この論文は国立情報学研究所の学術雑誌公開支援事業により電子化されました。Levopimaric acid (I), palustric acid (II), neoabietic acid (III), and abietic acid (IV) isomerized in chloroform, and rapidly approached to an equilibrium state under nitrogen atmosphere in the dark (92% abietic acid (IV), 5% palustric acid (II), 3% neoabietic acid (III), but the resin acids dissolved in a-pinene or octyl alcohol did not isomerize in the absence of air. Abietic acid (IV) gave dehydroabietic acid (V) and some complex oxidation products when kept in chloroform in the presence of air. The resin acids as well as apinene used as solvent were oxidized in the dark, but not oxidized in octyl alcohol even in the presence of air oxygen. Homoannular dienes, such as palustric acid (II) and levopimaric acid (I), yielded dehydroabietic acid (V) on oxidation, but heteroannular dienes, such as abietic acid (IV) and neoabietic acid (III), yielded only oxygen adducts, but not dehydroabietic acid (V). Levopimaric acid (I) was presumed to be the precursor in the biosynthesis of palustric acid (II), neoabietic acid (III), abietic acid (IV) and dehydroabietic acid (V)

ENOKI, Akio

Kyoto University Research Information Repository

Title Isomerization and Autoxidation of Resin AcidsAuthor(s)ENOKI, AkioCitationWood research : bulletin of the Wood Research Institute KyotoUniversity (1976), 59/60: 49-57Issue Date1976-03-31URL http://hdl.handle.net/2433/53442RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityIsomerization and~ Autoxidation of Resin AcidsAkio ENOKI*Abstract--Levopimaric acid (I), palustric acid (II), neoabietic acid (III), and abie-tic acid (IV) isomerized in chloroform and rapidly approached to an equilibrium state undernitrogen atmosphere in the dark (92% abietic acid (IV), 5% palustric acid (II), 3% neoa-bietic acid (III), but the resin acids dissolved in a-pinene or octyl alcohol did not isomerizein the absence of air. Abietic acid (IV) gave dehydroabietic acid (V) and some complex oxi-dation products when kept in chloroform in the presence of air. The resin acids as well as a-pinene used as solvent were oxidized in the dark, but not oxidized in octyl alcohol even in thepresence of air oxygen. Homoannular dienes, such as palustric acid (II) and levopimaric acid(I), yielded dehydroabietic acid (V) on oxidation, but heteroannular dienes, such as abieticacid (IV) and neoabietic acid (III), yielded only oxygen adducts, but not dehydroabietic acid(V). Levopimaric acid (I) was presumed to be the precursor in the biosynthesis of palustricacid (II), neoabietic acid (III), abietic acid (IV) and dehydroabietic acid (V).IntroductionIt has been known that resin acids isomerized in the presence of strong acids1 ,2)or with heat3) and readily absorb air-oxygen, especially in the powder form4).It has been previously observed in our laboratory that resin acids in the chloro-form solution are oxidized or isomerized easily to some complex compounds evenwhen they are kept at room temperature in the dark. Subsequently we havestudied on the mechanism and the reaction products in autoxidation of resin acidshaving conjagated double bonds. The reaction proceeded easily without using asensitizer under day-light and the main products were dehydroabietic acid (V)and transannular peroxide5- 7).The purpose of the present work is to investigate the isomerization and oxida-tion products of resin acids in the solutions of chloroform, a-pinene, and of octylalcohol when the reaction proceeds in the dark under air-oxygen atmosphere.ExperitnentalOptical rotations were measured by using a ]ASCO DIP-SL polarimeter.NMR spectra were measured by using a Hitachi R-22 spectrometer (90 MHz) inCDCb and TMS as the internal standard. Mass spectrography was conducted byusing a SHIMAZU-LKB 9,000 gas chromatograph-mass spectrometer.