466 BARGI-ER: THE CONSTITUTION OF CARPAINE. PART I.LI.-The Constitution of Cwpaine. Part I.By GEORGE BARGER.THE alkaloid carpaine was discovered by Greshoff in the leaves ofthe Papaw tree, Carica Papaya, L. (Mededeelingem uit 's LandsYlantentuin, No. 7 , Batavia, 1890, p. 5). Merck (Jahresber., 1891,p. 30) assigned to it the formula C,,H,,O,N, but van Ryn (Znaug.Diss. Marburg, 1892; Arch. Pharm., 1893, 231, 184; 1897, 235,332) corrected this to C,,H,,O,N. Van Ryn described a numberof salts, and showed that carpaine is a secondary base yielding anitroso-derivative, C,,H,~O,N*NO, and that on methylation andethylation a tertiary base and quaternary iodide are produced. Healso attempted to obtain a knowledge of the constitution byoxidation with potassium permanganate, but his experiments in thisdirection were unsuccessful.The alkaloid f o r the present investigation was prepared fromPapaw leaves from British India; the yield was 0.07 per cent., orthe same as that obtained by Greshoff from adult leaves (youngleaves contain three to four times as much).The experimental results which have been obtained so far showthat carpaine is the internal anhydride of a, substance possessingboth acid and basic properties, and closely resembling certain amino-acids; this substance contains a carboxyl group, and has the com-position C,,H,,O,N; the name carpamic acid is suggested for it.Byoxidation with potassium permanganate, or preferably with nitricacid, a dibasic acid of the composition C,H,,O, is formed, which isprobably as-dimethyladipic acid ; this acid might result from thebreaking down of a dimethylcy clohexane ring.Like carpaine itself,the ethyl ester of carpamic acid yields a nitroso-derivative, whenceit follows that the alkaloid cannot be a lactam, but must be alactone, and that its two oxygen atoms are arranged as follows:iC*O*OO*. Although there is at present no direct evidence, it thusappears very probable that carpamic acid contains an alcoholichydroxyl in addition to a carboxyl group and an imino-group; ifattached to the cyclohexane ring, this hydroxyl would be convertedon oxidation into one of the carboxyl groups of the acid C,H,,O,.In this case the carboxyl group of carpamic acid could not bedirectly connected to the cyclohexane ring, but would be attachedto the rest of the molecule.The oxidation of carpaine by potassiumpermanganate (see below) affords some evidence that the nitrogenatom is directly attached to the complex yielding the acid C8HI4O4;the rest of the molecule left unaccounted for is a bivalent groupBARGER: THE CONSTITUTION OF CARPAINE. PART I. 467C,H,,. The subjoined largely hypothetical formula will serve toMe Hshow that if carpaine contains 25 hydrogen atoms, there can onlybe one homocyclic ring, in addition to the lactone ring. Withregard to the complex C5HI0, nothing is known at present.EXPERINENTAL.Composition and Properties of Carpaine.Van Ryn’s analyses agree closely with the formula C,,H2,02N,and so far it was thought unnecessary to confirm this. It is,however, supported indirectly by the analyses of carpamic acidand its derivatives.Merck’s formula, C?,,H2,02N, is certainlyincorrect, and the only other formula, C,,H,,O,N, is hardly morelikely.The properties of carpaine have been fully described by van Ryn,except the fact that the alkaloid can be distilled without decom-position. I n a vacuum produced by charcoal and liquid air (thepressure was a fraction of a millimetre), 2 grams of carpaine weredistilled with the bath at 260-290°, and the vapour at 215-235O.The distillate crystallised in the receiver, and at once showed themelting point 121O (corr.), identical with that given by van Ryn.Action of Acids on Carpaine: Carparnic Acid.Van Ryn attempted to hydrolyse carpaine by boiling it with1 per cent.alcoholic hydrogen chloride, but after twelve hoursalmost the whole of the alkaloid was recovered unchanged. Thisacid was much too dilute, and the temperature too low. Whenheated in a sealed tube to 130-140° for a few hours with 10 percent. hydrochloric or sulphuric acid, carpaine is quantitativelychanged to a substance containing one molecule of water more thancarpaine. The same change may be brought about more slowlyby boiling with 20 per cent. hydrochloric acid. The completion ofthe change is best detected by the disappearance of the intenselybitter taste of carpaine. When sulphuric acid has been used it maybe removed with baryta, which