THE DJNITRO-DERIVATIVES OF DIMETHY L-P-TOLUIDINE. 2645CCLXX. -The Dinitro- de&vatives of Dimeth yl- p- toluidineBy GILBERT T. MORGAN and ARTHUR CLAYTON.THE nitration of aromatic arnines under various conditions presentscertain features of considerable theoretical interest in connexionwith the mode in which substitution occurs in the aromatic nucleus.In many cases it is found desirable to moderate the action ofnitric acid on these bases by nitrating them in the form of theiracyl derivatives, the acetyl compound being most frequentlyemployed for this purpose. This method of nitration leads, in thegreat majority of 'cases, t o the production of ortho- and para-nitro-VOL. XCVII. 8 2646 MORGAN AND CLAYTON: THE DINITRO-derivatives, the substitution of the nitro-group in these conditionsobeying the ortho-para law.When, however, the benzenoid amines are nitrated in concentratedsulphuric acid, the nitro-group tends to enter a meta-position withrespect to the aminic nitrogen, so that the chief product is frequently,although not invariably, a me$a-nitrederivative in conformity withthe meta law of substitution.Aniline, for instance, when nitratedin excess of concentrated sulphuric acid, gives a mixture of nitro-compounds, in which m-nitroaniline predominates. o-Toluidine,under similar conditions, yields 4-nitro- and 6-nitro-o-toluidine,whilst p-toluidine furnishes 2-nitro-p-toluidine, these three productseach having the nitro-group in a meta-position with regard to theaminic nitrogen.The nitration of the aromatic monoalkyl amines in concentratedsulphuric acid proceeds along similar lines, methyl-o-toluidine andmethyl-p-toluidine yielding respectively 4-nitromethyl-o-toluidineand 2-nitromethyl-p-toluidine (Gnehm and Blumer, Annalelt, 1899,304, 99; Pinnow, Ber., 1895, 28, 3040).The case of the tertiary bases presents several points of interest.Dimethylaniline yields a mixture containing three to four parts ofm-nitrodimethylaniline to one part of pnitrodimethylaniline (Groll,Ber., 1886, 19, 1944).Dimethyl-o-toluidine and dirnethyl-p-toluidinegive rise respectively to 4-nitrodimethyl-o-toluidine and 2-nitro-dimethyl-ptoluidine, in both of which the nitro-group is meta tothe aminic nitrogen (Gnehm and Blumer, Zoc. cit., p. 107, andWhen dimethyl-p-toluidine. dissolved in concentrated sulphuricacid, is treated with sufficient strong nitric acid to form di- or eventri-nitro-derivatives, the reaction nevertheless proceeds only to theextent of prod?cing 2-nitrodimethyl-p-toluidine, even when thetemperature of the concentrated acid solution is raised to 70°.But02 pouring this acid liquid into water so that the temperaturereaches 40°, further nitration occurs, with the production of adinitrodimethyl-p-toluidine (m. p. 103-104°) in practically quant-itative yield. This dinitrecompound is apparently identical witha by-product of the action of nitrous acid on dimethyl-ptoluidine(Pinnow, Ber., Zoc. cit., p. 2039).In the present communication the constitution of this dinitro-compound has been determined in the following manner.Since the compound can be prepared either directly from di-methyl-p-toluidine or by the further nitration of Z-nitrodimethyl-p-toluidine (I), it follows that one of the nitro-groups is in position 2with respect to t-he methyl radicle :D.R.-P.69188)DERIVATIVES OF DiMETHY L-P-TOLUIDINE. 2647N(cH3)2 N(CH3)2 w w 2 N(CH3)2NO,/\ NHA~()CH3 CH3 CH3()NO2 --+ (>,€€, --+ I \/ INHAc --3 vNHAc(IT.'(11.) / (111.)OH3(1.1Y( CH3) 2 N(CH3)2 KyT( CH3) 2 N(CH3'2N H 2 A --+ I INH,NH2/\B.(>NH*c+- v N H A c \)NO2 \/ CH3(VIII.)