Patent Publication Number: US-3876688-A

Title: Oxidation of alkyl aromatics

Description:
United States Patent 1 1 de Raditzky DOstrowick et al.  
 [ OXIDATION OF ALKYL AROMATICS [7 5] Inventors: Pierre M. J. G. de Raditzky DOstrowick; Jacques D. V. Hanotier, both of Brussels. Belgium [73] Assignee: Labofina, Soc. An.,Brussels,  
 Belgium Notice: The portion of the term of this patent subsequent to May 23, 1989. has been disclaimed.  
 [22] Filed: Nov. 17, I971 [21] Appl. No.: 199,722  
  Related US. Application Data [62] Division of Scr. No. 884,336. Dec. ll, 1969. Pat. No.  
 [52] [1.8. CI. 260/488 CD; 260/515 R; 260/592; 260/599; 260/600 [5 l] Int. Cl. C07c 45/02 [58] Field of Search 260/524 M, 599. 592  
 [56] References Cited UNITED STATES PATENTS 780,404 l/l905 Bazlcn et al. 260/524 *Apr. 8, 1975 3334.135 8/1967 lchikawa 260/524 3.665.030 5/1972 dOstrowicketal 260/488 FOREIGN PATENTS OR APPLICATIONS 22.105 9/1900 United Kingdom 260/524 Primary Examiner-Lorraine A. Weinberger Assistant Examiner-Richard D. Kelly [57] ABSTRACT Process of liquid phase oxidation of the alpha carbon atom of alkylbenzenes by a manganic or cobaltic salt and an acid activator with or without an oxidationresistant solvent either in an inert atmosphere to produce lower oxidation products of the alpha carbon atom such as alcohols or their esters; or. in the presence of molecular oxygen, to produce higher oxidation products such as aromatic aldehydes, ketones or carboxyl acids.  
 9 Claims, No Drawings 1 OXIDATION OF ALKYL AROMATICS The present invention relates to a process for selective oxidation of alkylaromatic compounds using an oxidizing system comprising a higher valent cobalt(lll) or manganese (Ill) salt of a carboxylic acid and this application is a division of our copending application, Ser. No. 884,336, filed Dec. ll, 1969, now US. Pat. No. 3,- 665,030, issued May 23, l972, by streamline refile and a relatively strong acid.  
  Oxidation of alkylaromatic compounds into oxygenated products in the liquid phase with molecular oxygen in the presence of a heavy metal catalyst is the best available to the chemical industry at this time. Its application remains restricted as a rule to the production of carboxylic acids. This-is principally due to the fact that to reach a sufficient rate of reaction, stringent conditions such as high temperatures and pressures must be applied so that intermediate oxidation products of the alcohol, aldehyde or ketonc type are rapidly converted into acids. During this process, the alkyl groups comprising several atoms of carbon undergo a cleavage of the carbon-carbon bonds except for those joining these to the aromatic nucleus. For this reason, the method is applied principally for oxidation of methylaromatic hydrocarbons like toluene and xylenes. Oxidations performed in the art under milder conditions with various catalysts have been non-selective or inapplicable.  
  we have now discovered that by employing an oxidizing system comprising the cobalt or manganese salt of a carboxylic acid in higher valent form and a relatively strong acid, the oxidation of the alkylaromatic compounds can be performed at distincly lower temperatures than those previously required, with a higher rate of reaction and a greatly improved selectivity. We have found, that by appropriate selection of the components of the oxidizing system and of the operating conditions, the oxidation of the alkylaromatic compounds can be controlled to form side chain alcohols, mainly in the form of esters; or to form aromatic ketones or aldehydes, depending on the structure of the alkyl substituent; or to form aromatic carboxylic acids selectively as principal products. Analogously, starting with a polyalkylated aromatic compound, the reaction can be limited to selectively oxidize a single alkyl group or carried further to oxidize several alkyl side chains. Finally, the oxidizing system employed has an activity such that the alkylaromatic compounds further substituted by a deactivating group are attacked rapidly. Such deactivating groups are chloro, nitro, carboxyl or other electron-attracting groups.  
  The main object of the present invention is to provide a process for the oxidation of alkylaromatic compounds, during which one or more alkyl groups thereof are converted quickly in satisfactory yield into oxygenated functions, with a high degree of selectivity and control. It is a further object to provide a process of carrying out such oxidations at low temperatures.  
  According to the present invention, alkylaromatic compounds having at least one hydrogen atom at the alpha position to the aromatic nucleus are oxidized in &#39;the liquid phase at that alpha position at a temperature in the range of -30 C to +100 C, with an oxidizing system comprising the higher valent cobalt(lll) or higher valent manganese (lll) salt of a carboxylic acid and a stable acid whose dissociation&#39;constant is higher than 10 or boron trifluoride, or a mixture thereof.  
