Improved synthesis and low-temperature performance of a series of saturated α-branched fatty acids

Article abstract of DOI:10.1007/s11696-017-0230-8

Five saturated α-branched fatty acids, also known as Guerbet acids, including α-propylhexyl acid (G ₁ ), α-butylhexyl acid (G ₂ ), α-propyloctyl acid (G ₃ ), α-butyloctyl acid (G ₄ ), and α-hexyloctyl acid (G ₅ ), were synthesized in high yields by four-step reaction. Colorless, almost odorless, and oily products were obtained with high purity, whose structures were confirmed by GC, ¹H/¹³C NMR, and ESI-MS characterization. G ₁, G ₃, and G ₄ had pour points lower than -60 °C, while G ₂ and G ₅ showed higher pour points (-42 °C and 6 °C, respectively) because of their molecular symmetry. Considering the low-temperature properties, G ₁, G ₃, G ₄, and even G ₂ held great potential applications in the lubricant and oilfield.

Full text of DOI:10.1007/s11696-017-0230-8

Chem. Pap.
DOI 10.1007/s11696-017-0230-8
ORIGINAL PAPER
Improved synthesis and low-temperature performance of a series
of saturated a-branched fatty acids
1
1
1
1
Yang Jiang
•
Wenjing Hu
•
Jian Xu
•
Jiusheng Li
Received: 11 January 2017 / Accepted: 17 June 2017
Ó Institute of Chemistry, Slovak Academy of Sciences 2017
Abstract Five saturated a-branched fatty acids, also
known as Guerbet acids, including a-propylhexyl acid
behavior at low temperature, saturated a-branched fatty
acids (SBFAs) have much broader applications than their
linear homologues in the lubricant industry (Haßelberg and
Behr 2016). Saturated linear fatty acids with more than ten
carbons are typically solid at room temperature, usually not
suitable to be used as lubricants due to their non-operability
and formula incompatibility at low temperature.
(
G ), a-butylhexyl acid (G ), a-propyloctyl acid (G ), a-
1 2 3
butyloctyl acid (G ), and a-hexyloctyl acid (G ), were
4
5
synthesized in high yields by four-step reaction. Colorless,
almost odorless, and oily products were obtained with high
1 13
purity, whose structures were confirmed by GC, H/ C
NMR, and ESI–MS characterization. G , G , and G had
1
Unsaturated long-chain acids, such as oleic acid,
although possessing lower melting point, are often thermo-
oxidatively unstable due to their unsaturated carbon–car-
bon bonds. Tremendous work has thus been carried out to
seek oxidatively stable ‘‘oily’’ acids, i.e., saturated bran-
ched fatty acids. Currently, these acids have been obtained
by a few industrial processes including the synthesis from
petro- and oleo-chemical feedstock. By employing Guerbet
reaction, Guerbet alcohols were produced branched in a-
position with two approximately equal-length side chains,
which were then oxidized to branched fatty acids (Guerbet
acids). Alkenes or alcohols can also be transformed to
branched fatty acids through oxo synthesis (Neweck and
Grafahrend 2012; Kent 2012) or Koch synthesis (Kinsman
et al. 1989; Keenan et al. 2007). Methyl-branched chain
fatty acids (isostearic acid) were obtained as by-products in
the clay-catalyzed dimerization process of unsaturated acid
from tall oil (fatty acid isomerization) (Denotter 1970a, b).
Ngo’s group (2007, 2011, 2012, 2013) has recently opti-
mized the reaction selectivity for isostearic acid. The a-
branched fatty acids could be prepared by alkylation of
dimethyl malonate and the appropriate alkyl bromides
using strong base NaH, and the yield of the decarboxyla-
tion in the literature was 46–78% (Erdmann et al. 2015).
Another method was by synthesis from aromatic azides,
which were particularly prone to explosion. The yield of
the final product was around 50% (Cassani et al. 2004).
3
4
pour points lower than -60 °C, while G and G showed
2
5
higher pour points (-42 °C and 6 °C, respectively)
because of their molecular symmetry. Considering the low-
temperature properties, G , G , G , and even G held great
1
3
4
2
potential applications in the lubricant and oilfield.
