2102 CLAYTON : THE CONSTITUTION OF COUMARINIC ACID.CCXX1.-The Constitution of Coumarinic Acid.By ARTHUR CLAYTON.WHEN coumarin is dissolved in aqueous sodium hydroxide, thesodium salt of coumarinic acid is produced, whereas the prolongedaction of an alcoholic solution of the alkali results in the productionof an alkali o-coumarate. Coumarinic acid has not yet beenisolated, being resolved into coumarin and water at the moment ofliberation from its salts, but its alkyl esters are known, thesecompounds being isomeric with the corresponding derivatives ofo-coumaric acid. When the dialkyl esters of 3-nitrocoumarinic acidare boiled with aqueous alkalis, 3-nitrocoumarinic acid is producedfrom the acidified liquid, whereas the dimethyl ester of 3-nitro-o-coumaric acid under similar conditions yields the methyl etherof 3-nitro-o-coumaric acid (Miller and Kinkelin, Ber., 1889, 22,1708 e t sep.).This difference of behaviour towards alkalis hasbeen explained by Michael’s formula, (‘I) for coumarinic acid( J . p. Chem., 1888, [ii], 38, 27), which has also received supportfrom Perkin (Trans., 1881, 39, 560), Miller and Kinkelin (Ber.,If the mixture be heated until action becomes violent it is difficult t o condensthe productq, torrents of brown fumes are evolved, and the quantity of tetranitromethane obtained is very small.CLAYTON : THE CONSTITtJTION OF COUMARINIC ACID. 21031889, 22, 1713), Roser (Ber., 1882, 15, 2347), and Anschutz(Annalen, 1889, 254, 181) :0--0 8" 0(1.1 (11.1 (111). (W.On the other hand, the view has been held that coumarinic acidis the cis-isomeride (formula 11) of o-coumaric acid.A thirdpossible formula (111) is suggested by the constitution which Morganand Micklethwait (Trans., 1906, 89, 868) have proposed forcoumarin (formula IV).In order to confirm or exclude Michael's formula, the author ofthe present communication has investigated the alkyl derivatives of5-nitrocoumarinic acid, the nitro-group being introduced in orderto obtain solid compounds. It is obvious that if formula I repre-sents the constitution of coumarinic acid, only one methyl ethylester could be prepared, whereas formulae I1 and I11 indicate thepossibility of the existence of two such derivatives. For con-venience, the two hydroxyl groups will in this paper be distinguishedby the letters a and P.6-Nitrocoumarin dissolves in aqueous alkalis, and the solution,when treated with silver nitrate, yields silver 5-nitrocoumarimte.This salt, by interaction with methyl iodide, yields aS-dimethyl5-.nitrocoumarinate (V).The identity of this substance is estab-lished by boiling it with aqueous sodium hydroxide, 6-nitrocoumarinbeing readily regenerated. The ap-dimethyl 5-nitrocoumarinate isconverted by partial hydrolysis into a-methyl 5-nitrocoumnri7tate(VI). The silver salt of the latter compound, when treated withethyl iodide, yields a-methyl i3-ethyl 5-nitrocoumarinate (VII).By a similar series of operations, aP-diethyl 5-nitrocouma~inate,a-ethyl 5-nitrocoumarinate, and P-methyl a-ethpl 5-nitroco.umarinateare obtained as indicated by formulze VIII-X.All the compounds V-X (p.2104) are shown t o be derivatives of5-nitrocoumarinic acid by their exceedingly easy reversion to 6-nitro-coumarin when boiled with weak aqueous sodium hydroxide.a-Methyl P-ethyl 5-nitrocoumarinate and P-methyl a-ethyl 5-nitro-coumarinate proved to be distinctly different compounds, the formermelting a t 75-77O, and the latter at 111-113°, thus showingMichael's formula to be incorrect.In order that the foregoing proof should not be invalidated bythe possibility of one or both of the isomeric methyl ethyl ester2104 CLAYTON : THE CONSTITUTION OF COUMARINlC ACID.C,HSO,*NO,6 -Nitrocouwaarin.OEt.. . aC9H50<OEt ... p(VII I. )p H(X.1M. p. 111"--113".being derived from 5-nitrocoumaric acid by the rupture of thelactonic ring, an investigation of the ethers and esters of the latteracid was made as indicated by formulz XI-XIX./\OMe /\OH /\OEt ' 'CHO f- \/ ' ICHO -(,!CHO \/(XII.)IJ./\olgeNO,~,!CHO(XIII.)