(3x3(VII. )CH, CH3(V. 1 (TI.)2-NitrodimethyI-p-toluidine (I), on reduction, yields as-4-dimethyl.2 : 4-tolylenediamine (11), which, when successively acetylated andnitrated, furnishes 5-nitro-2-acetylam~odirnethyZ-p-toluidine (111).The position of the entrant nitregroup in compound I11 is ascer-tained by reduction, when 2-acetyl-2 : 5-diaminodirnethyl-p-tot?uidine(VI) is obtained, and this triamine is converted by the Sandmeyerreaction into 5-bromo-2-acetylaminodimethyl-p-toluidine (V), theconstitution of which has been fully established (Morgan andClayton, Trans., 1905, 87, 946).But 5-nitro-2-acetylaminodimethyl-p-toluidine (111), when successively reduced and acetylated, gives2 : 5-diacetyldiaminodimet hyl-p-toluidine (IV), and this diacetylcompound can also be produced by reducing dinitrodimethyl-ptoluidine (m. p. 103-104O) and acetylat'ing the resulting 2 : 5-di-aminodimethyl-p-toluidine (VIII).These two methods of preparing the same diacetyl compound (IV)prove conclusively that the dinitrecompound melting at 103-104Ois 2 : 5-dinitrodimethyl-p-toluidine (VII).Before the foregoing direct proof was worked out, an indirectmethod had been adopted, which consisted in preparing 2 : 6-dinitro-dimethyl-p-toluidine (IX) and comparing its properties with thoseof the above-described 2 : 5-compound. The 2 : 6-compound is pre-pared by reducing 2 : 4 : 6-trinitrotoluene to 2 : 6-dinitro-p-toluidine,and methylating this base with methyl sulphate :N(CH3)2 ACH3(IX.M. p. 192".)\/CH3(X. Pinnow, ni. p. 95".)3 : 5-Dinitrodimethyl-p-toluidine was prepared by Pinnow andMatcovich (Ber., 1898, 31, 2518) by the action of dilute nitric andsulphuric acids on dimethyl-p-toluidine, a chemical change whichprobably takes place in two stages, for 3-nitrodimethyl-p-toluidin2648 MORGAN AND CLAYTON: THE DINITRO-(XI) is formed by the action of aqueous nitrous acid on dimethyl-p-toluidine (Pinnow, Ber., 1895, 28, 3039).It therefore followsthat the dinitrecompound melting at 103-104° must be either the2 : 5- or 2 : 3-dinitrodimethyl-p-toluidine. Reduction to the tri-amine (VIII) showed that the compound was the 2 : 5-isomeride,since the base had all the properties of a para-diamino-compound,and did not react at all like an ortho-diamine.These results indicate that the nitration of dimethyl-p-toluidinetakes place in two different ways, depending on the concentrationof the acid medium.I n strong sulphuric acid, a meta-position tothe aminic nitrogen is assumed by the entrant nitregroup, andthis formation of 2-nitrodimethyl-ptoluidine represents the onlystage of nitration so long as the acid remains concentrated. Dilutionof the acid with water leads to the introduction of nitro-groups inthe ortho-positions with respect to the basic nitrogen atom (compareformuk VII, X, and XI). I n strong acid, the meta-law of sub-stitution is obeyed, whereas nitration in presence of water conformst o the ortho-para law.These nitration phenomena may be profitably discussed in con-nexion with the rule put forward by Crum Brown and Gibson(Trans., 1892, 61, 367) for determining whether a benzenoid mono-derivative shall give a meta-di-derivative or a mixture of ortho-and para-di-derivatives. The rule is applied by considering thehydride of the radicle already present in the molecule, and if thishydride is directly oxidisable to the corresponding hydroxy-derivative, then substitution takes place according to the meta law.For example, the nitro-group, which determines the entry of thesecond radicle mainly into a meta-position, has the hydride nitrousacid, H*N02, and this is directly oxidisable to nitric acid, HO*NO,.On the other