1462 ARMSTRONG AND LOWRY: SULPHONATION OF CXLIIL-Studies o f the Tapenes and Allied Compounds. The Xulphonation of Camphor. 11. B-Brorno- camphor and its heifiivatives. $-B~*omocumphoric Acid. By HENRY E. ARMSTRONG and T. MARTIN LOWRY. IN seeking to determine the constitution of the Reychler camphor- sulphonic acid and of the other acids described in the previous communication, we naturally availed ourselves of the method used with such brilliant success in our laboratory by Kipping and Pope, which led them to discover the r-series of derivatives of camphor. It was t o be expected that if the Reychler acid were an a-derivative, its sulpho- chloride and sulphobromide would be decomposed by heat and give rise to ordinary a-chloro- and a-bromo-camphor respectively. The earlier experiments made from this point of view were unsatisfactory, and later experiments have shown that the decomposition takes place in a normal manner only under certain conditions.No difficulty was experienced in preparing a dibromocamphor fromCAMPHOR. 11. &BROMOCAMPHOR AND ITS DERIVATIVES. 1463 the bromide of the a-bromocamphorsulphonic acid prepared by Reychler's method (p. 1451) ; the compound so produced, however, was not the ordinary a-derivative but the /3-compound which was first prepared by Swarts and subsequently investigated by Knchler and Spitzer. Kachler and Spitzer had found that the ,@compound gave rise t o a dibromonitrocamphor when nitrated, so that there could be little doubt that only one of its bromine atoms was present in the a-position ; but as Swarts had shown that a-dibromocamphor was converted into the isomeride by merely heating it with hydrogen bromide, it was not improbable that the somewhat drastic treatment to which the sulpho- bromide was subjected had led to the transfer of a bromine atom, and the production of /3-dibromocamphor i n such a manner could not be regarded as final proof that the sulphonic group was not in the a-position, As the constitution of ,3-dibromocamphor had not been determined, we undertook the further investigation of this compound, and succeeded in obtaining from it a P-bromocamphoric acid isomeric with the w-acid investigated by Wreden, in which bromine displaces the tertiary hydro- gen atom in camphor, and also with the isomeric r-acid discovered by Kipping, in which bromine displaces hydrogen in one of the median &ethyl groups.The discovery led us t o persevere in the attempt to prepare P-bromocamphor from the Reychler acid, and i t was soon found that a '6 normal "mdecomposition of the sulphobromide could be effected by heating it rapidly, in quantities of 10 grams at a time, in test-tubes over the bare flame, but that if heated slowly it gave rise only t o '' condensation " compounds. Thus 30 grams of sulphobromide decomposed with great care by simply heating it under reduced pressure at 130°, gave no trace of bromocamphor. The amount formed, however, was small under all conditions. The bromocamphor obtained from the sulphobromide melted at about the same temperature as the ordinary compound, but a mixed melting point at once revealed a difference, a mixture of the two substances melting below 70" instead of at 76O; as it gave P-bromocamphoric acid on oxidation, there was no doubt that the new product was the hitherto unknown P-bromo- camphor.d great improvement in the method of preparing this P-compound was ul tiwately effected by carrying out the decomposition of the sulphobromide in a solvent. The discovery of P-bromocamphor must be credited, however, not only t o us, but also to Dr. Forster, who obta-ined it by the direct action of bromine on the compound which he originally described as hydroxy- camphene (compare Proc., 1901, 17, 245). Although his method is a more tedious one than ours, and gives a smaller yield, i t has the advantage of being applicable to the preparation of P-chlorocamphor,1464 ARMSTRONG AND LOWRY : SULPHONATION OF which we have r o t yet succeeded in preparing from camphorsulpho- chloride.P-Bromocamphor(n. sp.).-In preparing this substance, the formation of condensation products can be very largely avoided by carrying out the decomposition of camphor sulphobromide in a solvent of high boiling point, especially if a large quantity of solvent be used, Commercial xylene has proved to be an eminently suitable liquid, as its boiling point ( 1 3 7 O ) is just above the temperature (130') a t which the decomposition takes place, and it may readily be separated by means of steam. The following method allows of the preparation of P-bromo- camphor in quantities of 50 grams a t a time and with relatively little trouble; the operation lasts two days, but i t is not difficult to obtain about 50 grams of product each day.Four quantities of 40 grams of dry potassium camphorsulphonate are each ground in a mortar with 63 grams of phosphorus pentabromide; the liquid is left until it becomes a firm solid. Finely divided