CS261639B1 - Process for preparing alkylcyclohexylbiphenyls - Google Patents

Abstract

Method for preparing alkylcyclohexylbiphenyls of the general formula I, where R represents n-alkyl with 2 to 12 carbon atoms. By Friedel-Crafts alkylation of biphenyl in a solution of aliphatic halogenated hydrocarbons or carbon disulfide, in which biphenyl is alkylated with acylcyclohexylhalides of the general formula II, where Ri represents n-alkyl with 1 to 11 carbon atoms, X represents chlorine, bromine or iodine, in the presence of Lewis acids, at a temperature of 20 °C to 100 °C, the resulting reaction mixture is hydrolyzed and after distilling off the solvent, the distillation residue is reduced.

Description

(54) A process for preparing alkylcyclohexylbiphenyls

A process for the preparation of alkylcyclohexylbiphenyls of formula I wherein R is n-alkyl of 2 to 12 carbon atoms. By Friedel-Crafts alkylation of biphenyl in a solution of aliphatic halogenated hydrocarbons or carbon disulphide by biphenyl alkylating the acylcyclohexyl halides of formula II, wherein R 1 is n-alkyl of 1 to 11 carbon atoms, X is chlorine, bromine or iodine in the presence of Lewis The reaction mixture is hydrolyzed and, after distilling off the solvent, the distillation residue is reduced.

Formula I

R- ( _H Y- / O formula II)

- @ ~ ^x (l) (ll)

The invention relates to a process for the preparation of acylcyclohexylbiphenyls by Friedel-Crafts alkylation of biphenyl using acylcyclohexyl halides as alkylating agents.

Alkylcyclohexylbiphenyls are important components of mixed nematic liquid crystals used as dielectric in the construction of electro-optical displays. Commercial mixed nematic liquid crystals are a eutectic mixture of many components of different chemical structures, each component affecting the electro-optical properties of the entire mixture.

Alkylcyclohexylbiphenyls are added to mixed nematic liquid crystals, since their addition to the viscosity, dielectric and optical anisotropy of the nematic mixture is little influenced by the addition of a range of concentrations, but greatly extends the mesophase temperature temperature interval by increasing the phase transition. temperature dependence of threshold voltage for nematic mixture. Alkylcyclohexylbiphenyls are chemically stable substances, resistant to oxidation and UV radiation.

Alkylcyclobiphenyls have hitherto been prepared by multi-step synthesis associated with numerous difficult separation operations. (U.S. Pat. Nos. 4,154,697, 4,330,426, German Patent Nos. 2,701,591, 2,927,277, and 2,948,836.) In this isymesis, the starting material is biphenyl, brominated and the bromo derivative formed is used to prepare the Grignard reagent, which further reacts with alkylcyclohexanone to the corresponding alcohol. The alcohol is dehydrated to an alkylbiphenylylcyclohexene which is hydrogenated to give the alkylcyclohexylbiphenyl product.

A disadvantage of the above process for the preparation of alkylcyclohexylbiphenyls is the large number of synthesis steps whose intermediates must be separately isolated, in some cases using special, technically and economically demanding separation methods, for example preparative liquid chromatography.

It has now been found that the drawbacks of the above synthesis process can be overcome by carrying out the preparation of the alkylcyclohexylbiphenyls of the invention based on the alkylation of biphenyl using acylcyclohexyl halides as alkylating agents,

Surprisingly, it has been found that the acylcyclohexyl halides previously used for the alkylation of benzene derivatives can also be advantageously used for the alkylation of biphenyl according to the invention. The synthesis of the alkylating agents of acylcyclohexyl halides is a generally known reaction, described in detail, for example, in Mol. Cryst. Liq. Cryst. 1982, 88 (1-41, 55-64.

Process for the preparation of alkylcyclohexylbiphenyls of the general formula (I) - <H ')

wherein R is n-alkyl of 2 to 12 carbon atoms, Friedel-Crafts alkylation of biphenyl in a solution of aliphatic halogenated hydrocarbons, or carbon disulphide, according to the invention is characterized in that biphenyl is alkylated with acylcyclohexyl halides of the formula II

RfCO (II) wherein R1 represents n-alkyl of 1 to 11 carbon atoms, X represents chlorine, bromine or iodine, in the presence of Lewis acids, at a temperature of 20 ° C to 100 ° C, the resulting reaction mixture is hydrolyzed and distilled off the distillation residue is reduced.

