An environmentally friendly lipophilic coating of metal surface

Article abstract of DOI:10.1016/j.tetlet.2020.152242

An environmentally friendly coating method of lipophilic thiols on metal surface is described. Lipophilic thiols were chemically modified to a water-soluble derivative, prepared from lipophilic thiol, succinic linker, and symmetrically branched oligoglycerol. Due to the chemical modification, water was used as a solute of coating reagent. The anticorrosive effect of metal piece with the water-soluble derivative in water was as high as with lipophilic thiol in organic solvent.

Full text of DOI:10.1016/j.tetlet.2020.152242

Journal Pre-proofs
An Environmentally Friendly Lipophilic Coating of Metal Surface
Md. Idrish Ali, Hoque Md. Mahbubul, Tsuyoshi Matsushita, Md. Mayez
Mahmud, Yuhki Seno, Yusuke Shibuya, Shoichi Yamada, Toshio Hyuga,
Hisao Nemoto
PII:
S0040-4039(20)30709-7
DOI:
Reference:
https://doi.org/10.1016/j.tetlet.2020.152242
TETL 152242
To appear in:
Tetrahedron Letters
Received Date:
Revised Date:
Accepted Date:
28 May 2020
7 July 2020
10 July 2020
Please cite this article as: Idrish Ali, Md., Md. Mahbubul, H., Matsushita, T., Mayez Mahmud, Md., Seno, Y.,
Shibuya, Y., Yamada, S., Hyuga, T., Nemoto, H., An Environmentally Friendly Lipophilic Coating of Metal
Surface, Tetrahedron Letters (2020), doi: https://doi.org/10.1016/j.tetlet.2020.152242
This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover
page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version
will undergo additional copyediting, typesetting and review before it is published in its final form, but we are
providing this version to give early visibility of the article. Please note that, during the production process, errors
may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
©
2020 Elsevier Ltd. All rights reserved.

An Environmentally Friendly Lipophilic Coating of Metal Surface
Md. Idrish Ali,a, b Hoque Md. Mahbubul, Tsuyoshi Matsushita, Md. Mayez Mahmud, Yuhki Seno,
c
a
a
a
d
d
d
a*
Yusuke Shibuya, Shoichi Yamada, Toshio Hyuga, Hisao Nemoto
a
Department of Pharmaceutical Chemistry, Graduate School of Medicinal Sciences, Tokushima University, 1-78-1 Sho-machi, Tokushima 770-8505 Japan
TEL&FAX +81 88-633-7284
Department of Chemistry, Mawlana Bhashani Science and Technology University, Tangail-1902, Bangladesh Fax:+88-0921-51900
Department of ESRM, Mawlana Bhashani Science and Technology University, Tangail-1902, Bangladesh Fax:+88-0921-51900
Chemical Denshi Co., Ltd. 4-1-72 Onodai, Minami-ku, Sagamihara City, Kanagawa Prefecture, 252-0331 Japan TEL +81 42-730-4777 FAX +81 42-730-4778
b
c
d
ABSTRACT
An environmentally friendly coating method of lipophilic thiols on metal surface is described. Lipophilic thiols were chemically modified to a water-
soluble derivative, prepared from lipophilic thiol, succinic linker, and symmetrically branched oligoglycerol. Due to the chemical modification, water
was used as a solute of coating reagent. The anticorrosive effect of metal piece with the water-soluble derivative in water was as high as with lipophilic
thiol in organic solvent.
Keywords: Water-solubility, Environmentally Friendly, Symmetrically branched oligoglycerols, Anticorrosive
Introduction
Since Nuzzo et al found the disulfide adsorption on a gold surface [1], a lipophilic organothiol (RSH) has been often used as an
anticorrosive for metal [2]. Among various RSH, octadecane-1-thiol (1) has been one of the most representative chemicals [3] (Scheme
1
).
Metal
piece
Metal
piece
Metal
piece
(A)
Top
region
Diluted solution
(B)
Bottom
region
S
S
S
S
S
(C)
17
15
13
11
9
7
5
3
1
(1)
18
SH
16
14
12
10
8
6
4
2
Scheme 1. Major coating procedure by using octadecane-1-thiol (1).
A target such as a piece of metal (A), is dipped into a diluted solution of 1 (B). During this operation, a strong coordination is generated
between zero-valent metal surface and the thiolate generated from 1 to afford “self-assembled monolayers” (SAM) [3], as shown in (C).
No further layers are assembled on the surface of metal after the SAM is created, because the top region shown in (C) is occupied with
only chemically inert alkyl chains, which can generate no strong chemical bond such as covalent, ionic or dipole moment interaction.
Accordingly, a very thin and stable coating completes via the simple procedure illustrated in Scheme 1. Due to such a thin layer,
electroconductivity of the target metal is often retained after the coating procedure, in general. In contrast, required property of rust
anticorrosive is often satisfied, in spite of such a thin layer [3].
Due to high lipophilicity of 1, organic solvents, a lipophilic and volatile liquid, has been required for the coating procedure. If such an
organic solvent could be displaced to water, it would be environmentally friendly. In addition, total cost, including purchased price and
waste disposal costs, would be reduced, because the solute occupies major weight and volume of the commercial package such as (B).
However, RSH possessing a long hydrocarbon chain is extremely insoluble in water. Although it has been reported that a large amount
of surfactant was used to prepare a micellar solution [4], it means a top priority backwards since surfactant often facilitates rust.
Although a commercially available water-affinitive RSH such as oligoethyleneglycolated alkanethiols (2) [5,6,7] can be an alternative
idea, property of the top region with 2 can be totally different from that with 1 (Fig 1). Accordingly, 2 can be incompatible to lipophilic
thiol and use of organic solvent has been indispensable for lipophilic thiolate coating.