 The alkylaromatic compounds which are oxidized most satisfactorily by the process of the invention are those which comprise at least one alkyl radical having at least one hydrogen atom at the alpha position relative to the aromatic ring. Although higher alkyl radicals can be oxidized such as those having up to about 30 carbon atoms or even higher, the aromatic compounds with l to 6 alkyl radicals having from 1 to 4 carbon atoms are a preferred group of alkylaromatic compounds to be oxidized since they are easily and more economically available. Typical alkylaromatics oxidized herein are the mono-, diand tri-alkylbenzenes, like toluene, ethylbenzene, cumene, 0-, m&#39;-&#39; or pxylenes, o-, m or p-diethylbenzenes and trimethyl benzenes. Polynuclear alkylaromatic compounds such as the mono-, diand trialkylnaphthalenes, like methyl naphthalenes, ethyl naphthalenes and dimethylnaphthalenes are also easily oxidized. Apart from these purely hydrocarbon compounds, alkylaromatic compounds substituted by other radicals, for example. chloro, bromo, iodo, fluoro, nitro or oxygenated radicals such as acyl, alkoxy, carboxyl, l-acyloxyalkyl, may also be oxidized. Typical such substituted alkylaromatic compounds are p-chlorotoluene, p-bromoethylbenzene, m-nitrotoluene, o-acetyltoluene, 4-methoxyethylbenzene, p-toluic acid, 4-methyl-l-naphthoic acid, p-methylbenzyl acetate, and the like.  
  In order that the oxidation of these compounds by the process of the invention may be performed in the liquid phase, it is not essential, but often useful. to employ a solvent. In particular cases, the oxidizing system is soluble in the liquid alkylaromatic compound to be oxidized, and the reaction can occur in the solution thus obtained. Most frequently, however, the reactants are desirably dissolved in a solvent common to both. in general any liquid reasonably inert to oxidation, in which the alkylaromatic compound to be oxidized and the oxidizing system are soluble, may be used. The fatty acids containing from 2 to 10 carbon atoms and their lower esters, preferably their methyl and t-butyl esters, satisfactorily fulfill the preceding conditions. Acetic acid is a particularly advantageous solvent.  
  Among the metal compounds capable of oxidizing hydrocarbon or other organic substances, the cobalt- (lll) and manganeseflll) salts of carboxylic acids are preferred. They are powerful oxidizers; they are satisfactorily soluble in such organic solvents; they are easily produced by known methods. From these points of view, the cobalt(lll) and manganese(lll) salts of fatty acids containing from 2 to 10 atoms of carbon, and preferably their acetates, are particularly satisfacory. For example, cobalt(lll) acetate may be produced by cooxidation of cobalt(ll) acetate with acetaldehyde in acetic acid in the presence of oxygen. Manganeseflll) acetate may be produced by oxidation of manganese(ll) acetate with potassium permanganate in acetic acid. The cobalt(lll) and manganeseflll) salts of the other fatty acids can be produced in analogous manner or by exchange reaction between these and cobalt(lll) acetate.  
 , A fundamental and important aspect of the present invention is the discovery that the oxidizing power of these cobaltic and manganic salts in respect of alkylaromatic compounds is enhanced considerably by the presence&#39;of a relatively strong inorganic or organic acid. The acids which display this activating effect are those whose dissociation constant K is higher than 10&#39;. They should be soluble in the reaction medium and should not interfere with the reaction. Suitable acids are sulphuric acid (K l perochloric acid (K 1 p-toluenesulphonic acid (K l trifluoroacetic acid (K 610&#34;). trichloroacetic acid (K 210). dischloroacetic acid (K 3.3 X 10&#34;). phosphoric acid (K 7.5 X 10 and monochloroacetic acid (K 1.4 X l Some Lewis acids such as boron trifluoride. also have an activating action. The acids containing chlorine, bromine or iodine in ionic form. such as hydrochloric acid. hydrobromic acid or aluminium trichloride are unstable in the conditions of the process and should be avoided.  
  The activating action ofthe acids defined above is exerted both on the rate and the progress of the reaction. The effect is the more pronounced the stronger the acid and. up to a definite limit. the higher its concentration. On the other hand. the quantity of acid should be correlated to the quantity of cobaltic or manganic salt employed. For example, if sulphuric acid is employed to activate a cobaltic salt. a molar ratio between acid and salt of approximately 2 is needed to reach maximum activity. With an acid of lesser strength. such as trichloroacetic acid. a ratio from to is preferable. Although the mechanism of the activation has not been clarified yet. the facts which have been set forth lead to the possibility that the cobaltic or manganic salt reacts with the acid to produce a more oxidizing species which is assumed to be principally responsible for the attack of the substrate. The following scheme can be envisaged accordingly. where the acid. the metal salt and the reactive species are represented respectively by AH. M and M(lll):  
 It must be added. moreover. that the activating effect of a given acid can vary with temperature. the nature of the metal salt and the reactivity of the substrate. For example. the activating action of weaker acids such as trichloroacetic acid or manganic acetate is less effective. under identical conditions. than on cobaltic acetate; but. at increased temperature. it is improved the more effectively with the more reactive substrate. These different factors should be taken into account in selecting the oxidizing system and the conditions to apply to oxidize a particular substrate.  
  The activator allows the oxidation of alkylaromatics to be performed at low temperature. more specifically within a temperature range of to 100 C. In order that the reaction may be rapid as well as selective. it is preferable to operate at temperatures between 0 and 60 C. The reaction will frequently be too slow below 0 C. and the selectivity inadequate above 60 C. y  
  The nature of the oxidation products obtained by the present process is determined by the structure of the alkyl substituent. the composition of the oxidizing system, and the operating conditions. To produce alcohols in the form of esters. the reaction will be carried out in a carboxylic solvent such as acetic acid and in the absence of oxygen. For example. in these conditions. eth ylbenzene can be converted almost quantitatively into the acetate of alpha-methylbenzyl alcohol by use of an oxidizing system comprising a manganic or a cobaltic salt. The ester obtained may then be hydrolyzed to produce the corresponding alcohol. or pyrolyzed to produce styrene. Toluene is converted into benzyl acetate using the same conditions. By.contrast, if it is preferred to obtain products containing a carbonyl function, it is advisable to operate in the presence of oxygen and to make provision for vigorous stirring of the reaction mixture. in these conditions. ethylbenzene can be converted into acetophenone by preferential use of an oxidizing system comprising a cobaltic salt. Analogously,  
 in the presence of oxygen, toluene can be oxidized into benzaldehyde or benzoic acid, depending on whether a manganic or cobaltic salt is employed. These particular examples clearly demonstrate the extraordinary selectivity of the process of the invention and the high degree of control it provides by simple selection of the oxidizing system and of the operating conditions.  