The reduction can be carried out either with hydrazine hydrate or catalytically. Triethylene glycol is preferably used as the polyglycol.

The process for preparing the alkylcyclohexylbiphenyls of the invention is illustrated in the following examples.

Example 1.154 g (1 mol of biphenyl) are dissolved in 600 ml of dichloromethane and 200 g (1.5 mol) of anhydrous aluminum chloride are added thereto, and a solution of 174 g (1 mol) is slowly added to the suspension under stirring. The reaction mixture is stirred for 10 hours under reflux of dichloromethane and, after cooling, is poured into an ice spray acidified to 5% by weight with hydrochloric acid, the resulting two phases are separated and the organic phase is freed from the solvent by distillation. 200 g of hydrazine hydrate (98% by weight), 200 g of finely divided potassium hydroxide, 1000 ml of triethylene glycol are added to the distillation residue and the resulting mixture is refluxed for two hours.

Then replace the reflux condenser with a descending condenser and heat the reaction mixture slowly to distill off the hydrazine / water mixture. When the temperature of the reaction mixture reaches 195 ^and C, it is left at this temperature until the evolution of nitrogen is complete. After cooling to room temperature, the reaction mixture was diluted

6 1 N 3 9

6 with an equal volume of water and extracted three times with diethyl ether. The combined ether extracts (the ratio of the volume phases of the extraction, i.e. the aqueous phase: diethyl ether is 2: 1) are dried with calcium chloride after washing with 5% by weight hydrochloric acid and water.

After filtering off the desiccant, the diethyl ether is evaporated and the residue is treated by vacuum traction distillation. 90 g of the final product are isolated from the high product fraction after crystallization from ethyl alcohol in the form of white crystals, m.p. The content of 4- (4‘-propylcyclohexyl) biphenyl in the final compound is on average (by GLC-MS) 95% by weight, which corresponds to a yield of 28% of theory.

Using the same procedure as in Example 1, 1 mole of biphenyl in 600 ml of dichloromethane was added with the addition of 2 moles of ferric chloride instead of anhydrous aluminum chloride. The final product is 4- (4‘-propylcyclohexyl) biphenyl in 25% yield.

154 g (1 mol) of biphenyl are dissolved in 600 ml of dichloromethane and 200 g (1.5 mol) of anhydrous aluminum chloride are added to this solution. A solution of 174 g (1 mol) of 4-ipropionylcyclohexyl-1-chloride in 150 ml of dichloromethane is then slowly introduced into the resulting suspension. The reaction mixture is stirred for 10 hours while boiling dichloromethane and, after cooling, is introduced into an ice spray, acidified to 5% by weight. hydrochloric acid. The resulting two phases were separated and the organic phase was freed from the solvent by distillation. The distillation residue is hydrogenated in an ethanolic solution of 3% Pt / C at atmospheric pressure and room temperature. Ethanol was then separated from the reaction mixture, diluted with water and extracted with diethyl ether. The procedure was as in Example 1, with a yield of 27%.

Example 4

154 g (1 mol) of biphenyl are dissolved in 600 ml of dichloromethane - to this solution is added 2-00 g (1.4 mol) of anhydrous aluminum chloride. A solution of 1 mole of 4-decanoylcyclohexyl-1-bromide in 20-0 ml of dichloromethane is then slowly added to the resulting suspension. The procedure was as in Example 1, with a yield of 20 percent.

Claims (2)

I will invent the object A process for the preparation of alkylcyclohexylbiphenyls of general formula (I) R. _R CO (II) (I) wherein R is n-alkyl of 2 to 12 carbon atoms, Friedel-Crafts alkyl biphenyl in a solution of aliphatic halogenated hydrocarbons, or carbon disulfide, according to the invention consists in biphenyl is alkylated with acylcyclohexylh-allogemides of formula (II) wherein R 1 is n-alkyl of 1 to 11 carbon atoms, X is chlorine, bromine or iodine, in the presence of Lewis acids, at a temperature of 20 ° C to 100 ° C, The resulting reaction mixture is hydrolyzed and, after distilling off the solvent, the distillation residue is reduced. 2. A process according to claim 1 wherein the Lewis acid is aluminum chloride, ferric chloride or tin tetrachloride.