JP3107654B2 - Magnetic fluid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic fluid. More specifically, the present invention relates to a magnetic fluid comprising magnetic fine particles treated with a specific surfactant and a dispersion medium.

[0002]

2. Description of the Related Art Very fine magnetic fine particles having a particle size of about 10 nm are mainly used in magnetic fluids used for shaft seals of rotating machines. Even in the case of a bulk material, even if it is a stable oxide or metal, its surface state becomes more active as the particle size becomes finer, and it becomes susceptible to oxidation in air. On the other hand, in the case of magnetic fluid, the surface activity of a compound having a bent molecular skeleton represented by oleic acid and linoleic acid, or a compound having many functional groups and side chains in one molecule on the surface of fine magnetic fine particles It is known that the active surface is covered with a surfactant monomolecular film by adsorbing or reacting with the agent to stabilize the particles to some extent, thereby improving the dispersibility of the magnetic fine particles in the dispersion medium.

However, even now, the greatest problem in producing a stable magnetic fluid is deterioration due to oxidation. For example, when the dispersion medium is once removed from the magnetic fluid for purifying the magnetic fine particles, and then the magnetic fine particles are mixed again with the same dispersion medium, a phenomenon that the dispersibility of the magnetic fine particles is often reduced is often observed. This is considered to be due to an increase in the chances that the magnetic particles come into contact with air, resulting in oxidation and a decrease in dispersibility.

[0004]

As measures for preventing oxidation during production, 1) a production method which does not require a drying step by using a low boiling solvent, and 2) a surfactant which is much larger than the amount of monomolecular film formed. And 3) the use of antioxidants. However, regarding 1), the oxidation of the magnetic fine particles during evaporation of the low-boiling-point solvent, and 2) and 3), there is a problem that the magnetic fluid system becomes complicated due to excessive surfactant or antioxidant. Therefore, a method for obtaining a magnetic fluid that is stable against oxidation without using the above measures has been desired.

[0005]

Means for Solving the Problems The inventors of the present application have conducted studies to develop a magnetic fluid that is stable against oxidation, and as a result,
The present inventors have found that an intended magnetic fluid can be obtained by using a specific surfactant, and have completed the present invention. That is, the present invention

[0006]

Embedded image R—X— (CH ₂ CHR′O) _n — (CH ₂ ) _m —COOH (where R is an alkyl group having 1 to 18 carbon atoms, and X is —O
-, -COO-, -OCO-, -CONH-, or-
NHCO-, R 'represents a hydrogen atom or a methyl group, n represents an integer of 0 to 30 and m represents an integer of 8 to 12), a magnetic fine particle, and a dispersion medium. The present invention relates to a magnetic fluid characterized by comprising:

Specific examples of the surfactant represented by the above general formula used in the present invention include CH ₃ O (C
H ₂ ) ₈ COOH, CH ₃ O (CH ₂ ) ₁₂ COOH, C ₆ H
₁₃ O (CH ₂ ) ₁₀ COOH, CH ₃ OC ₂ H ₄ O (CH ₂ )
₁₀ COOH, C ₄ H ₉ OC ₂ H ₄ O (CH ₂ ) ₁₂ COOH,
_{H (C 2 H 4 O)} 3 (CH 2) 10 COOH, C 4 H 9 O (C 2
H ₄ O) ₂ (CH ₂ ) ₁₀ COOH, CH ₃ O (C ₂ H ₄ O) ₃
(CH ₂ ) ₁₀ COOH, CH ₃ O (C ₂ H ₄ O) ₃ (CH ₂ )
_{8 COOH, C 12 H 25 0} (C 2 H 4 O) 25 (CH 2) 10 CO
OH, CH ₃ O (CH ₂ CHCH ₃ O) ₂ (CH ₂ ) ₁₀ CO
OH, CH ₃ COO (CH ₂ ) ₁₂ COOH, CH ₃ COO
C ₂ H ₄ O (CH ₂ ) ₁₀ COOH, C ₃ H ₇ COO (C ₂ H ₄
O) ₃ (CH ₂ ) ₁₀ COOH, CH ₃ OCO (CH ₂ ) ₁₀ C
OOH, C ₆ H ₁₃ OCO (CH ₂ ) ₁₀ COOH, CH ₃ O
CO (C ₂ H ₄₀ ) ₃ (CH ₂ ) ₁₀ COOH, CH ₃ CON
H (CH ₂ ) ₁₁ COOH, C ₄ H ₉ CONH (CH ₂ ) ₁₁ C
OOH, C ₂ H ₅ CONHC ₂ H ₄ O (CH ₂ ) ₁₀ COO
H, C ₄ H ₉ NHCO (CH ₂ ) ₁₀ COOH, C ₂ H ₄ NH
CO (C ₂ H ₄ O) ₂ (CH ₂ ) ₁₂ COOH and the like.

When the number of methylene chains (m) in the surfactant represented by the above general formula is less than 8, a magnetic fluid stable against oxidation cannot be obtained. When m is larger than 12, it is difficult to obtain raw materials.

