Infreared Alkaloids

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Jan., 1951 THE N F R A R E D ABSORPTIONPECTRA O F ALKALOIDS 305[CONTRIBUTIONROM THE DIVISION F CHEMISTRYF THE NATIONALESEARCHOUNCILF CANADA]

The Infrared Absorption Spectra of AlkaloidsBY LBOMARION,D. A. RAMSAYND R. NORMANONES

Although several applications of infrared spec-trometry to the detection of functional groups inalkaloids are to be found in the recent literature,2nosystematic examination of the infrared spectra ofthe alkaloids has been reported.This paper is concerned with a comparative studyof th e infrared absorption spectra of a variety of al-kaloids in the regions characteristic of the principalstructural groups. Particular attention has beendevoted to th e regions 3700-3200 cm.- in whichboth the hydroxyl and the imino groups absorb,and 1780-1620 cm.-l in which the variously substi-tuted carbonyl groups absorb. The correlationswhich have been derived between the spectra andmolecular structures of various nitrogenous com-pounds (e.g., penicillin4r5) and the steroids,6 ncour-aged the view that similar correlations might be es-tablished for the alkaloids.

Experiment a1The spectra were determined on a Perkin-Elmer 12Bsingle beam spectrometer using a calcium fluoride prismand a 7-cycle GM amplifier. Chloroform was used as asolvent since it is transparent in the infrared regions ofprincipal interest (3700-3100,3000-2700, 1800-1540 cm.-l)and dissolves most alkaloids readily. The chloroform waswashed several times with water to remove ethanol, driedby repeated shaking with anhydrous sodium sulfate anddistilled, the middle fraction being ~o ll ec ted .~ he forma-tion of phosgene by photolysis produces an absorption bandat 1810 cm.- and the solvent was discarded as soon as thisband appeared.Standard solutions of the alkaloids (usually 3 mg. perml.) were employed to give some significance to the bandintensities, the absorptions being measured in a sodiumchloride cell of thickness 1mm. To make allowance for theappreciable variations in molecular weights of the alkaloids,apparent molecular extinction coefficients8a t the absorption(1) Published as Contribution No. 2274 from the laboratories of the

National Research Council of Canada. Presented in part at a Sym-posium on Alkaloid Chem istry held at the U niversity of New Bruns-wick, August, 1949.(2) See for instance (a) Adams and Govindachari, THIS JOURNAL,71, 1182 (1949) ; (h) Gates, Woodward, Newhall and Kunzli. i b i d . 72,1141 (1950).(3) Barnes, Liddel and Williams, Ind. Eng.Chrm. A n d . Ed. 5,659 (1943).

(4) Thompson, Bratt ain, Randall and Rasmussen, The Chemistryof Penicillin, Ch XI II , Princeton University Press, Princeton,N. J.

(5) Randall, Fuson, Fowler and Dangl, Infrared Determinationof Organic Structures, Van Nostrand Co. Inc., New York, N. Y.1949.(6) Jones, Humphries and Dohriner, THIS OURNAL, 72, 956 (1950),and earlier publications.(7) Chloroform purified as described above possesses an absorptionband at 3625 cm.-1. Thi s band is weak and of variable inten sity andhas been attr ibute d to traces of residual water in the solvent. Solutescontaining a non-associated hydroxyl group also give a band near 3625cm.-l, from which the solvent absorption can be subtracted. In afew cases, principally of hygroscopic solutes containing associatedhydroxyl groups, the intensity of the absorption band a t 3625 cm. -1may be diminished in the presence of t he solute, and if thi s occurs it isdifficult to evaluate th e solute absorption in the region between 3700and 3550 cm. -1. In explanation of thi s chloroform effect it is sug-gested tha t the hygroscooic solute combines with pa rt of the residualwater in the chloroform, with s hift of the band position,

(8) The apparent molecular extinction coefficient E: is defined asE: = (I/cZ) lOgIo(TdT)vwhere c is the concentration of the solute in moles per lite r; is the

cell length in cm.; and To designate the intensity of the radiation

maxima were calculated for the principal bands. Theseintensities are probably accurate to 10%. The estimatederrors in the frequencies reported are 5 cm.- for the re-gion 3700-2700 and 2 cm.-l for the region 1800-1540 em.-.Results and Discussion

