1696 POPE: A COJlPOUNI) OF CAMPHORIC AClD CXVTII.--A Compoum? of C'urnpho~k acid with, Acctozze. By WLLLLAV JACKSON P O P E . L)ESTROCAMPHORIC acid is moderately soluble in acetone, and the solu- tion on spontaneous evaporation deposits crjstds of the composition CIoH ,,O,,+COMeo ; the crystals are large, transparent, colourless tablets (Fig. 1): belonging to the orthorhombic system. F r G . 1.WITH ACETOSE. 1697 C rz s (,a 1 1 i n e system : 0 rt horhom bi c . (I : b : c = 0.8386 : 1 : 1.2386, Forms present : n = (1CO). z, = (010). p = (110). p'= (120). p = (011). The following angular measurements were obtained : Number of Angle. measurements. up = 100 : 110 24 "]I = 100 : 120 hp = 010: 110 18 611' = 010 : 120 yp = 110: 110 9 pp' = 110 : 120 64 = 010: 011 29 q y = 011 : o i l 5 21'1 = 110: 011 11 2 1 ~ = 110: o i l G 5 G 3 Liiiiit*P.40" 31' -49' 50' 59 37 -59 54 49 11 -49 27 30 1 -30 19 81 4 -81 31 18 59 -19 12 35 51 -39 5 101 58-102 24 55 17- 55 49 120 13-120 45 D h n . 40" 39' 59 49 49 19 30 11 81 17 19 5 38 55 10s 12 53 25 120 29 CsLlculn ted - 59" 47' 49 21 30 13 81 18 19 8 102 10 55 33 120 27 - - The crjstals niay readily be obtained of a centimetre in length, and usual!y grow quite separately in the solution. The dominant form is n(1@0), and this and the other pinaco'id, b(OlO), give good reflectioiis on the gonioimeter ; the dome form, q ( O l l ) , is frequently very layge, and only gives moderately sharp reflections. The prism p { 110) is very TTariable in size, and does not give good mcasuremeiits, whilst the prism p ' ( l 2 0 ) is not often observed ; the faces i u this zone are striated para1121 t o the zone axis.There is a perfect' cleai-age parallcl to c~(100), and a less perfect one parallel to b(010); the cleavage plates are usually striated parallel to the axis c. The axis b is the acute bisectrix, and the optic axial plane is n(IO0) ; the optic axial angle is large, the double refi-,zc!ion indium in strength and positive in sign, a d the optic: axial dispersion is slight. Although this substance is optically active i n solut>ion, no indica- tion of lieniihedrisni could be ohtained; the forms present would not be affected, so far as the number of faces is concerned, by eiiantio- morphous hemihechism, and attempts to obtain characteristic etch- fignres were unsuccessful. During cold weather, the crystals are perriisnent in the air, but after n few minutes' exposure in warm weather they become opal- escent, and when left exposed over night turn quite white and op:que, owing to loss of acetone of crystallisation; the crystals, however, retain their shape, and to a great extent their lustre, during1698 POPE: A COMPOUND OF CABlPLIORIC ,4ClD this change, and remain quite hard and brittle.Some of the porcc- lain-like crystals thus obtained were measured, and the results agreed with those tabulated above. It is ve1.y noteworthy that the crystals from which all the acetone has escaped retain the two cleavages. Attempbs were made to again render the opaque crystals transparent by soaking them in various liquids, with a view of obtaining results similar to those obtained by Mallard from his well-kuown experi- ments on zeolites, but with no success; if the opaque crystals be soaked i n acet.one, they slowly fall to a fine, white, opaque powder, without again becoming transparent!, and other liquids do not seem to be absorbed by the crystals.Although the transparent crystals lose acetone continuously on ex- posure to the air, the whole of the acetone of crystallisation isnot lost by the massive crystals even after several days’ exposure at ordinary temperatures ; 011 di=opping the crystals on to a metal plate heated by boiling aniline, the solvent of crystallieation is driven off so rapidly that the crystals disintegrate and the escaping acetone may be inflamed, but the massive crystals still decrease in weight after 10 hours’ heating at 100’.The weight becomes constant after four hours’ exposure at 1 5 0 O . The following analytical numbers 1iave been thus obtained : 2.6189 grams lost 03297 gram at 150’ = 12.59 per ceut. 2,4271 7, ,, 0.3061 ,, ,, = 12.61 ,, Theoretical loss f o r C,,,E,,O,,~COMe, = 12.66 ), On either slow or rapid heating, samples of camphoric acid crystal- lised either from water or from acetone, melt at the mme tempera- ture if placed in the same bath. I n view of the fact that the acetone is comparatively firmly retained by the camphoric acid, it is of interest to note that the specific rota- tion of the acid dissolved in acetone is not appreciably different from that observed in other solvents (Aschan, Acta