  The effect of oxygen exemplified by the above instances is another important aspect of the present invention. The manner in which oxygen operates in the reaction is not known with certainty. In the prior processes in which a compound ofa metal of high valency is employed as an oxidant. oxygen does not as a rule have an appreciable effect on the reaction. In the present case. it seems that the primary attack of the alkylaromatic compound leads to the formation of a free radical (reaction 3) which would then react with oxygen (reaction 4) to produce a peroxy radical which is subsequently convertible to produce a ketone, an aldehyde or even an acid. as the case may be. In the absence of oxygen. the radical would be oxidized in its turn. probably while producing a carbonium salt (reaction 5) which, in the presence of a carboxylic acid, would result in an ester (reaction 6) R 0 ROO ketone. aldehyde or acid R R&#39;COOH ROCOR&#39; H Corresponding to this pattern, the proportion of ester functions and of carbonyl functions in the reaction products is the result of competition between reactions (4) and (5 It will then be grasped that to promote the production of compounds having a carbonyl function, it is necessary to choose conditions allowing the reaction (4) to predominate. that is to say to operate in the presence of a gaseous phase containing oxygen and to make provision for vigorous stirring for rapid diffusion of the same into the liquid phase. This gaseous phase may consist of pure oxygen or of a mixture of oxygen with other gases which are inert in the conditions of the reaction, for example air. The partial oxygen pressure rmay be between 0.1 and atmospheres. In particular cases. it is possible to apply pressures lying outside this range. For example, a lower pressure than 0.1 atmosphere can be sufficient occasionally, subject to the condition of providing particularly effective stirring. On the other hand. higher pressures than 50 atmospheres may be applied, but those do not lead to an improvement in the results justifying additional plant investment costs. In the greater number of cases. an oxygen pressure of the order of 0.2 to atmospheres will suffice to secure a high degree of conversion into products having a carbonyl function.  
  The quantity of oxydant to be employed depends on the degree of conversion required and on the nature of the products it is desired to obtain. The preceding pattern shows that at least two molar equivalents of higher valent metal salts are needed to produce an ester in a high yield from a monoalkylbenzone. It might have been expected that a greater quantity of oxydant would be consumed to produce a ketone, an aldehyde or an acid. In reality, the production of these compounds by the process of the invention requires no more than a small quantity of oxidant. For example, the production of acetophenone by oxidation of ethylbenzene by means of the system consisting of colbaltic acetate and trichloroacetic acid in the presence of oxygen requires no more than 1.5 to 2.2 atoms of cobalt(lll) per molecule of hydrocarbon. 1n the same conditions. 0.3 to 0.5 atom of cobalt (lll) suffices to convert one molecule of toluene into benzoic acid. These small values demonstrate that a definite degree of regeneration of the oxidizing system occurs in the presence of oxygen. so that the quantity of oxidant consumed may in particular cases be smaller than the quantity of product formed.  
  In the case of polyalkyl aromatic compounds, the oxidation may be limited to a single alkyl group. or extended to several. It is plain to one versed in the art that. to limit the oxidation, it is appropriate to shorten the period of reaction and to employ ana excess of polyalkyl benzene in comparison with the oxidizing system. whereas the inverse of these conditions will be preferable if it is desired to oxidize several alkyl groups within one and the same molecule.  
  The invention will now be further described with reference to the following examples:  
 EXAMPLE 1 This example illustrates the effect of sulphuric acid on the oxidizing power of manganic acetate with respect to alkylaromatic compounds.  
  A solution containing 0.20 mol/Iiter of mdiethylbenzene and 0.04mol/liter of manganic acetate in acetic acid was heated to 70 C for minutes. In a second assay, sulphuric acid was added to the solution at the concentration of 0.5 mol/liter. after which this solution was kept at 25 C for ten minutes. A third assay was also carried out in the presence of sulphuric acid but in the absence of substrate. At the endof the three assays. the manganic ions present in the solution were determined by cerimetry. The results obtained are given in the following table.  
 &#39;It is apparent that, in the presence of sulphuric acid, the  
 EXAMPLE II This example illustrates the effect of trichloroacetic acid on the oxidizing power of cobaltic acetate in respect of alkylaromatic compounds. A solution containing 0.20 mol/liter of 2-ethylnaphthalene and 0.05 mol/- liter of cobaltic acetate in acetic acid was ketp at 25 C under a nitrogen atmosphere at atmospheric pressure for 15 minutes. The same assay was repeated after addition of triehloroacetic acid to the solution. in the proportion of 1.5 mol/liter. A third assay was also carried out in the presence of trichloroacetic acid. but in the absence of substrate. At the end of the three assays the cobaltic ions present in the solution were determined by cerimetry. The results obtained are given in the following table:  
 substrate triehloroaeetie acid reduced C o( 111) EXAMPLE 111 This example illustrates the oxidation of toluene by means of the system consinsting of manganic acetate and sulphuric acid.  