The method for producing the above surfactant is not limited at all, but a typical method will be described below. Surfactant X is _{-O- R-O- (CH 2 CHR'O} ) n- (CH 2) m
First, the method for synthesizing -COOH will be described.

[0010] Br- (CH ₂₎ adding _{p-CH 3 C 6 H 4} SO 3 H · H 2 O is heated to reflux in a toluene solvent as a catalyst to m-COOH and methanol. To give the product a is _{Br- (CH 2) m-COOCH} 3 by vacuum distillation. R-
O- and (CH ₂ CHR'O) n-H with sodium metal and potassium iodide is heated to reflux in a toluene solvent.
Previously obtained Br- a (CH ₂₎ m-COOCH ₃ dropwise and refluxed to the reaction solution. After distilling off toluene from the reaction solution under reduced pressure,
A new NaOH aqueous solution is added and the mixture is heated to reflux. After cooling,
A hydrochloric acid solution is added to the reaction solution until the pH becomes 1. Further NaCl is added to the reaction until it is saturated. The reaction solution is extracted with a solvent, and the obtained organic phase is washed with saturated saline. The solvent and raw material for _{R-O- (CH 2 CHR'O)} n-H
Is removed under reduced pressure to obtain a crude product. The crude product is purified by column or recrystallization.

A surfactant R--CO wherein X is --COO--
Then referred for _{O- (CH 2 CHR'O) n- (} CH 2) m-COOH synthesis of.

A hexane solution of t-C ₄ H ₉ (CH ₃ ) ₂ SiCl is dropped into a hexane solution of Br (CH ₂ ) mCOOH and heated. Hexane and unreacted raw materials are distilled off under reduced pressure to obtain Br (CH ₂ ) mCOOSi (CH ₃ ) ₂ -tC ₄
Obtain H _9. R-COO- (CH ₂ CHR'O) the nH with metallic sodium and potassium iodide is heated to reflux in a toluene solvent. T-C ₄ H ₉ that previously obtained (CH _{3) 2} SiC
1 is added dropwise to the reaction solution and refluxed. After toluene was distilled off under reduced pressure from the reaction solution, water was newly added and the mixture was stirred. After stirring, aqueous hydrochloric acid is added to the reaction solution until the pH becomes 1. Further N
Add aCl to the reaction until saturated. The reaction solution is extracted with a solvent, and the obtained organic phase is washed with saturated saline.
Of solvent and raw material _{R-COO- (CH 2 CHR'O)} n-H
Is removed under reduced pressure to obtain a crude product. The crude product is purified by column or recrystallization. X surfactants R-OCO- a -OCO- (CH ₂ CHR'O) n-
A method for synthesizing (CH ₂ ) m-COOH will be described.

HOCO- (CH ₂ CHR'O) n- (C
H ₂ ) p-CH ₃ C ₆ as catalyst on m-COOH and ROH
H ₄ SO ₃ H.H ₂ O is added, and the mixture is heated and refluxed in a toluene solvent. The crude product is obtained by removing the solvent under reduced pressure. The crude product is purified by column or recrystallization.

A surfactant RC wherein X is --CONH--
_{ONH- (CH 2 CHR'O) n- (} CH 2) m-COO
The synthesis method of H is described.

H ₂ N- (CH ₂ CHR'O) n- (C
H ₂ ) R-COO-R is dropped into an acetic acid solution of m-COOH and stirred. R-COO of solvent and raw material from reaction solution
A crude product is obtained by removing -R. The crude product is purified by column or recrystallization. X is -NHCO-
Surfactant R-NHCO- (CH ₂ CHR′O)
A method for synthesizing n- (CH ₂ ) m-COOH will be described.

HOCO- (CH ₂ CHR'O) n- (C
H ₂₎ m-COOH and R-NH ₂ and _{C 6 H 11 N = C =} NC 6
The H ₁₁ is stirred in a solvent. C ₆ H ₁₁ NH which is a by-product
Was filtered off CONHC ₆ H _11, the organic phase is washed with saturated sodium chloride solution. The crude product is obtained by removing the solvent under reduced pressure.
The crude product is purified by column or recrystallization.

The amount of these surfactants is generally in the range of 2 to 50% by weight with respect to the magnetic fine particles.
If the range is less than this range, the dispersibility of the magnetic fine particles becomes insufficient. If the range is larger than this range, improvement of the dispersibility cannot be expected and it is not economical.

As the magnetic fine particles used in the present invention, known magnetic particles can be employed without any limitation. Specifically, Fe, Ni,
Co or alloys thereof, and ferrites such as magnetite, Ba ferrite, Mn ferrite, and Zn ferrite. The particle size of these magnetic fine particles is preferably 500 nm or less, particularly 1 to be uniformly dispersed in the dispersion medium.
It is preferably not more than 00 nm. If it exceeds 500 nm, the magnetic fluid tends to precipitate, which is not desirable. The amount of the magnetic fine particles is generally 2 to 2 with respect to the total amount of the magnetic fluid.
A range of 60% by weight is employed. In a range smaller than this, it does not behave as a magnetic fluid, and in a range larger than this,
Magnetic fine particles are not stably dispersed.

