DD147667B1 - PROCESS FOR THE PREPARATION OF 2,5-BIS- (BENZOXAZOLYL) -THIOPHENES - Google Patents

Description

CTTFiMTKKOMBISAg ВИТЕЕЖЫ)

Bitterfeld, 3.12.1979 2021

Process for the preparation of. ' 2,5-bis (benzosazolyU thiophenes

Field of application of the invention

The invention relates to a process for the preparation of 2,5-bis (benzoxazolyl) thiophenes of the formula

Y Ί

(D

wherein the radicals X, which may be identical or different, are hydrogen or a non-aromatic hydrocarbon radical having at most 6 carbon atoms, and the radical Y is hydrogen or halogen.

- 2 - 2021

Characteristic of the known technical solutions

Are: (azolyl benzo3) -thiophenes in a one-step process by reacting 2,5-Thiophendicarbonsäuren with o-Hydroscy-aminobenzenes receive · The reaction is carried out in liquid, halogenated aromatic hydrocarbons having a boiling point above 200 ⁰ It is known that 2,5-bis C under nitrogen atmosphere and is advantageously introduced by gradual heating of the reaction mixture to the boiling point and continued so long, "until almost the theoretically cleavable amount of water is distilled off azeotropically very beneficial here are additives of boric acid, zinc chloride and nitrogen bases (DE-OS 1,795 394, DE-OS 1 949 334. The diamide formation of the first reaction stage normally proceeds without difficulty, whereas the ring reactions of the second reaction stage require high temperatures, These high thermal loads lead to the formation of a considerable proportion of unwanted lifting products, thereby preserving the use of the catalyst products as optical brightener is severely restricted. These byproducts are difficult to remove by repeated overturning or other known purification methods and with large yield losses.

This method of synthesizing precludes the possibility of synthesizing, in which first the corresponding diamide compounds. are formed and isolated from hydroxyarylamino compounds and the acid chlorides of 2,5-thiophenedicarboxylic acid. The ring closure reactants then take place again in halogenated aromatic hydrocarbons at high temperature with the addition of catalysts, such as

- 3 - 2021

Zinc chloride or boric acid. However, the two-stage processes are more economical because of the greater apparatus and time required.

Object of the invention

The aim of Erfindimg is an economical process for the preparation of 2,5-bis (benzo2: azolyl) thiophenes of the formula I, which provides without additional purification stages in very high yield a product in such pure form, which after appropriate formation directly as optical brightener can be used.

Explanation of the essence of the invention

It has been found that 2,5-bis (benzosazolyl) -thiophene of the formula I of the objective position is obtained accordingly, if one leaves the reaction environment of the final stage technology not in the neutral or alkaline range in the otherwise known manner in manufacturing, but in the pH range less than 4 laid. This altered condition of the system surprisingly leads to a significantly improved quality of the end products of these syntheses. In this acidic precipitation of the end products namely the strongly coloring by-products of the synthesis, the further use of the obtained 2,5-bis (benaoxazolyl) -thiophen · compounds in the form of their crude products as optical brighteners in the textile industry significantly disturb or their Use only after repeated redeposition appear suitable, transferred to the mother liquor and with this on separation of the

- 4 - 2021

removed solid end products. Because now. the amount of these interfering components depends, inter alia, on the length of the thermal load of the reaction system and on the amount of entrainment by an inert gas, it is advantageous to keep the time schedule as short as possible and to reduce the negative influence of residual admixtures due to larger amounts of inert gas > With an increased amount of inert gas, however, there is the danger that subordinate much larger amounts of o-Hydroxyarylaminoverbindungen into the cooler while maintaining the usual heating times and thus lead to a reduction in the final yield · Although a reduced heating rate, this just mentioned ITachteil could be partially recovered compensate, but thus increases the total time of the thermal load of the system. The novel implementation of the Sndstufentechnologie in acid precipitation milieu, however, with a reduced inert gas a-shortening of the heating time up to the reaction temperature of the final stage without Vorreaktionszeiten at Zwisch ^ temperature ranges of I40 to 180 ⁰ C. The procedure is such that the aliphatic alcohol, the Reaction mixture at 80 to 120 ⁰ G for the purpose of deposition of the 2,5-bis (benzoxazolyl) thiophene is added, such an amount of a concentrated inorganic acid added that in the reaction mixture, a pH between 1 and 4 is set.

