Efficacies of Novel Gemini Compounds Derived from Dibasic Acids

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Efficacies of novel Gemini compounds derived from dibasic acids as multifunctional additives for tribological applications Neha Karanwal, Praveen Khatri, Sandeep Joshi, Gananath D. Thakre, Rakesh C. Saxena, Savita Kaul, and Suman L. Jain Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.5b01208 • Publication Date (Web): 18 Jun 2015 Downloaded from http://pubs.acs.org on July 1, 2015

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Industrial & Engineering Chemistry Research

Efficacies of novel Gemini compounds derived from dibasic acids as multifunctional additives for tribological applications Neha Karanwal,a Praveen K. Khatri,b Sandeep Joshi,b Gananath D. Thakre,c* Rakesh C. Saxena,b Savita Kaula and Suman L. Jainb* a

Biofuel Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun-248005 (India)

b

Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun-248005 (India) c

Tribolgy & Combustion Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun-248005 (India)

AUTHOR INFORMATION *Corresponding Author Chemical Sciences Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun248005; Email: [email protected]; Tel +91-135-2525788; Fax: +91-135-2660202 Tribology & Combustion Division, CSIR-Indian Institute of Petroleum, Mohkampur, Dehradun-248005; Email: [email protected]; Tel +91-135-2525889; Fax: +91-1352660202

ACS Paragon Plus Environment


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Abstract A series of new Gemini compounds derived from the reaction of dibasic acids with N,Ndiethyl-2-aminoehanol followed by reaction with p-toluene sulfonic acid were synthesized and characterized by means of the Fourier transform infra-red (FTIR), nuclear magnetic resonance technique (1H NMR) and Mass spectral analyses. The synthesized compounds were used as multifunctional additives particularly as anti-wear, friction reducing agent and as corrosion inhibitors for tribological applications. To the best of our knowledge this is the first report describing the use of Gemini compounds in the tribological applications. Keywords: Gemini compound, multi-functional additive, corrosion inhibitor, Tribology

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Introduction The stringent environment regulations and depleting petroleum reserves have ascertained a quest to develop new and environmentally benign lubricants for the industrial applications.1,2 The aqueous lubricants are being seen as one of the best possible option to save the environment from further pollution and degradation.3 Numerous attempts have been made in recent past to develop aqueous lubricants for metal working, gear and hydraulic fluids and the compressor lubricants.4-7 Water as a lubricant along with polyethylene glycols has been investigated for their performance characteristics in food processing, biological systems and metal working applications.8,9 However, the major limitation with aqueous lubrication is their corrosion resistance and poor tribological properties.10,11 Attempts are being made to enhance the desired properties of aqueous lubricants with the help of additives and surfactants. In this scenario the Gemini compounds are currently being explored as multifunctional additives for aqueous lubricants.7

Gemini compounds consisting of two or more amphiphilic moieties and two polar head groups connected by a spacer group are a class of compounds with their own unique properties.12-14 Short or long chain alkyl groups, polar (polyether) and non-polar (aliphatic or aromatic) groups may be used as spacer and the polar ionic heads may be positive (ammonium) or negative (phosphate or carboxylate). These compounds have attracted considerable interest in recent decades because of their exceptional structural feature and versatile applicability.15-17 Because of these unique properties, they have shown great potential to be used as effective emulsifiers, bactericidal agents, dispersants, anti-foaming

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agents, and detergents, etc.12-13,18-19 They have also applied in the solubilization of dyes and pigments in the textile industry20 and gene therapy.21

However, to the best of our knowledge the potential of these novel compounds has been remained unexplored as multifunctional additives for tribological applications. The lubricants in industrial environment are used to lubricate the conformal and non-conformal geometries of the components like the bearings, gears, cam-followers, pumps etc. These components while in operation are susceptible to rolling and sliding motion thereby resulting into friction and wear. The major role of lubricant used in these contacts is to separate the contacting surfaces by forming thick lubricating films. Thus, minimizing the friction and wear22,23. The tribo-performance behavior of the lubricants is an assessment of the lubricating films about their capabilities of minimizing the friction and wear. Therefore, the studies concerned with the development and synthesis of lubricants and additives are rendered incomplete without the discussion on the tribo-performance behavior.

