CA1216308A - Process for oxidizing p-alkenylphenols - Google Patents

Abstract

Abstract of the Disclosure p-Alkenyl phenols are prepared by reacting an alkylated phenol having a replaceable hydrogen atom at the 4- position with an aliphatic aldehyde having two carbon atoms up to at least 20 carbon atoms in the molecule and a secondary amine; the p-alkenyl phenols are converted to substituted hydroxybenzaldehydes by direct oxidation in the presence of a catalyst.

Description

;3~i PROCE.SS FOR p-ALKENYL PHENOLS AND THEIR
SUBSEQUE.NT OXIDATION FORMING S~gTITUTED ~E;N-~LDE~IYnES

This invention relates to a novel process for the preparation oE p-alkenyl phenols and the subsequent preparation of the corresponding substituted benzaldehydes. More particularly, this invention relates to a novel process for the preparation of 1,1-hydrocarbyl-substituted-2-(3'-hydrocarby:L or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)-ethene compounds which are especially useful as intermediates in the preparation of phenolic antioxidants for gasoline, lubricants, plastics and rubber.
In accordance with one aspect of the invention, an alkylated phenol having a replaceable hydrogen atom at the 4- position and at least one hydrocarbyl substituent ortho to the hydroxyl group is reacted with an aliphatic aldehyde having two carbon atoms up to at least 20 carbon atoms in the molecule and a secondary amine to form the corresponding l,l-hydrocarbyl-substituted-2-(3`-hydrocarbyl- or 3',5'-dihydro-carbyl-4'-hydroxyphenyl)-ethene.

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The invention cnn best be understood by the fol-lowing detailed discussion oE the reactants and conditions by which the p-aLkerlyL phenol products of the present process are produced. The structure of these products will, of course, be determined by the nature of the starting phenolic and aldehyde reactants.
In general, any monohydroxybenzene compound having a replaceable hydrogen atom on the ring carbon atom para to the hydroxyl substituent and at least one hydrocarbyl substituent ortho to the hydroxyl group, as in the case of o-tert-butyl phenol, will serve as the starting phenol. Since the products of the process are principally useful as antioxidants or as intermediates in the preparation of antioxidants, it is desirable that the hydrocarbyl substituents be alkyl, aralkyl or cycloalkyl groups sufficiently large to offer some degree of hindrance to the phenolic group. It is especially desirable that the hydrocarbyl substituent be branched on the alpha-carbon atom and have at least 3 carbon atoms and, preferably, up to 8 carbon atoms;
although any number of carbon atoms, for example up to about 40 carbon atoms, may be present in the hydrocarbyl substituent as long as the substituents do not interfere with the formation of the desired phenolic styrene.
Suitable o-hydrocarbyl phenols meeting these require-ments include secondary alkyl-substituted phenols such ~Z~L63~3 as o-isopropyl phenol, o-sec-butyl phenol, o-sec-amyl phenol and o-cyclohexyl phenol; while suitable tertiary hydrocarbyl phenols are o-tert-butyl phenol and o-tert-amyl phenol. Additionally, primary hydrocarbyl phenols, such as o-benzylphenol, cun serve as starting phenols.
~ iost preEerred phenolic reactants in the process oE this invention are dialkyl phenols wherein the phenol has a replaceable hydrogen atom on the para ring carbon atom and two hydrocarbyl substituents ortho to the hydroxyl group. Preferably, at least one of the hydro-carbyl substituents i9 branched on the alpha-carbon atom and has from 3 to 8 carbon atoms. The substituents need not both be the same hydrocarbyl radical. Specific examples of particularly appropriate phenols are repre-sented by 2,6-dimethyl phenol, 2,6-di-n-butyl phenol,

2,6-di-sec-butyl phenol, 2-isopropyl-6-methyl phenol, 2,6-diisop~opyl phenol, 2,6-di-tert-butyl phenol, 2,6-di-sec-octyl phenol, 2-methyl-6-cyclohexyl phenol, 2,6-di-(alpha-methylbenzyl)phenol, 2,6-dibenzyl phenol, 2-methyl-6-benzyl phenol and the like. A particularly - preferred phenolic reactant for use in the present pro-cess is 2,6-di-tert-butyl phenol.
Substituent groups other than those previously listed such as aryl, chlorine, bromine, fluorine and nitro groups and the like may be present at any of the ring carbon atoms with the sole exception of the para , . .. , . _ _, ring carbon atom ln the aromatic phenolic reatant provided they do not adverseLy affect the formation of the desired l,l-hydrocarbyl-substituted-2-(3'-hydro-carbyl or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)ethene product.
Preferred starting phenolic reactunts may be described by the structure OH
1 0 ~