2
Tetrahedron Letters
Figure 1. Comparison between 1 and a commercially available water-affinitive thiol 2 after coating procedure.
In this paper, we report a preparation method of lipophilic-thiolate-chemisorbed SAM on metal ((C) in Scheme 1) in an aqueous
solution. In this method, original lipophilic thiol was modified to a water-soluble derivative such as 3 [8] (Scheme 2). Due to the result
in a previous paper [9], it is anticipated that the thioester moiety of 3 is cleaved to afford the corresponding oxidative adduct 5, followed
by releasing the water-solubilizing fragment 4 into an aqueous solution. The fragment 4 can be finally converted to succinic acid [10]
and BGL003 [11,12] (Fig 2), both of which are known to have extremely low toxicity. Accordingly, the released fragment 4 is also
designed to be environmentally friendly.
Scheme 2. Proposed mechanism of metal surface coating with thioester 3.
As a water-solubilizing fragment, our originally developed molecules, glycerol trimer BGL003 [13,14] and heptamer BGL007 [14]
were used. Various functional groups X at apex have been used for the covalent bond formation with poorly water-soluble compounds
[15,16,17] such as 1. Primary hydroxy groups, four in BGL003 and eight in BGL007, respectively (terminal side of the dendric
structure), have stronger water-affinitive property than another polyhydroxylated molecules such as cyclic carbohydrates, due to the
high conformational flexibility and three-dimensional spread.
Figure 2. Our originally designed symmetrically branched glycerol trimer and heptamer.
Synthesis
In Scheme 3, the detail of the synthetic procedure of 3 (=6d) as well as the related derivatives 6a–6c, 6e and 6f is illustrated. The
reaction of 8 with succinic anhydride in pyridine afforded thioester 9 in a range of 87–96% chemical yield. Condensation between the
alcohol 10, and carboxylic acid 9 was carried out in dichloromethane with 3-(((ethylimino)methylene)amino)-N,N-dimethylpropan-1-
aminium chloride (EDC•HCl) and 4-(N,N-dimethyl)pyridine (DMAP) to give the corresponding ester 11 in a range of 75–88% yield.
®
Finally, 11 in anhydrous methanol was stirred for several hours in the presence of Amberlyst-15 , an acidic polystyrene polymer, to
afford tetraol 6 in a range of 83–98% yield.

Scheme 3. Synthesis of various alkanethiol–BGL003 6a–6f.
Scheme 4. Synthesis of octadecane-1-thiol–BGL007 7
Next, instead of BGL trimer 10, condensation of BGL heptamer 12o [14] and 9d was examined (Scheme 4). However, chemical
yield of the corresponding ester was extremely low with almost quantitative recovery of both 12o and 9d. Therefore, more nucleophilic
amine 12n [14] was used instead to afford 13 in 25% yield. We did not optimize this step further, because water-solubility of smaller
BGL derivative 6d was high enough as mentioned later in this paper. Methanolic deprotection of 13 under acidic condition was carried
®
out with Amberlyst-15 to afford octaol 7 in 93% yield.
Property and performance of a water-soluble thiol
Water-solubility of the final product was examined as follows. Water after distillation and deionization (50.09 g) and 6d (0.320 g, 0.526 mmol)
and was mixed. Although small drops of 6d were visibly observed in the initial mixture, homogeneous solution was afforded after stirring for
6
6
h at 60˚C. After the solution was cooled to room temperature, homogeneity of the solution was maintained. Accordingly, water-solubility of
d was recorded to be over 10.0 mmol/L with a large margin. H NMR analysis indicated that pure 6d was observed after the aqueous solution
1
was stocked for three months at room temperature in a simple screw-capped plastic bottle.
For usual anticorrosive treatment in an organic solvent, less than 5.00 mmol/L of thiol has been usually reported [3,4]. Therefore, the prepared
solution (10.0 mmol/L) was diluted with water again. By using the diluted aqueous solution of 6d, various examinations such as observation by
digital microscope, reflection of visible light (380–780 nm), measurement of the contact angle of small water-droplet, and resistance against
hydrogen sulfide gas was carried out. Among these comparisons, the results with aqueous potassium sulfide solution (K
representatively [18] described (Fig 3).
2
Saq) were