hand, methyl has the hydride methane, H-CH,,which is not readily oxidisable to methyl alcohol, HO-CH,.I n thiscase the group methyl determines the entry of other radicles intoortho- and para-positions.This generalisation, although quite empirical, is a remarkablycomprehensive rule, and it may be applied successfully to severalcases which had not been examined eighteen years ago, when CrumBrown and Gibson first proposed it.The triazo group N, has the hydride H*N, not directly oxidisableto a compound HO*N,, and, in accordance with the rule, N, inducesthe entry of other radicles into ortho- and para-positions.The group AsO,H, present in phenylarsinic acid has the hydrideH*AsO,H,, which is directly oxidisa?ble to arsenic acid, HO-AsO,H,,and in conformity with the rule this group favours substitution inmeta-positionsDERIVATIVES OF DINETHYL-P-TOLUIDINE.2649The primary benzenoid amines were placed by Crum Brown inthe category of substances obeying the ortho-para law; this modeof substitution agreeing with the fact that the hydride H*NH2 isnot directly oxidisable to hydroxylamine, HO*NH2.The general-isation can be extended to the acetyl derivatives; the hydridoH*NH*CO*CH, is not directly oxidisable to HO*NH,*CO*CB,,which is in acctordance with the fact that the nitration of acetylderivatives generally follows the ortho-para law.When, however, the bases are nitrated in strong sulphuric acid,one must consider the group NH,-H,SO, having the hydrideH*NH2*H,S0,, which is not directly oxidisable to HO*NH2-H2S0,.I n accordance with the Crum Brown and Gibson rule, the presenceof this sulphate group should lead to the formation of ortho-pa.ra-derivatives, but in many cases substitution occurs by preference inthe meta-position. Aniline and dimethylaniline each give productsin which the meta-nitro-derivative predominates.The case of the tertiary bases is of especial interest, because i tmay be argued that, under certain conditions, the hydride H-NR, isdirectly oxidisable to HO-NR, ; thus diethylamine with hydrogenperoxide yields diethylhydroxylamine (Dunstan and Goulding,Trans., 1899, 75, 1009), and dimethylmiline itself can be oxidisedto dimethylaniline oxide.Yet, strangely enough, in dilute solutions,where these tertiary amines may be supposed to be reacting partly inthe free state, they nitrate in accordance with the ortho-para law,and only in combination with concentrated sulphuric acid do theyreact in conformity with the meta law.I n whichever way the tertiary amines are nitrated, whether instrong or dilute acid, there is a discrepancy between the facts andthe application of the Crum Brown and Gibson rule to thesephenomena.While indicating this limitation to a rule which hasproved fairly general, the authors do not wish to put forward atheory sufficiently comprehensive to include all cases of the nitrationof aromatic amines, but they suggest as a working hypothesis thatthe nitration of an aromatic base or its acetyl derivative is a processessentially different from the nitration of the sulphate of the basein concentrated sulphuric acid (compare Armstrong, Trans., 1887,51, 589).I n the former case, the nitric acid is attracted first to the amino-o r the acetylamino-group, giving rise to a nitrate by direct addition ;dehydration leads to the production of a nitroamine, and then fQllowssubstitution in the sympathetic orthe and parapositions.I n the latter method of nitration the radicle *NH,*HSO,,*NH&*HSO,, or *NHR2*HS04 acts as a strongly acidic group,which, so far from attracting the nitric acid, actually exerts a sligh2650 MORGAN AND CLAYTON: TEE