Thus, in the present investigation we report for the first time the use of Gemini compounds derived from dibasic acids such as malonic acid, succinic acid, glutaric acid, adipic acid etc and the polar heads derived from N,N-diethylethanolamine followed by reaction with ptoluene sulfonic acid (Fig. 1). The synthesized compounds were used as anti-wear, friction reducing agents and corrosion inhibitors for aqueous lubricants. The tribo-performance of Gemini compounds has been investigated when blended as additives in PEG300. When blended into PEG300 the representative characteristic performance over and above the performance of base PEG300 can be attributed to the additive and its concentration. Hence, with a small quantity the required tribo-performance can be easily studied. The chemical structures of synthesized Gemini compounds are presented in Fig. 1 4


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C2H5 SO3NH

CH3

C2H5

O

C2H5

O

NH

n

O

SO3

CH3

C2H5

O

n=1; malonic acid n=2; succinic acid n=3; glutaric acid n=4; adipic acid

Figure 1: Gemini compounds derived from dibasic acids

2. Experimental 2.1 Materials and methods Malonic acid, succinic acid, glutaric acid, adipic acids and N,N-diethyl-2-aminoehanol were purchased from Alfa Aesar and used without further purification. Azelaic acid, Sebasic acid and p-toluene sulfonic acid were procured from Lancaster and used as received. FT-IR spectra were taken using a Thermo Scientific Nicolet iS 50 spectrophotometer with samples prepared as KBr pellets. 1H NMR spectra were obtained using a 500 MHz Bruker FT spectrometer. Chemical shifts (ppm) were referenced either with an internal standard (Me4Si) for organic compounds or the residual solvent peaks.

2.2 General procedure for the synthesis of Gemini compounds A solution of dicarboxylic acid (10 mmol) in 20 ml of ethanol was added gradually to N,Ndiethyl-2-aminoethanol (22 mmol) using p-toluene sulfonic acid (5 wt%) as catalyst with stirring at 150oC for 10 h. After being cooled the reaction mixture to room temperature ptoluene sulfonic acid was added (20 mmol) and the resulting mixture was heated at 78 oC 5



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for 10 h. The resulting mixture was concentrated using rota-evaporator under reduced pressure to give colourless to pale yellow viscous liquids in almost quantitative yields which were finally dried at 80oC for 24 h.

2.3 Characterization of the Gemini compounds The successful synthesis of the Gemini compounds was confirmed by FTIR, 1H NMR and ESI-Ms analyses as shown in the Table 1.

Table 1: Characterization data of Gemini compounds

Gemini compound 1

1

FTIR (cm-1)

CH3

C2H5 SO3 NH C2H5

O

O O

O

C2H5 NH SO3 C2H5

CH3

1a

CH3

C2H5 SO3 NH C2H5

(CH2)2 O

O O

O

C 2H 5 NH SO3 C2H5

CH3

1b

CH3

C2H5 SO3 NH C2H5

(CH2)3 O

O O

1c

O

C 2H 5 NH SO3 C2H5

CH3

H NMR

ESIMS

(ppm)

3403 (N-H), 3058 (C-H Ar.), 2980 (s, C-H), 1731 (s, C=O), 1601 (C=C), 1123 and 1007 (S=O)

1.26 (t, NCH2CH3), 2.28 (s, CH3 of PTSA), 3.14 (q, NCH2CH3), 3.36(s, COCH2CO), 3.8 (t, NCH2CH2O), 4.19 (t, OCH2), 7.09-7.11 (m, ArH), 7.67 (m, ArH)

646.26

3398 (N-H), 3045 (C-H Ar), 2918 (s, C-H), 1722 (s, C=O), 1602 (C=C), 1124 and 1008 (S=O)

1.24 (t, CH3), 2.33 (s, CH3 of PTSA), 2.70 (t, COCH2CH2CO), 3.20 (t, NCH2CH3), 3.89 (t, NCH2CH2O), 4.17 (t, OCH2), 7.10-7.18 (m, ArH), 7.71 (ArH)

660.28


1.27 (t,CH3), 2.31 (s, CH3 of PTSA), 2.38 (q, CO(CH2)3CO), 2.81 (t, COCH2CH2CH2CO), 3.17 (t, NCH2CH3), 3.83 (t, NCH2CH2O), 4.14 (t, OCH2), 7.137.15 (m, ArH), 7.68

