NOVELTY - Preparation of retigabine or its salt involves a) contacting N-ethoxycarbonylamino-para-phenylene diamine with amine protecting reagent in a solvent and nitrating agent to produce substituted nitro compound (A1); b) contacting (A1) with amino compound; c) contacting 5-amino-2-ethoxycarbonylamino-nitrobenzene (R1) with 4-fluorobenzaldehyde in solvent; d) contacting 2-ethoxycarbonylamino-5-(4-fluorobenzylideneamino)-nitrobenzene (S1) with metal borohydride in a solvent system; and e) reducing 2-ethoxycarbonylamino-5-(4-fluorobenzylamino)-nitrobenzene (T1).    USE - For preparation of retigabine or its salt (claimed) which is useful as anticonvulsant for treatment for partial epilepsies and for muscle relaxing, fever-reducing and as peripheral analgesic agent; for treatment of neurologic conditions, including migraine and neuropathic pain.    ADVANTAGE - The method is an efficient, economical and industrially viable process for the preparation of 2-amino-4-(4-fluorobenzylamino)-1-ethoxycarbonylaminobenzene (retigabine) (I); provides compound (I) or (IA) with improved yield and purity (95% yield and 99.5% purity) as compared to prior art processes; and allows preparation of retigabine intermediate 2-ethoxycarbonylamino-5-(4-fluorobenzylideneamino)-nitrobenzene (S1) or (4-fluorobenzylidene)-3-nitrobenzene-1,4-diamine (M1), while avoiding the use of any external catalyst/ion exchanger or water separator or water separator technique like azeotropic distillation. The method allows replacement of genotoxic and potentially hazardous hydrazine hydrate as a deprotecting agent by new set of deprotecting agents selected from set of ammonia, urea, thiourea, and alkylamines and thus avoiding the formation of by-products like phthaloyl hydrazide which is difficult to be removed from the product resulted into the isolation of product 5-amino-2-ethoxycarbonylamino-nitrobenzene (R1) of higher purity in better yield; eliminates the use of catalyst or acid ion exchanger or water separator or azeotropic distillation technique while preparing retigabine intermediates (4-fluorobenzylidene)-3-nitrobenzene-1,4-diamine (M1) and 2-ethoxycarbonylamino-5-(4-fluorobenzylideneamino)-nitrobenzene (S1) comprising the condensation of respective amines with 4-fluorobenzaldehyde; eliminates the use of methanol as solvent during borohydride reduction of retigabine intermediate (S1), thus avoiding the formation of transesterified impurity 2-methoxy carbonylamino-5-(4-fluorobenzylamino)nitrobenzene; allows direct reductive amination of 5-amino-2-ethoxycarbonylamino-nitrobenzene (R1) or 2-nitrobenzene-1,4-diamine (K1) with 4-fluorobenzaldehyde in presence of borohydrides and aqueous solvent, thus avoiding the formation/isolation of hygroscopic and comparatively less stable imine compound (S1) or (M1); allows using catalytic hydrogenation concept in presence of alcohol-base combination for simultaneous reduction of double bond (imine) and nitro group, thus eliminating the use of metal borohydride for reduction, and retigabine base or its acid addition salt is directly formed from the compound (S1) in single step without isolation/formation of compound (T1), which is particularly advantageous as number of unit operations are reduced; allows using transfer hydrogen reaction technique for the reduction of nitro group comprising ammonium formate in combination with hydrogenation catalyst, which avoids pressure reaction and use of external source of hydrogen gas; and allows using alcohol-base combination as a solvent system for the reduction of the intermediates (S1) and (T1) through catalytic hydrogenation, which results into the formation of retigabine base and its salt in higher yield and better purity.    DETAILED DESCRIPTION - Preparation (P1) of retigabine (I) or its salt involves a) contacting N-ethoxycarbonylamino-para-phenylene diamine with amine protecting reagent in a solvent and then contacting the reaction mixture with nitrating agent to produce substituted nitro compound (A1) of formula (II); b) contacting (II) with amino compound of formula RNH2 to produce 5-amino-2- ethoxycarbonylamino-nitrobenzene (R1); c) contacting 5-amino-2-ethoxycarbonylamino-nitrobenzene (R1) with 4-fluorobenzaldehyde in a solvent to produce 2-ethoxy carbonylamino-5-(4-fluorobenzylideneamino)-nitrobenzene (S1), optionally removing water formed during the reaction; d) contacting 2-ethoxycarbonylamino-5-(4-fluorobenzylideneamino)-nitrobenzene (S1) with metal borohydride in a solvent system comprising water as one of the solvent to produce 2-ethoxycarbonylamino-5-(4-fluorobenzylamino)-nitrobenzene (T1); e) reducing 2-ethoxycarbonylamino-5-(4-fluorobenzylamino)- nitrobenzene (T1), by catalytic hydrogenation comprising alcohol-base combination as solvent system or by catalytic transfer hydrogen reaction in presence of ammonium formate or formic acid optionally in alkaline medium to obtain pure retigabine base (I), optionally isolating the base, contacting the retigabine base in-situ with an acid in a solvent to produce retigabine acid addition salt (IA).    Pr=amine protecting group;    R=H, lower alkyl, NH2-CO-, NH2-CS- or Ar-CH2-;    Ar=phenyl (optionally substituted) or linear or branched 1-12C lower alkyl.    INDEPENDENT CLAIMS are included for the following:    (1) preparation (P2) of 2-ethoxycarbonylamino-5-(4- fluorobenzylideneamino)-nitrobenzene (S1) as key intermediate for preparation of retigabine (I);    (2) preparation (P3) of 2-ethoxycarbonylamino-5-(4-fluorobenzylamino)-nitrobenzene (T1) as key intermediate for preparation of retigabine (I) and its salts;    (3) preparation (P4) of retigabine and its salt;    (4) preparation of intermediate (4-fluorobenzylidene)-3-nitrobenzene-1,4-diamine (M1); and    (5) preparation of (4-fluorobenzyl)-3-nitrobenzene-1,4-diamine (N1).