74 MARSH AND UARDNER: V III .- Researches on the Terpenes. V I . Products of the Oxidation of Camphene; Carnphoic acid and its Deriva t z'ves. By J. E. MARSH and J. A. GARDNER. IN the Transactions for 1891, p. 64, we describe the method em- ployed for the oxidation of camphene by nitric acid, by which we obtained camphoic acid, anew acid of the formula CIOH1406. I n this paper we give an account of some further experiments made with camphoic acid, and describe the isolation of other acids formed along with it by the oxidation of camphene; we also make some general observations as to the chemical nature of camphene, and its relationship to the terpenes, to camphor, and to camphoic acid. Camphoic acid. This acid was obtained in the way already described by heating camphene with nitric acid of sp.gr. 1.3 on the water bath ; the crude acid is best purified by crystallisation from hot nitric acid of sp. gr. 1-42, in which it is readily soluble, crystallising out almorjt completely on cooling. The melting point was wrongly given at 184!-185" in the former paper; we find, however, that the acid melts at a temperature approaching 200", whether crystallised from ether, from nitric acid, or from water, but the melting point is not quite exact as the substance begins to decompose before it melts ; thus a specimen of the acid crystallised from ether melted at 197-198", whilst another specimen twice crystallised from nitric acid melted at 19P, and after two further crystallisations from water it stiIl melted af 1 9 6 O , in each case decomposing at the same time.The specimen of highest melting point was that, obtained from anhydrocaraphoic acid, a compound described in this paper; prepared in this way, it melts and decomposes at 199--200°. A specimen of the acid obtained from anhydrocamphoic acid gave on analysis Found. Calculated for C1,,Hl4O6. 51.97 Carbon.. . . . . . . 52.1 per cent. Hydrogen . . . . . 6.19 6.0 9,PRODUCTS OF THE OXIDATION OF CAMPHENE. 75 Camphoic acid was also obtained by the oxidation of chloro- camphencphosphonic acid, CloHlaC1*P03H2, by means of nitric acid. This acid is produced by the action of phosphorus pentachloride on carnphene and subsequent treatment of the product with water ; i t was treated with nitric acid in the same way as described for camphene. The carnphoic acid obtained from it was crystallised from ether and analysed.It gave Found. Calcidsted for CloH,,OG. Carbon .......... 52.23 52.1'7 per cent. Hydrogen. ...... 6-39 6.08 ,, This acid also split up on distillation into carbon dioxide, and cam- p hopyri c anhydride. Camphoic acid has a sharp, acid taste, and is very soluble in water, alcohol, and ether, but less so in benzene or petroleum. I t is a tribasic acid, and forms salts with one, two, or three molecular pro- portions of base. A crystalline barium salt of the formula BaCIoH,,O6 was described i n the former paper; it had an acid reaction. Most of the salts of camphoic acid are soluble in water, but the copper and lead salts are almost insoluble. The sodium salt was not prepared, but on mixing weighed quantities of camphoic acid with two and three equivalents of caustic soda me found that the disodic camphoate is acid while the trisodic camphoate is alkaline.The triammonium camphoate is prepared by dissolving dry cam- phoic acid in dry ether and passing in dry gaseous ammonia. The precipitated salt must be collected rapidly and placed in a dry atmosphere over sulphuric acid, as it is deliquescent and turns yellow on exposure to moist air. It is obtained i n this way as a white, friable mass, melting at 198-199O and at the same time decomposing. A determination of nitrogen gave Calculated for Cslculated for Found. CIOH*106\NH4)3' 40H1206(NH4)2* N ....... 13.51 14.94 10.6 per cent. This salt is very soluble in water, and on evaporating the solution, ammonia is evolved and the monoammonium salt formed; this separates in white, glistening crystals, which melt a t 208-210°, and at the same time decompose.A determination of nitrogen gave the following result. Calculated for Found. C10HI130ti.NH4. N ........ 5-86 5-67 per cent. The copper salt is obtained by boiling a solution of sodium camphoate with copper sulphate, when it separates as a pinkish preci- pitate, whioh redissolves on cooling the solution. The triplumbic a 276 3IARSH ASD GARDNER : camphoate is obtained as a white precipitate on adding lead acetate or lead chloride to a solution of sodium camphoate. The precipitate when dried at 100' gave on analysis Calculated for Fo un (1. Pb,(C,OH,,O6)2. Lead.. .... 56.5 57.7 per cent. A specimen dried at t203 gave lead 58.3.