 hours, lead to a low productivity in spite of high yields (about 70%). Furthermore, the recovery of dimethylsulphoxide and the unsatisfactory quality of the resulting product render this process little attractive for industrial scale utilization. Generally, in all the known processes for producing (2,2)-paracyclophane, rather large amounts of poly-p-xylylene are formed, which, in the presence of large amounts of organic solvent in the reaction medium, assumes a gelatine-like appearance and is difficult to be filtered off. Further, from EP-A-183 083 a process for the preparation of (2,2)-paracyclophane has been known carried out in the presence of a biphasic system consisting of an inert organic solvent and of an aqueous solution of an alkaline hydroxide having a concentration of at least 20 percent by weight. No catalyst is used to promote the formation of (2,2)-paracyclophane. In addition thereto in Synthetic Communications, Vol. 6, No. 8 (1976), pages 591 - 596, the reaction conditions with regard to solvents, inhibitor and concentration for the synthesis of multilayered (2,2)-paracyclophanes have been studied. The synthesis described there starts from (2,2)-paracyclophane which is the end product of the present invention. It has now been discovered by the Applicant that (2,2)-paracyclophane and derivatives thereof having formula (II) may be prepared in a pure form, with high industrial yields, even higher than 80% by moles, by carrying out the Hofmann elimination of p -methylbenzyltrimethylammonium hydroxide, optionally substituted in the nucleus, of formula (III) in an alkaline aqueous solution of an alkali metal hydroxide at a temperature of 50°C to 150°C and in the presence of 5 to 30 mol% of a compound having the formula (I): (R) m - A - (X) n (I) wherein A represents an aromatic group, X represents -OR ₁ , -N(R₁)₂ and -SR₁, wherein R₁ is hydrogen, an alkyl radical having from 1 to 6 carbon atoms or an aryl, alkylaryl or aryl-alkyl radical having from 6 to 18 carbon atoms, R represents hydrogen or an alkyl radical having from 1 to 4 carbon atoms, n is an integer comprised between 1 to 6, and m is zero or an integer comprised between 1 and a value such that the sum m+n be equal to the number of substituable positions in the aromatic group A. In particular n is the integer 1, 2, 3, 4, 5 or 6. According to the present invention, the compounds of formula (I) wherein A represents a phenyl or naphthyl group, n is equal to 2 or 3, m is zero or an integer comprised between 1 and 3 and X has the above-reported meanings, which may be equal or different to each other are particularly preferred. A non-limitative list of compounds having formula (I) is: 1,4-hydroquinone; ortho-, meta-and para- amino-phenol; ortho-, meta-and para- phenylen-diamine; 2,6-di- ter. butyl-paracresol; p,p′-diamine-diphenylmethane; phenol; N,N′-di-phenyl-1,4-phenylen-diamine; 3-ter. butyl -4- hydroxy anisol; 2,4-di-ter. butyl -phenol; hydroquinone mono-ethyl ether. These compounds are well known in the literature or can be found on the market or may be prepared according to conventional synthesis methods. The catalytic compound of formula (I) may be used in amounts which also may vary over a wide range, depending on the values taken by the other parameters, such as the temperature, reaction times. However, excellent results are achieved by using molar amounts between 5% and about 30%, preferably between 10 and 20%, referred to the p-methylbenzyltrimethylammonium derivative optionally substituted in the nucleus, of formula (III). According to this invention, the Hofmann elimination is carried out in an aqueous solution and preferably in the absence of a solvent. The aqueous phase is constituted by an alkali metal hydroxide solution having a concentration higher than 10% by weight. As an alkali metal hydroxide, sodium or potassium hydroxide may be used. The concentration of the aqueous solution is preferably maintained during the Hofmann elimination reaction at a concentration between about 20 and 50% by weight. In the process of the present invention, the Hofmann elimination is carried out on p-methylbenzyltrimethylammonium hydroxide which may be either prepared separately or formed in situ by the reaction of the corresponding halide with the alkali metal hydroxide. The Hofmann elimination is carried out at a temperature comprised between 50° and 150°C, preferably between 90° and 130°C, and for a time comprised between 1 and 50 hours, and, preferably for 2 to 10 hours. Even if not necessary, inert organic solvents which are immiscible with water, such as, e.g., toluene, xylene, benzene, or tetraline, may be added to the reaction medium. At the end of the elimination reaction, the resulting product is separated according to per se known and substantially conventional methods. The process of this invention permits one to obtain, with industrially acceptable yields, (2,2)-paracyclophane and its derivatives substituted in the nucleus with a high degree of purity (above 99.5% ) and a high productivity. The present invention is still further elucidated by the following examples. In the examples, unless otherwise specified all parts, percentages, and ratios are by weight. Example 1 (comparative test) Into a 1,000 ml flask equipped with a stirrer, thermometer, and condenser, there were charged: 100 g of an aqueous solution containing 40% by weight of NaOH (1 