Keywords Saturated a-branched fatty acids Á Guerbet
acids Á Low-temperature performance Á Pour point
Introduction
Low-temperature property is an important parameter to
measure the performance of lubricant. The ideal lubricant
should have a continuous, stable viscosity. Specifically
speaking, the viscosity of lubricant should be big enough at
high temperature to maintain the integrity of the lubricant
film, aiming to prevent contact friction. On the other hand,
the low-temperature fluidity needs to be excellent to ensure
that the lubricant can quickly attach to the lubricating parts
and reduce the mechanical wear. Due to their outstanding
&
Jiusheng Li
lijs@sari.ac.cn
1
Laboratory of Advanced Lubricating Materials, Shanghai
Advanced Research Institute, CAS, Shanghai, China
123

Chem. Pap.
The existing branched fatty acid products, derived from
either petro- or oleo-chemical industry, are mixtures of
different acids/esters/alcohols with unsatisfactory SBFA
content. Some linear acids are also formed in such petro- or
oleo-chemical processes and cannot be removed com-
pletely from the final products. The accompanying linear
acids, to a large extent, influence their performance and
application in lubricant field.
Chemicals
General procedure
Alkylation (two steps) To a solution of dimethyl malonate
(1, 100 g, 0.758 mol) in DMF (500 mL), sodium methano-
late (45.0 g, 0.833 mol) was added slowly under a N
atmosphere. The reaction mixture was kept at room tem-
perature for 30 min. Alkyl bromide (R Br, 0.758 mol, R
2
The preparation of a-branched fatty acids from
malonic acids, previously described by Browning et al.
1
1
represents the first substituent group) was added dropwise,
and the reaction mixture was heated to 100 °C and kept for
1 h. Cooled to room temperature, another portion of sodium
methanolate (45 g, 0.833 mol) was added slowly to the
mixture and stirred for 30 min. To it was added alkyl bro-
(
1930), was a classical method. In the literature, various
allyl alkyl acetic acids were prepared and tested for
bactericidal action to B. Leprae. In this paper, we
improved this synthesis process; both yield and purity of
the products were greatly raised. We hope that through
this research we can develop the industrial applications.
Two alkyl groups, either same or different, were intro-
duced to the a-carbon of malonic ester. The length of the
backbone and the side chain of these SBFAs can thus be
controlled by careful selection of alkyl chains. Five
SBFAs, a-propylhexyl acid (G ), a-butylhexyl acid (G ),
mide (R Br, 0.833 mol, R represents the second substituent
2 2
group) dropwise. The reaction mixture was heated to 100 °C
and kept for 1 h. After salt was filtered, solvent and the
unreacted alkyl bromide were removed under reduced pres-
sure. The filtrate was crude product of dialkyl dimethyl-
malonate 2, which was used directly in the next step.
1
2
a-propyloctyl acid (G ), a-butyloctyl acid (G ), and a-
hexyloctyl acid (G ), were synthesized in high yields by
5
Hydrolysis To crude product 2, were added an aqueous
solution of sodium hydroxide (4 mol/L, 121 g, 3.032 mol)
and 100 mL of ethanol. The mixture was heated and
refluxed overnight. The reaction was cooled to room tem-
perature and neutralized and acidified to pH 1.8–1.9 by
sulfuric acid (4 mol/L). The mixture was transferred to a
wide-mouth beaker and stayed for a few hours. The organic
layer was turned to solid on the top of the aqueous layer.
The crude product (dialkylmalonic acid) was dried and
recrystallized with petroleum ether to yield a white solid.
Five malonic acids, propylbutylmalonic acid (3a),
dibutylmalonic acid (3b), propylhexylmalonic acid (3c),
butylhexylmalonic acid (3d), and dihexylmalonic acid (3e),
were synthesized, as shown in Scheme 1.
3
4
four-step reaction sequences, and their low-temperature
behavior was presented. Some physical properties,
including pour points, acid values, and kinematic vis-
cosities, were also characterized.
