Experimental and Theoretical Studies on Acid Corrosion Inhibition of API 5L X70 Steel with Novel 1-N-α-d-Glucopyranosyl-1H-1,2,3-Triazole Xanthines.

A series of novel 1-N-α-d-glucopyranosyl-1H-1,2,3-triazole xanthines was synthesized from azido sugars (glucose, galactose, and lactose) and propargyl xanthines (theophylline and theobromine) using a typical copper (I)-catalyzed azide-alkyne 1,3-dipolar cycloaddition. The corrosion inhibition activities of these new carbohydrate-xanthine compounds were evaluated by studying the corrosion of API 5 L X70 steel in a 1 M HCl medium. The results showed that, at 10 ppm, a 90% inhibition efficiency was reached by electrochemical impedance spectroscopy. The inhibitory efficiency of these molecules is explained by means of quantum chemical calculations of the protonated species with the solvent effect, which seems to better represent the actual situation of the experimental conditions. Some quantum chemical parameters were analyzed to characterize the inhibition performance of the tested molecules.

Bridged N-Heterocyclic/Mesoionic (NHC/MIC) Heterodicarbenes as Ligands for Transition Metal Complexes.

Following a copper catalyzed alkyne azide cycloaddition (CuAAC) and N-alkylation protocols, we report the preparation of a hybrid N-heterocyclic/mesoionic [NHC(H+)-MIC(H+)][2I]2- salt (1) in high yields. The treatment of salt 1 with Cu2O and KI yields a second hybrid NHC/MIC proligand featuring a tetraiodocuprate anion [NHC(H+)-MIC(H+)][Cu2I4]2- (2). Through selective deprotonation and metalation, both salts 1 and 2 can generate either the chelate heterodicarbene complexes (3) with the rare [NHC·(M)·MIC]+[MX2]- general formula (M = PdII, RhI) or NHC-anchored/pendent triazolium species (4) [NHC·(M)-MIC(H+)]. If the triazolium moiety of type 4 complexes is deprotonated with KHMDS in the presence of a second metal center, a series of heterobimetallic complexes of the type [NHC·(M)-MIC·(M')] (5) are achieved. Interestingly, the reaction of salt 2 with KHMDS yields the bimetallic copper heterodicarbene (6) which can be a useful transfer reagent for the preparation of type 3 complexes. A variety of synthetic routes for the preparation of complexes 3-5 and their full characterization in solution and in the solid state will be discussed.

Multicomponent Synthesis and Evaluation of New 1,2,3-Triazole Derivatives of Dihydropyrimidinones as Acidic Corrosion Inhibitors for Steel.

An efficient one-pot synthesis of 1,2,3-triazole derivatives of dihydropyrimidinones has been developed using two multicomponent reactions. The aldehyde-1,2,3-triazoles were obtained in good yields from in situ-generated organic azides and O-propargylbenzaldehyde. The target heterocycles were synthesized through the Biginelli reaction in which the aldehyde-1,2,3-triazoles reacted with ethyl acetoacetate and urea in the presence of Ce(OTf)3 as the catalyst. The corrosion inhibition of steel grade API 5 L X52 in 1 M HCl by the synthesized compounds was investigated using the electrochemical impedance spectroscopy technique. The measurements revealed that these heterocycles are promising candidates to inhibit acidic corrosion of steel.

Pseudo-four component synthesis of mono- and di-benzylated-1,2,3-triazoles derived from aniline.

The pseudo-four component click synthesis of dibenzylated 1,2,3-triazoles derived from aniline is reported. The cycloaddition of sodium azide to N-(prop-2-ynyl)-benzenamine (I) in the presence of equimolar amounts of p-substituted benzyl derivatives, yields a mixture of mono- and dibenzylated 1,2,3-triazoles. When two equivalents of the benzyl derivative are added to the multicomponent reaction, the selective preparation of the dibenzylated compounds is achieved. The reactivity of the aniline N-H bond in monobenzylated 1,2,3-triazoles was tested by treatment with one equivalent of a p-substituted benzyl chloride at 40 °C, rendering the dibenzylated derivatives quantitatively.

