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Proceedings of the Chemical Society. August 1963 |
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Proceedings of the Chemical Society ,
Volume 1,
Issue August,
1963,
Page 229-252
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PROCEEDINGS OF THE CHEMICAL SOCIETY AUGUST 1963 PRESIDENTIAL ADDRESS* Contributions of X-RayAnalysis to Natural-product Chemistry By J. MONTEATH ROBERTSON THEincreasing power of the X-ray method as a means of solving molecular structures is now so well known that I feel it is hardly necessary for me to stress it. During the past four years my own group in Glasgow have determined the complete structure and stereochemistry of well over 20 natural products from various sources whose chemical constitution was hitherto either unknown or only partially known. Many other laboratories throughout the world are now likewise engaged on work of this kind and tremendous progress is being made. To mention only a few A. McL. Mathieson in Australia Maria Przybylska in Canada R.Pepinsky and others in the United States and the laboratories of Professor A. J. C. Wilson here in Cardiff have all made out- standing contributions to this field. I would also refer particularly to the beautiful work on the ex- tremely complex molecules of the vitamin B, group that has been carried out in the laboratories of Dorothy Hodgkin in Oxford and which has initiated a whole new field of chemical research. In the case of several even more complex biological molecules in- cluding some of the globular proteins exciting pro- gress has recently been made and complete solutions for some of these are now in sight. It would not be either possible or appropriate for me to attempt a survey of this whole field in the time that is available.Instead I propose to confine myself to a few results that have been obtained recently in my own laboratories in Glasgow. Because of the close and helpful collaboration of a number of organic chemists it has been possible to choose structures that have been important in adding to our knowledge in the natural product field &Ray crystal analysis is a powerful and often an essential tool in chemistry but I am convinced that the fullest use of the potentialities that now exist can only be achieved by means of such collaboration between chemist and crystallographer. For the crystallographer it is often unrewarding just to take a crystal from a bottle and try to deter- mine its structure. This is all very well as an exercise in crystallography but it may not add greatly to knowledge.For the chemist it may be equally un- profitable to spend years in trying to elucidate a structure when the solution may sometimes be obtained more quickly and directly by X-ray analysis. Before I describe these structures I would like to outline very briefly the methods which have made work of this kind possible. It is well known that the central problem in X-ray analysis is that of deter- mining the relative phases of the diffracted waves. Intensity measurements provide the amplitudes but not the phases. During the last 20 years many attempts have been made to solve structures from a knowledge of the amplitudes alone and this mathe- matical approach has led to many valuable results.But when the number of atoms is considerable the complexity of the problem is usually too great even with the aid of fast electronic computers. * Delivered at the Anniversary Meeting of the Chemical Society at Cardiff on March 28th 1963. 229 The methods that have proved effective in solving most of the very complex organic structures in- cludmg some of the protein molecules depend upon a chemical rather than a physical or mathematical approach and this is why it is appropriate that I should mention them here They are the heavy-atom f" b FIG 1 Superposition of waves and isomorphous-substitution methods which were first developed and applied to organic structures during the 1930s starting with Linstead's phthalo- cyanine compounds Once again this represented a fruitful and most important collaboration between PROCEEDINGS ference to give a resultant F of known amplitude but unknown phase If a centre of symmetry is present the phase may be represented by either a peak or a trough at a fixed reference point as in the diagram We now perform a chemical experiment and add another atom at this point preferably an atom con- taining a good many electrons We also assume that the new atom will not disturb the remainder of the structure to any large extent The contribution of this atom is represented by the dotted peak f, and the resultant amplitude given by the heavy-atom deriva- tive is FH We can only measure amplitudes but by noting whether the resultant FH increases or de-creases we can determine whether the original ampli- tude F was a peak or a trough We have thus trans- formed the unknown differences in phase which cannot be measured into amplitude differences which can be measured This is the principle of the isomorphous-substitu- tion method If the conditions are rigorously ful- filled and if accurate intensity measurements can be made we can always determine the unknown phases The phthalocyanme structures shown in Fig 2 as electron-density projections of the metal-free and nickel compounds provided an almost perfect example and these complex structures were deter- ._..-FIG 2 Electron-density projection of metal- free and nickel phthalocyanine chemist and crystallographer (An earlier application mined in this way without any chemical assumptions of isomorphous substitution to inorganic alum struc- and indeed without even assuming the existence of tures by Cork in 1927 did not lead to very conclusive atoms in the molecules results ) However very few structures and especially very The prmciple of this method is illustrated in Fig 1 few natural-product structures show the high degree The waves scattered by the atoms in the unknown of isomorphism and symmetry displayed by the structure combine by the principles of optical inter- phthalocyanines But the simple heavy-atom method Robertson J 1935 615 1936,1195 Robertson and Woodward J ,1937,219 AUGUST 1963 developed at the same time has a wider application although it is less exact.We now assume no sym- metry and merely suppose that the heavy atom or some group of heavy atoms can be attached to the structure by any convenient chemical method. It will then usually be possible to find the position of this small group in space by a simple application of the Patterson method and so calculate its contribution to the structure amplitude. As we are not assuming any symmetry it is now convenient to represent the vector equation by a diagram in the complex plane (Fig. 3a). Frepresents the contribution of the un- known part of the structure and the end of this vector may lie anywhere on the circumference of the white circle. f' is the known or calculable contribu- tion of the heavy atom or atoms and we assume this vector to be completely known.The addition offH 231 ture factor IF[ from a group of about 34 randomly placed carbon atoms with a heavy-atom contribution If~l from a single bromine atom. An iodine atom would be equally effective for a random group of about 78 carbon atoms whereas a chlorine atom would only suffice for a group of about 8 carbon atoms on this basis. However the heavy-atom con- tribution will in general be somewhat more effective than is indicated by this calculation which does not take account of variation of scattering power with angle of incidence. Furthermore the phases of the very large number of structure factors of less than average magnitude will in general be more effectively determined. iff^ is larger (or F relatively smaller) the effect on our diagram is to move the shaded circle to the right (Fig.3b) with the phases of F' now more closely restrained to those off'. On the other hand iff^ is smaller (or Frelatively larger) the effect is to move the shaded circle to the left (Fig. 3c) and now the approximation is worse with some of the phases of I;B very much in error. Such difficulties may be lessened by the use of a weighting function for the Fourier terms based on the probable magnitudes of the phase-angle errors as discussed by sin^.^ If the heavy-atom derivative (Fir) is isomorphous with the parent compound and if accurate measure- ments can be made then the more powerful method of isomorphous substitution may be used equally well in the asymmetric case although there are some complications.Here we may assume as before that f~ is completely known representing perhaps the difference in scattering power of two successively substituted heavy atoms or groups of such atoms. With f' completely known but only the magnitudes 13'1 and IFa 1 there are two solutions for F in the = F +f~, as Bijvoet4 has shown. These are indicated in Fig. 4 at the points of inter- vector equation 3"' to I; gives the structure factor of the heavy-atom derivative FH and the end of this vector is now constrained to lie somewhere on the circumference of the shaded circle. We see therefore that the phases of the structure factors of the heavy-atom derivative (FH)are restricted to a considerable extent by the known and calculable phases of the heavy atoms themselves CfH).By merely assigning these phases to the structure factors F' we are therefore usually able to obtain a first very rough approximation to the structure of the heavy-atom derivative. This can later be refined as further recognisable atoms are included in the phasing calculations. Fig. 3a assumes that If'[ is equal to IFI. This would be approximately true for the average struc- section of the two circles at Uand V. FIG.4. lsomorphous substitution showing two solu- tions for F in the asymmetric case. It is now possible to proceed by employing both values of F. In this case it can be shown that the result is equivalent to the heavy-atom method but Patterson Phys.Rev. 1934,46 372; 2.Krist. 