chemistry of complex compounds
New coordination compounds of a number of s and d metals with β-dicarbonyl
ligands, which promise much as inhibitors of replication of pathogenic viruses,
including human immunodeficiency viruses.
The interest in magnesium β-ketoesterates, especially lipophilic ones, is due
to their ability to inhibit the replication of pathogenic viruses, including HIV.
In spite of the long time of investigation of β-dicarbonyl derivatives of
metals, no procedures suitable for the preparative of the above magnesium compounds
are reported in literature. Therefore, the development of preparative methods
for the synthesis of anhydrous bis-complexes of magnesium with β-etoesters
of higher alcohols, including cage alcohols, is an urgent problem.
We have developed new procedures for the synthesis of magnesium β-ketoesterates.
The first of them involves interaction between magnesium chloride in an aprotic
solvent and β-dicarbonyl proligand in the presence of triethylamine with
complete isolation from atmospheric moisture. The second procedure (alternative
synthesis route) involves replacement of acetylacetonate ligand by β-ketoester
ligand in magnesium acetylacetonate under the conditions of continuous slow
distillation of acetylacetone together with the solvent in vacuo.
Complexes of the general formula MgL2 (L – deprotonated fragments of
hexyl-, dodecyl-, tert-butil-, cyclohexyl-, bornyl- and adamantlyl acetoacetate,
which are readily soluble in organic media, have been synthesized. The alternative
synthesis of the above coordination compounds confirms their chemical structure.
All compounds obtained have been purified by recrystallization (narrow melting
point ranges) and characterized by the methods of elemental analysis, IR, X-ray
crystallography and 1H NMR spectroscopy.
Development of multifunctional additives
for eco-friendly bio-based lubricating composition.
Objective of the work.
To the study the action of eco-friendly solution of d- and s- metal coordination
compounds in a base oils of vegetable origin on the formation of antiwear nanolayers
of steel friction surfaces. To generalize the effect of the central atoms of chelate
compounds and the structure of ligands (as additives to the lubricating compositions
under investigation) on their antioxidation properties and the phenomenon of
self-organization of tribosystems. To lay the scientific foundations for
goal-directed development and to develop pilot samples of marketable eco-friendly
lubricants based on renewable raw materials of vegetable origin.
The lubricant industry uses a large variety of criteria which determine the
"eco-friendliness" of lubricant compositions. The term
"environmentally acceptable (EA)" lubricant is most frequently used, which was
reflected in the ASTM D 5864-95 standard. A number of marketable lubricating
oils, greases, hydraulic liquids based on vegetable oils, synthetic esters,
polyglycols company with the criteria of this standard, viz: 60% biodegradability
into CO2 and water within 28 days. However, since February 2005 to the Kyoto
protocol, only the lubricating compositions whose base fluids have been made
using renewable raw materials and contain appropriate additives can be classed
with certainty as eco-friendly lubricants. They include fats of plants and
microalgae, which are formed by photosynthesis with absorption of atmospheric
CO2, and their synthetic derivatives (esters of fatty acids and simple
alcohols or polyols), which fully comply with present-day requirements as base
fluids for lubricants.
Biodiesel (ethyl or methyl esters or fatty acids) can easily purified by vacuum
distillation with drawing off the close-cut fraction (130-140
oC, 0.1 mm Hg) of desired product. The distillate obtained acquires,
after the addition of appropriate additives to it, the properties of low-viscosity
lubricant, which in superior to low-viscosity petroleum-based lubricating oils
tribological properties. It can be transesterified into a trimethylol propane
derivative according to the following scheme:
where R is fatty-acid substituents of original methyl esters.
The product obtained possesses a viscosity factor which is optimal for many
applications (~ 34 mm2/s, 40oC) and good antiwear properties.
It should be noted that fatty-acid substituents R are hydrocarbons with one or
several unsaturated (double, -HC=CH-) bonds. Therefore, the addition of efficient
antioxidant additives to this class of substances is a determining factor for their
possible use as base fluids for lubricating compositions. We have developed a
computerized method for the determination of induction period of oxidation of
organic substrates, which is on a par with known standardized methods (ISO 6886,
vegetable oils; EN 14112, biodiesel) in terms of repeatability criterion of
measurements. This method has not been patented and not been described in
literature as yet, but we can evaluate already today the antioxidant properties
of the novel compounds synthesized by us in comparison with known antioxidants.
Moreover, a setup for corresponding measurements has been developed, which is much
cheape than that used today for these purposes.
In our view, using the procedure developed, one can determine the oxidation stability
of edible fats of vegetable origin (sunflower, corn, olive and other) as well,
which is one of the characteristics of the fitness of these vital products for use.
Besides, the method can be employed, after updating, for characterize the quality
of other fat-containing foodstuffs.
The importance of antiwear additives for the stable operation of machines and
equipment can scarcely be exaggerated; nevertheless, the molecular mechanism of
the action of such additives in friction assembly has hot been established yet.
It has been found by a semiempirical method that of the large variety of the types
of antiwear additives based of mineral and synthetic oils, coordination compounds
of transition metals with different polydentate organic ligands, such as phosphorus-
and sulfur-containing ones, are some of the most efficient additives. However,
these ligands are classed as environmentally dangerous substances; besides,
sulfur-containing additives are “poisons” for copper-containing friction pairs,
such as bronze/steel since they cause their increased wear. Attempts of some
companies to adapt marketable phosphorus- and sulfur-containing additives for
use in lubricating compositions containing base oils of biological origin gave
no positive result: the above base fluids acquire in operation properties of
environmentally dangerous lubricants. Basing themselves upon their experience
in the development of lubricants and lubrication systems for such unique and huge
machines as turbines for hydroelectric power stations, the experts of the US
Army Corps of Engineers (USACE) came definitely to the conclusion that it is
necessary to create new types of additives oriented towards use in really
eco-friendly, biobased lubricating compositions.