DINITRO-but appreciable repulsive action, so that the introduction of thenitro-group takes place in the apathetic meta-position, this beingshielded from the direct influence of the aminosulEhate complex.The process is comparable to the nit'ration of a sulphonic acid:S0,H SO,H NH,*HSO, NH,*HSO,/\ /\ /\I I - + I I\/ \ 7 * 2 r, -+\and in both instances the meta-derivatives predominate (compareFliirscheim, J .pr. Chem., 1902, [ii], 66, 324).This view of the nitration of aromatic amines in concentratedsulphuric acid affords an explanation of the course of substitutionin the naphthalene as well as in the benzene series.EXPERIMENTAL.N i t rat i o n of Dime t ?q Lp-t o hidine.Dimethyl-p-toluidine, dissolved in twelve parts of cold con-centrated sulphuric acid and treated with two to three molecularproportions of nitric acid also dissolved in strong sulphuric acid,underwent nitration only to the extent of forming 2-nitrodimethyl-ptoluidine (m. p. 37O), for this base separated in practicallyquantitative yield when the acid solution was poured into ice-coldwater or dilute aqueous ammonia.The nitration proceeded no further than the formation of themononitro-compound, even when excess of fuming sulphuric andnitric acids were employed at 70°.A t higher temperatures,sulphonation and even destructive oxidation set in, but no highernitro-compounds could be detected.When, however, the solution of 2-nitrodimethyl-ptoluidine inconcentrated sulphuric acid, and one molecular proportion of nitricacid was poured into four volumes of water, so that the temperaturerose to 40°, further nitration occurred, with the production of2 : 5-dinitrodimethykp-tohidine (m. p. 103-104°), the yield beingpractically quantitative :0.1650 gave 0.2872 CO, and 0.0742 H,O.C9H,,O4N, requires C = 47-99 ; H = 4-89 per cent.-2 : 5-Dinitrodimethyl-p-toluidine (VII) can also be prepared bydissolving 2-nitrodimethyl-p-toluidine in concentrated nitric andsulphuric acids, and pouring the solution into four volumes of water.C =47.45 ; H = 5-00.5-Nit ro-2-n ce'tylaminodimet hy I-p-t oluidine (111).2-Nitrodimethyl-p-toluidine was reduced with tin and hydro-chloric acid (Trans., 1905, 87, 948), and the resulting 2-amino-dimethyl-p-toluidine acetylstedDERIVATIVES OF DIMETHY L-P-TOLUIDINE. 26513-Acetylaminodimethyl-p-toluidine was dissolved in 10 parts ofcold concentrated sulphuric acid, and treated with about half itsweight of nitric acid (sp.gr. 1*4), diluted with three volumes ofstrong sulphuric acid. N o reaction occurred in the strong acid,but on pouring the solution into water, so that the temperaturerose to 70°, nitration set in, and on adding dilute ammonia, 5-nitro-2-ac e t ylam'inodime f h yl-p-t oluidine separated, and was crystallisedfrom alcohol, yielding yellow needles, melting at 155O :0.1272 gave 0.2594 CO, and 0.0768 HiO.0.1229C =55-61; H = 6.71.Cl1H,,O3N3 requires C =55*69 ; H = 6-32 ; N = 17.72 per cent.,, 19.0 C.C.N, at 1B0 and 760 mm. N=17*85.2-8 cetyl-2 : 5-diaminodimethyLp-tol~~idine (VI).The foregoing nitroacetyl compound underwent simultaneousreduction and hydrolysis on treatment with tin and hydrochloricacid, and was accordingly reduced with iron filings and waterslightly acidified with acetic acid, the reducing agent being slowlyadded to the boiling solution until the colour disappeared. Thesolution, after neutralisation wit.h sodium carbonate and filtration,wax evaporated to dryness, and the residue, when dissolved in water,crystallised therefrom in colourless crystals, melting at 131-133O :0.1056 gave 18.2 C.C. N, at 16O and 759 mm.CllH170N3 requires N = 20.28 per