1935,90 517. Sim in "Computing Methods and the Phase Problem in X-ray Crystal Analysis," ed. Pepinsky Robertson and Speakman Pergamon Press Oxford 1961 p. 227. Bokhoven Schoone and Bijvoet Actu Cryst. 1951 4 275. PROCEEDINGS with a very advantageous weighting factor attached to the structure amplitudes.6 However a complete solution can be obtained if a third isomorphous derivative is available. This double isomorphous-replacement method has been outlined by Bokhoven Schoone and Bijvoet4 and very fully discussed by Harker.6 It is of great im- portance for by this means very direct solutions of some of the complex protein structures are now being achieved. Returning to our diagram let us now suppose that another isomorphous heavy-atom derivative is avail- able with structure factors F“ and a known heavy- atom contributionf~’.With centre at the end of the -fHpvector we now describe a third circle (Fig. 5) of radius IFH?1. The point of intersection of the three circles (U) now defines the end of the F vector uniquely. If the isomorphism were perfect and all measurements could be made with sufficient accuracy this method would yield solutions as com- plete and direct in the asymmetric case as those obtained for the phthalocyanines in the centrosym- metric case. In practice there are of course many difficulties and only rarely will such a set of closely isomorphous derivatives be available. It is also diffi- cult to carry out the many structure-factor measure- ments that are involved with a sufficient degree of accuracy.Instead of the clean intersection of the three circles shown in Fig. 5 we are therefore more FIG. 5. Double-isomorphous substitution. likely to obtain a scatter of points and the best value for the phase angle has to be assessed on a prob- ability basis. For the smaller natural-product molecules with which we are concerned the attachment of a heavy atom usually causes a considerable change in the overall crystal structure. It is therefore difficult to find a suitable series of isomorphous derivatives with 6 Sim ref. 3 p. 315. * Harker Acta Cryst. 1956 9 1. crystal structures sufficiently similar. However for some of the very complex protein molecules it is fortunately possible to prepare a considerable number of isomorphous heavy-atom derivatives.The attachment of one or two heavy-metal atoms to these giant molecules may not affect the overall crystal structure to any appreciable extent but it is sufficient to cause measurable intensity changes in the diffraction spectra as Perutz’ has shown in the case of hzmoglobin. For the structure of myoglobin to a resolution of 24 A Kendrew and his co-workers8 employed a series of no less than five isomorphous heavy-atom derivatives and a total of some 48,000 reflections were measured and analysed. For these molecules it is therefore possible to apply the iso- morphous-substitution method at its full power and with the same directness as in the case of the original ph t halocyanine structures .With the more usual natural-product molecules that we now describe the heavy-atom method already outlined must generally be used and this is usually successful if a single really suitable derivative can be found. Difficulties and ambiguities often occur depending on the particular symmetry that may be present but instead of struggling with these it is usually better policy to search for another more suitable derivative. Owing to the partial and incom- plete nature of the phase determination the first electron-density distributions are often hard to interpret. But if a few recognisable atoms can be found and included correctly in a further set of phasing calculations the picture generally clears and can then be refined and made more accurate by further application of the powerful Fourier tech- nique.I now wish to illustrate these methods by describ- ing some of our recent results in the natural-product field. For this purpose some of my favourite struc- tures are alkaloids where the ionic nature of the heavy atom halides often ensures a comparatively rigid and consequently well resolved molecule. How- ever Dr. Sim has already described a number of these structures in a paper to one of the Symposia so I propose to confine my illustrations to some of the terpenoids bitter principles and a few other mole- cules. I am indebted to a number of organic chemists for providing these interesting problems but particularly to Professor Barton who has supplied most of them.In the terpenoid field we have made quite a number of studies beginning with /3-caryophyllene alcoholg (I) and one of its curious dehydration products iso- Green Ingram and Perutz Proc. Roy. Soc. 1954 A 225,287. * Kendrew Dickerson Strandberg Hart Davies Phillips and Shore Nature 1960,185,422. Robertson and Todd J. 1955 1254. AUGUST 1963 233 cloven&O @I), whose structure was previously quite unknown. The conversion of the alcohol into iso- clovene presents an unusual problem in mechanism which is not yet fully understood and which calls for further chemical work. Although the X-ray method is extremely powerful in elucidating structures the result very often as in this case does not end the problem but merely indicates the need for further chemical investigation.Another sesquiterpenoid whose structure has to be revised as a result of our X-ray work is a-santonin (IV). The reversal of the accepted configuration at position 11 first became apparent in Asher and Sim’s studyll of the stereochemistry of isophotosantonic lactone which was defined by the complete three- dimensional analysis of 2-bromodihydroisophoto- a-santonic lactone acetate (III). Superimposed sections of the electron-density distribution which define the stereochemistry are shown in Fig. 6. Barton’s work12 showed that inversion of configuration at position 11 does not occur during the conversion of santonin FIG. 6 Electron-density distribution in bromodi-hydroiso- a-photosantonic lactone acetate.into this derivative and this was confirmed by Asher and Sim’s later study13 of 2-bromo- a-santonin itself. To obtain still further evidence we are now engaged at the suggestion of Professor Cocker on an analysis lo Clunie and Robertson. J.. 1961. 4382. of the 2-bromo-desmotropo-santonins(V) but this work is still in progress. Earlier work by Barton and Levisallesf4 had established the constitution of the related sesquiter- penoid lactone geigerin (VI) and here the stereo- chemistry has been confirmed and made fully quanti- tative (VII) by the beautiful three-dimensional X-ray analysis of Hamilton McPhail and Sim,15 which is illustrated in Fig. 7. AcO Bt (VII) In the diterpenoid series the stereochemistry of gibberellic acid (VIII) has now been established by the complete X-ray analysis of methyl bromogib- berelate (IX) by McCapra Scott Sim and Young.16 The stereochemistry of cafestol (X) has also now been revised by their similar analysis1’ of a bromo- l1 Asher and Sim,Proc.&em. Soc. 1962 11 1. l2 Barton Miki Pinhey and Wells Proc. Chem. SOC.,1962,151. l3 Asher and Sim,Proc. Chem. Soc.,1962 335. l4 Barton and Levisalles J. 1958 4518. l6 Hamilton McPhail and Sim,J. 1962 708. l6 McCapra Scott Sim and Young Proc. Chem. SOC.,1962 185. l7 Scott Sim,Ferguson Young and McCapra J. Amer. Chem. SOC.,1962,84 3197. PROCEEDINGS f Iy FIG.7. Electron-density distribution in acetyibromogeigerin.Y .1 FIG.8. Electron-density distribution in bromoepoxy- norcafestanone. (Reproduced with permission from Scott Sim Ferguson Young and McCapra J. Amer. Chem. Soc. 1962 34 3197.) Is Sim and Sutherland unpublished results. lo Paul Sim Hamor and Robertson J. 1962,4133. derivative of epoxynorcafestanone (XI) which gives the well-defined electron density distribution shown in Fig. 8. Rosololactone has also been analysed as the dibromo-derivative (XII) by Sim and Suther- land.ls This work provides the stereochemistry shown in (XIII) and now establishes the position of the hydroxyl group. From these results and many related chemical studies a consistent picture of a tran~-anti-(9,IO)-backbone in the diterpenoids begins to emerge.I would now like to mention briefly our work on a number of bitter principles and the first two of these clerodin and cascarillin also belong to the diter- penoid series. Clerodin the bitter principle from Ciei-odendrun in fortcmnatirm was examined as the bromo-lactone (XIV) and with phasing based on the bromine atom the X-ray work established the con- stitution and stereochemistry of this derivative as shown in (XIV) and hence of clerodin as (XV). The X-ray workfs was carried out at a very early stage even before the correct molecular formula for clerodin was established but the number and kind of atoms in the molecule as well as the entire geo- AUGUST 1963 235 metry is shown clearly