The following examples serve to illustrate the invention without wishing to be limited thereto.

- 5 - · 2021

Exemplary embodiments Example 1

400 ml of 1 ^^ - trichlorobenzene, 68.8 g of 2,5-thiophenedicarboxylic acid, 87.2 g of o-aminophenol and 2.4 g of boric acid are introduced into the stirred flask and the flask is blown through with nitrogen gas · With a reduced amount of gas (5 l / h) the contents of the flask are boiled within 50 minutes. The total heating time is 4 hours. During this time the internal temperature rises from 212 ^° C. to 221 ^° C. During this time, 60 to 80 ml of trichlorobenzene "» water mixture are distilled off and the suspension is transformed into a clear, dark-brown solution. The contents of the flask are cooled with stirring to 120 ⁰ C, then followed within 30 minutes, the feed of a mixture of 650 ml of methanol with 1 ml of conc. Sulfuric acid · Hach cooling to room temperature, the precipitated crystals are filtered off with suction and freed by methanol washing of the violet-colored mother liquor

Yield: 117.2 g (92 % of theory); P = 217 to 219.5 ° (

Example 2

50 ml of 1,2,4-trichlorobenzene, 12.05 g of 3,4-dichloro-2,5-thiophenedicarboxylic acid, 10.9 g of o-aminophenol and 0.3 g of boric acid are stirred in the flask and a moderate stream of nitrogen over the surface of the surface In 40 minutes, the flask contents are heated to boiling with stirring. The gas velocity for nitrogen is 3 l / h; the sabbatical time

Distillation temperature is 4 hours. During this time, a clear brown solution gradually forms. Thereafter, the contents of the flask are cooled to 110 ^° C. with stirring. At this temperature, the feed of a mixture of 80 ml of methanol with 0.3 ml kcnz. Sulfuric acid within 20 minutes with attached reflux condenser. While stirring, the suspension is cooled to 25 ⁰ C. The extracted end product is washed by methanol until the colorless filtrate

Yield: 17.7 g (91.1 % of theory); P = 274 to 275 ⁰ C

Example 3

200 ml of 1,2,4-trichlorobenzene oil, 34.4 g of 2,5-thiophenedicarboxylic acid, 70.2 g of 4-tert. 3-butyl-2-aminophenol and 1.5 g of boric acid are stirred in the flask and heated to 200 ⁰ G in 40 minutes while passing a stream of nitrogen at 5 l / h. This starts the distillation of a Trichlorbenzoi-water mixture. During the following 4 hours, while maintaining the gas flow, the internal temperature of the flask is increased to 215C. The initially precipitated intermediate is converted into a brown solution. The flask contents are cooled to 100 C with stirring. Subsequently, a mixture of 350 ml Methanoi with 2 ml of 32 / Siger aqueous hydrochloric acid is added dropwise in 30 minutes. The crystal suspension is cooled to room temperature and stirred for 30 minutes. The deposited crystals are filtered off with suction and washed with methanol. Yield: 79.9 g (92 % of theory); ¥ * 200 to 201 ⁰ G

Claims (1)

Erf indungsan claim Process for the preparation of 2,5-bis (benzoxazolyl) thiophenes of the formula -C wherein XsH or a non-aromatic hydrocarbon radical having at most 6 C atoms and Y = H or halogen, in particular Cl, mean, in a form free of nitrogen, which, after appropriate formation, can be used directly as an optical brightener, by reacting a thiophene-2,5-dicarboxylic acid of the formula - 8 - 2021 HOOC ^{4s /} и wherein Y has the meaning given above _h with an o-hydroxyaminobenzene of the formula III in which Σ has the abovementioned meaning, in a molar ratio of 1: 2 in a halogenated aromatic hydrocarbon with stirring at the boiling temperature under an inert gas atmosphere in the presence of a catalyst, then adding an aliphatic alcohol at temperatures between 80 and 120 ⁰ C, cooling to room temperature, isolating the Reaction product and washing it with an aliphatic alcohol, in particular Methanoi, to the parity of the Piltrats, characterized in that with the order to deposit the reaction product to be added aliphatic alcohol such an amount of a concentrated inorganic acid is added that in the heatsing mixture has a pH between 1 and 4 is set.