CH138025A - Process for the preparation of polymethine dyes. - Google Patents

Description

  

  Process for the preparation of 1'olymethine dyes. It is known that dyes of the polymethine series can be produced by mixing cyclammonium salts with reactive methyl groups, that is to say in a or y position to the nitrogen, with the orthoesters or. Formic acid salts condensed.



  It is also known that indocyanines, i.e. the polymethine dyes of the indolenine series, are also formed with very low yields by condensation of formaldehyde with the 1,3,3-trialkyl-2-methylene indolines with subsequent oxidation in an alkaline medium.



  It has now been found that polymethine dyes of the indolenine series are obtained in good to very good yields if the condensation products are obtained from the action of two moles of a methylene base, which is formed from a cyclammonium salt with more reactive, that is to say in a -Position to the nitrogen standing methyl group is obtained by treating with alkalis, to form an L- <B> - </B> formaldehyde,

   treated with oxidants in a non-alkaline medium.



  The oxidation can be carried out either without the addition of acids or in the presence of organic acids such as acetic acid, formic acid, propionic acid, benzoic acid, or in a mineral acid medium such as sulfuric acid; Hydrochloric acid, etc.



  The most diverse oxidizing agents, such as oxygen, air, silver oxide, silver acetate, lead superoxide, nitrosobenzene, can be used as oxidizing agents.

         Example <I> 1: </I> 35 parts of the 346 parts of 1,3; 3-trimethyl-2-methylene indoline and 83.2 parts of 38% solution of formaldehyde produced condensation product are in 6000 parts of alcohol are suspended and 160 parts of glacial acetic acid and 250 parts of silver oxide are added at 0-5o over a period of 1/4 hour with stirring and cooling.

   The mixture is stirred for 15 to 20 hours at this temperature, the silver suspended in the alcoholic dye solution is filtered off, 3000 parts of 10 0% hydrochloric acid are added to the filtrate and it is concentrated.

   After cooling down
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    In accordance with this scheme, the oxidation in an alkaline medium by the alkali also takes place, but the monosalt of the condensation product b is partly converted into the free base a, which is unsuitable for the oxidation, and this is in addition to the destructive properties that the alkali has on the products I> a </I> and <I> b </I>, the reason why the oxidation in an alkaline medium leads to the dye c only in extremely low yields.

      <I> Example 2 </I> <B> 358 </B> parts of the formaldehyde condensation product used in example 1 are dissolved in 15-25000 parts of benzene and 1250 parts of lead peroxide (about 50%) and 50 parts of anhydrous chlorealcium are added. The mixture is heated to low boiling while stirring and a solution of 125 parts of glacial acetic acid in 500 parts of benzene is then added dropwise. The reaction mixture immediately turns red.

   After some time, the mixture is filtered hot, the benzene solution is extracted with dilute hydrochloric acid and the extract is concentrated. On cooling, the 1,3,3,1 ', 3', 3'-13examethyl-streptomonovinylene-2,2'-indocyanine chloride separates out, is filtered, washed with dilute hydrochloric acid and the yield obtained is 75-80% Dye dried. The reaction takes place according to the following scheme: violet-red crystals, which are filtered off, washed with dilute hydrochloric acid and dried ge.



       It is also possible to proceed in such a way that after the condensation has ended and the reaction mixture has been allowed to cool, it is filtered off and the residue is extracted with alcohol. The dye can be precipitated from the concentrated extraction solution with hydrochloric acid. <I> Example 3: </I> 358 parts of the formaldehyde condensation product used in Example 1 are dissolved in 4000 parts of benzene with stirring and 60 parts of glacial acetic acid are added. While passing air through, the mixture is heated to 60-70 ° and kept at this temperature for 1-2 hours.

    The benzene solution is then extracted with 10% hydrochloric acid, whereby the chloride of the dye precipitates. After filtering off, washing with dilute hydrochloric acid and drying, the same dye as in Examples 1 and 2 is obtained.



  In a very analogous manner, the formaldehyde condensation products from substituted methylene bases of the benzene and naphthalene series can be converted into the corresponding indocyanine dyes, for example the condensation product of 1,3,3,5-tetramethyl-2-methyleneindoline and formaldehyde from Melting point 150 in the oxy dation a blue-violet dye, while the condensation product of 1.3,

  3-Trimethyl-2-methylene-a-naphthindoline and formaldehyde with a decomposition point 180-200 is converted into a blue dye by oxidation.

 

Claims (1)

<B> PATENT CLAIM </B> Process for the production of polymethine dyes of the indolenine series, wherein the condensation products, as they are produced by the action of two moles of a methylene base, are reactive from a cyelammonium salt, that is to say in the a-position Nitrogen standing methyl group is obtained by treating with alkalis, formaldehyde to form one mole, are oxidized, characterized in that they are treated with oxidizing agents in non-alkaline Me dium.