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Ion-Molecule Reactions in Acetaldehyde and Methanol

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Ion-Molecule Reactions in Acetaldehyde and Methanol MASS SPECTROSCOPY Original Papers Vol.20,No.4,December1972 Ion-Molecule Reactions in Acetaldehyde and Methanol SATOSHI OKADA*,AKIRA MATSUMOTO**,TAKAAKI DOHMARU*, SETSUO TANIGUCHI*AND TERUO HAYAKAWA** (Received10November1972) The thermal energy ion-molecule reactions in acetaldehyde and methanol have been studied by mass spectrometry using a pulsed ion source.The rate constants of transfer of light hydrogen and deuterium from methyl and formyl groups of acetaldehyde have been separately treated ,and those of transfer of light hyd rogen from methyl and formyl groups have been estimated to be0 .98•~10-9and1.97•~10-9cm3.molecule-1•E sec-1,respectively.In the methanol system ,the indirect isotope effect and the ion repeller voltage dependence on the rate constants for hydrogen transfer reactions are given and compared with the results reported by other workers. 1.Introduction these points,we have studied the thermal The studies of the ion-molecule re energy ion-molecule reactions of acetal actions involving polar molecules like dehyde and methanol including those acetaldehyde1),2)and methanol3),4)are of labeled with deuterium. interest in the field of ion-molecule reac tions itself,and have also given us many 2.Experimental important informations on the mechanisms The experiments were performed on a of the radiation chemical reactions in these Hitachi-RMU5 mass spectrometer pro systems. vided with the pulsed ion source which In the formation of protonated acetal had been described by Harrison and co dehyde from the reaction between the workers.7)The operating condition in this acetaldehyde ion and its neutral molecule, study was•|10V bias and10V pulse of however,the respective probabilities of 0.2ƒÊsec width to the electron beam slit, hydrogen transfer from methyl and formyl and10V pulse of1ƒÊsec width to the ion groups have not yet been evaluated. repeller plate and the repetition rate was In methanol,the measurements of rate preferred100kHz.In some cases,a con constants or cross sections have been tinuous voltage was supplied to the ion reported3),5),6),but these results do not repeller plate so that primary ions posses indicate a good consistence with each the kinetic energy.A10-stage electron other.This may mainly come from the multiplier of Ag-Mg(2%)electrodes was difference in experimental conditions, used as a detector of the ion current.The especially in the kinetic energy of ions correction of gains for primary and studied. secondary ions produced from acetal To provide further informations on dehyde and methanol was not done, *RadiationCenter of OsakaPrefecture ,Sakai,Osaka,Japan. **Departmentof Chemistry,Facultyof LiberalArts and Sciences,Universityof Osaka Prefecture,Sakai,Osaka,Japan. －311－ S.Okada,A.Matsumoto,T.Dohmaru,S.Taniguchi and T.Hayakawa because the measurable difference in the several concurrent reactions in its for gain was not observed in the mass range mation is given by studied. kiIpi[M]t+C,(4)Is= Normal CH3CHO was prepared from paraaldehyde and was purified by vacuum where Is is the intensity of the secondary