* Division of Wood Chemistry- 49-WOOD RESEARCH No. 59/60 (1976)Preparation of starting substancesPalustric acid was prepared from pine gum b>,: the method of Joye et at. S) [aJo+70°; m.p. 162"" 166°C; ),~~~Hnm ($): 265 (8600). Neoabietic acid (III) wasobtained from pine gum by amine salt technique of Loeblich et at. g); [aJo +159°;m.p. l66""169°C; ),~~<iHnm: 252. Levopimaric acid (I) was isolated from freshpine oleoresin by the amine salt method of Loeblich et at. m ; m.p. 150"" 151°C; [aJo-275°; ),~~<iH nm ($); 273 (7200). Abietic acid (IV) was prepared from commercialrosin by the amine salt method of HarrislD ; [aJo-llOo; m.p. 170"" 173°C; ),~~<iH nm($): 241 (23000). Dehydroabietic acid (V) was isolated from the commerciallydisproportionated rosin by the amine salt method using 2-amino-2-methyl-l-propanol;[aIn+ 163°; m.p. 171°C. Methyl esters of the acids were prepared by esterificationwith diazomethane.Isomerization of resin acidsa) Changes in specific rotation during isomerization of resin acidsResin acid (50 mg) was dissolved in 5 ml of chloroform (spectroscopy-grade)containing 1 % ethanol, a-pinene, and octyl alcohol respectively in a polarimeter tube.The air in the tube was completely replaced by nitrogen and the tube was sealed.The tube was kept in the dark at 25°C and readings were taken occasionally.b) Chqnges in NMR spectrum during isomerization of resin acidsResin acid (100 mg) was dissolved in 10 ml chloroform containing 1 % ethanolat 25°C. The aliquots were taken out at intervals and the solvents were removed invacuo. The samples were submitted to NMR measurement. The vinyl protonsof abietic acid (V) appeared at 5.78 ppm (IH, s) and at 5.37 ppm (IH, broad). Thevinyl protons of levopimaric acid (I) appeared at 5.53 ppm (lH, s) and at 5.13 ppm(IH, broad). Only one vinyl proton in palustric acid (II) appeared at 5.38 ppm(lH, s). That of neoabietic acid (III) appeared at 6.20 ppm (lH, s). For quan-titative determination of the component acids present in the resin acid, the respectiveareas of the vinyl proton signals were used throughout of this experiment. Ten mili-gram resin acid was dissolved in deuterated chloroform (0.5 ml) in a NMR tube.After the air was completely replaced by nitrogen, the tube was sealed and keptin the dark at 25°C and then the NMR spectra of the solution were measured atintervals.Autoxidation of resin acidsa) GC-Mass spectra measurementMethyl ester of resin acid (20 mg) was dissolved in 20 ml of chloroform con-taining 1 % ethanol, a-pinene, and octyl alcohol respectively and kept in the darkwith occationaI aeration. The aliquots were uptaken occasionally for GC-Mass- 50-ENOKI: Isomerization and Autoxidation of Resin Acidsspectra measurement (5 % SE 52 on Chromosorb W at 25°C; 5 % Versamide-900on Chromosorb W at 250°C). Peak assignment was verified by use of purifiedresinacids specimens. The area of a signal was compared with that of a standardspecimen for quantitative purpose.b) Preparative layerchromatographyResin acid was dissolved in one liter of the solvents (a-pinene, spectroscopy-grade chloroform containing I % ethanol, and octyl alcohol) and kept in the darkwith occational aeration. The aliquots were taken at intervals and the solvent wasremoved zn vacuo. The residue was esterified with freshly prepared diazomethaneand was submitted to preparative layer chromatography on Merk silicagel PF-254by using cyclohexane-ether (3 : 2) as solvent and on silica gel containing 5 % AgNOsby using cyclohexane-ether (20 : I). The products were isolated with ether from thecorresponding silica gel layer.The composition of resin acids of raw oleoresinRaw oleoresin was collected from Japanese black pine (Kuromatsu, Pinus Thun-bergii) by inserting a glass tube with a receiver through the bark. Th fresh oleo-resin was immediately subjected to preparative layer chromatography to obtainthe fraction