&hy dr ocanapho ic acid, C loH,20,. This acid is obtained by the action of acetyl chloride on camphoic acid. When camphoic acid is heated with ncetyl chloride, i t slowly (lissolves with evolution of hydrogen chloride ; the solution is then evaporated to dryness, and the residue crptallised from ether. It crystallises in large, trimsparent plates from ether or ethylic acetate, melting and decomposing at 205". Its formula, CI0Hl2O5~ is that o E camphoic acid less 1H20. On analysis it gave Xound. Calculated for CloH120,. Carbon.. ........ 56-51 56.6 per cent. Hydrogen ....... 5-93 5.6 ,, Anhydrocamphoic acid has a sweet taste very different from the sharp acid taste of camphoic acid. It is ouiy slightly soluble in benzane, chloroform, petroleam, or cold water ; i t is readily soluble in hot water, and on cooling crystallises out in part unchanged ; part, however, is hydrolysed.It crystallises best from dry ether or from ethylic acetate, and is precipitated from its solution in ether 011 the addition of light petroleum. It dissolves in sodium carbonate, and is precipitated unchanged by the addition of hydrochloric acid. When anhydrocamphoic acid is boiled with water preferably con- taining a little acid, it is gradually hydrolysed with production of camphoic acid. The camphoic acid obtained in this way melts a$ 199--200' with decomposition. Theanalpis of it is given on page 74. It was stated in the former paper that when camphoic acid is dis- tilled it undergoes decomposition yielding carbon dioxide, water, cam- phopyric anhydride, and isocamphopyric acid. CIOHNO~ = CgH120, -k H20 -k Go,, CioHi,06 = CgH1401 + (302.When anhydrocamphoic acid is heated above its melting point, it decomposes intb camphopyric anhydride and carbon dioxide. C10H1205 = CgHi203 + Co2. The reaction appears to be quantitative, bat it is difficult t o obtain an exact result owing to the sublimation of thc camphopyric an-PRODUCTS OF THE OXlDATION OF CAMPHENE. 77 hydride. A weighed quantity of anhgdrocampboic acid was heated in a tube connected with a drying tube and potash bulbs ; the tube was heated in a sulphuric acid bath above the melting point of the substance until the effervescence ceased, and the decomposition appeared to be complete ; a current of air was then drawn through the apparatus.The experiment gave Total loss of weight of anhydro- Found. CaIculated. camphoic acid .............. 20 20 per cent. Gain of weight of drying tube. .. 1 0 9 7 (carbon dioxide) 17 20 11 Gain of weight of potash bulbs ............ The loss of weight in excess of the amount of carbonic acid appeared to be due to snblimation of the anhydride, some of which may have found its way into the drying tube. Anhydrocamphoic acid is a monobasic acid, neutralising one equivalent of caustic soda; but the point of neutralisation is difficult to hit, owing to the rapid hydrolysis of the anhydride by the action of caustic soda, the colour produced on the iadicator, phenol- phthalein, rapidly disappearing as the soda is taken up. The relation subsisting between camphoic acid and anhydro- camphoic would be that represented by the formuh H H Camphoic acid.Anliydrocamphoic acid. Canipltopyric acid, cis-. When camphoic acid is distilled, camphopyric anhydride, CeHI2O3, is obtained; this, when dissolved in hot caustic soda, is converted into camphopyric acid, C,Hl*O,. Camphopyric anhydride is also obtained by heating anhydrocamphoic acid above its melting point ; further, if camphoic acid is heated above its melting point, it undergoes decomposition, with loss of carbonic acid, but without appreciable loss of water if the temperature be not allowed to rise much above the melting point of the substance. In this may, the acid is produced directly from camphoic acid, the reaction taking place thus : C1oH& = CO, + CgHlt04. The product thus obtained dissolved almost entirely in cold solution of sodium carbonate, and the precipitate produced by hydrochloric acid after two crystallisations from water melted at 203-204O.It contains some mesocampho- pyric acid, a substance to be mentioned later (p. 79). Carnphopyric acid is a dibasic acid, and requires two molecular78 MARSH AND GARDNER: proportions of sodium hydroxide for neutralisation. 0.186 grnm acid required 10 C.C. of standard sodium hydrate ( 1 C.C. = 0908 NaHO) for neutralisation (calculated for dibasic acid 10 c.c.). It closely resembles camphoric acid as to the solubility of its salts, they being in general soluble in water, but the lead and copper salts, like those of camphoric acid, are insoluble in water, and are precipitated on adding a soluble lead or copper salt to a solution of the sodium salt of the acid.The lead salt thus obtained as a white precipitate was analysed after being dried at 110". Found. Calculated. It gave Lead .. . ... .. 