distillation.Acetaldehyde-d1 was produced ion formed in the reaction time t,Ipi is by the isotopic exchange reaction between the intensity of the reactant ion of i-species, nitromethane and D2O and was purified and ki is the rate constant of the reaction by vacuum distillation.The composition producing the secondary ion from the of acetaldehyde-d1was90%of CH3CDO, reactant ion of i-species and a neutral 8%of CH2DCHO and2%of CH3CHO, molecule whose concentration is[M]. and no existence of acetaldehyde-d2was By selecting energy of ionizing confirmed by mass spectrometry and electrons each of reactions(1),(2),and(3) N.M.R.CD3OH and CH3OD obtained may be separated in this system.Figure1 from E.Merck.AG.and Dohme of Canada shows a typical I45/I44vs.delay time plot had purity of more than99%and were at10eV electron energy where reaction used without further purification. (1)occurred predominantly.From the slope The rate constants of the ion-molecule obtained in these measurements the rate reactions studied were calibrated by k constant for reaction(1)has been deter =1 .22•~10-9cm3.molecule-1.sec-1of the mined to be k1=2.95•~10-9cm3•Emolecule-1•E hydrogen transfer reaction for CH+4+CH4 sec-1.The experiments at10•`12eV H+5•{CH3which was reported •¨C by electron energy where CH3CHO+and Gupta and co-workers.4) CH3CO+were the significant primary ions give the plot of[k1+(I43/I44)k2]with 3.Results and Discussion various I43/I44ratios as shown in Fig.2. 3.1Acetaldehyde Evidently from Fig.2the value of k2is The ion-molecule reactions in the very small.In a higher electron energy CH3CHO system have been studied at range(12•`30eV),reactions(1)and(3) pressures up to10-4Torr and at10•`30 are thus significant.The plot of[(I44/I29)k1•{ eV electron energy.In agreement with k3]with various I44/I29ratios gives a the results obtained by Harrison1)and good straight line as seen in Fig.3.The Munson2),the only significant product ion slope and the intercept give k1=2.8•~10-9 was CH3CHOH+,The main primary ions and k3=3.69•~10-9cm3•Emolecule-1•Esec-1, were CH3CHO+,CH3CO+and CHO+in this respectively.This k1value obtained from energy range of electrons.The following Fig.3is in good agreement with k1=2.95 reactions are thus occurring: 10-9cm3•E molecule-1•Esec-1 obtained •~ at 10eV electron energy within the experi CH3CHO++CH3CHO•¨CH3CHOH++{CH3CO CH2CHO,(1) mental errors.The present study gives CH3CO++CH3CHO•¨CH3CHOH++CH2CO,(2) the rate constant ratio k3/k1=1.25in CHO++CH3CHO•¨CH3CHOH++CO.(3) good agreement with the ratio1.2 8 reported previously by Harrison.1) According to Harrison and co-workers,7) The experiments were performed by the intensity of a secondary ion having using monodeuterated acetaldehyde － 312－ Ion-Molecule Reactions in Acetaldehyde and Methanol 5. / O1O 誉4101 蚕 σ(y・'○ 遣3' ,o'。' 2 1 012 Delay time(μsec) Fig.1.Typical plot of I45/I44vs.delay time at10eV electron energy in the acetaldehyde system. 10 § 三 芝9 濤(艦 ・・o ミ ーOoo ～ミ8 ミ 羊 ご37 6 00.050.100.15 I43/I44 Fig.2.Plot of[k1+(I43/I44)k2]vs.I43/I44at10•`12eV electron energy in the acetaldehyde system. －313－ S.Okada,A.Matsumoto,T.Dohmaru,S.Taniguchi and T.Hayakawa 4/ o 糞 × 一3 三 12/. 