Montedison S.p.a.

Farmitalia Carlo Erba

Montedison Fibre S.p.a.

Aziende Colori Nazionali Affini Acna S.p.a.

Giuseppe Ribaldone

Giampiero Borsotti

Renato Grecu

Camillo Paffoni

Giovanni Agnes

Giuseppe Sironi

Maria G Felicioli

Claudio Santini

Franco Gonzati

A process for the preparation of a pyrazine derivative of the formula ##STR1## wherein R.sub.1 represents hydroxy, C.sub.1 -C.sub.6 alkoxy, or a group of the formula NR.sub.2 R.sub.3 in which R.sub.2 and R.sub.3 are independently a hydrogen atom or C.sub.1 -C.sub.6 alkyl or, together with the nitrogen atom to which they are linked, form a saturated ring having five or six atoms which may contain one or more additional heteroatoms; which process comprises reacting a compound of the formula: ##STR2## wherein R represents a hydrogen atom, C.sub.1 -C.sub.6 alkyl, or C.sub.1 -C.sub.6 alkoxy, Y represents a hydrogen atom or a sodium, lithium, or potassium ion, and A is a nitrile group or a substituent of the formula COR.sub.1 where R.sub.1 is as defined above either with pyruvic aldehyde oxime of the formula: ##STR3## or with a pyruvic aldehyde oxime acetal derivative of the formula: ##STR4## wherein R.sub.4 and R.sub.5 are independently a hydrogen atom or C.sub.1 -C.sub.6 alkyl or may be linked together so that the compound of formula IV is a cyclic acetal; and, when A is a nitrile group, hydrolyzing the reaction product.

Preparation of pyrazine derivatives

The present invention relates to a new class of compounds belonging to the anthraquinone series, having the general formula: ##STR1## wherein R, R', R', R'', R' are indifferently H or Chlorine, ##STR2## Such compounds exhibit a color varying from yellow to violet depending on the nature and position of substituents R, R', R', R'', R'.sup.v and, in virtue of their excellent stability characteristics, they are particularly useful as pigments and vat dyes. This invention relates furthermore to the preparation of compounds having general formula (I) and to the utilization thereof, particularly in the following applications:

Anthraquinone compounds and process for preparing same

Process for the preparation of the monopotassium salt of 1,2,5-thiadiazol-3,4-dicarboxylic acid (I). Involves double-stage saponification of 3,4-dicyano-1,2,5-thiadiazole (II), 3-cyano-4-carbamoyl-1,2,5-thiadiazole (III) is obtained from an aqueous suspension of 3,4-dicyano-1,2,5-thiadiazole (II) by catalytic hydration through the addition of aqueous KOH, desirably at a temperature of from 20.degree. to 50.degree. C. and with a molar ratio of 3,4-dicyano-1,25-thiadiazole (II) to KOH of from 1:0.01 to 1:0.8. This is followed by hydrolysis, by the further addition of aqueous KOH, desirably at a temperature of from 85.degree. to 100.degree. C., until attaining an overall molar ratio of 3,4-dicyano-1,2,5-thiadiazole (II) to KOH of from about 1:2.0 to 1:2.35, a molar ratio of 3,4-dicyano-1,2,5-thiadiazole (II) to H.sub.2 O of from about 1:20 to 1:23. Thereafter, from the resulting solution of dipotassium salt of 1,2,5-thiadiazole-3,4-diccarboxylic acid, the monopotassium salt is separated by acidification of said solution.

Method for the preparation of the monopotassium salt of

3,4-DICYANO-1,2,5-THIADIAZOLE IS PREPARED BY REACTING DIAMINOMALEONITRILE (DAMN) with thionyl chloride (SOCl.sub.2) at a temperature of 40.degree. C. up to the boiling point of thionyl chloride wherein the molar ratio of SOCl.sub.2 /DAMN is between 2:1 and 10:1.

Process for preparing 3,4-dicyano-1,2,5-thiadiazole

New compounds are disclosed having the general formula: ##STR1## wherein R.sub.1, R.sub.2 and R.sub.3 may be the same or different and are selected from the class consisting of H, Cl and OCH.sub.3. They are useful as pigments. They are prepared by reacting a substituted or unsubstituted 1-aza-2-hydroxybenzanthrone with 2,3-dichloro-1,4-naphthoquinone, in the presence of pyridine, at a temperature between 80.degree. and about 120.degree. C.

Heterocyclic polynuclear pigments and process for preparing same

A process is disclosed for the preparation of 2-hydroxybenzanthrone and substituted derivatives thereof having the general formula: ##STR1## wherein: R.sub.1 = H, OH

Method for the preparation of 2-hydroxybenzanthrone compounds

1-AZA-2-HYDROXYBENZANTHRONE, USEFUL AS AN INTERMEDIATE FOR SYNTHESIZING DYES IS OBTAINED BY THE DIRECT REACTION OF ALKYL ESTERS OF ANTHRAQUINONE-1-ACETIC ACID WITH AMMONIA IN HYDROXYLATED SOLVENTS AND IN THE PRESENCE OF STRONG BASES AND/OR REDUCING SUBSTANCES.

Process for preparing 1-aza-2-hydroxybenzanthrone

A new process for preparing 3,3 - thio - bis[2-Methoxy-1-azabenzanthrone], a useful intermediate in the synthesis of dyestuffs, is disclosed. The process involves reacting 2-methoxy-1-azabenzanthrone with sulfur chlorides in suspension or solution in an inert solvent under heating, and recovering the reaction product from the reaction mass, e.g., by filtering.

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Gallarate (Varese), Italy

Giuseppe Ribaldone