US2444816A - Production of acetophenone - Google Patents

Description

@atented Jetty d, 119% PRQDUUEEON @F AGETOPHENONE William S. Emerson and Victor Lucas, Dayton,

Ohio, assignors to Monsanto Chemical Company, St. Louis, Man, a corporation of Delaware No Drawing. Application March Seriai No. 582,802

Claims: (Cl. 260-592) ,benzene, for example, as described in the Binapfl Patent No. 1,813,606, or in the copending application of William S. Emerson, Serial No. 496,078, filed July 24, 1943, which issued as Patent No. 2,3765% on May 22, 1945, there is usually formed a certain amount of methylphenylcarbinol. When the desired product is acetophenone, the problem of disposing of the constantly increasing quantities of the carbinol thus arises. In order to achieve an economy of the starting material it is desired to convert the carbinol-to acetophenone by further oxidation. However, in spite of the fact that the catalytic, liquid phase oxidation of such materials as cymene is accelerated by the presence in the starting material of a small quantity of the crude oxidation reaction mass from a previous run, in the present reaction the presence of methylphenylcarbinol in such material is seriously detrimental. Wehave discovered that the presence of methylphenylcarbi- 1101 in ethylbenzene, even in small amountsat the start of the oxidation, seriously retards the omdation reaction; in amounts of 5% by weight noi.

' Table 1 Per cent Carbinol Present Conversion, Experiment No. Mole Per cent UIRWNH 9mm; COMO:

w ream @WNQO- All of the above'experiments were made under, the same conditions. These were as follows:

Charge 1800 g. ethylbenzene Time 6.5 hours Temperature 140 C. y Pressure 100 p. s. L gauge' Air flow '15 cu. ft./hour Catalyst concentration--. 1% by weight of charge Stirring speed 750 R. Eli/1.;

Ir'r'experiments 1 to 4, inclusive, in Table i, the carbinol was added to the ethylbenuene in the cold at the beginning of the experiment.. The air was then bubbledthrough the ethylbenzene, heat applied to the container in amount so as to raise the temperature of the contents to 140 Q,

and the testcontinued at this temperature for conditions than those shown above.

i We have now found that the adverse effect ex hibited by the presence of methylphenylcarbinol at the start of the reaction, is not experienced ifthe norm-a1 oxidation of the ethylbenzene in the absence of the carbinol is carried to the point where the refractive index thereof shows an increase over that of pure ethylbenzene. When this point is reached, the addition of methylphenylcarbinol may be made, and the oxidation continued to completion. We have found that the conversion of the carbinol to acetophenone proceeds at a high rate and that actually less carbinol is produced with this method of opera.- tion than is normally formed when no carbinol is added.

Into a closed vessel containing ethylbenzene and from, say, 1% to 5% by weight of any metal oxide oxidation catalyst, air in finely divided form is introduced. Observations of the refractive index of the reaction mass are made from time to time. After a period of, time, which may vary depending upon the temperature, rate of air influx and catalyst activity, a sudden, sharp-in crease in the refractive index of the reaction mixture will be observed. at this point, or at any time thereafter during the oxidation. there may be added methylphenylcarbinol in amounts of, say, up to 25% by weight of the ethylbenzene originally present without in any way affecting the progress of the oxidation. Thenceforth. the reaction proceeds normally, the oxidation of the ethylben'zene and the added carbinol being converted to acetophenone in excellent yields. While there is formed some carbinol during such oxidation, there is no, accumulation thereof, because when operating according to our invention the capacity for converting carbinoi to acetophenone greatly exceeds the rate of carbinol' production. When working with a chromium sesquioxide catalyst, for example, we recover from the oxidation product amixture consisting-of about 85% by weight of acetophenone and 15% by weight of methylphenylcarbinol, this mixture representing approximately 33% conversion of the initial ethylbenzene. We separate the acetophe'none from the methylphenylcarbinql and then add all of the latter to a subsequent reaction mixture after the refractive index of such mixture has increased, as described above. There is obtained in this subsequent run a product consisting of 85% by weight of acetophenone and 15% by weight of methylphenylcarbinol, the total amount of these two compounds being at least as great as that obtained in the first nm, and in many cases being substantially greater.

The length of the induction period. during which no apparent oxidation occurs, varies from, say, 15 minutes to an hour, or even two hours, depending upon the quantities of reactants employed, the speed of stirring, catalyst temperature, pressure, etc. When oxidationbegins there is noted a sharp increase in the refractive index of the reaction mixture, which increase is due to thepresence of' oxidation products. This is also generally accompanied by a rise in temperature. For many purposes, especially when running a series of reactions under the same conditions, it

is sufllcient only to note this temperature rise and then to add the carbinol or the carbinol-containing material to the reaction mixture. However,

it is somewhat more satisfactory to determine the point at which addition of the carbinol may be safely made by noting the change of refractive index of the reaction mixture. This may be readily effected by removing samples of the reaction mixture at regular intervals, say, at intervals of from to minutes, and notingthe refractive index of each sample. Addition of the carbinol to the reaction mixture may be safely made immediately after an increase in refractive index of as little as 0.0002 or 0.0003 has been noted.

The present invention is further illustrated, but not limited, by the following examples:

Exnrrti: 1 a k s. This example illustrates the change in temperature and refractive index which accompanies the oxidation of ethylbenzene in the liquid phase and in the presence of chromium sesquioxide catalyst.