in the electron-density belonging to the triterpenoid family.The first of these distribution (Fig. 9). to be determined was limonin with an X-ray analysis based on the iodoacetate of epilirnonol. This was a major undertaking because both the prepara- tion of suitable crystals and the crystallography were difficult with two complete molecules in the asym- metric unit and 228 positional parameters to deter- mine. The electron-density distribution as finally analysed is shown in Fig. 10. It was a rewarding task however not only because of the interest of this structure but because of the number of other struc- tures that are now seen to be closely related. The structure and stereochemistry of limonin21 is shown in (XVIII) cedrelone22 in (XIX),and ged~nin~~ in ocpo & \ 0 Q Fi (xvlll) 0 OH (XIX) €3 D FIG.9. Electron-density distribution in clerodin I c brorno-lac tone. Our examination of the related bitter principle cascarillin kindly supplied by Dr. Halsall is not yet complete but the structure and stereochemistry of the iodoacetate of the acetal on which our work has been based appears to be as shown in (XVI) which would indicate that the structure of cascarillin is (XVII). This is closely related to the structure sug- gested by Halsall apd his co-workers.20 O&H HOIH OHC 1cH;co.o (XVO (XVII) We now come to a most interesting and important FIG.10. Electron-density distribution in epihonol series of bitter principles and heartwood constituents iodoacetate. Birtwistle Case Dutta Halsall Mathews Sabel and Thaller Proc.Chem. Suc. 1962 329. Amott Davie Robertson Sim and Watson J. 1961 4183. 22 Grant Hamilton Hamor Hodges McGeachin Raphael Robertson and Sim Proc. Chem. Soc. 1961,444. 23 Sutherland Sim and Robertson Proc. Chem. Suc. 1962 222. ocx).They were all determined as iodoacetates e.g., OMJ) with phasing based on the iodine atom. The results now show that they are all triterpenoids of the euphol type in different oxidation patterns gedunin being intermediate between limonin and cedrelone. The remaining problems whose solution I wish to describe all relate to important fungal metabolites with unusual and difficult structures. The constitu- tions of the first two of these the antibiotics fumagil- lin and griseofulvin were known and our X-ray work was directed towards elucidating the stereo- chemistry quantitatively.Fumagillin was studied by McCorkindale and SimeM as the p-bromobenzene- sulphonate of the tetrahydroalcohol degradation product (XXII). The electron-density distribution (Fig. 11) shows the whole structure very clearly. Further refinement is proceeding however to measure certain interesting features more accurately such as the internal hydrogen bonding between the tertiary hydroxyl group and the epoxide oxygen atom. FIG. 11. Electron-density distribution in the furnagillin cierivative (XXII). Griseofulvin the antibiotic metabolite of Penicil-lium patulum was analysed by Brown and Sim%as the 5-bromo-derivative with phasing on the 24 McCorkindale and She Proc.Chem. Soc. 1961,331. 26 Brown and Sim J. 1963 1050. 26 Baldwin Barton Bloomer Jackman Rodriguez-Hahn PROCEEDINGS bromine and the chlorine atom. The stereochemistry derived from this work is summarised in (XXIII). (XXI I I) Byssochlamic acid the characteristic metabolite of BpsochZarnys fulva and glaucanic and glauconic acids from Penicillium purpurogenum have been the subject of intensive chemical studies by Barton Sutherland and their Our X-ray work proceeded simultaneously and has resulted in a full determination of the constitutions and relative stereochemistries which are also in agreement with the chemical evidence except that in glauconic acid ocxv)the oxygen substituent at position 4 is in the opposite configuration to that which was suggested.A beautifully crystalline bis-p-bromophenyl-hydrazide of byssochlamic acid which belongs to the Y FIG. 12. Electron-density distribution in bysso-chlamic acid bis-p-bromopknylhydrazide. (Repro-duced with permission from Hamor Paul Robert- son and Sim Experientia 1962 18 352.) and Sutherland Experientia 1962 18 345. AUGUST 1963 tetragonal system was the subject of our first X-ray determinati~n.~' The large molecule provides a well- defined electron-density distribution (Figs. 12 and 13) from which structure (XXIV) for byssochlamic acid can be derived. P' Y '"40, W FIG. 13. Atomic arrangement corresponding to Fig. 12. (Reproduced with permission from Hamor Paul Robertson and Sim Experientia 1962 18 352.) Glauconic acid was analysed% in the form of the rather simpler m-iodobenzoate derivative (XXV ;R = m-IC,H,.CO,).This yielded the full structure and relative stereochemistry as shown. The atomic arrangement in this derivative and the conformation of the nine-membered ring are illustrated in Fig. 14. Finally the structures of atrovenetin and the related compound herqueinone have now been revised by the X-ray work of Paul Sim and Morrison.29 Atrovenetin the metabolite of Penicil- 237 iium atrovenetum was examined as the crystalline ferrichloride of atrovenetin orange trimethyl ether (XXVI). The crystal structure is complex and diffi- cult to refine but the results show that atrovenetin must now be represented by structure (XXVII) with the orientation of the ether ring reversed as com- FIG.14. Atomic arrangement in gfauconic acid m-iodobenzoate. pared to the earlier formulation. It also follows that the structure of herqueinone should now be repre- sented by (XXVIII) but the position of the methyl group may be at either R or R'. 0 (xxvr) (xxvrI) (XXVI 1 I) This account is only a very condensed summary of our work in these fields during the past four or five years. There has not been time to discuss at all fully the many points of vital chemical interest that emerge or to dwell upon the many difficulties and complexities of the crystal structure determinations 27 Hamor Paul Robertson and Sim,Experientia 1962,18 352. as Ferguson Sim and Robertson Proc.Chem. Suc. 1962 385. Paul Sim and Morrison Pruc. Chem. SOC.,1962 352. PROCEEDINGS and the various ways in which they have been over- parts in this work are given in the list of references. come. My object has been rather to present a brief In addition we have of course enjoyed helpful picture of what has been accomplished to illustrate co-operation and guidance from a very large number the potentialities of the method in the natural pro- of organic chemists not only from my own Depart- duct field. When I add that during the same period ment in Glasgow but from all over the country who we have also determined the structures and stereo- have suggested problems and prepared suitable chemistries of nine complex alkaloids the power of derivatives.the method will be apparent. Finally I would like to mention that the very In the terpenoid and fungal metabolite field my extensive numerical calculations involved were principal collaborator has been George Sim who performed mainly on the Glasgow University has been independently responsible for a great deal DEUCE computer and most of the programmes of the work that I have described. The names of our used were devised by Dr. J. S. Rollett and Dr. J. G. many:other collaborators who have played prominent Sime. COMMUNICATIONS The Nucleophilic Reactivity of Akoxide and Mercaptide Ions towards Hydrogen By J. F. BUNNETT and ENRICO BACIOCCHI OF CHEMISTRY PROVIDENCE, (DEPARTMENT BROWNUNIVERSITY R.I. U.S.A.) SODIUMTHIOETNOXDDE C2H,SNa was found by the transition state.When the C-H bond is largely Bunnett Davis and Tanidal to effect elimination broken as in formation of menthone enolate ion the from aa-dimethylphenethyl chloride (I; X = Cl) alkoxide is the stronger reagent whilst when the about ten times as fast as does sodium methoxide. C-H bond is but slightly sundered as in “nearly El” Similar observations have been made by other E2 eliminations the mercaptide is the more reactive. workers.2 These reactions were taken to be E2 A test of this hypothesis was to determine the PhCH,-CMe,.X + PhCH=CMe + PhCH,*CMe = CH EtS- MeO- rate ratio in elimination from structures (1) (11) tlli) (I) as a function of the leaving group X. On the eliminations,3 and EtS- was judged to be a stronger hypothesis formulated this ratio should decrease as nucleophile than MeO- towards hydrogen.X is changed to a poorer leaving group. Accordingly MeO-EtS-k(EtS-)/k( MeO-) A T-L-7 Temp. k (11)-(%I (111)-(%I 75.8” f .,..-A -.--k (11) (%I (111) (%) (11) (111) 6.5l 11*4l C1 -__. SMe2+ 29.6 2.28~ 70.3 29.7 2.46~ 5.6t 2-27 0.86 0-79 SO,.Me 113-5 4.40 x 94.4 5.6 -2x lo-’$ -100 -0 -0.05 V. small * Extrapolated to zero ionic strength. 