()OM.NO,\,CH: CH*CO,H(X1 V.)/\OMe I ICH:CH*CO,Et(XV. )3. Ag salt+ EtTM. p. 85".(XI. 1 (XVI.)IJ.O O E tNO,,,CHO(XVII.) 4/\OEt(XVII I. )/\OEtNO,?ICH:CH*Jbp salt + Me1NO,()CH :CH*CO,MeM. p. 163".(XIS.)The methyl ether of 5-nitrocoumaric acid (XIV) was preparedaccording to Schnell's directions (Ber., 1884, 17, 1382) as indicatedby formulae XI-XIV, and the silver salt of this acid heated withethyl iodide, thus yielding the methgl ether of etlhyl 5-nitroCLAYTON : THE CONSTITUTION OF COUMARINlC ACID.2 LO5coumarinate (XV). By a similar series of reactions the ethyl etherof 5-nitrosalicylaldehyde, the ethyl eth#er of 5-nitrocoumaric acid,and the ethyl ether of methyl 5-nitrocoumarate are obtainedThe two methyl ethyl derivatives of 5-nitrocoumaric acid thusobtained proved to be distinctly different from the methyl ethylderivatives of 5-nitrocoumarinic acid. The existence of these fourisomeric methyl ethyl derivatives permanently excludes the possi-bility of Michael's formula being correct.I n order to ascertain which of the two remaining formulaerepresents the constitution of coumarinic acid, UP-dimethylcoumarinate and the methyl ether of methyl 5-nitrocoumarute wereseparately treated with bromine.In each case methyl ufl-dibronzp-5-nitro-2-methoxy-P-phenylprop'onate was produced, thus excludingformula 111.Coumarinic acid is therefore proved to be the cis-isomeride ofo-coumaric acid.The positions occupied by the hydroxyl groups, which have beendistinguished by the letters a and P, are indicated by treating theethyl ether of m.ethyl 5-nitrocournarate, and. P-methyl a-ethyl5-nitrocoumarinate separately with bromine. Methyl ap-dibromo-5-nitro-2-ethoxy-P-phenylpropionat e (XX) is produced in each case,thus showing that the a-group is phenolic, and that the P-groupforms part of the carboxyl group (see formula XXI) :(XVII-XIX).(\OEt(XX). (XXI).Formula I1 being established, the chemical behaviour ofcoumarinic acid can easily be explained.If a representation ofthe molecule be built up with suitable models, the side-chain is seento follow approximately the sides of a regular hexagon, and thecarboxyl group is brought into close proximity with the phenolicgroup (formula XXI), thus indicating the ready elimination of theelements of water. I f , however, a nitro-group be introduced intoposition 3, the negative phenolic and nitregroups exert a combinedand powerfully repellent effect on the carboxyl group, which, beingrepelled from the immediate neighbourhood, no longer enters intochemical action with the phenolic group. This accounts for thefact that 3-nitrocoumarinic 'acid (XXII), 3 : 5-dinitrocoumarinicacid (XXIII), and 3-nitro-4-hydroxycoumarinic acid (XXIV) existin the free state (Miller and Kinkelin, Ber., 1889, 22, 1706;Clayton, this vol., p.1390 et sep.):VOL. XCVII. 2106 CLAYTON : THE CONSTITUTfOK OF COUMARINIC ACID.