US2772305A - Oxidation of toluate esters and xylene mixtures - Google Patents

Description

United States Patent OXIDATION OF TOLUATE ESTERS AND XYLENE MIXTURES Irving E. Levine, Albany, and William G. Toland, In, San Rafael, Calif., assignors to California Research Corporation, San Francisco, Calif., a corporation of Delaware N 0 Drawing. Application August 26, 1952, Serial No. 306,497

3 Claims. (Cl. 260-475) This invention relates to a processfor producing monoesters of phthalic acids and saturated aliphatic alcohols containing 1 to 4 carbon atoms per molecule.

Mono-esters of phthalic acids and saturated aliphatic alcohols containing from i to 4 carbon atoms per molecule can be produced by oxidizing esters of toluic acids and saturated aliphatic alcohols containing from 1 to 4 carbon atoms per molecule with air at about 400 F. in the presence or absence of catalysts. The yields of phthalic acid mono-esters thus obtained are ordinarily in the range from 30 to 70 mole percent based on toluic acid esters converted. That higher yields are not obtained is probably due to the fact that rather high temperatures and long contact times are required to oxidize the toluic acid esters to phthalic acid mono-esters.

It has now been found that by oxidizing a liquid mixture of an alkyl benzene hydrocarbon, preferably xylene, and esters of toluic acids with saturated aliphatic alcohols containing 1 to 4 carbon atoms with a free oxygen-containing gas in the presence or absence of catalysts, considerably higher yields of phthalic acid mono-esters are obtained and that the oxidation of the toluic acid esters to phthalic acid mono-esters proceeds at a satisfactory rate at substantially lower temperatures. This oxidation can be performed in a continuous process in which a free oxygen-containing gas is passed through a liquid mixture of xylene and an ester of toluic acid with a saturated aliphatic alcohol containing 1 to 4 carbon atoms at a temperature in the range from 200 F. to 400 F., and preferably in the range from 220 F. to 375 F., in an oxidation zone, fractionally distilling the reaction product to separate an overhead fraction comprising unreacted xylene, unreacted methyl toluate and toluic acid and a bottoms fraction comprising half-esters of phthalic acid, esterifying the toluic acid of the overhead fraction with a saturated aliphatic alcohol containing 1 to 4 carbon atoms and then returning the overhead fraction including the esterified toluic acid to the oxidation zone with further quantities of xylene. Alternatively, the entire crude oxidation product can be contacted with an alcohol containing 1 to 4 carbon atoms under esterifying conditions to esterify the phthalic acid mono-ester and the toluic acid contained therein. The esterification product is then distilled to separate xylene and toluic acid ester as an overhead fraction and phthalic acid diesters as the bottoms fraction. The overhead is returned to the oxidation zone with further quantities of xylene. When it is desired to operate continuously and produce only phthalic acid mono-esters as the end product of the reaction, a mole ratio of toluic acid ester to xylene of at least 1:1 and in the range 1:1 to 5:1 is maintained in the oxidation zone.

The advantages of the process of the invention are illustrated by the following examples.

Example 1 500 g. of mixed xylenes containing 61.8% meta-xylene, 30.6% para-xylene, 4% ortho-xylene and 3.6% of paraffins boiling in the xylene range and 500 g. of mixed methyl ice 2 toluates containing85% methyl meta-toluate and methyl para-toluate and 2 g. of cobalt naphthenate con taining 6% by weight of cobalt were introduced into an oxidation reactor. The reactor consisted of 6 feet of stainless steel pipe mounted vertically and encased in an electrically heated jacket. Temperature control is obtained by controlling the pressure applied to the boiling water in the jacket. The overall volume of the oxidation reactor was 4 liters. High pressure air metered through a vrotameter was introducedinto the base of the reactor 1 through a inch jet. A reflux condenser provided with a water separator was mounted above the oxidation reactor. Tail gases from the condenser passed through a drop-out pot to a Grove pressure regulator and then to a vent. The reactor was heated to 325 F. and maintained under a 50 p. s. i. g. pressure. Air was introduced at the rate of 10 cubic feet per hour. After a 10 minute induction period tail gas analysis indicated 0.2% of carbon dioxide and 14.2% of oxygen present. After 30 minutes operation the tail gas contained 0.8% carbon dioxide and 8.4% oxygen. The effect of temperature was de termined by raising the temperature of the reactor to 340 F. and the pressure to p. s. i. g. while maintaining the air rate at 10 cubic feet per hour. Under these conditions tail gas analysis showed 1.4% of carbon dioxide and 8.5% of oxygen. These conditions were maintained for a period of 35 minutes, at which time the temperature was dropped to 300 F. and the pressure was reduced to 50 p. s. i. g. Under the latter conditions tail gas contained 1% carbon dioxide and 13% of oxygen. These conditions were maintained until the end of the run, which had a total duration of minutes. Products were drained from the reactor and water separator and consisted of 30 cc. of a water layer and 993.2 g. of an organic layer. The products were worked up by steam stripping to remove unreacted xylene and part of the unreacted ester. The stripped reaction product was then fractionally distilled to remove the remaining xylene and methyl toluate. Phthalic acid was separated by filtering the distillation bottoms. Chloroform extraction was employed to remove the remaining products which consisted of toluic acid, methyl toluate and methyl acid phthalate from the bottoms. Yields were as follows: 8.8% of phthalic acid based on the weight of xylene converted; 73.6% toluic acid based on the weight of xylene con verted; and 109% by weight of methyl acid phthalate based on the weight of methyl toluate converted. High molecular weight side reaction products amounted to less than 1% of the charge to the reactor. Some xylene was lost with the tail gases.