does not precipitate the product ofhydrolysis; in the case of hydrochloric acid, the excess of the acidcan be removed by distillation under diminished pressure.TheVOL. XCVII. I 468 BARGEll: THE CONSTITUTION OF CARPAINE. PART I.hydrochloride of carpamic acid remains behind as a syrup, andcrystallises on cooling. It may be recrystdlised from acetone, orby adding ether to its alcoholic solution, and forms needles meltinga t 161O:0.1320 gave 0.2778 CO, and 0.1107 H20. C = 57.4 ; H = 9.3.0.1270 ,, 0.0627 AgC1. C1=12*2.C,,H,,03N,HC1 requires C = 57-2 ; H = 9-5 ; C1= 12-1 per cent.The free base may be obtained from the hydrochloride by decom-position with the calculated quantity of sodium carbonate, but it5the substance is readily soluble in water and scarcely more solublein alcohol than sodium chloride, it is d a c u l t to obtain it quite freefrom salt by this means.It is therefore better to decompose thesulphate with baryta, or the hydrochloride with moist silver oxide,and to crystallise the residue left on evaporating the aqueousfiltrate from dilute alcohol. It also crystallises very well on addingacetone to the cold alcoholic solution.Carpamic acid, obtained in this manner, forms long needles, melt-ing a t 224O. Under a pressure of less than 1 mm., the substancesublimes unchanged ; when heated under atmospheric pressure, itdistils with slight decomposition :0.1212 gave 0.2925 CO, and 0.1139 H20.The substance is optically active ; in aqueous solution :+ 7*0°.C = 65.8; H = 10.4.C1,H2,O3N requires C = 65.4 ; H = 10.5 per cent.I = 1-dcm.; c = 3.727 ; a, + 0-26O ; [a]Carpamic acid is readily soluble in cold water, but only verysparingly so in alcohol; it is insoluble in acetone, ether, and mostother organic solvenb. The salts with mineral acids and with thealkali metals are readily soluble in water; the barium salt is a stiffjelly, so that the, test-tube in which it is formed can be inverted.Carpamic acid has a hardly perceptible, faintly sweet taste, like someamino-acids; when pure and free from carpaine, the intense bittertaste of the latter alkaloid is absent. In dilute solution carpamicacid does not yield preciEitates with potassium tri-iodide or withpotassium mercuri-iodide, differing therein from carpaine ; bothbases, however, yield a precipitate with phosphomolybdic acid.In solubilities, volatility, and chemical reactions, carpamic acidclosely resembles certain amino-acids like leucine, but it has moredefinitely basic properties than are associated with a-amino-acids.The presence of a carboxyl group is demonstrated by esterification.Thus, when carpamic acid is suspended in absolute alcohol andtreated with hydrogen chloride, there remains on evaporation ofthe acid a syrup, which crystallises on the addition of ether to itBARGER: THE CONSTITUTION OF CARPAINE. PART I.469concentrated alcoholic solution, forming needles, melting at171--172O, and consisting of the hydrochloride of etliyl carpamate :0.1354 gave 0.2968 CO, and 0.1178 Hi0C,,H,,O,N,HCl requires C =59.7 ; H = 9.9 per cent.The same hydrochloride is formed almost quantitatively directfrom carpaine by hydrolysis with alcoholic (instead of with aqueous)hydrochloric acid.For instance, 0.5 gram of carpaine, heated with5 C.C. of 10 per cent. alcoholic hydrogen chloride for two hours to160°, yielded 0.51 gram of this hydrochloride on addition of etherto its concentrated alcoholic solution.The hydrochloride of ethyl carpamate is tasteless ; its aqueoussolution is precipitated by sodium carbonate. The free ester baseis readily soluble in ether; it has not yet been crystallised.From the above description it will be seen that carpaine andcarpamic acid are related to each other in the same way as ergotinineand ergotoxine (Barger and Ewins, this vol., p. 284). Both carpaineand ergotinine are converted by acids in alcoholic solution intosalts of an ester.C=59*8; H=9*7.Action of Alkulis on Carpaine.Thus, after 0.2 gramhad been heated with 2 C.C.of 10 per cent. aqueous sodiumhydroxide to 140-150° for three and a-half hours, 0.16 gram ofcarpaine was recovered unchanged. The carpaine was hardlyattacked, because it is insoluble in water. In a similar experimentwith 2 C.C. of 2.5N-sodium ethoxide, carpamic acid was formed, andwhen 0.2 gram had been heated to 180° for two hours with 4 C.C.of 3.3N-sodium ethoxide, 0.12 gram of carpamic acid was obtained.When0.5 gram of carpaine was heated with 7 grams of potassiumhydroxide