On the formation of protonated acetic acid from ionized <i>n</i>‐alkanoic acids in the gas phase

Halim, Herman; Schwarz, Helmut; Terlouw, J. K.; Levsen, K.

doi:10.1002/oms.1210180403

Cited by 15 publications

(10 citation statements)

References 11 publications

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“…Nevertheless the compound 1 is one of the ethyl esters, the McLa#erty ῌ1 rearrangement precedes the conventional McLa#erty one. 6) This result is supported by the fact that the total heats of formation of the former reaction (231 kJ mol ῍1 ) is lower than that of the latter (300 kJ mol ῍1 ) by 69 kJ mol ῍1 , 12) which values were calculated by use of the PM3 method. 13), 14) It has been proposed that this C 2 H 3 loss occurs via five and four membered ring transition states.…”

Section: Resultsmentioning

confidence: 87%

“…Consequently, nearly the same amounts of C 2 H 2 D and C 2 HD 2 are eliminated. Therefore, the random losses of C 2 H 2 D and C 2 HD 2 from 1-d 6 ῌῌ is reasonably explained without assuming any hydrogen scrambling in an ethyl group. The m/z 132 ions from 1 ῌῌ are generated through a conventional McLa#erty rearrangement.…”

Section: )῎19)mentioning

confidence: 88%

“…6) This is the second highest fragment peak in its mass spectrum. Molecular ion of ethyl acetate (CH 3 C(῎O)OC 2 H 5 , M w : 88) also decomposes into the m/z 61 ion by the loss of C 2 H 3 through a McLa#erty ῌ1 rearrangement.…”

Section: )῎4)mentioning

confidence: 94%

“…Further, the generation of the m/z 91 from 1-d 6 ῌῌ can not be explained by this mechanism, because this ion contains only three D-atoms. The latter disadvantage has also been pointed out by Wilson and McCloskey,9) because the m/z 91 ion from 1-d 6 ῌῌ must be generated by the migration of a-hydrogen in the ethyl group, not b-hydrogen.…”

Section: )῎19)mentioning

confidence: 99%

“…20) According to the Grutzmacher and Masur, 20) we propose an alternative mechanism of the generation of the m/z 88 ions by the loss of C 3 H 4 O 2 (CO ῌ CH 3 CHO) from 1 ῌῌ . Scheme 2 shows the fragmentation mechanism of 1-d 6 ῌῌ instead of 1 ῌῌ . At first the ethoxy-carbonyl ion, CD 3 CH 2 OC῍ O ῌ , and the neutral radical, CH 2 C(῍O)OCH 2 CD 3 , are generated by the a-cleavage at the ionized carbonyl oxygen.…”

Section: )῎19)mentioning

confidence: 99%

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Unimolecular Reactions of Diethyl Malonate Cation in Gas-phase

Tajima

Ishiguro

Mamada

et al. 2004

J. Mass Spectrom. Soc. Jpn.

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Unimolecular reactions of diethyl malonate cation (CH3CH2OC(῎O)CH2C(῎O)OCH2CH3ῌῌ ; 1 ῌῌ , Mw : 160) induced by electron ionization, have been investigated by use of mass-analyzed ion kinetic energy (MIKE) spectrometry and D-labeling in conjunction with thermochemistry. In the metastable time window, the molecular ions ῌ ) ions decompose into the ions at m/z 115, 106, and 105 by the losses of H2O, C2H3, and C2H4, respectively. A large part of the first fragment ions would be in the keto form and it decomposes into the m/z 71 and 43 ions by the losses of CO2 and C3H4O2 (or C2O3), and a small part would be in the enol form and decomposes into the m/z 87 ions by the loss of C2H4, not CO. The m/z 43 ions are isobaric, C2H3Oῌ and C3H7 ῌ .

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Section: Resultsmentioning

confidence: 87%

Section: )῎19)mentioning

confidence: 88%

Section: )῎4)mentioning

confidence: 94%

Section: )῎19)mentioning

confidence: 99%

Section: )῎19)mentioning

confidence: 99%

See 3 more Smart Citations

Unimolecular Reactions of Diethyl Malonate Cation in Gas-phase

Tajima

Ishiguro

Mamada

et al. 2004

J. Mass Spectrom. Soc. Jpn.

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A novel fragmentation process in RC+(OCH3)2 ions (R = H, CH3). The transfer of a hydrogen atom and a methyl group

Tajima

Fujizuka

Sekiguchi

1999

Rapid Commun. Mass Spectrom.

