Synthesis, characterization and tribolgical properties of the complexes of light rare earth with dioctyldithiocarbamate

Zhong Yun, Zhang Weiguang, Ren Tianhui^#
(Dept.of Chem., South China Normal University, Guangzhou 510631; Dept.of Chem., ^#Shanghai Jiaotong University,Shanghai,201100, China)

Recerived Jan.7, 2001. This work is funded by the National Natural Science Foundation of China and the Natural Science Foundation of Education office in Guangdong Province.

Abstract Eight complexes of light rare earth with dioctyldithiocarbamate have been prepared by using dioctylamine,carbon disulfide and rare earth chloride(RE=La-Tb,except for Pm) as reactants in air. They are characterized by elemental analyses, IR spectra, H NMR spectra and TG-DTA technique. The results show that in the complexes every ligand coordinates to RE ion through two sulphur atoms. The load-carrying capacity and anti-wear properties of two complexes(La,Nd) are evaluated by using a four ball test machine. It is shown that these novel compounds have excellent load-carrying capacity and good anti-wear property.
Keyword rare earth complex, dioctyldithiocarbamate, preparation, tribological properties

1. INTRODUCTION     
Since Brown^[1] had prepared the solid rare earth complexes with diethyldithiocarbamate firstly. many complexes of rare earth ions with dithiocarbamates were extensively studied. RNH₃[RE(RHDTC)₄] (RHDTC=RHNCS₂; R=Me, Et; RE=La, Nd, Sm-Gd)^[2], RE(Et₂DTC)₃bipy (RE=La, Pr, Nd, Sm-Lu, Y; Et₂DTC=N,N-diethyldithiocarbamate; bipy=2,2'-bipyridyl)^[3] and other similar complexes^[4] had been prepared before 1996. These similar complexes used as additives of lubricating oils^[5-7], rubber accelerators^[8] and their biochemical activity^[9] have been reported. However, the syntheses of these complexes need to be carried out at the condition without air and water. In this paper, we improved the process of synthesis and prepared eight rare earth ( RE=La-Tb, except for Pm ) complexes with dioctyldithiocabamate (see the Fig.1) in air. The composition and tribological properties of these new complexes were investigated.

2. EXPERIMENTAL
2.1 Reagents 
Rare earth oxides(Shanghai Yuelong Chemical Company) with purity not less than 99.9%.
    Dioctylamine and carbon disufide are analytically pure and made in China.
2.2 Measurements  
The metal ion was determined by EDTA titration using xylenol-orange as indicator.Carbon, nitrogen and hydrogen were determined by using a Carlo Erba 1106 elemental analyser. The IR spectra were recorded on a 170 SX FTIR spectrometer in the region of 600 - 200 cm^-1 and on 5D-X spectrometer in the region of 4000- 400 cm^-1 in KBr pellets. The H NMR spectra were recorded on a EM360 spectrometer by using carbon tetrachloride as solvent. Thermal analyses(TG and DTA)were performed on a Beijing PCT-2 thermobalance.The load-carrying capacities and anti-wear properties were evaluated on a MRS-10A four-ball lubricant test machine(Jinan test machine factory) at 1450 rpm with a test duration of 30 min at room temperature.
2.3 Preparation of anhydrous rare earth chlorides and the ligand       
Rare earth chlorides were prepared according to the literature method^[10].
    Potassium dioctyldithiocarbamate((C₈H₁₇)₂NCS₂K) was obtained by reaction of dioctylamine, carbon disufide and potassium hydroxide(molar ratio 1:1:1) in methanol medium.The product was washed by water,vacuum dried over P₄O₁₀-CaCl₂ and verified by IR and H NMR spectroscopy.
2.4 Preparation of the complexes    
0.066 mol dioctylamine was dissolved in 10 ml methanol. To this solution was slowly added 0.028 mol carbon disulfide at 0掳C and continually stirred at room temperature for 1 hour. Then 10 ml solution of 0.014 mol RECl₃ (RE=La-Tb, except for Pm) in methanol was slowly added to this solution. Continually stirred at room temperature for 10 hour. The product was filtered and washed with methanol three times. Dissolved the product in ethyl ether and filtered. Filtrate was volatilized in air and then dried in vacuum over P₄O₁₀-CaCl₂.

3. RESULTS AND DISCUSSION
3.1 The composition of the complexes

Table 1 Elemental analyses data

Table2  The most important IR bands (cm^-1)

3.3 H NMR spectra        
The H NMR data of potassium salt and rare earth complexes were reported in Table3. The d (H₃C-CH₂-) and d (-H₂C-) of the potassium salt and the rare earth complexes had little difference. The d (-N-H₂C-) of rare earth complexes were somewhat small comparing to the potassium salt because of different metal ions.

Table3 H NMR data (ppm)

3.4 Thermal analyses         
The thermal analysis studies were performed by means of TG and DTA techniques. K(S₂CNC₁₆H₃₄)路 XH₂O loses water molecules at 137掳C. It decomposed at 248掳C and continuous weight loss was detected to 491掳C , at this temperature the ligand decomposed completely. Lanthanum complex (La(S₂CNC₁₆H₃₄)₂Cl路 5H₂O) lost five water molecules when heated to 121掳C. The weight loss found in this process is 9.75% (calc. 10.03%). On raising the temperature further, the complex decomposed exothermically at 231掳 C. Subsequently other exothermic peaks and continuous weight loss was detected up to 490掳C. At this temperature La₂(S₂O₇)₃ is formed. The total weight loss found(56.25%) was approximately consistent with that calculated(55.09%).
    According to the above experimental results of elemental analysis, IR spectra, H NMR spectra and TG-DTA technique, we propose that the possible structure of the complexes is

路X H₂O
                                RE=La-Tb, except for Pm; X=0~ 5

Fig. 2 The P_B value of complexes

Two novel rare earth complexes (La,Nd) added to liquid paraffin in concentration of 0.25wt% and 1.00wt%, respectively. The load-carry capacity (P_B value) of these two complexes and liquid paraffin are shown in Fig. 2. The result indicates that P_B value raised 90% than that of liquid paraffin when the concentration was 0.25wt% and raised 134% when the concentration was 1.00wt%. It expresses that these two complexes had excellent load-carrying capacity. We can learn that there is no difference between these two complexes from Fig. 2.

	銆?
Fig. 3 Effects of concentration of complexes on wear (four-ball, 300N, 30min)	Fig. 4 Effects of load on wear     (four-ball, 0.25wt%, 30min)

3.5.2 Anti-wear property
The anti-wear properties of complexes as additives in liquid paraffin relative to concentration and load are shown in Fig. 3 and 4. The result in Fig. 3 indicates that these complexes possess good anti-wear property in liquid paraffin when the concentration varied from 0.25wt% to1.00wt%. The smaller the concentration is, the better the anti-wear capacity. The result in Fig. 4 indicates that these complexes also possess good anti-wear capacity in liquid paraffin when the load varied from 100N to 300N. The harder the load is, the better the anti-wear capacity. We can also learn from figures 3 and 4 that there is no obvious difference between different rare earth element.

REFERENCE  
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