  A solution containing 0.10 mol/liter of toluene. 0.21 mol/liter of manganic acetate and 1.0 mol/liter of sulphuric acid in acetic acid, was kept at 25 C. without stirring. under a nitrogen atmosphere at atmospheric pressure. 78 per cent of the manganic ions had been reduced after one hour. An aliquot part of the reaction mixture was diluted with ether and then treated at 0 C with anhydrous sodium carbonate until the acidity was neutralized. The ether solution was analyzed by vapour phase chromatography to establish the composition of the neutral oxidation products. The acid products were identified by analysis of another aliquot part of the reaction mixture. The combined results of both analyses show that 54 per cent of the toluene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 benzyl alcohol (mainly in the fomi of its 74 &#39;7:  
 acetate ester) benzaldehyde 25 7t henzoic acid 1 &#39;7:  
 EXAMPLE IV This example illustrates the effect of oxygen on the oxidation of toluene by means of the oxidizing system employed in the preceding example.  
  .The experiment of Example III was repeated. but this time while stirring the reaction mixture in the presence of pure oxygen at atmopsheric pressure. By treating and analyzing the reaction mixture as in Example lll. it was established that 65 percent of the toluene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 benzaldehyde 7l 7! benzyl alcohol 24 /1 (mainly in the form of its acetate ester) benzoic acid 5 &#39;/r Comparing the results of this example to those of Example lll. it is plain that in the presence of oxygen. toluene is converted preferentially into benzaldehyde rather than into benzyl alcohol.  
 EXAMPLE V This example illustrates the oxidation of toluene by means of the system consisting of cobaltic acetate and trichloroacetic acid. in the presence of oxygen.  
  A solution containing 0. l0 mol/liter of toluene, 0.20 mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acid in acetic acid was stireed at 25 C in the presence of pure oxygen at atmospheric pressure. 16 percent of the cobaltic ions had been reduced after four hours. The reaction mixture was then treated and analyzed as in Example lll. It was found that 81 percent of the toluene employed had been converted into pure benzoic acid.  
  In another experiment performed in identical manner but while extending the reaction period to 24 hours, the conversion of toluene into benzoic acid rose to 92 percent.  
  From this data it is calculated that the formation of a molecule of benzoic acid required the reduction of no more than 0.3 atom of cobalt. which demonstrates that a substantial proportion of the oxidant is regenerated &#34;in situ during the reaction.  
 EXAMPLE Vl This example illustrates the use of propionic acid as a solvent.  
  The experiment of the preceding example was repeated, while replacing acetic acid with propionic acid. Analysis of the reaction mixture after 24 hours showed that 55 percent of the toluene employed had been converted mainly to yield benzoic acid (98%) and small quantities of benzaldehyde (2%) Identical results were obtained by replacing cobaltic acetate with cobaltic propionate.  
 EXAMPLE Vll This example illustrates the oxidation of ethylbenzene by means of the system consisting of manganic acetate and sulphuric acid.  
  A solution containing 0.10 mol/liter of ethylbenzene. 0.19 mol/liter of manganic acetate and 1.0 mol/liter of sulphuric acid in acetic acid was kept at 25 C. without stirring. under a nitrogen atmosphere at atmospheric pressure. 67 percent of the manganic ions had been reduced after one hour. The reaction mixture was then treated and analyzed as in Example 1]]. It was thus established that 56 percent of the ethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages.  
 alpha-methylbenzyl alcohol 9 (mainly in the form of its acetate ester) acetophenone benzoic acid EXAMPLE Vlll This example illustrates the oxidation of ethylbenzene by means of the system consisting of cobaltic acetate and trifluoroacetic acid.  
  A solution containing 0.10 mol/liter of ethylbenzene, 0.20 mol/liter of cobaltic acetate and 1.4 mol/liter of trifluoroacetic acid in acetic acid was kept at 25 C. without stirring, under a nitrogen atmosphere at atmospheric pressure. 77 percent of the cobaltic ions had been reduced after 24 hours. The reaction mixture was then treated and analyzed as in Example lll. It was thus established that 56 percent of the ethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages.  
 alpha-methylhenzyl alcohol 86 &#34;/1 (mainly in the form of its acetate esters) acetophenone 9 &#34;/2 benzoic acid 5 /2 By operating in identical manner but omitting the addition of trifluoroacetic acid to the system, only 9 percent of the ethylbenzene was converted to yield the following products:  
 alpha-methylbenzyl alcohol 0 l: acetophcnone 67 7: benzoic acid 33 It is plain that in the absence of the acid activator, the reaction is not only slowed down considerably, but its selectivity is completely changed.  
 EXAMPLE lX This example illustrates the oxidation of ethylbenzene by means of the system consisting of cobaltic acetate and boron trifluoride.  
  The experiment of Example Vlll was repeated, but trifluoroacetic acid was replaced by boron trifluoride in the same concentration. Analysis of the reaction mixture after three hours showed that 27 percent of the ethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 alpha-methylhenzyl alcohol 87 2 (mainly in the form of its acetate ester) acctophenonc 5 7r benzoic acid 8 7r By operating in identical manner, but without adding boron triluoride to the system. only percent of the hydr&#39;ocarbon had been converted to yield the following products:  
 alpha-methylbenzyl alcohol acetophenone benzoic acid The action of the activator set forth in the preceding example is confirmed in every respect by these results.  