Oxidation was carried der an air pressure of 100 p. s.'i. gauge and at an initial temperature of 133 C., 2500 g. of ethylbenzene and 25 g. of chromium sesquioxide was charged into the autoclave, and air was passed through continuously withstirring at the rate of cubic feet per hour. Over a period of about 2 hours the temperature and the refractive index of the reaction mixture were observed at ten out in an autoclave unminute intervals. Table 2 shows the results obtained:

Table 2 'lempera- Time, Minutes mm.

From the above table it is readily apparent that after a time of from to 60 minutes there is a. sudden and sharp increase in the refractive index of the reaction mixture.

composition of the reaction mixture it may be used to denote a point at which oxidation isv accarbinol to the reaction mixture.

.This example shows the extent to which math ylphenylcarbinol may be consumed when the latter is added to ethylbenzene after oxidation has started. The following conditions were employed in all oi the experiments reported below:

A mixture consisting of.1800 g. of ethylbenzene and 18 g. of chromium oxide catalyst was charged to an autoclave and the oxidation was conducted at an initial temperature of 140 C., a pressure of 100 -p. s. i., an air flow of 15 cubic feet per hour and a stirring speed of 750 R. P. M. In each case the methylphenylcarbinol or the mixture containingthe same was added to the reaction mass after the refractive index had increased by at least 0.0002. The data obtained in the several experiments are summarized in the following Table 3:

Table 3 Cong. Caryen Oar- Added Mater al 8101!, inol No. Hrs. at

rstart at End cent a l 6.6 200g.oimixture 32.8 36 i9 2.---.- 6.6 38 g. each of aceto- 33.0 86 26.5

phenone and methylphenyl-carbinol. 3..---- 6.5 00 g. each'o! aceto- 33.2 90 2o phenone and methylphenyl-carbinol. 4 5.5 36 g. each of aceto- 31.0 36 18 phenone and methylphenyl-carbinol. 5 6.5 90 methylphanyl- 44.3 90 trace oar incl. v

binol containing 08.5 mole per cent scatophenone.

l Mole percent bwcd on ethylbenaenecharged.

From the above table, it is obvious that addition of more methylphenylcarbinol to the reacsmaller amount of carbinol than that which was introduced and without. substantial eflect on Since the change in refractive index indicates a change inthe I Mixture of ethylbenzene, aoetophenoae and methylphenylcarconversion of the ethylbenzene to acetophenone.

While the above runs were made in the presence 01 a chromium sesquioxide catalyst, other catalysts which are known to induce oxidation of ethylbenzene to a mixture oi acetophenone and carbinol may be employed, for example, the oxides or hydroxides 01' copper, calcium, manganese, iron, lead, cobalt, vanadium or mercury. Organic thereupon adding methylphenylcarbinoi to said ethylbenzene and further oxidizing said ethyl-- benzene to acetophenone.

or inorganic salts containing these metals may be employed, for example, cobalt oxalate, lead benzoate, etc. Mixtures of such catalytic materials may be employed.

Instead of employing air as the oxidation agent, oxygen, either alone or in admixture with inert gases, may be used. The oxidation may be of i'ected at ordinary or added pressures. An inert liquid diluent may be used in thereaction mixture.

Instead of employing an autoclave or other pressure device for the reaction, other means of contacting air or oxy en with the material to be oxidized may be employed. For example, air and the liquid'material may be passed in countercurrent through reaction towers.

Reaction temperatures may be widely varied, these being regulated by the nature of the catalyst used as well as by other as may be apparent to those skilled in the art.

What we claim is:

1. The process for producing acetophenone which comprises passing an oxygen containing gas through liquid ethylbenzene containing an oxidation catalyst, whereby oxidation products oi ethylbenzene are formed, thereupon adding to said ethylbenzene, methylpheny-l carbinol and then further oxidising said ethylbenzene to form acetophenone.

2. The process for producing acetophenone which comprises passing an oxygen containing gas through liquid ethylbenzene containing an oxidation catalyst, whereby oxidation products are iormed therein and the refractive index thereoi has been increased by at least 0.0002,

reaction conditions 3. The process for producing acetophenone which comprises passing an oxygen containing gas through liquid ethylbenzene containing an oxidation catalyst, whereby oxidation products are formed therein and the refractive index thereof has been increased by at least 0.0003, thereupon adding methylphenylcarbinol to said ethylbenzene and further oxidizing said ethylbenzene to acetophenone.

4. The process :for producing acetophenone which comprises passing an oxygen containing gas through liquid ethylbenzene containing an oxidation catalyst, whereby oxidation products are formed therein and the refractive index thereof has been increased by at least 0.0002, thereupon adding methylphenylcarbinol to said ethylbenzene and further oxidizing said ethylbenzene and methylphenylcarbinol to acetophenone.

5. The process for producing acetophenonc which comprises passing an oxygen containing gas through liquid ethylbenzene containing an oxidation catalyst, whereby oxidation products are formed therein and the refractive index thereof has been increased by at least 0.0003, thereupon adding methylphenylcarbinol to said ethylbenzene and further oxidizing said ethyl- -benzene and methylphenylcarbinol to acetophenone.

WILLIAM S. EMERSON. VICTOR. E. LUCAS.

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

UNITED STATES PATENTS Emerson May 22, 1945