52.5 52.9 per cent. The sodium salt was prepared and analysed; it is extremely soluble in water, and, on evaporating, the solution is left in rz syrupy condition, but it can be crystallised from a mixture of ether and alcohol. After drying at 120°, it gave Found. Calculated. Sodium.. . . . . 19.5'7 20.00 per cent. Canaphopyric Anhydride, cis-. This compound, described in sl former paper, is formed by distil- ling camphoic acid, by heating anhydrocamphoic acid above its melting point, and also by the action of acetyl chloride on cis-cain- phopyric acid; the yield in the last case is over 90 per cent.It is also formed by the action of water on camphopyryl chloride. The analogy between camphopyric acid and camphoric acid is also borne out by the nature and modes of production of their anhydrides. The two anhydrides are very similar in appearance and in properties; they are both very stable with regazd to the action of water ; they may both be crystallised from water unchanged ; they are both vola- tile at looo, and may be sublimed a t this temperature, and they are both volatile in steam. In one point, however, they differ, the melt- ing point of camphoric anhydride being higher, whilst that of cam- phopyric acid is lower than the melting points of their respective acids. Camphopyric acid, m. p. 209". Camphoric acid, m.p. 185'. Camphopgric anhydride, rn. p. 178". Ce.mphoric anhydride, m. p. 220*. Cumphopyryl chloride, C,,H,,O,Cl,.- -When camphopyric acid is treated with phosphorus pentachloride, it gives the acid chloride C,,H,,02C12 ; this is best obtained by mixing camphopyric acid with a slight excess of the pentachloride in a mortar, the acid being added gradually, and the whole well stirred ; in this way, the formation of anhydride is avoided. The oxychloride of phosphoras is then din-PRODUCTS OF THE OXIDATION OF CAMPHENE. 79 tilled off uuder ordinary pressure, and the campbopyry 1 chloride under diminished pressure ; it comes over at 125-130' under 13 mm. pressure. The above method is also satisfactory in the preparation of camphoryl chloride from camphoric acid.Camphopyryl ch1oride:is a colourlesu liquid, resembling camphoryl chloride in smell, reacting slowly in cold water, but readily soluble in and Iydrolysed by hot water ; it is only slowly acted on by sodium hydrate sointion when cold. The amount of sodium hydrate required to neutralise the acids formed on hydroIysis of camphopyryl chloride was determined by dissolving the chloride in standard sodium hydroxide in excess, the excess of sodium hydrate being determined by standard nitric acid. It was found that one molecular proportion of camphopyryl chloride required 3.86 (theory 4.0) molecular propor- tions of sodium hydroxide. The chlorine was also determined by titration with standard d v e r nitrate solution, using potassium chro- mate as indicator. Found.Calculated. Chlorine ........ 31.1 31.8 per cent. Action of Water o n Caniphopyvyl Chloride.-It was found by Marsh (Proc. Roy. Xoc., 1890,47, 6 ) that when the acid chloride of ordinary dextrocamphoric acid was treated with boiling water, it was converted into a mixture of the anhydride of dextrocamphoric acid and a new camphoric acid which was found to be lavorotatory. This acid was readily separated from the anhydride of the dextro-acid, with which i t was mixed, by treatment with a cold solution of sodium carbonate. The relationship of these two camphoric acids to oiie another led Marsh to consider one of them, namely, the dextrorotatory, as the cis-, and the laevorotatory as the trans-modification, corresponding to Baeyer's cis- and tm~ns-hydrotei.ephthalic acids.Shortly before the publication of Marsh's paper, Professor Friedel had announced the discovery of the same laevocamphoric acid which he had obtained from the long known mesocamphoric acid. It then appeared that rnesocamphoric acid was nothing else but a mixture of the dextro- and Iavo-camp horic acids. 21 esocamphopyric acid. When camphopyiyl chloride is treated with boiling water, it does not behave quite in the same way as camphoryl chloride, but the whole of the chloride readily goes into solution, and is hydrolysed ; the acid was obtained from this solution, the yield beiiig theoretical. It was found to be quite different from the original camphopyric acid, and subsequent examination proved it to be a mixture of the original acid, which we call the cis-modification, with a new isomeric80 BihRSH AND OARDNER: acid, trans-camphopyric acid.This mixture of acids we call meso- camphopyric acid to recall its analogy to mesocatnphoric acid. The mesocamphopyric acid. crystallises well from water, having all the appearance of a single substance ; its melting point, however, is not quite