The dispersion medium used in the present invention is not particularly limited as long as the magnetic fine particles are stably dispersed, but has a relative dielectric constant of 1.9.
It is preferable to use a dispersion medium in the range of from 50 to 50 because the magnetic particles are more stably dispersed. It is particularly preferable to use a dispersion medium in the range of 1.9 to 40. When a dispersion medium having a relative dielectric constant exceeding 50 is used, the magnetic fine particles tend not to be stably dispersed. Examples of a low boiling point dispersion medium having a preferable relative dielectric constant include hexane (relative dielectric constant ε = 1.9), toluene (ε = 2.4), diethyl ether (ε = 4.2), and chloroform (ε = 4.2). 4.7), ethyl acetate (ε = 6.
0), tetrahydrofuran (ε = 7.4), dichloromethane (ε = 8.9), dichloroethane (ε = 10.
4), pyridine (ε = 12.3), 4-methyl-1-butanol (ε = 15.2), 1-butanol (ε = 1
7.7), acetone (ε = 20.5), ethanol (ε
= 24.3), methanol (ε = 32.6), acetonitrile (ε = 37.5), glycerin (ε = 42.5)
And the like. Similarly, kerosene (ε = 2.0 to 2.2), decalin (ε = 2.20), alkylnaphthalene, polyalkylene glycol, mineral oil, and the like, which are frequently used as a dispersion medium of the magnetic fluid, can be used. . These dispersion media may be used alone or as a mixture of two or more.

An antioxidant may be added in order to further prevent deterioration of the surfactant or the dispersion medium due to oxidation. Such antioxidants include hydroquinone, hydroquinone monomethyl ether, 2,5-di-t-butyl-4-.
Examples include phenols such as methylphenol, or aromatic amines such as phenyl-α-naphthylamine and tetramethyldiaminodiphenylmethane.
Other examples include sulfur-based antioxidants such as dilauryl thiodipropionate and phosphorus-based antioxidants such as triphenyl phosphite. Ultraviolet absorbers such as 2-hydroxy-4-methylbenzophenone can also be added.

The magnetic fluid of the present invention can be manufactured by a known method. When Fe, Ni, Co or an alloy thereof is used as the magnetic fine particles, a method of thermally decomposing or photodecomposing the carbonyl complex of the metal in the presence of a surfactant may be used.

Fe treated with pyrolytic surfactant
An example of a method for producing fine particles is as follows. Fe
A carbonyl complex of Fe such as ₂ (CO) ₉ or Fe ₃ (CO) ₁₂ , a surfactant, and a dispersion medium are mixed in an atmosphere of an inert gas, and the mixture is heated to a temperature equal to or higher than the decomposition temperature of the complex. Thus, Fe fine particles are obtained. In addition, Fe
When (CO) ₅ is used as a raw material, it is desirable to use light irradiation at the time of thermal decomposition. Fe remaining in the liquid even after completion of the reaction
By removing (CO) ₅ by distillation, magnetic fine particles having a surfactant adsorbed thereon can be obtained.

Ni treated with a surfactant by photolysis
An example of a method for producing fine particles is as follows. Using a container made of quartz or the like that can transmit ultraviolet rays, Ni (C
O) ₄ , a surfactant, and a dispersion medium are mixed in an atmosphere of an inert gas, and the mixture is irradiated with ultraviolet rays to obtain Ni fine particles. By removing the remaining raw material Ni (CO) ₄ by distillation, magnetic fine particles having a surfactant adsorbed thereon can be obtained.

The obtained particles are mixed with a desired dispersion medium with stirring, or the mixed particles are stirred to obtain a magnetic fluid. Next, the magnetic fine particles having poor dispersibility are removed by centrifugation to obtain a purified magnetic fluid. The stirring method is not particularly limited, and known mechanical stirring, ultrasonic stirring, shaking stirring and the like are employed.

When a ferrite such as magnetite, Ba ferrite, Mn ferrite, or Zn ferrite is used as the magnetic fine particles, a method of synthesizing a ferrite colloid in an aqueous solution by a coprecipitation method and then treating with a surfactant is mentioned.

An example of a method for producing a magnetic fluid in which the magnetic particles are magnetite is as follows. Fine particles of magnetite can be obtained by reacting an aqueous solution comprising a ferrous salt and a ferric salt with an aqueous alkali solution such as sodium hydroxide. An aqueous solution in which an equimolar aqueous alkali solution is added to a surfactant is separately prepared, and the resulting solution is dropped into the reaction solution and heated. After cooling, an acid is added dropwise to the reaction solution to obtain an acidic aqueous solution. Repeat washing of the precipitate with water to remove excess surfactant and salts. By heating and drying the precipitate under vacuum, magnetic fine particles having a surfactant adsorbed thereon can be obtained.

A magnetic fluid is obtained by mixing the obtained powder with an intended dispersion medium. By removing the fine magnetic particles having poor dispersibility by centrifugation, a purified magnetic fluid can be obtained.

[0028]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto.