(XXII). (XXI 11). (XXIV).The ease with which the alkyl ether esters of the coumarinicacids undergo complete hydrolysis is unusual, since phenyl ethersare generally not affected by aqueous alkalis. I n all probability,however, after the removal of the alkyl from the carboxyl group,two causes operate in the second stage of the hydrolysis, namely,(l), the usual hydrolytic action of aqueous alkalis, and (2), thatcause which effects the elimination of the elements of water fromcoumarinic acid itself. These two influences, acting concurrently,bring about the hydrolysis of the phenyl ether which aqueousalkalis alone are generally unable to effect.SzC??WlUq.1.The two methyl ethyl ether-esters of 5-nitrocoumarinic acidand the two corresponding isomeric ether-esters of 5-nitrocoumaricacid have been prepared.2. The two methyl ethers of methyl 5-nitrocoumarate and methyl5-nitrocoumarinate yield the same bromine additive product whentreated with bromine.3. The above facts show that coumarinic acid is the cis-isomerideof o-coumaric acid. This view of the constitution of coumarinicacid affords a ready explanation of its chemical reactions.EXPERIMENTAL.The Ethers and Esters of 5-iVitrocou~marirtic Acid.6-Nitrocoumarin was found t o be best prepared by dissolvingcoumarin in sulphuric acid (10 parts), and treating the solutionwith one molecular proportion of nitric acid (D 1.4) mixed withthree times its volume of sulphuric acid, the temperature being keptbelow 20°.After one hour the solution is poured on crushed ice,and the precipitated solid crystallised from acetic acid.Silver 5-)zztrocoumarimte was obtained by dissolving 6-nitro-coumarin (10 grams) in an aqueous solution of sodium hydroxide(4.2 grams), and then adding a solution of silver nitrate (19 grams).The orange-red precipitate was washed with a little water and dried.When treated with dilute acids, the salt yields 6-nitrocoumarin :0.2813 gave 0.1908 AgCl. Ag=51*04.C,H,03N(OAg)2 requires Ag = 51.06 per centCLAY'I'ON : THE CONSTlTUTION OF COUMARINIC ACID. 2107The Methyl Ether of Methyl 5-Nitrocoumarinate.-Siltrer 5-nitro-coumarinate (6 grams) wits mixed with about 30 C.C.of ether, andthen shaken with a mixture of methyl iodide (1.5 grams) and ether(10 c.c.) for one hour, the temperature rising during this operittion.When cold, the contents were extracted with alcohol, from whichsolvent colourless needles, melting at 124-1 25O, were obtained :0-1375 gave0.2790 CO, and 0.0610 H,O. C=55.34; H=4.92.0.2146CllHl,O,N requires C = 55-70 ; H=4.64 ; N = 5-91 per cent.T7be Ethyl Ether of Ethyl 5-Nitrocoumarimte.-Silver &nitro-coumarinate (10 grams) was treated with ethyl iodide (4 gra.ms) inethereal solution in the manner described in the preceding experi-ment, and the product extracted with alcohol. Colourless needles,melting at 104-105°, were obtained :,, 11.3 C.C.N, at 24O and 770 mm. N=5.99.0.1404 gave 0.3020 CO, and 0.0740 H,O. C = 58.66 ; H = 5.85.0.2376C13H,,0,N requires C = 58.87 ; H = 5-66 ; N = 5.28 per cent.The MetKyl Ether of 5-Nitrocoumarinic AcS.--The methyl etherof methyl 5-nitrocoumarinate (6 grams) was dissolved in dilutealcohol, and heated to 100° with aqueous sodium hydroxide (1 gram)for about thirty minutes, when a portion of the liquid produced noturbidity on dilution with water. The mixture was then acidifiedwith dilute hydrochloric acid, and the voluminous precipitatecrystallised from alcohol or dilute acetic acid. Colourless needleswere obtained, melting at 202-203° :,, 11.7 C.C. N, at 25O and 750 mm. N=5.41.0.1647 gave 0.3230 CO, and 0.0650 H,O.C = 53.48 ; H = 4*3,9.0.1706C,,H9b5N requires C = 53-81 ; H = 4.04 ; N = 6.28 per cent.The Ethyl Ether of 5-Nitrocoumarinic Acid.