constant, varying betwoen 160' and 170'. This acid appears to be identical with the acid which we formerly described as isocam- phopyric acid produced along with camphoppric anhydride by the distillation of camphoic acid; it is also produced when camphoic acid is heated just above its melting point, in which case there is excess of the ordinary cis-camphopyric acid produced. C'amphopyric acid, trans-. Mesocamphopyric acid, when treated with acetyl chloride, is sepa- rated into its constituents, the cis-acid being converted into anhy- dride, while the trans-acid is left unaltered, and the two can then be separated by the action of a solution of sodium carbonate, which dissolves the trans-acid and IeaTes the cis-anhydride unaltered.The acid so obtained, after a second treatment with acetyl chloride, mas crystallised from water. I t melted at 190-191O. It was analysed and gave Found. Calculated for CsH,404. Carbon .......... 57.7 58.0 per cent. Hydrogen.. ...... 7.7 7.5 9 7 A better way to obtain the trans-camphopyric acid is to leave camphopyryl chloride exposed to moist air for some hours, I n this way tho liquid becomes converted into a dry, white, crystalline mass consisting of a mixture of the tram-acid with the anhydride of the cis-acid. The two are then separated by treatment with a solution of sodinni carbonate. On precipitating the sodium carbonate solutioii by hydrochloric acid and crystallising from water, the acid is obtained melting at 191".The meso-acid was prepared synthetically by mixing equal weights of the cis- and trans-acids, and crystallising from water; it is obtained thus as a homogeneous, crystalline substance, melting between 163" and 170". The melting points of the three campho- pyric acids are thus closely analogous to thotJe of the three corrc:- sponding camphoric acids, the trans-acid in each case melting at a lower temperature than the cis-, and the meso-acid lower than either of its constituents. Chlorocamphopyryl Chloride.In preparing camphopyryl chloride by the action of phosphorus pentachloride on camphopyric acid, we found that if the pentachlo-PRODUCTS OF TEE OXIDATION OF CA4XPHEXE. 81 ride is in excess and the mixture is heated on the water bath, the acid chloride produced contains more chlorine than is required by the formula C,H,,O,CI,; thus a specimen prepared in this way and distilled under diminished pressure at 1.32-133" was analysed, the chlorine being estimated by Carius' method. It gave Found. Calculated for CgHI2O2C1,. Chlorine ......... 32.9 31.8 per cent. ......... - ,, 33.1 9 ) T t was suspected that, by the action of heat on the camphopyrjl chloride in presence of excess of pentachloride of phosphorns, chlorine is substituted for hydrogen, as was found by Marsh to occur in the case of camphoric acid under similar circumstances (Proc.Roy. SOC., Zoc. cit.). Accordingly camphopyric acid was treated in order to produce chlorocamphopyryl chloride in the same way as camphoric acid was treated to produce chlorocamphoryl chloride. Eight g r a m s of camphopyric acid were heated with 33 grams of phosphorus pentachloride in a flask on a sand bath, the flask being provided with a reflux condenser; hydrogen chloride was evolved, and the product became liquid. After about seven hours' heating, the evolu- tion of hydrogen chloride had practically ceased, and, on cooling, the liquid was poured off from the excess of pentachloride, which had crystallised out. It was distilled a t first under ordinary pressure, when it began to boil at So, the temperature rising slowly, showing the presence of phosphorus trichloride along with the oxychloride.The substance was then distilled under 15 mm. presBure, when it boiled at 142'. The chlorine was de- termined. It is a colourkss liquid. Found. Calculated for Cg'Fz1102C13. Chlorine ......... 41.7 41.3 per cent. It thus appears that camphopyric acid undergoes the same reaction as camphoric acid, as expressed by the following equations. ~II)H,,O~ -+ 3PC1, = C,H,,C1302 + PCl, + 2POC13 + 3HC1. C ~ H ~ ~ O J + 3PC1, = CgHl,C1302 + PCls + 2POC13 + 3RC1. Chlorocamphoryl Chloride. As the notice in the Proceedings of the Royal Society with regard to this substance was very brief, i t may not be out of place here to give some further details about it.Camphoric acid, mixed with about 49 times its weight of phos- phorus pent.achloride, was heated i n flr flask provided with a reflux condenser on a sand bath for 17 hours ; the trichloride and oxychlo- ride of phosphorus were then dktilled off under ordinary pressure,82 MARSH AND GARDNER and the residue fractionally distilled under diminished pressure- After three distillations, a liquid was obtained boiling at 145- 148O under pressure (11 mm.), which solidified on cooling. The chlorine was determined in this specimen. Calculated. Found. C16H13C1302. Chlorine ....... 