RU2764518C1 - Method for producing 4,4-dimethyl-1,3-dioxane using polyarylene phthalide - Google Patents

Abstract

FIELD: organic synthesis.

SUBSTANCE: invention relates to the field of basic organic and petrochemical synthesis, namely to a method for producing 4,4-dimethyl-1,3-dioxane (DMD) by condensation of tert-butanol with an aqueous solution of formaldehyde in the presence of phosphoric acid at elevated temperature and pressure and subsequent separation of DMD from the reaction mass, while condensation is carried out in the presence of porous polyarylene phthalide, the content of which is maintained in an amount of 3.5-5 wt.% of the reaction mass.

EFFECT: increased selectivity of DMD formation.

1 cl, 1 tbl, 2 ex

Description

The invention relates to the field of basic organic and petrochemical synthesis, namely to the technology for obtaining 4,4-dimethyl-1,3-dioxane from tert-butanol and formaldehyde.

One of the most common industrial methods for obtaining isoprene is the dioxane method through the intermediate synthesis of 4,4-dimethyl-1,3-dioxane (DMD). DMD is obtained by liquid-phase condensation of isobutylene or tert-butanol contained in C4 fractions with formaldehyde used in the form of a 20-40% aqueous solution, followed by isolation of 4,4-dimethyldioxane-1,3 from the reaction mass [Ogorodnikov S.K., Idlis G.S. Isoprene production. L: Chemistry, 1973 pp. 48-58]. The principal disadvantage of this method is the low selectivity of the process. The yield of high-boiling by-products (HBP) is 440-460 kg per 1 ton of isoprene, more than 90% of which are HBP from the dimethyldioxane synthesis stage.

A known method for producing 4,4-dimethyl-1,3-dioxane from isobutylene and formaldehyde at a temperature of 100-110°C in the presence of sulfuric acid. The disadvantage of this method is the high corrosivity of the reaction medium and the need for additional processing of the oil layer with an alkali solution [USSR Author's certificate No. 361174, IPC C07D 319/06, publ. 12/07/1972].

Known methods for producing DMD in an aqueous medium from isobutylene and formaldehyde using carboxylic acid as a catalyst [French Patent No. 2490642, IPC C07D 319/06, publ. 03/26/1982], salts of polysulfonic acid and a metal of group I or II [French Patent No. 2490643, C07D 319/06, publ. 03/26/1982], oxalic acid [USSR author's certificate No. 991715, IPC C07D 319/06, publ. 12/27/1999; RF patent No. 2255936, IPC C07D 319/06, publ. 07/10/2005].

A known method for producing DMD from formaldehyde and isobutylene at a weight ratio of 1.1-1.2 in an aqueous solution at 90-110°C and a pressure of 17-25 atm. in the presence of oxalic acid. To increase the selectivity for DMD by reducing the formation of by-products and loss of isobutylene, 3-6% TMK trimethylcarbinol is returned to the reaction zone per DMD and 5-20% DMD from the amount received. According to the authors, the return of TMK to the reaction zone makes it possible to reduce the formation of TMK esters with WFP components and at the same time slow down the hydrolysis reaction of DMD with the formation of WFP [RF Patent No. 2062270, IPC C07D 319/06, C07C 31/12, publ. 06/20/1996].

The disadvantage of these methods for obtaining DMD is the lack of selectivity for the target DMD due to the formation of runway due to poor mutual solubility of the C 4 fraction and the aqueous layer containing the catalyst and formaldehyde.

Closest to the proposed technical essence and the achieved result is a known method for producing 4,4-dimethyl-1,3-dioxane [RF Patent No. 2330848, IPC C07D 319/06, publ. 08/10/2008] by condensing the isobutylene-containing fraction C 4, or substances that are their sources with an aqueous solution of formaldehyde in the presence of phosphoric acid, taken as an acid catalyst, at elevated temperature and pressure and subsequent isolation of 4,4-dimethyl-1,3- dioxane from the reaction mass, while the condensation is carried out in the presence of surface-active substances (surfactants). The content of surfactants is maintained in the amount of 0.001-10.0 wt. % of the reaction mass. The method allows to increase the selectivity of the formation of DMD.

The disadvantages of this method are insufficiently high selectivity for the target DMD due to the formation of the runway, including HP, as well as the need to dispose of spent surfactants.

The aim of the invention is to increase the selectivity of the formation of DMD by reducing the amount of hydrogenated pyrans formed. This goal is achieved by the proposed method for obtaining 4,4-dimethyl-1,3-dioxane by condensation of isobutylene with an aqueous solution of formaldehyde in the presence of phosphoric acid at elevated temperature and pressure and subsequent isolation of DMD from the reaction mass, while the condensation is carried out in the presence of porous polyarylenephthalide. The content of the porous porous polyarylenephthalide is maintained in the amount of 3.5-5.0 wt. % of the reaction mass. Porous polyarienphthalide is a porous carbon-containing material [Kraykin V.A., Egorov A.E., Salazkin S.N. Pyrolysis and carbonization of polymers in the series: polyphthalide-polyphenylenephthalides-polyphenylene. // Plastic masses. - 2008. - No. 4. - S. 17-20; Kraikin V.A., Musina Z.N., Galkin E.G., Kuznetsov S.I., Egorov A.E., Salazkin S.N. Destruction of polyterphenylenephthalide at high temperatures // High Molecular Compounds. - 2006. - A. - T. 48. - No. 11. - S. 2159-2177].

