Esmat F. Saad

SUBSTITUENT EFFECTS AND CONFORMATIONAL PREFERENCE OF 2,4-DINITROPHENYL 4-SUBSTITUTED PHENYL SULFIDES SULFOXIDES AND SULFONES

Abstract The conformation of 2,4-dinitrophenyl 4′-substituted phenyl sulfides, sulfoxides and sulfones are explored. 1H-NMR and IR data are represented. The results obtained indicate that the chemical shift of the ortho proton (H-6) in the dinitro ring in sulfides under consideration is dependent on the nature of substituents present in the 4′-position, affording a further evidence for the adoption of a skew conformation. Different conformations are assigned to sulfoxides and sulfones. The chemical shift for H-6 in the nitro ring nicely correlates with σP Hammett in sulfides. Correlation for μC-S, and μSO2 with Hammett σ values are poor.

Nucleophilic substitutions at the pyridine ring. Conformational preference of the products and kinetics of the reactions of 2-chloro-3-nitro- and 2-chloro-5-nitro-pyridines with arenethiolates†

The reactions of 2-chloro-3-nitropyridine 1 and 2-chloro-5-nitropyridine 2 with arenethiolates 3a–i result in arylthio-dechlorination to give 2-arylthio-3-nitropyridines 4a–i and 2-arylthio-5-nitropyridines 5a–i. A 1H NMR study and AM1 calculations of 5a–i have shown that these compounds assume a skew conformation except the 2-(4-nitrophenylthio) derivative 5f which has a twist one. An addition–elimination mechanism is suggested based on second order kinetics and the dependence of rates on the nature of the nucleophile. It is found that 2 (para-like) reacts faster than 1 (ortho-like). Good correlations are obtained from plots of log k2 against Hammett σ constants, pKa and log K (thermodynamic affinity of arenethiolates towards carbon).

Mass spectrometric study of some pyrazoline derivatives

The structures of some new carboxamide, thiocarboxamide, nicotinoyl and isonicotinoyl pyrazoline derivatives have been related to their mass spectral data. The ions produced under electron impact showed both the characteristic pyrazoline ion and unusual azete fragmentation patterns. These results suggest that the mass spectra of these pyrazoline derivatives are both position and substituent dependent. Fragmentations of the ions are discussed in view of their metastable transitions.

Skeletal rearrangements in 2,4-dinitrophenyl-4'-substituted phenyl sulfides and sulfones upon electron impact

Abstract The mass spectral fragmentation patterns of a various 2,4-dinitrophenyl-4′-substituted phenyl sulfides and sulfones help define the role of substituent effects under electron impact, and subsequently determines the appearance of the base peak. These substituent effects correlated well with the Hammett σ-values. The mass spectral features arise from the elimination of the sulfur atom with recombination of the terminal end groups or with scission across 4′-substituted phenyl ring in sulfides, whereas in sulfones the most abundant ion is formed through the sci-ssion of the rearranged aryl sulfinate ester. A comparison between the spectra of the two types is discussed. The results suggest that the skeletal rearrangement of the molecular ion occurring in these S-bridged compounds is a sensitive diagnostic tool in structure elucidation.

SPECTRAL CHARACTERIZATION OF SOME PHENYLAZODIHYDROXY NAPHTHALENE DERIVATIVES

Abstract A series of azo dyes namely: 4-phenylazo-1,3-dihydroxynaphthalene 1, 4-phenylazo-1,5-dihydroxynaphthalene 2, 1-phenylazo-2,8-dihydroxynaphthalene 3, 1-phenylazo-2,3-dihydroxynaphthalene 4 and 1-phenylazo-2,7-dihydroxynaphthalene 5 have been prepared and their UV, IR, NMR and mass spectra are recorded. The spectra have been analysed to give a complete picture of the hydroxyazo-quinone hydrazone tautomerism present in these class of compounds. It is found that dyes 1, 2 and 4 exhibit quinone hydrazone tautomerism while dyes 3 and 5 exist as a mixture of hydroxyazo and quinone hydrazone tautomers. The change due to a second hydroxyl group in the naphthalene moiety is compared with azonaphthols. The fragmentation process in the mass spectra displays C-N and -N = N-cleavage and indicated that the two tautomers are present except in dye 2 which exhibits a quinone hydrazone form.