39.37 39.23 per cent. )) 39.27 7 ? The amount of the pure substance so obtained was 70 grams from 100 grams o€ camphoric acid, 40 grams of less pure substance being also obtained. Chlorocamphoryl chloride is a nearly colourless, crjstalline solid, melting when the flask containing it is held in the hand at a temperature of about 28"........ - Chlorocamphoric Anhydride. When chlorocamphoryl chloride is poured into seven or eight times its weight of boiling water, it remains a t the bott.om of the vessel in the for= of an oil, which gradually becomes solid; the solid xas washed with sodium carbonate solution, in which very little dis- solved, and, as i t gave off hydrogen chloride on drying, it was again treated with hot water, then washed with sodium carbonate, and dried. From 70 grams of chlorocamphoryl chloride, 50 grams of chlorocamphoric anhydride were thus obtained, or over 90 per cent. of the theoretical yield. The substance, crystallised from benzene, melted at 233-234" ; mother specimen melted at 235'.The chlo- rine was estimated. Calculated. Found. Cl,Hl,C~O,. Chlorine ......... 16.22 16.39 per cent. If chlorocamphoryl chloride is boiled with water until it is entirely cfissolved, camphanic acid is obtained on concentrating the solu- tion ; it separates at first as an oil, which crystallises after a time. I, a portion was dried a t 100' and analysed ; I1 is another specimen prepared in the same way. The crptals effloresce in the desiccator. Found. r--7 Calculated. I. 11. C10H1404- Carbon. ..... 60.25 60.31 60.60 per cent. Hydrogen ... 7.07 7-27 7.07 ,, The barium salt gave 25.4 per cent. Ba, found. 9 , 9 9 25.8 ,, ,, calculated. The salt is completely soluble in water and on slow evaporation gives crystals.PRODUCTS Oh' THE OXIDATIOX OF CAXPHEXE.53 Asclian has recently described the production of chlorocamphoric anhydride in another way, and has shown that it is converted into camphanic acid by boiling with caustic soda. We may be permitted tc say that our work above described on chlorocaniphoric chloride, chloi~ocaniphoi~ic anhydride and camphanic acid, was done during 01- before th(! year 1889. Ch 1 oroca my hopy r ic A nh y drid e . Chlorocamphopyryl chloride is only very slowly acted on by water; if, however, it is dissolved in ether and this solution is allowed to remain in contact with water, large, colourless crystals gradually form between the ethereal and aqueous layers. These crystals are nearly insoluble in light petroleum or benzene, more soluble in ct'ner and still more so in chloroform.They melt a t 288-229' and gave the following rasults on analysis. Calculated. Found. C9HllC103. Carbon ........ 53.04 53.33 per cent. Hydrogen ...... 5-80 5.44 ,, C hloriiie ....... 17-50 17.50 ,, The substance is chlorocamphopyric anlijdride analogous to chlorocamphoric anhydride. We: have not yet obt.ained sufficient of the substance to determine whether an acid analogous to camphanic acid is produced from it, but we have evidence that the acid obtained by dissolving chlorocamphopyryl chloride in sodium hydroxide is not a monobasic lactonic acid like camphanic acid, but a dibasic hydroxy- acid. This point, however, we must reserve, and we hope to make it the subject of a, future communication t o the Society.Camphopyranilic acid. Camphopyric acid forms a.n anilic acid, again closely annlogons to the anilic acid from camphoric acid. Camphopyric anhjdride was heated with aniline and the melt, which became solid on cooling, after being washed with di1ut.e hydrochloric acid to free i t from aniline, was crystallised from alcohol. Camphopyranilic acid is then obtained in colourless crystals, melting at 212", of the formula "9HlACooH C0*NH*C6H5. It is soluble in soda and reprecipitated by hydrochloric acid. Found. Calculated. Carbon ........ 68.84 68-96 per cent. Hydrogen.. .... 7.39 7.23 ,, Nitrogen ...... 5-41 5-36 .,84 MARSH AND GBRDSER: Action of Hydmgen Iodide on Camphopyric acid. Sixteen grams of camphopyric acid were heated with 32 C.C. of hydriodic acid of sp.gr. 1.8, and a little red phosphorns in sealed tubes ; the action is very slow, the tubes containing some crystalline matter after prolonged heating. They were heated in all for 40 hours at first> at 220°, and finally to 280'; t*he contents of the tubes were then liquid. The liquid was made alkaline with soda and distilled in steam, when a pale yellow, volatile oil came over, this was separated, dried with calcium chloride, and distilled from sodium, when moat of it came over a t 105-125". On redistilling this fraction, it boiled at 105-115'; the amount was 2 C.C. On analysis it gave Found. Calculated. C,H16. Carbon ........ 