Multicomponent click synthesis of new 1,2,3-triazole derivatives of pyrimidine nucleobases: promising acidic corrosion inhibitors for steel.

A series of new mono-1,2,3-triazole derivatives of pyrimidine nucleobases were synthesized by one-pot copper(I)-catalyzed 1,3-dipolar cycloaddition reactions between N-1-propargyluracil and thymine, sodium azide and several benzyl halides. The desired heterocyclic compounds were obtained in good yields and characterized by NMR, IR, and high resolution mass spectrometry. These compounds were investigated as corrosion inhibitors for steel in 1 M HCl solution, using electrochemical impedance spectroscopy (EIS) technique. The results indicate that these heterocyclic compounds are promising acidic corrosion inhibitors for steel.

Synthesis of new 1,2,3-triazole derivatives of uracil and thymine with potential inhibitory activity against acidic corrosion of steels.

Ten 1,4-disubstituted 1,2,3-triazoles were synthesized from one of 1-(azido-methyl)benzene, 1-(azidomethyl)-4-fluorobenzene, 1-(azidomethyl)-4-chlorobenzene, 1-(azidomethyl)-4-bromobenzene or 1-(azidomethyl)-4-iodobenzene, generated in situ from sodium azide and the corresponding benzyl halide, and dipropargyl uracil or dipropargyl thymine. Optimal experimental conditions were established for the conventional click chemistry. The corrosion inhibiting properties of some of these compounds, which were determined by means of an electrochemical technique, are also presented.

Synthesis of azanucleosides through regioselective ring-opening of epoxides catalyzed by sulphated zirconia under microwave and solvent-free conditions.

New azanucleosides were obtained using sulphated zirconia (ZS) as catalyst in the nucleophilic oxirane ring opening reaction of 1-allyl-3-(oxiran-2-ylmethyl) pyrimidine-2,4(1H,3H)-dione and 1-allyl-5-methyl-3-(oxiran-2-ylmethyl)-pyrimidine-2,4(1H,3H)-dione, with (S)-prolinol. The new templates were obtained with good yields following a route which exploits the reactivity of epoxides in the presence of sulphated zirconia as catalyst. The key step was carried out using microwave and solvent-free conditions and proceeds with high selectivity.

Synthesis of new pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-dione (PCU) cyanosilylated derivatives using sulphated zirconia and hydrotalcite as catalysts in microwave-assisted reactions under solvent free conditions.

A comparison was made of the effectiveness of the functionalization reactions of pentacyclo[5.4.0.0(2,6).0(3,10).0(5,9)]undecane-8,11-dione (PCU) using sulphated zirconia in protection-deprotection reactions and Mg/Al hydrotalcite in a cyanosilylation reaction, under classical thermal conditions and imposing microwave radiation; improved yields and reaction times were considered.

Cu-Al mixed oxide-catalysed multi-component synthesis of gluco- and allofuranose-linked 1,2,3-triazole derivatives.

A series of carbohydrate-linked 1,2,3-triazole derivatives were synthesized in good yields from glucofuranose and allofuranose diacetonides using as key step a three-component 1,3-dipolar azide-alkyne cycloaddition catalysed by a Cu-Al mixed oxide. In this multi-component reaction, Cu-Al mixed oxide/sodium ascorbate system serves as a highly reactive, recyclable and efficient heterogeneous catalyst for the regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles. The reported protocol has significant advantages over classical CuI/N,N-diisopropylethylamine (DIPEA) or CuSO4/sodium ascorbate conditions in terms of efficiency and reduced synthetic complexity. In addition, the selective deprotection of synthesized di-O-isopropylidene derivatives was also carried out leading to the corresponding mono-O-isopropylidene products in moderate yields. Some of the synthesized triazole glycoconjugates were tested for their in vitro antimicrobial activity using the disc diffusion method against Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis), Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa), as well as fungus (Aspergillus niger) and yeast (Candida utilis). The results revealed that these compounds exhibit moderate to good antimicrobial activity mainly against Gram-negative bacteria.