 EXAMPLE X This example illustrates the oxidation of ethylbenzene by means of the system consisting of cobaltic acetate and p-toluenesulphonic acid.  
  The experiment of Example Vlll was repeated but trifluoroacetic acid was replaced with p-toluenesulphonic acid at the concentration of 0.3 mol/liter. 33 percent of the cobaltic ions had been reduced after 24 hours, and analysis showed that 14 percent of the ethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 alpha-methylbenzyl alcohol (mainly in the form of 75 7! its acetate ester) acetophenone l5 &#34;/1 benzoic acid EXA&#39;MPLE Xl alpha-methylbenzyl alcohol 88 7:  
 (mainly in the form of its acetate ester) acetophenone 9 7t benzoic acid 3 &#34;/1 EXAMPLE xu The experiment of Example Xl are repeated, but operating at 60 C instead of C. 66 percent of the cobaltic ions had been reduced after minutes. and analysis showed that of the ethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 alpha-methylhenzyl alcohol 86 (mainly in the form of its acetate ester) acetophenone 7 benzoic acid 7 Compared to those of Example XI, these results show that an increase in the temperature can speed up the reaction without appreciably changing its selectivity.  
 EXAMPLE Xlll This example illustrates the effect of oxygen on the oxidation of ethylbenzene by means of the oxidizing system employed in Examples Xl and XI].  
  A solution containing 0.10 mol/liter of ethylbenzene, 0.20 mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acid in acetic acid was stirred at 25 C in the presence of pure oxygen at atmospheric pressure. 62 of the cobaltic ions had been reduced after 4 hours. The reaction mixture was then treated and analyzed as in Example ll]. It was thus established that 67 percent of the ethylbenzene had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 acetophenone 71 alpha-methylbenzyl alcohol l5 l1 (partially in the form of its acetate cster) benzoic acid 6 9 By comparing these results to those of Examples XI and Xll, it is plain that in the presence of oxygen. ethylbenzene is converted mainly into ketone rather than into alcohol.  
 EXAMPLE XlV The experiment of Example Xlll was repeated. but on this occasion operating under an oxygen pressure of 10 kg/cm2. Analysis of the reaction mixture after 4 hours showed that 48 percent of the ethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molasr percentages:  
 acetophenone X4 9;  
 alpha-methylbenzyl alcohol 16 92 (partially in the form of its acetate ester) benzoic acid undetectable By comparing these results to those of Example Xlll, it is apparent that the proportion of acetophenone has been increased slightly by operating under a higher oxygen pressure. No additional increase is observed, however, if the test is performed under, the oxygen pressure of 30 kg/cm2.  
 EXAMPLE XV This example illustrates the use of methyl acetate as a solvent.  
  A solution containing 0.10 mol/liter of ethylbenzene. 0.2l mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acid in methyl acetate was kept at 25 C. without stirring, under-a nitrogen atmosphere at atmospheric pressure. 44 percent of the cobaltic ions had been reduced after 5 hours. The reaction mixture was then treated and analyzed as in Example lll. It was thus established that 14 percent of the ethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 alpha-methylbenzyl alcohol 73 71 (mainly in the form of its acetate ester) acetophenone 22 &#39;7:  
 benzoic acid 5 &#39;4 By operating in analogous manner but in the presence of pure oxygen instead of an atmosphere of nitrogen, acetophenone becomes the principal product.  
 EXAMPLEXVl This example illustrates the use of t-butyl acetate as a solvent.  
  The experiment of Example XV was repeated while replacing methyl acetate with t-butyl acetate. 45 percent of the cobaltic ions had been reduced after three hours. and analysis showed that 1 1 percent of the ethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 alpha-methylbenzyl alcohol 82 7:  
  (mainly in the form of its acetate ester) acetophenone 18 71 EXAMPLE XVll This example illustrates the use of pelargonic acid as a solvent.  
  A solution containing 0.51 mol/liter of ethylbenzene. 0.17 mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acid in pelargonic acid was kept at 25 C. without stirring, under a nitrogen atmosphere at atmospheric pressure. 78 percent of the cobaltic ions had been reduced after 24 hours. The reaction mixture was then neutralized by means of alcoholic potash and subjected to specification for 4 hours in such manner as to hydrolyze the pelargonic esters formed during the reaction, to facilitate the identification of the oxidation products of ethylbenzene. After filtering the insoluble salts. the alcoholic solution thus obtained was analyzed directly by vapor phase chromatography. The analysis enabled to identify the following oxidation products whose relative proportions are expressed as molar percentages:  
 alpha-meth \&#39;lbenzyl alcohol acetophenone EXAMPLE XVlll This example illustrates the possibility of not employing any solvent.  
  A solution containing 0.2 mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acid in ethylbenzene was kept at 25 C. without stirring, under a nitrogen atmosphere at atmospheric pressure. 59 percent of the cobaltic ions had been reduced after thirty minutes. Analysis of the reaction mixture by a method analogous to that described in Example 111 enabled to identify the following oxidation products whose relative proportions are expressed as molar percentages:  
 aeetophenone 67 /&amp; alpha-methylbenzyl alcohol 31 alpha-methylbenzyl acetate 2 &#34;/1 benzoic acid 0 /1 This example also shows that, in the absence ofa carboxylic solvent, the formation of ester is negligible, as in the presence of oxygen.  
