United States Patent (19) 11 Patent Number: 4,822,930 Liu 45 Date of Patent: Apr. 18, 1989 (54) PROCESS FOR PREPARING 3,890,326 6/1975 Tobin .................................. 570/206 MONOBROMINATED CYCLOBUTARENES 4,540,763 9/1985 Kirchhoff............................ 526/281 (75) Inventor: Ming-Biann Liu, Midland, Mich. OTHER PUBLICATIONS (73) Assignee: The Dow Chemical Company, Lloyd et al., "The Electrophilic Substitution of Ben Midland, Mich. zocyclobutene-II', Tetrahedron, 1965, vol. 21, pp. 245 (21) Appl. No.: 64,714 to 254. Lloyd et al., "Tetrahedron', vol. 20, pp. 2184-2194 22) Filed: Jun. 22, 1987 (1964). (51) Int. Cl'....................... C07C21/24: CO7C 17/00 52 U.S. C. .................................... 570/206; 570/207; Primary Examiner-Werren B. Lone 570/208; 570/209; 570/211 57 ABSTRACT 58) Field of Search ............... 570/206, 207,208, 209, Monobrominated cyclobutarenes are prepared by bro 570/210 minating a cyclobutarene in the presence of an organic (56) References Cited complexing agent, an acid scavenger, or water. Faster U.S. PATENT DOCUMENTS reaction rates highly selective to monobrominated cy clobutarenes are obtained without conventional heavy 3,420,035 2/1969 Bremmer ............................. 570/206 metal or halogen catalysts. 3,607,883 9/1971 Schneider ........ ... 570/206 3,755,444 8/1973 Schneider et al. .................. 570/206 3,763,248 10/1973 Mitchell .............................. 570/206 32 Claims, No Drawings 4,822,930 1. 2 high performance monomeric and polymeric composi PROCESS FOR PREPARNG tions for the electronics industry. MONOBROMINATED CYCLOBUTARENES DETALED DESCRIPTION OF THE BACKGROUND OF THE INVENTION 5 INVENTION This invention relates to a process for preparing bro As the term is used herein, "cyclobutarene' refers to minated organic compounds. More specifically, it re a compound oontaining at least one aromatic ring to lates to a process for preparing monobrominated cy which is fused one or more cyclobutane rings or one or clobutarenes. more substituted cyclobutane rings. An aromatic ring Monobrominated cyclobutarenes are intermediates 10 contains (4N --2)n electrons as described in Morrison for the preparation of high performance monomeric and and Boyd, Organic Chemistry. 3rd Edition, (1973). Suit polymeric compositions for the electronics and aero able compounds containing at least one aromatic ring space industries. U.S. Pat. No. 4,540,763 discloses that include benzene, naphthalene, biphenyl, binaphthyl, monobrominated cyclobutarenes can be processed to phenanthrene, anthracene, and diphenylbenzene. The prepare poly(cyclobutarene) polymeric compositions. 15 aromatic ring of the cyclobutarene can be substituted These compositions possess thermal stability at high with groups stable to the bromination reaction, includ temperatures, as well as chemical resistance and low ing but not limited to groups such as methyl, methoxy, sensibility to water. and acetate. Heterocyclic compounds such as pyridine Processes for preparing monobrominated cyclobuta and picoline are also included. Preferred compounds renes are difficult because multiple bromination reac 20 are benzene, naphthalene, and biphenyl. The most pre tions occur and the strained cyclobutane ring of the ferred compound containing at least one aromatic ring cyclobutarene is easily susceptible to ring-opening side is benzene. Therefore, the most preferred cyclobutarene reactions (see J. B. F. Lloyd et al., Tetrahedron 20, pp. is benzocyclobutene. 2185-94 (1964)). U.S. Pat. No. 4,540,763 discloses a process for preparing monobrominated cyclobutarenes 25 As disclosed in U.S. Pat. No. 4,570,011, cyclobuta which involves diluting a cyclobutarene in acetic acid renes useful in this invention can be prepared by dis and then contacting the solution with pyridinium per solving an ortho alkyl halomethyl aromatic hydrocar bromide hydrobromide in the presence of a mercuric bon, such as ortho methylchloromethylbenzene, in an acetate catalyst. The reaction occurs over a four day inert solvent, and then pyrolyzing the solution under period and uses approximately 300 percent excess bro 30 suitable reaction conditions. minating agent. J. B. F. Lloyd et al., Tetrahedron, 21, pp. "Brominating” refers to the introduction of bromine 245-54, (1965), disclose a process for preparing mono into an organic compound by treating the compound brominated benzocyclobutene which involves diluting with a brominating agent. Suitable brominating agents benzocyolobutene in a 95 percent aqueous solution of useful in this invention are those compounds which are acetic acid and then contacting the solution with molec 35 capable of reacting with the aromatic ring of the cy ular bromine in the presence of an iodine catalyst. The clobutarene