wherein Rl and R2 are the same or different and are hydrogen or hydrocarbyl radicals, preferably alkyl, aralkyl or cycloalkyl radicals having up to at least 40 carbon atoms, and preferably from 3 to B carbon atoms, at least one of which is branched on the alpha-carbon atom with the provision that at least one of Rl or R2 must be other than hydrogen.
Aldehydes which are applicable to the present process are those aldehydes having a single aldehyde radical of the general formula H O

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.. . . . .

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wherein R3 and R4 can be the same or different and are selected Erom hydrogen or linear and branched alkyl radicals having up to at least 40 carbon atoms, prefer-ably up to 20 carbon atoms. Typical aLdehydes which mny be used in the process of the invention include, by way of example only, acetaldehyde, propionaldehyde, butyraldehyde, isobutyraldehyde, caprylaldehyde, decylaldehyde, tetradecylaldehyde, and the like.
Amine reactants which are applicable to the present process are secondary amines; that is, deriva-tives of ammonia having one hydrogen atom bonded to the amino nitrogen atom and can be represented by the formula wherein R5 and R6 are the same or different and are linear or branched alkyl radicals having up to at least 40 carbon atoms. It is deemed, however, that secondary amines containing nitrogen atoms in a ring structure such as piperidine, pyrrolidine, morpholine and the like also may be used. Preferred amines are dimethylamine, diethylamine, dipropylamine, dibutylamine, disecondary propyLamine, ethylmethylamine, metbylpropylamine, methyl-n-butylamine, ethylisopropylamine and the like.

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Under the reaction conditions, the a0ino reactant lnitially combines with the phenolic and aldehyde reflc-tants to yield a Mannich base type of intermediate which upon further reaction spontaneously eliminates the amine component to produce the olefinic Einal product. The carbonyl carbon atom oE the aldehyde reactant, along with the organic groups bonded to the carbonyl carbon atom of the aldehyde, becomes bonded to the 4-carbon atom of the phenol ring. Some aldol condensntion by-product is produced during the reaction.
The 1,1-hydrocarbyl-substituted-2-(3'-hydrocarbyl or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)etherle products of the process can be represented as those compounds having the general formula:

Rl H0 ~ CH - C

wherein Rl and R2 are the same or different and are hydrogen or hydrocarbyl radicals selected from the group consisting of alkyl, aralkyl or cycloalkyl radicals having up to at least 40 carbon atoms with the provision that at least one of the Rl or R2 radicals must be ~L63~

other than hydrogen and R3 and R4 are the same or different and are hydrogen or linear or branched alkyl radlcals having up to at least 20 carbon atoms in the molecule with the provision that one of R3 or R4 must be other than hydrogen.
The process of the invention is carriecl out by reacting the phenolic starting material with at least one molar equivalent of aldehyde and at least û.l. molar equi~alent oE amine. It is preEerred, however, that the reaction be conductecl witl- a molar excess of both aldehyde and amine reactants with respect to the start-ing phenol. A preerred range of aldehyde to phenolic reactant is from 1 to 10 moles of aldehyde per mole of phenol. A preferred molar range of amine reactant to phenolic reactant is from 0.1 to 10 moles of amine per mole of phenol.
The reaction can be conducted at a temperature from S0C. to 250C. While lower temperatures can be used, the reaction rates are generally too low to be of interes~. Temperatures above 250C. can be used, but excessive decomposition of the reaction components can occur. The preferred reaction tempera-tures are from 50C. to 200C.
The reaction can be conducted at atmospheric pressure or at higher pressures, with moderate pressures up to about 300 psig being preferred.

