A METHOD FOR DEALKYLATION OF ALKYL-ARYL ETHERS

Abstract: A method for the dealkylation of alkyl-aryl ethers with aluminium iodide, in the presence of a catalytic amount of a quaternary ammonium compound with the formula R4N<+>I<->, wherein R is alkyl, in an inert solvent. The inert solvent is preferably benzene or cyclohexan.

Description: A method for dealkylation of alkyl*- < aryl ethers. The present invention relates to a method for dealkylation of alkyl-aryl ethers with aluminium iodide. Dealkylation of ethers is a well known method in organic syn¬ theses and many reagents can be used. Earlier methods have however considerable disadvantages when used on a technical scale. Hydrogen iodide, hydrogen bromide and hydrogen chloride as well as aluminium trichloride and ferrichloride give bad yields. Aluminium tribromide gives better yield but is an ex¬ pensive raw material. Good yields can be obtained with boron trichloride, boron tribromide and boron triiodide but these reagents are very expensive and the methods are only of in- terest for laboratory work. Some phosphorus compounds can be used but are not very selective. The use of aluminium triodide for dealkylation has earlier beer- tested.Aluminium metal and iodide reacted in carbon dis _- phide and the ether was then added in a carbon disulphide so- lution . The disadvantages with this method is the use of the toxic and inflammable carbon disulphide and the rather long reaction times. Biproducts are formed, which in some cases have very bad smell and involve industrial hygiene problems. The present method has important advantages as to- industrial hygiene compared to the earlier known method and also gives a more pure product and higher yields. The reaction times are also shorter. The method is characterized by the use of inert solvents which are inexpensive and relatively easy to handle and the reaction takes place, in the presence of catalytic + - amounts of a quaternary ammonium salt of the type R^N I . The reaction can be expressed as follows: 1) R 4 NI R - 0 - Ar + Al I 3 v Ar - OH + R - I 2) H 2 0 R = alkyl Ar= aryl The metod will be further illustrated with the following example Example 1 Aluminium powder (2,5 g, 93 mmol) and iodide (19,0 g, 150 mmol) were mixed in 130 ml benzene (or cyclohexane) and were refluxed until the red colour of iodine disappeared (about 1,5 hours) . The mixture was cooled. A solution of anisol (phenyl - methyl ether, 5,4 g, 50 mmol) and n-Bu.N I (tetra-n-butyl ammonium- iodide, 0,05 g, 0,14 mmol) dissolved In 25 ml benzen (cyklo- hexane) was added dropwise. The mixture was heated and was re- fluxed for 20 in, then cooled and hydrolysed with 150 ml water The organic phase was separated and the water phase was ex- tracted with 2 x 25 ml diethyl ether. The organic phases were collected and were extracted with 30 ml 2 molar NaOH. The wa¬ ter phase was separated, acidified with concentrated HC1 and was extracted with 3 x 25 ml diethyl ether. The organic phases were dried (Na~S0.) and were evaporated to give pure crystalline phenol. Yield = 99 %. M.p. 41-42 °C. Example 2 . Aluminium powder (75 g, 279 mmol) and iodide (57 g, 450 mmol) were mixed and refluxed as in example 1. After cooling a solu¬ tion of pyrogalloltrimetylether, 1,2 ,3-trimetoxibenzene (8 , 4 g, 50 mmol) and n-Bu.N I (0,1 g, 0,28 mmol) in 25 ml benzene was added. After reflu ing for 0,5 hours the mixture was hydro- lyzed with 150 ml water. The benzene phase was separated and washed with 2 x 20 ml water, which was added to the water phase. The combined water phases were extracted with 6 x 50 ml ethyl- acetate (EtOAc) . The EtOAc-phases were combined, dried(Na SO ) and evaporated to give pure pyrogallol in a 95 % yield. M.p. 132-133 °C. The following table gives a survey of other dealkylations made according to the method. Ether Solvents Molar ratios . Reaction Yie ld Product ALI 3 /ether ettør/R^ tims (h) 2-metoxy- 2-hydroxy- naftalene naftalene benzene 360 1/2 78 p-Met.oxyben- p-Hydroxy- ?aldehyde benzalde- hyde Molar ratios Ether Solvents Reaction Yield Product All 3 /ether ether/R Nl " time(h) -aldehyde bensalde- hyde benzene 180 .1/2 95 pyrogallol- trimetylether pyrogallol 4-Hydroxy-3- 3.4-Dihy- metoxytoluene droxytolu¬ ene Molar ratios Ether Solvents All 3 /ether ether/R.Nl " Reaction Yield Product time(h) cyklo¬ hexane 5.5 120 2.5 14 isovanil- 3.4-Dihy- line droxybensal ronal=hel otro- pin metoxyben- toxysalicyl zaldehyde aldehyde l Molar ratio ether/R.NI was 100 in all these experiments with 3 , 4, 5-trimetoxylbenzaldehyde 3 , 5-Dimetoxy -4-hvdroxy- benzaldehyde 3,4-Dihydroxy- -5-metoxyben_- zaldehyde CHO 3,5-Dihydroxy- -4-metoxybenz- aldehyde

Claims: CLAIMS 1. Method for dealkylation of alkyl-aryl ethers with alumi- niumtriodide, prepared in situ from iodide and aluminium powder,c h a r a c t e r i z e d in that the reaction is conducted in the presence of a quaternary ammonium salt 5 in catalytic amount. 2. Method according to claim 1, c h a r a c t e r i z e d in,that the quaternary ammonium salt has the general formula R 4 N + I ~ , where R is an alkyl group. 3. Method according to claim 2, c h a -r a c t e r i z e d 10 in, that the quaternary ammonium salt is tetra-n-butyl- ammonium iodide. 4. Method according to claims 1-3,c h a r a c t e r i z e d in, that the reaction is conducted in an inert aliphatic, cycloaliphatic or aromatic solvent. 15 5. Method acording to claim 4, c h a r a c t e r i z e d in, that the solvent is cyclohexan. 6. Method according to claim 4, c h a r a c t e r i z e d in, that the solvent is benzene. 7. Method according to claim 4, c h a r a c t e r i z e d 20 in, that the solvent is toluene. f 8. Method according to claim 4, c h a r a c t e r i z e d in, that the solvent is xylene.

Inventors: ANDERSSON SVEN GOERAN BERTIL, ANDERSSON, SVEN, GOERAN, BERTIL
Applicants: CHEMICAL DYNAMICS DEV AB, CHEMICAL DYNAMICS DEVELOPMENT AB
Application year: 1985
Main classification: C07C37
IPC codes: C07C37, C07C45