to break the carbonhydrogen bond and to yield of monobrominated benzocyclobutene is 78 per form a carbon-halogen bond under the reaction condi cent after 48 hours. Unfortunately, both of these pro tions. H. P. Braendlin et al. Friedel-Crafts and Related cesses require large quantities of brominating agent to Reactions. Vol. III, Chapter 46, pp. 1517-1593, John complete a very slow bromination reaction. Also, both Wiley & Sons, New York (1964), disclose brominating processes require either a heavy metal catalyst or a agents useful for brominating organic compounds. The halogen catalyst. The residual catalyst that inevitably brominating agents that can be employed in this inven finds its way into the final product is detrimental for tion can include molecular bromine, bromine chloride, electronics and aerospace industry applications. Fur pyridinium perbromide hydrobromide, dioxane dibro thermore, these catalysts create environmental prob 45 mide, and N-bromosuccinimide. Preferred brominating lems related to their disposal. agents include molecular bromine and bromine chlo Therefore, it would be desirable to have a process for ride. The most preferred brominating agent is molecular preparing monobrominated cyclobutarenes that does bromine. not require a halogen catalyst or a heavy metal catalyst. The monobrominated cyclobutarenes useful in this It would also be desirable to have a process providing a 50 invention are prepared by brominating a cyclobutarene. faster bromination reaction highly selective to mono The term "monobrominated” refers to the replacement brominated cyclobutarenes without requiring excessive of one hydrogen atom on the aromatic ring with one quantities of brominating agent. bromine atom. The products produced from the bromi SUMMARY OF THE INVENTION nation of the cyclobutarene include not only the mono 55 brominated cyclobutarenes but also small quantities of This invention is a method of preparing mono hydrogen bromide, unreacted brominating agent and brominated cyclobutarenes consisting essentially of undesirable side reaction products. The hydrogen bro brominating a cyclobutarene in the presence of an or mide can either dissolve in the reaction mixture or ganic complexing agent, an acid scavenger, or water. evolve from the reaction mixture as a gas. Surprisingly, reaction rates faster than the rates dis 60 The organic complexing agents that improve the closed in the prior art are achieved by the method of selectivity of the reaction to monobrominated cy this invention without requiring a catalyst. In addition, clobutarenes are organic compounds that will donate the reaction is highly selective to monobrominated electrons to form donor-acceptor adducts with the un cyclobutarenes and neither requires excessive quantities reacted brominating agent and the hydrogen bromide of brominating agent nor creates an environmental 65 produced during the reaction. The adduct formed re problem related to the disposal of the catalysts. duces the reactivity of the brominating agent and hy The monobrominated cyclobutarenes of this inven drogen bromide with the cyclobutane ring of the cy tion are useful as intermediates for the preparation of clobutarene and therefore reduces formation of undesir 4,822,930 3 4. able side products. A. J. Downs et al., Comprehensive metal and alkali earth metals, such as sodium bicarbon Inorganic Chemistry, Chapter 26, pp. 1196-1197 and pp. ate and potassium carbonate. 1201-1209, New York, New York, (1973), discuss the When the cyclobutarene is brominated in the pres crystalline structure of halogen adducts based on X-ray ence of water, the water acts in a manner similar to that diffraction studies. They describe organic compounds 5 of the organic complexing agent by forming donor which form halogen adducts and the factors influencing acceptor adducts with the unreacted brominating agent their stability. They also describe the relative capacities and the hydrogen bromide. of organic compounds to donate electrons. Preferably, In a preferred embodiment of this invention, the solu the organic complexing agent has an electron donor bility of hydrogen bromide produced during bromina capacity equal to or slightly greater than the electron 10 tion in the reaction mixture is reduced. The reduced donor capacity of the cyolobutarene. solubility will increase the quantity of hydrogen bro Suitable organic complexing agents include aliphatic mide that will evolve from the reaction mixture as a gas. alcohols and diols having less than 10 carbon atoms, Since more hydrogen bromide will evolve from the such as methanol, isobutyl alcohol, and ethylene glycol: reaction mixture as a gas, there will be less hydrogen aliphatic polymeric diols having an average molecular 15 bromide in the reaction