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The use of a solvent for the reaction mixture is noL generally required, though, iE desired, a solvent which is inert un(ler the reaction conditions, i.e., those solvents which do not enter lnto the reflction, may be added to the reaction vessel. Useful solvents comprise aprotic solvents which include ethers such as diethyl ether, dibutyl ether, I-ethoxyhexane, tetra-hydroeuran, 1,4-dioxane, 1,3-dioxolane, diglyme, 1,2-diethoxyethane and tertiary amines such as pyridine, N-ethylpiperidine, triethylamine, tributylamine, N,N-di-phenyl-N-methyl amine, N,N-dimethylalanine, etc. Espe-cially useful solvents are dipolar aprotic solvents such as dimethyl sulfoxide, N,N-dimetbylformamide, N,N-dimethylace~amide, dimethyl suleone, tetramethylene sulfone, N-methylpyrrolidinone, acetonitrile and like lS materials. Other solvents which are inert under th,e reaction conditions may be used: for example, low boil-ing hydrocarbons, halogenated hydrocarbons, examples Oe which are benzene, toluene, tetrachlornethane, the chlorinated benzenes, the chlorinated toluenes, etc.
Especially preferred solvents are lower alkanols having up to about 6 carbon atoms. These include methanol, etbanol, n-propanol, isopropyl alcohol, n-butanol, sec-butyl alcohol, tert-butyl alcohol, n-pentanol, isopentyl alcohol, n-hexanol and isohexyl alcohol.

.. _. . _.. . . . . ., . . .. . . , . __ _ _.. _ .

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The amount of solvent can be expressed fl6 a volume rat;o of solvent to phenollc reactant. Suitable volume ratior~ of solvent to phenollc reactant can be from 0/1 to 500/1 and preferably from 1/1 to 300/l.
The mode oE addition in the process is not par-ticularly critical. Accordingly, it is convenient to add the phenolic reactant to a mixture of the other materials, add the aldehyde to a mixture of the other materials, add the amine reactant to a mixture of the other materials, add the reactants to a mixture of the amine and solvent, introduce all ingredients simul-taneously into the reaction zone, or the like.
Ii a gaseous amine is selected for use in the process, the reaction is carried out by passing the amine in its gaseous state through the reaction mixture in a reaction vessel with agitation to olutain intimate contact of the reactants. To ensure that the a~ount of amine does not exceed that amount required, as hereinabove shown, the amount of amine in contact with the other reactants can be controlled by limiting the flow of amine through or into the reaction vessel.
The process should be carried out for the time sufficient to convert substantially all of the phenolic reactant to the corresponding p-alkenyl phenol. The length of time for optimum yield will depend primarily ~63~13 upon the reaction temperature and l:he particular aol-vent, if any, used in the renction. In gener~l, excel-lent yislda oE p-alkenyl phenol are obtalned in from about two to Eorty-eight hours.
Although not required, the process can be con-ducted in a substantially anhydrous reaction sysLem, and accordingly, the components oE the reaction system are brought together and maintained under a substan-tially dry, inert atmosphere. ~y "substantially anhydrou9" is meant a reaction system wherein the total amount of water present is no more tban about 5 percent by weight, based on the reaction mixture. When the amount oE water in the system exceeds this, both reac-tion rate and yield of product decrease.
The process may readily be conducted in a batch-wise, semi-batch or continuous manner and in conven-tional equipment.
The product p-alkenyl phenol is easily separated from the reaction mixture by such means as distillation, extraction, crystallization and other methods obvious to those skilled in the chemical processing art.
The practice of this aspect of the invention will be still further apparent by the Eollowing illustrative examples.

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Example I
Preparation oE 1 1-Dimethyl-2-(3',5'-Di-t-ButYl-hr-llydroxyphenyl)E-hene 2,6-di-tertiary-butyl phenol (4.1 g; 20 mmol), isobutyraldehyde (3 ml; 33 mmol), dimethylamine (1.5 g;
34 mmol) dissolved in isopropanol (7.5 g) were charged to a 100 ml glass vessel and reEluxed at ambient pres-sure under nitrogen for 48 hours. The resultant reac-tion mixture was allowed to cool to ambient tempetature and concentrated to a yellow oil which was recrystal-lized Erom a mixture oE ethanol and water (90:10) to give yellow crystals (3.7 g; 71% yield) oE l,l-dimethyl-2-(3',5'-di-t-butyl-~ hydroxypheny])ethene as charac-terized by VPC, mass spectrocopy and NMR.
ln a manner similar to ExampLe I above, a number of experiments were carried out varying the temperature, reaction time, pressure, reactants and ratio oE reac-tants. The results were analyzed by vapor phase chromo-tography with internal standards and are shown in the Table below.