1(I; X = SMe) is the main product. $ Slowness of reaction was shown to limit the formation of (11). However Stauffer4 showed that sodium thioeth- oxide in ethanol is much less effective than ethoxide in effecting the isomerisation of menthone to iso- menthone which presumably goes through an enolate-ion intermediate.The seeming contradiction between these observations finds interpretation in the hypothesis that the relative nucleophilicities of RS- and RO-reagents towards carbon-bound hydrogen depend on the degree of rupture of the C-H bond in kinetics and products were determined for EtS- and MeO--induced eliminations from the tertiary sul-phonium salt (I; X = SMe,+) and the sulphone (I; X = S02-Me) in methanol. SMe,+ is a somewhat poorer leaving group than C1,3 and SO,.Me is much poorer. Rates were measured photometrically and products determined by gas-liquid chromatography. Results are given in the Table. In fact there was a great change in the direction Bunnett Davis and Tanida J. Amer. Chem. SOC.,1962 84 1606. de la Mare and Vernon J.1956,41; Eliel and Haber J. Amer. Chem. SOC.,1959,81 1249. Bunnett Angew. Chem. Internat. Edn. 1962 1,225; Ingold Proc. Chem. SOC.,1962,265. Stauffer Sc.B. Thesis Brown University 1962. AUGUST 1963 anticipated. The mercaptide reagent is slightly less effective than the alkoxide in reaction with the sul- phonium salt and lags far behind in reaction with the sulphone. The extent of C-H breaking in the transition state or of nucleophile to hydrogen bond formation appears to be an important factor in-fluencing relative nucleophilicity towards hydrogen bound to carbon. 239 This research was supported in part by a grant from the Petroleum Research Fund administered by the American Chemical Society. Grateful acknow- ledgment is hereby made to the donors of this fund.One of us (E.B.) thanks the Italian National Research Council for a grant. (Received June 8th 1963.) The Total Synthesis of (-J-)-Clovene I. R. MACLEAN, By P. DOYLE W. PARKER and R. A. RAPHAEL (CHEMISTRYDEPARTMENT GLASGOW, THEUNIVERSITY W.2) THEtricyclic structure (=I) assigned to clovene? one of the acid rearrangement products of caryophyllene has now been confirmed by the following unam- biguous synthesis. The bicyclic acid2 (I) was trans- formed by the Amdt-Eistert method into the homo- logous ester (11) which was converted smoothly into a homogeneous lactone (111) m.p. 56-57" by treat- ment with selenium dioxide in acetic acid. Reduction of the lactone by lithium aluminium hydride gave the diol (IV) which was selectively oxidised to the hydroxy-ketone (V) by manganese dioxide.Oxida- tion of this ketone(V) by chromium trioxide followed by catalytic hydrogenation and esterification led to the saturated keto-ester (VI) which was converted into the ketal-ester (VII) by treatment with ethylene glycol. frhe great susceptibility of the allylic lactone (111) to hydrogenolysis precluded its conversion into the ketal (VI) by seemingly more direct routes.] The ketal-acid corresponding to (VII) was con- verted into the ketal-ketone (VIII) by treatment with ethyl-lithium and the derived diketone cyclised under strongly basic conditions to the tricyclic cyclo- pentenone (IX). Birch reduction of the last compound gave the corresponding saturated alcohol which was then oxidised to the crystalline sterically homo- geneous cyclopentanone; this was converted into the gemdimethyl homologue (X) by the standard methylation procedure involving the methylanilino- methylene blocking That this ketone possessed the stereochemistry as well as the carbon framework of clovene was shown by ozonolysis of its furfurylidene derivative whereby (f)-clovenic an-hydride (XI) m.p.76-78" was obtained. The infra- red spectrum of this material (in CClJ was identical with that of the anhydride (m.p. 50-51") obtained by oxidation of (-)-clovene.* ~~~~ Go (VIO (VII I) (XI) (XI0 Finally the ketone (X) was reduced with lithium aluminium hydride and pyrolysis of the carbonate of the resulting alcohol gave (f)-clovene (XII).This material when purified through the crystalline mix- ture of diastereoisomeric dibromides5 was indistin- guishable (Lr. n.m.r. mass spectra and g.1.c.) from the naturally derived f -)-clovene. We thank the Department of Scientific and Industrial Research (P.D. and 1.R.McL.) and the Salter's Institute (P.D.) for studentships. (Received June 13th 1963.) Aebi Barton Burgstahler and Lindsey J. 1954,4660. Murray Parker Raphael and Jhaveri Tetrahedron,1962 18 55. Birch and Robinson J. 1944 501. Gibson and Ruzicka Hdv. Chim.Am 1931 570. Lutz and Reid J. 1954 2265. PROCEEDINGS Heat of Ionisation of Water By J. D. HALE,R. M. IZATT,and J. J. CHRISTENSEN (DEPARTMENTS OF CHEMISTRY AND CHEMICAL ENGINEERING YOUNG UNIVERSITY BRIGHAM PROVO UTAH U.S.A.) THEclassical method of determining the standard heat of ionisation of water AH" has been to measure calorimetrically at 25" the heat of reaction of a strong acid with a strong base at a particular ionic strength and to correct this measured heat of reaction to infinite dilution by use of appropriate heat-of-dilution data.This procedure followed by several workers,l using AH data obtained in solu- tions of high ionic strength gives AH" values ranging from 13.27 to 13.37 kcal./mole. The AH" value calculated from the temperature coefficient of the ionisation constant of water as determined from electrochemical-cell data1s2 is 13.52 kcal./mole. Since the experimental uncertainty of each of these independent methods is approximately f.0.050 kcal./mole the results are obviously not in good agreement. Papee Canady and LaidleP were the first to measure the heat of ionisation of water AH in very low ionic-strength regions. Their AH" value 13.50 -& 0-05 kcal./mole. obtained by extrapolation of dH values to infinite dilution agrees well with values calculated from the temperature coefficient of the ionisation constant of water. The reactions studied by these workers were those of sodium hydroxide with hydrochloric and sulphuric acid. Vanderzee and Swanson4 report a AH" value calculated from AH values for the reaction of perchloric acid with sodium hydroxide in a low ionic-strength region to be 13.336 f 0.009 kcal./mole.This value obtained by correction of AH values to infinite dilution with appropriate heat-of-dilution data agrees well with the values obtained by the classical calorimetric procedure. Vanderzee and Swanson4 carried out their calori- metric study in the same concentration range as that used by Papee et al.;3 however the AH" values ob- tained in the two studies differ appreciably (200 cal.). It would not be expected that in this low ionic- strength region the difference between the heats of neutralisation of hydrochloric and perchloric acid with sodium hydroxide would be as great as this difference indicates. An uncertainty in the value of AH" is particularly unfortunate since most reactions in aqueous solu- tion involve pH changes.In addition acid-base reactions are frequently used to calibrate calori- metric equipment. An accurate knowledge of the standard heat of ionisation of water at infinite dilu- tion and how this heat varies through low ionic- strength regions is of particular importance since it is in low ionic-strength regions that much calori- metric work is now being carried out. We have just completed a study of the heat of neutralisation of both hydrochloric and perchloric acid with sodium hydroxide in a low ionic-strength region comparable with that used by Papee et aL3 and by Vanderzee and Swanson? The AH data were obtained by using a non-isothermal constant-temperature-environment calorimeter. The results are given in the Table. AH Values (kcaE./mole) for reaction of NaOH with HC1 and HClO,.Values are averages of at least 10 determinations at each p value where initial and base concentrations are equal to final salt concentrations. Acid P AH HCl 0.00496 13.375 0.0171 13.405 0.0341 13-430 HCIO 0.00496 13.370 0.0171 13.395 0-0341 13.410 AH" values were obtained from the tabulated dlrr data both by extrapolation to p = 0 of the linear plot of dH against P**~,and by correction of the individual AH values to infinite dilution by using heat-of-dilution data. The AH" value obtained by either extrapolation method from determinations with both acids is 13.337 f 0.015 kcal./rnole in excellent agreement with the AH" value reported by Vanderzee and Swanson.* Acknowledgement is made to the United States Atomic Energy Commission and National Institutes of Health for financial support.(Received June 17th 1963.) A review is found in C. T. Mortimer "Reaction Heats and Bond Strengths," Pergamon Press London 1962 p. 166. Harned and Owen "The Physical Chemistry of Electrolytic Solutions," 3rd ed. Reinhold Pub. Corp. New York 1958 p. 754. 