# US 11,028,044 B2 · Versatile, concise and convenient process for the commercial scale preparation of highest pure 3,3′5,5′-tetramethylbenzidine (TMB) and its salts, a chromogenic substrate used in staining procedures in immunohistochemistry and visualizing reagent in enzyme-linked immunosorbent assays

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- Number: US 11,028,044 B2
- Document ID: US11028044B2
- Status: Granted
- Kind: B2
- Application number: 16/654,814
- Filed: 2019-10-16
- Published: 2021-04-22
- Granted: 2021-06-08
- Earliest claimed: 2019-10-16
- Assignees: SLR Biosciences, LLC
- Applicants: Sekar Reddy Alla; Rahul R. Alla; Rupini Alla
- Inventors: Sekar Reddy Alla; Rahul R. Alla; Rupini Alla
- Web page: https://patentgrep.com/patent/US11028044B2

## CPC

- C07C 245/08: with the two nitrogen atoms of azo groups bound to carbon atoms of six-membered aromatic rings, e.g. azobenzene
- C07C: ACYCLIC OR CARBOCYCLIC COMPOUNDS

## Abstract

The present invention relates to a process for the preparation of 3,3′,5,5′-Tetramethylbenzidine represented by formula I, and processes for the preparation of intermediates used in the preparation of 3,3′,5,5′-Tetramethylbenzidine.

## Claims

### Claim 1

A process for the preparation of 1,2-bis(2,6-dimethylphenyl)diazene (III), which comprises reacting 2,6-dimethylaniline of Formula (II) with KMnO4 in an aprotic solvent dialkyl ketone with a boiling point greater than about 55° C.; wherein Formula (II) is
and Formula (III) is
and wherein the solvent is acetone and the reaction temperature is between 0° C. and 60° C.

### Claim 2 (depends on 1)

The process according to claim 1, wherein the compound of Formula (III) is further treated with ammonium chloride and zinc dust in a suitable solvent; wherein the solvent is a mixture of methanol and water and the resulting product in treated with conc. HCl or H2SO4.

### Claim 3 (depends on 2)

The process according to claim 2, which is performed sequentially after a process for the preparation of 1,2-bis(2,6-dimethylphenyl)diazene (III).