155 THE NITRATION OF W%-BROMOPHENOL. XXIV.-The Nitration of rn-Bromophenol. HENRYHODGSON HARRYMOORE. By HERBERT and FRANCIS THE systematic study of the direct nitration of m-bromophenol does not appear to have been undertaken although the following derivatives have been obtained by indirect means S-bromo-&nitrophenol (Laubenheimer Ber. 1876 9 1155) 3-bromo-6- and -4-nitrophenols (Auwers and Deines Zentr. 1924 11 No. 18) and 3-bromo-4:6-dinitrophenol (Korner J. 1876 1 2317) Tijmstra (Rec. trav. chim. 1902 21,292) has described S-bromo- 2 :4 :6-trinitrophenol. HODQSON AXD MOORE The present investigation on the direct nitration of m-bromo- phenol was carried out on similar lines to that of m-chlorophenol (J. 1925 127 1599). 2- 4-,and 6-Nitro-3-bromophenols 4 :6- 2 :6- and 2 :4-dinitro-3-bromophenols,and 2 :4 :6- and 2 :5 :6-trinitro-3-bromophenols have been prepared in excellent yield.Their properties are very similar to those of the corresponding chloro-compounds. 3-Bromo-2-nitrophenol forms a remarkably labile colourless hydrate m. p. 35" which changes on keeping particularly in dry air to a bright yellow anhydrous form of m. p. 65-67'; this reverts to the colourless hydrate in moist air. The sensitiveness of the compound is such as to make it an approximate indicator of atmospheric humidity. This behaviour of the substance led to a further examination of the previously reported colourless 3-chloro-2-nitrophenol (Zoc. cit. p. 1601) which was found to be likewise a hydrate but much more stable in air than that of the bromo-compound.Our analyst reported on a sample which he had thoroughly dried but made no comment on the change of colour. This we ascribed at that time to atmospheric ammonia.) The analytical datum therefore is for anhydrous 3-chloro-2-nitro- phenol. Since 3-bromo-5-nitrophenol has been described by Blanksma (Rec. trav. chim. 1892 21 254) and Heller and Kammann (Ber. 1909 42,2191) the anhydrous substance mentioned above must have the only remaining constitution vix. that of 3-bromo-2-nitrophenol. The order of increasing solubility in water of the three dinit'ro- compounds is 2 :6- 4 :6- and 2 :4-. They form characteristic silver salts that of 3-bromo-4 :6-dinitrophenol existing in three forms (two yellow and one red); Korner's observation (Eoc.cit.) is thus confirmed and supplemented. The orientations tentatively proposed for the dinitro-com-pounds follow from the modes of preparation and by analogy with the corresponding chloro-compounds (Zoc. cit.). In addition is the following evidence (1) All three dinitro-compounds are convertible into 3-bromo-2 :4 :6-trinitrophenol; the two nitro-groups ih each compound are therefore in the meta-position with respect to each other. (2) The constitution of 3-bromo-4:6-dinitrophenol is definitely settled by its preparation from 3-bromo-4- and -6-nitrophenols and from 1 :3-dibromo-4:6-dinitrobenzene. (3) 3-Bromo-2:6-and -2 :4-dinitrophenols not only differ in melting point and solubility and in the properties of their silver salts but the former can be prepared from both 3-bromo-2- and -6-nitrophenols whereas the 2 :4-dinitro-compound is obtainable THE NITRATION OF m-BROMOPHENOL.157 only from a sulphonated 3-bromo-2-nitrophenol. (4) The 2 6-and 2 :4-dinitro-compounds both yield 2 :4-dinitro-m-phenylene-diamine when heated in a sealed tube with ammonia and each specimen of this compound gives 2 :4-dinitroresorcinol when boiled with aqueous sodium hydroxide. The vicinal positions of the four atoms or groups in each of these two bromodinitrophenols are thus established. Also these two compounds are converted