containing pure resin acid (Merk silica gel PF-254, cyclohexane-ether,(20 : I)). The resin acid mixture was analyzed by MNR. Dehydroabietic acid(V) and neoabietic acid (III) were able to be determined without being disturbedby the presence of other resin acids. Abietic acid (IV), levopimaric acid (I) andpalustric acid (II) were roughly estimated although a small amount of pimaricacid ""as present as a contaminant. While this method can afford only appro-ximate estimation, the error due to isomerization is believed to be low.Results and DiscussionFrom the changes in specific rotation and of NMR spectra it turned out thatlevopimaric acid (I), neoabietic acid (III), and palustric acid (II) begin to isome-rize after a certain time (I 6 hours, II 80 hours, and III 7 hours) and rapidlyapproach to an equilibrium state when these resin acids were dissolved together inchloroform and allowed to stand in the dark under nitrogen atmosphere (Fig. I, 2,3, and 4). It was found by means of NMR and GC-mass techniques that the equi-librium mixture of the resin acids consists of 92% abietic acid (IV), 50/0 palustricacid (II), and 3% neoabietic acid (III) (Fig. 1,5). These conjugated dienoic resinacids showed the phenomena similar to those described above even in chloroform-D(CDCh), as in spectroscopy-grade chloroform. When dissolved in chloroform con-taining a very small quantity of hydrochloric acid (about 7 ppm), these resin acids- 51-WOOD RESEARCH No. 59/60 (1976)immediately began to isomerized. By stopping the isomerization at adequateintervals and analyzing the products with GC-Mass and NMR, either levopimaricacid (I) or neoabietic acid (III) in chloroform was found to isomerize to abietic acid(IV) through palustric acid (II). But it failed to confirm the isomerization ofneoabietic acid (III) to palustric acid (II) through levopimaric acid (I). Since thevelocity of isomerization of levopimaric acid (I) to palustric acid (II) was very rapidthan that of neoabietic acid (III) to levopimaric acid (I), the presence of levopimaricacid (I) as an intermediate was impossible to identify by means of NMR or GC-Massalthough a part of neoabietic acid (III) is suspected to be isomerized to palustricacid (II) through levopimaric acid (I).6 5 ppmFig. 1. NMR spectra: A, levopimaric acid; B, neoabietic acid; C, palustric acid;D, abietic acid; E, levopimaric acid isomerized and aproached an equilibriumin CHCh. Also neoabietic acid, palustric acid and abietic acid apporachedan equilibrium state and gave the same spectra as E.-0200o CHCI,• CHCI, contains 7ppm HCI32 hr.I!I \ --~~-"'~----~--B-O'OOI~V- , , ,4 8 12 16 20 24 28Fig. 2. Changes in rotations during the isomerization of levopimaric acid(0.33 X 10-4 M) in CHCI3•52 ~ENOKI: Isomerization and Autoxidation of Resin Acids+0.100o-0.100o : CHCI!• : CHCI! contoins7ppm HCIhr. 20 40 60 80 100 120 140+0.100o-0.100o : CHCI!• : CHCI! contoins 7ppm HCI! I I I ! I20 25 30 35 40 45 50Fig. 3. Changes in rotations during the iso-merization of palustric acid (0.33 X1O-4 M) in CHCh.Fig. 4. Changes in rotations during the iso-merization of neoabietic acid (0.33 X10-4 M) in CHCI3 •Methyl esters of these conjugated dienoic acids in chloroform also isomerizedand approached to an equilibrium state.The methyl ester of abietic acid (IV) yielded the methyl ester of dehydroabie-tic acid (V) (300/0) and unknown oxidation products when kept in chloroform atSE 52 5%250"(;min. 4 6 8 10Fig. 5. Gass-liquid chromatogram: solid curve, methyl abietate kept in CHCl 3containing 1% EtOH for ten days in the dark under nitogen; dottedcurve, methyl abietate kept in chloroform containing 1 % EtOH for tendays under the air in the roomlight.- 53-WOOD RESEARCH No. 59/60 (1976)ISOMERIZATION IN CHCI 3I~~(),L:- . :: O"""ON 'N CH~A~/ crYI ~~.( I RIVii30%1( I ~ ~ +UnknownsRIN) (92%) 'RI][)(5%1 R=COOHFig. 