Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25B—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES FOR THE PRODUCTION OF COMPOUNDS OR NON-METALS; APPARATUS THEREFOR
  • C25B3/00—Electrolytic production of organic compounds
  • C25B3/20—Processes
  • C25B3/27—Halogenation

Definitions

• the present invention relates to the electrochemical iodination of aromatic compounds to selectively and efficiently form a para-substituted iodobenzene derivative.
• lodoaromatics are desirable materials because of the wide variety of transformations they can undergo. For example, they can be catalytically carbonylated to form aromatic carboxylic acids and esters. lodoaromatics are therefore possible starting materials for polycarbonates, polyamides, polysulfides, and polyesters.
• the halogenation with molecular halogen is one of the classic reactions of aromatic substitution and has been thoroughly investigated owing to its theoretical as well as synthetic value (H. P. Braendlin and E. T. McBee in Friedel-Crafts and Related Reactions ed. G. A. Olan, Wiley, New York, 1964, Volume 3, Ch.
• the present process is an electrolytic process that provides selective and efficient formation of a para-substituted iodobenzene derivative. This process makes use of a graphitic carbon anode. More specifically, the present invention is directed to an electrolytic process for the formation of a para-substituted iodobenzene derivative comprising contacting:
• the present invention also encompasses an electrolytic process for preparing iodobenzene comprising contacting:
• Process II This process for preparing iodobenzene shall be referred to herein as "Process II.”
• the present invention is also directed to an electrolytic process for preparing iodobenzene comprising contacting a catholyte solution of a divided electrolytic cell wherein said divided electrolytic cell comprises
• Process III This cathodic deiodination process shall be referred to herein as "Process III.”
• halo refers to chloro, bromo, fluoro or iodo
• alkyl refers to C, to C 16 straight, branched or cyclic alkyls
• aryl refers to aryls containing six to 14 carbon atoms.
• Process I Any of Process I, Process II, or Process III can be carried out batchwise; however, for most industrial applications, it is preferred to perform these processes continuously. Therefore, it is preferred to couple Process I with Process II and/or Process III.
• a preferred process of the present invention is a continuous process in which Process I is performed simultaneously with Process III. This preferred process can be described as a continuous electrolytic process for the formation of para-diiodobenzene comprising:
• Process I When Process I is coupled with Process II, it is preferred that such process be performed consecutively in the same electrolytic cell. As a result, the iodobenzene formed from Process II is used as a starting material for Process I.
• the electric potential applied to the anode and cathode is about 1.5 to about 2.5 volts, more preferred is about 2 volts.
• the processes of the present invention are performed at a temperature of about 25° to about 100 ° C, more preferred is about 25 to about 50 C; and at a pressure of about 1 atmosphere (atm) to about 10 atm, more preferred is about 1-2 atms.
• one or more processes of the present invention is run as a batch process, typically the electric potential is applied for a period of time of about 1 to about 25 hours, preferred is about 2 to about 8 hours.
• additives such as CF 3 C0 2 H, (Et) 4 NBF 4 , or trisbromophenyl amine can be added to the reaction medium in the processes of the present invention; however, the presence of such additives are not necessary. If one or more additives are used, they are typically present in a concentration of up to about 10 percent, based on solvent weight.
• the cathode compartment and anode compartment are separated by a separator such as a membrane, fritted glass, and the like.
• a separator such as a membrane, fritted glass, and the like.
• this separator is a membrane.
• a preferred membrane is a NafionTM membrane.
• the nature of the anode is important. It has been found that the anode must be comprised of graphitic carbon in order for the iodination process to be sufficiently effective.
• the graphitic anode can be comprised of spectral grade graphite or can be any other suitable graphite electrode.
• the nature of the, cathode for any of the processes of the invention, is not particularly critical.
• the cathode can be comprised of platinum, carbon, copper, lead, tin, palladium, stainless steel, or combinations thereof.
• Process III since Process III must proceed in the presence of palladium or carbon, it is convenient for the cathode in Process III to be comprised of palladium on carbon.
• the solvents and electrolyte in the cathode and anode compartments for any of the processes of the present invention can be the same or different; however, it is usually more convenient for the electrolyte and solvents to be the same in each compartment.
• Preferred solvents are polar organic aprotic or protic solvents. Examples include methanol, ethanol, acetonitrile, tetrahydrofuran, dimethylformamide, dimethylsulfoxide, dimethyl ether, diethyl ether, acetic acid (HOAc), or a mixture thereof. The most preferred solvent is acetonitrile.
• the electrolyte is present in a concentration sufficient to give the total reaction medium sufficient conductivity at reaction conditions in order for the desired process to proceed satisfactorily.
• a preferred electrolyte is a tetrafluoroborate. Examples include substituted tetrafluoroborates such as, HBF 4 , NaBF4, (Me)4NBF4, (Et) 4 NBF4., (Pr) 4 NBF 4 , or (Bu)4NBF4 wherein Me is methyl, Et is ethyl, Pr is propyl and Bu is butyl. The most preferred electrolyte is HBF 4 , (Me) 4 NBF 4 or (Bu) 4 NBF 4 .