9 Papee Canady and Laidler Canad.J. Chem. 1956 34 1677. Vanderzee and Swanson J. Phys. Chem. 1963 67 285. The experimental details have not yet been published; however a full account is given by J. A. Swanson Ph.D. Thesis University of Nebraska January 16th 1962; cf. Dzss. Abs. 1962 62-2688. AUGUST1963 241 The Hexamethylbenzene Cation By ROGERHULME and M. C. R.SYMONS (DEPARTMENT THEUNIVERSITY, OF CHEMISTRY LEICESTER) ALTHOUGH cations formed by loss of one n-electron Attempts to reduce the observed line width to from polynuclear aromatic hydrocarbons are well below 250 milligauss failed although the Varian known attempts to prepare cations from mono- spectrometer used has resolved lines with widths in nuclear hydrocarbons have been unsuccessful.lt2 In the region of 30 milligauss. Further as has been view of its relatively low ionisation potential (7-8ev) found for benzene anions the spectrum is not hexamethylbenzene should form a stable cation. saturated at high R.F. power levels. These results are However our attempts to prepare this ion by characteristic of radicals with the unpaired electron chemical oxidation have failed.in an orbitally degenerate level as expected for this We now report the detection of a radical formed cation. by photolysis of a solution of hexamethylbenzene in The isotropic hyperfine constant of 6-45 gauss is sulphuric acid by use of a high-pressure mercury in fair agreement with expectation corresponding to lamp. The electron spin resonance spectrum of this a value of Qs,in the relation aaH = &pC of 38.7. radical is in good accord with expectation for the Here as in other instances of coupling to /%protons cation of hexamethylbenzene provided that all the in radical methyl groups are magnetically equivalent. hyperconjugation appears to be Only 13 of the expected 19 lines have been particularly important. detected since we have not been able to accumulate sufficiently high concentrations of this radical.How- We thank the Department of Scientific and ever relative intensities of these lines are very close Industrial Research for financial assistance and to those expected for a radical with eighteen equi- “Shell” Research Ltd. for a grant to R.H. valent protons and definitely exclude radicals with twelve or fourteen equivalent protons. (Received June 20th 1963.) Bolton and Carrington Proc. Chem. SOC., 1961 385. Brivati Hulme and Symons Proc. Chem. Soc. 1961 384. Tuttle and Weissman J. Amer. Chem. SOC. 1958 80 5342. De Boer and Mackor MoE. Phys. 1962,5493; Bolton Carrington and McLachlan ibid. p. 31. The Formation of Abnormal Valency States in the Radiolysis of Aqueous Metal-ion Solutions By G.E. ADAMS and J. W. BOAG J. H. BAXENDALE (RESEARCHUNITIN UDIOBIOLOGY HOSPITAL, B.E.E.C. MOUNTVERNON NORTHWOOD and CHEMISTRY UNIVERSITY, DEPARTMENT MANCHESTER) IT has been concluded from the effect of certain has no effect on the spectrum given by Zn2+ solu- metal ions such as Zn2+ Ni2+,Co2+,Cd2+ and Pb2+ tions. Except for a decrease in density the spectra on the yields of hydrogen from y-irradiated neutral from Zn2+ and Cd2+ are the same with methanol aqueous 0.1M-methanol solutions that the ions react ab~ent.~ Hence they probably originate in the metal rapidly with the hydrated electron produced in these ions and are due to the lower valency states or some conditions to give ions in abnormal valency states other form of association of M2+ with an electron.as transient intermediates1 The absorption produced with Mn2+ seems sur- We have now obtained (Fig. 1) the absorption prising since it had no effect on the yield of hydr0gen.l spectra of some transient species using the technique The higher concentration used here is probably of pulsed radiolysis.2 They were taken 2 psec. after responsible since absorption is not obtained in solutions of Zn2+ Cd2+ Co2+ and Mn2+ in de- similar conditions3 with 2 x lo-*~-Mn~+. grated 0.1 M-aqueous methanol had been irradiated The absorptions decay at about the same rate and by a 2 psec. pulse of 2Mev electrons from a linear we have examined the Zn2+ solution in most detail accelerator. No absorption is produced in the same (Fig. 2). The absorption maximum at 3000 A de-conditions by 0.1M-methanol in the absence of the creases according to second-order kinetics but after to 10-3~ metal ions and change from 0.1~ methanol it has disappeared (100 psec.) there is still consider- Baxendale and Dixon Proc.Chem. Soc. 1963 148. Hart and Boag J. Amer. Chem. Sac. 1962 84,4090. Baxendale Fielden and Keene following communication. PROCEEDINGS 08 0.6 > 4x .c .-u) W 0 0.4 .-4 0-2 28 32 36 40 Wave length (IOQA ). RG.1. Transient absorption of lO-%-solutions in 0-1M-detzrated aqueous methanol (IO"M for Zn2+) afer irradiation by an electron pulse. able absorption below 2700 8,. The presence of 1 O-2N-sulphuric acid decreases considerably the ab-sorption at 3000 8 (Fig.2) as might be expected since H+and Zn2+ will compete for the electron. Acid also removes the steeply rising absorption below 2700 8,. These observations may be understood in terms of the further reduction in neutral solution of Zn+ to the atom (Zn metal has been observed as a product1) either by dismutation or by reaction with the radical I I I I r'\c I I I1 22 24 26 28 30 32 34 36 38 Wavelength (lo"&) FIG. 2. Transient absoration of 10-2M-Zn2+ in 1O3wdetzrated aqueous methanol "at various times after the electron pulse. CH,.OH which will be present in almost equal con- centration. Thus at short delay times the absorption spectrum. of the solution is a composite of those of Zn+ and ZnO the latter being responsible for the rising absorption at the lower wavelengths.In lo-%-acid this component is absent since Zn+ is oxidised back to Zn2f by H+ and Zno is not formed. (Received May 7th 1963.) Absolute Rate Constants for the Reactions of Some Metal Ions with the Hydrated Electron By J. H. BAXENDALE and J. P. KEENE E. M. FIELDEN DEPARTMENT MANCHESTER LABORATORIES, (CHEMISTRY UNIVERSITY 13 and PATTERSON CHRISTIE MANCHESTER) HOSPITAL RECENT work1 has shown that the hydrated electron produced by y-radiation in aqueous solution will reduce Zn2+ Cd2+ Co2+,Ni2+,and C0(NH3);f ions. Other work2y3 has established that the hydrated electron in water has a broad absorption in the visible spectrum with a maximum at 7000 A. Baxendale and Dixon Proc. Chem. SOC.,1963 148.Boag and Hart J. Aier. Chem. Soc. 1962,84,4090. a Keene Nature 1963 197 47. Keene to be published. We have now followed the decay of this absorp- tion produced by a 2 psec. pulse of 4 MeV electrons in the presence of the above metal ions using a sensi- tive photomultiplier/oscilloscope technique and find that the decay rate is considerably increased. We have been able to obtain conditions where the decay AUGUST 1963 of the hydrated electron in pure water is negligible compared with that in the presence of 50-500 ,UM-metal ions which is a first-order process. From these and similar data we have obtained the bimolecular rate constants given in the Table referring to the hydrated electron-ion reaction. Metal ion .... Znw COS 10-lo k(mo1e-l 1. sec.-l) . . 0.17 -'*~n 2 Y \\. 400 500 Wavelength (my) 1.35 Transient ultraviolet spectrum produced in 5.3 x 10-5~-NiS04 solution taken 2 psec. after the ead of the electron pulse. The rate for Cu2+ compares well with the previously determined value of 3.3 f0.3 x 10'O mole-l l.sec.-l.6 The results are fairly consistent with the semi- quantitative data and we also confirm that the Mn2+ reaction is at least an order of magnitude slower than the slowest measured. Ni2+ cu2+ Cd2+ Co(NH&+ 2.3 3.0 5.8 >9 Transient absorption has been observed at 3000 A in these solutions and ascribed6 to the unstable valency states produced in these reactions e.g. Zn+ We have confinned this using the photo- multiplier technique and have also observed the ultraviolet transient absorption spectrum for Ni+ shown in the Figure.In support of this interpretation we find that all these absorptions build up in the time-period ob- served for the enhanced electron decay. Further the effect of the ions on the build up of the hydrated- electron absorption during the pulse confirms the order of reactivity of the ions given in the Table. It seems probable that the transient ultraviolet absorp- tions are the charge-transfer spectra of the reduced ions the molar extinction coefficient of the Zn+ species being at least 1-3 x l@. (Received May 7th 1963.) Gordon Hart Matheson Rabani and Thomas in the press. Adams Baxendale and Boag Proc. Chem. Soc.,1963 preceding communication.A Direct Oxidation of cis-4Hydroxycinnamic Acid to Umbelliferone By M. B. MEYERS (DEPARTMENT GLASGOW) OF CHEMISTRY THEUNIVERSITY THEconversion of 4-hydroxycinnamic acid into glucoside which after isomerisation to the cis-acid is umbelliferone (I) and its derivatives in plant systems1 dehydrated to the lactone.6 involves an apparent oxidation meta to the estab- It is now shown that treatment of aqueous solu- m* lished phenolic group. Of the several theories pro- posed to rationalise this mechanistically unfavour- able process two involve oxidative cyclisation through a quinol intermediate2 (11) or a spirolactone3 (III) where subsequent migration of the inserted oxygen would lead -to umbelliferone. Alternatively a direct cyclisation by carboxyl radical or cation species has been envisaged.* In the biosynthesis of coumarin it is known that ortho-hydroxylation prob- ably takes place in trans-cinnamic acid to give a 0-p HO\ -(1) (n) 0~ -p2H 0 Meo' OGlU (m) (IV) Brown Science 1962 137 977.Waworth J. 1942,448. Grisebach and Ollis Experientia 1961 17 4; Scott Proc. Chem. Soc. 1962 207. Chambers Kenner Temple-Robinson and Webster Proc. Chem. SOC. 1960,291. Brown Canad. J. Biochem. Physiol, 1962 40 607; Stoker and Bells J. Biol. Chem. 1962 237 2303; Kahnt Naturwiss. 1962 49 207; Brown Towers and Wright. Canad..J. Biochem. Physiol. 1960 38 143. PROCEEDINGS tions of cis-4-hydroxycinnamic acid in the presence coumarin and the hydroxy-acid corresponding to of ferrous-ethylenediaminetetra-acetic acid complex 01).and ascorbic acid (phosphate buffer pH 4-6) with It is not very probable that the second oxidation air or oxygen at room temperature (19”) for 12-18 product 6,7-dihydroxycoumarin is formed by hours produces umbelliferone (0.1 % yield) and further oxidation of umbelliferone as the latter is not 6,7-dihydroxycoumarin the latter in similar but appreciably oxidised under these conditions. Its variable yields. Practically no umbelliferone is de- likely mode of formation involves hydroxylation tected in the absence of ascorbic acid and as the ortho to the phenol group of cis-4-hydroxycinnamic metal ion-ascorbic acid system is a hydroxylating acid to give cis-caffeic acid which is then further reagent,s participation of the carboxyl group may be hydroxylated to 6,7-dihydroxycoumarin.The latter excluded. Under these mild conditions the plausible conversion has been observed in these circum- intermediate (III)* does not undergo rearrangement stances.8 and known compounds structurally similar to (11) are likewise insensitive to acids.’ Moreover the The above results suggest that the biosynthesis of forced acidic rearrangement of compound (111) leads 7-oxygenated coumarins is related to that of couma-almost entirely to 6-hydroxycoumarin through car- rin without participation of the phenol or carboxyl bon migration and an acid (IT) would be expected group in the first instance and that it is unnecessary to behave in the same way no 6-hydroxycoumarin to use “quinol” intermediates.This view is supported was found among the products. Haworth2 has sug- by Brown’s isolation1 of the 2-glucoside of 2-gested that umbelliferone could be formed from an hydroxy-4-methoxy-cicinnamic acid (IV). acid (11) by lactonisation on to the b-position of the a/hnsaturated ketone followed by dehydration. The author thanks Mr. D. J. Austin for assistance This is unlikely as treating the spirolactone (111) with with the experimental work. This investigation was one equivalent of sodium hydroxide gives no trace carried out during the tenure of an I.C.I. Fellowship. of umbelliferone but a mixture of 6-hydroxy-(Received June 12th 1963 .) * Preparation of this compound by electrolysis of cis4hydroxycinnamic acid will be described later.9 Norman and Radda Proc.Chem. Soc. 1962 138; Green Ralph and Scofield Nature 1963 198 754. Bamberger Ber. 1900,33 3652. * Butler and Siegelman Nature 1959,183 181 3 ;Van Sumere Parmentier and Van Poucke Naturwiss.,1959,46,668. Scott Dodson McCapra and Meyers J. Amer. Chem. SOC,in the press. The Effect of Cup& and Thallous Ions on the Radiolysis of Aqueous Solutions of Ethylenediamine Propane-i,Z-diamine and Glycine By M. ANBAR (ISOTOPE THEWEIZMANN OF SCIENCE ISRAEL) DEPARTMENT INSTITUTE REHOVOTH and P. RONA ENERGY SOREQRESEARCH REHOVOTH, (ATOMIC COMMISSION ESTABLISHMENT ISRAEL) THE rate and mode of single-electron reactions of propane-l,2-diamine and glycine in triply distilled organic compounds are modified on complex-forma- water were irradiated with s°Co-gamma rays at a tion with metal ions.lY2 The extent of radiolytic de- dose rate of 12,400 rad./min.with total doses of carboxylation of salicylic acid in highly concentrated 100,000--150,OOO rads. The radiolysis of ethylene- solutions increases in the presence of ferric and diamine in dilute aqueous solution is characterised cupric ions.3 However since the effect of appropriate by the production of ammonia and was shown by to be the sole volatile scavengers was not investigated it is hard to mercuric oxide pre~ipitation,~ interpret these results. base produced. The Conway microdiffusion method5 In the present study thallous or cupric sulphate in was used for the standard determination of the yields dilute aqueous solution is shown to induce radiolysis of ammonia.Another major product is glycine- of certain organic compounds in the presence of aldehyde which was identified and determined after scavengers which otherwise co.rlpletely inhibit their oxidation to glyoxal. Glyoxal was shown not to be decomposition. present as such in the irradiated solution. The Oxygen-saturated solutions of ethylenediamine. radiolysis yields of glycinealdehyde and hydrogen Gritter and Patmore Proc. Chem. SOC.,1962 328. Anbar Guttman and Friedman Proc. Chem. SOC.,1963 10. Sugimori and Tsuchihashi Bull. Chem. SOC.Japan 1960,33 713. Weber and Wilson J. Bid. Chem. 1918 35 385. Conway “Microdiffusion Analysis and Volumetric Error.” Lockwood London 1947. AUGUST1963 peroxide were determined spectrophotometrically:6 G(NH,CH,CHO) = 1.05 and G(H,O,) = 2.35 were found in 0.3~~ethylenediamine solutions.No organic hydroperoxide was detected in the irradiated solutions as the peroxide yields determined by the titanium sulphate and the iodide methods were identical. The G-value of ammonia increased with the ethylenediamine concentration up to 0.03~; at the compounds studied. However substantial non- scavengable G(NHJ values were found in the presence of low concentrations of either thallous sulphate or cupric sulphate. As shown in Table 1 propan-2-01 and formic acid inhibit the formation of ammonia completely and benzoic acid to a great extent. When thallous or cupric sulphate was added the G(NH,) values were TABLE 1. Yield of ammonia in oxygen-saturated amine solutions at pH = 5 irradiated with 120,750 rads of 6oCo-gumma rays.(en = ethylenediamine; pn = propane-1,Zdiamine; gly = glycine) Scavenger None Propan-2-01 (0.03~) Formic acid (0.03~) G(NHd* Metal ion en Pn glY (0.03~) (0.03~) (O'WM) None Tl,S04 (0406~) &so4 (0012M) None Tl,SO (0.006~) CUSO4 (O'O12M) None Tl,S04 (0.006~) CUSO4 (0012M) None 2.75 2.75 1.33 2.75 2-75 1.33 3.6 2.75 2.45 0.0 00 0.0 2.0 1.8 0.44 3-6 2.3 0.66 0.0 0.0 0.0 2.0 1 *6 0.0 2.7 1.1 07 0.0 033 04 0.9 2.7 1.55 3-4 4.7 2.3 Benzoic acid (0.015~) T12S04 (0.006~) cUso4 (0.012M) * Each G-value quoted is the result of at least four analyses.TABLE 2. The effect of EDTA andof acidity on the action of metal ions on ethylenediarnine solutions. (Experimental conditions are as in Table 1) Scavenger Metal ion EDTA (0.005~) EDTA (0.005~) H2S04(0.8~) H,S04 (0.8~) None n2s04(0.006M) None T12S04(0.06~) G(NHJ 0-0 0.0 1.6 0.0 1.6 0.0 0-4 H2S04(0.8~) &SO4 (0.03~) H2SOp(0.8~)+ Propan-2-01 (0.03~) None H2S04(0.8~)+ Propan-2-01 (0.03~) &SO4 (0.03~) this concentration a plateau value of G(NH$ = 2.75 f0.30 was obtained. This yield was independent ofacidity between pH 3.0-5.0. In radiolysis of solu- tions saturated with nitrous oxide G(NH$ increased to 6.3 so that the reaction seems to be initiated by OH radicals,7 in agreement with previous results on amines.8 The addition of various scavengers at equimolar concentrations completely inhibited the radiolysis of close to those obtained in the absence of scavengers.Tls could not be detected in the irradiated solutions by spectrophotometric analysk9 EDTA inhibited the action of thallous sulphate. In @8~-sulphuric acid cupric sulphate affected the scavenging action of propan-2-01 to a smaller extent than in neutral solu- tion whereas thallous sulphate was a scavenger even in the absence of propan-2-01 (Table 2). These metal ions produced similar effects when Neuberg and Straws Arch. Biochem. 1945 7 211; Satterfield and Bonnell Analyt. Chem. 1955 27 1174; Hocwadel J. Phys. Chem. 1952,56,587. 'I Dmton Peterson and Sills Discuss.Faradby SOC.,1960,29 257. Jayson Scholes and Weiss J. 1955,2594; Jayko and Garrison J. Chem. Phys. 1956,25,1084. Bode 2.Analyt. Chem. 1955,144 165. added to ethylenediamine solutions which were irradiated in the absence of oxygen (by saturation with argon). The presence of nonscavengable G(NH3) could not be demonstrated in ethylenediamine solu- tions containing nickel or caesium sulphate or lead perchlorate. The organic scavengers (Table 1) in- hibited radiolysis completely in propane-l,3-diamine and in butane-lP-diamine solutions also in the presence of thallous sulphate. Cupric sulphate had no effect on the radiolysis of ethylenediamine solu- tions saturated with nitrous oxide in the presence or absence of scavengers. Thallous ions on the other hand inhibited the scavenging action of propan-2-01 in the presence of nitrous oxide.lo Sworski Radiation Res. 1956 4 483. PROCEEDINGS These results indicate that metal ions act by com- plex formation with the substrate undergoing rddio- lysis. The absence of any effect of nickel ions implies that this is not due merely to complex-formation. It seems likely that thallous and cupric ions become involved in electron-transfer processes. It is sug-gested that cupric ions act by reduction to Cu+ since they have no effect under nitrous oxide. Thallous ions on the other hand may act via the T1+2 state formed by their reaction with OH radicals.1° The authors are indebted to Mr. R. A. Munciz for help in performing part of the analyses.(Received March 28th 1963.) Structure of Amorphigenin the Aglycone of the First Natural Rotenoid Glycoside By L. CROMBIE and R. PEACE (DEPARTMENT UNIVERSITY STRAND, OF CHEMISTRY OF LONDONKING’SCOLLEGE LONDON, W.C.2) AMORPHIN, a glycoside which occurs in the insecti- cidal seeds of Amorpha fruticosa,l gives glucose arabinose and amorphigenin on acid hydrolysis. The genin is also formed by hydrolysis with p-glucosidase and gives a positive Durham test like rotenone. Russian authors2 recently have presented further evidence of its rotenoid character and suggest that it has the molecular formula C22H2oO7 (Acree and co- workers1 proposed C22H22O7) and possesses a D/E system as in (I) with the hydroxyl group unassigned and the rest of the molecule as in rotenone.Our results lead to structure (11) for amorphigenin C23H2207 amorphin with the sugar attachment at 8’ is thus the first rotenoid glycoside. Amorphigenin forms tenaceously solvated crystals (nuclear magnetic resonance evidence) from meth- anol benzene and aqueous acetone and the mole- cular formula was established from analysis of deri- vatives mass-spectral molecular weight (410) and nuclear magnetic resonance proton counts on amorphigenin and its derivatives. Infrared and ultra- violet spectra simulate closely those of rotenone except for hydroxyl absorption (vmax 3498 cm.