85.75 85.71 per cent. Hydrogen.. .... 13.84 14-24 ,, By analysis alone it is not possible to distinguish between Lexa- hydro-xylene, C8H16, and hexahydrotoluene, C7HIb, or any other hydro- carbon of the series.The vaponr density, however, showed that the substance was hexahydro-xylene. Weight of substance taken.. .... Volume of air.. ................ Barometer, 761 mm. Hence density (H = 1) ......... Density of hexahydro-xylene (cal~ulat~ed). ... 0.0891 gram. 18.75 C.C. 66.3. Temperature, 13' C. 56 .. hexahydrotoluene ( .. ).. .. 49 The substance was also nitrated; for this purpose 14 C.C. of the hexahydro-xylene was heated with 25 C.C. of a mixture of 2 parh of strong sulphuric acid and 1 part of nitric acid. As nothing separated on cooling, the mixture was poured into water, when, on standing, fine crystalline needles were deposited ; these, after being washed with water and crjstallised from alcohol, melted at 178', and mere evidently trini trometaxy lene.Hence the reduction of camphopyric acid by hydrogen iodide yields hexahydrometaxylcne. Furtlter Products of the Oxidation of Camphene. Among the other products of the oxidation of camphene by nitric acid, we obtained terephthalic acid, carnphoric acid, and succinic acid, besides other substances, the nature of which we have not yet determined. After camphoic acid has been separated from the crude product of oxidation, a syrupy mass is left; most of this dissolves on treating i t with ether, leaving terephthalic acid as an insoluble whitePRODUCTS OF THE OXIDATION OF CAMPHENE. 55 powder. This mas converted into its dimethylic salt by treatment with phosphorus pentachloride and methylic alcohol.On crystal- lising the product from methylic alcohol, it mejted a t 140-141'. When tlhe etheral solution of the syrupy mass was shaken up with sodium carbonate solution, a considerable amount was left, dissolved in the ether, having apparently no acid properties, and on separating the ethereal solution, n yellow oily residue was left. On attempting to distil this yellow oil, it suddenly and violently decomposed, after removal of the flame, evolving gas and leaving a small qaa.ntity only of carbonaceous residue in the flask. The sodium carbonate solutions were acidified, bat no definite substance could be obtained from them ; on distilling the product which separated, however, a large quantity of camphopyric anhydride was obtained, hence the oily matter probably still contained cam- phoic acid.Besides the campbopyric anhydride, an oil was ob- tained on distillation; this was volatile in steam, lighter than water, a,nd had a camphorous smell. I t was shaken out with ether and dist+illed. It boiled at about 250°, and gave on analysis Carbon .. .... .. 68.46 68.57 per cent. Found. Calculated. C,H,20,. Hydrogen.. . . . . 8-76 8.57 ,) It appears to be saturated as i t does iiot take up bromine, One gram was heated at 100' with baryta water, and the barium salt obtained was converted into the sodium salt by means of sodium carbonate ; the sodium salt, after having been freed from carbonate by solution in alcohol, was analysed. Calculated. Found. C,H13Na03. Sodiam.. .. . . . . 13.0 12.7 per cent. The oil thus appears to be a lactone, but it was not obtained in mfficient quantity to enable us to examine it further.The presence of succinic acid was suspected, by its characteristic taste, in the crude crystals obtained from the mother liquors after separation of the camphoric acid. It was isolated by suitable means, and, after crystallising from water, it melted a t 186". It gave a bArium salt insoluble in ammonia ; this was analysed. Found. Calculated. Barium.. . . . . . . 53.67 54.15 per cent. Camphoric acid was obtained in small quantity from the crude crystalline csmphoic acid by treatment with acetyl chloride, and separated as anhydride from the anhydrocamphoic acid by snblima- tion at 100' or by treatment with water. After being purified by recrystallisation from boiling water, it was obtained sometimes i n86 MARSH AND GARDNER: small needles, sometimes in thin leaf-like crystals.The specimens from different samples of camphoic acid, varied somewhat in melt- ing point; one, prepared by sublimation melted at 204O, another., after recrystallisation from water, at 220-221', and another at 215-216'. Another specimen, obtained by treatment with watw, melted at 204-205' after recrystallisation from absolute alcohol. Several of these different samples were analysed. Found. r----h-- 7 Calculated for I. 11. 111. C:oH1403. C ......... 65.05 6-5-48 65.35 65.93 H . ........ 