Forty-seven alkaloids were investigated in chlo-roform solution under the conditions specifiedabove. The principal bands will be discussed inorder of decreasing frequency.A. Hydroxyl Bands 0-H Stretching Vibra-tion) .-It is well established3p5 hat unassociatedhydroxyl groups show sharp absorption bands inthe region 3700-3500 cm.- while hydrogen bond-ing produces a broadening of these bands and ashift to lower frequencies (usually 3500-3200cm.- .Fifteen of the alkaloids contained hydroxylgroups and of these thirteen produced sharp bandsin the region 3625-3540 cm.- while lupinine and ce-vine produced a broad absorption in the region of3400 cm.- (see Table I and Fig. 2). The apparentmolecular extinction coefficients of the sharp bandsranged from 30-90 with the exception of hunneman-ine which produced a value of 160. This high in-tensity and low frequency may be associated withthe phenolic character of the hydroxyl group. Theremaining thirty-two alkaloids, which did notcontain hydroxyl groups, showed no band in the re-gion 3700-3500 cm. l with an apparent molecularextinction coefficient greater than 10.

TABLESOLUTIONOH STRETCHING BANDSN SOME ALKALOIDSN CHLOROFORM

OH frequency,Compound cm-1 EA

Non-associated hydroxyl groupsQuinine 3625 61Dihydrolycopodine 3625 75Chelidonine 3625 30Yohimbine 3625 35+Conhydrine 3620 692 Hyoscyamine 3620 50Tropine 3620 61Cinchonidine 3620 82Jervine 3615 90Ochrobirine 3580 81cy-Methylmorphimethine 3580 70Codeine 3580 64Hunnemanine 3540 160Cevine 3520,3400Lupinine ~ 3 4 0 0Hence the presence of a sharp band in the region3625-3540 cm.-l with an apparent molecular ex-

Associated hydroxyl groups

transmitted by th e solution and solvent, respectively, when the spcc-trometer is set a t the frequency v and is the slit width in wavenumbers. Thi s differs from the molecular extinction coefficient com-monly employed in ultraviolet spectrophotometry in tha t it does notassume the radiation to be stric tly monochromatic. E: varies with theslit width and with the optical characteristics of the spectrometer.


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tinction coefficient of 30-160 may be accepted asevidence of a hydroxyl group, though the absenceof such a band does no t entirely exclude the pos-sibi lity of a hydroxyl group being present. A broadband in the region of 3400 cm.-' may indicate hy-droxyl groups in a s ta te of hydrogen bonding.B. Imino Bands N-H Stretching Vibration).-Imino groups are known to produce sharp ab-sorption bands between 3500 and 3200 C I I ~ . - ~when unassociated, and broad absorption bands he-tween 3300 and 3000 cm-l when as~oci a tect . ~~~Sixteen of the alkaloids investigated containedimino groups. Eight of these contaliieti the indolenucleus and produced sharp absorption bands be-tween 3480 and 3460 cm.-l with apparent molec-ular extinction coefficients ranging from 140-210(see Table 11). Physostigmine and gelseminewhich contain secondary amido groups also givesharp bands between 3480 and 3440 cni. withslightly lower intensities. Ergotinine which con-tains one indole nucleus and two secondary EES 1800 AND 1550 CM. - l FOR

SOMF ALK 1,OIDS S CITLOROFORM SOLTJTIOV

CompoiindAdlumidineBicucullineAnnotinineIIydrastinr.4dluminePhysostigmineErgotininehGelsemineI-IIyoscyaminrI'ohimbineJervine1,ycopodineCevineKutaecarpineIsoevodiamineN-AcetylhurmalinrStrychnineCryptocavincProtopineHunnemaninrCryptopineAllocryptopineCytisineN-MethylcytisinrThermopsineAnagyrineEvodiamineOxysparteinrPiperineAphyllidineLupanine

Bandsattributedto thecarbonylgroup,C l l l - 11778177617761775176217341728 16581720171617121703169816916771676I 668166510611GW16.5816581658165816%16.5316j216491630163516281 6 3

1. t600730590450890550

1160 1650710430340480400340760

1200540510310340330320320750750370fi60770630570750730

Otherabdnds,C l l l 1

161516151605161910041630

1613 16001665 1600

16011630 1576

1600160316171620160216201566156715661570

1814 1588

a-MethylmorphimetliineI-Iarmalin?HarmailQuininePapaverineCodeineChelidonineGramineAnabasineCinchonidine

a For assignments 5ee teut.four carbonyl group?.