into 2 4-dinitroresorcinol by boiling alkalis. After prolonged sulphonation followed by treatment with excess of nitric acid m-bromophenol gives a trinitro-sulphonic acid ; this on hydrolysis yields 3-bromo-2 5 6-trinitrophenol which is volatile in steam.E XP E RIM E N T AL. Unless otherwise stated the methods of prepamtion of the 3-bromonitrophenols are those of the corresponding chloro- com- pounds (Zoc. cit.) with appropriate modifications. Mononitration of m-Bromophenol. (a) By Sodium Nitrate and Sulphuric Acid (loc. cit. p. 1600).- 3-Bromo-6-nitrophenoz (yield 8.9 g. from 29 g. of m-bromophenol) is volatile in steam and crystallises from light petroleum in yellow prisms m. p. 42" having a characteristic odour (Auwers and Deines m. p. 41-542.5") (Found Br,36.7 Calc. Br 36.7%). The methyl ether forms colourless plates m. p. 85-5",the benzoate crystallises in cream-coloured needles m.p. 104" and the sodium sa.lt in scarlet needles. [The corresponding derivatives of 3-chloro- 6-nitrophenol form colourless plates m. p. 72" colourless needles ILL. p. 91" and scarlet needles respectively.] 3-Bromo-4-nitrophenoZ (yield 18 g.) is non-volatile in steam and crystallises from light petroleum in yellowish-white odourless needles m. p. 131" (Found Br 36.6. Calc. Br 36.7%). It is also formed readily by oxidation of 4-nitroso-3-bromophenol (J. 1925 127,2262). The methyl ether crystallises in short colour- less needles m. p. 45" the benzoate in cream-coloured needles m. p. 102" and the sodium salt in amber needles. [S-Chloro-4-nitrophenol methyl ether short colourless needles m. p. 56-5"; benzoate colourless needles m.p. 96"; orange sodium salt.] (b) By Nitric Acid in Olezcm (loc. cit. p. 1600).-On dilution of the nitration mixture and hydrolysis in a current of steam the first distillates were oily but from the later ones almost colourless needles separated on cooling; m. p. 35" (yield 13 g. or 60%). The product at first separated from light petroleum in bright yellow HODQSON AND MOORE curly needles m. p. 65-67" but later crystals were admixed with the colourless product which when separated mechanically had m. p. 33". The yellow compound dissolves in aqueous sodium hydroxide to a red solution from which the colourless variety is precipitated on acidification in the cold. The yeZZow variety is anhydrous 3-brorno-2-nitrophenol (Found Br 36.6.C,H,03NBr requires Br 3607%). It has a characteristic odour distinct from that of 3-bromo-6-nitrophenol. The sodium salt crystallises in red needles the methyl ether from dilute alcohol in white needles m. p. 73" (Found Br 34.2. C,H603NBr requires Br 34.4%) and the benzoate from alcohol in white feathery needles m. p. 133" (Found Br 24.7. C,,H,O,NBr requires Br 24-85!40). The coZourZess variety could not be dried in sufficient quantity for analysis owing to its ready conversion into the anhydrous form and in consequence its degree of hydration has not been determined. 3-Chloro-2-nitrophenol.-The anhydrous yellow variety after pro- longed drying over concentrated sulphuric acid melts at 4547" (Found c1 20.6. C6H,03NC1 requires c1 20*5y0).The hydrated white variety crystallised from light petroleum had m. p. 37-5-38" (Found C1 18.5. C,H403NC1,H20 requires C1 18.5%). On desiccation over concentrated sulphuric acid 1.2108 g. lost 0.1128 g. after 20 hours and 0-1136 g. after 24 hours. The calculated loss for 1mol. H20 is 0.1138 g. (M,cryoscopic in phenol 99. C,H403NC1 requires -&f,173.5; and C6H,03NCl H,O requires M 96 if the water is completely abstracted by phenol). Dinit rat ion of m-BromophenoZ. The mixed acid referred to below contained 98% sulphuric acid (15 vols.) 70% nitric acid (12 vols.) and water (9 vols.). 