ice is then carefully added, together with a little sulphite t o remove bromine .; the white, powdery sulphobromide is ultimately drained on the filter-pump and then dissolved in xylene. The xylene, of which about 500 grams are required for 160 grams of potassium salt, is separated from water and the solution is left overnight in contact with calcium chloride. TO effect the decomposition, the dry solution is boiled in a Jena flask over a small flame during about 20 minutes, and the hydrocarbon is then distilled off by passing a current of steam into the liquid. The xylene distils off very rapidly and is carried over with about its own weight of water; when most of the xylene has been removed, the rate of distillation is somewhat checked in order that the solid bromocamphor may be held back in the condenser, whilst a certain amount of xylene is still carried forward by the water.When the whole of the xylene has been removed, the receiver is changed and the distillation carried out rapidly; 1 gram of bromocamphor is carried over by about 50 grams of water, The yield of P-bromocamphor is usually about one- third of the weight of potassium salt used or about 40 per cent. of the theoretical quantity ; under the conditions described, the weight of non-voIatile condensation product is only about 20 per cent.of the weight of P-bromocamphor produced. Loss of material occurs almost entirely in preparing and handling the very unstable sulphobromide ; probably the weight of sulphobromide in the dried xylene solution is only 50 per cent. of the theoretical quantity, and of thia 80 per cent. is converted into /3-bromocamphor and 20 per cent. into condensation products. A smaller yield is obtained on the first occasion, as some 10 or 20 grams of bromocamphor are carried over with the xylene, but the full yield is obtained in subsequent experiments if the xylene beCAMPHOR. 11. &BROMOCBMPHOR AND ITS DERIVATIVES, 1465 used repeatedly. The properties of F-brornocamphor are in some respects very like those of the a-compound. Its melting point is only two degrees higher than that of the isomeride, but it has a much lower rotatory power.per 100 c.c.). We are indebted to Dr. Perkin, sen., for determination8 of the magnetic rotatory power and refractive power. Magnetic .rotatory power.-The substance was dissolved in ethylene chloride ; the solution contained 43.75 per cent. of the bromocamphor and its composition may be represented by the formula CloH1,OBr + 3C,H,C12. Bromine converts it into up-dibromocamphor. Constants.-M. p. 78". [a]y + 19.2' (Solv. - acetone ; c - 3.33 grams Relative density of solution : d 15"/15', 1,3082 ; d 25'/25*, 1,2984. The relative density of a similar solution of a-bromocamphor was d 15'/15O, 1.2993, or 0.0089 less (this vol., 310).Magnetic rotation (twice determined) : t Sp. rot. Mol. rot. 15.3" 1.2887 28-903 Less 3 mol. C2H,C1, 16.455 3101. rot. C,,,H,,OBr 12.448 This value is lower than that of a-bromocamphor, which is 18.761, the difference amounting to -0.313. A similar kind of difference was found to exist between ua- and ap-dibromocamphor, although in this case the difference only amounted to about 0.100 (this vol., 31 1). Ref~*active power.-This was determined with the aid of the solution in ethylene chloride, __ P I p d k?-Bromocamphor. a-Bromocarnphor. Diff. Ha ............... 87.756 88.083 0.327 H, ............... 89.480 89.872 0.39 1 H, ............... 90.517 90.919 0.398 I n both cases, the P-compound gives the inferior values; the superiority of the a-compound may be ascribed t o the cooperative influence exercised by the bromine atom and the ketonic group in contiguity./3-Bromocamphor separates from light petroleum in well-formed crystals, of which the following measurements were made : VOL. LXXXI. 5 F1446 ARMSTRONG AND LOWRY: SULPHONATION OF &,&em.-Orthorhombic. Axial ratios.-a : Z, : c = 1.062 : 1 : 0.822. -8"ormspresent.--cc{lOO), b{010), p{110), r(101). The form ~ ( 1 0 1 ) is always small and frequently absent. Ha6it.-Stout prisms, elongated along the axis of b, and often flattened into plates in which a(100) is the dominant form. Angles observed. a : r (100) :(101) : p (100) : (119) p : r (110) : (101) T : T (101) : ( i o i ) a : 6 (100) : (010) p : b (110) : (010) b : T (010) : (101) p : (110) : ( i o i ) .Limits. Number of observations. 18 10 14 11 11 4 2 2 56°37f- 52" 1' 76 13- 76 32 80 50- 90 15 46 34 - 46 55 43 6- 43 26 64 50 - 64 57 114 58-115 0 a9 5 6 - 90 7 Mean. 51"49' 76 23 90 0 46 43 43 16 90 0 64 53 114 59 Calculated. - 76'22' 90 0 46 44 90 0 64 42 115 18 - Optical properties.