Example 2 Mixed methyl toluates alone were oxidized in the manner described in Example 1. The cobalt naphthenate was again employed as a catalyst, the amount introduced being suflicient to give the reaction mixture a cobalt content of 0.05% by weight. Air was blown through the methyl toluates for a period of 3.2 hours, during which the temperature of the oxidation reactor was maintained at 400 F. 1.21 moles of methyl toluate were charged to the reactor and the oxygen content of the air passed into the reactor was 1.67 moles. The reaction product was worked up as in Example 1, except that steam stripping was omitted and the yield of phthalic acid mono-esters produced was 54.4% based on the weight of methyl toluate converted.

From the above examples it is clear that toluate esters can be oxidized to phthalic acid mono-esters at lower temperatures and at higher yields if the toluic acid esters are subjected to oxidation in the presence of substantial amounts of xylene.

Similar comparative yields are obtained when ethyl toluate, isopropyl toluate and butyl toluate are oxidized with air alone and in the presence of xylenes.

Similar comparative yields are also obtained when the oxidations are conducted in the absence of a catalyst, although the rates of oxidation are appreciably lower. If it is desired to employ a catalyst in the reaction, oil-soluble compounds of metals of groups VII and VIII of the periodic table are useful catalysts.

No solvent need be employed in the work-up of the reaction product as was done in Example 1. Satisfactory separation can be obtained by fractionally distilling the reaction product to remove unreacted xylene, filtering the bottoms fraction to remove phthalic acid, and then fractionally distilling to separate toluic acid and unreacted methyl toluate from the methyl acid phthalate. The toluic acid is then esterified and returned to the reaction zone together with unreacted methyl toluate, unreacted xylene and incremental xylene.

The reaction as indicated above is carried out at a superatmospheric pressure sufiicient to maintain the xylene in liquid phase. Pressures ranging from 50 to 300 p. s. i. g. are satisfactory for this purpose. Xylene vapors are readily recovered from the tail gas for return to the reaction zone.

We claim:

1. An oxidation process which comprises forming a liquid mixture of 'a xylene and an ester of toluic acid with an alkanol containing 1 to 4 carbon atoms and passing a free oxygen-containing gas through the liquid mixture at a temperature in the range from 200 F. to 400 F.,

4 the mol ratio of toluic acid ester to xylene in the liquid mixture being in the range 1:5 to 5:1.

2. The method as described in claim 1, wherein the oxidation is conducted in the presence of an oil-soluble compound of the metals selected from groups VII and VIII of the periodic table.

3. A process for producing mono-esters of phthalic acids with lower aliphatic alcohols containing 1 to 4 carbon atoms which comprises passing a free oxygen-containing gas through a liquid mixture of a xylene and methyl toluate at a temperature in the range from 220 F. to 375 F. in an oxidation zone, the mole ratio of said methyl toluate to xylene being in the range of 1:1 to 5:1, fractionally distilling the reaction product to separate an overhead fraction comprising unreacted xylene, unreacted methyl toluate and substantially all of the toluic acid contained therein and a bottoms fraction comprising a phthalic acid mono-ester, esterifying the toluic acid of the overhead fraction with methanol and then returning the overhead fraction including the esterified toluic acid to the oxidation zone with further quantities of xylene.

References Cited in the file of this patent UNITED STATES PATENTS

Claims (1)

1. AN OXIDATION PROCESS WHICH COMPRISES FORMING A LIQUID MIXTURE OF A XYLENE AND AN ESTER OF TOLUIC ACID WITH AN ALKANOL CONTAINING 1 TO 4 CARBON ATOMS AND PASSING A FREE OXYGEN-CONTAINING GAS THROUGH THE LIQUID MIXTURE AT A TEMPERATURE IN THE RANGE FROM 200* F. TO 400* F., THE MOL RATIO OF TOLNIC ACID ESTER TO XYLENE IN THE LIQUID MIXTURE BEING IN THE RANGE 1:5 TO 5:1.