US2490601A - Dealkylation of alkoxyaryls - Google Patents

Description

Patented Dec. 6, 1949 Bernard:W.- Rottschaefer, East-:GreenbusmhN; Y.,. assignor to. General Aniline &.;F;ilm Corporal tion, New York, Y., a..cornorationpf.Delae ware.

NoiDrawinga ApplicationaIill'y 35 19463 SerialLNo. 681312 6 Claims.

Thewpresent invention relates to sa-method; of dealkylating alkoxyaryls and is particularly concerned with an improved method in which anal.- koxyaryl compound (especially analkoxy arylamino compound)v is dealkylated by treatment with a Friedel-Crafts reagent ina saturated-all.- phatic or alicyclic hydrocarbon solvent free, from unsaturates and aromatics.

The use of a Eriedel-Crafits reagent as a dealkylating agent for thedealkylation of alkoxy aryls has heretofore been suggested. However, such prior art processes have-generally beenaccompanied by the formation of tarsandgums. I have now found that if the aromatic solvents. (such as benzene, toluene and the. like) which have heretofore been employed, are. replaced by. a saturated aliphatic or alicyclic hydrocarbon me.- dium free from unsatunates and aromatics, the. dealkylation of alkoxyaryl compounds. using. a Friedel-Crafts reagent is readily carriediout with a goodyield of the desired product in a high degree of purity and'free of tars and other undesirable lay-products. I have also found that somewhat smaller amounts of Friedel-Crafts reagent can be employed and in-the'case of alkox-yaryl amines, the reaction can be carried outemploying the free base instead ofrthe salt .ofthe base.

The process of the present invention is applicableto the dealkylation ofcompoundsrepresented :by the following-general formula:

in which R represents an aromatic-hydrocarbon ring which may be either mono-cyclic or polycyclic and-which may contain such nuclear-substituents as alkyl, aryl, halogen; hydroxy, alkoxy; nitro, amino and the-like, but whichispreferably free of aryloxy substituents. As examples of such compoundsmay be mentioned anisol, anisi-- dine, phenetole. phenetidine, guaiacol, dianisidine and the like.

In practicing the process of this invention, the alkoxyaryl compound to be dealkylated is dissolved or suspended in a saturated aliphatic or alicyclic hydrocarbon solvent free from unsaturates and aromatics. Any saturated hydrocarbon which is liquid at the reaction conditions may be employed as the solvent for the reaction. As examples of suitable solvents may be mentioned methylcyclohexane, heptane, octane, nonane and various petroleum fractions free of unsaturates and aromatics. A suitable solvent can readily be prepared by treating a gasoline or similar liquid petroleum fraction with approximately an equal volume of sulfuric acid in order to remove any unsaturat-es or: aromatics; whicnit': may; contain. In orderl to; avoid-the "use;ofzilre ssur.e,-;v ilhiS-z (18811:- a-blepthat the solvent; employed, have: anx. initial boiling point; of.:'at-.least-.:9.0..' C... Attheasame; time; too high. aiboiling solvent :is :pref-enablyi-avoidedr-in order; that thesolvent'l may;readilyrbe recovered by distillation. I therefore. preferabl employras solvent a saturated, hydrocarbon boiling within the range of approximately -150 C. The relative amount. of fsolvent' employed duringv the reaction' isnot;'highlyicritical so long as'a sufficient amountiis .used that thereactionrniittureas read ilyfluid:

In ordersto efiectihe *dealkylationoflthealkoxy aryl compound dissolvedion-suspendeddn=the-saia uratedi' hydrocarbon solvent, a1 FriedelI-Crafts reagent iszadded toxwthermixturezof alkoxyaryl com:- pound; and solvent; preferably: atiuartemperature below about: 50?-- C... and; the; reacti m mixture is then heated toa'temperatureatwhich :thedesired dealkylaitionz reactionz. proceeds at as satisfactoryrate, but below that at which undesirediseconde ary reactions takemlace. A. temperature of at least approximately 90 ,C. is preferred in order torobtain a satisfactory rate or reaction; while temperatures :much xaibovet C. are preferabl-m avoide dcin .order to lpreventundesirable side rea'ce tionsh If'thessolvent:employedfior the'reaction res fluxesgwithlna range'vofiabout llof CT-to 150 C; the reaction may advantageouslybe carried outiat at mospheric.pressurezandflat;the refluxtempenature of, the solvent; However; superatmospheric.. pres-- sure; may be employed: if. necessary in order" to maintain theimaterialin; liquid phase.

As a.Frie.delCraftsmeagentI preferably employaluminum chloride or bromide; The relative amount: of; Friedel-Crafts: reagents employed will vary with i the; specific reagenmuseds. lip-general, the.-- approximate amoi-intv of oneumol. aluminum chlorideis employed per: an equivalent: of alkoxy exceptwhere; an-active. group-such as-ran :a-mine group is present, in which; case an. additionalequivalen-t quantity of Friedel-Cnafts reagent is used. For example, when dealkylating phenctol, only one mol aluminum chloride need be used. However, in the case of dianisidine, four mols of aluminum chloride are used, two tion in dealkylating the two methoxy groups present, and two for reaction with the two amine groups present.