Xoc.h’cieytt. f e w . , 21, [51,1). comparison of the crystallographic properties of this substance with those of the ordinary monosymmetric crystals of camphoric acid reveals the existence of very little i f any true morphotropic relation- ship between them ; on comparing the crystalline form of the acetone compound witch that of camphoric anhydride, however, a remarkably close morphotropic relationship is found to exist. Camphoric anhydride has been crystallographically examined by v. Zepharovich (Sitzungsbey. Wz’en. Akad., 1876, 73, i, 7), who determined its geome- trical aud optical constants, and from his data it was obvious that the new substance now described is rnorphotropically related to cam- phoric anhydride. There beiug, however, a few points in whichWITH ACETONE.1699 comparison mas impossible, owing, it seemed, to inconiplete descyip- tic;n, i t was thought advisable to re-examine the anhydride. This was done, with the result that the crystallographic similarity of the two substances was found t o be even closer than was at first supposed. Camphoric anhydride dissolves freely in acetone, and cry stallises from it in large prisms which do not contain acetone of crystal- Iisation ; it crystallises from ethylic acetate 01- ether in very lustrous transparent prisms 01- plates, each of these habits being closely similap in appearance t o the corresponding habits of the camphoric acid compound with acetone. The moat suitable crystals for goiiionietric examination are obtained by the spontaneous evaporation of an alcoholic solutioii containing acetone, the substance being sparingly soluble in cold alcohol; the crystals thus deposited are small, flat,teriecl plates showing much internal striation, and which, prob- ably owing to this, are very friable.The crystals show the forms named by Zepharovich and also the dome ~ ( 1 2 0 ) ; the latter if; rarely present, and, although its faces give good reflections. is always very small. Crystalline sys tern : Orthorhombic. a : B : c = 0.9990 : 1 : 1.7251 (Pope). n : 2, : c = 0.9973 : 1 : 1.7170 (Zepharovich). Forms observed : 4 100 1 c ~ o 0 1 1 q~01Ll P W W 1'( LO1 1 T'( 102 1 In the following table of angles the values obtained by Zepl~aro- vicli are given for the sake of comparison, the numbers which he took as the basis of calculation being indicated by asterisks.Angle. 01 a,?. = 100 : 101 ni" = 100 : 102 9.1.' = 101 : 102 cis = 001 : 101 Pi'' = 001 : 102 cq = 031: 011 2g = 011 :oii 4p = 011 : o i l pq = 120: 011 pr = 120: 101 fp' = 011 : 101 ap = 100 : 120 No. of wervations. 41 29" 8 49 10 18 34 59 8 40 47 59 6 59 8 119 1 2 63 4 39 7 66 6 15 Calculated. 7 r------ Limits. Mean. Pope. Zeph. 49'- 30"25' 30" 49' -- 30" 9' 50- 449 31 49 13 49" 11i' 49 17 54- 19 18 19 d . L 19 7 19 8 17- 60 38 59 54 - 59 47* 9 - 63 46 63 26 G3 24g - 7- 39 31 39 24 39 19 - 58- 67 27 67 14 67 13 - 14- 75 50 '75 29 75 26h - 29- 60 24 59 54 50 559 59 51" S1- 40 59 40 47 40 43: 40 4 3 54- 60 30 60 15 60 12 60 26 16-120 0 119 44 119 $53 119 34 There is a fairly good cleavage parallel to c(OOl), and a. less perfect one parallel to ~(100); these two cleavages were apparently not1700 POPE: h COJlPOUND OF CAMPHORIC ;lCIi) 010 : 012 001 : 011 noticed by Zepharovich.The optic axial plans is c,( 1 WO), and t h e c-axis is the acute bisectrix; t’he double refraction is weak and uegative in sign. The optic axial angle is small-about 30’ in air- and the axial dispersion slight ; the interference picture is visible through a cleavage plate cut parallel to c(OO1). Although the substance is optically active in solution no indication of ppo-electricity could be obtained. Many Rttempts t o develoFe etch- figures iiidicative of hemihedrsl structure were made, a number of solvents being used as corrosive agents, but these were uniformly unsucccssful. It must be admitted, however, that tlie failure to obtain evidence of hemihedral strncture cannot be regarded as n particularly strong argument in favour o F the holohedral nature of the crystals ; very probably asymmetric etch-figures might be ob- tained by a happy choice of condit,ions (compare.Walden, Bey., 1897, 29, 1692 ; Traube, Ber., 1896, 29, 2446). 