-l in CCl, c < 0.005~; intramolecular bonding to 1’-0) and the nuclear magnetic resonance spectrum shows two methoxyl groups with an aromatic proton pat- tern as for rotenone? The 1- and 4-hydrogen atoms give peaks at r 3-19 and 3.52 respectively and the 10,l l-hydrogen atoms give rise to the characteristic quartet r 3.47 and 2.12 (J 9 c./sec.) leaving no doubt that the E ring is angularly fused as shown.Chemical description of the B/C rings is given by 6a 12a-dehydrogenation which occurs with charac- teristic shift of the carbonyl frequency (1672 cm.-l for amorphigenin 1634 cm.-l for dehydroamorphi- genin) and r value of the l-hydrogen atom (1.90). Treating the dehydro-compound with nitrous acid affords the keto-lactone (III) verifying the presence of the 5,6,6a,12a,12-system as in (11). The 6a,12a- dehydro-compound is hydrolysed to the derrisic acid analogue (IV) which is recyclised by hot acetic an- hydride to the 8’-acetate of the 6a 12a-dehydro- compound.Acree Jacobson and Haller J. Org. Chem. 1943 8 572. a Kondratenko and Abubakirov Doklady Akad. Nauk S.S.R. 1962,146 1340; Uzbek. Khim. Zhr. 1962,6,60 73; 1961,5 66; Doklady Akad. Nauk Uzbek. S.S.R. 1960 35. Crombie and Lown J. 1962 775. AUGUST1963 247 The primary nature of the hydroxyl group is shown by two pieces of information. First the 8’-methylene band at r 5.73 in amorphigenin (and its derivatives) moves to 5.33 on acetylation (the unsplit band also demands no proton on the carbon bearing the CH,-OH group). Secondly on careful oxidation with manganese dioxide amorphigenin is oxidised to a 6’-formyl-l2-ketone with an aldehydic hydrogen peak at r 0.46.The corresponding hydroxyroten- one (cf. 111) gives an analogous aldehyde when oxidised. The oxidation conditions and increased absorption at 225 mp support an allylic primary alcohol system and amorphigenin absorbs one mol. of hydrogen over a palladium catalyst. In addition amorphigenin has a band at T 4.73 assignable to the two vinyl protons (cf. rotenone). With this in mind the two carbon atoms unassigned must form a di-hydrofuranoid ring E. The whole 5-carbon addendum to ring D is isoprenoid since attachment of the acyclic residue is at 5’ and not 4’. This is so because the three hydrogen atoms at 5’ and 4‘ form multiplets below T 5.1 (S’ one proton) and near 6.8 (4’ two protons) with a splitting pattern similar to the corresponding situation in rotenone.The stereochemistry of amorphigenin is assigned as follows. The r value of the 1-hydrogen atom in Djerassi Ollis and Russell J. 1961 ld8. Cf. Crombie and Peace J. 1961 5445. amorphigenin indicates a CiS-B/C fusion and the positive Cotton effect (first extremum 357 mp) sup- ports this and indicates that the absolute conflgura- tion at positions 6a,12a is as in rotenone? As both derrisic acid and the corresponding compound from amorphigenin (cf. IV) [both of which possess asym- metry only at 5’1 have similar negative plain curves the rotenone configuration is assigned at this centre.5 This information defines completely the structure and stereochemistry of amorphigenin. The conclu- sions have been confinned by hydrogenolysing the 8‘-hydroxyl group in amorphigenin and hydro-genating the 6’,7’-olefinic link.The product is identical with (-)-6’,7’-dihydror~tenone~from natural rotenone. (-)-12-Deoxy-6’,7’-dihydroro-tenone is also formed in the hydrogenolysis by elision of the keto-group. We are indebted to Dr. J. W. Lown (University of Alberta) for the optical rotatory dispersion curves and for some preliminary nuclear magnetic resonance spectra. Dr. R. I. Reed (University of Glasgow) kindly provided the mass spectral molecular weight. One of us thanks the D.S.I.R. for a postgraduate award and we are grateful to Shell Research Ltd. for financial support. (Received May 23rd 1963.) LaForge and Keenan J. Amer. Chem. SOC.,1931,53,4450.An 8-Co-ordinate Compound of Zinc(@ By D. P. GRADDON and D. G. WEEDEN OF INORGANIC UNIVERSITY WALES, (DEPARTMENT CHEMISTRY OF NEWSom~ SYDNEY AUSTRALIA) SEVERAL first-row transition metals have recently been shown by structural studies to form compounds in which the co-ordination number exceeds six; thus manganese and iron have been shown to form 7-co-ordinate complexes with ethylenediamine-tetra- acetic acid and titanium tetrachloride to form an 8-co-ordinate adduct with o-phenylenebisdimethyl- arsine. By crystallisation of bis(dibenzoyhethanato)-zinc(@ from 4-methylpyridine we have obtained a tetra-(4methylpyridine) adduct as yellow needles m.p. 95” (decomp.) (Found C 73.6; H 5.9; N 6.3; Zn 7.3. C,,H,,N,O,Zn requires C 73.3; H 5.7; N 6.3; Zn 7.4%).This apparently 8-co-ordinate compound could achieve a co-ordination number of six if two of the molecules of 4-methylpyridine filled spaces in the crystal lattice or if the chelate rings were opened. However determination of the molecular weight in benzene gave a mean value of 789 (theor. for mono- mer 884) showing that only slight dissociation occurs and the infrared spectrum in the 6 p region showed two very strong bands at 1520 and 1600 cm.-l characteristic of chelated p-diketones; open- ing of the chelate rings would be expected to result in the disappearance of these bands and the appear- ance of a new band near 1700 cm.-l characteristic of the conjugated carbonyl group then present as found recently for some /?-diketone complexes of mercury(@ for which the open enolate structure has been ~uggested.~ We have also obtained the corresponding nickel@) compound.(Received June 7th 1963.) Hoard Pedersen Richards and Silverton J. Amer. Chem. SOC.,1961 83 3533; Hoard Lind and Silverton ibid. p. 2770. Clark Lewis NyhoIm Pauling and Robinson Nature 1961 192 222. Nonhebel J. 1963 738. PROCEEDINGS The Synthesis of a New Fragmentation Product of a Cephalosporanic Acid Derivative By S. H. EGGERS V. V. Urn,and G. Lowe T. R. EMERSON PERRINS OXFORD (THEDYSON LABORATORY UNIVERSITY) THE elucidation of the structure of cephalosporin C (I; R = D-O,C.CH(NH~+).[CH,]~CO)~ an anti- biotic from a species of Cephalosporium revealed a close similarity to the penicillins (11; R = acyl) and in particular to penicillin N* (11; R = D-O,CCH(NH,+)+ [CH,],-CO ).2 Unlike the penicil- lins it was not inactivated by penicillinase,3 but had much weaker antibacterial activity? It has been shown however that replacement of the a-amino- adipyl side chain by other acyl residues can greatly increase this acti~ity.~.~ The elegant method now available’ for the preparation of 7-aminocephalo-sporanic acid (I; R = H) has made a wide range of acylated derivatives easily available.6 We report the transformation of one of these namely 7-phenylacetamidocephalosporanic acid6 (I; R = PhCH,CO) into the 6H-1,3-thiazine (IV) and describe its synthesis.(I) C02H I - I- + The inactivation of the penicillins by alcohols is known to be due to the cleavage of the p-lactam ring to give the corresponding penicilloic ester (III);8 it is claimed that metal ions are required for this reaction.Similar treatment of the acid (I; R = Ph*CH,CO) in the presence or absence of metal salts failed to cleave the p-lactam ring. When the acid (I; R = Ph-CH,CO) was treated with two equivalents of sodium benzyl oxide in benzyl alcohol however it was smoothly trans- formed in 1 hr. at 15” into the acid (IV; R = PhCH,-CO R’ = H) which was isolated in 60% yield. The acid (IV; R = PhCH,CO R = H) and its benzyl ester (IV; R = Ph.CH,*CO R = PhCHa were identical with synthetic materials in ultraviolet infrared and nuclear magnetic resonance spectra melting point and mixed melting point and elemental analysis.Their nuclear magnetic resonance spectra indicated that they exist largely (> 80%) in the enolic form as shown. This transformation of the cephalosporanic acid nucleus can be regarded as an extended fragmenta- tion reaction (cf. ref. 9) the product of which under- goes a prototropic rearrangement to give the 6H-lY3-thiazine system. The facility of the reaction and the high yield of the fragmentation product is unusual for a molecule in which the leaving group is at a primary centre. It seems likely therefore that the fragmentation is a concerted reaction the driving force arising largely from the cleavage of the p-Iactam ring. The synthesis of this new fragmentation product was achieved by the annexed route.(9 (ii) CH,(CN)*COg*CH,Ph-+ H0.N=C(CN)*CO,.CH,Ph + (iii) Ph*CH2*CO*NH*CH(CN).CO2CHaPh -+ Ph.CHg.CO*NH.CH(CS.NHJ*COa*CHgPh\ (V) (tV) p+ (iv) / CH2= CMeCH(OH)*C02R -+ CH,=CMeCOCO,R (W (”‘I) (i) NaN0,-AcOH. (ii) At-Hg Ph-CH,-COCt. (iii) H2S.