8.00 7.9 7.75 7.69 Another sample, melting at 215-216', was boiled for a long time with water, in which it gradually became more soluble ; after being allowed to remain for a long time, i t was concentrated to a small bulk, when white, glistening, crystalline leaves separated.These crystals had an acid reaction and melted at 182-186O. A small portion, on treatment with acetyl chloride, gave an anhydride melt- ing at 213". The acid was analysed, with the following results. Found. Calculated for CloU,60,. C .......... 59-71 60.0 per cent. H.. 8.29 8.0 7, ........ From this it appears that the product of oxidation of camphelie contains tt camphoric acid, but whether a new one or one already known it is impossible to say, as the quantity was insufficient t o determine its optical rotation or to purify it further. Theoretical Considerations. The hydrocarbon camphene, from which camphor, camphoric acid, and camphoic acid are derived, is n very stable substance, differing in that respect from the turpentines and citrenes.It appears to be a, saturated hydrocarbon, to contain no double linkings, whereas tur- pentine appears to have one, and citrene two double linkings. Wallach has shown that camphene does not form an additive compound with bromine, but a substituted compound, and our own work on the phosphonic and chlorophosphonic derivatives of camphene shows that the hydrocarbon readily forms substituted, but not additive compounds. Camphene, it is true, forms an additive compound with hydrogen chloride, and this circumstance appears to have led chemists to ascribe a, double linking to camphene. But hydrogen chloride and the halogen acids are not, like bromine, reagents specially characterised by their capability of saturating a double linking, although in certain cases they may do so.Hydrogen chlo- ride does not, for example, under ordinary circumstances, if at all,PRODUCTS OF THE OXIDATION OF CAMPHENE. 87 saturate the double linking in ethylene or in ally1 alcohol. Now, i f camphene contain no double linking, it must be constituted of a t least three closed rings, for a compound having ten carbon atoms derived from a fully saturated open chain formula Clr,Hn must, if i t remain saturated, close a chain for every pair of hydrogen atoms i t loses. If, then, camphene, CIOH166, is a, saturated hydrocarbon consti- tuted of three closed rings, in order to form camphene hydrochloride, CIOH&l, or camphor, C10H160, from it, one of the three closed rings must be broken, leaving two, and to forin camphoric acid, Cl0H,,OI OY camphoic acid, CIoHlrO6, two of the closed rings must be broken, leaving on17 one.Hence when hydrogen chloride acts on camphene we regard the union of the two, not as the saturating of a double liuking, but as the breaking of a ring formation. This is by no means an uncommon action of a halogen acid. Indeed the halogen acids are characterised by their power of breaking feebly united ring structures much more so than is bromine. For example, Frennd found that the trimethylene ring is readily broken by hydrogen iodide, but with great difficulty by bromine. Perkin also found that trimethylenedicarboxylic acid was not acted on by bromine at tho ordinary temperature, while substlitution took place on warming ; on fhe other hand, the r i n g is immediately broken by hydrobromic acid.Similar instances might be given in the case of other rings. If, then, camphene may be regarded ad constituted of several ring formations, we have next to consider the evidence as to the parti- cular nature of these rings. The production of camphoic acid from camphene, together with its relationship to camphoric acid and to hexamethylene, appears to throw light on this question. The close analogy of camphopyric acid to cainphoric acid, aud the production of hexahydrometaxylene from each of them, warrants us in assuming that both acids, and also camphoic acid, are substituted derivatives of hexamethylene. Now, since camphoic acid is not formed from camphor or from camphoric acid, it would appear that the cam- phene molecule is broken down in two ways : (1) to yield camphor and camphoric acid, (2) to yield camphoic acid, in both cases leaving a hexamethylene nucleus untouched. The forlnuls given by Marsh (Proc.Roy. Soc.: 1890, 47, 6) for camphor and camphoric acid represented them, if we disregard for the moment the position ob t h e methyl group, as follows- x2 H2C C H ~ CH.CH,-COOH .T H2C C H ~ CH*CH2 I L%n I \CO I i E n I v CH2 v H2C ring CH.CH2/ H2C CH-COOH CHZ Camphor. Camphoric acid.88 XARSH AND GARGNER: with a methyl group substituted for hydrogen in the hexamethylene ring. The most probable view of the constitution of camphoic acid appears to us to represent i t as a hexamethylene ring with two carboxyl groups replacing hydrogen attached to the same carbon