• Process I in addition to the formation of said para-substituted iodobenzene derivative, typically minor amounts of the other isomers are also formed, especially an ortho-substituted iodobenzene derivative. It is an advantage of the present invention that the yield of the para-substituted compound is greater than the yield of the ortho-substituted compound. Preferably the mole ratio of para-substituted iodobenzene derivative to ortho-substituted iodobenzene derivative after reaction is greater than about 1:1 to about 100:1.
• the weight ratio of the iodine source to the mono-substituted compound to the anolyte solution is about 2.5:3.0:100 to about 1.0:15.0:100, and the weight ratio of electrolyte to solent of the anolyte solution is about 1:1 to about 1:100; said electron-donating group is alkyl, hydroxyl, thiol, -OR , or -SR';
• the iodine source is iodine (1 2 ) or an iodine salt such as HI, Nal, KI, or an alkyl ammonium iodide.
• R is I and the iodine source is most preferably 1 2 .
• the purity of the para-substituted iodobenzene derivative is typically greater than about 98 weight percent, preferably greater than about 99 weight percent, after isolation by standard techniques.
• this compound can be isolated simply by cooling the electrolysis mixture until the desired compound becomes a solid, typically less than about 15°C, followed by filtering. By this simple isolation procedure, typically greater than about 80 weight percent of the available para-isomer can be obtained.
• the yield of para plus ortho derivatives is greater than about 60 percent preferably greater than about 90 percent, based on the weight of consumed iodine source. Typical by-products formed include iodonium salts.
• the weight ratio of the iodine source to benzene to the anolyte solution is about 1.25:2.0:100 to about 2.5:1.0:100, the weight ratio of electrolyte to solvent in the anolyte and catholyte solutions is about 1:10 to about 1:100, and that the iodine source is iodine.
• the weight ratio of the diiodobenzene compound:catholyte solution is about 1:10 to about 1:100; the weight ratio of electrolyte: solvent in the anolyte and catholyte solutions is about 1:10 to about 1:100; and that the diiodobenzene starting material is ortho-diiodobenzene.
• Process III must be performed in a catalytic amount of palladium on carbon catalyst.
• a catalytic amount is typically at least about 0.001%, based on the weight of diiodobenzene starting material, preferably about 0.01 %.
• Electrolysis was performed in an H-type cell where the anode and cathode were separated by a Nafion membrane.
• the cathode was a spectroscopic (UltraCarbon, U50) carbon rod. All reactions were run at the indicated constant potential by way of an ESC Model 410 potentiostatic controller.
• the electrochemical apparatus was fitted with an ESC Model 630 digital coulometer and, in each case, the theoretical number of coulombs was collected.
• the cell temperature was not controlled and usually rose to about 28 * C in the course of an experiment.
• the potential is set at 2.00 volts versus SCE (saturated calomel electrode), and current is passed through the electrolysis solution. The electrolysis is stopped after 1930 coulombs are passed.
• the product is isolated by pouring the anode solution into 500 mL of water and extracting three times with 50 mL of methylene chloride each time. The extracts are combined and washed with 100 mL of water. The organic layer is dried over magnesium sulfate and the solvent is removed in vacuo to afford 4.3 g of a light color oil.
• the product is analyzed by capillary gas chromatograph versus authentic samples to establish the yield and ortho-para ratio.
• the electrolysis apparatus employed is as previously described.
• the catholyte and anolyte solutions are prepared as described for the electrolysis of toluene.
• To the anode compartment is added 1.26 g of iodine (5 mmols) and 2.04 g of iodobenzene (10 mmols).
• the system is electrolyzed at a constant potential of 1.7 volts versus SCE. After passing 965 coulombs, the electrolysis is stopped.
• the anode mixture is cooled to 15° C and the resulting solid isolated by filtration. After water wash and air drying, the solid weighs 2.1 g (64% isolated yield) and is shown by capillary gas chromatography to be 100% p-diiodobenzene.
• the electrolysis apparatus is as previously described.
• the catholyte and anolyte solutions are prepared as described for the electrolysis of toluene.
• To the anode compartment is added 2.54 g (0.01 mole) iodine and 2.42 g (0.031 mole) benzene.
• the system is electrolyzed at a constant potential of 2.0 volts vs SCE.
• the electrolysis is stopped after 1950 coulombs are passed.
• the product is isolated by pouring the anode solution into 500 mL water and extracting three times with 50 mL of methylene chloride. The extracts are combined and washed with 100 mL water.
• the organic layer is dried over magnesium sulfate and the solvent removed in vacuo to afford 4.1 g of a light yellow oil.
• the product is analyzed by capillary gas chromatography to afford iodobenzene chemical yield of 95% based on iodine.
• Example 3 The procedure of Example 1 is substantially repeated except that the working potential is varied.
• the para selectivity versus working potential is shown in Table 3.

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• 1989
  • 1989-11-09 CA CA002002599A patent/CA2002599A1/en not_active Abandoned
  • 1989-11-21 EP EP89420454A patent/EP0376858B1/de not_active Expired - Lifetime
  • 1989-11-21 AT AT89420454T patent/ATE101206T1/de not_active IP Right Cessation
  • 1989-11-21 DE DE68912920T patent/DE68912920T2/de not_active Expired - Fee Related
  • 1989-11-21 ES ES89420454T patent/ES2062081T3/es not_active Expired - Lifetime

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