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. ~ ~ N ~ ~1 ~ Ul ~ N ~1 '~ S
_ e C C C c c C c S. ~ ~3 E U ) R ~ e ~ ~ Ul ~7 -- K ~ ~ ~ ~ ~ a o ~ ~ a u~
O ~ o~ O a~ ,n ,~
n-ZO ~ ~ ~ C O ~ i s ~ ~ ~"
a~ u~ u~ o _ H H ~ E~ '¢ H Z ~ :IC a ~ Z

N ~i Ul ~ C ~
v .,. ~ u~ ~ o .~1 . _ ~ 1 ~
c3 5~' OO ~ E ~ o o o 0 l~ ~ ~ ~ N
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I ~1 O o o O o U~ "~ o ~ ~ ~ o _ . ' ¦ N "~ 0 ~ O --I 1`1 ~') .r ~; Z ~

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E ¦ '`I ' C ¦ N
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3 o~ ~:

N ~ _ N ~ E
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zl ~ t~;zl ,, _ 13 - ;

-` ~L2~3 .,.1 ~ 1~
~- r~ ~
OP ~I dP

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~4 1 Cl Eo~ 0 a~ '~: '',~

~OD ~ ~

C' ~ ~ o ~--e~
n i ~ I

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In another aspect of this invention, the 1,1-hydrocarbyl-substituted-2-~3'-hydrocarbyl- or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)ethene products produced by the process of the present invention can be directly oxidized to the corresponding 3-hydrocarbyl-4-hydroxybenzaldehyde or 3,5-dihydrocarbyl-4-hydroxyben-zaldehyde by contacting with good agitation the afore-mentioned l,l-hydrocarbyl-substituted-2-(3'-hydrocarbyl-or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)ethene with at least a stoichiometric amount o~ oxygen in the presence of a small catalytic quantity of a catalyst selected ~rom the group consisting of a Lewis acid, an alkali metal salt of a weak acid or an alkaline mearth metal salt of a weak acid, an alkali metal hydroxide or an alkaline earth metal hydroxide, or amine bases until a reaction product containig a substantial amount of the corresponding 3-hydrocarbyl-4-hydroxybenzaldehyde or 3,5-dihydrocarbyl-4-hydroxybenzaldehyde is formed.
Alkylated hydroxyphenyl aldehydes and methods for their preparation are known. For example, U.S.

4,009,210 discloses a method for preparing 3,5-di-tert-butyl-4-hydroxybenzaldehyde, a chemical intermediate for the manufacture of pesticides of the benzylidene-malononitrile type, by reacting 2,6-di-tert-butylphenol with bexamethylenetetramine or a combination of formal-dehyde and ammonium acetate in aqueous acetic acid reaction medium.

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SaZ~L63~)8 A new process Eor the synthesis o~ 3-hydrocalbyl-4-hydroxybenzaldehydes or 3,5-dihydrocarbyl-4-hydroxy-benzflLdehydes has now been discovered in which these materials can be prepared in A simple and straight-S Eorward manner. In this new process, p-alkenyl pbenols, in particular l,l-hydrocarbyl-substituted-2-(3'-hydro-carbyl- or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)ethenes are contacted with oxygen in the presence of a catalyst selected from a Lewis acid, an alkali metal hydroxide or arl alkaline earth metal hydroxide, an alkali metal oE a weak acid or an alkaline earth metal salt oE a weak acid or an amine base. In accordance with the pro-cess, cleavage of the oleEinic bond located at the 4-position oE the phenyl ring oE the p-alkenyl phenol reactant takes place by a radical process whereby the desired alkylated hydroxyphenyl aldehyde product is produced.
The 1,l-hydrocarbyl-substituted-2-(3'-hydro-carbyl- or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)ethenes which are oxidized according to the aEorementioned process are those compounds described and prepared here-inabove.
The process is readily conducted by placing the 1,1-hydrocarbyl-substituted-2-(3'-hydrocarbyl- or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)ethene and other reaction mixture components in a reaction vessel having agitation .. ...... , , . _ .. . .. . _ _ _ . .

