3,151,173 United States Patent Office Paiented Sept. 29, 1964 i 2 p-toluene sulfonic acid (which is the preferred catalyst 3,151,173 of the present invention). Weaker acids, having first EPOCESS FOR PRGEJCNG SALKY DENE pixa values above 2.5, are less effective. The second class NGREORNENE - Sasks. Tyce, RAS Creek H.Rindred, e., assignor to E. E. of catalysts includes compounds Sugh as boron trifluoride, di Post de NextGE's and Copany, Wisnington, Dei, boron trichloride, aluminum chloride, aluminum bromide, a corporation of Delaware Zinc chloride, titanium tetrachloride, ferric chloride, ferric Na Drawing. Fied Jay 8, 1961, Ser. No. 24,783 bromide, stannic chloride, antimony pentachloride, ni f6 (Cairns. (C. 268-666) obium tetrachloride, tellurium dichloride, bismuth tri chloride, mercuric chioride, and tantulum tetrachloride. This invention relates to a new method for the prepara O The Friedel-Crafts catalysts tend to induce polymeriza tion of Substituted norbornene compounds. More par tion which is evidenced by a darkening of the reaction ticularly this invention relates to a new method of pre mixture. It is preferred to stop the reaction when this paring 5-alkylidene-noirborneine compounds. discoloration occurs. Certain norbornene compounds have been found to The catalyst concentration may range from about be very useful for the preparation of ethylene copolymers. 0.0025 mole to 2.5 mole per mole of the 2-alkylnorborna Jinfortunately, the present methods for the preparation diene compound. The preferred concentration often. f these norbornene compounds, such as 5-methylene ranges from about 0.02 mole to 0.04 mole. However, norbornere, are rather costly and thereby restrict the use When catalysts are used, such as hydrogen chloride, fulness of such compounds in commercial production. which exhibit a tendency to add to the unsubstituted it is as object of this invention to provide a new 20 double bond of the norbornadiene, it is preferred to keep process for the preparation of substituted norbornene the concentration below about 0.02 mole. Concentra compounds. A further object is to provide a new tions above 2.5 mole are unnecessary. Concentrations process for the preparation of 5-aikylidene-norbornene below 0.0025 mole can be used but the conversions to coincinds. Other objects will appear hereinafter. the desired product are not as favorable. These and other objects of this invention are accom 25 The temperature may range from about 0° to at least plished by a new process which comprises treating a 2 275 C., about 30 to 120° C. being preferred. At tem alkyinorbornadiene having the structure peratures below 0° C. the reaction is undesirably slow and the percent conversion to the desired product is less favor able than that obtained at temperatures above 0° C. A representative temperature when p-toluene sulfonic acid is employed as the catalyst is about 60° C. The reaction time can vary from about 1 to 100 hours, Representative periods are 2 to 21 hours at 60-61° C. where R and R2 are hydrogen atolins or aikyl radicals The higher the reaction temperature, the shorter the time which can have between them a total of 16 carbon atons, 35 required. When darkening of the reaction mixture oc with a catalyst selected from the group consisting of (a) curs, it is best to stop in order to minimize polymer for nonoxidizing acids having a first pKa at 25 C. below mation. about 2.5; and (b) Friedel-Crafts metal halides; and re The isomerization can be carried out at sub-atmos covering the 5-alkylidenenorbornene, pheric pressure, atmospheric pressure, or super-atmos pheric pressure. Atmospheric pressure is frequently con venient. No solvent is needed. However, the process of the pres ent invention may be carried out in an inert solvent, that is, an inert liquid solvent which does not interfere with thereby formed, wherein R1 and R2 are as defined above. 45 the desired course of the reaction. Any solvent meeting Representative examples of the 2-alkyl norbornadienes this criterion may be selected by those skilled in the art. which can be isomerized according to this invention in In general, it is desirable to pick a solvent which has a clude: 2-methylnorbornadiene; 2-ethylnorbornadiene; 2 low boiling point at atmospheric pressure, that is, a vola isopropylnorbornadiene; 2-isobutylnorbornadiene; 2-neo tile solvent which is readily removed at the end of the penty incrbornadiene; 2-n-heptylinorbornadiene; 2-n-decyl 50 reaction and permits ready isolation of the product di. norbornadiene; 2-n-tridecylnorbornadiene; 2-n-hexadecyl olefin. Chloroform is a convenient solvent. forbornadiene; and 2-m-heptadecylnorbornadiene. The Other representative solvents, which boil between about 2-alkyl norbornadienes can be made by heating alkyl 30 and 180 C., include: saturated aliphatic hydrocar acetylenes having the formula R-C=CH, where R is bons (such as neopentane, isopentane, n-hexane, 2,2,4- C-C alkyl, in the absence of a polymerization initiator trimethylpentane and n-octane); cycloaliphatic hydrocar with cyclopentadiene, preferably at about 175 to 225 C. bons (such as cyclopentane, cyclohexane, and methyl for 2 to 24 hours. Closed reaction vessels made from cyclohexane); aromatic hydrocarbons (such as: benzene, stainless steel or glass-lined steel are quite satisfactory. toluene, orthoxylene, and cumene); halogenated saturated This class of compounds and a procedure for its prep aliphatic hydrocarbons (such as methylene chloride, car aration are described in Belgian Patent 498,176 (1950). 