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Received 24 December 1998; Revised 10 February 1999; Accepted 11 February 1999 Information about the mechanism of hydrogen or skeletal rearrangement during the fragmentation of ions plays an important role in the interpretation of mass spectra. Double hydrogen atom transfer (so-called transfer of two hydrogen atoms) is observed in the mass spectra of propyl and higher alkyl esters, 1,2 isobutanol, 3-5 1,2-ethanediol, 6-8 hydroxyacetone, 9,10 methyl glycolate 6,8,11 and methyl lactate. 12 In particular, in the mass spectra of isobutanol, 1,2-ethanediol and methyl lactate, a fairly intense oxygen-protonated methanol ([CH 3 OH 2 ] , m/z 33) is generated by double hydrogen atom transfer.Recently, we have noticed that the ion at m/z 47 (m/z 33 14 u) is generated in the metastable decomposition of the ions from dimethyl acetals, dimethoxymethane, CH 2 (OCH 3 ) 2 (1) and 1,1-dimethoxyethane, CH 3 CH(OCH 3 ) 2 (2). In this short communication, we investigate the fragmentation processes of the ions at m/z 75 [HC (OCH 3 ) 2 ] from 1 and m/z 89 [CH 3 C (OCH 3 ) 2 ] from 2, with attention to the formation of CH 3 OH CH 3 (m/z 47), by a combination of mass-analyzed ion kinetic energy (MIKE) spectrometry and deuterium labeling. EXPERIMENTALThe mass and MIKE spectra were obtained using a JEOL JMS-HX 100 tandem mass spectrometer. Samples were introduced via a heated (100°C) inlet system from which they were leaked into the ion source (180°C). The electron energy was 70 eV, and the ion accelerating voltage was 5 kV. MIKE spectra were obtained by scanning the voltage of the second electric sector, to observe the decompositions in the third field-free region of the ions of interest selected by the magnetic sector.Samples 1 and 2 were research grade products from Tokyo Kasei Co. Ltd., and were used without further purification. Samples 1-d 6 , (CH 2 (OCD 3 ) 2 ), and 2-d 6 , (CH 3 CH(OCD 3 ) 2 ), were prepared from formaldehyde and acetaldehyde with CD 3 OD, respectively. RESULTS AND DISCUSSIONThe MIKE spectra of the ions at In the metastable time window, the ion at m/z 75 (HC (OCH 3 ) 2 ) from 1 eliminates, essentially exclusively, a neutral species with mass 28 u to generate the m/z 47 ion. The peak at m/z 47 shifts fully to m/z 53 in the MIKE spectrum of the ion at m/z 81 (HC (OCD 3 ) 2 ) from 1-d 6 (see Fig. 1(b)). This means that the 28 u fragment lost is CO, not C 2 H 4 . Taking into account the known fragmentation of O-protonated methyl formate (HC (OH)OCH 3, m/z 61), 6,8,12 we propose the fragmentation mechanism shown in Scheme 1(a), of HC (OCH 3 ) 2 ion at m/z 75 from 1 to m/z 47. This mechanism includes the transfer of a hydrogen atom and a methyl group to the ether oxygen followed by the loss of CO.As shown in Fig. 2(a), although its relative abundance is not so high, the m/z 47 ion is also generated by the loss of CH 2 CO from the m/z 89 ion of 2. This m/z 47 ion also shifts to m/z 53 in Fig. 2(b). This result is explained by a similar mechanism. This fragmentation is also shown in Scheme 1(b). In other words, the tra...

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Chemical ionization mass spectrometry of carbamates. 1—N-phenylcarbamates—propham and chlorpropham

Cairns

Siegmund

Stamp

1984

Biol. Mass Spectrom.

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Under ammonia and methane chemical ionization conditions, using a liquid chromatographic moving belt interface for sample introduction, molecular weight information has been observed for two representative N-phenykarbamates, propham (isopropyl N-phenylcarbamate) and chlorpropham [isopropyl N-(3 -chlorophenyl)carbamate]. Displacement reactions can occur in which the side-chain is expelled as a neutral olefin via a hydrogen rearrangement. The temperature dependence of these spectra has been studied and the relative concentration of [MH 1' ions increases with decreasing temperature. INTRODUCTIONAnalysis of carbamate pesticides by gas chromatography has been seriously hampered by their reported thermal lability.17' Attempts at analytical separation and identification of N-phenylcarbamates have employed derivatization3 or liquid chromatogra hy4 to avoid thermal decomposition to isocyanates.' More recently, liquid chromatography/mass s ectrometry (LC/MS) has been successfully emp1oyed7,'in the quantitative analyses of carbamates and ureas. While the use of the moving belt interface employed in these previous studies has avoided thermal decomposition via flash vaporization from a polyimide belt, a full explanation of the resultant fragmentation processes was not forthcoming. As a first preliminary step to developing an analytical protocol for residue work, the characterization of such compounds is commonplace in ascertaining the appropriate temperature, reagent gas and ions to be monitored. In the course of characterizing two representative carbamates, propham (1) and chloropropham (2) by LC/MS, certain spectral elements emerged which required detailed study and comment. To assist in this structural investigation, the corresponding N-methylated chlorpropham (3) was prepared and also studied. In this paper, we now report an SE2 reaction as responsible for the major fragment ion in these two compounds via a hydrogen rearrangement mechanism. t Author to whom correspondence should be addressed. EXPERIMENTALAll spectra were obtained on a Finnigan Model 3300 quadrupole mass spectrometer equipped with a chemical ionization (CI) source, INCOS data system and Finnigan liquid chromatographic moving belt interface. Kapton belts were used with a variable flash vaporizer temperature, a CI source temperature of 180°C and a source pressure of 0.8 Torr (adjusted to maximize the intensity of the CH: or the NH: signals). Compounds were spotted on the moving belt using 2 ~1 of standard solutions made up at the concentration level of 1 mg m1-I.The N-methyl derivative of chlorpropham was prepared by alkylation with iodomethane and sodium hydride. The isolated product was estimated by mass spectrometry to be greater than 95% pure and was used without further purification. Figure 1 illustrates the mass spectra obtained for propham (1) using CH4, C2H4 and NH3 as reagent gases. At 220 "C a protonated molecular ion at rn/z 180 is observed with a low relative abundance. The major fragment ion at m / z 138 represents a loss of 42 u from [MH]+. Whi...

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On the formation of protonated acetic acid from ionized n‐alkanoic acids in the gas phase

Cited by 15 publications

References 11 publications

Unimolecular Reactions of Diethyl Malonate Cation in Gas-phase

Unimolecular Reactions of Diethyl Malonate Cation in Gas-phase

A novel fragmentation process in RC+(OCH3)2 ions (R = H, CH3). The transfer of a hydrogen atom and a methyl group

Chemical ionization mass spectrometry of carbamates. 1—N-phenylcarbamates—propham and chlorpropham

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