Preparation of selectively N-methylated X-nitro-1,2-phenylenediamines.

Milata Viktor, Bella Maroš

Department of Organic Chemistry, Faculty of Food and Chemical Technology, Slovak Technical University, Radlinského street 9, SK-812 37 Bratislava, Slovak Republic

Keywords: nitrobenzoselenadiazoles, nitrophenylenediamines, ¹H NMR

Abstract: Nitrobenzoselenadiazoles had been methylated using dimethylsulphate to gave methosulphate salts clevable to N-methylated-nitro-1,2-phenylenediamines.

Introduction

1,2-Phenylenediamines are important group of starting materials for the synthesis of benzotriazoles, benzimidazoles, benzothiadiazoles, benzoselenadiazoles, quinoxalines¹ etc. Their preparation is based on partial reduction of polynitroderivatives of benzenes or anilines² or ring transformations^3,4. Direct methylation is described only in the case of 4-nitro-1,2-phenylenediamine through tosylation⁵.

Results and Discussion

We tried to prepare N-methylated nitro-1,2-phenylenediamines by exploiting the possibility to open N-methyl-X-nitrobenzo[2,1,5]selenadiazolium methosulphates. The latest ones could be prepared by regioselective methylation of 4- or 5-nitrobenzo[2,1,5]selenadiazole using an excess of dimethylsulphate without base to about 130 °C by simple heating under reflux according to^3,4:

Alkaline ring opening of the N-methyl-X-nitrobenzo[2,1,5]selenadiazolium methosulphates using concentrated sodium hydroxide solution, washing with water to remove excess of alkalies and rests of the dimethyl sulphate. Resulted dark red N-methylated X-nitro-1,2-phenylenediamines could be recrystallized from methanol or use raw to the next reaction.

            To establish the position of the methyl group on the amino groups in relation to nitrogroup we convert these N-methylated X-nitro-1,2-phenylenediamines to corresponding 1-methyl-X-nitrobenzimidazoles by simple cyclisation with formic acid³. Then we simple compared the set of the values for proton ¹H NMR signals with the known data in CDCl₃ (Table 1, taken from ref. 6):

Table 1: ¹H NMR shifts of 1-methyl-X-nitrobenzimidazoles in CDCl₃

When the starting compound has been 4-nitro isomer, then we could expect 4- or 7-nitro-1-methylbenzimidazole and when 5-nitro-benzo[2,1,5]selenadiazole then 5- or 6- nitro-1-methylbenzimidazole. We obtained following values (Table 2):

Table 2: ¹H NMR shifts of obtained 1-methyl-X-nitrobenzimidazoles

Simple deduction give us the structures of benzimidazoles: starting from 4-nitro-benzoselenadiazole we obtained 7-nitro-1-methylbenzimidazole and therefore starting diamine has been 3-nitro-2-N-methyl-1,2-phenylenediamine and starting from 5-nitro-benzoselenadiazole we obtained 5-nitro-1-methylbenzimidazole and therefore starting diamine has been 4-nitro-1-N-methyl-1,2-phenylenediamine. We can conclude that in 4-nitro-benzoselenadiazole is more basic nitrogen N-2, while in the case 5-nitro-benzoselenadiazole is more basic nitrogen N-1:

Literature

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