16371629

1625 1602 15731624 1594

1620 1591 1570160516041600

l59? 15761593 1573This compound coutains


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Jan., 1951 THE NFRAREDBSORPTIONPECTRAF ALKALOIDS 307

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W P V E N U M BER S , cn: ),Fig. 1 -Infrared absorption spectra of piperidine and

anabasine in the regions 3700-2700 and 1800-1550-, liquid film (0.025mrn. ); - - - -, chloroform solution.a C=N stre tching vibration. Acetylharmalinegave two strong bands a t 1668 and 1630 cm.-l,the former being almost certainly the C=O stre tch-ing frequency and the latter a phenyl ring fre-quency. Ergotinine contains four carbonyl groupsand produced two bands a t 1728 and 1650 em.-'both with double the normal intensity. Seventeenof the remaining nineteen alkaloids which containno carbonyl groups produced no strong absorptionbands in the region 1780-1620 em.-'.Th e presence of a band in the region 1780-1620cm. l with an apparent molecular extinction co-efficient between 300 and 1200 in general indi-cates the presence of a carbonyl group. This isparticularly useful for detecting carbonyl groupsin compounds where the carbonyl group is re-sistant to chemical attack as in the protopine :alkaloids.The molecular extinction coefficients fall intothe same range as for the steroids (350-1350) and 5for a var iety of esters (350-770).9 Hence it ap- 3pears that carbonyl groups may be recognized anot only by characteristic band frequencies bu talso by characteristic band intensities.Correlations between the carbonyl frequenciesand molecular structures of the alkaloids are notas well defined as in the case of the steroids6This is due to the more diverse types of chemicalstructure found in the alkaloids. Nevertheless

compounds investigated is insufficient to justifythe establishment of correlatioris.

The two steroid alkaloids, jervine and cevine,gave spectra which call for separate comment.The curves of these compounds are shown in Fig.2. Th e bands a t 1703 cm.-l (E : 480) in jervineand a t 1692 cm.-' E: 340) in cevine are typicalcarbonyl maxima, and indicate the presence of acarbonyl group in each of these alkaloids. Althoughchemical evidence indicating the presence of a car-bonyl group in jervine has been p ut forward,l0 thepresence of a carbonyl group in cevine has nothitherto been suspected. The displacement of theband in cevine is not readily explained, bu t i t couldarise from internal hydrogen bonding with one ofthe hydroxyl groups.D. Other Bands. i) CH Stretching.-These vibrations produce absorption bands above3000 em.-' when the carbon atom is unsatura tedand between 3000 and 2800 em.-' when the carbonatom is ~ a t u r a t e d . ~he former bands are ob-

C E V I N E6 0 /

I

I1 . 1I

similarities of chemical structure in the neighbor- Fig. 2.-Infrared absorption spectra of cevine and jervine : --,hood of the carbonyl group are found to bepardlleled by similarities in carbonyl frequency.Thus the five lactone alkaloids listed in Table 111-adlurnidine, bicuculline, annotinine, hydrastine andadlumine-all show absorption bands in the region1778-1762 cm -I . The protopine alkaloids-crypto-cavine, protopine, hunnemanine, cryptopine andallocryptopine-containing the ten-membered ringsystem I absorb in the region 1001-1B58 em.-' withsimilar intensity. Cytisine, N-methylcytisine, ther-mopsine and anagyrine which contain the partialstructure I1 absorb at 10X-lA.S2 an.-'. Othersimilarities have been noted but the number of specific groups in the molecule.

chloroform solution; - - - Nujol mull.scured by the chloroform absorption between 3100and 3000 cm.-l bu t may be observed in othertransparent media. Thu s a thin film of anabasineshows a band a t 3030 em.-' due to the CH link-ages of the pyridine nucleus which is absent fromthe spectrum of piperidine (see Fig . 1). The bandsbetween 3000 and 2800 cm.-' may be observedin chloroform solution, but although each alkaloidproduces several absorption bands in this region,it has not been possible to assign these bands to

9) Hampton and N ew e l l , A n a l C h c m . 91, R14 1949) (10) Jacobs and Craig, J . B i d . C h c m . 170 633 1017).