Production Example 1 Synthesis of Br (CH ₂ ) ₁₀ COOCH ₃ Br (CH ₂ ) ₁₀ COOH 20 in a 1 l Erlenmeyer flask
0 g, 242 g of methanol, p-CH ₃ C ₆ H ₄ SO ₃ H
· H ₂ O 2.00g, put toluene 400 ml, and heating was continued under reflux for 10 hours. Water from the reaction solution
After removing with O ₄ , toluene and methanol were distilled off under reduced pressure. The product was purified by distillation under reduced pressure to obtain 198 g of a colorless liquid (boiling point 125 ° C./0.3 mmHg).

Production Example 2 Synthesis of H (C ₂ H ₄ O) ₃ (CH ₂ ) ₁₀ COOH H (C ₂ H ₄ O) ₃ H was placed in a 300 ml two-necked round bottom flask.
40.24 g, 6.67 g of Na, 4.98 g of KI, and 100 ml of toluene were added and heated under reflux for 9 hours. Na
After confirming that all of them have been consumed, Br (CH ₂ ) ₁₀
A solution of 41.9 g of COOCH _{3 in} 50 ml of toluene was added to 7
It was dropped over time. Thereafter, the reaction was terminated by continuing heating and refluxing for another 10 hours.

After toluene was distilled off from the above reaction solution under reduced pressure, 10 g of NaOH and 100 ml of water were added, and the mixture was refluxed for 18 hours. After heating under reflux, methanol produced by the reaction was distilled off under reduced pressure. Aqueous hydrochloric acid was added until the pH reached 1. NaCl was added to the reaction until it was saturated. The reaction solution was extracted with chloroform, and the obtained organic phase was washed with saturated saline. After the chloroform was removed under reduced pressure, the raw material H (C ₂ H ₄ O) ₃ H was removed by vacuum distillation. As a crude product, 35.8 g of a brown liquid, which was a residue, was obtained.

20 g of the above crude product was purified by a column. A 11 cm diameter column was packed with Wakogel C-200 to a height of 8 cm. The developing solvent is chloroform /
Methanol (99/1) was used. By-product CH ₂ =
After CH (CH ₂ ) ₈ COOH was eluted, the developing solvent was changed to chloroform / methanol (97/3) to elute the desired purified product. 1 pale brown liquid as purified product
2 g were obtained.

1H-NMR of the purified product (CDCl ₃ , T
MS is used as a reference (0.00 ppm). ) And IR analysis gave the following results.

1H-NMR: 1.0 to 1.8 ppm
_{(M; 19H, CH 3,} CH 2), 2.34ppm (t;
_{2H, CH 2 COO), 3.3~3.8ppm} (m; 1
2H, CH ₂ OCH _2).

IR: 1110, 1460, 1710, 1
735, 2840, 2920 cm-1 From these analysis results, the purified product was found to be H (C ₂ H ₄ O) ₃ (C
It was confirmed to have a structure of H ₂ ) ₁₀ COOH. In addition, although the result of IR analysis suggests the presence of an acid anhydride, it does not pose any problem in the production of the magnetic fluid.

Example 1 H (C ₂ H ₄ O) ₃ (CH ₂ ) ₁₀ C
FeSO the in the preparation under nitrogen Fe ₃ 0 ₄ based magnetic fluid that has a surfactant OOH ₄ · 7H ₂ O and Fe ₂ (SO _{4) 3}
50 ml of a 1 molar aqueous solution of nH ₂ O was mixed, and the pH was adjusted to 11.5 while stirring a 6N aqueous solution of NaOH.
It dripped until it became. This was heated at 70 ° C. for 5 minutes to produce a magnetite colloid. On the other hand, H (C ₂ H
_{4 O) 3 (CH 2)} 10 COOH 4.17g of weighed into another vessel under nitrogen, to which aqueous NaOH 3N 4.3
7 ml and 50 ml of water were added to obtain a homogeneous solution. The above surfactant was added to the magnetite colloid prepared above, and the mixture was kept at 80 ° C. for 30 minutes with stirring. After cooling, a 1N aqueous hydrochloric acid solution was added to the reaction solution to adjust the pH to 5.5, and the colloid was aggregated. The aggregate was washed with water repeatedly to remove the electrolyte, and finally the solid obtained by vacuum filtration was dried at 90 ° C. under reduced pressure for 10 hours. After allowing to cool to room temperature, it was taken out of the dryer. The obtained crude product weighed 12.5 g,
It was a black non-viscous powder. The crude product did not generate heat even after being taken out of the dryer. The obtained crude product was hexane (ε = 1.9) and water (ε = 78.
5) Although not dispersed in 5), toluene (ε = 2.4), chloroform (ε = 4.7), dichloromethane (ε = 8.
9), acetone (ε = 20.5), methanol (ε = 3)
It dispersed in 2.6).

[0037] 2.0 g of the crude product was dispersed in 30 ml of chloroform. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant. The solvent in the supernatant was distilled off under reduced pressure, and 1.29 by dry weight.
g of powder was obtained. The whole amount of this powder was again dispersed in 2.0 ml of chloroform to obtain a magnetic fluid. It was confirmed that the ferrofluid was a stable magnetic fluid without precipitation even after storage for 3 months at room temperature.