4
Tetrahedron Letters
Xn
X1
X6d
Reference
No thiol coating)
After coating
by 1 in ethanol
After coating
by 6d in water
(
2
K Saq
2
K Saq
2
K Saq
Yn
Y1
Y6d
2
Figure 3. Color change of silver plates after aqueous K S (0.6 wt%) soaking
Three pieces of silver-plating metal (30 mm length) were prepared from commercially available long strings (20 mm width, 0.2 mm thickness).
The three pieces were washed with deionized water, and dried at 100–120˚C for 5 sec to afford Xn, X1 and X6d. The pieces X1 and X6d were
dipped into 1 in ethanol (0.1 wt% = 3.50 mmol/L) [19] and 6d in water (0.2 wt% = 3.30 mmol/L) at 55˚C for 30 sec, respectively, and washed
with deionized water, and dried at 100–120˚C. No pre-treatment was carried out for Xn. After being cooled to room temperature, all the three
pieces Xn, X1 and X6d were soaked with K Saq (0.6 wt%) at 22˚C for 1 min. Then, these surfaces were washed with deionized water at 22˚C
2
and dried at 100–120˚C for 5 sec to afford Yn, Y1 and Y6d, respectively.
The color of Yn was dark yellow, which indicated the direct effect from K
2
Saq. In contrast, color change from X1 to Y1, as well as from X6d
to Y6d, was highly suppressed. It is noteworthy that mottled pattern was partially observed in Y1 [20] but smooth surface was observed in all
the area of Y6d.
Conclusion and perspective
In conclusion, synthesis of organothiol–BGL003 was successfully carried out within a few steps in high chemical yields. A thioester of
each synthetic intermediate was stable during the following chemical reactions (carbodiimide condensation and methanolic solvolysis
under acidic condition). In contrast, the thioester in the organothiol–BGL003 was probably cleaved to release original organothiol in
situ at the metal surface. Accordingly, predictable result after coating with organothiol–BGL003 in water is as exactly same as with
organothiol in organic solvent, due to the molecular design of organothiol–BGL003.
In fact, anticorrosive performance of organothiol–BGL003 in water was as high as, or slightly higher than, that of organothiol in
organic solvent. We believe that the result reported in this paper will solve one of the environmental problems. To deploy this result for
the practical use, the synthetic process in a large scale is under optimization.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to
influence the work reported in this paper.
Acknowledgments
HN acknowledges the major financial support from Chemical Denshi Co. Ltd., as well as official support from Tokushima University.
MIA acknowledges the financial support from Chemical Denshi Co. Ltd for his doctor course study in Tokushima University.
References and notes
1
2
3
4
.
.
.
.
Nuzzo, R. G.; Allara, D. L. J. Am. Chem. Soc. 1983, 105, 4481–4483.
Guo, Q.; Li F. Phys. Chem. Chem. Phys. 2014, 16, 19074-19090.
Ulman, A. "Ultrathin Organic Films from Langmuir-Brodgett to Self-Assembly" Academic Press, San Diego, 1991, p. 237.
In this case, 40g/L of cetyltrimethylammonium bromide was used as a surfactant. Liang, C.; Yang, C.; Huang, N. Surface & Coating
Technology 2009, 203, 1034–1044
5
6
.
.
Brockman, J. M.; Frutos, A. G.; Corn, R. M. J. Am. Chem. Soc. 1999, 121, 8044–8051.
Williams, B. A. R.; Diehnelt, C. W.; Belcher, P.; Greving, M.; Woodbusy, W. W.; Johnston, S. A.; Chaput, J. C. J. Am. Chem. Soc. 2009, 131,
1
7233–17241.
7
8
.
.
Solanki, P. R.; Arya, S. K.; Nishimura, Y.; Iwamoto, M.; Malhotra, B. D. Langmuir 2007, 23, 7398–7403.
Nemoto, H.; Araki, T.; Kamiya, M.; Kawamura, T.; Hino, T. Eur. J. Org. Chem. 2007, 2007, 3003–3011. This paper reported that a lipophilic
compound (molecular weight is ca. 248) was modified with BGL003 to afford >1,000,000 times more water-soluble analogue than original
molecule. Accordingly, it was highly expected that 1 (molecular weight is ca. 286) was converted to highly water-soluble analogue 6d.
Oxidative addition of thioesters with low-valent metal complex was reported. Pan, F.; Shi, Z.-J.; ACS Catal. 2014, 4, 280–288.
9
1
.
0. It is authorized that succinic acid is a food additive as a supplement by FDA.