We believe that the use of individual chemical compounds as acting substances in
contrast to commercially available additives, which are as a rule mixtures, and
on the other hand, the use of chemically pure base fluids (marketable base oils
are also mixtures) can enable unambiguous interpretation of results of tribological
tests of lubricating compositions, which simulate future marketable lubricants.
Ethyl laurate (lauric acid ethyl ester) was selected as an environmentally
acceptable base fluid for the lubricating compositions under investigation.
The compound is nontoxic and has wide temperature range of liquid state; it
was synthesized by the esterification of lauric acid with ethanol from readily
available and cheap raw materials of vegetable origin. After double fractional
distillation (bp 92oC, 12 Pa), the compound had an acceptable purity, 99.7%
(GC/MS Agilent 6890/5973 inert).
Ethyl laurate is one of the base oils that are most resistant to thermal oxidative
degradation, which minimizes the effect of autoxidation on the tribological
characteristics of lubricating composition. To satisfy the environmental challenges
to the full, a biomimetic approach was employed to select chemical structures
of the model additives being developed by, us viz the central atom (copper and
molybdenum) of these coordination compounds is one of the metals among the
indispensable elements (Mg, Ca, Fe, Cu, Zn, ets) of the biochemical systems of
living organisms. The organic constituents (ligands, L) of the above complexes
are structural analogs of compounds that occur in Nature. It should be noted that
copper and molybdenum complexes with various ligands are patented as lubricant
additives. We have synthesized a number of copper (II) complexes of general formula
Cu(L)2 (1-4), where HL is bidentate ligands with donor oxygen atoms.
Moreover, molybdenum (VI) complexes (5, 6) of the general formula
MoO2(L)2, where HL is nitrogen-containing bidentate ligands
with donor oxygen atoms.
Ethyl laurate as a base fluid and the lubricating composition 1-4, solutions of
copper complexes (0.07 mol/L), the solutions 5, 6 of molybdenum complexes
(0.03 mol/L) in base fluid were tested for antiwear and antifriction properties of
accordance with the requirements of the ASTM D 4172-94 standard (four-ball method)
at a load of 392 N (40 kgf). The results of the tests showed that though the base
fluid has a low viscosity (2.63 mm2/s, 40oC), it possesses
good tribological characteristics: wear scar diameter Ds = 0.53 mm, average friction
coefficient fav=0.054. The wear scar diameter in the lubricating composition turned
out to be of the same order of magnitude as in ethyl laurate.
The IAVF AG company (FRG, Karlsruhe) is carrying out tribological investigations
under the orders of such well-known machine-building corporations as Audi, Bosch,
Mercedes-Benz, Man, Ford, Volvo, etc, as well as for corporations manufacturing
lubricants and additives. Research workers of this company have proved by the
radionuclide technique (RNT) and Auger spectroscopy that the required chemical
elements (metal atoms) penetrate to a depth of up to several hundred nanometers
under the friction surfaces of steel specimens under investigation. The depth of
penetration of elements into the friction body correlates with the microtopography
of the friction surface, its waviness (wavelength, amplitude between valleys and
hills). The above nanoeffects are reflected at macrolevel, viz by friction
coefficient values and amounts of wear of friction pairs under investigation.
We investigated surfaces and near near-surface layers of wear tracks on steel balls
by Auger spectroscopy (JAMP microprobe, JEOL). It has been found by layer-by-layer
etching in an Ar+ ion beam that the maximum depth of tribodiffusion of copper ions
(65 nm, sample 1; 11 nm, sample 2), molybdenum atoms (147 nm, sample 5; 550 nm,
sample 6) into the metal matrix is affected by the structure of alkyl substituents
of ligands rather than by the chemical structure of the nearest environment of the
central atom of complexes.
We used in tests the ASTM D 4625-99 method, where testing is performed at much
larger specific loads on the friction assembly than in the four-ball method. The
results of tests at a load of 300 N are listed in the table.
Comparative analysis of the data given in the table shows that lubricating
compositions with our additives improve greatly both the antiwear and antifriction
characteristics of the base fluid and is the basis for the development of
eco-friendly commercial lubricants. The work is in progress, and we hope that the
approach described above will be common to a number of other coordination compounds
as additives, complexes with different biometals as central atoms and other
polydentate organic ligands, structural analogs of compounds occurring in vivo.
A number of novel coordination compounds with biometals as central atoms
will be synthesized using a biomimetic approach to the choice of the structure
of their polydentate organic ligands.
Solutions of these compounds as model additives to base oils of vegetable
origin will be tested for antiwear and antifriction properties by standard testing
methods (ASTM D 4172-94, ASTM D 6424-99).
Friction surfaces and near-surface nanolayers of friction zones and the effect of
the structure of the complexes on the depth of penetration of additive metals
into the metal matrix will be investigated by Auger spectroscopy.
Additives with the best characteristics will be selected, and the effect of their
concentrations in base oils on the antiwear, antifriction and antioxidant properties
will be studied.
The generalization of experimental data will be the basis the goal-directed
development of novel additives to marketable eco-friendly lubricants based on
renewable raw materials.
Candidate of Chemical Sciences Koval Lyudmila I.,
leader engineers Dzyuba Valeriy I. and Ilnitska Olena L.