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means, or can be advantageously carrLed out, for exam-ple, by passing the l,l-hydrocarbyl-substitutecl-2-(3'-hydrocarbyl- or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)-ethene through appropriate reaction tubes and slmply contacting the same with oxygen or an OKygen containing gas and catalyst. The oxidation reaction should be carried out with agitation and preEerably with vigorous agitation or using other means that affotd intimate contact between the oxygen containing gas and the reac-tion mixture.
An essential component of the reaction mixtureis a catalytic amount of a catalyst, the suitable cata-lysts being selected from the group consisting of alkali metal hydroxides, alkali metal salts of a weak acid, alkaline earth metal hydroxides, alkaline earth metal salts of a weak acid, amine bases, mixtures oE the same and Lewis acid catalysts. Illustrative of suitable catalysts are sodium hydroxide, potassium hydroxide, barium hydroxide, rubidium hydroxide, cesium hydroxide, potassLum carbonate, sodium carbonate, cesium carbonate, rubidium carbonate, potassium sulfite, sodium borate, potassium acetate, diazabicyclononane, pyridine, tetra-methylguanidine, 1,4-diazabicyclo-(2,2,2)-octane, FeC13, LF3, ZnC12, TiC14, HF, H2S04, H3P04, SnC12, SnC14, and CuC12. Copper chloride and ferric chloride are preferred catalysts.

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The amount o~ catalyst used is not narrowly critical but only a small amount is suf~icient to pro-mote cleavage of the olefinic bond at the 4- position of the l,l-hydrocarbyl-substituted-2-(3'-hydrocarbyl or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)ethene reactant.
In general, the amount used can be as little as 0.1 weight percent through amounts up to 1 weight percent, based on the ~seight of p-alkenyl phenol reactant, and evcn greater amounts of catalyst may be used if desired.
In the practice of the invention, the amount of oxygen employed relative to the l,l-hydrocarbyl-substi-tuted-2-(3'-bydrocarbyl- or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)ethene starting reactant is not critical.
In general, only an amount of oxygen required for the direct oxidative cleavage of the p-alkenyl phenol to the corresponding benzaldehyde should be used. For best results, however, it is preferable that at least a stoichiometric amount of oxygen or an amount greater than that stoichiometric required is used.
The reaction is conducted, for example, by pas-sing oxygen, and preferably an oxygen containing gas such as air, through the reaction mixture in a reaction vessel with agitation to obtain intimate contact of the reactants. Typically, the reaction is conducted at atmospheric pressure, however, higher pressures up to about 200 psig may be used, if desired. The amount of ~lZ3L~3~
oxygen reacting with the p-alkenyl phenol reactant can be, in general, easily controlled by llmiting the flow oE gas through or into the reaction zone.
The reaction can be conducted at mildly elevated temperatures of, for example, from 25C. up to higher temperatures of 250C. and preferably at fl temperature that ranges from 50C. up to 150C.
Reflux temperature at atmospheric pressure i8 effective and preferred.
The use of a solvent for the reaction mixture is not generally required, though, if desired, a solvent which is inert under the reaction conditions, i.e., those solvents which do not enter into the reaction, may be added to the reaction vessel. Especially pre-ferred golvents are dipolar aprotic solvents such as dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethyl-acetamide, dimethyl sulfone, tetramethylene sulfone, N-methylpyrrolidinone, acetonitrile and like materials, Other solvents which are inert under the reaction conditions may be used: for example, tertiary amines such as pyridine, N-ethylpiperidine, triethyl-amine, trlbutylamine, N,N-diphenyl-N-methylamine, N,N-dimethylalanine; low boiling hydrocarbons and halogenated hydrocarbons, examples of which are benzene, toluene, tetrachloroethane, the chlorinated benzenes, the chlorinated toluenes, etc, and lower 3~

alkano1s having up to about 6 carbon atoms which in-clude methano1, ethanol, n-propanol, isopropyl alcohol, n-butanol, sec-butyl alcohol, tert-butyl alcohol, n-pentanol, isopentyl alcohol, n-hexanol and isohexyl alcohol.
The amount of solvent can be expressed as a volume ratio oE solvent to alkenyl phenol reactant.
Suitable volume ratios of solven~ to alkenyl phenolic reactant can be from 0/1 to 500/1 and preferably from 1/1 to 300/1.
The process should be carried out for a time sufficient to convert substantially all of the para-alkenyl phenol reactant to the corresponding alkylated hydroxyphenyl aldehyde. In general, the length of time for optimum yield depends primarily on the reaction temperature, the type and amount of catalyst and the particular solvent used in the reaction. In general, excellent yields of product are obtained in Erom 1.5 to 6 hours.
If desired, the process alternatively may be cortducted to continuously produce the benzaldehyde products oE the invention. A suitable continuous reac-tor generally consisting of a length of vertically mounted reactor tubing having heating or cooling means surrounding it may be employed.

