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ISSN 2522-1841 (Online) AZERBAIJAN CHEMICAL JOURNAL № 4 2023 97
ISSN 0005-2531 (Print)
UDC 661.726:541.427:543.876
SYNTHESIS OF S,P,N-CONTAINING ORGANIC COMPOUNDS AND THEIR THERMOSTABILITY WITH RESPECT TO METALS
E.Sh.Mamedov, T.N.Kulibekova, D.S.Veliyeva, Z.S.Safaraliyeva, I.R.Rushinaz
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, Ministry of Science and Education
of the Republic of Azerbaijan
Received 10.01.2023 Accepted 07.04.2023
The results of thermal studies of some derivatives of dithiophosphoric, xanthogenic, dithiocarbamic acids are presented. The thermal parameters of the compounds were determined both in pure form and in the presence of iron and copper powders. Their chemical activity with respect to iron and copper was studied. It has been found that the temperature at which the thermal stability of the studied compounds is maintained exceeds 1700C, and they are chemically active with respect to iron and copper: the lower the interaction temperature within the same row with iron and copper and the lower its mass loss corresponding to this temperature, the more effective it is like an extreme pressure (EP) additive. It has been found that compounds of the same series, reacting with metal by the type of synchronous and exchange reactions, have better indicators of extreme pressure properties than compounds interacting with metal by the type of asynchronous reaction.
Keywords: xanthogenic, dithiocarboxylic and dithiophosphoric acids, thermal stability, gear oil, extreme pressure additive, scuff index, thermoanalytical studies.
doi.org/10.32737/0005-2531-2023-4-97-103
As a result of natural processes and human economic activity, i.e. anthropogenic sources, various impurities enter the atmosphere, which include emissions from motor vehicles. The wide spread of thermal research methods contributes to the speed of obtaining various physical and chemical information about the capabilities of various types of internal combustion engines [1-4]. As you know, an integral part of the operation of engines are oils, the protection of which by various chemically active compounds - additives - leads to a decrease in environmental pollution. When synthesizing additives, one should also take into account the need to ensure thermal stability and their ability to work at high temperatures.
We have carried out studies to determine the thermal stability and chemical activity of new synthesized compounds - esters of dithiophosphoric (DTP), xanthogenic (CTG) and dithiocarbamic (DTC) acids on the metal surface. This class of compounds is known to have lubricating properties [5, 7]. General schemes for the preparation of esters and data on the IR and NMR spectra of some of the synthesized compounds are given below.
With interaction of chloromethyl esters of carboxylic acids with alkali metal xanthates in benzene at 50-600C, new acyloxymethyl esters of xanthogenic acids with a yield of 8588% were synthesized:
RCOCH2Cl + R'OCSK —► RCOCH2SCOR'+ KC1 II II II II
O SOS
I, IV
R = CH3, (I), C6H5 (IV) R' = H30-C3H7, (I, IV)
In the IR spectrum of acetoxymethyl ester of isopropylxanthic acid (I), an intense band
at 1750-1740 cm-1 is found, which is characteristic of C=O groups.
The stretching vibrations of the C-S and C=S groups correspond to a weak absorption band in the region of 610cm-1 and 1100cm-1. The methylene group gives a band with a frequency of 1450cm-1. The spectrum also shows a band at 1140 cm-1 corresponding to the absorption of the C-O-C group.
In the PMR spectrum of acetoxymethyl ester of isopropylxanthogenic acid (I), the methyl protons of the isopropyl radical appear at 1.4-1.45 ppm, and the protons of the methylene and a proton of the methine groups appear in the region of 0=5.43-5.6 ppm.
Due to the presence of spin-spin interaction in the isopropyl radical, the methine group proton signal is in the form of a singlet at 5=5.43 ppm, and the methyl protons are in the form of a quadruplet at 5=5.6 ppm. The signal shift in the region of weak fields is due to the influence of the electronegative oxygen atom. The methyl protons of the acetyl group appear as a singlet at 5=2.0 ppm.
DTP esters were obtained by the reaction of carboxymethylation of salts of DTP acids with chloromethyl esters of carboxylic acids in the temperature range of 60-800C for 5-7 hours [9]:
RCOCH2O + NaSP(OR')2 O S
R = CH3, ( II) , C6H5 (V)
RCOCH2SP(OR')2 + NaCl
O
S
II, V
R' = H30-C3H7, (II, V)
In the IR spectrum of the benzoyloxy-methyl ester of O,O-diisopropyldithiophospho-ric acid (V), an intense absorption band is found at 1740 cm-1 corresponding to the C(=O) group. The main absorption bands in the IR spectrum are the bands due to vibrations of P=S and P-S
S'
bonds included in the fragment (- P ^ ), which
correspond to 680 cm-1 and 650 cm-1.