Production Example 3 Synthesis of C ₂ H ₅ O (CH ₂ ) ₁₀ COOH Ethanol 2 instead of H (C ₂ H ₄ O) ₃ H as a raw material
Synthesized according to Production Example 2 except that 7.4 g was used. 3
4.2 g of solid were obtained as a crude product. The above crude product was purified by recrystallization. 160 parts of crude product
After dissolving in ml of methyl ethyl ketone, it was crystallized by cooling to -20 ° C. 16 g of a white powder was obtained as a purified product.

1H-NMR of the purified product (CDCl ₃ , T
MS is used as a reference (0.00 ppm). ) And IR analysis gave the following results.

1H-NMR: 1.1 to 1.8 ppm
_{(M; 19H, CH 3,} CH 2), 2.34ppm (t;
_{2H, CH 2 COO), 3.3~3.6ppm} (m; 4
H, CH ₂ OCH _2).

IR: 1105, 1465, 1695, 2
845, 2910 cm-1 From these analysis results, the purified product was found to be C ₂ H ₅ O (CH ₂ ) ₁₀
It was confirmed to have the structure of COOH.

Example 2 C ₂ H ₅ O (CH ₂ ) ₁₀ COOH
Which is a preparation material of Fe ₃ 0 ₄ based magnetic fluid that has a surfactant _{H (C 2 H 4 O)} 3 (CH 2) instead of the _{10 COOH C 2 H 5 O (} CH 2) 10 COOH 3.02g Was prepared according to Example 1 except that was used. The obtained crude product weighed 12.6 g and was a black non-viscous powder. The crude product did not generate heat even after being taken out of the dryer. The obtained crude product was methanol (ε = 32.
6), not dispersed in water (ε = 78.5), but in hexane (ε = 1.9), toluene (ε = 2.4), chloroform (ε = 4.7), dichloromethane (ε = 8. 9),
Dispersed in acetone (ε = 20.5).

2.0 g of crude product were dispersed in 30 ml of dichloromethane. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant. The solvent of the supernatant was distilled off under reduced pressure and the dry weight was 1.48.
g of powder was obtained. The whole amount of the powder was dispersed again in 2.0 ml of dichloromethane to obtain a magnetic fluid.
It was confirmed that the ferrofluid was a stable magnetic fluid without precipitation even after storage for 3 months at room temperature.

Production Example 4 Production of H (CH ₂ ) ₆ O (CH ₂ ) ₁₀ COOH Production Example 2 except that 35.76 g of n-hexanol was used in place of H (C ₂ H ₄ O) ₃ H as a raw material. Synthesized according to the following procedure. Note that hexane was used as the extraction solvent instead of chloroform. 32.5 g of a liquid as a bottom was obtained as a crude product. The above crude product was purified by recrystallization.
After dissolving the whole amount of the crude product in 140 ml of methyl ethyl ketone, it was crystallized by cooling to −20 ° C. 13 g of a white powder was obtained as a purified product.

1H-NMR of the purified product (CDCl ₃ , T
MS is used as a reference (0.00 ppm). ) And IR analysis gave the following results.

1H-NMR: 0.89 ppm (t; 3
_{H, CH 3), 1.1~1.8ppm (} m; 24H, C
_{H 2), 2.34ppm (t;} 2H, CH 2 COO) ,,
_{3.3~3.5ppm (m; 4H, CH 2} OCH 2).

IR: 1130, 1465, 1710, 2
845, 2920 cm -1 From these analysis results, the purified product was H (CH ₂ ) ₆ O (CH
₂ ) It was confirmed to have a structure of ₁₀ COOH.

Example 3 H (CH ₂ ) ₆ O (CH ₂ ) ₁₀ C
OOH which is a preparation material of Fe ₃ 0 ₄ based magnetic fluid that has a surfactant _{H (C 2 H 4 O)} 3 (CH 2) 10 COOH instead H of _{(CH 2) 6 O (CH} 2) 10 COOH 3.75g
Was prepared according to Example 1 except that was used. The obtained crude product weighed 13.2 g and was a black non-viscous powder. The crude product did not generate heat even after being taken out of the dryer. The obtained crude product is acetone (ε = 2
0.5), methanol (ε = 32.6), water (ε = 7)
8.5) does not disperse in hexane (ε = 1.
9), toluene (ε = 2.4), chloroform (ε =
4.7), dispersed in dichloromethane (ε = 8.9). Further, it could be dispersed in kerosene and decalin.

2.0 g of the crude product were dispersed in 30 ml of hexane. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant. The solvent of the supernatant was distilled off under reduced pressure to obtain 1.56 g of a powder by dry weight. A magnetic fluid was obtained by dispersing the entire amount of this powder in 2.0 ml of toluene. It was confirmed that the ferrofluid was a stable magnetic fluid without precipitation even after storage for 3 months at room temperature.

Production Example 5 CH ₃ O (C ₂ H ₄ O) ₃ (C
Synthesis of H ₂ ) ₁₀ COOH Instead of H (C ₂ H ₄ O) ₃ H as a raw material, CH ₃ O (C ₂
H ₄ O) except using ₃ H _79.18g was synthesized according Manufacturing Example 2. As a crude product, 40.5 g of a brown liquid as a residue was obtained. 15 g of the above crude product was purified by a column. 4. Light brown liquid as purified product
0 g was obtained.