 EXAMPLE XIX This example illustrates the oxidation of cumene by means of the system consisting of cobaltic acetate and trichloroacetic acid in the presence of oxygen.  
  A solution containing 0.10 mol/liter of cumene, 0.20 mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acid in acetic acid, was stirred at 25 C in the presence of pure oxygen at atmospheric pressure. 54 percent of the cobaltic ions had been reduced after 24 hours. The reaction mixture was then treated and analyzed as in Example lll. It was thus established that 2] percent of the cumene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
  s. Ll okll sea EXAMPLE XX This example illustrates the oxidation of 2- ethylnaphthalene by means of the system consisting of cobaltic acetate and trichloroacetic acid.  
  A solution containing 0.10 mol/liter of 2- ethylnaphthalene, 0.19 mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acid in acetic acid was kept at 25 C, without stirring, under a nitrogen atmosphere at atmospheric pressure. 71 percent of the cobaltic ions had been reduced after 30 minutes. The analysis of the ether extract obtained as described in Example 111 showed that 57 percent of the 2- ethylnaphthalene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 2( l-hydroxycthyl )naphthalenc 98 Z (mainly in the fonn of its acetate ester) Z-acetylnaphthalene 2 71 EXAMPLE XXl The experiment of the preceding example was repeated at 0 C instead of at 25 C. while employing propionic acid instead of acetic acid as a solvent. 43 percent of the cobaltic ions had been reduced after 5 hours. and analysis showed that 21 percent of the 2- ethylnaphthalene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 2-( l-hydroxyethyl)naphthalene (mainly in the 82 71 form of its propionate ester) 2-acetylnaphthalene l8 7:  
 EXAMPLE XXll This example illustrates the possibility of operating at lower temperatures than 0 C.  
  A solution containing 0.51 mol/liter of 2- ethylnaphthalene, 0.18 mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acid in propionic acid was kept at -20 C without stirring. under an atmosphere of nitrogen at atmospheric pressure. 47 percent of the cobaltic ions had been reduced after 5 hours, and analysis showed that 5 percent of the 2- 2-( l-hydroxyethyl )naphthalene 94 (mainly in the form of its propionic ester) Z-acetylnaphthalene 6 &#34;/1 EXAMPLE XXlll This example illustrates the oxidation of pchlorotoluene by means of the system consisting of manganic acetate and sulphuric acid.  
  A solution containing 0.10 mol/liter of pchlorotoluene, 0.2l mol/liter of manganic acetate and 1.0 mol/liter of sulphuric acid in acetic acid was kept at 25 C, without stirring, under a nitrogen atmosphere at atmospheric pressure. 87 percent of the manganic ions had been reduced after 2 hours. The analysis of the ether extract obtained as described in Example Ill showed that 62 percent of the p-chlorotoluene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 p-chlorobenzyl alcohol 74 &#34;/2 (mainly in the form of its acetate ester) p-chlorobenzaldehyde 26 EXAMPLE XXIV This example illustrates the oxidation of pmethoxytoluene by means of the system consisting of cobaltic acetate and trichloroacetic acid.  
  A solution containing 0.10 mol/liter of pmethoxytoluene. 0.21 mol/liter of cobaltic acetate and L5 mol/liter of trichloroacetic acid was kept at C. without stirring. under a nitrogen atmosphere at atmospheric pressure. 88 percent of the cobaltic ions had been reduced after 5 minutes. The analysis of the ether extract obtained as described in Example lll showed that 56 percent of the p-methoxytoluene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 p-methoxybenzyl alcohol 82 7( (mainly in the form of its acetate ester) p-methoxybenzaldehyde l8 &#34;/1 EXAMPLE XXV This example illustrates the oxidation of mnitrotolucne by means of the system consisting of cobaltic acetate and trichloroacetic acid.  
  A solution containing 0.50 mol/liter of mnitrotoluene, 0.19 mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acid in acetic acid was kept at 25 C, without stirring, under a nitrogen atmosphere at atmospheric pressure. 51 percent of the cobaltic ions had been reduced after 3 hours. The analysis of the ether extract obtained as described in Example lll enabled to identify the following oxidation products whose relative proportions are expressed as molar percentages:  
 m-nitrobenzyl alcohol 7r (mainly in the form of its acetate ester) n-nitrobenzaldehyde l0 &#39;7:  
 EXAMPLE XXVI This example illustrates the oxidation of p-xylene by means of the system consisting of cobaltic acetate and trichloroacetic acid, in the presence of oxygen.  
  A solution containing 0.05 moi/liter of p-xylene, 0.20 mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acid was stirred at 25 C in the presence of pure oxygen at atmospheric pressure. 19 percent of the cobaltic ions had been reduced after 24 hours. The reaction mixture was then diluted with an equal volume of ether. An insoluble residue was filtered, washed for a first time with a mixture of acetic acid and ether l/l a second time with water, then dried. The infrared spectrum of the product thus isolated was identical to that of pure terephtalic acid and its acidity amounted to 11.98 meq./g (theoretical value: 12.04). On the other hand, the ether filtrates were collected before being treated and analyzed as described in Example lll. It was thus established that 59 percent of the p-xylene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 terephtalic acid p-toluic acid EXAMPLE XXVll This example illustrates the oxidation of mdiethylbenzene by means of the system consisting of manganic acetate and sulphuric acid.  
