Method for dealkylation of alkyl-aryl ethers

Details Method for dealkylation of alkyl-aryl ethers Method for dealkylation of alkyl-aryl ethers

1986-06-20

1987-09-22

Lone, Werren B.

Organic compounds -- part of the class 532-570 series

Organic compounds

Oxygen containing

568806, C07C 3700, C07C 37055

Patent

active

046956590

DESCRIPTION:

BRIEF SUMMARY
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 syntheses 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 expensive 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 interest for laboratory work. Some phosphorus compounds can be used but are not very selective.
The use of aluminium triodide for dealkylation has earlier been tested. Aluminium metal and iodide reacted in carbon disulphide and the ether was then added in a carbon disulphide solution.
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.sub.4 N.sup.+ I.sup.-.
The reaction can be expressed as follows:
The method will be further illustrated with the following examples:


EXAMPLE 1

Aluminium powder (2.5 g, 93 mmol) and iodine (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.sub.4 N.sup.+ I.sup.- (tetra-n-butyl ammoniumiodide, 0.05 g, 0.14 mmol) dissolved in 25 ml benzene (cyclohexane) was added dropwise. The mixture was heated and was refluxed for 20 min, then cooled and hydrolysed with 150 ml water. The organic phase was separated and the water phase was extracted with 2.times.25 ml diethyl ether. The organic phases were collected and were extracted with 30 ml 2 molar NaOH. The water phase was separated, acidified with concentrated HCl and was extracted with 3.times.25 ml diethyl ether. The organic phases were dried (Na.sub.2 SO.sub.4) and were evaporated to give pure crystalline phenol. Yield=99%. M.p. 41.degree. -42.degree. C.


EXAMPLE 2

Aluminium powder (75 g, 279 mmol) and iodine (57 g, 450 mmol) were mixed and refluxed as in example 1. After cooling a solution of pyrogalloltrimetylether, 1,2,3-trimetoxibenzene(8.4 g, 50 mmol) and n-Bu.sub.4 N.sup.+ I.sup.- (0.1 g, 0.28 mmol) in 25 ml benzene was added. After refluxing for 0.5 hours the mixture was hydrolyzed with 150 ml water. The benzene phase was separated and washed with 2.times.20 ml water, which was added to the water phase. The combined water phases were extracted with 6.times.50 ml ethylacetate(EtOAc). The EtOAc-phases were combined, dried (Na.sub.2 SO.sub.4) and evaporated to give pure pyrogallol in a 95% yield. M.p. 132.degree.-133.degree. C.
The following table gives a survey of other dealkylations made according to the method.


__________________________________________________________________________ Molar ratios Reaction Yield Ether Solvents AlI.sub.3 /ether ether/R.sub.4 NI.sup.- time (h) % Product __________________________________________________________________________ ##STR1## benzene 1 360 1/3 100 ##STR2## anisol phenol ##STR3## cyclohexane 1 360 1/3 100 ##STR4## ##STR5## CS.sub.2 1 360 1/3 91 ##STR6## ##STR7## benzene 1 360 1/3 94 ##STR8## 2-methoxynaphthalene 2-hydroxynaphthalene ##STR9## benzene 1 360 1/2 78 ##STR10## p-Methoxybenzaldehyde p-Hydroxybenzalde

REFERENCES:
patent: 4087410 (1978-05-01), Dominianni et al.
patent: 4112003 (1978-09-01), Huber
patent: 4172960 (1979-10-01), Baldwin et al.
Bhatt et al., Tetrahedron Letters, vol. 25, No. 32, pp. 3497-3500 (1984).
Mincione, "Chemical Abstracts", vol. 73 (1970), p. 24547s.
Cabdidu et al., "Chemical Abstracts", vol. 78 (1973), p. 71603y.
Orgen et al., "Chemical Abstracts", vol. 83 (1975), p. 36919j.

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