US 12,441,694 B2
Process for the preparation of methylene blue
Janmejay Rajnikant Vyas, Ahmedabad (IN); Himani Dhotre, Ahmedabad (IN); Denish H. Shah, Ahmedabad (IN); and Krunal Parikh, Ahmedabad (IN)
Assigned to DISHMAN CARBOGEN AMCIS LTD., Ahmedabad (IN)
Appl. No. 17/802,565
Filed by DISHMAN CARBOGEN AMCIS LTD., Ahmedabad (IN)
PCT Filed Feb. 27, 2021, PCT No. PCT/IB2021/051604
§ 371(c)(1), (2) Date Aug. 26, 2022,
PCT Pub. No. WO2021/171235, PCT Pub. Date Sep. 2, 2021.
Claims priority of application No. 202021008602 (IN), filed on Feb. 28, 2020.
Prior Publication US 2023/0138553 A1, May 4, 2023
Int. Cl. C07D 279/18 (2006.01)
CPC C07D 279/18 (2013.01) 9 Claims
 
1. A process for preparation of 3,7-bis (dimethylamino)-phenothiazin-5-ium chloride of formula (I):

OG Complex Work Unit Chemistry
wherein said process comprises the steps of:
(a) preparing 3,7-dibromophenothiazin-5-ium bromide wet crude of formula (III)

OG Complex Work Unit Chemistry
by reacting phenothiazine of formula (II)

OG Complex Work Unit Chemistry
along with a promoter, catalyst and brominating agent in the presence of an organic solvent;
(b) preparing 3,7-bis-(dimethylamino)-phenothiazin-5-ium bromide of formula (IV)

OG Complex Work Unit Chemistry
from the 3,7-dibromophenothiazin-5-ium bromide of formula (III)
(c) preparing of 3,7-bis (dimethylamino)-phenothiazin-5-ium chloride of formula (I) from the 3,7-bis-(dimethylamino)-phenothiazin-5-ium bromide of formula (IV); and
(d) purifying and removing metal content from the 3,7-bis-(dimethylamino)-phenothiazin-5-ium chloride of formula (I), using a metal scavenger.