Experimental
Materials and instruments
Dimethyl malonate (99%), 1-bromopropane (98%),
1
-bromobutane (99%), 1-bromohexane (99%), sodium
methanolate (AR), N,N-dimethylformamide (99%), sul-
furic acid (95–98%), and sodium hydroxide (99%) were
obtained from Tansoole, an internet shopping platform of
chemicals and materials. All of the chemicals were used
without further purification. GC analysis of five SBFA
products was carried out on Agilent 7890B equipped
with an FID detector. A HP DB-1HT capillary column
Decarboxylation The
malonic acids were heated to 150–160 °C under N
atmosphere, and CO was released. The reaction was fin-
above-obtained
disubstituted
2
2
ished until no bubbling formed. The final products were
clear, colorless, and odorless oils, and no further post-
treatment was needed.
1
3a. A white solid (three steps, 67%). H NMR
(500 MHz, DMSO, ppm): d = 12.53 (COOH, s, 2H),
(
30 m 9 250 lm 9 0.1 lm) was used, and H was used
2
as carrier gas with an average linear velocity of 55.7 cm/
s. The oven temperature raising profile was: initial
temperature 50 °C, hold 2 min; ramp 15 °C/min to
1.73–1.67 (CH
2
, m, 4H), 1.30–1.23 (CH
, m, 2H),
2
1
3
1.16–1.05 (CH
, m, 4H), 0.88–0.84 (CH , m, 6H).
3
C
2
NMR (125 MHz, DMSO, ppm): d = 173.6, 57.0, 34.4,
31.9, 26.3, 23.0, 17.5, 14.8, 14.3. MS (ESI): m/z (%) calcd
1
13
3
50 °C, hold 10 min. H and C NMR spectra were
?
?
recorded at 25 °C on a Bruker Avance 500 spectrometer
in CDCl3 or DMSO-d6 with TMS as reference. Mass
spectra were obtained on Bruker Esquire 6000 (ESI), and
the scan was set from 120 to 1200 m/z.
for C10H O : 203.2 [M ? H] , 225.2 [M ? Na] .
18 4
1
3b. A white solid (three steps, 72%). H NMR
(500 MHz, DMSO, ppm): d = 12.6 (COOH, s, 2H), 1.71
(CH , dd, J = 10.0 Hz, J = 5.0 Hz, 4H), 1.31-1.24
2 1 2
1
23

Chem. Pap.
Scheme 1 Synthetic route of
the five saturated branched fatty
acids
(
CH , m, 4H), 1.11–1.05 (CH , m, 4H), 0.86 (CH , t,
2
ppm): d = 183.5, 45.4, 34.3, 31.9, 29.5, 22.6, 20.6, 13.9,
13.8. MS (ESI): m/z (%) calcd for C H O : 159.1
2
3
1
J = 5.0 Hz, 6H). C NMR (125 MHz, DMSO, ppm):
3
9
18
2
?
[M ? H] , 181.1 [M ? Na] .
?
d = 173.6, 56.9, 31.8, 26.3, 23.0, 14.3. MS (ESI): m/z (%)
calcd for C H O : 217.3 [M ? H] , 239.1 [M ? Na] .
?
?
1
G . A clear, colorless, and odorless oil (95%). H NMR
1
1
20
4
2
1
c. A white solid (three steps, 68%). H NMR
3
(500 MHz, CDCl , ppm): d = 11.7 (COOH, s, 1H),
3
(
500 MHz, DMSO, ppm): d = 12.6 (COOH, s, 2H),
2.39–2.33 (CH, m, 1H), 1.66–1.64 (CH , m, 2H), 1.51–1.50
2
1
1
.73–1.67 (CH , m, 4H), 1.28–1.24 (CH , m, 6H),
2
(CH , m, 2H), 1.33 (CH , m, 8H), 0.90 (CH , t,
3
2
2
2
1
3
13
J = 5.0 Hz, 6H). C NMR (125 MHz, CDCl , ppm):
.16–1.10 (CH , m, 4H), 0.88–0.84 (CH , m, 6H).