The product aldehyde can be easily separated ~rom the reactant mixture by such means as distillatlon, recrystallizution and other methods obvious to those skilLed in the chemical processing art.
The following examples serve to illustrate the formation of alkylated hydroxyphenyl aldehydes from para-alkenyl phenols.
Example 19 Preparation of 2,6-Di-t-Butyl-4-HydroxYhenzaldehyde A lûO ml glass reaction vessel was charged with 1.1 g (4.3 mmols) 1,1-dimethyl-2-(3',5'-di-t-butyl-4'-hydroxyphenyl)-ethene. Ferric chloride hexahydrate (0.03 g; 0.12 mo)ols) was suspended in approximately 6 g of N,N-dimethylformamide and added to the reaction ves-15 sel. Oxygen (17.7 g; 550 mmols) was slowly introduced into the solution in the reactor which gradua]ly dar-kened the solution. After 1.75 hours, the black reac-tion mixture was filtered through a silica gal pad and the filtrate was concentrated to give a black semi-solid 20 product (0.75 g; 74~ yield) of 2,6-di-t-butyl-4-hydroxy-benzaldehyde as identified by gas chromotography and thin layer chromotography.
In a manner similar to Example 19 above, a number of experiments were carried out varying the temperature, reaction time, solvent and type of catalyst. The results are shown in the Table below.

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a, I o ~ ~D O U~
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In o~Ul U~
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X X X X
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a) E~ o 1 S
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N '~-: o O ~o ~ ~ o H . o U
., :' ~ ,.,E3,.1 --~ o ~¢, m o~ ~ ~ ~ ~ I s ~c> O S o o ¦ H ~ H H E- ~, O X
.~ V S
E
~4 v E3 --' V
C~ ~ , n :., ~ V ~
~ J o ~: . ~ :
æ C~ 1~ æ æ , _ r V I S
o _~ ~1 111 _, v P~ 3 ~ 'r o ~_~ E
I
~ ol o ~
~ Z ~ ~ ~I N N

Claims (7)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. The process for converting a 1,1-hydrocarbyl-substituted-2-(3'-hydrocarbyl- or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)ethene to the corresponding 3-hydrocarbyl-substituted-4-hydroxybenzaldehyde or 3,5-dihydrocarbyl-4-hydroxybenzaldehyde which comprises intimately contact-ing said 1,1-hydrocarbyl-substituted-2-(3'-hydrocarbyl or 3',5'-dihydrocarbyl-4'-hydroxy-phenyl)ethene with at least a stoichiometric amount of oxygen or an oxygen-containing gas in the presence of a catalytic quantity of a catalyst selected from the group consisting of alkali metal hydroxides, alkali metal salts of a weak acid, alkaline earth metal hydroxides, alkaline earth metal salts of a weak acid, amine bases, mixtures of the same and a Lewis acid for the time necessary to react at least a stoichiometric amount of oxygen with said 1,1-hydrocarbyl-substituted-2-(3'-hydrocarbyl- or 3',5'-dihydrocarbyl-4'-hydroxyphenyl)-ethene to form a reaction product containing a substantial amount of the corresponding 3-hydrocarbyl-substituted-4-hydroxybenzaldehyde or 3,5-dihydrocarbyl-4-hydroxybenzaldehyde.

2. The process as claimed in Claim 1 in which said 1,1-hydrocarbyl-substituted-2-(3',5'-dihydrocarbyl-4'-hydroxyphenyl)ethene is 1,1-dimethyl-2-(3',5'-di-t-butyl-4'-hydcoxyphenyl)ethene and the reaction product formed therefrom is the corresponding 2,6-di-t-butyl-hydroxybenzaldehyde.

3. The process as claimed in Claim 1 in which said reaction is carried out at a temperature of from 50°C. to 250°C.

4. The process as claimed in Claim 1 in which the reaction mixture is substantially free of any solvent.

5. The process as claimed in Claim 1 in which said reaction is carried out in the presence of a solvent.

6. The process as claimed in Claim 5 in which said solvent is a dipolar aprotic solvent.

7. The process as claimed in Claim 5 in which said solvent is selected from the group consisting of low-boiling hydrocarbons, halogenated hydrocarbons and lower alkanols having up to about 6 carbon atoms.