1H-NMR of the purified product (CDCl ₃ , T
MS is used as a reference (0.00 ppm). ) And IR analysis gave the following results.

1H-NMR: 1.1 to 1.8 ppm
_{(M; 16H, CH 2)} , 2.34ppm (t; 2H,
_{CH 2 COO), 3.2~3.8ppm (m} ; 17H,
_{CH 3 O, CH 2 OCH 2} ).

IR: 1110, 1465, 1710, 1
735, 2860, 2930 cm-1 From these analysis results, the purified product was CH ₃ O (C ₂ H ₄ O) ₃
It was confirmed to have a structure of (CH ₂ ) ₁₀ COOH. In addition, although the result of IR analysis suggests the presence of an acid anhydride, it does not pose any problem in the production of the magnetic fluid.

Example 4 CH ₃ O (C ₂ H ₄ O) ₃ (C
H _{2) 10} COOH of FeSO in Fe ₃ 0 ₄ system prepared under nitrogen ferrofluid was surfactants ₄ · 7H ₂ O and Fe ₂ (SO _{4) 3}
50 ml of a 1 molar aqueous solution of nH ₂ O was mixed, and the pH was adjusted to 11.5 while stirring a 6N aqueous solution of NaOH.
It dripped until it became. This was heated at 70 ° C. for 5 minutes to produce a magnetite colloid. On the other hand, CH ₃ O (C ₂
4.57 g of H ₄ O) ₃ (CH ₂ ) ₁₀ COOH were weighed out in a separate container under nitrogen, and 3N aqueous NaOH solution was added thereto.
37 ml and 50 ml of water were added to make a homogeneous solution. The above surfactant was added to the magnetite colloid prepared above, and the mixture was kept at 80 ° C. for 30 minutes with stirring. After cooling, a 1N aqueous hydrochloric acid solution was added to the reaction solution to adjust the pH to 5.5, and the colloid was aggregated. The reaction solution was separated into a precipitate and a supernatant by centrifugation at 1,500 g. The precipitate was dried at 90 ° C. under reduced pressure for 10 hours. After allowing to cool to room temperature, it was taken out of the dryer. The crude product obtained was 15.0 g,
It was a black, slightly viscous powder. The crude product did not generate heat even after being taken out of the dryer. The obtained crude product does not disperse in hexane (ε = 1.9) and brine, but toluene (ε = 2.4), chloroform (ε = 4.7), dichloromethane (ε = 8.9), Acetone (ε = 20.5), methanol (ε = 32.6),
Dispersed in water (ε = 78.5). 2.0 g of the crude product was dispersed in 30 ml of methanol. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant. The solvent in the supernatant was distilled off under reduced pressure to obtain 1.49 g of powder by dry weight. The whole amount of the powder was dispersed again in 2.0 ml of methanol to obtain a magnetic fluid. It was confirmed that the ferrofluid was a stable magnetic fluid without precipitation even after storage for 3 months at room temperature.

Production Example 6 C ₁₂ H ₂₅ O (C ₂ H ₄ O) ₂₅ (C
Synthesis of H ₂ ) ₁₀ COOH Instead of H (C ₂ H ₄ O) ₃ H as a raw material, C ₁₂ H ₂₅ O
It was synthesized according to Production Example 2 except that 390 g of (C ₂ H ₄₀ ) ₂₅ H was used. As a crude product, 420 g of a brown liquid, which is a residue, was obtained. 20 g of the above crude product was purified by a column. 5g of pale brown liquid as purified product
Obtained.

1H-NMR of the purified product (CDCl ₃ , T
MS is used as a reference (0.00 ppm). ) And IR analysis gave the following results.

1H-NMR: 0.89 ppm (t; 3)
_{H, CH 3), 1.1~1.8ppm (} m; 36H, C
_{H 2), 2.34ppm (t;} 2H, CH 2 COO),
_{3.3~3.8ppm (m; 104H, CH 2} OC
H _2).

IR: 1110, 1460, 1710, 1
735, 2840, 2920 cm -1 From these analysis results, the purified product was found to be C ₁₂ H ₂₅ O (C ₂ H
₄ O) have a ₂₅ (CH ₂₎ a ₁₀ COOH structure was confirmed. In addition, although the result of IR analysis suggests the presence of an acid anhydride, it does not pose any problem in the production of the magnetic fluid.

Example 5 C ₁₂ H ₂₅ O (C ₂ H ₄ O) 25
(CH ₂₎ C ₁₂ to ₁₀ COOH instead of _{CH 3 (C 2 H 4 O} ) 3 (CH 2) 10 COOH is the preparation raw materials of Fe ₃ 0 ₄ based magnetic fluid that has a surfactant H ₂₅ O (C ₂ H ₄ O) ₂₅ (CH2) ₁₀ COO
Prepared according to Example 4 except using 19.3 g of H. The obtained crude product weighed 26.5 g and was a black viscous powder. The crude product did not generate heat even after being taken out of the dryer. The obtained crude product does not disperse in hexane (ε = 1.9) and water (ε = 78.5), but toluene (ε = 2.4) and chloroform (ε =
4.7), dichloromethane (ε = 8.9), acetone (ε = 20.5), and methanol (ε = 32.6).