2
C
3
3
NMR (125 MHz, DMSO, ppm): d = 173.6, 57.0, 34.4,
2.1, 31.5, 29.5, 24.0, 22.5, 17.5, 14.8, 14.3. MS (ESI): m/z
d = 183.4, 45.6, 31.9, 29.5, 22.6, 13. 9. MS (ESI): m/z (%)
calcd for C H O : 173.2 [M ? H] .
?
3
1
0 20 2
?
%) calcd for C H O : 231.0 [M ? H] , 253.1
1
G . A clear, colorless, and odorless oil (98%). H NMR
(
[
1
2
22
4
3
?
M ? Na] .
d. A white solid (three steps, 71%). H NMR
500 MHz, DMSO, ppm): d = 12.6 (COOH, s, 2H),
(500 MHz, CDCl , ppm): d = 11.85 (COOH, s, 1H),
3
1
3
2.40–2.34 (CH, m, 1H), 1.67–1.60 (CH , m, 2H), 1.50–1.42
2
(
(CH , m, 2H), 1.41–1.29 (CH , m, 10H), 0.94–0.88 (CH ,
2
2
3
1
3
1
1
.73–1.70 (CH , m, 4H), 1.30–1.24 (CH , m, 8H),
2
m, 6H). C NMR (125 MHz, CDCl , ppm): d = 183.5,
2
3
1
3
.11–1.05 (CH , m, 4H), 0.87–0.84 (CH , m, 6H).
3
C
45.4, 34.4, 32.2, 31.7, 29.2, 27.3, 22.6, 20.6, 14.0, 13.9. MS
?
(ESI): m/z (%) calcd for C H O : 187.2 [M ? H] , 209.2
2
NMR (125 MHz, DMSO, ppm): d = 173.7, 57.0, 32.1,
1.9, 31.5, 29.5, 26.3, 24.0, 23.0, 22.5, 14.3, 14.2. MS
1
1 22 2
?
[M ? Na] .
3
?
ESI): m/z (%) calcd for C H O : 245.2 [M ? H] , 267.1
1
G . A clear, colorless, and odorless oil (96%). H NMR
(
[
1
3
24
4
4
?
M ? Na] .
e. A white solid (three steps, 73%). H NMR
500 MHz, DMSO, ppm): d = 11.3 (COOH, s, 2H),
.97–1.93 (CH , m, 4H), 1.30 (CH , m, 16H), 1.11–1.08
(500 MHz, CDCl , ppm): d = 11.61 (COOH, s, 1H),
3
1
3
2.39–2.33 (CH, m, 1H), 1.68–1.61 (CH , m, 2H), 1.52–1.48
2
(
(CH , m, 2H), 1.33–1.30 (CH , m, 12H), 0.93–0.88 (CH ,
2
2
3
1
3
1
m, 6H). C NMR (125 MHz, CDCl , ppm): d = 183.3,
2
2
3
1
3
(
CH , m, 4H), 0.90 (CH , t, J = 5.0 Hz, 6H). C NMR
3
45.6, 32.2, 31.9, 31.7, 29.6, 29.2, 27.3, 22.6, 22.6, 14.0,
2
(
125 MHz, DMSO, ppm): d = 178.0, 58.0, 34.4, 31.4,
9.4, 24.5, 22.6, 14.0. MS (ESI): m/z (%) calcd for
13.9. MS (ESI): m/z (%) calcd for C H O : 201.0
1
2
24
2
?
[M ? H] .
2
?
C H O : 273.2 [M ? H] , 295.1 [M ? Na] .
?
1
G . A clear, colorless, and odorless oil (94%). H NMR
1
5
28
4
5
1
G . A clear, colorless, and odorless oil (96%).
