Ezzat A. Hamed

Characterization and Dating of Blue Ballpoint Pen Inks Using Principal Component Analysis of UV–Vis Absorption Spectra, IR Spectroscopy, and HPTLC

Abstract:  The ink of pens and ink extracted from lines on white photocopier paper of 10 blue ballpoint pens were subjected to ultraviolet–visible (UV–Vis) spectroscopy, infrared (IR), and high‐performance thin‐layer liquid chromatography (HPTLC). The Rf values and color tones of the bands separated by thin‐layer chromatography (TLC) analysis used to classify the writing inks into three groups. The principal component analysis (PCA) investigates the pen responsible for a piece of writing, and how time affects spectroscopy of written ink. PCA can differentiate between pen ink and ink line indicates the influence of solvent extraction process on the results. The PCA loadings are useful in individualization of a questioned ink from a database. The PCA of ink lines extracted at different times can be used to estimate the time at which a questioned document was written. The results proved that the UV–Vis spectra are effective tool to separate blue ballpoint pen ink in most cases rather than IR and HPTLC.

Kinetics of the reaction of 2‐chloro‐3,5‐dinitropyridine with meta‐ and para‐substituted anilines in methanol

The kinetics of the reaction of 2-chloro-3,5-dinitropyridine (1) with meta- and para-substituted anilines (2a–j) to give 2-anilino-3,5-dinitropyridine derivatives (3a–j) were studied in methanol at different temperatures. IR studies of the products (3a–j) indicated the presence of hydrogen bonding between N—H and an o-nitro group, and UV spectra showed a red shift resulting from the interaction between an amino group and aza and nitro groups. A plot of ΔH‡ versus ΔS‡ gave a good straight line with a 324 °C isokinetic temperature. Good linear relationships were obtained from plots of log k2 against σ values at all temperatures with relatively large negative ρ values (−3.75 to −3.16) indicating the formation of a Meisenheimer σ-complex intermediate. Plots of log k2 against pKa values (β = 0.85) gave good straight lines at 25 °C, except for 2f (4-COCH3), indicating that the reactions involve a significant bond formation in the transition state. An SNAr mechanism is suggested to proceed via two stages, with the first being rate determining. Copyright

Nucleophilic substitution at the pyridine ring. Kinetics of the reaction of 2‐chloro‐3,5‐dinitropyridine with arylthiolates in methanol

The reaction rates of 2-chloro-3,5-dinitropyridine 1 with a series of arylthiolates 2a-h in methanol have been measured at 25°C. The products are the corresponding 2-thioaryl-3,5-dinitropyridine 3a-h. Good Hammett correlation with ρ value −1.19 was obtained suggesting an elimination-addition mechanism SNAr and the formation of Meisenheimer-like intermediates. Plot of log k2 vs. pKa values of arylthiols gave straight line with β=0.38 indicating that the π-bond breaking in the pyridine ring is so much advanced over bond making between the nucleophile and the carbon that bears the chlorine atom. Excellent correlation between log k2 and log K (carbon basicity of arylthiolates) was obtained.

Nucleophilic substitutions at the pyridine ring: Kinetics of the reaction of 2‐chloro‐3‐nitro and 2‐chloro‐5‐nitropyridines with piperidine and morpholine in methanol and benzene

The kinetics of the reactions of 2-chloro-3-nitropyridine (ortho-like) and 5-nitro (para-like) isomer with morpholine and piperidine were studied in methanol and benzene at several amine concentrations and temperatures in the range 25–45°C. The data show that k/k ratios are less than unity in methanol. The steric hindrance in the transition state of the 3-nitro (ortho-like) isomer retards o-substitution while the stability of p-quinonoid structure of the 5-nitro (para-like) isomer favors p-substitution. In benzene, the k3-NO2/k5-NO2 ratios are greater than unity. The hydrogen bonding formation between the ammonium hydrogen and the ortho-nitro group in the transition state of 3-nitro isomer favors the o-substitution.

Reaction of 4-chloro-3,5-dinitrobenzotrifluoride with aniline derivatives. Substituent effects

N-(2,6-Dinitro-4-trifluoromethylphenyl)aniline derivatives were prepared by anilino-dechlorination of 4-chloro-3, 5-dinitrobenzotrifluoride. IR, UV and 1H NMR studies suggested an intramolecular hydrogen bond between the amino hydrogen and one o-nitro group. An addition-elimination mechanism was suggested based on the second-order kinetics and the dependence of rates on the nature and the position of the substituent in the aniline ring, as well as the high negative values of ρ(-3.14, −3.16, −3.01). Such values indicate a positive charge on the aniline nitrogen in the transition state and that the rate is affected by the polar effect of the substituent. The β value (0.85 at 30°C) indicates an appreciable degree of bond formation in the transition state.

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).

Kinetics of the alkaline hydrolysis of 2-thioaryl-3, 5-dinitropyridine derivatives in 50% v/v DMSO-water

The kinetics of the alkaline hydrolysis of substituted 2-thioaryl-3,5-dinitropyridine have been studied in 50% DMSO– water. The observed rate constants and the second order rate constants were calculated. The thermodynamic parameters for the unsubstituted compound reveals the activating power of the two nitro- and aza-groups.

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.

Synthesis and spectral studies of some novel ethyl (substituted phenylthio) acetate and propionate derivatives

Abstract Ethyl (substituted phenylthio) acetate and propionate derivatives have been synthesised, their structures were proved by IR, NMR and mass spectra.