-This substance wasobtained by the interaction of the ethyl ether of ethyl 5-nitro-coumarinate (6.5 grams) and sodium hydroxide (1 gram) in weakalcoholic solution, in the manner described in the preceding experi-ment.,, 10.1 C.C. N, at 26O and 754 mm. N=6-52.Colourless needles were produced, melting at 171-17Z0 :C = 56.07 ; H = 4.94.CiiH,iO,fJ requires C = 55.70 ; H = 4.64 ; N = 5.91 per cent.0.1498 gave 0.3080 CO, and 0-0662 H,O.0.1442 ,, 8.0 C.C. N, at 25O and 754 mm. N=6.14.The Methyl Ether of Silver 5-1\Titrocoumari~ate.--The methylether of 5-nitrocoumarinic acid (10 grams) was dissolved in anaqueous solution of sodium hydroxide (1.8 grams), and the yellowsolution treated with aqueous silver nitrate (8 grams), when thesilver salt was precipitated as an almost colourless powder:0*3100 gave 0.1004 Ag.Ag = 32.39.C,,H,O,NAg requires Ag = 32-73 per cent.6 ~ 2108 CLAYTON : THE CONSTITUTION OF COUMARINIC ACID.The Ethyl Ether of Silver 5-Nitrocoumum’nate.--The ethyl etherof 5-nitrocoumarinic acid (10 grams) was dissolved in an aqueoussolution of sodium hydroxide (1.7 grams). An aqueous solution ofsilver nitrate (8 grams) was then added. The salt forms an almostcolourless powder :0-3116 gave 0*0980 Ag. Ag=31.45.C,,H,,05NAg requires Ag = 31-40 per cent.The Methyl Ether of Ethyl 5-Nitrocoumarinate.--The methylether of silver 5-nitrocoumarinate (10 grams) was heated with ethyliodide (5 grams) and a little ether for one hour at looo.Theproduct, when extracted with alcohol, yielded colourless needles,melt’ing at 75-77O:0.1178 gave 0.2462 CO, and 0.0580 H,O. C = 57.00 ; H = 5.47.0.1092 ,, 5.7 C.C. N, at 24O and 756 mm. N=5.82.C12H130,N requires C = 57.37 ; H = 5-18 ; N = 5.58 per cent.The Ethyl Ether of Methyl 5-Nitrocoumarinate.-The ethyl etherof silver 5-nitrocoumarinate (10 grams) was mixed with ether andmethyl iodide (5 grams), and subjected to the treatment describedin the preceding experiment. The alcoholic extract yielded colour-less needles, melting at 11 1-1 13O :0.1594 gave 0.3328 CO, and 0.0744 H,O.0.1192 ,, 6.4 C.C. N, at 24O and 756 mm.N=5*98.C = 57.00 ; H = 5.19.Cl2H1,O,N requires C=57*37; H=5.18; N=5*58 per cent.The Ethers and Esters of 5-Nitrocoumaric Acid.The Methyl Ether of Silver 5-Nitrocoumarate.-The methyl etherof 5-nitrocoumaric acid (1.6 grams), prepared according to Schnell’sdirections (Bw., 1884, 17, 1382), was dissolved in a solution ofsodium hydroxide (0.29 gram). To this solution silver nitrate(1.3 grams), dissolved in water, was added, when an almost colour-less, gelatinous precipitate was produced :0.2868 gave 0.0936 Ag. Ag=32*63.C,,H805NAg requires Ag = 32.73 per cent.The Methyl Ether of Ethyl 5-Nitrocoumarate.-The methyl etherof silver 5-nitrocoumarate (1 gram), ethyl iodide (0.5 gram), and a,little ether were heated together for three hours at looo.Afterevaporating off the ether, the mixture wits extracted with alcohol,from which solvent colourless needles, melting at 85O, were obtained :0.1398 gave 0.2942 CO, and 0-0666 H,O. C=57.38; H=5*29.0.1716 ,, 9.0 C.C. N, at 25O and 764 mm. N=5*88.C,,H130,N requires C= 57.37 ; H = 5.18 ; N = 5-58 per cent.TA e Methyl Ether of Nethpl 5-Nitrocoumarate.-The methyl etherof silver 5-nitrocoumarate (1 gram) wits mixed with methyl iodidCLATTON : THE CONSTITUTION OF COUMARINIC ACID. 2109(0.5 gram) and a little ether, and heated to 100° for three hours.After evaporating off the ether, the residue was extracted withalcohol, when colourless needles, melting at 163O, were obtained :0.1050 gave 0-2150 CO, and 0-0454 HiO. C = 55-84 ; H= 4-80.0.1812 ,, 9.9 C.C.N, at 764 mm. and 25O. N=6.07.C,,H,,O,N requires C = 55.70 ; H = 4.64 ; N = 5-91 per cent.5-N~tro-2-et~~oxyZ,enzaZde7~yde.