In the PMR spectrum of the benzoyloxy-methyl ester of O,O-diisopropyldithiophosphoric acid (V), a doublet signal is observed from the SCH2OC=O group in the region of 5.38 ppm.
The nature of the splitting is explained by the spin-spin interaction with the phosphorus nucleus (Jph ~ 20 Hz). Signals of methyl protons of isopropyl radicals appear at 1.27 ppm, and signals of methine groups appear at 4.58 ppm, the spin-spin bond constant in CH-CH3 groups of the isopropyl radical is J-6.4 Hz.
Carboxymethyl esters of DTK acids are synthesized by the interaction of chloromethyl esters of carboxylic acids with sodium diethyl-dithiocarbamate in benzene at 40-450C for 1-2 hours. The reaction proceeds according to the scheme [10]:
RCOCH2Cl + NaSCN(C2H5)2 —► RCOCH2SCN(C2H5)2 + NaCl
O S OS
III, VI
R = CH3 (III), C6H5(VI)
In the IR spectrum of acetoxymethyl ester of diethyldithiocarbamic acid (VI), there is an absorption band at 1740 cm-1 corresponding to vibrations of C=O groups. Strong absorption bands are observed in the region of 1160 cm-1
for the thioamide group c - N ( •
11 S
The characteristic band for the C=S group appears at a frequency of 1080 cm-1.
In the NMR spectrum of acetoxymethyl ester in diethyldithiocarbamic acid (VI), the signals of the methylene protons of the OCH2SC=S fragment appear as a singlet in the region of 5.65
ppm, and the CH3C(=O) group appears as a singlet at 2.0 ppm. Methyl protons of ethyl radicals appear as a triplet in the region of 1.27 ppm. The signals of methylene protons of the same groups come out in the region of 3.75-3.8 ppm.
In this regard, we carried out studies to determine the thermal stability and chemical activity of the synthesized compounds on the metal surface.
Quantitative assessment of various processes occurring during heating of samples is carried out according to the curves of heat release or mass change during processing of thermograms [11-13].
The effectiveness of EP additives to oils is determined by their ability to form strong layers on juvenile metal surfaces under conditions of high contact temperatures and pressures, the structure of which depends on friction conditions and on the type of compounds used as additives [14-16]. The interaction of the additives with the metal must occur within a known range of temperatures above the bulk oil temperatures and below the seizing transition temperatures.
Given that the action of acetoxy- and benzoyloxymethyl esters of xanthogenic, dithi -ophosphoric, and dithiocarbamic acids as anti-wear additives occurs on the metal surface at certain temperatures [17-19], it seemed necessary to study their thermal characteristics both in pure form and in the presence of iron and copper powders. In order to establish both the performance of these compounds in the required temperature regime and to determine their chemical activity with respect to metals, we have synthesized compounds that are good antiwear and extreme pressure additives for oils and allow in some cases to characterize the relative effectiveness of such compounds.
Experimental part
Below, the authors present the synthesis of some acids and their physical and chemical parameters.
Acetoxymethyl ester of isopropylxantho-genic acid (I). To a suspension of 32 g (0.2 mol) of potassium ethyl xanthate in 50 ml of benzene was added 21.7 g (0.2 mol) of chloromethyl acetate and stirred for 3 hours at 40-500C. The
product was treated with water, fractionated in vacuum condition. Received was 34.9 g (88% of theory).
Boiling point (bp) 0C /mm Hg (mercury)
77-78/0.4.
20
1.5252, dT 1.2089, MRDh
49.26, MRDb 49.7
Found, %: C 36.90, H 5.04, S 33.04.
Calculated, %: C 37.11, H 5.15, S 33.18.
Diethyldithiocarbamic acid acetoxyme-thyl ester (III). To a suspension of 45 g (0.2 mol) of sodium diethylithiocarbamate in 50 l of benzene was added 21.7 g (0.2 mol) of chloro-methyl acetate. Stirring was continued for 2-3 hours at 400C. The product was taken up in water and distilled under vacuum. Yield was 37.5 g (85% of theory).
bp 0C /mmHg 130-131/0.5. nf 1.5567,
d420 1.1646, MRDH 61.16, MRDB 61.32. Found, %: C 43.11, H 6.58, N 6.40, S 28.71. Calculated, %: C 43.41, H 6.83, N 6.33, S 28.95
Benzoylokymethyl ester of O,O-diizo-propyldithiophosphpric acid (V). To 42.8 g (0.2 mol) of diisopropyldithiophosphoric acid in 50 ml of benzene was added 8 g (0.2 mol) of ground sodium hydroxide. The reaction mixture was stirred at 500C until the hydroxide was completely dissolved. Then, 34.1 g (0.2 mol) of benzoyl chloroacetate was added, stirred for 3 hours at 700C. The resulting mass was washed with water, benzene was distilled off and dried under vacuum. The residue was purified by liquid column chromatography using activated silica gel. The eluent was isopropyl alcohol. Yield was 58.5 g (84% of theory) nf 1.5346, d420 1.1737, MRDH 92.35, MRDB 91.82.