6room temperature for ten days under room-light and air-oxygen (Fig. 5, 6).The methyl ester (IV), on the other hand, showed little changes even after thetime when kept in chloroform for ten days under nitrogen in the dark (Fig. 5).The resin acids (I), (II), (III), and (IV) also showed little changes when keptin octyl alcohol under nitrogen for ten days at room temperature in the dark. Theseresin acids showed neither isomerization nor oxidation when kept in octyl alcohol forten days in the dark and in contact with air.The resin acids (I), (II), (III), and (IV) and their methyl esters in a-pineneshowed little changes when kept at room temperature for ten days in the darkunder nitrogen. NMR and GC-Mass spectra of a-pinene in above condition alsoshowed little changes. Those acids were, however, suffered to oxidation withaeration in the dark (Fig. 7). Methyl palustrate gave methyl dehydroabietate inabout 50 % yield and the products absorbed oxygens when kept in a-pinene withaeration in the dark (Fig. 8). In the course of aeration, it was observed that a-pinene gradually absorbs oxygen and becomes more than 150 of molecular weight(MW of a-pinepe 136) in company with the oxidation of methyl palustrate (Fig.8). The oxidation products of a-pinene may be the same one with the productsobtained by Moore in the autoxidation of a-pinene as is shown in Fig. 912).Similarly methyl dehydroabietate (50 % yield) and unknown oxidation productswere obtained from levopimarate in a-pinene solution by aeration in the dark at~I OXYGEN-ADDUCTS,~ OXYDATION+ PRODUCTS ofo:.-plneneCOCH3 150%1det9~I h O2 OXYDATIONPRODUCTS of,I , ----> OXYGCN-ADDUCTS, o(-plneneCOCH3 COCH3 t£JFig. 7. Autoxidation of resin acids in a-pinene.- 54-ENOKI: Isomerization and Autoxidation of Resin AcidsSE-52 5%250"(mIn. 4 5 8Fig. 8. GC-Mass chromatogram: --, methyl palustrate kept in a-pinene in thedark with earation for zero day; - - -, kept for 8 days; - • -, kept for14 days.dJ ~ tb~ cl)'o; uSol.-pinene (VI) IVllI IVIIlI~OOH OXYDATIONc:bJ ---> PRODUCTS(IX)Fig. 9. Autoxidation of a-pinene in the dark12).25°C. Methyl abietate and methyl neoabietate in a-pinene also absorbed oxygen onaeration in the dark gave a mixture of complex oxidation products, but no methyldehydroabietate (Fig. 7).Methyl dihydroabietate (MW 318) was not detected Ry GC-Mass spectra ofthe resin acids oxidaized with air-oxygen in the presence of a-pinene or chloroform.Both the transannular peroxides of the resin acids and other products which areformed through the peroxides5- 7) were not detected by TLC or NMR spectra ofthe oxidation products.It is thought that the degradation products liberated by the interaction betweenresin acids and chloroform catalyze the isomerization of conjugated dienoic resinacids from the following facts. (a) The appearance of the isomerization productsof resin acids needed a certain lag time but a very small quantity of acid caused im-mediately isomerization. (b) When the solution of chloroform (lOml) containingabietic acid (IV) (200mg) was kept for ten days in contact with air at 25°C and then- 55-WOOD RESEARCH No. 59/60 (1976)the solution was shaken with distilled water (2 mg), the PH of the water layer wasabout 3. But when only chloroform was exposed under the same condition, thePH of the aqueous layer was about 7.Following observations indicate that dehydroabietic acid (V) is yielded by hy-drogen abstraction from homoannular dienoic resin acid like palustric acid (II) orlevopimaric acid (I) on the autoxidation in chloroform. (a) The conjugated die-noic acids did not isomerize each other in a-pinene in the presence of air-oxygen.