-2-Ethoxybenzaldehyde was slowlyadded to nitric acid (D 1.5), the temperature being kept below loo.After fifteen minutes the liquid was poured on crushed ice, and theprecipitate crystallised from dilute alcohol. The substance crys-tallises in pale yellow needles, melting at 71-72O:0.2910 gave 19.3 C.C. N, at 25O and 77.0 mm.C,H,O,N requires N=7.65 per cent.The Ethyl Ether of 5-Nitrocoumam'c Acid.-5-Nitro-2-ethoxybenz-aldehyde (5 grams), anhydrous sodium acetate (5 grams), and aceticanhydride (15 grams) were boiled together for six hours. Thecooled product was ground with water and extracted several timeswith ether.The ethereal extract was shaken with a solution ofsodium carbonate, and the aqueous solution so obtained treatedwith an excess of hydrochloric acid, when a white precipitate wasformed, which crystallised from dilute alcohol in colourless needles,melting at 194-195O :N=7*54.0.1766 gave 0.3622 CO, and 0.0780 H,O. C = 55.94 ; H = 4.91.0.2288CllH,,O,N requires C = 55.70 ; H = 4.64 ; N = 5-91 per cent.The Ethyl Ether of Silvcr 5-Nitrocoumnrate.-The ethyl ether of5-nitrocoumaric acid (10 grams) was dissolved in an aqueous solutionof sodium hydroxide (1.7 grams)? and a solution of silver nitrate(7.2 grams) then added, when the silver salt was precipitated as analmoat colourless, gelatinous mass :,, 12.0 C.C. N, at 25O and 762 mm.N=5-87.0.3620 gave 0.1132 Ag. Ag=31*27.C,,H,oO,NAg requires Ag = 31.40 per cent.The Ethyl Ether of Methyl 5-Nitrocoumarate.-The ethyl etherof silver 5-nitrocoumarate (1 gram), methyl iodide (0.5 gram), anda little ether were heated together at looo for three hours. Afterevaporating the ether from the product, the residue was extractedwith alcohol, from which solvent colourless needles, melting at141-14Z0, were obtained :0-1174 gave 0-2458 CO, and 0.0536 H,O.0.1624 ,, 8.4 C.C. N, at 25O and 764 mm. N=5*80.C=57*10; H=5*07.CI2Hl30,N requires C = 57.37 ; H = 5.18 ; N = 5.58 per cent2110 PATTEltSON AND STEVENSON : INFLUENCE OF SOLVENTSThe Bromine Additive Products.Methyl a~-Dib~~omo-5-nitro-2-met?~oxy-~-phercylln.opite, - Themethyl ether of methyl 5-nitrocoumarate (1 molecule) was dissolvedin carbon disulphide, and treated with bromine (2.5 molecules).After twelve hours the liquid was evaporated, and the residuecrystallised from alcohol. Colourless needles, melting at 126O, wereobtained. The same product resulted when the methyl ether ofmethyl 5-nitrocoumarinate was treated in a similar manner :0.1498 gave 0.1834 CO, and 0.0400 H,O.0.38060.1460 ?, 0.1380 AgBr. Br=40*22.C= 33.39 ; H = 2.97.,, 11-5 C.C. N2 at 25O and 770 mm. N23.44.C,,H,,0,NBr2 requires C = 33-25 ; A = 2.87 ; N = 3.53 ;B r = 40.30 per cent.Methyl a/3-Bibromo-5-nitro-2-ethoxy-/3-phenyZpropiomte. - Thiscompound was prepared from the ethyl ether of methyl 5-nitrecoumarate and bromine by the method described in the precedingexperiment, and also by a similar treatment of the ethyl ether ofmethyl 5-nitrocoumarinate. The substance crystallises from alcoholin colourless needles, melting at 125O:0*3010 gave 0-2760 AgBr. Br = 39.02.0-4020 ,, 12-5 C.C. N, at 25O and 770 mm. N=3*53.CI2Hl30,NBr2 requires N = 3-41 ; Br = 38.93.The author desires to express his thanks to the Research FundCommittee of the Chemical Society for a, grant which has in partdefrayed the expense incurred during this research.ROYAL COLLEGE OF SCIENCE, IJONDON.SOUTH KENSINGTON, S. W