1
H
(500 MHz, CDCl , ppm): d = 11.20 (COOH, s, 1H),
3
NMR (500 MHz, CDCl , ppm): d = 11.62 (COOH, s,
2.39–2.33 (CH, m, 1H), 1.65–1.64 (CH , m, 2H), 1.51
2
3
1
1
0
H), 2.41–2.35 (CH, m, 1H), 1.65–1.62 (CH , m, 2H),
2
(CH , m, 2H), 1.32–1.30 (CH , m, 16H), 0.91–0.89 (CH , t,
2
2
3
1
3
J = 5.0 Hz, 6H). C NMR (125 MHz, CDCl , ppm):
.51–1.47 (CH , m, 2H), 1.40–1.32 (CH , m, 6H),
2
2
3
1
.95–0.90 (CH , m, 6H). C NMR (125 MHz, CDCl3,
3
d = 183.4, 45.7, 32.2, 31.7, 29.2, 27.3, 22.6, 14.0. MS
3
123

Chem. Pap.
Purity
?
ESI): m/z (%) calcd for C H O : 229.2 [M ? H] , 251.3
(
Table 1 GC data of SBFAs
1
4 28 2
?
M ? Na] .
[
Entry
SBFA
Retention time (min)
1
2
3
4
5
G
G
G
G
G
1
2
3
4
5
9.9
10.7
11.8
12.5
14.5
99.6%
99.3%
95.6%
99.7%
98.7%
Results and discussion
Synthesis and structure confirmation
Scheme 1 shows the synthetic route of five saturated
branched fatty acids from dimethyl malonate 1. Using
sodium methanolate as the strong base, either the same or
different alkyl groups were introduced to the a-carbon of
the malonate 1. Then, the generated five disubstituted
malonates 2 were hydrolyzed to the corresponding malonic
acids, 3a, 3b, 3c, 3d, and 3e, respectively. The malonic
acids were finally transformed to the designed SBFAs via a
decarboxylation reaction at ca 150–160 °C.
The structures of the five malonic acids and the five
1
13
SBFAs were confirmed by GC, H/ C NMR, and ESI–MS
characterization. As listed in Table 1, the purities of the
SBFAs were very high. As the molecular weights of the
SBFAs increase, from G to G , the retention time turned
1
5
regularly longer.
1
13
The H and C NMR spectra of the five SBFAs are
shown in Figs. 1 and 2.
1
Fig. 1 H NMR spectra of SBFAs in CDCl
3
ESI–MS analysis further supported the formation of the
ten products. All of the ten acids exhibited a peak of
?
M ? H] , and eight of the ten compounds gave a peak of
[
[
?
M ? Na] . Two exceptional samples, G and G , had
2
4
been distilled under reduced pressure, and trace of sodium
salts (introduced from the hydrolysis reaction) had been
removed before MS characterization. To verify it, we dis-
tilled another sample, G for ESI–MS analysis, and the
3
?
M ? Na] peak disappeared, indicating that sodium salt
[
could be removed by distillation.
Physical properties of SBFAs
The acid values, kinematic viscosities, and pour points of
SBFAs are listed in Table 2. As the molecular weights
increased, from G1 to G , their acid values decreased
5
regularly. This is because the acids with lower molecular
weight have higher acidic contents and thus larger acid
values. However, their kinematic viscosities (40 or 100 °C)
increased with the incremental molecular weights of
SBFAs.
13
Fig. 2 C NMR spectra of SBFAs in CDCl
3
molecular structure resulted in the tendency to crystallize
and hence a higher pour point. This phenomenon happened
for G possessing extended side chains. To a large extent, G
5
However, the performance of their pour points did not
follow the order of their acid values and viscosity properties.
It was hard to find the change pattern between the pour points
and the molecular weights. G , G and G had pour points
5
intensified the trend to precipitate as crystals and yielded a
much higher pour point of 6 °C.
In general, G , G , G and even G had very good per-
2
1
3
4
1
3
4
formance at low temperature, whose pour points were much
lower than those commercially available saturated branched
TM
lower than -60 °C, which was our measure limit. G , with a
2
molecular weight between G and G , had relatively higher
pour points, because of its molecular symmetry. Symmetric
1
3
fatty acids, for instance Versatic Acid Neo 10 (Hexion)
1
23

Chem. Pap.
