DE2346560A1 - METHOD FOR PRODUCING LIGHT COLORED DIPROPYLENE GLYCOL DIBENZOATE - Google Patents

Description

Troisdorf, Sept. 14, 1973 OZ: 73 089 (2253)

DYNAMIT NOBEL AKTIENGESELLSCHAFT Troisdorf, District Cologne

Process for the preparation of light colored dipropylene glycol dibenzoate

The invention relates to a process for the production of light-colored dipropylene glycol dibenzoate from the in the large-scale production of dimethyl terephthalate by means of the catalytic air oxidation of p-xylene and Methyl p-toluate, esterification of the oxidates with methanol and separation of the ester by-products.

After esterification of the p-xylene resulting from the air oxidation Acids with methanol become the methyl esters - mainly methyl p-toluate, dimethyl terephthalate and methyl esters other mono- and polyfunctional acids - by distillation or recrystallization, or by one of these two steps Combined process separated from each other: Dimethyl terephthalate is obtained, utilizable intermediate products are made returned to the process and by-products discharged. The latter partly consist of methyl benzoate, which is produced by a Number of compounds with almost the same boiling points is accompanied. Without prior removal of this methyl benzoate close neighboring compounds in their boiling points

- For example, by oxidative pretreatment according to the method of DAS 1 927 554 - it is not possible to obtain pure methyl benzoate even with great technical effort in the distillation. The methyl benzoate production occurring in the large-scale plants for the production of dimethyl terephthalate usually contains over $ 80> of this ester,

If one tries now to mix such a technical, non-pretreated at least 80% methyl benzoate with dipropylene glycol (ß, ß - Dihydroxy-di-n-propyl ether) in the presence of known transesterification catalysts transesterification, it is found that some of these, such as antimony trioxide and boron trioxide, are contrary to expectations are completely ineffective and others, such as sodium methylate, catalyze the reaction only slowly, an indication of the formation of inhibiting substances from the accompanying substances of the Methyl benzoate. A number of other transesterification catalysts such as tetrabutyl titanate, zinc and magnesium compounds, are indeed sufficiently active; is the color of the esters obtained however brown to brown-black. Iodine color numbers up to 150 are available. In many cases the esters are as deep brown to black colored that a measurement of the iodine color numbers is not possible. Some examples are listed in Table 1. It it can be seen which iodine color numbers of the transesterification products from technical methyl benzoate and dipropylene glycol in the same standard batches and under comparable conditions were measured using different catalysts. The examples are selected so that the end products are approximately the same

5098U / 1185

: high degree of Uiaeeterungsgrad, characterized by their hydroxylj count in the range from 10 to 30, templates:

Table 1

catalyst

Catalyst duration of the amount (jS) Transesterification OHZ JPZ (Hours)

Sodium methylate Magnesium acetate Magn e s lum methylate Zinc stearate zinc dust dibutyltin dilaurate tin-IY-butylate Titanium silicon alkoxide glycerine titanate tetrabutyl titanate Tetrabutyl titanate tetrabutyl titanate

0.2 11 24 100 0.2 5 30th 80 0.2 3 19th 130 0.2 7th 13th loo; 0.2 3 18th 30th 0.2 4th 17th 70 0.2 4th black * -brown 0.2 4th black-brown 0.2 8th 17th 80 0.2 2 27 60 0.1 4th 30th 60 0.5 2 20th 70

The deep color of the esters cannot be significantly lightened by bleaching agents such as activated charcoal or bleaching earth. as well oxidizing agents such as hydrogen peroxide or ozone remain without any significant effect. Distillation in vacuo results deep yellow distillates. The color quality is insufficient for technical use. It also occurs when the applicable

509814 / V185

j high temperatures thermolysis of the ester with cleavage

J from benzoic acid, which gives the acidity of the distillates,

Yield reductions and · significant technical difficulties

j resulting from the accumulation of sublimates in the apparatus.

This is widely available as a technical by-product. falling iTethylbenzoat could therefore not so far for the

: Manufacture of light-colored IT esterification products recycled.

It has surprisingly been found that light-colored dipropylene glycol dibenzoate can be prepared in such a way that contaminated methyl benzoate with contents of over 80 is obtained, especially as a by-product in the production of dimethyl terephthalate from p-xylene by catalytic air oxidation, for example according to DBP 1 041 145 Gew .- ^ of methyl benzoate with dipropylene glycol in the presence of aluminum alkoxides and / or aluminum silicon alkoxides which contain the group AlOSi in the core and whose alkoxy group contains the same or different alkoxy radicals of 1 to 4 carbon atoms, such as Al ethylate, Al — n Propylate, Al-sec-butylate or (CgH 0) SiOAl (OC H _g -sec.) ₂ as catalysts, preferably in an inert atmosphere, transesterified at temperatures above 150 ° C., after the elimination of methanol, the compounds with a lower boiling point than dipropylene glycol dibenzoate, preferably in Yakuum distilled off, the cooled to less than 150 ⁰ C the transesterification product, if necessary to improve the color, ozoni sated and if necessary. refined in the usual way.

50981 A / 1185

The inert atmosphere is created by displacing the air with gases containing little or no oxygen such as Nitrogen, helium or if necessary. Hydrogen produced.

