4.04 – Pyrazoles and their Benzo Derivatives

Atmospheric pressure ionization (API) mass spectrometry is a novel form of mass spectrometry in which the ionization process is carried out in a reaction chamber external to the mass analyzer region. The mass analyzer serves as a device to detect positive or negative ions present in the reaction chamber, which is maintained at atmospheric pressure.

Atmospheric Pressure Ionization Mass Spectrometry

Selective Preparation of 3,4,5-Trinitro-1H-Pyrazole: A Stable All-Carbon-Nitrated Arene

Ammonia chemical ionization mass spectrometry

Stereochemical effects in mass spectrometry

For compounds C6H5X (XCl, Br, I) under chemical ionization conditions, methylamine causes ipso substitution of X by [NH2CH3]+ and by [NH2]+˙. C6H5F is less reactive; it gives some [C6H5NH2]+˙. Nitrobenzene gives an adduct ion [M+CH3NH3]+, a reduction product ion [C6H5NO2]+˙, and an ion at m/z93, probably a substitution product [C6H5NH2]+˙, but no [C6H5NH2CH3]+. It is also shown that the ion m/z94, formed from nitrobenzene with ammonia as reagent gas, is a substitution product rather than a reduction product ion. Carbonyl compounds C6H5. CO. X give adduct ions and some substitution, mainly [C6H5NH2]+˙.

Electrophilic aromatic substitution under chemical ionization conditions. Methylamine and ammonia as reagent gases

It is shown by ion cyclotron resonance measurements that ion/molecule reactions, leading to substitution or reduction product ions from chloro- and nitrobenzene with the title amines, are those between the molecular ions [RNH2]+ or [C6H5X]+˙ and their respective counterparts C6H5X or RNH2. The protonated reagent gas ions [RNH3]+ are not involved in these reactions. In the case of nitrobenzene, adduct ions [C6H5NO2·RNH3]+ do not decompose within the time scale of the measurements. The results obtained are compared with those found under chemical ionization conditions.

Ion/molecule reactions of ammonia and methylamine with chloro‐ and nitrobenzene. A comparison of chemical ionization and ion cyclotron resonance experiments

The mass spectra of six isomers of methylnitroimidazoles are reported and discussed. All compounds exhibit strong molecular ions, along with the characteristic fragmentations of aromatic nitro compounds. In some cases ortho effects—losses of OH., H2O, CHO., CH2O—are observed, due to interactions of adjacent substituents.

Mass spectrometry of nitroazoles 1–The mass spectra of methyl substituted nitropyrazoles

The electron impact and chemical ionization (ammonia and methane) mass spectral behaviour of the cis- and trans-(2-hydroxycyclohexyl)-mercapturic acid methyl esters, metabolites of cyclohexeneoxide, was examined. Only with chemical ionization was it possible to differentiate between these two configurational isomers, by observing the stereoselective loss of H2O from the protonated molecular ions. Using this stereoselective process, a method was developed for the assessment of the relative amounts of stereoisomeric mercapturic acids, excreted as metabolites in the urine of rats treated with cyclohexeneoxide.

Electron impact and chemical ionization mass spectrometry of cis- and trans-S-(2-hydroxycyclohexyl)-N-acetyl-(1)-cysteine methyl esters

The interaction between methyl and nitro groups in some methyl substituted nitropyrazoles and -imidazoles causes the expulsion of CHO˙ and CH2O. This may occur when the two substituents are at adjacent positions in the ring. Labelling with deuterium and 13C shows that the loss of CHO˙ and CH2O originates exclusively from the substituents. The isotope effects observed in partially deuterated 3(5)-methyl-4-nitropyrazole are consistent with a hydrogen transfer prior to fragmentation.

W. C. M. M. Luijten

Papers

Electrophilic aromatic substitution under chemical ionization conditions. Methylamine and ammonia as reagent gases

Ion/molecule reactions of ammonia and methylamine with chloro‐ and nitrobenzene. A comparison of chemical ionization and ion cyclotron resonance experiments

Mass spectrometry of nitroazoles 1–The mass spectra of methyl substituted nitropyrazoles

Electron impact and chemical ionization mass spectrometry of cis- and trans-S-(2-hydroxycyclohexyl)-N-acetyl-(1)-cysteine methyl esters

Mass spectrometry of nitroazoles: 4—ortho effects: The loss of CHO˙ and CH2O from methyl substituted nitrodiazoles