Table 2 Physical properties of saturated branched fatty acids
Entry
SBFA
Molecule weight
Pour point (°C)
Acid value
Kinematic viscosity
2
at 40 °C (mm /s)
Kinematic viscosity
2
at100 °C (mm /s)
1
2
3
4
5
G
G
G
G
G
1
2
3
4
5
181.1
173.2
209.2
201.0
251.3
\-60
-42
360
325
304
275
249
6.55
9.03
10.5
13.2
18.2
1.73
2.11
2.44
2.82
3.63
\-60
\-60
6
(
pour point of\-30 °C) (Hexion 2015) and isostearic acid
prepared by Ngo’s group (pour point of 0 °C) (Ngo et al.
007). Another important application of saturated branched
Denotter MJ (1970a) The dimerization of oleic acid with a
montmorillonite catalyst I: important process parameters; some
main reactions. Fette Seifen Anstrichmittel 72:667–673. doi:10.
2
1
002/lipi.19700720809
fatty acids was used as water-based additives to resist hard
water and antifoam in metalworking fluids. Comparing with
the commercially available additives, such as octanoic acid,
isocaprylic acid, and oleic acid, the reported acids possess
the advantage of colorlessness and odorlessness, meaning
that they can be used in higher demanding occasions.
Denotter MJ (1970b) The dimerization of oleic acid with a
montmorillonite catalyst II: GLC analysis of the monomer; the
structure of the dimer; a reaction model. Fette Seifen Anstrich-
mittel 72:875–883. doi:10.1002/lipi.19700721010
Erdmann N, W o¨ lk C, Schulze I, Janich C, Folz M, Drescher S,
Dittrich M, Meister A, Vogel J, Groth T, Dobner B, Langner A
(2015) Tris(2-aminoethyl)amine-based a-branched fatty acid
amides—synthesis of lipids and comparative study of transfec-
tion efficiency of their lipid formulations. Eur J Pharm Biopharm
9
6:349–362. doi:10.1016/j.ejpb.2015.08.011
Conclusions
Haßelberg J, Behr A (2016) Saturated branched fatty compounds:
proven industrial processes and new alternatives. Eur J Lipid Sci
Technol 118:36–46. doi:10.1002/ejlt.201500461
A series of new saturated branched fatty acids have been
designed and synthesized, which have good performance at
low temperature. Four-step reaction sequences were
employed, and five SBFAs were obtained in high yields.
TM
Hexion (2015) Technical Data Sheet: Versatic
Acid 10. http://
www.hexion.com/products/technicaldatasheet.aspx?id=6018
Kent JA (2012) Handbook of industrial chemistry and biotechnology,
vol 1. Springer, New York, pp 353–355
Kinsman DV, Johnson RW, Fritz E (eds) (1989) Fatty acids in
industry. Marcel Dekker, New York, pp 233–276
Keenan MJ, Krevalis MA, Kirk R, Othmer D (eds) (2007) Encyclo-
pedia of industrial chemistry, vol. 5, Willy-VCH, New York,
pp 27–77
1
13
Their structures are confirmed by GC, H/ C NMR, and
ESI–MS characterization. The colorless, almost odorless,
and oily SBFAs products are pure enough for corre-
sponding experimental tests. G , G , and G have pour
1
3
4
Neweck K, Grafahrend W (2012), ullmanns encyclopedia of indus-
trial chemistry, vol 1, no 4. Willy-VCH, Weinheim, pp 117–141.
doi:10.1002/14356007
points lower than -60 °C, while geometrically symmetric
G2 and G5 have higher pour points (-42 and 6 °C,
respectively). Considering the low-temperature properties,
the benefit of these new molecules is specifically in pro-
viding an extension to the use of ester-based lubricants into
regions of extreme low temperature.
Ngo HL, Nu n´ ez A, Lin W, Foglia TA (2007) Zeolite-catalyzed
isomerization of oleic acid to branched-chained isomers. Eur J
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Ngo HL, Yee WC, McAloon AJ, Haas MJ (2012) Process and cost
modeling of saturated branched-chained fatty acid isomer
production. Ind Eng Chem Res 51:12041–12045. doi:10.1021/
ie300451x
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