[0060] 2.0 g of crude product was dispersed in 30 ml of chloroform. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant. The solvent of the supernatant was distilled off under reduced pressure and the dry weight was 1.53.
g of powder was obtained. The whole amount of this powder was again dispersed in 2.0 ml of chloroform to obtain a magnetic fluid. It was confirmed that the ferrofluid was a stable magnetic fluid without precipitation even after storage for 3 months at room temperature.

Production Example 7 CH ₃ O (CH ₂ CHCH ₃ O) ₂
Synthesis of (CH ₂ ) ₁₀ COOH Instead of H (C ₂ H ₄ O) ₃ H as a raw material, CH ₃ O (CH
₂ CHCH ₃ O) except for using ₂ H47.42G (isomer mixture) was synthesized according to Preparation Example 2. As a crude product,
30.2 g of a brown liquid, which was a residue, was obtained. 15 g of the above crude product was purified by a column. 6.1 g of a pale brown liquid was obtained as a purified product. 1H of purified product
-NMR (in CDCl ₃ , TMS based (0.00 pp
m). ) And IR analysis gave the following results.

1H-NMR: 1.0 to 1.8 ppm
_{(M; 22H, CH 3,} CH 2), 2.34ppm (t;
_{2H, CH 2 COO), 3.2~3.8ppm} (m; 1
_{1H, CH 3 O, CHOCH 2} ).

IR: 1105, 1455, 1705, 1
735, 2845, 2910 cm-1 From these analysis results, the purified product was CH ₃ O (CH ₂ CHC
It was confirmed to have a structure of H ₃ O) ₂ (CH ₂ ) ₁₀ COOH. In addition, although the result of IR analysis suggests the presence of an acid anhydride, it does not pose any problem in the production of the magnetic fluid.

Example 6 CH ₃ O (CH ₂ CHCH ₃ O) ₂
(CH2) ₁₀ COOH and a Fe ₃ 0 ₄ system prepared raw material of a magnetic fluid that has a surfactant _{H (C 2 H 4 O)} 3 (CH 2) instead of the _{10 COOH CH 3 O (CH 2} CHCH 3 O ) ₂ (CH ₂ ) ₁₀ COO
Prepared according to Example 1 except that 4.36 g of H was used. The obtained crude product weighed 13.1 g and was a black non-viscous powder. The crude product did not generate heat even after being taken out of the dryer. The obtained crude product is not dispersed in hexane (ε = 1.9) and water (ε = 78.5), but toluene (ε = 2.4), chloroform (ε = 4.7), dichloromethane ( (ε = 8.9), dispersed in acetone (ε = 20.5), and methanol (ε = 32.6).

2.0 g of the crude product were dispersed in 30 ml of dichloromethane. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant. The solvent of the supernatant was distilled off under reduced pressure, and the dry weight was 1.89.
g of powder was obtained. The whole amount of the powder was dispersed again in 2.0 ml of dichloromethane to obtain a magnetic fluid.
It was confirmed that the ferrofluid was a stable magnetic fluid without precipitation even after storage for 3 months at room temperature.

Example 7 H (C ₂ H ₄ O) ₃ (CH ₂ ) ₁₀ C
Preparation of Fe-based magnetic fluid using OOH as a surfactant 5.00 g of H (C ₂ H ₄ O) ₃ (CH ₂ ) ₁₀ COOH, 4.00 g of pyridine and 100 ml of butyl acetate were equipped with a reflux condenser under an argon atmosphere. Weighed into a 1 l separable flask. Fe (CO) ₅ 50.
An additional 0 g was added. Until the generation of carbon monoxide ends,
The mixture was heated and refluxed on a hot plate while performing light irradiation. After cooling, the solvent and the starting materials were distilled off under reduced pressure. Further drying was performed at 90 ° C. under reduced pressure for 10 hours to obtain 14.8 g of a black powder as a crude product. The crude product did not exotherm after removal to air. The obtained crude product is not dispersed in hexane (ε = 1.9) and water (ε = 78.5), but is dissolved in toluene (ε = 2.4) and chloroform (ε = 4.
7), dichloromethane (ε = 8.9), acetone (ε =
20.5) and dispersed in methanol (ε = 32.6).

2.0 g of the crude product were dispersed in 30 ml of chloroform. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant. The solvent in the supernatant was distilled off under reduced pressure and the dry weight was 1.32.
g of powder was obtained. The whole amount of this powder was again dispersed in 2.0 ml of chloroform to obtain a magnetic fluid. It was confirmed that the ferrofluid was a stable magnetic fluid without precipitation even after storage for 3 months at room temperature.