Mass Spectral Study of Some Phenyl‐mono and Dinitropyridyl Sulfide, Ether, Amine and Sulfone Derivatives

The electron impact ionization of some mono- and dinitropyridylphenylsulfide, ether, amine and sulfone derivatives were studied at 70 ev energy. All the 8 compounds studied underwent ring closure during the formation of a carbazole radical cation as a general feature in their mass spectra. The basic differences in the mass spectral behaviour are mainly attributed to the position of the nitro group in the pyridyl ring and the fragmentation pathway is directed by the sulfur, oxygen or nitrogen moiety. The base peak in the mass spectra is determined by such differences.

Tandem mass spectrometry of some nitropyridylaryl sulfides

The electron impact tandem mass spectrometry of 3- and 5-nitropyridinylaryl sulfides are reported and discussed. The [M-1](+) ion is observed as the base peak for all the 5-nitropyridinylaryl sulfides, series I, whereas the 2-mercapto-3-nitrosopyridine fragment at m/z 139 represents the base peak for the 3-nitro isomers, series II, with the exception of the 3-substituted derivatives and the unsubstituted parent sulfide. The proposed fragmentation processes are substantiated by tandem mass spectrometry (MS/MS). Hammett correlation analysis of the substituent effect on the formation of fragments [RH(4)C(6)S](+), [C(6)H(4)R](+) and [M-HNO(2)](+) is discussed. Copyright 2000 John Wiley & Sons, Ltd.

SYNTHESIS AND SPECTRAL STUDIES OF SOME ARYL SULFIDES AND SULFONES

Abstract The reaction of 2-chloro-1,3,5-trinitrobenzene (picryl chloride) and an equivalent amount of arylthiolate (R = H, CH3, OCH3, Br, Cl, NO2) gave 2-arylthio-1,3.5-trinitrobenzenes (1–6). It is found that the chemical shifts of H-4.6 gave good linear relationship with Hammett u constants indicating that the inductive effect of the substituents of the arylthio moieties is transmitted to the picryl ring through the sulfur atom. Meanwhile the reaction of picryl chloride with two fold arylthiolate gave 1.2-bis arylthio-3.5-dinitrobenzenes (%13) except with 4-nitrobenzenethiolate. The 1H NMR spectra of bis arylthio compounds indicate that these sulfides exist in a skew conformation. The oxidation of bis arylthio compounds with KMnO4 gave the corresponding 1,2-bis-arylsulfonyl-3,5-dinitro-benzenes (1519). Fragmentation processes using tandem mass spectrometry (MS/MS) in relation to structure and substituent are discussed.

Protiodeacylation of 4-substituted 1-acetyl-2,6-dimethylbenzenes in sulphuric acid: kinetics and mechanism

In 89.8%(w/w) sulphuric acid rate coefficients (104k1/s–1) for the protiodeacetylation of 4-substituted (X) 1-acetyl-2,6-dimethylbenzenes (1) were, at 25 °C; X = Br, 0.468; I, 0.509; Cl, 0.635; H, 1.345; F, 2.52; Ph, 31.5; But, 38.6; and Me, 47.2. At 25 °C the reaction of the ketone (1; X = OMe) was too fast, and at 80 °C reactions of the ketones (1; X = CONH2 or CO2H) were too slow, for convenient measurement. The carboxy nitrile (X = CN) underwent hydration to the amide (X = CONH2) rather than protiodeacylation. The rate coefficients at 25 °C of eight ketones (1) gave an accurate Hammett correlation, with σ+ constants, giving ρ=–4.64 ± 0.05. The reaction of 1-acetyl-2,4,6-trimethyl-benzene (1; X = Me) was studied of a range of acidity (73.6–99.9% sulphuric acid), and a maximum was found near 86.0% acid. Rates were also measured in D2SO4–D2O. The mechanism is discussed.

Kinetics of protiodeacylation of mono- and di-acylmesitylenes in 89.8% sulphuric acid

Rate and activation data have been obtained for the protiodeacylation in 89.8%(w/w) sulphuric acid of 10 alkyl mesityl ketones, with straight chain or branched chain alkyl groups, and of four diacylmesitylenes. The reactions have been analysed in terms of a sequence of two or three component ψ-first-order processes.