674.29

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(ArH)

CH3

C2H5 SO3 NH C2H5

(CH2)4 O

O O

O

C 2H 5 NH SO3 C2H5

CH3

1d

CH3

C2H5 SO3 NH C2H5

(CH2)7 O

O O

C2H5 NH SO3 C 2H 5

O

CH3

1e

CH3

C 2H 5 SO3 NH C 2H 5

(CH2)8 O

O O

C2H5 NH SO3 C 2H 5

O

CH3

1f

O CH3

C2H5 SO3 NH C2H5

O

O O

NH2

C2H5 NH SO3 C2 H5

1g

CH3


1.26 (t, CH3), 2.31 (s, CH3 of PTSA), 2.33(q, CO(CH2)4CO), 2.79(t, COCH2CH2CH2CH2CO ), 3.16 (t, NCH2CH3), 3.83 (t, NCH2CH2O), 4.14 (t, OCH2), 7.137.15 (m, ArH), 7.64 (ArH)

688.31


1.29 (t, CH3), 2.30 (m, CO(CH2)7CO), 2.34 (s, CH3 of PTSA), 3.22 (t, NCH2CH3), 3.89 (t, NCH2CH2O), 4.15 (t, OCH2), 7.17-7.18 (m, ArH), 7.73 (m, ArH)

730.35

3414 (N-H), 3046 (C-H Ar.), 2929 (CH), 1733 (s, C=O), 1605 (C=C), 1124 and1008 (S=O)

1.29 (t, CH3), 2.34 (s, 744.37 CH3 of PTSA), 2.34 (m, CO(CH2)8CO), 3.22 (t, NCH2CH3), 3.72 (s, COCH2CH2CO), 3.89 (t, NCH2CH2O), 4.15 (t, OCH2), 7.17-7.18 (m, ArH), 7.73 (m, ArH)

3394 (N-H), 3042 (C-H Ar), 2910 (s, C-H), 1733 (s, C=O), 1605 (C=C), 1121 and 1007 (S=O).

1.15 (t, CH3), 2.28 (s, CH3 of PTSA), 3.14 (t, NCH2CH3), 3.79 (s, COCH2CH(NH2)CO), 3.93 (t, NCH2CH2O), 4.19 (t, OCH2), 7.117.09 (m, 2 ArH), 7.66 (m, ArH)

675.29

2.4. Lubricant blend preparation The synthesized Gemini compounds (1a-g) were used as additive to determine their performance efficiency in terms of anti-friction, anti-wear and corrosion resistance characteristics. The lubricant blends were prepared using PEG300 as base fluid. PEG300 has been used as aqueous lubricant in metal working applications. All of the synthesized 7



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compounds were low viscosity liquids at room temperature, except 1a, 1e, 1f and 1g. The lubricant blends were prepared by mixing the additives in varying concentrations into PEG300 at room temperature followed by mechanical stirring for 30 min. Due to the hydrophilic nature the synthesized compounds were easily dispersed into the base fluid. The 1a, 1e, 1f and 1g compounds were highly viscous with jelly like appearance at room temperature. Hence, these compounds were heated in an oven at 50 ±5 °C for 30 min prior to blending. The as prepared blends were sonicated in an ultrasonic bath for 15±5 min prior to their performance investigation.

2.4.1 Tribo-performance investigation The tribo-performance investigation of the lubricant blends was carried out on a four-ball tribo-tester under the low load conditions. As the aqueous lubricants have lower load bearing capacity the experiments were performed at lower loads. The experimental set-up used in the present investigation is shown in Fig. 2. The tribo-tester utilizes a four-ball geometry assembled in a tetrahedral shape. The top ball being mounted into the spindle rotates at the predefined motor speed. The bottom three balls are submerged into the lubricant blend to be tested in the ball pot and are tightened using the torque wrench. The top ball forms a pure sliding contact with the bottom three balls at three distinct locations. With a low load and high speed and has been made to simulate the elasto-hydrodynamic lubrication conditions on the four-ball tester. The test specimens used were the standard AISI steel no. E-52100 balls of 12.7 mm diameter and hardness of Rockwell C 64-66. The experiments were performed at a load of 196N, 1200 rpm speed, 50°C for 1 hr. duration. Every experiment was performed twice and the repeatability in the results was within 5 %. The friction torque was measured during the entire test duration and was converted into 8


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coefficient of friction using empirical relation. The wear scar obtained on the bottom three balls at the end of each test was measured using Leica Stereo zoom apochromatic Industrial microscope. An average of six readings per test was made. The average values of kinetic friction along with the wear scar diameter at the end of two tests were reported.

