International Research Journal of Pure and Applied Chemistry

A New Zinc(II) Thiocyanate Complex of a Pyridine-4-carbohydrazide Schiff Base: Crystal Structure and Redox Properties of a Related Copper(II) Complex

Ousmane Sall — 2026-08-03

A new zinc(II) complex, ZnCl(SCN)(H₂L)₂, derived from the Schiff base ligand N′-[(E)-(2-hydroxy)methylidene]pyridine-4-carbohydrazide (H₂L), was synthesised and structurally characterised by single-crystal X-ray diffraction. The complex crystallises in the orthorhombic space group Ama2, with unit-cell parameters a = 26.0306(2) Å, b = 16.0094(1) Å, and c = 6.840(1) Å. The asymmetric unit comprises two neutral H₂L ligands coordinated to the Zn²⁺ ion through their pyridine nitrogen atoms, one thiocyanate anion (SCN⁻) coordinated through nitrogen, one chloride anion, and one lattice water molecule. The zinc centre adopts a distorted tetrahedral geometry, with Zn–N bond lengths of 1.979(4) and 2.052(3) Å, a Zn–Cl bond length of 2.1919(12) Å, and bond angles that depart markedly from the ideal tetrahedral value (103–125°). To complement the structural study, the redox behaviour of the related copper(II) complex [Cu(H₂L)Cl·H₂O]Cl (L-4) was investigated by cyclic voltammetry in acetonitrile containing 0.1 M TEATFB, using a Pt disk working electrode (r = 2 mm), a stainless-steel wire counter electrode, and an Ag/AgCl reference electrode. Over the potential range −1.0 to +1.0 V versus SCE and at scan rates of 10–50 mV s⁻¹, the voltammograms displayed a single quasi-reversible redox couple, characterised by a sharp cathodic peak at −0.75 V and a broader anodic peak at −0.45 V versus SCE. The observation of a single redox wave indicates a uniform Cu(II) coordination environment, consistent with the structural and spectroscopic data obtained for the complex.

Extraction and Characterization of Chitosan from Crab and Periwinkle Shells

Chioma K. Anyiam — 2026-08-12

Chitosan is a biopolymer obtained by deacetylating chitin and is commonly produced from crustacean shell waste. This study compared the extraction and characterisation of chitosan from crab (Callinectes amnicola) and periwinkle (Tympanotonus fuscatus) shells under identical chemical conditions. The shell powders were subjected to demineralisation with 1.25 M HCl, deproteinisation with 2.5% NaOH, and deacetylation with 25% NaOH. The products were assessed for percentage yield, degree of deacetylation (DDA) by potentiometric titration, solubility, and functional groups by Fourier-transform infrared spectroscopy. Crab shells produced a chitosan yield of 18.4% and a DDA of 80.3%. The corresponding FTIR spectrum showed characteristic amine and polysaccharide bands and no residual carbonate peaks, indicating effective demineralisation and deacetylation. In contrast, periwinkle shells produced a lower yield of 10.9%, while the resulting product had a DDA of <10% and poor solubility. Its FTIR spectrum showed strong carbonate bands and an absence of characteristic amine bands, indicating incomplete demineralisation and deacetylation. The periwinkle-derived product was therefore predominantly chitin rather than chitosan under the applied conditions. These findings show that identical processing conditions do not yield equivalent products from crustacean and molluscan shell matrices. Source-specific optimisation, particularly more intensive demineralisation and deacetylation for periwinkle shells, is required to improve conversion to chitosan.

Physicochemical Characteristics and Selected Metal Concentrations in Sachet, Bottled, and Freshly Blended Fruit Juices at the Kenya-Uganda Border