3-Bromo-4 6-dinitrophenoZ.-(a) m-Bromophenol (4-4 g.) was added gradually to a mixture of 90.5% nitric acid (5 c.c.) and glacial acetic acid (5 c.c.) and after 12 hours the red solution was warmed for 30 minutes on the water-bath poured into water and steam-distilled.A little 3-bromo-6-nitrophenol passed over fol- lowed by the main product which solidified in colourless crystals m. p. 90" (yield 2 g.). Recrystallised from light petroleum this melted at 92" (Found N 10.7; Br 30.4. Calc. for C6H3O5N,Br N 10-6; Br 30.4y0). (b) 3-Bromo-6- and -4-nitrophenols (2 g.) were each added gradually to the mixed acid (8 c.c.) cooled in running water the mixture was kept 2 hours heated at 80" for 15 minutes diluted and steam-distilled. The product extracted from the distillate by ether crystallised from water or light petroleum in white needles THE NITRATION OF 1?2-BROMOPHENOL. m. p. 92" in both cases.The liquor in the steam flask deposited in each case on cooling 3-bromo-2 :4 :6-trinitrophenol. (c) 1:3-Dibromo-4 6-dinitrobenzene (3 g.) was boiled for 6 hours with aqueous sodium carbonate (3 g. in 20 C.C. of water) and the solution filtered hot and made just acid The precipitate was crystallised from water; m. p. 92". The identity of the products in (a),(b) and (c) was established by the melting points of their mixtures. The silver salt formed as a voluminous yellow gelatinous pre- cipitate when a neutral solution of the ammonium salt was treated with aqueous silver nitrate. It gradually changed to a red crystalline variety on keeping (the transition being accelerated by rubbing with a glass rod) which was but sparingly soluble in aqueous ammonia and in the presence of which conversion into a yellow crystalline form occurred (Found Ag 29-0.Calc. Ag 29.2%). 3-Bromo-2:6-dinitrophenol.-(a) This was obtained from it mixture of I g. of 3-bromo-2-nitrophenol and 4 C.C. of mixed acid (Zoc. cit. p. 1602). The steam-volatile product solidified as a feathery crystalline mass m. p. 124" and crystallised from light petroleum in colourless needles m. p. 131" (Found Br 30-6. C,H,05N,Br requires Br 30.4%). A non-volatile product was 3-bromo-2:4 :6-trinitrophenol. (b) 3-Bromo-6-nitrophenol (4 g.) was slowly added to 7 C.C. of oleum (27% SO,) with cooling. The deep red solution was kept for 3 hours at lo" then nitrated with 0.8 C.C.of nitric acid (90.5%) in 4 C.C. of oleum (27% SO,) and after 1 hour the mixture was poured into water.Much decomposition occurred on hydrolysis but a small quantity of 3-bromo-2 6-dinitrophenol was obtained m. p. 131" (Found Br 3@3y0). By the same procedure 3-chloro-2 :6-dinitrophenol was obtained from 3- chloro-6-nitrophenol. The red crystalline silver salt is fairly easily soluble in water and readily in ammonia (Found Ag 29.1%). 3-Bromo-2:4-dinitrophenol was prepared as was 3-chloro-2 :4-dini-trophenol (loc. cit. p. 1602). The steam distillate deposited 3-bromo- 2 :6-dinitrophenol (0.7 g.) which was identified by its red silver salt m. p. 131" and by analysis (Found Br 306%). The filtrate gave to ether 0.8 g. of a product probably 3-bromo-2 :4-dinitro-phenol which crystallised from water in fine silky cream-coloured needles m.p. 175" (Found Br 30.6. C,H,05N,Br requires Br 30.4%). The yellow crystalline silver salt was insoluble in ammonia (Found Ag 2976,). "HE NITRATION OF m-BROMOPHENOL. Attempts to prepare 3-bromo-2 :4-dinitrophenol from 3-bromo- 4-nitrophenol were unsuccessful owing to its decomposition during the sulphonation-nitration process described under (b) above. Separation of a Mixture of 3-Bromo-2:6- and -2 :4-dinitrophenols. -The mixture was converted by the method described under 3-bromo-4:6-dinitrophenol above into silver salts which were digested with cold aqueous ammonia. The red silver salt of 3-bromo-2:6-dinitrophenol dissolved completely the yellow isomer- ide was insoluble. The pure phenols liberated by hydrochloric acid had m.p. 131" and 175" respectively. Action of Ammonia on 3-Bromo-2 6- and -2 :4-dinitropheno1s.