The technical, over 80% methyl benzoate is in at least equivalent amount of 2 moles, based on the methyl benzoate content, is used per mole of dipropylene glycol. A minor one An excess of up to 25 mol-jS of methyl benzoate can be used for one It may be useful to carry out the reaction quickly. The methyl benzoate falls in the industrial dimethyl terephthalate process with contents below 80 wt .- ^ an, so it is by simple Enrich the distillation to at least 80% by weight.

The catalyst concentration should not exceed 0.8% , but is generally from 0.02 to 0.5%, preferably from 0.05 to 0.2%, based on the sum of the weights of methyl benzoate and dipropylene glycol used.

When the batches are heated up, small amounts of low-boiling compounds and water initially distill off. At about 150 ⁰ C boiler temperature, the elimination of methanol commences. During the duration of the transesterification, the Reaktionstem-perätur rises steadily to about 270 ⁰ C. The transesterification is expediently carried out under an inert gas, for example nitrogen.

When the special catalysts to be used according to the invention are used, surprisingly, the per se remain very good

5G98U / H85

¹ reactive accompanying substances of the ethyl benzoate, which otherwise! in chemical reactions, as can be seen in Table 1, for example, easily transform into deep-colored products, im! essentially unchanged: hence the light color of the transesterification products. Because of the large difference in the boiling points of the accompanying substances and the dipropylene glycol dibenzoate

the former needle-ended transesterification easily by distilling off,! preferably in vacuum. If an excess of methyl benzoate has been used, so. this is also '· ■ distilled off. This ester distillate can be used in a new way

can be added without affecting the color quality of the end proi ducts deteriorated.

After the "Hledrigsieder" have been distilled off, there is light-colored ! total dipropylene glycol dibenzoate. By treating with one ; Ozone-containing gas stream can further the color if desired

ι be brightened, in contrast to what was described at the beginning

I Finding that the deep color of the esters produced with conventional catalysts is not clear due to oxidizing agents is improved.

If the methyl benzoate used contains low levels of free acids, the end product has corresponding acid numbers. In these cases, a less expensive deacidifying refining, which is customary in the production of plasticizers, for example by treatment with aqueous alkaline solutions, can be carried out. Small proportions of highly volatile substances can - 5098U / t185

finally removed by blowing with air or steam.

Dipropylene glycol dibenzoate is a high quality, fast gelling plasticizer for polymers, e.g. for polyvinyl chloride.

The method according to the invention is illustrated by the following examples:

example 1

2144 parts by weight of bipropylene glycol (= 16 mol) and 5227 parts by weight of technical methyl benzoate with a content of 93.6 wt .- ^ (= 36 Mol of pure ester content) with the addition of 7.4 parts by weight of aluminum sec-butoxide as a catalyst (= 0.1% by weight, based on the Sunme of the quantities used). At temperatures in the reaction flask to 16O ⁰ C 'fnichtige compounds and water from the mixture distilled from first light. At 160 ^° C., the splitting off of methanol began. The flask temperature rose steadily to 240 ^° C. over the course of 5 hours. After this time, the elimination of methanol was complete. The methanol-containing distillate had a gas chromatographically determined content of $ 95; the remainder consisted of substances accompanying the technical methyl benzoate feedstock. Medrigsieder and the excess of diethyl benzoate were then after cooling at temperatures

50981 4/1185

"to 20O ⁰ C in a vacuum of 20 torr. The dipropylene glycol dibenzot obtained in a yield of 98% of theory, based on the dipropylene glycol used, had an acid number of 1.6, a saponification number of 326.5 (calc. 328) and an iodine color number of 10. The product v / urde after cooling to 150 ⁰ C ozonized for 30 minutes (ozone type device S ?; supplier Argentox, Hamburg; power: 0 1.5 g / hour at 12 KY and 90 W) after. During ozonization, the iodine color number was 3, after aqueous-alkaline refining it was 2. The acid number of the end product was 0.3 and the saponification number was 329.5.

Example 2

Example 1 was repeated, instead of 5227 parts by weight techn. Methyl benzoate (content: 93.6% by weight) 5818 Parts by weight (= 40 KoI pure ester content) were used. The transesterification was complete after 4 hours under otherwise identical conditions.

Example 3

The use of other catalysts to be used according to the invention resulted in otherwise identical reaction conditions and apparatus the following reaction times and iodine color numbers of the products:

5098U / 1 1 85

Tabel ? lot Duration of
reaction Hour ° catalyst 0.05 5.5 It Jodlarb number des
End product Al ethylate 0.1 4th Il 1 - Al ethylate 0.2 3.5 Il 1 - Al ethylate 0.1 4.5 Il 1 - Al-n-propylate 0.1 4th It 1 - Al-i-propylate 0.1 5 1 - Al-Si alcoholate - 2 - 2 - 2 - 2 - 2

5 0 9 8 U / 1 1 8 5

Claims (2)

- ίο - claims 1. A process for the production of light-colored dipropylene glycol dibenzoate, characterized in that methyl benzoate with contents of over 80 wt transesterified above 150 ° C., after the elimination of ethanol has ended, the compounds with a lower boiling point than dipropylene glycol dibenzoate are distilled off , preferably ir. refined in the usual way. 2. The method according to claim 1, characterized in that the catalysts are used in amounts of up to 0.8, preferably 0.05 to 0.2 S ^, based on the sum of the weights of methyl benzoate and dipropylene glycol used . Dr.Ia / Hü 5 Ö sTÜTTTe 5