atom, and oue carboxgl group replacing hydrogen attached to an adjacent carbon atom, with methyl replacing hydrogen in the ring, thus : CH, In order to derive the foregoing formule for camphor and for cam- phoic acid from camphene, we have tso explain the six carbon and five carbon rings of camphor and the six carbon ring of campboic acid, which it appears to us is necessarily different from the six carbon ring in camphor and in camphoric acid.We have, then, in camphene a pentamethylene ring and two different hexamethylene rings. These we cannot express by the ordinary cyclic formule. We have t o give to camphene a tridimensional formula, a formula in which the atoms are not regarded as situated i n a plane, but cn the surface of a sphere.Such formulae, which can only be imperfectly represented on paper, may be called spheric formulae to distinguish them from cyclic formula. They may be regarded as derived from triply-linked carbon atoms in the same way that Baeyer has repre- sented cyclic formulse as derived from doubly-linked carbon. Baeyer has derived cyclic formulee from doubly-linked carbon atoms, regard- ing the carbon atoms as not directly doubly linked, but indirectly through the intervention of other carbon atoms, as, for example, in his comparison of the hexahydroterephthalic acids with maleic and fumaric acids- H COOH Y c! H COOH \’ ‘i /\ t i c c c c P\ H COOH /\ H COOH In a similar manner we may regard spheric formulae as derived from triply-linked carbon atoms, the carbon atoms not being directlyPRODUCTS OF THE OXIDATION OF CAMPHENE.89 linked by thrze bonds, but indirectly by the intervention of other carbon atoms, thus (Fig. I) : FIG. 11, H H i C H H a formula made up of three hexamethylene rings. The formula we propose for camphene is derived from this triple hexamethylene spheric formula, thus (Fig. 11). By breaking the link marked a, we derive the formula of camphor ; whereas by breaking the two links marked p, and leaving the link a, we derive camphoic acid. In the first case, a pentamethylene and a hexamethylene ring are left, while when the links /3/3 are broken, a hexamethylene ring only is left, which is, moreover, different from the hexamethylene ring of camphor. Further, we represent turpentine or pinens by the same structure as camphene, omitting the link y, and introducing one double link- ing.The production of camphene from turpentine hydrochloride is readily explained by this hypothesis, which, we believe to be borne out by other reactions of turpentine and its oxidation products. The universally-accepted structure for citrene and cymene is also readily derived from that of turpentine by eliminating tbe linking 6, and from camphene by elimination of both and 6 links. The cam- phor and camphoric acid formulce, derived from the above camphene formula, differ from those proposed by Marsh in 1889 only in the position of the methyl group in the ring. Against those formule, no serious objection has been brought forward except that they do not account for the production from camphoric acid of trimethylsuc- cinic acid. But the formation of trimethylsuccinic acid appears to us to indicate such a complete breaking down of the camphoric acid molecule, that i t would not seem likely to have any more value for the determination of the formda of that compound than, for example, va. LXIX. H90 PRODUCTS OF TEE OXIDATION OF CARTPHICNE. the formation of methylsuccinic acid from tartaric acid or of alcohol from sugar has for determining the constitution oE tartaric acid 01' of sugar respectively. The formula now proposed €or camphor and camphoric acid, differ- ing, as we have said, from the earlier ones only in the position of methyl group, are represented below as derived from camphene. the A 1. 2. 3. 4. 5. 6. 7. 8. CH? Camphene. Campl1or. co (3x2 /\ I I \/ ca2 H2C CH-COOB CH,CH CH.CH,*COOH Camphoric acid. In conclusion, we believe that the formulm suggested in this paper account in a. simple manner for the principal facts relating to t'he temene and camphor groups. They account- For the conversion of turpentine, citrene, and camphor into For the conversion of camphor into carrncrol. For the conversion of turpentine into camphene and into citrene. For the oxidation of camphene to camphor and to camphoic acid. For the absence of double linkings in camphene, and €or the presence of one double linking in turpentine and two in citrene. For the production from camphoric acid of carnphanic acid, and campholactone. For the relationship of camphoric acid and camphoic acid to hexahydroisox ylene. For the general analogy of camphoric acid and camphopjric acid, and for the stereoisomerism manifested by them. cymene. Univemit y La bo ra toy y, Ozf o rd.