Ethyl 4,4-difluoro-4-phenoxyacetoacetate was obtained and studied as a precursor to new heterocyclic compounds. 6-Hydroxypyrimidine, 1,3-dihydro-1,5-benzodiazepin-2-one, quinolin-2-one and 6-hydroxypyrazolo[3,4-b]pyridine derivatives containing phenoxydifluoromethyl groups were synthesized. These results make it possible to introduce aryloxydifluoromethyl substituents for the design of biologically active heterocycles.
A comparative study of the protective properties of zinc chelate complexes with various ohydroxyazomethine derivatives having substituents of various nature at the ligand benzene ring has been carried out for zinc acid corrosion in H 2 SO 4 solutions. Key words: corrosion, inhibitor, chelates, ligands, zinc.Received: June 26, 2014June 26, . doi: 10.17675/2305June 26, -6894-2014 The corrosion resistance of zinc in acidic media is quite low. The most popular methods of metal protection from corrosion in aqueous media include inhibition of the corrosive medium and electrochemical methods based on the negative difference effect upon imposition of cathodic polarization on the corroding metal. Implementation of these methods with high-efficiency prevention of acid corrosion of zinc encounters serious difficulties. To protect zinc, it is most reasonable to use cationic inhibitors that bear a positive charge and hence readily undergo electrostatic adsorption on a zinc electrode surface in an acid solution. Normally, a molecule of a cationic inhibitor contains N 3-nitrogen that is readily protonated to give an 3 R-NH group. The latter is readily discharged to produce hydrogen and thus catalyzes the slow discharge reaction. Thus, a cationic inhibitor can slow down corrosion considerably if its screening effect dominates over its catalytic effect. The efficiency of zinc protection by cathodic polarization is low. The high rate of zinc spontaneous dissolution would require high-density external cathodic current to be applied since the polarizability of zinc is low. Application of such cathodic current densities would result in enhanced hydrogen evolution that is quite dangerous, as well as a large consumption of external polarizing current. In view of the above, the feasibility of zinc protection from acid corrosion by insoluble inner-complex compounds, namely, Zn chelates, is of certain interest. The specific features of metal corrosion in the presence of oxyazomethine have been studied
The inhibitive effect of a 8-hydroxyquinoline derivative (1) and the corresponding Fe 2+ chelate (2) in the corrosion of Fe in 1 M HCl was studied. The adsorption mechanism of these compounds was considered and the post-treatment effect of these compounds was studied. An increase in the concentration of compounds 1 and 2 increases corrosion inhibition for all the compounds studied. The residual protective effect of chelates is much higher than that of the corresponding ligands. The results that we obtained were interpreted in terms of organic compounds -metal surface interactions. Key words: corrosion, inhibitor, iron, chelates, residual protective effect.Received: June 26, 2014June 26, . doi: 10.17675/2305June 26, -6894-2014 The use of metal chelates as corrosion inhibitors is very promising because they are usually poorly soluble, highly adsorbable, and have high coverage capacity due to the formation of a chelate structure containing several molecules of the original inhibitor as ligands. These factors enhance the inhibitive properties of the complex and strengthen the complex-metal surface bonds. The latter factor should also prolong the post-treatment effect (residual protective effect of the inhibitor) when a pre-inhibited metal is transferred to a noninhibited corrosive environment [1,2]. Earlier, 8-mercaptoquinoline derivatives were tested as inhibitors of the acid corrosion of some metals. Their inhibitive effect is associated with the formation of insoluble chelate complexes between the corrosion products of metals (Fe, Cu, cast iron, etc.) and the 8-mercaptoquinoline molecules that cover the surface of a corroding metal, thus preventing access to the corrosive environment [3,4]. We found it interesting to compare the protection mechanisms of 8-mercaptoquinoline itself and its chelate complex with a corroding metal. In the latter case, the chelate used as an inhibitor is a preformed complex (in contrast to previous tests where a chelate complex was formed during metal corrosion). ExperimentalCorrosion tests were carried out using iron band specimens (11.25 cm) containing the following impurities, %: P 0.035; C 0.12; S 0.045; Cr 0.15; Ni 0.2; Mn 0.45; Si 0.005; Mg 0.05.
The regularities of changes in the residual protective effect of o-hydroxyazomethine derivatives on the acid corrosion of Al have been studied. The duration of the residual protective effect (τ) is a function of the polarity of substituents in o-hydroxyazomethine molecules, inverse temperature of the solution, and the additive concentration in the preadsorption solution. The identified regularities of the effect of these factors on τ is interpreted in terms of the Linear Free Energy Relationship approach. The changes in the near-electrode concentration of a desorbed inhibitor as a function of time and solution temperature are discussed. It is noted that the effects of various factors on the regularities of changes in the residual protective effect of o-hydroxyazomethine derivatives toward Al and Fe corrosion are similar.
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