Denis Magero — 2026-08-18

Fruits form an important part of the human diet as they are rich in fibre and vitamins such as A, B, C, D and K. They can be consumed fresh or whole, in liquid forms such as juices and smoothies/blends, as well as in cooked or baked form. The objective of this study is to assess the physicochemical parameters of locally produced and bottled fruit juices at the Kenya – Uganda border. Three broad categories (five samples in each category) of juice samples were analysed for pH, TDS, electrical conductivity and heavy metals. The physical parameters were measured using a Hanna Instruments combo portable meter, while heavy metals were measured using an inductively coupled plasma mass spectrometer (ICP-MS 7900, Agilent Technologies, USA). For heavy metals, cadmium and copper were below the WHO recommended limits. For iron, all samples recorded concentrations below the WHO limit with the exception of one sachet sample whose concentration was above the WHO limit. Chromium and nickel concentrations were above the WHO recommended levels. The high levels of chromium and nickel point to the use of heavy-metal-contaminated water during the manufacturing process; contamination of juice by equipment during manufacture; heavy-metal-contaminated soil leading to bioaccumulation of heavy metals in fruit tissues as well as the use of metal-based pesticides and herbicides in agriculture. However, this study was designed to measure the levels of heavy metals in fruit juice samples and did not include direct source tracing analysis of the potential contamination sources. The explained sources are therefore treated as possible contamination pathways rather than confirmed causes of the observed heavy metal concentration. The study recommends the use of acid-resistant machinery to avoid corrosion and leaching of heavy metals into juice products during manufacture; treatment of water to remove heavy metals before its use in the juice manufacturing process; and thorough washing of fruits to remove pesticides before blending. All the juice brands demonstrated strong correlations between a few metal pairs. In sachet brands, iron showed a strong correlation with cadmium (r = 0.83) while copper showed a strong correlation with chromium (r = 0.90). All the other metal pairs showed very low and negative correlations. In bottled brands, there was no strong correlation between the metal pairs. Copper and iron registered a moderate correlation (r = 0.66); cadmium and chromium registered the same moderate correlation (r = 0.50) and the same was observed for nickel and copper (r = 0.55). In blended brands, only copper and nickel demonstrated a strong correlation (r = 0.80) whereas all the other metals demonstrated weak and negative correlations. The strong correlation between metal pairs indicates that an increased concentration of one metal leads to a higher concentration of another paired metal, but does not indicate a similar contamination pathway or causal relationship between metal pairs. Some metals demonstrated negative correlations. These included: Chromium and iron (r = – 0.84), cadmium and nickel (r = – 0.69), cadmium and copper (r = – 0.80), copper and iron as well as cadmium and chromium (r = – 0.64 in both cases). This indicates that the higher concentration of one metal tends to cause a lower concentration of the corresponding metal. However, this does not mean that one metal causes the other metal to decrease in concentration. Although strong negative correlations were observed for some metal pairs, the correlations were not statistically significant at p = 0.05.

Deep Purification of Wet-process Phosphoric Acid Using Acetone as a Green Organic Solvent

B. N. Karshiev — 2026-08-18

Wet-process phosphoric acid contains a range of mineral impurities that negatively impact acid quality and restrict its use in producing high-purity phosphate products. This study investigates an integrated purification process that combines defluorination using microcrystalline silica, desulfation with strontium carbonate, and acetone-assisted purification. After preliminary treatment, the phosphoric acid was standardised to 35 wt.% P₂O₅ and subjected to acetone treatment under varying acid-to-acetone weight ratios and contact times. The optimal conditions were identified as an acid-to-acetone mass ratio of 1:3 at 25 °C for 30 minutes, which achieved an effective balance between impurity removal and phosphorus retention. Under these parameters, the precipitation efficiencies for CaO, MgO, Fe₂O₃, Al₂O₃, SO₃, and F were 75.99%, 95.37%, 99.40%, 99.50%, 99.66%, and 98.97%, respectively, while P₂O₅ precipitation was limited to 18.02%. Following separation and vacuum acetone removal, the purified acid contained 35.06 wt.% P₂O₅, with CaO and MgO concentrations reduced to 0.13 and 0.03 wt.%, respectively, and Fe₂O₃, Al₂O₃, SO₃, and F below detection limits. The purified acid exhibited a consistent decrease in density and dynamic viscosity as temperature increased from 20 to 90 °C, indicating improved flowability for handling and transport. Material balance analysis indicated an acetone recovery rate of 98.96% and a solvent loss of 1.04%, with 78.27% of the initial P₂O₅ retained in the final product. These results indicate that the acetone-assisted purification route shows considerable promise for laboratory-scale production of high-quality phosphoric acid suitable for further phosphate fertiliser processing. Keywords: wet-process phosphoric acid, acetone, deep purification, defluorination, desulfation, rheological properties, phosphate products.