(iv) MnO,. (v) HCI. * Also known as cephalosporin N and synnematin B see ref. 2. Abraham and Newton Biochem. J. 1961 79,377; Hodgkin and Maslen ibid. P.393. Abraham Newton and Hale Biochem. J. 1954 58 94; Newton and Abraham ibid. p. 103; Abraham Phmm. Rev. 1962 14 473. Abraham and Newton Biochem. J. 1956,63 628. Newton and Abraham Biochem. J. 1956,62 651. Loder Newton and Abraham Biochem. J. 1961 79,408. ‘ Chauvette Flynn Jackson Lavagnino Morin Mueller Pioch Roeske Ryan Spencer and Van Heyningen J.Amer. Chem. Soc. 1962 84 3401. ’ Morin Jackson Flynn and Roeske J. Amer. Chem. Soc. 1962,84 3400. * “The Chemistry of Penicillin,” ed. C!arke,, Johnson and Robinson Oxford Univ. Press 1949. Grob in “Theoretical Organic Chemistry KekulC Symposium Buttenvorths London 1958 p. 114. AUGUST1963 The hydroxy-ester1° (VI; R = Et) on transesteri- fication with benzyl alcohol in the presence of toluene-p-sulphonic acid gave the hydroxy-ester (VI ; R = PhCH,). Both hydroxy-esters were oxidised to the corresponding keto-esters (VII; R = PhCH and Et) with manganese dioxide. The keto-ester (VII R =PhCH,) and the thioamide (V) were dissolved in dioxan saturated with hydrogen chloride at 15".The thiazine (IV; R = PhCH,CO R = PhCH,) isolated after 2 days crystallised in two forms m.p. 155-156" (needles) and 173-175" (cubes). The keto-ester (VII; R = Et) when treated with the thio- amide (V) under similar conditions gave the thiazine (IV; R = Ph-CH,-CO R' = Et) m.p. 138". lo Vogel and Schinz Helv. Chim. Acta 1950 33 116. Selective hydrolysis of both the thiazine-esters (IV; R =PhCH,CO R' = Et and Ph-CH,) was effected with sodium carbonate solution to give the thiazine- carboxylic acid (IV; R = Ph.CH,*CO R' = H) m.p. 211-21 3 ". We thank Glaxo Research Ltd. for a supply of 7-phenylacetamidocephalosporanicacid for Fellow- ships (to T.R.E. and V.V.K.) and for many discus- sions. We also express our thanks for a Common- wealth Scholarship (to S.H.E.) and to Professor Sir Ewart R.H. Jones F.R.S. for his interest and advice. (Received May 27th 1963 .) The Structure of the Tetraphenylcyclobutadiene Dimer By H. H. FREEDMAN and R. S. GOHLKE (THEDow CHEMICAL EASTERN LABORATORY, COMPANY RESEARCH FRAMINGHAM, MASS. U.S.A.) UNTIL X-ray results are complete structure (I) (octaphenylcubane) for the dimer m.p. 430" of tetraphenylbutadienel cannot be considered as established. However we now report evidence that excludes the alternative (11) proposed by Cookson and Jones. (n) The prominent ion fragments occurring in the mass spectrum of the dimer as obtained at 180"by a technique described elsewhere are tabulated below. The observation of an ion fragment of m/e 635 which is considered to arise by loss of a phenyl group from the molecular ion of m/e 712 strongly favours structure (I) since production of this ion from a compound (11) requires cleavage of two bonds with concomitant transfer of a proton to the leaving Mass spectrtrm of dimer mle Rel.int. mie Rel. int. 43 100 356 46 75 -368 20 76 -380 14 77 54 392 10 89 36 404 11 166 32 457 9 178 22 469 15 190 15 48 1 11 233 31 546 10 245 15 558 9 257 42 623 5 269 27 635 9 28 1 15 712 94 293 7 713 50 group. The loss of phenyl from structure (11) is con- sidered to be no more likely than that from a com-pound such as 9-methylfluorene (IIl) since both (11) and (111) have potentially migratory a-protons and it has been found that phenyl loss from 9-methyl- Freedman and Petersen J.Amer. Chem. Soc. 1962 84,2837. a Cookson and Jones Proc. Chem. SOC.,1963 115. Gohlke Chem. and Ind. in the press. fluorene (III) does not occur to a significant extent (< 1% rel. int.). Similarly the presence of a high intensity (54%) phenyl-ion peak at mfe 77 is con- sistent with structure (I) but not with (11). A classical chemical technique leads to the Same conclusion. Oxidative degradation of the dimer should produce benzoic acid if formula (I) is correct PROCEEDINGS but a compound (11) should yield diphenic and possibly phthalic acid. Prolonged exposure of the dimer to chromic anhydride in acetic acid causes its dissolution and yields benzoic acid (30 %) as the only base-soluble constituent.The residual oxidative fragments appear to be mainly ketonic. (Received June 14th 1963) PUBLICATIONS OF THE SOCIETY WHEN presenting the Accounts of the Society at the Annual General Meeting in Cardiff on March 28th last the Honorary Treasurer referred (Proceedings 1963 157) to the continuous upward trend of the cost of producing the Journal and Proceedings and the increasing number of pages to be printed at steadily increasing cost per page. Since 1959 the increase in size of the Journal and Proceedings has resulted in a 50% increase in cost of production although during that period the selling price remained constant. The present situation demands that the Society should take steps to protect its income and whilst every effort is made to contain the cost of production the Council has decided most regretfully that the selling prices must be increased.For similar reasons the selling price of Current Chemical Papers must be raised but the prices of the Annual Reports on the Progress of Chemistry and Quarterly Reviews are to remain unchanged. 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Young (March 1963) Bourne- mouth a Fellow since 1898; Dr. B. Lambert (1.7.63) Emeritus Fellow of Merton College Oxford. International Symposia.-The First Canadian Wood Chemistry Symposium sponsored jointly by the Chemical Institute of Canada and the Technical Section Canadian Pulp & Paper Association will be held in Toronto Ontario on September 4-6th 1963.Further enquiries should be addressed to the Chemical Institute of Canada 48 Rideau Street Ottawa 2 Ontario Canada. An International Symposium on Microbiology of Crude Oil will be held in Greifswald on October 1 st-6th 1963. Further enquiries should be addressed to Professor Dr. W. Schwartz Institut fur Mikro- biologie Ludwig-Jahn-Str. 15 Greifswald Germany. The Eighteenth Plastics-Paper Conference ar- ranged by the Technical Association of the Pulp and Paper Industry will be held in Cleveland on October 14-16th 1963.Further enquiries should be addressed to the Executive Secretary 360 Lexington Avenue New York 17 N.Y. 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A Conference on The Measurement of High Temperatures will be held in London on May ll-l3th 1964. Further enquiries should be ad- dressed to the Administration Assistant The Institute of Physics and The Physical Society 47 Belgrave Square London S.W. 1. Personal.-Dr. C. A. Barson and Dr. M. H. B. Hayes have been appointed Senior Research Fellows at the University of Birmingham. Dr. D. Betteridge has been appointed Lecturer in Chemistry at the University College of Swansea.Mr. H. C. Butcher has taken a post as Technical Officer with the Federation of British Industries. Dr. J. W. Clark-Lewis Reader in Organic Chem- istry at Adelaide University has been appointed to the Chair of Chemistry at the Bedford Park Division of that University. Mr. R. B. Collins and Dr. G. F. DuBn have been appointed to the Board of Minnesota 3M Research Limited. Dr. R. Colton has resigned his Research Fellow- ship at A.E.R.E. 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P. Pascal. Vol. 20. Part 2. Pp. 773-1926. Masson et Cie. Paris. 1963. (Pre-sented by the publisher.) Volatile silicon compounds. E. A. V. Ebsworth. (Inter- national Series of Monographs on Inorganic Chemistry. Voi. 4). Pp. 179. Pergamon Press. Oxford. 1963. Mass spectrometry of organic ions. Edited by F. W. McLafferty. Pp. 730. Academic Press. New York. 1963. Synthetic methods of organic chemistry. Vol. 17. Edited by W. Theilheimer. Pp. 507. S. Karger. Basle. 1963. (Presented by the publisher.) Progress in the chemistry of fats and other lipids. Vol. 6. Edited by R.T. Holman W. 0. Lundberg and T. Malkin. Pp.364. Pergamon Press. Oxford. 1963. Physical methods in heterocyclic chemistry. Edited by A. R. Katritzky. Vol. 1. Pp. 346. Vol. 2. Pp. 398. Academ-ic Press. New York. 1963. Naturally occurring oxygen ring compounds. F. M. Dean. Pp. 661. Butterworths. London. 1963. Phthalocyanine compounds. F. H. Moser and A. L. Thomas. (American Chemical Society Monograph No. 157.) Pp. 365. Reinhold. New York. 1963. (Presented by the publisher.) Organic chemistry of bivalent sulfur. E. Emmet Reid. Vol. 5. Pp. 461. Chemical Publishing Co. New York. 1963. Fortschritte der Arzneimittelforschung progress in drug research. Edited by E. Jucker. Vol. 5. Pp. 654. Birkhauser Verlag. Basle. 1963. Textile chemistry.R. H. Peters. Vol. 1. Pp. 477. Elsevier. Amsterdam. 1963. Tobacco Research Council Research Papers No. 3 the constituents of tobacco smoke an annotated biblio- graphy. 2nd supplement edited by E. G. N. Berry. Pp. 24. Tobacco Research Council. London. 1963 (Presented by the publisher.) Photography its materials and processes. 6. B. Neblette. 5th edn. Pp. 500. Van Nostrand. New York. 1958. (Presented by Dr. A. A. Newman.) International Symposium on Microchemical Tech- niques; proceedings. Edited by N. D. Cheronis. Based on a symposium organised by the Metropolitan Micro- chemical Society under the sponsorship of the Inter- national Union of Pure and Applied Chemistry com- mission on Microchemical Techniques Section of Analytical Chemistry in Pennsylvania 1961.(Micro-chemical Journal Symposium Series-Vol. 2.) Interscience Publ. Inc. New York. 1962. Ninth Symposium (International) on Combustion, held at Ithaca New York 1962. Organised by the Com- bustion Institute. Pp. 1091. Academic Press. New York. 1963. Proceedings of the 10th Colloquium Spectroscopicum Internationale held in Maryland 1962; sponsored by the University of Maryland Department of Chemistry and the International Union of Pure and Applied Chemistry Commission on Spectrochemical and Other Optical Procedures of Analysis. Edited by E. R. Lippincott and M. Margoshes. Pp. 806. Spartan Books. Washington 1963. 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ISSN:0369-8718
DOI:10.1039/PS9630000229
出版商:RSC
年代:1963
数据来源: RSC
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