Telescoping synthesis of 5-amino-4-nitroso-1-alkyl-1H-pyrazole salt
View Patent ↗A telescoping synthesis of 5-amino-4-nitroso-1-alkyl-1H-pyrazole salt derivatives of formula (I), the compound (I) itself, and its use as an intermediate in the fabrication of 1-alkyl-4,5-diaminopyrazole salts of general formula (IX). The compounds of formula (IX) can be used as precursor dyes in oxidative hair dye compositions. R is a mono- or poly-substituted or unsubstituted, straight or branched, saturated or mono- or poly-unsaturated, alkyl group. HZ and HZ′ are organic or mineral acids.
1. A telescoping process for synthesizing 5-amino-4-nitroso-1-alkyl-1H-pyrazole salt (I), the process comprising the steps of:
a) synthesizing the intermediate 3-hydrazinylpropanenitrile (IV) via a 1,4 Michael addition using acrylonitrile (III) and hydrazine hydrate;
b) synthesizing the intermediate 3-(2-alkylidenehydrazinyl)propanenitrile (VI) via a condensation with intermediate (IV) and aldehyde (V):
wherein R is a mono- or poly-substituted or unsubstituted, straight or branched, saturated or mono- or poly-unsaturated alkyl group;
c) synthesizing the intermediate 5-amino-1-alkyl-1H-pyrazole (VII) via a cyclisation with intermediate (VI) in the presence of a base;
d) synthesizing 5-amino-4-nitroso-1-alkyl-1H-pyrazole salt (I) via a nitrosation step with intermediate (VII) in the presence of an acid HZ;
2. A telescoping process according to claim 1 wherein R is a C1-C11 straight unsubstituted alkyl group.
3. A telescoping process according to claim 2 , wherein R is a C3-C7 straight unsubstituted alkyl group.
4. A telescoping process according to claim 3 , wherein R is pentyl.
5. A telescoping process according to claim 1 , wherein the base for step c) is selected from the group consisting of sodium methylate, potassium methylate, lithium methylate, sodium hydroxide, potassium hydroxide, ammonium hydroxide, calcium hydroxide, magnesium hydroxide, barium hydroxide, aluminum hydroxide, ferrous hydroxide or hydroxide, ferric hydroxide or Iron (III) hydroxide, zinc hydroxide, lithium hydroxide, sodium bicarbonate, sodium tert-butylate, potassium tert-butylate and mixtures thereof.
6. A telescoping process according to claim 5 wherein the base for step c) is selected from the group consisting of sodium methylate, potassium methylate and lithium methylate.
7. A telescoping process according to claim 1 , wherein the acid HZ for step d) is HCl.
8. A telescoping process according to claim 1 , wherein the nitroso source for step d) is selected from the group consisting of 3-methylbutyl nitrite, nitrosylsulfonic acid, tert-butylnitrite, butylnitrite and mixtures thereof.
9. A telescopic process according to claim 8 wherein the nitroso source is 3-methylbutyl nitrite.
10. A telescopic process according to claim 1 for synthesizing 5-amino-4-nitroso-1-n-hexyl-pyrazole-HCl (I-a), wherein said process comprises the steps of:
a) synthesizing 3-hydrazinylpropanenitrile (IV):
b) synthesizing 3-(2-hexylidenehydrazinyl)propanenitrile (VI-a):
c) synthesizing 5-amino-1-n-hexyl-pyrazole (VII-a):
d) synthesizing 5-amino-4-nitroso-1-n-hexyl-pyrazole-HCl (1-a):