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iii) Carbonyl Overtone.-Since carbonylgroups produce strong absorption bands in theregion 1780-1620 cni. -I , weak overtone bands maybe expected a t approximately twice this frequencyrange, D~z. 3560-3240 ern.--'. Such bands overlapthe regions of the OH and NH stretching bandsand may confuse the interpretation of weak bandsi n this region, though no cases of this have yet beenencountered.Bands between 1640 and 1550 Cm.-l.-Bands of moderate intensity a re frequently ob-served in the region 1640-1550 cm.-' (see Table111). Such bands generally indicate unsaturationin the molecule (C=C, C=N stretching vibra-tions), though there is the possibility that theycould be caused by NH bending vibration^.^Phenyl rings generally give absorption bands in th eranges 1640-1615 or 1605-1600 cm.-' while al-kaloids containing aromatic nitrogen rings (e. g.pyridine, quinoline rings) generally give bandsbetween 1600 and 1560 cm.-l. Thus the bandsa t 1592 and 1376 cm.-' present in the spectrumof anabasine bu t absent froni the spectrum ofpiperidine (see Fig. 1) may be assigned to thepyridine ring. Similarly the band between 1570and 1566 cm.-' found in the spectra of cytisine,S-methylcytisine, thermopsine and anagyrine maybe assigned to the a-pyridone ring 11). The ob-servation of bands in this region gives an indica-tion of t he types of structure which might be presentbut does not permit an unambiguous choice to bemade owing to the multiple interpretations possibleizliz., cevine and jervine).(iv) Bands at Lower Frequencies-The spec-tra included in this survey do not extend beyond1340 cni. -' due to the strong absorptions of thechloroform. Satisfactory spectra are obtained,however, by using Nujol mulls2aor thin films of thealkaloids. X great deal of complex structure isfound in the region 1500-GO0 c i i i . ~ ~ ,nd as yetthe assignment of bands in this region to specificgroups in the molecule is comparatively untle-

(iii)

veloped. The chief value of such spectra lies inthis high specificity, which offers a very delicatemethod for the identification of individual alkaloids.Thus they have been used to confirm the identityof monolupine, rhombinine and anagyrine.Acknowledgments.-The authors wish to thankMr. li. Lauzon for technical assistance in therneasurenient of t he spectra.

SummaryThe infrared absorption spectra of forty-seven alkaloids have been investigated in theregion 3700-1 340 cm.-' in dilute chloroform solu-tion.2. Hydroxyl groups may generally be detectedby t he appearance of a sharp band in the region3625-3540 cm.-l with an apparent molecular ex-tinction coefficient of 30-160 though there areexceptions.Imino groups produce a sharp band in theregion 3480-3440 cm.-' with an apparent molec-

ular extinction coefficient of 100-210 when theimino group is present in an indole nucleus orsecondary amido group. When the imino groupis present in a piperidine ring, however, the ab-sorption is much weaker but may be observed atincreased path lengths.Carbonyl groups may be detected by theappearance of a s trong band in the region 1780-1620 cm.-l with an apparent molecular extinctioncoefficient from 300-1200. Certain correlationshave been established between the carbonyl fre-quency and the type of carbonyl group present.Phenyl rings generally give absorption bandsin the region 1640-1600 ern.-' while aromaticnitrogen rings generally give bands between 1600and 1560ern.-'.The presence of a carbonyl group both inceviiie and jervine is indicated by the infraredabsorption spectra.OTTAWA, ANADA

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(11) Marion and Ouellet,THISOURNAL TO 3076 (1948).RECEIVED AP27, 1950

[CONTRIBUTIONROM THE DEPARTMESTF CHEMISTRY,TNIVERSITPF MICHIGAN]Energetics of the Adsorption of Aliphatic Amines by Silica Gel1

RY DONALD . DO RAY,^ YINGF u AND F. E. BARTELLIn a previous communication3 adsorption iso-therms of diethylamine, n-butylamine and di-n-butylamine on silica gel a t 25 were presented andtheir significance as relating to the nature of theadsorption process discussed. In the present paperthese adsorption systems will be considered fromth e basis of energy changes.Isosteric Heats, AH , A F and as of Adsorption.-In order to determine the isosteric heats, ad-sorption isotherms for these amines a t 40 were

_ _

(1) A portion of the material in this paper is from a dissertation sub-mitted to the Horace H . Rackham School of Graduate Studies byDonald G. Dobay in partial fulfillment of th e requirement- for the rleFree of Doctor of Philoso phy, Septemher, 1948.

2) Linde Air Products Company, Tonawanda, N Y.( 3 ) Bartell and Dobay, THIS OURNAL, 72, 4388 (19601

obtained and the pressure range employed wasfrom zero to a value higher tha n t ha t correspond-ing to t he inception of th e hysteresis effect.These da ta are given in the first column of Table I.The isosteric heats were calculated by means ofthe Clapeyron equationwhere dQ/d(x/m) represents the differential iso-steric heats of adsorption and the p-values repre-sent th e pressures a t which equal amounts of theamines were adsorbed by the solid at the twodifferent temperatures. This method of calculatingthe isosteric heats requires that the surface area ofthe solid be considered as being independent of th etemperature. While this is not strictly true, the

d Q l d ( x ' ~ ) RTiTZlog, p , l p J ,(Ti - T?) (1)

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Infreared Alkaloids