遣/ 等 L.1 〕 0 01234 I44/I29 Fig.3.Plot of[(I44/I29)k1+k3]vs.I44/I29in a higher electron energy range in the acetaldehyde system. (CH3CDO:90%,CH2DCHO:8%,and CH2DCHO++CH3CDO kfD•¨CH2DCHOD++CH3CO,(5e) CH3CHO:2%)as an attempt to determine CH2DCHO++CH3CDO kmD+•¨CH3CDOD++CH2CHO,(5f) the hydrogen transfer reaction from methyl CH2DCHO++CH2DCHO kmD+•¨CH2DCHOD++CH2CHO,(5g) and formyl groups at10eV electron CH2DCHO++CH2DCHO kmD•¨CH2DCHOD++CH2CHO,(5h) energy.To obtain the sum of concurrent where kmD+,for instance,is the rate reactions having different contribution, constant of the deuteron transfer reaction both of the proton transfer reaction from from the monodeuterated methyl group of the parent ion and the hydrogen atom the acetaldehyde ion,kmD is the rate transfer reaction from a neutral molecule, constant of deuterium atom transfer from and further,two occasions from methyl the monodeuterated methyl group of the and formyl groups for each of them must acetaldehyde molecule,and the suffix m be taken into consideration.Neglecting or f denotes that transfer occurs from the isotope effects except those between trans methyl or formyl group,respectively. ferring particles,the following eight Similarly,for the formation of m/e reactions giving m/e=47ions are con =46ions the following twenty-four sidered: reactions are considered: C H3CDO++CH3CDO kfD+•¨CH3CDOD+•{CH3CO,(5a) CH3CDO++CH3CDO kmH+•¨CH3CDOH++CH2CDO,(6a) CH3CDO++CH3CDO kfD•¨CH3CDOD+•{CH3CO,(5b) CH3CDO++CH3CDO kmH•¨CH3CDOH++CH2CDO,(6b) CH3CDO++CH2DCHO kfD+•¨CH2DCHOD++CH3CO,(5c) CH3CDO++CH2DCHO kmH+•¨CH2DCHOH++CH2CDO,(6c) CH3CDO++CH2DCHO kmD•¨CH3CDOD++CH2CHO,(5d) －314－ Ion-Molecule Reactions in Acetaldehyde and Methanol CH3CDO++CH2DCHOkmHCH3CDOH++CHDCHO,(6d) As seen in Table1,the rate constants CH3CDO++CH2DCHOkfHCH3CDOH++CH2DCO ,(6e) (k'fHand k'fD)of hydrogen transfer from the CH2DCHO++CH3CDOkmH+CH3CDOH++CHDCHO,(6f) formyl group are about twice as large as CH2DCHO++CH3CDOkmHCH2DCHOH++CH2CDO,(6g) those(k'mHand k'mD)fromthe methyl group. CH2DCHO++CH3CDOkfH+CH3CDOH+CH2DCO,(6h) It should also be noted that k'mHand k'fH CH2DCHO++CH2DCHOkmH+CH2DCHOH++CHDCHO,(6i) are smaller than k'mDand k'fD respectively, CH2DCHO++CH2DCHOkmHCH2DCHOH++CHDCHO,(6j) though k'mD,has a relatively large uncer CH2DCHO++CH2DCHOkfH+CH2DCHOH++CH2DCO,(6k) tainty in its evaluation since it has the CH2DCHO++CH2DCHOkfHCH2DCHOH++CH2DCO,(6l) small factor as shown in Eqs.(7)and(8). CH3CDO++CH3CHOkmHCH3CDOH++CH2CHO,(6m) 3.2Methanol CH3CDO++CH3CHOkfD+CH3CHOD++CH3CO,(6n) As have been studied by many CH3CDO++CH3CHOkfHCH3CDOH4+CH3CO,(6p) workers2),3),5),8),under the experimental CH2DCHO++CH3CHOkmD+CH3CHOD4+CH2CHO,(6q) conditions in this study that10-16eV CH2DCHO++CH3CHOkmHCH2DCHOH++CH2CHO,(6r) electron energy and relatively low pres CH2DCHO++CH3CHOkfHCH2DCHOH++CH3CO,(6s) sure range,the significant secondary ions CH3CHO++CH3CDOkmH+CH3CDOH++CH2CHO,(6t) observed were CH3ODD+and CH3ODH+ CH3CHO++CH3CDOkfH+CH3CDOH++CH3CO,(6u) and the significant primary ions were CH3CHO++CH3CDOkfDCH3CHOD++CH3CO,(6v) CH3OD+and CH2OD+in the CH3OD CH3CHO++CH2DCHOkmH+CH2DCHOH++CH2CHO,(6w) system.These CH3ODD+and CH3ODH+ mDCH CH3CHO++CH2DCHOk 3CHOD++CH2CHO,(6x)ions are considered to be produced by CH3CHO++CH2DCHOkfH+CH2DCHOH++CH3CO.(6y)the following reactions: Applying Eq.(4)to our experimental CH3OD++CH3ODkhCH3OD+CH3OD+CH3O,(9)
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