Evaluation of 2,5,7-Triphenyl-1,2,4-triazolo[1,5-a] pyrimidine as an Efficient Corrosion Inhibitor for Stainless Steel in 1.0 M Hydrochloric Acid

Madhuram Ayush — 2026-08-19

Corrosion inhibition of 316 L stainless steel in 1.0 M hydrochloric acid by 2,5,7-triphenyl-1,2,4-triazolo[1,5-a]pyrimidine (TPTP) was evaluated using weight-loss measurements, electrochemical impedance spectroscopy (EIS), and potentiodynamic polarisation (PDP). The effect of inhibitor concentration was examined over the reported test range, and adsorption behaviour and thermodynamic parameters were assessed to elucidate the inhibition process. Weight-loss measurements showed a progressive decrease in corrosion rate as TPTP concentration increased, with inhibition efficiency reaching 94.0% at 500 ppm and 303 K. Surface coverage increased with concentration, consistent with progressively greater adsorption of TPTP molecules on the stainless-steel surface. The tabulated EIS results showed that charge-transfer resistance increased from 32 to 535 Ω cm², while double-layer capacitance decreased from 162 to 33 μF cm⁻² between the uninhibited solution and 500 ppm TPTP. The tabulated PDP results showed a reduction in corrosion current density from 126.4 to 7.6 μA cm⁻², accompanied by a 19 mV shift in corrosion potential, supporting mixed-type inhibition. The adsorption data were described by the Langmuir adsorption isotherm, while the reported Gibbs free-energy values indicated spontaneous adsorption with contributions from physical and chemical interactions. Overall, the reported gravimetric and electrochemical data indicate that TPTP reduces stainless-steel corrosion through adsorption and formation of a protective interfacial layer under the investigated conditions.

Production and Physicochemical Characterization of Polyethylene Pyrolysis Oil from Sachet Water LDPE Waste

Uhiene Titus — 2026-08-20

This study investigated the production and characterisation of polyethylene pyrolysis oil obtained from waste low-density polyethylene materials, specifically sachet-water packaging bags. The polyethylene waste was collected, sorted, washed, rinsed, and dried. A 15 kg portion of PE was subjected to thermal pyrolysis at 400 °C for 3 hours in the absence of oxygen and was then distilled for a further 3 hours in a batch reactor. The condensed liquid product comprised 3.0 kg of polyethylene pyrolysis oil and was evaluated for selected physicochemical and instrumental properties. The residue obtained was 9.5 kg. The measured physicochemical properties included viscosity, density, refractive index, turbidity, pH, adhesion, drying time, and water solubility. The oil had a viscosity of 17.7 mPa·s, a density of 0.99 g/mL, a refractive index of 1.400, a turbidity of 50 NTU, and a pH of 6.7, and it was insoluble in water. Fourier-transform infrared spectroscopy indicated the presence of hydrocarbon-related and oxygen-containing functional groups in the pyrolysis oil. X-ray diffraction analysis suggested low crystallinity and predominantly amorphous characteristics. Scanning electron microscopy showed a relatively smooth and homogeneous surface in the prepared sample, while thermogravimetric and differential thermal analyses indicated thermal degradation behaviour, with mass-loss events observed during heating. The findings show that waste polyethylene can be converted into a liquid pyrolysis product with measurable physicochemical and structural characteristics. Further studies are required to determine its detailed chemical composition, safety, distillation behaviour, and suitability for specific industrial applications.

Design, Synthesis and Antibacterial Evaluation of 3-oxo-2-[2-(1-phenylethylidene)hydrazinyl]-3,4-dihydroquinoxaline-6-sulfonyl Azide Derivatives

Festus O. Taiwo — 2026-08-25

This study was designed to synthesized some 3-oxo-2-(2-(1-phenylethylidene)hydrazinyl)-3,4-dihydroquinoxaline-6-sulfonyl azide derivatives and study their antibacterial potentials on some bacterial strains. 3-oxo-2-(2-(1-phenylethylidene)hydrazinyl)-3,4-dihydroquinoxaline-6-sulfonyl azide derivatives were synthesized from the reaction of 2-hydrazinyl-3-oxo-3,4-dihydroquinoxaline-6-sulfonyl azide with different acetophenones in a typical condensation reaction. FT-IR, ¹H-NMR and ¹³C-NMR spectroscopic analysis were used to characterized the newly synthesized 3-oxo-2-(2-(1-phenylethylidene)hydrazinyl)-3,4-dihydroquinoxaline-6-sulfonyl azide derivatives. The compounds were investigated for their potential antibacterial properties. The results showed that all the compounds including the standard antibiotics activity increase with time and concentration showing that the agents' activity is time of exposure and concentration-dependent. Also, the killing rate pattern of B. steatrothermophilus by the agents differs from that of B. subtilis showing that the activity of the agent is also bacterial type dependent.