Ethylation of ethanol in the gas phase

Abstract

Etbylation of Ethanol in the Gas PhaseIn the gas phase, alkyl halides RX lead either to alkylation' or protonation reactions. ' The reagent in these processes (RX", R+ or R-X+-R) can often be determined by ion cyclotron resonance but not so easily under chemical ionization conditions. In this work, CH, CD, I and CD, CH, I have been used to determine the mechanism of the ethylation of ethanol by CH, CH, I in the source of a mass spectrometer (VG ZAB 2F).In the ion source, equimolecular quantities of C, H, OH and of ethyl iodide lead to the formation of the symmetrical protonated ether CH, CH,-OH-CH, CH, . This ion has been selected with the magnetic field and characterized by the fragmentations observed in the 2nd field-free region (2nd FFR).In Table 1, the spontaneous fragmentations of metastable protonated diethyl ether 1 and its deuterated analogues la-lc have been compared to those of the corresponding ions 2 and 3 generated by ion-molecule reactions. The metastable ion 1 loses ethylene after H(B) migration leading to the CH,CH,OH, fragment ion (m/z 47). The results from la-lc show that the H(B) migration is selective; a strong primary isotopic effect (lc) and a less important secondary isotopic effect (lb) are observed: CH, CH,-OD--CH,CH,, la gives only CH, CH,OHD' + + m/z 48 + CH, CH,-OH--CD, CH, , l b leads to m/z 47 (43%), m/z 49 (56.5%), and + CH, CH,-OH-CH, CD,, lc leads to m/z 48 (29%) and m/z 50 (70%).The same results are obtained for the isomeric ions 2a, 2b and 2c generated by reaction of labelled ethanols with CH, CH, I (Table 1).However, the behaviour of 3a and 3b ions, formed by reaction between labelled alkyl iodides and ethanol, shows that two mechanisms are implied in the ethylation reaction. The first one is dominant and selective while, for the second one, hydrogens of the ethyl iodide exchange before alkylation. The non-specific mechanism corresponds, most probably, to the reaction between the ethyl cation and ethanol. Indeed, spontaneous and collision induced dissociations of [CD,CH,] + and [CH2CD3]+ metastable cations show that extensive H/D exchange occurs before the 2nd FFR.However, the collision-induced dissociations of [CH,CD,I]+' and [CD,CH,I]+' metastable ions indicate that in the 2nd FFR these ions still have their initial structures: H/D exchange is not observed. The same conclusion has been obtained by neutralization-reionization mass spectrometry., It is possible to conclude from these results that the reaction between [ICH,CH3]+' and C,H,OH corresponds to the dominant and selective mechanism.The existence of the adduct ion [CH,CH,I/CH,CH,OH]+ has been proved: this adduct ion has been selected with the magnetic field; in the 2nd FFR this ion leads to[CH3CH21]+' and CH,

Determination of branching ratios for the reactions of H3O+ with ethylbenzenes as a function of relative kinetic energy

“…1c- Our results indicate that H atom migration from both the ␣ and ␤ positions of the side chain occurred in the ethylene elimination reaction, as reported previously [7,8]. In the mass spectrum of C 6 D 5 CD 2 CH 3 , the H/D exchange was substantial for both the benzenium-type ions and the ethylbenzenium-type ions, as was the case for C 6 D 5 CD 2 CD 3 ; whereas H/D exchange seems to have been suppressed for C 6 H 5 CH 2 CD 3 and C 6 H 5 CD 2 CH 3 .…”

“…Fig. 4 shows a plot of i vs. ␣ 1 ; the data obtained in the present study are shown as filled circles with error limits, and data from previous studies [7,8] are also plotted. Our data overlapped with the data for CH 4 , CD 4 , and H 2 O CI, but the data for H 2 and D 2 CI gave higher ␣ 1 values and lower i values.…”

“…Audier et al [8] [11]. The similarity between the results by CH 4 CI and H 2 O CI is thought to be coincidental [6].…”

“…(1)), a hydrogen atom migrates from the alkyl group to the ring. Isotope-labeling studies are useful for elucidating mass spectrometric fragmentation mechanisms, and CI-MS studies involving deuterium labeling of the side chain have been performed for primary alkylbenzenes [7][8][9][10]. H 2 , D 2 , CH 4 , and CD 4 CI studies of ethyl-and n-propylbenzenium ions by Leung and Harrison [7] showed that the migrating hydrogen atoms originate from all positions of the side chain for both compounds but that the positions are slightly preferred as donor sites.…”

Isomerization reaction of [C6H6 C4H] π complexes

“…In metastable protonated ethylbenzene 1 the permutation of the aliphatic hydrogens prior to C2H4 loss is incomplete but observed. This is in agreement with isomerization via 1,2-hydrogen shift in the n-complex [c6& C,H:] , 34 but a concerted pathway cannot be discarded. Metastable protonated n-propylbenzene 2 isomerizes irreversibly but completely to protonated isopropylbenzene 3 prior to d i s s~c i a t i o n ,~~,~~ while for the less energetic metastable ion 3 two interconverting complexes [C6H, s-C,H;] and [C,H; C,H,] are intermediates in the reaction process.…”