The following examples describe in detail spetc fific preferred embodiments of the present invenion.

Example I A gasoline fraction which refluxed at approxifor consumpmately 100l10 C. was refluxed for several hours with an equal volume of 100% H2804 in order to remove any unsaturated or aromatic hydrocarbons which it might have contained, and was then separated from the H2s04 layer. To 2,000 cc. of the saturated hydrocarbon thus obtained there were added 244 grams (1 mol) of dry dianisidine and 580 grams (4.36 mols) of anhydrous aluminum chloride were then added at a temperature of approximately 50 C. The material was then gradually heated to reflux (100-110 C.) and was refluxed for approximately '6 hours to complete the reaction. The charge'wa's then poured into 7,000 cc. of water containing 4 mols of hydrochloric acid. The solvent was removed by steam distillation and the charge diluted to approximately 8 liters. The product-3,3-dihydroxy benzidinewas completely dissolved in the acid mother liquor and an traces of impurities were removed by treating with charcoal and filtering.

--The 3,3-dihydroxy benzidine was then recovered from the acid mother liquor in the form of its sparingly soluble sulfate by adding about 800 grams of NazSOa to the mother liquor and cooling to room temperature. By this procedure a very pure grade of 3,3-dihydroxy benzidine was obtained in excellent yield.

Example II I 142.5 grams of 5-chloro-o-anisidine were added to 2,000 cc. oi gasoline fraction treated as described'in Example I. There were then added 267 grams (2 mols) of anhydrous aluminum chloride at a temperatur of approximately 45 C. The charge was then gradually raised to reflux (125 C.) and refluxed for 6 hours to complete the reaction. The charge was then drowned into water containing an excess of hydrochloric acid and the gasoline removed by steam distillation. The product-4-chloro-o-aminophenolwas recovered in excellent yield by crystallization from the acid mother liquor. Example III 244 grams '(1 mol) f dry dianisidine and 533 grams (4 mole), of anhydrous aluminum chloride were added to,2,000.cc..of methylcyclohexane at a temperaturegoi approximately 50 C. The material,- was then gradually heated to reflux and was refluxed for approximately 6 hours to complete the reaction." The charge was then poured into 7,000 cc. of water containing 4 mols of hydrochloric acid. The solvent was removed by steam distillation and the charge diluted to approximately 8 liters. The product3,3-dihydroxybenzidine-was purified as in Example I.

It will be understood that the foregoing examples are illustrative only of preferred embodiments of the present invention and various modifications within the limits heretofore specified may be made therein without departing from the teachings-of this invention.

I claim:

1. The process of dealkylating alkcxy andamino compounds free of aryloxy groups, which comprises heating to a temperature of 90-150 C. in a. distillable saturated hydrocarbon liquid a mixture of said alkoxy aryl-amino compound and an aluminum halide Friedei-Crafts agent in such molar proportions that one mol of said Friedel- Crafts agent is present for each alkoxy and amino group in said alkoxy aryl-amino compound.

2. The process of dealkylating alkoxy arylamino compounds free of aryloxy groups, which comprises heating to a temperature of 90-150 C., in a saturated hydrocarbon liquid boiling within the range of about 90150 C., a. mixture of said alkoxy aryl-amino compound and an aluminum halide Friedel-Crafts agent in such smaller proportions that 1 mol of said Friedel-Crafts agent is present for each alkoxy aryl-amino group in said alkoxy aryl-amino compound.

3. The process as defined in claim 2 wherein the aluminum halide specified is aluminum chloride.

4. The process of dealkylating anisidine, which comprises refluxing in a saturated hydrocarbon liquid boiling at from 90-150 C, a mixture of anisidine and an aluminum halide Friedel-Crafts agent in a molar ratio of 1 :2.

5. The process of producing 3,3'-dihydroxy benzidine by dealkylating dianisidine, which comprises refluxing in a saturated hydrocarbon liquid boiling at from 90-150 C. a mixture of dianisidine and an aluminum halide Friedel-Crafts agent in a Y molar ratio of 1:4.

6. The process of producing 4-chloro-o-aminophenol by dealkylating 5-chloro-o-anisidine, which comprises refluxing in a saturated hydrocarbon liquid boiling at from 90-150 C. a mixture of 5-chloro-o-anisidine and an aluminum halide Friedel-Crafts agent in a molar ratio of 1:2.

BERNARD W. ROTTSCHAEFER.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS OTHER REFERENCES Hartmann et al., Ber. Deut. Chem, vol. 25,

Ullmann et al., Ber. Deut. Chem, vol 39, pp. 622-625 (1906).

Oesterlein, Monatsh. vol. 57, pp. 31-44 (1931) Fernholtz et al., J. Am. Chem. Soc, vol. 60, p. 2404 (1938).