-These (1.3 g.) were separately heated in a sealed tube with con- centrated ammonia (5 c.c.) to 150" during 2 hours. On cooling the products were obtained quantitatively as brownish-yellow needles (0.9 g.) in each case m. p. 258". Recrystallised from water or glacial acetic acid they melted separately or mixed at 258". The substance was sparingly soluble in water alcohol ether or glacial acetic acid (Found N 28.1 and 28.5 respectively. Calc. for C,M,04N, N 28.3y0). Barr states (Ber. 1888 21 1545) that 2 :4-dinitro-m-phenylenediamine melts at 250" with partial decomposition. 4 6-Dinitro-m-phenylenediamine melts at about 300" (Nietzki and Schedler Ber.1897 30,1667). The 2 :4-dinitroresorcinol obtained from each of these products by the action of boiling aqueous sodium hydroxide melted alone or mixed with the other at 146" (Beilstein gives m. p. 142") (Found N 14.1 and 13-9 respectively. Calc. for c6H40,N2 N 14.0y0). Each product gave a red gelatinous silver salt. Mixtures of 3-bromo-2 :6-and -2 :4-dinitrophenols gave 2 :4-dinitro-m-phenylenediaminewhen heated with ammonia as above and 2 :4-dinitroresorcinol on subsequent boiling with aqueous sodium hydroxide. Barr's statement (Zoc. cit.) that conversion into 2 :4-dinitroresorcinol does not occur is therefore disproved. Finally 3-bromo-2 :6- and -2 :4-dinitrophenols when separately boiled with aqueous sodium hydroxide gave the same 2 :4-dinitro-resorcinol of m.p. 146" and mixed m. p. 146". Trinitration of m-Bromophenol. 3-Bromo-2:4 :6-trinitrophenol prepared as was the corre-sponding chloro-compound (loc. cit. p. 1603) is non-volatile in steam and crystallises from water in characteristic clusters of colourless leaf-like forms m. p. 149" (Tijmstra Zoc. cit. gives 144" for the m. p. of the compound crystallised from acetic acid) (Found Br 25.8. Calc. Br 26.0~0). The same compound was also obtained by nitrating 3-bromo- 3-BROMO-AND ~-NITRO-~-DIXETHYKJA.MINOBENZBLDEHYDE, ETC. 161 4 :6- -2 :6- and -2 :4-dinitrophenols 0.5 g. of each was dis-solved by gentle warming in 98% sulphuric acid (3 c.~.),and the cooled solution treated with 70% nitric acid (1 c.c.) in 98% sulphuric acid (2 c.c.).After 3 hours the solution was warmed on the water- bath for a few minutes and poured into water. On passage of steam no volatile product was detected and the solution on cooling deposited crystals of m. p. 149". The yellow silver salt was insoluble in ammonia. 3-Bromo-2 :5 :6-trinitrophenol was prepared as was the chloro- compound (Zoc. cit. p. 1603). It is volatile in steam and crystallises from water in fern-like clusters m. p. 146" (Found Br 26.0. C6H20,N3Br requires Br 26.0%). The yellow silver salt is soluble in water but insoluble in ammonia. Potassium 3-bromo-2 :5 :6-trinitrophenol-4-sulphonate,isolated during the above preparation gave characteristic yellow crystals from alcohol which exploded when heated [Found S 6-7; Br 17.4. calc. for C6Br(OK)(N02),*S03K 8 6.8; Br 17.2%]. The authors desire to thank the British Dyestuffs Corporation for gifts of chemicals used in this investigation. TECHNICAL COLLEGE,HUDDERSFTELD,[Received August 17th 1925.J