  A solution containing 0.05 mol/liter of mdiethylbenzene. 0.22 mol/liter of manganic acetate and 1.0 mol/liter of sulphuric acid in acetic acid was kept at 25 C under a nitrogen atmosphere at atmospheric pressure. 63 percent of the manganic ions had been reduced after 30 minutes. The reaction mixture was then diluted with a saturated solution of sodium chloride in water, then subjected to repeated extractions with ether. The ether extract was neutralized by an aqueous solution of sodium carbonate and dried over anhydrous sodium sulphate before being analyzed by vapor phase chromatography. Analysis showed that the total quantity of the m-diethylbenzene employed had been converted, yielding the following oxidation products the relative proportions of which are expressed as molar percentages:  
 m&#39;( l-hydroxyethyl)ethylbenzenc 78 &#39;7( (mainly in the form of its acetate ester) m-bis( l-hydroxyethyl)benzene l8 &#34;/1 (in the form of its diacetate ester) m-ethylacetophcnone 4 &#34;/2 By operating under the same conditions but omitting sulphuric acid, only 0.2 percent of the manganic ions were reduced after one hour (that being twice the time necessary hereinabove) and no oxidation products were detectable by analysis.  
 EXAMPLE XXVIII The experiment of Example XXVI] was repeated, ex-  
 cept that the concentration of manganic acetate as increased by approximately 30 per cent (0.28 mol/liter instead of 0.22) and the reaction was extended to a total period of hours. With these conditions. 97 percent of the manganic ions were reduced and the oxidation products were shown to be distributed, in mols. in the following manner:  
 m-bis( l-hydroxyethyl)bcnzecne 6t 7? (in the form of its diacetate ester) m-( l-hydroxyethyl)ethylbenzene lo &#34;/1 (mainly in the form of its acetate ester) m-ethylacetophcnone Zl 7r m-diacetylbenzene 2 &#34;/2 Compared to those of Example XX&#39;VIl. these results show that. by increasing the quantity of oxidant in comparison to the substrate, and by extending the reaction time, it is possible to oxidize the two alkyl substituents of a dialkylaromatic compound.  
 EXAMPLE XXIX The experiment of Example XXVII was repeated except that the concentration of m-diethylbenzene was doubled (0.10 mol/liter instead of 0.05). The reaction was extremely fast. since 77 percent of the manganic ions were reduced within 3 minutes.  
  The reaction mixture was then treated by an extraction method analogous to that applied in Examle XXVll. and also analyzed by vapor phase chromatography. Analysis showed that 85 percent of the mdiethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are the following oxidation products whose relative proportions are expressed as molar percentages:  
 m-( l-hydroxyethyl)ethylhenzene 96 &#34;/2 (mainly in the form of its acetate ester) m-bist l-hydroxy&#39;ethyl )benzenc 3 /2 (mainly in the form of its diacetate ester) m-cthylacetophenone l Compared to those of Example XXVll. these results show the gain in reaction rate and in selectivity achieved when increasing the amount of substrate compared to the oxidant.  
 EXAMPLE XXX m-( l-hydroxyethyl)ethylbenzene 97 7:  
 (mainly in the form of its acetate ester) m-bis( l-hydroxyethyl )benzene traces (in the form of its diacctate ester) 1 7 methylaeetophenone EXAMPLE XXXI This example illustrates the oxidation of mdiethylbenzene by means of the system consisting of 5 cobaltic acetate and sulphuric acid.  
  A solution containing 0.05 mol/liter of mdiethylbenzene, 0.20 mol/liter of cobaltic acetate and 0.5 moi/liter of sulphuric acid in acetic acid was kept at C under a nitrogen atmosphere at atmospheric pressure. 44 percent of the cobaltic ions had been reduced after 20 minutes. The reaction mixture was then treated and analyzed as in Example XXVI]. It was thus established that 55 percent of the m-diethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
  m-t l-hydroxyethyl)ethylbenzene 70 70 (mainly in the form of its acetate ester) m-bis( l-hydroxyethyl)benzene 4 9? (in the form of its diacetate ester) m-ethylaeetophenone 24 &#39;7: m-( l-hydroxyethyl)acetophenone 2 &#39;7:  
 EXAMPLE XXXll m-( l-hydroxyethyl)ethylbenzene 79 /r 40 (mainly in the form of its acetate ester) m-bis( l-hydroxyethyl )benzene 6 &#34;/1 (in the form of its diacetate ester) m-ethylacetophenone l5 &#39;7:  
 EXAMPLE XXXIII This example illustrates the oxidation of mdiethylbenzene by means of the system consisting of cobaltic acetate and perchloric acid.  
  The experiment of Example XXXI was repeated while substituting perchloric acid at the concentration of 1.0 mol/liter for sulphuric acid. 47 percent of the cobaltic ions had been reduced after ten minutes. and analysis showed that 79 percent of the mdiethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages: n  
 m-( l-hydroxyethyl)ethylbenzene 86 &#39;71 (mainly in the form of its acetate ester) m-his( l-hydroxyethyl)benzene 4 it (in the form of its diacctate ester) m-ethylacetophenone l0 7:  
 EXAMPLE XXXIV This example illustrates the oxidation of mdiethylbenzene by the system consisting of cobaltic acetate and trichloroacetic acid.  