cent.2-A c c t yl-2 : 5-diaminodimet h yEp- t o hidine was dissolved in hydro-bromic acid containing cuprous chloride, the solution warmed to 80°,and slowly treated with aqueous sodium nitrite (1 mol.).The cooledliquid was rendered ammoniacal, and the precipitate crystallisedfrom alcohol, when it separated in colourless, woolly needles, meltingat 163O, and was identified by the method of mixed melting pointsas 5-bromc+2-acetylaminodimethyl-p-toluidine (V), the constitutionof which has already been determined (Trans., 1905, 87, 948).2 : 5-DiaminodirnethyZ-p-tolut2'ine (VIII) (compare Pinnow andMatcovich, Zoc.tit.).-Granulated tin was added to a hot solution of24 grams of 2 : 5-dinitrodimethyl-p-toluidine in 150 C.C. of con-centrated hydrochloric acid and 50 C.C. of water until the colourdisappeared. After removing the tin as sulphide, the filtrate wasevaporated until 2 : 5-diaminodimethyl-p-toluidine hydrochlorideseparated in colourless crystals. The base set free by ammonia wasextracted with chloroform, and on evaporating off the solvent fromthe carefully dried extract, t.he triamine was left as an oil, whichrapidly oxidised on exposure to the atmosphere and solidified oncoaling.2 : 5-DiclcetyldiaminodimlethyLp-tolu~~ne (IV), obtained by treat-ing the preceding base with acetic anhydride, crystallised from veryN=20.062652 THE DINITRO-DERIVATIVES OF DIMETHYL-P-TOLUIDlNE.dilute alcohol in colourless needles, and after repeated crystallisationsoftened at 2 3 3 O , and melted at 236O.(Found, N=16*99. Calc.,N = 16.86 per cent.)When heated at 245O for thirty minutes, this diacetyl compoundremained unchanged, showing that it wax not an ortho-diacetylatedcompound.When used in the form of its hydrochloride, 2 : 5-diaminodimethyl-ptoluidine gave the colour reactions of a para-diamine. Oxidationwith chromic acid, either alone or in presence of aniline, gave adeep red coloration, indicating the production of a safranine dye.Alkaline hypochlorite, in presence of a-naphthol, led to the pro-duction of a blue indophenol.When heated in alcoholic acetic acidsolution with phenanthraquinone and sodium acetate, no azinecondensation occurred. The triamine underwent diazotisation inacid solution, and the product coupled with alkaline &naphthol,yielding an azo-derivative. These reactions afforded additionalevidence that the triamine has the constitution (VIII) assigned toit on p. 2647. A final confirmation was obtained by preparing2 : 5-diacetyldiaminodimethyl-p-toluidine by an alternative method,using 2-acetyl-2 : 5-diaminodimethyl-p-toluidine (VI), since the lattercompound has been shown to contain its free amino-group inposition 5.2 : 6-Dinit rodim e t hy Lp-t oluidine (IX) .2 : 6-Dinitro-ptoluidine, prepared by reducing 2 : 4 : 6-trinitro-toluene with alcoholic ammonium sulphide (Holleman andBoeseken, Bee. trav. chim., 1897, 16, 425), was slowly added tomethyl sulphate at 160-165O, and the solution maintained at thistemperature f o r thirty minutes. The liquid was then renderedalkaline with sodium hydroxide, and the solid product crystallisedfrom 50 per cent. acetic acid:0.1307 gave 0.2290 CO, and 0.0614 H,O.0.13442 : 6-Dinitrodirnethyl-p-toluidine separates in yellow needles, melt-C = 47.79; H = 5-21.C',H,,O,N, requires C= 47.99 ; H;= 4-89 ; N = 18.66 per cent.,, 22.2 C.C. Nz at 23O and 756 mm. N=18.52.ing at 192O.The authors desire to express their thanks t o the Research FundCommittees of the Royal Society and Chemical Society for grantswhich have partly defrayed the expenses of this investigation.ROYAL COLLEGE OF SCIENCE. LONDON,SOUTH KENSINGTON, S . W