CS227249B1 - Method for Activating Adkins Catalyst for Hydrogenolysis 4-Phenyl, -? 3-dioxane - Google Patents

Abstract

The catalyst is activated in a 4-phenyl-1,3-dioxane environment directly in the reactor in which hydrogenolysis is performed, with activation being carried out in the temperature range of 150 to 250 °C and the reaction mixture being rapidly heated to this temperature in an internal hydrogen atmosphere and the actual activation being initiated by a sudden increase in hydrogen pressure to a value of 5 to 50 MPa while simultaneously stirring intensively.

Description

The present invention relates to a process for activating the Adkins catalyst for the hydrogenolysis of 4-phenyl-1,3-dioxane to 3-phenyl-1-propanol. This alcohol finds use primarily in perfumery as such or as an intermediate for the preparation of esters, aldehyde, acids and other compounds, also useful in perfumery, the pharmaceutical industry, as plasticizers for plastics and the like. The starting dloxane is readily prepared by the Frins reaction of formaldehyde with styrene in an acidic medium.

For the hydrogenolysis of 4-phenyl-l, 3-dioxane are suitable catalysts based on copper, then the most suitable on the basis of CuO-Cr ₂ Oj, as is evident for example from CS. No. 198,081. Hydrogenolysis is carried out at high temperatures and pressures, most often at temperatures of about 200 ° C and pressures of 15 MPa.

In cases where the reaction is carried out in an electrically or steam-heated apparatus, the heating of the reaction mixture is usually sufficiently rapid and the catalyst is activated in a satisfactory manner. By increasing the reactor volume or changing the heating method to less efficient (heating with a low flow rate liquid heat exchanger), the heating rate of the reaction mixture is significantly reduced and the catalyst activation process may not be suitable for the reaction. In the present case of hydrogenolysis of 4-phenyl-1,3-dloxah, this is manifested by the fact that the catalyst has a lower activity resulting in a disproportionate prolongation of the reaction time, there is no total conversion of 4-phenyl-1,3-dioxane and the catalyst thus activated moreover, it is non-selective and 3-phenylpropionic acid methyl ester is formed as a by-product in the reaction mixture. Its formation is undesirable in view of the use of 3-phenyl-1-propanol in the perfumery industry, since it is difficult to separate from the main product and distorts its scent note.

The problem is solved by the method for activating the Adkins catalyst for the hydrogenolysis of 4-phenyl-1,3-dioxane according to the invention, which is characterized in that the catalyst is activated in the 4-phenyl-1,3-dioxane medium directly in the reactor in which hydrogenolysis, wherein the activation is carried out in a temperature range of 150 to 250 ° C and the reaction mixture is rapidly heated to this temperature under an inert or hydrogen atmosphere and the actual activation is initiated by stepwise increasing the hydrogen pressure to 5 to 30 MPa with vigorous stirring. The basic effect is to activate the catalyst, and only on the catalyst thus activated is hydrogenolysis of 4-phenyl-1,3-dioxane with sufficient speed and selectivity. In order to ensure perfect activation, it is necessary to maintain the temperature and pressure ranges and ensure a sufficiently rapid supply of hydrogen to the catalyst surface. At lower temperatures, lower hydrogen pressure, and incomplete mixing, catalyst formation proceeds more slowly and apparently in another way, since an incorrectly activated catalyst cannot be converted to a sufficiently active and selective form.

The invention is illustrated by the following Examples.

Example 1

A 300 L autoclave was charged with 150 L of 4-phenyl-1,3-dioxane and 15 kg of a CuO-Cr2O4 catalyst modified with 5% manganese dioxide. The autoclave was purged with nitrogen, then with hydrogen, leaving a hydrogen overpressure of 0.5 MPa. Heating was initiated by introducing hot oil into the autoclave housing. The reaction mixture was heated to 150 ° C over half an hour. The hydrogen pressure was stepped up to 10 MPa, the autoclave was set to high intensity. There was a rapid increase in temperature up to 200 ° C and the temperature was maintained at this value (by occasional cooling with condensate in the inner coil of the autoclave) for 3 hours, the pressure was maintained by hydrogen injection at 10 MPa. The end of the reaction was indicated by stopping the pressure drop in the autoclave. After cooling, the liquid reaction mixture contained 2.4% propylbenzene, 96.6% 3-phenyl-1-propanol and 4% phenyl-1,3-dioxane in addition to methanol.

Example 2

The experiment was carried out in the same manner as in Example 1 except that the residual hydrogen pressure before heating was 6 MPa and the reaction mixture was gradually heated with vigorous stirring. The catalyst was thus activated already at lower temperatures and, as a result, for a longer time than in Example 1.

After two hours, the reaction conditions were adjusted to the values given in Example 1.

Due to improper activation of the catalyst, the hydrogenolysis of 4-phenyl-1,3-dioxane was carried out for 8 hours and its course was highly non-selective. The liquid reaction mixture contained 26.8% propylbenzene, 56.8% 3-phenyl-1-propanol, 12.8% 3-phenylpropionic acid methyl ester, and 3.6% unreacted 4-phenyl-1,3- dioxane.

Claims (1)

SUBJECT OF THE INVENTION Method for activating the Adkins catalyst for hydrogenolysis of 4-phenyl-1,3-dioxane, characterized in that the catalyst is activated in a 4-phenyl-1,3-dioxane medium directly in a hydrogenolysis reactor, wherein the activation is carried out at a temperature range of 50 to 250 ° C and the reaction mixture is rapidly heated to this temperature under an inert or hydrogen atmosphere and the actual activation is initiated by stepwise increasing the hydrogen pressure to 5 to 30 MPa with vigorous stirring.