  The experiment of Example XXXl was repeated while substituting trichloroacetic acid at the concentration of 1.5 moi/liter for sulphuric acid. 23 percent of the cobaltic ions had been reduced after 30 minutes. and analysis showed that 42 percent of the mdiethylbenzene employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 m-( l-hydroxyethyl )ethylbenzene 90 &#34;/1 (mainly in the form of its acetate ester) m-bis( l-hydroxyethyhbenzene 3 7! (in the form of its diacetate ester) m-ethylacetophenone 7 &#39;71 By operating in the same conditions but in the absence of trichloroacetic acid, only 10 percent of the cobaltic ions were reduced after 2 hours (this being a period which is 4 times as long as in the experiment hereinabove) and only 9 percent of the m-diethylbenzene was converted to yield the following products:  
 m-( l-hydroxyethyl)ethylbenzene 36 &#34;/1 (in the form of its acetate ester) m-ethylacetophenone 64 &#34;/1 Hereagain. it is apparent that in the absence of the acid activator, the reaction is not only slowed down considerably. but its selectivlity is changed completely.  
 EXAM&#39;PLE xxxv m-ethylacetophenone 66 &#34;/1 m-( l-hydroxyethyl)ethylhenzene l7 acetate ester of m l-hydroxyethyl)ethylbcnzene l6 &#34;/1 m-bis( l-hydroxyethyl)benzene l By continuing the same experiment up to 24 hours, 57 percent of the cobaltic ions were reduced and 89 percent of the m-diethylbenzene employed was converted to yield the following products:  
 m-ethylacetophenone 7 m-( l-hydroxyethyl )ethylbenzenc acetate ester of m-( 1-hydroxyethyl)ethylbenzene m-bis( l-h \droxyethyl )benzene m-( l-hydroxyethyl )acetophenone m-diacetylhenzene By comparing these results to those of Example XXXlV. it is apparent that in the presence of oxygen the hydrocarbon is oxidized preferentially into ketone rather than into alcohol.  
 EXAMPLE xxxvr This example illustrates the oxidation of the acetate of m-( l-hydroxyethyl )ethylbenzene by means of the system consisting of cobaltic acetate and phosphoric acid.  
  A solution containing 0.05 mol/liter of the acetate of m-( l-hydroxyethyl)ethylbenzene. 0.10 moi/liter of cobaltic acetate and 1.0 mol/liter of phosphoric acid was kept at 25C undera nitrogen atmosphere at atmospheric pressure. 43 percent of the cobaltic ions had been reduced after 4 hours. The reaction mixture was then treated by an extraction method analogous to that employed in Example XXVI] and the extract was also analyzed by.vapor phase chromatography. It was thus established that 25 percent of the ester employed had been converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 m-bis( l-hydroxyethyl )benzene (mainly in the form of its diacetate ester) m-ethylacetophenone 3 m-( l-hydroxyethyl)acctophenone 2 EXAMPLE XXXVI] This example illustrates the oxidation of durene by means of the system consisting of cobaltic acetate and trichloroacetic acid.  
  A solution containing 0.05 mol/liter of durene. 0.30 mol/liter of cobaltic acetate and 1.5 mol/liter of trichloroacetic acid in acetic acid was stirred at 60 C in the presence of pure oxygen under a pressure of 10 kg/cm2. 78 percent of the cobaltic ions had been reduced after 24 hours. After evaporation of the solvent. the acidic products were separated by extraction with aqueous potash followed by acidification with hydrogen chloride; they were then analyzed by paper chromatography. It was thus established that durene had been quantitatively converted to yield the following oxidation products whose relative proportions are expressed as molar percentages:  
 durylic acid 4 7t dimethylphthalic acids 68 71 methyltrimellitic acid 23 7: pyromellitic acid 5 7:  
 What is claimed is:  
  l. The process of oxidizing an alkyl carbocyclic aromatic compound having at least one methyl radical directly linked to the aromatic nucleus, to selectively produce an aromatic aldehyde, comprising reacting said alkylaromatic compound in the liquid phase with a salt consisting essentially of a manganic carboxylate in the presence of an activator selected from the group consisting of the acids having a dissociation constant higher than 10&#34; and which are stable in the conditions of the reaction, boron trifluoride, and mixtures thereof, at a temperature between 30 and C, and under a partial pressure of oxygen between 0.1 and 50 atmospheres.  
  2. The process as defined in claim 1 wherein the aromatic nucleus of said alkylaroinatic compound is selected from the group consisting of benzene and naphthalene.  
  3. The process as defined in claim 2 wherein said aromatic nucleus has from I to 6 alkyl substituents each having from I to 4 carbon atoms.  
  4. The process as defined in claim 2 wherein said aromatic nucleus is further substituted with a polar radical selected from the group consisting of halo. nitro. acyl. l-acyloxyalkyl. carboxy and alkoxy.  
  5. The process as defined in claim 1 wherein said manganic carboxylate is the salt of a fatty acid having from 2 to 19 carbon atoms.  
  6. The process as defined in claim 5 wherein the manganic salt is manganic acetate. 4  
  7. The process as defined in claim 1 wherein said activator is selected from the group consisting of sulfuric, perchloric, p-toluenesulphonic, trifluoroacetic, trichloroacetic, tribromoacetic, dichloroacetic, phosphoric and monochloroacetic acids, boron trifluoride and mixtures thereof.  
  8. The process as defined in claim 1 wherein the reaction is effected in the presence of a solvent selected from the group consisting of the fatty acids having from 2 to 10 carbon atoms. and the methyl and t-butyl esters of said fatty acids.  
 9. The process as defined in claim 8 wherein said solvent is acetic acid.