Sulphated zirconia as an eco-friendly catalyst in acylal preparation under solvent-free conditions, acylal deprotection assisted by microwaves, and the synthesis of anhydro-dimers of o-hydroxybenzaldehydes.

A solvent-free approach is described for the regioselective synthesis of acylals (1,1-diacetates) in shorter reaction times and higher yields, compared to conventional methodology using solvents. In the protection reaction of the o-hydroxybenzaldehyde the formation of acetyl compounds and anhydro-dimers was observed. The deprotection reaction involves microwave (MW) exposure of diluted reactants in the presence of solid sulphated zirconia (SZ) catalyst that can be easily recovered and reused. The sulphated zirconia was recycled several times without any loss of activity.

Adsorption and corrosion inhibition behaviour of new theophylline-triazole-based derivatives for steel in acidic medium.

The design and synthesis of a series of theophylline derivatives containing 1,2,3-triazole moieties are presented. The corrosion inhibition activities of these new triazole-theophylline compounds were evaluated by studying the corrosion of API 5 L X52 steel in 1 M HCl medium. The results showed that an increase in the concentration of the theophylline-triazole derivatives also increases the charge transference resistance (R ct) value, enhancing inhibition efficiency and decreasing the corrosion process. The electrochemical impedance spectroscopy under static conditions studies revealed that the best inhibition efficiencies (approx. 90%) at 50 ppm are presented by the all-substituted compounds. According to the Langmuir isotherm, the compounds 4 and 5 analysed exhibit physisorption-chemisorption process, with exception of the hydrogen 3, bromo 6 and iodo 7 substituted compounds, which exhibit chemisorption process. The corrosion when submerging a steel bar in 1 M HCl was studied using SEM-EDS. This experiment showed that the corrosion process decreases considerably in the presence of 50 ppm of the organic inhibitors. Finally, the theoretical study showed a correlation between EHOMO, hardness (η), electrophilicity (W), atomic charge and the inhibition efficiency in which the iodo 7 substituted compound presents the best inhibitor behaviour.

Visible-Light-Promoted AuI to AuIII Oxidation in Triazol-5-ylidene Complexes.

Reaction of triazolium precursors [MIC(CH2 )n - H+ ]I- (n=1-3) with potassium hexamethyldisilazane (KHMDS) and AuCl(SMe2 ) generates the gold(I) complexes of the type MIC(CH2 )n ⋅AuI. Visible light exposure of the latter complexes promotes a spontaneous disproportionation process rendering gold(III) complexes of the type [{MIC(CH2 )n }2 ⋅AuI2 ]+ I- . Both the AuI and AuIII complex series were tested in the catalytic hydrohydrazination of terminal alkynes using hydrazine as nitrogen source.

Solvent-free synthesis of 6ß-phenylamino-cholestan-3ß,5α-diol and (25R)-6ß-phenylaminospirostan-3ß,5α-diol as potential antiproliferative agents.

In this paper is described a synthetic route to 6ß-phenylamino-cholestan-3ß,5α-diol and (25R)-6ß-phenylaminospirostan-3ß,5α-diol, starting from cholesterol and diosgenin, respectively. The products were obtained in two steps by epoxidation followed by aminolysis, through an environmentally friendly and solvent-free method mediated by SZ (sulfated zirconia) as catalyst. The use of SZ allows chemo- and regioselective ring opening of the 5,6α-epoxide during the aminolysis reaction eliminating the required separation of the epoxide mixture. The products obtained were spectroscopically characterized by 1H, PENDANT 13C NMR and HETCOR experiments, and complemented with FTIR-ATR and HRMS. The antiproliferative effect of the ß-aminoalcohols was evaluated on MCF-7 cells after 48h of incubation, by MTT and CVS assays. These methodologies showed that both compounds have antiproliferative activity, being more active the cholesterol analogue. Additionally, the cell images obtained by Harris' Hematoxylin and Eosin (H&E) staining protocol, evidenced formation of apoptotic bodies due to the presence of the obtained ß-aminoalcohols in a dose-dependent manner.