and 0.5 C.C. of water, no apparent change took placebelow 300O. Then a dark brown solution was gradually formed,and, on cooling, hydrochloric acid yielded an oily precipitate solublein ether with intense fluorescence.On evaporation, the ether lefta red oil, which with ferric chloride yielded a reddish-browncoloration. It would appear that under these conditions a phenolis formed (by oxidation of a cyclohexane ring); a similar productwas also obtained on chlorinating carpaine and treating the productwith alkali (see below).Carpaine is extremely resistant to alkalis.On fusion with alkali, a further change may take place.Further Degradation of Carpamic Acid.I none experiment 0.2 gram of carpaic acid was boiled with 6 C.C. ofThis cannot readily be brought about by boiling with alkali.I 1 470 BARGER: THE CONSTITUTION OF CARPAINE. PART I.50 per cent.potassium hydroxide solution. The potassium salt ofthe acid floated on top as a brown oil, and during half an hour'sboiling very little, if any, of a volatile base was given off,corresponding a t most to one-fiftieth of the nitrogen present. Oncooling, the upper layer crystallised ; it yielded, on acidification,unchanged carpamic acid.By distilling carpamic acid with lime under diminished pressure,a little of an oily base is formed, insoluble in water, but soluble inether. A similar base is formed on heating carpamic acid (orcarpaine) with concentrated hydrochloric acid to 225-250O. Inboth cases the carboxyl group of carpamic acid seems to beeliminated, but neither reaction has been studied further for wantof material.Oxidation of Carpahe.Van Ryn foundthat acid potassium permanganate is only very slowly decoloriseda t room temperature.By heating on the water-bath (in dilutesulphuric acid solution), oxidation was more rapid, and he obtaineda mixture of crystalline, non-nitrogenous acids, the yield of whichwas, however, only 74 per cent. of the alkaloid employed. Bycrystallisation from water, three fractions were obtained, meltingcontinuously from 70-124O ; the small yield of material availabledid not enable van Ryn t o isolate any of the acids in a state ofpurity, and no analysis was made. The only other product obtainedwas ammonia.In view of the difficulties encountered by van Ryn, it was thoughtadvisable to modify the conditions of oxidation by using neutralpotassium permanganate in acetone solution, a method which hasof late yielded such good results in the case of brucine andstrychnine (Leuchs, Ber., 1908, 41, 1711).Five grams of carpainewere dissolved in 125 C.C. of acetone, and 1-11 grams of finelypowdered potassium permanganate (half an atomic proportion ofoxygen) was added to the solution after cooling to Oo. The pinkcolour disappeared only very slowly. The solution was thereforewarmed t o room temperature, when the permanganate was com-pletely reduced in a fep. hours. The same quantity was then againadded; finally, when two atoms of oxygen had been used up, thesolution was filtered, and was found to contain 24-3 grams ofthe unchanged alkaloid.In a, second experiment 5 grams of carpaine in 140 C.C.of acetonewere at once treated with 3-33 grams of potassium permanganate( = 14 atoms of oxygen) ; the temperature gradually rose from 23Oto 37O, and then fell; the pink colour disappeared in half an hour.In all, 9 atoms of oxygen were supplied; the addition of per-Carpaine is fairly resistant to oxidising agentsBARQER: THE CONSTITUTION OF CARPAINE. PART I. 471manganate, representing the last atom of oxygen, produced a, riseof temperature only from 21-25O, and this time the pink colourpersisted after seven hours. On filtration, the acetone was foundto contain only a minute quantity of a neutral substance, meltingat about 50°. The mixture of manganese dioxide and potassiumsalts was extracted with water (by shaking, glass beads beingadded). The pale brown solution was washed with ether, whichdid not remove an appreciable amount of substance; the solutionwas then acidified and became turbid; by repeated extracting withether, 2.5 grams of a brown syrup were now obtained, but theaqueous solution still held in suspension a considerable quantity ofa brown, oily substance, which was almost insoluble in ether.Thesyrup extracted by ether was esterified with methyl alcohol andhydrogen chloride, and was %hen distilled ; between 1 10-120° a t apressure of 3-4 mm., there was collected a small quantity of a dis-tillate, which was hydrolysed by boiling with potassium hydroxide ;a t the same time an alkaline gas (ammonia or an amine) wasevolved. On acidification, 0.15 gram of an acid was obtained,which, on crystallisation from benzene, formed leaflets, melting notquite sharply at 98-looo.This acid was free from nitrogen, andwas analysed:0.0682 gave 0.1398 CO, and 0.0496 H20. C=55*9; H =8-1.