Found, %: C 48.13, H 5.95, S 18.11, P 8.81. Calculated, %: C 48.26, H 6.07, S 18.14, P 8.90.
Thermoanalytical studies of esters of xan-thogenic, dithiophosphoric and dithiocarbamic acids were carried out (with use of) on an OD-102 type derivatograph of the Paulik-Paulik-Erdei system (Hungary) in a dynamic heating mode at a rate of 50/min in the temperature range of 20-5000C. Aluminum oxide served as a reference. The weighed compound was 0.1 g; the ra-
d
tio "compound: metal" in experiments for copper powder was 1:1, in the case of iron powder - 1:2. The comparative thermal stability of the studied compounds was evaluated by temperatures corresponding to equal percentages (10%, 50%) of their mass loss (T10% T50%). It should be noted that T10% in this case characterizes mainly the volatility of these compounds, and the decomposition of the latter is observed at higher temperatures.
The chemical activity of the studied ethers with respect to metals was characterized by a set of thermodynamic parameters, including the temperature of the interaction of the compound or the products of its thermodynamic transformations with the metal, the intensity of this reaction and the mass loss corresponding to the temperature of the interaction.
There are many varieties of thermal analysis methods that enable to determine the continuous change in some important lubricating properties of oils in the process of heating it. Thermal analysis methods make it possible to obtain versatile information about the most important physicochemical properties of the compounds synthesized by us. The thermal degradation of the obtained compounds in TB-20 transmission oil was studied in the temperature range 130-2500C in the presence of iron and copper powders.
Results and discussions
As shown by the results of thermoana-lytical studies presented in the table, the thermal stability of the studied acetoxy - (compounds I-III) and benzoyloxymethyl compounds (compounds IV-IV) in esters of isopropylxan-thogenic, diethyldithiocarbamic and di(isopro-pyloxy)-dithiophosphoric acids, depending on the nature of the acid residue, is within 135-1560C and 170-2150C, respectively (the temperature at which the mass loss of these compounds has been 50% is in the range 170-2300C and 194-2360C). Esters of isopropyl xanthogen-ic acid have the least stability against temperature influences in both series: ...-SC (S) N (C2H5)2 - ...-SP(S)(OC3H7)2 -...-SC(S)OC3H7
The results of the studies have showed that all the studied compounds are chemically active with respect to metals - their primary more or less energetic interaction with metal powders is fixed at different temperatures: with iron - 170-1950C, and with copper at 130-1750C with more or less intense release of heat. As an example, Figure 1 shows curves of differential thermal analysis (DTA curves) of benzoyloxymethyl ester of diethyldithiocarbamic acid (compound VI) in pure form (a) and mixed with iron powder (b) and copper (c) powders. The first endothermic effect on these DTA curves is observed in the temperature range of 45-550C, which corresponds to the melting of compound VI. The next endoeffect on curve (a) at a temperature of 2150C characterizes the thermochemical transformations of the studied compound associated with its decomposition. DTA curves of benzoyloxymethyl ester of diethyldithiocarbamic acid in pure form (a) and mixed with iron (b) and copper (c) powders.
From the figure you can see that a synchronous type of reaction takes place here. This type implies the formation of a donor-acceptor bond between the compound and the metal, followed by decomposition. DTA curves of ether in the presence of metal powders record exothermic effects with a more or less significant amount of heat released, characterizing the interaction of the compound with metals. Compound VI interacts with iron (curve b) at temperatures of 190-2200C, at which the weight loss was 4 and 50%, respectively; with copper (curve c) - at temperatures of 155, 180, 220, 2500C and above with a weight loss of 23, 26, 38, 46%, respectively. The start of the first reactions of compound VI with metals, occurring practically without loss of its mass (2-4%), can be attributed to the formation of a more or less strong donor-acceptor (type) bond between the compound and the metal.
Given in the table, some thermoanalytical data on the interaction of synthesized esters with metal powder characterize the different chemical activity of these compounds with respect to metals.
DTA curves of benzoyloxymethyl ester of diethyldithiocarbamic acid in pure form (a) and mixed with iron (b) and copper (c) powders.