The difference of the present invention is that to increase the selectivity of the formation of DMD, porous polyarylene phthalide is additionally introduced into the reaction mixture. The use of porous polyarylenephthalide provides a higher degree of conversion of the initial reagents - tert-butanol and formaldehyde and an increase in selectivity for DMD due to a decrease in the formation of runaways, including HP.

The process under consideration belongs to the category of heterogeneous liquid-phase catalytic reactions. Phase separation in the reactor, due to insufficient mutual solubility of the aqueous layer containing formaldehyde and catalyst, and the C 4 fraction containing mpem-butanol, is the main problem of the selective formation of the target product of the condensation of tert-butanol with formaldehyde. To solve this problem and increase the chemical affinity of the components of the reaction mixture, it is proposed to use synthetic zeolites with a certain pore diameter as porous cocatalysts. The introduction of porous co-catalysts with a certain pore diameter into the reaction mass ensures a more intense reaction of condensation of tert-butanol with formaldehyde, increases the yield of DMD and reduces the formation of HP. 80-85% solutions of phosphoric acid are used as an acid catalyst, tert-butanol can be used as an isobutylene-containing fraction, formaldehyde is used, for example, in the form of a 16-22% aqueous solution. As a porous co-catalyst, for example, porous polyarylene phthalide can be used.

The synthesis of DMD is carried out as follows. Calculated amounts of formalin, phosphoric acid, porous polyarylene phthalide and tert-butanol are placed in a reactor equipped with a feed opening at a formaldehyde/tert-butanol molar ratio of 1.8:1. The reactor is fixed on a stirrer and placed in a coolant with a predetermined temperature in the range of 120-125°C. Next, stirring is included. The reactor is maintained overpressure in the range of 5-6 atm, ensuring the flow of the process in the condensed phase. At the end of the experiment, the reaction mixture is cooled, unloaded from the reactor, the zeolite is separated by filtration from the reaction mass, then the oil and water layers are separately subjected to further processing. DMD is isolated from the oil layer by extraction. The DMD content is then determined chromatographically by the internal standard method. The selectivity of the process was determined by the ratio of DMD/VPP in the resulting reaction mixture.

The implementation of the proposed method for obtaining DMD is illustrated by the examples below.

Example 1 (control, for comparison)

5.2 g of a formalin solution with a formaldehyde concentration of 16.1 wt. % (0.028 mol), 1.33 g of tert-butanol (0.018 mol), 0.29 g of 81% phosphoric acid. The molar ratio of formaldehyde/tert-butanol is 1.8:1. The reactor is fixed on a stirrer and placed in a coolant with a predetermined temperature. Next, stirring is included. The reactor maintains a temperature of 125°C, a pressure of 6 atm. The reaction mass is kept under constant stirring for 1 hour. At the end of the experiment, the reactor is cooled to 25-30°C, the reaction mass is unloaded from the reactor, the synthetic zeolite is separated from the reaction mass by filtration, then the oil and water layers are separately subjected to further processing. DMD is isolated from the oil layer by extraction. Get DMD 0.16 g (39% of theoretical), the ratio of DMD/VPP is 2.8: 1.

Example 2

The process is carried out analogously to example 1. 5.2 g of a formalin solution with a formaldehyde concentration of 16.0 wt. % (0.028 mol), 1.33 g of tert-butanol (0.018 mol), 0.29 g of 81% phosphoric acid. The molar ratio of formaldehyde/isobutylene is 1.55:1. 0.25 g of porous polyarylene phthalide is added to the reaction mixture, which is 4.0% by weight of the reaction mixture. The reactor maintains a temperature of 125°C, a pressure of 6 atm. Get DMD 0.51 g (99.0% of theoretical). There are no high-boiling by-products, including hydrogenated pyrans, in the reaction mass.

The optimal conditions for the process of selective formation of DMD as a result of the condensation of formaldehyde with mpem-butanol in the presence of porous polyarylene phthalide and the content of porous polyarylene phthalide in the amount of 3.5-5.0 wt. % of the reaction mass. The feasibility of the selected limits of indicators of the technological process of condensation is presented in table 1.

Conditions for the synthesis of DMD: molar ratio of formaldehyde : tert-butanol=1.8:1, temperature 125°C, pressure 6 atm, duration of synthesis 1 hour.

Application for the process of porous polyarylenephthalide in an amount less than 3.5% wt. leads to a decrease in the output of DMD, and more than 5.0% May. - does not lead to a significant increase in the yield of DMD, but causes an additional consumption of the reagent.

As can be seen from the above examples, the present invention makes it possible to increase the selectivity of the DMD formation process by reducing the amount of high-boiling by-products formed, including hydrogenated pyrans.

Claims (2)

1. Method for obtaining 4,4-dimethyl-1,3-dioxane by condensation of tert-butanol with an aqueous solution of formaldehyde in the presence of phosphoric acid at elevated temperature and pressure and subsequent isolation of 4,4-dimethyl-1,3-dioxane from the reaction mass , characterized in that the condensation is carried out in the presence of porous polyarylenephthalide 2. The method for producing 4,4-dimethyl-1,3-dioxane according to claim 1, characterized in that the content of porous polyarylene phthalide is maintained in an amount of 3.5-5.0 wt.% of the reaction mass.