Figure 2: Four-ball tribo-tester

2.4.2 Corrosion behavior studies The corrosion behavior studies of the synthesized blends were performed on carbon steel test specimens. The carbon steel test specimens were incised into small coupons of size 15 mm×10 mm×2 mm (area 0.6 sq. inches) by machining and milling processes. The machined test specimens were smoothened using surface finishing operations. The smooth test specimens were further hand polished using carborundum emery paper of number C 201 AH extra fine grade. The polished test specimens were then degreased using xylene–isopropanol mixture (1:1). The thus prepared carbon steel coupons were weighed accurately to 9



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0.1 mg before exposure to the test lubricant. The experiments were performed for the base oil and the lubricant blends separately for comparative assessment of the performance. Experiments were performed by suspending the carbon steel test specimens into the base oil and lubricant blends separately using a Teflon thread in stopped measuring cylinders. The experiment was carried out for duration of 25 days (600 hrs) at 110 °C in an air oven. The test specimens were then evaluated for qualitative and quantitative estimation of corrosion [1, 2].

On completion of the tests the test specimens were derusted with derusting solution (36% HCl containing 5% Sb2O + 4% SnCl2) prior to weighing. The weight loss of each test specimen was recorded and the corrosion rate or penetration was calculated [2] according to the formulae given by:

Corrosion Rate =

Wt.Loss * ×15.5 = mg /( sq.dm)(day ) or mdd ( Area)(Time)

(1)

Considering the density of carbon steel (7.8 g/cm3) into account penetration rate was calculated [2] according to the formulae given by:

Penetration Rate =

Wt. loss * ×22.3 = mils / year or mpy ( Area)(time)(metal density ) (2)

where, the *Weight loss was obtained after de-rusting metal samples using 36% HCl containing 5% Sb2O3+4% SnCl2.

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3.0 Results and discussion The performance behavior of synthesized additives blended in PEG300 base fluid reveals that the additives are capable to impart resistance to friction, wear and corrosion. The base fluid PEG300 in itself being a versatile aqueous lubricant, the performance of the blended lubricants have been bench marked with PEG300.

3.1 Tribo-performance tests The tribo-performance test results are shown in fig. 3-5. Due to the brevity of space only the results for 4% concentration of the additives is reported. The anti-wear performance of the lubricant blends as shown in fig. 3 reveals that the compounds 1b and 1d possess better anti-wear characteristics than the other synthesized compounds. The compounds 1b and 1d report a minimum of 0.64 mm of wear scar diameter. The base oil PEG300 on the contrary has a wear scar diameter of 0.88 mm. The comparative assessment reveals that all the compounds synthesized possess anti-wear behavior.

Figure 3: Anti-wear performance of the lubricant blends 11



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The anti-friction behavior of the lubricant blends is shown in fig. 4. It can be seen from the histogram that the PEG300 has the highest coefficient of friction with the value of 0.12, while all the lubricant blends have reported the values of coefficient of friction to the order of 0.04. The lubricant blend with compound 1b has a slightly higher coefficient of friction of 0.06 when compared with the other lubricant blends. A comparative assessment of the performance reveals that the Gemini compounds possess superior anti-friction properties.

Figure 4: Anti-friction behavior of the lubricant blends.

The percentage change in the friction and wear behavior of the blended lubricants has been bench marked with PEG300 and the results is shown in fig. 5. It is clearly observable that the blending of Gemini compounds results into reduction in friction to the order of 60%. Similarly the reduction in wear is to the order of 28% in case of 1d. Of all the compounds tested the best performance is reported for the compounds 1b, 1d, and 1g. The other

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compounds have excellent friction reduction characteristics, but the reduction in wear is not very much significant.