Data from thermoanalytical studies of some compounds in pure form and in the presence of iron and copper powders
№ Sample Thermal and chemical transformations, °C Reactions with metals Load wear index of a 5% compound solution in TB-20 oil (9490-60 GOST -compliant)
Temperature of reaction start, 0C Mass loss corresponding to the temperature of reaction start, %
I CH3COCH2SCOC3H7 II II O S +Fe +Cu 135-270 137-240 138-245 180 130; 175 64 7; 52 54
II CH3COCH2SP(OC3H7)2 II II O S +Fe +Cu 156-240 170-230 173-240 170; 204 175; 205 10; 50 11; 64 59
III CH3COCH2SCN(C2H5)2 II II O S +Fe +Cu 148-300 160-270 162-270 170;230 165 12; 50 11 64
IV C6H5COCH2SCOC3H7 II II O S +Fe +Cu 170-305 170-330 170-340 195 170; 200 57 10; 62 52
V C6H5COCH2SP(OC3H7)2 II II O S +Fe +Cu 176-255 175-300 180-245 190 170; 185 18 16; 16 56
VI C6H5COCH2SCN(C2H5)2 II II O S +Fe +Cu 215-290 207-260 205-270 190;220 155; 180 4; 50 23; 26 60
For example, compound I in the series of studied acetoxymethyl ethers interacts with iron at a higher temperature of 1800С with little heat release, and at this temperature the weight loss is already 64%. The interaction probably proceeds according to the type of asynchronous reaction, suggesting at the beginning the decomposition of the compound, and then the interaction of the transformation products with iron. Compounds II and III interact with iron at a temperature of 1700С, at which the weight loss reaches only about 10%.
Thermo-analytical studies have shown that in the series of benzoyloxymethyl ethers, compound IV interacts most vigorously with iron, exhibiting a higher chemical activity with respect to the metal at a temperature corresponding to a lower weight loss.
Undoubtedly, the chemical activity of compounds with respect to metals plays a significant role in the manifestation of their anti-seize properties. Our previous studies of a number of anti-wear and extreme pressure additives have found that the lower the temperature of interaction of structurally similar compounds with metal, the more effective the compound as an additive. The lower the weight loss, the more effective the compound is likely to be as an additive.
Of the studied series of compounds I-VI, compounds III and VI should have the most effective anti-seize properties, while compounds I and IV should have the least effective ones. Really, the values of the studied compounds, obtained for 5% solutions in TB-20 oil and given in the table, confirm the above. This is also consistent with the results of our earlier similar studies of a large number of derivatives of xan-thogenic, dithiophosphoric, and dithiocarbamic acids [8-10].
Conclusions
1. Thermal analytical studies of acetoxy-ben-zoyloxymethyl derivatives of xanthogenic, dithiophosphoric and dithiocarbamic acids as extreme pressure additives have been carried out.
2. The temperature up to which the thermal stability of the studied compounds is maintained exceeds 1700C, which satisfies the relevant requirements for extreme pressure additives.
3. The investigated compounds are chemically active with respect to metals - iron and copper. It has been found that the lower the interaction temperature and the lower the weight loss corresponding to this temperature, as well as the more intense the reaction, the more effective is the compound as an additive for the specified purpose.
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TORKiBiNDO S, P, N OLAN ÜZVi BiRLO§MOLORiN SiNTEZi УЭ METALLARA QAR§I
TERMOSTABiLLiYi
E.^.Mammadov, T.N.Qulubayova, D.S.Valiyeva, Z.S.Saf3r3liyeva, i.R.Ru$maz
Maqala bazi ditiofosfat, ksantogenat, ditiokarbonat tur§ularinin efirlarin termiki tadqiqlarina hasr edilmi§dir. Öyranilan birla§malari ham tamiz halda ham da damirin va misin i§tiraki ila termoanalitik tadqiqatlarinin va metallara qar§i kimyavi aktivliyinin naticalari maqalada §arh edilir. Müayyan edilmi§dir ki, tadqiq olunmu§ birla§malara termiki stabillik haddi 1700C temperaturunda yüksakdir va onlar damir va mis metallarina qar§i kimyavi aktivdirlar. Göstarilmi§dir ki, öyranilan birla§malar damir va mis metallarina qar§i kimyavi aktivdir va eyni sira birla§malarinin metallara qar§iliqli tasir temperaturu va hamin temperaturda onlarin kütlavi itkisi na qadar az olarsa, onlarin siyrilmaya qar§i a§qar kimi tasiri o qadar yuksak olur. Müayyan edilmi§dir ki, metallarla sinxron mexanizm üzra qar§iliqli tasirda olan eyni sira birla§malari, metallarla sinxron mexanizm üzra (parcalanma mahsullari ila) qar§iliqli tasirda olan birla§malara nisbatan daha yüksak siyrilma xassalarina malikdir.
Agar sözlzr: ksantogenat, ditiokarbonat ditiofosfat tur§ulari; termiki stabillik; trasmissiya yagi; siyrilmaya qar§i a§qar; siyrilma indeksi; termoanalitik tadqiqatlar.