-A n optic axis emerges almost perpendicularly t o the faces of the form r(101) ; the optic axial plane is therefore parallel to the form b{OlO), the acute bisectrix is parallel to the c axis, and the optic axial angle is about 76'. The double refraction is positive in sign. The crystalline symmetry of P-bromocamphor is intermediate be- tween that of its isomerides ; thus 7r-bromocamphor crystallises in forms belonging to the tetragonal system, P-bromocamphor is ortho- rhombic, and a-bromocamphor is monosymmetric.afl-Bibi*omo-a'-nitrocarnphor,-As Kachlor and Spitzer have shown, this compound is the chief product obtained on heating ap-dibromo- camphor with nitric acid. The substance we prepared in this mannerCAMPHOR. 11. P-BROMOCAMPHOR AND ITS DERIVATIVES. 1467 crystallised from acetic acid in brilliant, transparent needles or prisms, but it was necessary to recrystallise it eight times from acetic acid t o free it from admixed tribromocamphor, and t o raise the melting point to that given by Kachler and Spitzer (139O). A very considerable amount of dibromonitrocamphor-apparently unmixed with tribromocamphor-is obtained on oxidising P-bromo- camphor with nitric acid. I n this case, the liberation of the necessary bromine must be due to the oxidation of the bromocamphor beyond the bromocamphoric acid stage.Constants.-[ u]F - 25.7' (Solv. -acetone; c - 4.74 grams per 100 c.c.). aa'P-(rribromoc~cm~l~or.-This substance was separated from the im- pure once-crystallised dibromonitrocamphor above referred to by reduc- ing the nitro-compound with absolute alcohol and the calculated amount of caustic potash. It remained as an insoluble residue, which was easily purified by recry stallisation from dilute spirit, from which it separated in long, white needles. The compound prepared by Swarts, by heating ap-dibrornocamphor with phosphorus pentabrornide, was doubtless this substance. To judge from the evidence afforded by a mixed melting point, it is isomorphous with the dibromochlorocam- phors obtained on brominating a-chlorocamphor (Lowry, Trans., 1898, '73, 731). Constants.-M.p. 66". [a]: + 2" (Solv. - acetone ; c - 2.42 grams per 100 c.c.). P-Bromocamphoric Acid, CsHI,Br(C0,H)2 (n. sp.).--'l'his acid is ob- tained on oxidising either P-bromo- or up-dibromo-camphor with nitric acid (d. 1-4). On evaporating the acid, i t separates as a crystalline powder, indistinguishable in appearance from camphoric acid, P-Bromocamphoric acid dissolves much more readily in nitric acid than in water, in which it is only slightly soluble ; i t does not crystal- lise well from organic solvents. The acid may be freed from neutral impurities, either by washing the crude substance with chloroform, or by dissolving it in dilute ammonia and precipitating with nitric acid.When heated, it softens a t about 205' and melts at 208-210°, liberating gas. I n its physical properties, the acid and its anhydride present a remarkably close resemblance t o T- bromocamphoric acid, but the two acids differ considerably in chemical properties. A solution of the ammonium salt is not precipitated by calcium chloride. A number of attempts were made to convert the acid into a camphanic or hydroxy- camphoric acid by heating its alkaline solution, but in no case was a product free from halogen obtained; the bromine atom appears to be f a r less readily displaced than is that in T-bromocamphoric acid.1468 ARMSTRONG AND LOWRY : SULPRONATION OF Constants.-[a]:" + 39.3' (Solv. - alcohol ; c - 5 grams per 100 c.c.) P-Bromocamphoric AniLydride (n.sp.).-This may be prepared by boiling a solut,ion of the acid in acetic anhydride during two or three minutes ; it crystalliscs magnificently from hot dilute acetone in long, glistening, flat needles. The anhydride has no acid action, and does not dissolve in a solution of sodium carbonate even when this is boiled for a few seconds. Constants.-M. p. 142'. [ a]g - 2.8' (Solv. - acetone ; c - 5 grams per 100 c.c.). rr-Bromocamphoric anhydride La]F - 37.4' (Solv. -acetone ; c - 43 grams per 100 c.c.). Monoinethyl Bvomocamphorate.-HHydrogen chloride was passed into a solution of the acid in methyl alcohol, and the liquid was then allowed to evaporate ; a stiff and sticky mass remained which was redissolved in methyl alcohol. The salt separated slowly in a crystalline form as the liquid evaporated. It was recrystallised twice from dilute methyl alcohol, and was then obtained in glistening, white flakes. Constants.-M. p. 140'. [a]: + 53.6' (So1v.-acetone ; c - 4.79 grams per 100 c.c.). isoCamphoronic Acid.-This acid was obtained on boiling P-bromo- camphor with nitric acid and silver nitrate until silver bromide was no longer produced ; as we have not been able to prepare it by oxidising P-bromocamphoric acid in a similar way, i t is probable that the latter acid is not the intermediate product of oxidation when silver nitrate is used. Our product formed beautiful, trans- parent prisms melting a t 166". The identity of the acid from bromo- camphor with isocamphoronic acid was directly proved by a com- parison of the angular measurements with the values given by Zepharovich (Tien, Akad. Ber., 1876, 73, i, 19) : Zepharovich. A. and L. o i f : 100 75'25' 75'25' 011 : 100 '74'57' 74'56' o i l : 100 67'6' 67O11