1
1
1. Miyamoto, L.; Watanabe, M.; Tomida, Y.; Kono, M.; Fujii, S.; Matsushita, T.; Hattori, H.; Ishizawa, K.; Nemoto, H.; Tsuchiya, K. J. Toxicol.
Sci. 2012, 37, 1253–1259.
2. Miyamoto, L.; Watanabe, M.; Tomida, Y.; Kono, M.; Matsushita, T.; Hattori, H.; Ishizawa, K.; Nemoto, H.; Tsuchiya, K. J. Toxicol. Sci. 2012,
3
7, 1059–1063.
1
1
3. The first report of BGL project. Nemoto, H.; Wilson, J. G.; Nakamura, H.; Yamamoto, Y. J. Org. Chem. 1992, 57, 435–435.
4. Preparation of BGL with acetonides (10, 12o and 12n). Nemoto, H.; Kamiya, M.; Nakamoto, A.; Katagiri, A.; Yoshitomi, K.; Kawamura, T.;
Hattori, H. Chem. Lett. 2010, 39, 856–857.
1
1
1
1
5. Nemoto, H.; Katagiri, A.; Kamiya, M.; Kawamura, T.; Matsushita, T.; Matsumura, K.; Itou, T.; Hattori, H.; Tamaki, M.; Ishizawa, K.;
Miyamoto, L.; Abe, S.; Tsuchiya, K. Bioorg. Med. Chem. 2012, 20, 5559–5567.
6. Nemoto, H.; Kamiya, M.; Nakamoto, A.; Matsushita, T.; Matsumura, K.; Hattori, H.; Kawamura, T.; Taoka, C.; Abe, S.; Ishizawa, K.;
Miyamoto, L.; Tsuchiya, K. Bioorg. Med. Chem. Lett. 2012, 22, 6425–6428.
7. Nemoto, H.; Katagiri, A.; Kamiya, M.; Matsushita, T.; Hattori, H.; Matsumura, K.; Itou, T.; Kawamura, T.; Kita, T.; Nishida, H.; Arakaki, N.
Bioorg. Med. Chem. Lett. 2012, 22, 5051–5054.
8. Water (10 mL) and 6d (1 mg) were mixed, and the resulting milky liquid was heated for 5h at 60˚C to convert to homogeneous solution. After
1
evaporation of the solvent, H NMR analysis of the residue indicated no hydrolysis.
1
2
9. Detail of other examinations are planning to be submitted to the more suitable journals such as Surface & Coating Technology.
0. At early period, lipophilic thiol was used as a solution of halogenated hydrocarbons such as 1,2-dichloroethane [3], which is negative impact on
the environment. After the use of such a solvent was strictly prohibited under the law in various countries, ethanol has been used instead.
1. When the experiment reported in Figure 3 was carried out, the solution of 1 in ethanol was slightly cloudy. The solubility of 1 in ethanol was not
as high as expected. Due to the inhomogeneity, the mottled pattern may be generated on the surface of Y1.
2
Supplementary Material
Supplementary material can be found online at https://doi.org/10.1016/j.tetlet.XXXX.XXXX.
Click here to remove instruction text...
Environmentally friendly anticorrosive
Symmetrically branched oligoglycerols
thioester
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to
influence the work reported in this paper.
Graphical Abstract
Leave this area blank for abstract info.
An Environmentally Friendly Lipophilic Coating of Metal Surface
Md. Idrish Ali, Hoque Md. Mahbubul, Tsuyoshi Matsushita, Md. Mayez Mahmud, Yuhki Seno, Yusuke
Shibuya, Shoichi Yamada, Toshio Hyuga, Hisao Nemoto

4
Tetrahedron