40 48k 30 4f On transforming t.he axial ratios a : b : c = 0.9989 : 1 : 1.7251 of camphoric anhydride in such a way that the old maxis becomes the new b-axis and rice ziei-scZ, it is found that the new CG : b : c = 1 : 0.9989 : 1.7251 = l*QOll : 1 : 1.7270, whilst the new indices of the forms become a(010), c(OOl), q { l O l > , r(011), ~’{012], a i d ~ ( 1 1 0 ) . Similarly, the axial ratios assigned to the new compound of cainphoric acid and acetone may be so transformed that the new ratio a : b : c assumes the value of the old ratio c : b : 2n aucl is thus a : Z, : c = 1.2386 : 1 : 1.7172; the indices of the forms present siniul- taneonsly change to b(010), a(001), p(O12), ~ ’ { O l l ] , and q(110).The very close similarity between the two crystal forms is now apparent. The cr~stitls having the composition C10H1604,~COMe2 exhibit the forms ( O l O ) , ( O O l ) , ( O l l ) , (0121, and {110), whilst tlhose of camphoric anhydride show the same forms and also { 101 ). The similarity is not confined t o this, for in the zone [loo] which contains the four common forms (OlO), (OOl), (Oll), and (012), it is observed that, each angle measured on the one substance is nearly identical in mngnitude with the corresponding angle on thc other compound.The following table shows this clearly. 1 On C,oTI,40,. j Pope. 1 Zeplmrovicli. 011 C,olfl,O.$,i MC:CO. Angle. I ---I-_- FBO 51/ 4.0 43 30 9 49 1’1 19 8 69” 47’ 40 39 30 13 If) 21 19 sWITH ACE'TOKE. 1 T O 1 The same morphotropic relationship is also clearly expressed by the practical equality of the ratio c : 2, in the new form into which the axial ratios have been cast ; thus On C,,H,,O,.. .. . . .. ,, CI,,HIG04,hC@Mell a : b I c = la0O11 : 1 : 1.7270. a : b : c: = 1.2386 : 1 : 1.i172. There is, fnrther, a very close correspondence between the cleavages on the two sets of crystals, The crystals of caniplioric aiihydride show a fairly good cleavage on ~(001) and a poorer one on a( 1001, whilst the crystals of camphoric acid with acetone exhibit a fairly good cleavage on a(100) and a less perfect one on b(O1O) ; on transforming the indices of these forms in accordance with the method described above for the two substances respectively, it is found that them is in each case a good cleavage on (001) and a corn- payatively poor one on { O l O ) .The correspondence between the cleavages is hence very complete. Again, in crystals of camphoric anhydyide, the optic axial plane is (010) and the acgte bisectrix is the c-axis, whilst on the compound of the composition C,oH1601,$CONe2, tlie optic axial plane is (100) and the Laxis is the acute bisectrix ; on transforming these indices and axes as before, it becomes evident that in each case the optic axial plane is (OOl), and the 6-axis is the acute bisectrix.Here, again, the correspondence is singularly complete. The sign of double refraction is the same in both substances, but the optic axial angle is niuch smaller in the crystals of camphoric anhydride than in those of the acid. Lastly, there is complete coi-respondence between the striations observed on the two sets of cryc;tals; all the forins in the comn1011 zone [loo] are striated parallel to the zone axis. It should be noted that the second set of indices and axial ratios given above for each of the two carnphoric derivatives .are quite possible, and might. have been chosen for describing the crystals in the first place, were it not aavisable to respect the usual conventions in crystallographic description, naniely, that the dominant dome forms should make unit intercepts upon two axes, and that the c-axis should be tlie longest, whilst the a-axis should be the shortest axis.A little consideration of the intimate nature of the crystallographic resemblances existing between these two compounds is sufficient to remove any suspicion that the similarity miglit be only fortuitous, and we are forced to the conclusion that what is probably one of the most striking morphotropic relationships yet recorded exists between two substances which although diff eying widely in composition arc constitutionally very closely related. The fact tllat obvious morphotropic relationships exist betvreen1702 A COMPOUND OF CAJIPHORIC ACID WITH ACETONE. camphoric anhydride and tlic coinpound of camphoric acid with acetone, whilst both are ciaystnllogrraphically very different from camphoric acid, a substance of intermediate composition, may very possibly be clue to dimorphism in camphoric acid, the missing form being an orthorhombic one morphotropically related to cainphoric anhydride and the new compound; attempts t o find evidence of pol~rnorphisni in camphoric acid aiid its anhydride mere maae by sel7eral methods, but all proved unsuccessful. The importance of searching for morphotropic relations such as that now demonstrated amongst camphor derivatives-of which the coiistitutions and constitutional inter-relations are st ill so problema- tical-can scarcely be exaggerated. Chemical Department, C'e?ztraE Technical C'ollep, City and Guilds of London Institrite.