(b) Heteroannular diene like abietic acid (IV) or neoabietic acid (III) gave oxi-dation products which absorbed oxygen, but did not yield dehydroabietic acid (V)(Fig. 7). (c) In chloroform, either heteroannular diene or homoannular dieneisomerized and reached the same equilibrium state, and methyl abietate, hetero-annular diene, yielded methyl dehydroabietate as one of the oxidation productsIII the presence of air.Following facts mean that, in the oxidation of the resin acids in a-pinene, a-pinene is initially oxidized, and then the resulted oxidation products of a-pineneoxidize the resin acids. When the resin acids were kept in octyl alcohol in thedark in the presence or absence of oxygen, both the solvent and the solute showedlittle changes. When the resin acids were kept in a-pinene in the absence of oxygenin the dark, both the solvent and the solute showed little changes. But the resinacids were oxidized in company with a-pinene when the acids were kept in a-pineneIII the presence of oxygen.The following observations indicate that levopimaric acid (I) is the precursorof palustric acid (II), neoabietic acid (III), abietic acid (IV) and dehydroabieticacid (V) in Japanese black pine (Kuromatsu, pinus thunbergii) (Fig. 10). (a) Tablel, 2, Fig. land 4 show that levopimaric acid (I) readily isomerizes to the doublebond isomers with heat or acid. (b) Levopimaric acid (I) is the major componentof resin acids in the raw oleoresin (Table 1, 2). (c) The raw oleoresin containsthe great amounts of a-pinene. (d) Levopimaric acid (I) is readily oxidized todehydroabietic acid (V) in a-pinene in the presence of oxygen. (e) The equilib-rium mixture of the resin acids consists of a great deal of abietic acid (IV), smallamounts of palustric acid (II) and neoabietic acid (III).Although methyl dehydroabietate (MW 314) was yielded, it is believed thatdisproportionation of the resin acids did not occur because methyl dihydroabietateFig. 10- 56-ENOKI: Isomerization and Autoxidation of Resin AcidsTable 1. Composition of rosin products4).Pimaric+isopimaricacid %Neoabietic+ I Dehydroabietic+ Ipa1ustric+ hydroabieticabietic acid % acid %ILevopimaric acid I%Fresh oleoresin 30-50 30-50 trace 16-30Gum rosin 0-15 65-85 trace 15-30Wood rosin less than 1 about 50 15-25 16Tall oil rosin less than 1 about 40-50 20-30 16-30Table 2. Composition of resin acids of raw oleresin.Levopimaricacid %Neoabietic acid%,Dehydroabietic I Abietic acid : Pa1ustric aCidl Piamric acidacid % I % % %__5_0 8__11...__8 _--l..1__11_--:..[ 1_6_ ...1__7__(MW 318) was unable to detect.In the present conditions, the reaction of resin acids with singlet oxygen to givetransannular peroxide is very unlikely because any of the peroxide, the correspond-ing diepoxide, hydroxy-ketone and epoxyketone were not detected. Therefore,the oxidation reaction of the resin acids would be proceed by only a radical chainmechanism caused by radicals of a-pinene.Referenc'es1) P. F. RICHIE and 1.. F. McBURNEY, J. Am. Chern. Soc., 71, 3736 (1949).2) P. F. RICHIE and 1.. F. McBURNEY, J. Am. Chern. Soc., 72, 1197 (1950).3) H. TAKEDA, H. KANNO, W. H. SCHULLER and R. V. Lawrence, I & EC Product Research andDevelopment, 70, 86 (1968).4) P. W. SANDERMAN, "Naturharze Terpentino1 Tallo!", Springer-Verlag, Berlin (1960).5) A. ENOKI and K. KITAO, Mokuzai Gakkaishi, 20, 34 (1974).6) A. ENOKI and K. KITAO, ibid., 20, 600 (1974).7) A. ENOKI and K. KITAO, ibid., 21, 101 (1975).8) N. M. JOYE, Jr., V. M. LOEBLICH and R. V. LAWRENCE, J. Org. Chern., 30, 654 (1965).9) V. M. LOEBLICH and R. V. LAWRENCE, J. Org. Chern., 21, 610 (1956).10) V. M. LOEBLICH, D. E. BALDWIN, R. T. O'CONNOR and R. V. LAWRENCE, J. Am. Chern. Soc.,77, 6311 (1955).11) G. C. HARRIS and T. F. SANDERSON, J. Am. Chern. Soc., 70, 334 (1948).12) N. MOORE, C. GOLUMBIC and G. S. FISHER, J. Am. Chern. Soc., 78, 1173 (1956).- 57-

Isomerization and Autoxidation of Resin Acids

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Isomerization and Autoxidation of Resin Acids

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