Methanol ions, decomposition

The reaction chemistry of simple organic molecules in supercritical (SC) water can be described by heterolytic (ionic) mechanisms when the ion product 1 of the SC water exceeds 10" and by homolytic (free radical) mechanisms when <<10 1 . For example, in SC water with Kw>10-11 ethanol undergoes rapid dehydration to ethylene in the presence of dilute Arrhenius acids, such as 0.01M sulfuric acid and 1.0M acetic acid. Similarly, 1,3 dioxolane undergoes very rapid and selective hydration in SC water, producing ethylene glycol and formaldehyde without catalysts. In SC methanol the decomposition of 1,3 dioxolane yields 2 methoxyethanol, il lustrating the role of the solvent medium in the heterolytic reaction mechanism. Under conditions where K klO"11 the dehydration of ethanol to ethylene is not catalyzed by Arrhenius acids. Instead, the decomposition products include a variety of hydrocarbons and carbon oxides. 

Intermolecular isotope effects have been studied in the El mass spectra (at low energies of 11—35eV) of variously deuterated methanols [197]. Studies of metastable ion decompositions in deuterated methanols revealed small intermolecular isotope effects for H atom loss [76, 536]. 

Treatment of A-nitroso-iV-(cr5-2-phenylcyclopropyl)urea with excess sodium formate in methanol at 25 "C for 15 hours affords ( )-3-methoxy-l-phenylprop-l-ene (25%) and 3-methoxy-3-phenylprop-l-ene (60%, Table 15, entry 7). An almost identical result is obtained when the tran -isomer is used as substrate. Formation of the 2-phenylcyclopropyldiazonium ion, decomposition with loss of nitrogen to the 2-phenylcyclopropyl cation, followed by ring opening to form the phenylallyl cation, can explain the result. When [l- Hi]aminocyclopropane is subjected to deamination with nitrous acid in water at 0°C (Table 15, entry 8), allyl alcohol is obtained, which is isolated as the 4-(phenylazo)benzoate derivative in 44% yield. In this case, the deuterium is only located at the C2 allyl position. ... 

On the basis of the nucleophilicity parameters B, NBs, and fi (see Table 8-2) one expects less of the homolytic product in water than in methanol. This is, however, not the case. It has been known for many decades that a very complex mixture of products is formed in the decomposition of diazonium ions, including polymeric products, the so-called diazo tars. In alcohols this is quite different. The number of products exceeds three or four only in exceptional cases, diazo tars are hardly formed. For dediazoniation in weakly alkaline aqueous solutions, there has, to the best of our knowledge, been only one detailed study (Besse et al., 1981) on the products of decomposition of 4-chlorobenzenediazonium fluoroborate in aqueous HCOf/ CO]- buffers at pH 9.00-10.30. Depending on reaction conditions, up to ten compounds of low molecular mass were identified besides the diazo tar. 

Ethylenethiourea (ETU) is a toxic decomposition product/metabolite of alky-lenebis(dithiocarbamates). This compound could be generated during processing of treated crops at elevated temperature. Different chromatographic methods to determine the residue levels of ETU have been published. After extraction with methanol, clean-up on a Gas-Chrom S/alumina column and derivatization (alkylation) with bro-mobutane, ETU residues can be determined by GC with a flame photometric detector in the sulfur mode. Alternatively, ETU residues can also be determined by an HPLC method with UV detection at 240 nm or by liquid chromatography/mass spectrometry (LC/MS) or liquid chromatography/tandem mass spectrometry (LC/MS/MS) (molecular ion m/z 103). ... 

Reactions of Phosphonium Salts.- Interest continues in the effects of solvent on the rate of alkaline decomposition of phosphonium salts. It has now been shown that, in the respective reactions of hydroxide ion and methoxide ion with tetraphenyl-phosphonium bromide in mixtures of DMSO and methanol, the rates of the reactions increase as the proportion of the dipolar aprotic... 

It was found that the rate constant of the forward decomposition of the surface bidentate formate (DCOO ) to produce D2 and C02 increased from 0.34X10 4 sec-1 under vacuum to 5.3 X10-4 sec-1 under ambient water. Electron donors such as NH3, CH3OH, pyridine, and THF also increased the decomposition rate the rate constants of the forward decomposition of the surface formates at 553 K were determined to be 28.0X10 4, 7.7X10 4, 8.1X10-4, and 6.0X10 4 sec-1 under NH3, methanol, pyridine, and THF vapors (0.4 kPa), respectively. It is likely that the driving force for the forward decomposition of the formate is electron donation of the adsorbed molecule to the Zn ion on which the bidentate formate adsorbs. The reactant-promoted mechanism for the catalytic WGS reaction on ZnO is illustrated in Scheme 8.2. 

As noted after equation 4.17, the procedure to evaluate standard enthalpies of formation from appearance energies is somewhat controversial. When the threshold energies are determined from electron impact experiments, it has been argued that the correction terms (H%9S - Hq)a+ + (77298 - o)b - 6.197 in equation 4.17 should not be included in the calculation [66], Consider, for instance, reactions 4.21, and 4.22 where the ion CH2OH+ was produced from the decomposition of 1-propanol or methanol. 

Figure 3. Scheme of ozone decomposition mechanism in water. P = promoter (e.g. ozone, methanol), S = scavenger or inhibitor (e.g. /-butanol, carbonate ion), I = initiator (e.g. hydroxyl ion, perhydroxyl ion) (adapted by Beltran [35]). 

I2]. The substantial solubilities of these compounds in chloroform and other less polar organic solvents are in agreement with their formulation as nonelectrolytes. In methanol at 25° C., the molar conductivities of 166 and 167 ohm-1 for [Ni-(NH2CH2CH2S-CH3)2I2] and [Ni(NH2CH2CH2S-CH2C6H5)2I2], respectively, are characteristic of di-univalent electrolytes in this solvent, indicating almost complete solvolysis of the coordinated iodide ions in this relatively polar solvent. Decomposition of these complexes was observed upon dissolving in water. Visible and near-infrared spectra results are also consistent with structure VI. 

Recently, a novel reaction mechanism was proposed for the alkylation of aniline with methanol on acidic zeolite HY (243). By SF MAS NMR spectroscopy, the formation and decomposition of N, AA-trimethylanilinium ions on the working catalyst were observed. Figure 29 shows the MAS NMR spectra recorded under CF conditions during methylation of aniline by methanol at reaction temperatures of 473-523 K. In these experiments, a mixture of aniline and C-enrichcd methanol (WjF — 40gh/mol) in a molar ratio of 1 2 was injected into the MAS NMR rotor... 

The reaction mechanism including the formation and decomposition of quaternary cations may be a general pathway in amine alkylation processes on acidic zeolites. Pouilloux et al. (247), for example, synthesized dimethylethylamine from ethylamine and methanol on an acidic catalyst. At the reaction temperature of 503 K, trimethylamine was determined by gas chromatographic analysis, which can be explained by the formation and decomposition of trimethylethylammonium ions, (CIl3)3N CH2CH3. 

The mass spectrum of compound 1 and of its 3-deutero derivative has been reported.33 Apart from a strong molecular ion, the principal feature is a peak at 91 m.u. due to a C6H5N radical ion. This ion or interconverting ions 139-141, which are obtained from many other compounds, heterocyclic and nonheterocyclic, have been studied by the technique of collision-induced decomposition (CID).210 A study of some triazolopyridine-7-methanols has shown that other pathways, notably loss of the CHN2 fragment, can become important.23... 

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