mole); and 62,5 g of aqueous solution containing 63.9% by weight of p-methylbenzyltrimethylammonium chloride (0.2 moles). Under continuous stirring, the solution was gradually heated to a temperature of 120°C. The NaOH concentration was maintained at 35% by weight. The solution was maintained at the boiling temperature over the course of 6 hours. The resulting (2,2)-paracyclophane was separated from the reaction mass by solubilization in 300 ml of xylene. For this purpose,xylene was added to the reaction mass and the slurry was maintained at full reflux under stirring during 0.5 hours. The reaction mass was filtered at 95°C, the aqueous phase was separated from the organic solution, and this solution was repeatedly washed with water and concentrated to a small volume. The xylene solution was cooled down to 20°C and the precipitated solid was recovered by filtration. After washing the solid with acetone and drying, there were obtained 1.08 g of a crystalline white solid (yield 5.2% by moles), having a melting point of 283°-285°C, which, on gas-chromatographic analysis, proved to be (2,2)-paracyclophane having a degree of purity of about 99.5%. Examples 2 - 13 Example 1 is repeated by adding a compound of the type and in an amount reported in the following Table 1 to the Na OH aqueous solution. The amount of the obtained (2,2)-paracyclophane, the relevant melting point and the reaction yield are reported in the following Table 1. EX ADDED COMPOUND OBTAINED PRODUCT NO TYPE AMOUNT by moles AMOUNT YIELD % by moles MELTING POINT C° g. moles 2 Hydroquinone 0,016 5,1 0,0245 24,5 282-286 3 Ortho-aminophenol 0,016 5,1 0,0245 24,5 282-287 4 Meta-aminophenol 0,016 4,8 0,0230 23 282-284 5 Para-aminophenol 0,016 9,1 0,0438 43,8 283-285 6 Para-aminophenol 0,033 8,4 0,0404 40,4 281-284 7 Ortho-phenylendiamine 0,016 6,3 0,0303 30,3 283-284 8 Meta-phenylendiamine 0,016 4,7 0,0226 22,6 282-285 9 Para-phenylendiamine 0,008 7,3 0,0351 35,1 283-285 10 Para-phenylendiamine 0,016 10,5 0,0505 50,5 283-284 11 Para-phenylendiamine 0,024 11,1 0,0533 53,3 282-285 12 p,p'-di-amino-di-phenyl methane 0,016 5,9 0,0284 28,4 283-287

Claims: A process for preparing (2,2)-paracyclophane and derivatives thereof of the formula (II): wherein B is a halogen atom, an alkyl radical, an aralkyl radical, or a halo-aralkyl radical, having up to 20 carbon atoms, and p is zero or an integer from 1 to 4, by the Hofmann elimination of a p-methylbenzyltrimethyl-ammonium derivative of the formula (III): wherein B and p are the same as defined hereinabove and Y is a hydroxy radical or a halogen atom, in an alkaline aqueous solution of an alkali metal hydroxide, characterized in that said elimination is carried out at a temperature of 50°C to 150°C and in the presence of 5-30 mol% of a compound having the formula (I), based on the compounds of (III), (R)m - A - (X)n (I) wherein: A represents an aromatic group, X represents -OR₁, -N(R₁)₂ and -SR₁, wherein R₁ is hydrogen, an alkyl radical having from 1 to 6 carbon atoms, an aryl radical, an alkyl-aryl radical or an aryl-alkyl radical containing from 6 to 18 carbon atoms, R represents a hydrogen atom or an alkyl radical having from 1 to 4 carbon atoms, n is an integer comprised between 1 and 6 and m is zero or an integer comprised between 1 and a value such that the sum m+n be equal to the number of substituable positions of the aromatic group A and that the alkaline aqueous solution has a concentration higher than 10% by weight of alkali metal hydroxide. The process according to claim 1, wherein in the compound of formula (1) A represents a phenyl or naphthyl group, n is equal to 2 or 3, m is zero or an integer comprised between 1 and 3 and X has the values reported in claim 1, which may be equal or different to each other. The process according to anyone of the preceding claims, characterized in that the compound of formula (I) is selected from the group consisting of: 1,4-hydroquinone; ortho-, meta- and para-aminophenol; ortho-, meta- and para-phenylen-diamine; 2,6-di-ter.butyl-para-cresol; p,p'-di-amino-di-phenyl-methane; phenol; N,N'-di-phenyl-1,4-phenylen-diamine; 3-ter.butyl-4-hydroxy-anisol; 2,4-di-ter.butylphenol; hydroquinone-mono-methyl ether. The process according to anyone of the preceding claims, characterized in that the catalyst of formula (I) is used in a molar amount ranging from 10 % to 20 % based on p-methylbenzyltrimethylammonium derivative of formula (III). The process according to anyone of the preceding claims, characterized in that the concentration of the aqueous solution of an alkali metal hydroxide is maintained, during the Hofmann elimination reaction, at from 20 % to 50 % by weight. The process according to anyone of the preceding claims, characterized in that the p-methylbenzyltrimethylammonium hydroxide of formula (III) is prepared in situ by the reaction of the corresponding halide with the alkali metal hydroxide present in the reaction medium. The process according to anyone of the preceding claims, characterized in that the Hofmann elimination is carried out at a temperature between 90°C and 130°C, over the course of 1 to 50 hours, preferably of 2 to 10 hours, and preferably in the absence of a solvent.

Inventors: SOGLI, LORIS, UNGARELLI, RAFFAELE
Applicants: SYREMONT S.P.A.
Application year: 1988
Main classification: C07C13
IPC codes: C07C67, C07C17, C07C25, C07C1, C07C13, C07B61, B01J31