[C,H1204 requires C = 55.8 ; H = 7.0 per cent.]C8H1404 ,, C=55.2; H=8*0 ,,The molecular weight was determined by the author’s microscopic0.0487, in 1.2744 grams methyl alcohol, was intermediate betweenmethod (Trans., 1904, 85, 286) :0.20 and 0.21 mol. bend. M.W.=182-191, mean 186.C,H,404 requires M.W. = 174.0-0164 gram of acid required for neutralisation 1-62 C.C.In the distillation of the ester a small quantity of a semi-solidfraction was further collected, boiling at 120-200°/3 mm., butthe bulk of the material decomposed in the flask.It thus becameevident that much more than 5 grams of the alkaloid would berequired for the complete characterisation of the acid (van Rynobtained no result from the oxidation of 10 grams with potassiumpermanganate). Other oxidising agents were therefore employed,and among these nitric acid was found to be much the mostsuitable. 0.2 Gram of carpaine, heated in a sealed tube with2 C.C. of nitric acid (D 1.41) to 140-170°, yielded only a minutequantity of an acid soluble in water, which on heating gave anodour similar to that of succinic anhydride; there was no trace ofN/lO-KOH, whence M.W. for a dibasic acid = 204472 BARGER: THE CONSTITUTION OF CARPAINE. PART I.an alkaloidal substance. On opening the tube there was greatpressure, most of the alkaloid having been oxidised to carbondioxide.In a similar experiment with acid of density 1-32, 40 percent. of a dibasic acid was obtained, and after a large number ofsuch experiments the exact conditions were found for obtaining amixture of non-nitrogenous acids weighing 75 per cent,. of thealkaloid employed. This mixture is at present under investigation,and from it an acid of the composition C,H1404 has been isolated,which is probably a mixture of the two stereoisomeric forms ofas-dimethyladipic acid, the same mixture having previously beenobtained in very much smaller amount with potassium per-manganate.The oxidation of carpaine by halogens was also attempted.When chlorine is passed into a cold aqueous solution of the hydro-chloride, the whole of the alkaloid is gradually precipitated as anamorphous chloro-derivative, which is decomposed by boiling alcohol,but can be crystallised from methyl alcohol (with considerable loss),forming leaflets, melting and decomposing at 77O :0.0981 * gave 0.1854 CO, and 0.0618 H,O.C = 51.7 ; H = 7.0.0.1247 5- ,, 0'1132 AgC1. C1=22.5.C14H,,0,NC1, requires C = 51.8 ; H = 7.1 ; C1= 21.9.This substance is neutral; two hydrogen atoms have been replacedby an oxygen atom and two chlorine atoms; it is therefore dichloro-oxycarpaine, and as it is formed quantitatively, it was thought thatit might form a suitable starting point for further degradation.The chlorine is very readily removed, by cold pyridine, for instance,but the substance is not simply a perchloride. A somewhat pro-found change has taken place; carpaine cannot be recovered fromit, and by treatment with alkali a pink, fluorescent solution isobtained (benzene derivative 2). So far it has been found impossibleto obtain any further derivative in a pure state.On passing chlorine into a solution of carpamic acid, a similarderivative is formed, which could not, however, be crystallised.Bromine produces in a solution of a carpaine salt an orangeprecipitate of a perbromide, from which carpaine is readilyregenerated.In comparing the oxidation by potassium permanganate inacetone solution with that by nitric acid a t 130°, it should be notedthat the latter reagent first hydrolyses the alkaloid to carpamicacid, which thus becomes open to attack. A non-nitrogenous acidis then formed, but potassium permanganate first produces a nitro-genous acid, which is only slightly soluble in ether. After dis-* Crystallised. j- Amorphous, dried in a vacuumMCRENZIE AND WREN : OPTICALLY ACTIVE GLYCOLS. 473tillation the ester of this acid gave off an amine or ammonia onhydrolysis, the same acid, C8HI4O4, resulting. From this it wouldappear that the nitrogen atom is directly attached to the complexyielding this acid.THE GOLDSMITHS’ COLLEGE,NEW CROSS, LONDON, S.E