60 bon tetrachloride, 1-bromo-2-chloroethylene, trichloro A catalyst useful for carrying out the isomerization of Inonoiuoromethane, trichlorotrifluoroethane, monofluoro the present invention should neither oxidize nor add to heptafluorocyclobutane, dichlorodifluoroethylene); and the carbon-carbon double bonds of the norbornadiene halogenated aromatic hydrocarbons (such as chloroben compound during the reaction. Furthermore, it should Zeine, and orthodichlorobenzene). not significantly promote the polymerization of the un 65 The 2-alkyl-norbornadiene concentration in the inert substituted carbon-carbon double bond of norbornadiene Solvent may be varied over a wide range. Those skilled in competition with the desired isomerization. in the art can readily select suitable concentrations for Suitable catalysts are selected from the group consisting convenient operation. In representative operations about of (a) non-oxidizing acids having a first pKa at 25 C. 10 to 25 grams of 2-methyl norbornadiene have been em below about 2.5, and (b) Friedel–Crafts metal halides. O ployed in 100 grams of chloroform solvent. The first class of catalysts includes compounds such In carrying out the process of the above invention, it is as hydrogen cilloride, sulfuric acid, phosphoric acid, and merely necessary to contact the 2-alkyl-norbornadiene 3,151,178 se - s A. compound with the catalyst and recover the isonerized EXAMPLE 2 product thereby formed. in general, the product can be separated from unchanged diolefin or by-products by frac Isonerization of 2-Ethylnorbornadiene With p-Toluene tional distillation. When a solvent has been used, it can Sulfonic Acid be removed by conventional methods such as evaporation The 2-ethylnorbornadiene (6.6 g., 0.0559 mole) was under reduced pressure or by drum drying or the like. put into a 100 ml, round-bottom flask equipped with a Representative examples of the 5-alkylidene-norbornene reflux condenser, magnetic stirrer, and heating mantle. compounds which may be prepared according to the pres After chloroforin (30 cc.) and p-toluene Sulfonic acid ent invention include 5-methylidene-2-norbornene (also monohydrate (0.3 g., 0.001.57 mole) had been added cold, called 5-methylene-2-norbornene); 5-ethylidene-2-nor O the mixture was heated at the reflux temperature of bornene, which is preferred; 5-isopropylidene-2-nor chioroform for 20 hours. The chloroform was then bornene; 5-isobutylidene-2-norbornene; 5-neopentylidene distilled off at atmospheric pressure and the residue 2-norbornene; 5-n-heptylidene-2-norbornene; 5-n-decyl vacuum distilled to give 4.4 g. (67%) of 5-ethylideine-2- idene-2-norbornene; 5-n-tridecylidene-2-norbornene; 5-n- norbornene. Both the infrared spectrum and vapor phase hexadecylidene-2-norbornene; and 5-n-heptadecylidene-2- chromatography indicated that isomerization had norbornene. occurred. No trace of the starting diene could be de These 5-alkylidene-2-norbornenes are significantly use tected by either of the methods mentioned. ful as comonomers in the preparation of sulfur-curable EXAMPLE 3 hydrocarbon elastomers. The carbon to carbon double bond at the 5-position provides the cure site for the elas 20 A ten gram sample (0.0816 mole) of 2-methylnorbor tomers. These elastomers are rubbery copolymers of eth nadiene, 0.7 milliliter (0.29 g., 0.1 moie) of 85% aque yeine, at least one alpha olefin having the structure ous phosphoric acid, and 30 milliliters of chloroform were introduced simultaneously into a 250-milliliter flask R-CH-CH equipped with a reflux condenser, a magnetic stirrer and a heating mantle. Heat was applied and the mixture, where R is a C-C alkyl radical, and a 5-alkylidene-2- while agitated, was refluxed (61) over a 3-hour period. norbornene, said copolymer having an iodine number be The chloroform was then distilled off at atmospheric pres tween 5 and 60 and containing by weight about 20 to 71.4 sure. After 22 miili liters had been collected, the pressure percent ethylene monomer units, about 25 to 76.4 percent over the system was reduced and the residue was sub R-CH=CH2 monomer units, and about 3.6 to 20 per jected to vacuum distillation. Three cuts were obtained cent 5-alkyiidene-2-norbornene monoiner units. 30 whose combined weight was 8.7 grains. Infrared analysis Representative examples of these copolymers include: showed about 15% chloroform, 81.4% 2-methylnorbor ethylene/propylene/5 - methylidene - 2 - norbornene; eth nadiene and 3.6% of 5-methylenenorbornene were ylene/propylene/5 - ethylidene - 2 - norbornene; eth ylene/propylene/5 - isobutylidene - 2 - norbornene; ethyl present.