Figure 5: Percentage change in the friction and wear behavior of the lubricant blends.

3.2 Corrosion behavior The Corrosion behavior of carbon steel in base oil and the lubricant blend in terms of weight loss (milligram), corrosion rate (milligram per decimeter square per day), and thickness reduction (mill inches per year) is tabulated in Table S1. The Total acid number (TAN), a measure of the extent of oxidation as well as corrosion before and after corrosion test is also reported. As evident from Table S1, the corrosion rate with Base oil is of 69.03 mdd. However, with the addition of Gemini compounds the corrosion rate has substantially reduced for blends of compound 1a-c, 1f and 1g. There is very nominal reduction in corrosion rate for 1e compound. However, the 1d has reported a corrosion rate of 80.08

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mdd, which is higher than base oil. The blend for compound 1f has reported the lowest corrosion rate of 0.62 mdd.

The penetration rate too being a function of wt. loss, surface area, time and density of test specimens have reported similar trends like the corrosion rate. The penetration rate for 1f compound is 0.08 mpy as compared to 8.85 mpy of the base fluid. The blend of 1d compound has the higher penetration rate of 19.27 mpy which is higher than that of the base oil.

The results pertaining to the acid value reveals that the base oil PEG300 has an acid value of 0.0 before the start of the test that increased to 8.8 at the end of the test. Similarly all the lubricant blends have an Acid value in the range of 9-12 mg/g KOH before the test that increased monotonically in most of the compounds. However, in case of 1b and 1f, the acid value decreased at the end of the test. The lubricant blend with 1f reported the smallest change in the acid value of the order of 0.2 as compared to 8.8 in case of base oil. The 1d compound reported the highest change in acid value of 9.5 which is higher than the base oil.

The visual inspection of surfaces was also carried out for the qualitative assessment of corrosion product, tarnishing, pitting, cracking etc. The photographs of test specimens were taken after washing with 50:50 (xylene + isopropyl alcohol). Fig. 6 shows the photographs of the used test specimens. Due to the brevity the results for the corrosion behavior of compounds 1a and 1c is shown in the figure.

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Figure 6 Test specimens before and after the corrosion studies.

Conclusion We have demonstrated for the first time the use of Gemini compounds as efficient anti wear, anti-friction and corrosion inhibitor additives for lubricating oils. A series of novel Gemini compounds were synthesized from the reaction of dibasic acid with N,N-diethyl-2aminoethanol followed by reaction with p-toluene sulfonic acid. The synthesized Gemini compounds were used as additives and have shown higher performance efficiency in terms of anti-friction, anti-wear and corrosion resistance characteristics when compared with PEG300 aqueous lubricant. To the best of our knowledge this is the first report describing the use of Gemini compounds for tribological applications which will open new possibilities for exploring the potential of these compounds for other tribo-chemical applications.

Acknowledgements We are thankful to director IIP for his kind permission to publish these results. NK and SJ are thankful to CSIR, New Delhi for working as Technical HR in XII Five Year projects. 15



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Supporting Information Corrosion behavior of carbon steel in base oil and various blends of additive vis a vis acid values are described in the supporting information. This material is available free of charge via the Internet at http://pubs.acs.org Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. P K Khatri, N Karanwal and S Joshi are involved in the experimental work such as synthesis and characterization of the compounds. R. C. Saxena has carried out corrosion studies and G. D. Thakre is involved in the tribological studies as reported in the paper. S. Kaul, SL Jain are contributed in the technical discussion and writing of the manuscript.

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(22)

Dowson, D.; Higginson, G. R. Elasto-hydrodynamic Lubrication. Oxford; Pergamon Press: U.K, 1966.

(23)

Laine E.; Olver, A.V.; Beveridge, T. A. Effect of Lubricants on Micropitting and Wear, Tibol. Int. 2008, 41, 1049.

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For Table of Contents Only Efficacies of novel Gemini compounds derived from dibasic acids as multifunctional additives for tribological applications

C2H5 CH3

SO3NH C2H5

O

O O

C2H5 NH

n

O

SO3 C2H5

20


CH3

Efficacies of Novel Gemini Compounds Derived from Dibasic Acids

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