Production Example 8 CH ₃ COOC ₂ H ₄₀ (CH ₂ )
Synthesis of ₁₀ COOH Br (CH ₂ ) ₁₀ CO was added to a 300 ml three-necked round bottom flask.
41.9 g of OH and 50 ml of hexane were added. t-
A solution of 45.2 g of C ₄ H ₉ (CH ₃ ) ₂ SiCl in 50 ml of hexane was added dropwise to the above solution at 30 ° C. over 1 hour. Thereafter, heating at 50 ° C. was continued for 1 hour. HCl generated in the reaction was removed by passing a stream of nitrogen through the reaction system. After completion of the reaction, hexane and unreacted raw materials are distilled off under reduced pressure to obtain Br (CH ₂ ) ₁₀ COOSi (CH ₃ ) ₂
It was obtained -t-C ₄ H _9.

In a newly prepared 300 ml two-necked round bottom flask, 36.4 g of CH ₃ COOC ₂ H ₄ OH, Na
6.67 g, KI 4.98 g, toluene 100 ml
And heated to reflux for 9 hours. After confirming that all the Na has been consumed, the Br (CH ₂ ) ₁₀ C
OOSi (CH ₃ ) ₂ -tC ₄ H ₉ Total amount of toluene 50
ml solution was added dropwise over 7 hours. Thereafter, the reaction was terminated by continuing heating and refluxing for another 10 hours.

After toluene was distilled off from the above reaction solution under reduced pressure, 100 ml of water was added, and the mixture was stirred at 30 ° C. for 5 hours.
After stirring, aqueous hydrochloric acid was added until the pH reached 1. The methanol produced by the reaction was distilled off under reduced pressure. NaCl was added to the reaction until it was saturated. The reaction solution was extracted with chloroform, and the obtained organic phase was washed with saturated saline. After the chloroform was distilled off under reduced pressure, the raw material CH ₃ COOC ₂ H ₄ O
H was removed by distillation under reduced pressure. As a crude product, 32.8 g of a brown liquid, which was a residue, was obtained.

20 g of the above crude product was purified by a column. 7.5 g of a light brown liquid was obtained as a purified product.

1H-NMR of the purified product (CDCl ₃ , T
MS is used as a reference (0.00 ppm). ) And IR analysis gave the following results.

1H-NMR: 1.0 to 1.8 ppm
(M; 16H, CH ₂ ), 2.02 ppm (S; 3H,
CH ₃ ) 2.34 ppm (t, 2H, CH ₂ COO),
3.3 to 4.2 ppm (m; 6H, COOCH ₂ CH ₂ O
CH _2).

IR: 1130, 1245, 1375, 1
460, 1710, 1735, 2840, 2920 cm
-1 From these analysis results, the purified product was CH ₃ COOC ₂ H ₄ O
It was confirmed to have a structure of (CH ₂ ) ₁₀ COOH. In addition, although the result of IR analysis suggests the presence of an acid anhydride, it does not pose any problem in the production of the magnetic fluid.

Example 8 CH ₃ COOC ₂ H ₄₀ (CH ₂ )
₁₀ COOH which is a preparation material of Fe-based magnetic fluid that has a surfactant _{H (C 2 H 4 O)} 3 (CH 2) instead of the _{10 COOH CH 3 COOC 2 H 4} 0 (CH2) 10 COOH 4.
Synthesized according to Example 7 except that 53 g was used. 14．
1 g of a black powder was obtained as a crude product. The crude product did not exotherm after removal to air. The obtained crude product was hexane (ε = 1.9) and water (ε = 78.
5) Although not dispersed in 5), toluene (ε = 2.4), chloroform (ε = 4.7), dichloromethane (ε = 8.
9), acetone (ε = 20.5), methanol (ε = 3)
It dispersed in 2.6). This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant. Even after storage at room temperature for 3 months, a stable magnetic fluid without precipitation was obtained.

2.0 g of the crude product were dispersed in 30 ml of acetone. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant. The solvent in the supernatant was distilled off under reduced pressure to obtain 1.15 g of a powder by dry weight. The whole amount of the powder was dispersed again in 2.0 ml of acetone to obtain a magnetic fluid. It was confirmed that the ferrofluid was a stable magnetic fluid without precipitation even after storage for 3 months at room temperature.

Production Example 9 Synthesis of CH ₃ OCO (CH ₂ ) ₁₀ COOH HOOC (CH ₂ ) ₁₀ COOH was placed in a 1-liter Erlenmeyer flask.
200 g, methanol 42.0 g, p-CH ₃ C ₆ H ₄ S
2.00 g of O ₃ H.H ₂ O and 400 ml of toluene were added, and the mixture was heated under reflux for 10 hours. Water from the reaction solution
After removal with SO ₄ , toluene was distilled off under reduced pressure. By recrystallization from ethanol, 20.3 g of the purified product was isolated (melting point: 52 ° C.).

Example 9 CH ₃ OCO (CH ₂ ) ₁₀ COO
Preparation of Fe-based Magnetic Fluid Using H as Surfactant Except for using 3.84 g of CH ₃ OCO (CH ₂ ) ₁₀ COOH instead of H (C ₂ H ₄ O) ₃ (CH ₂ ) ₁₀ COOH as a raw material Prepared according to Example 7. 13.5 g of a black powder were obtained as a crude product. The crude product did not exotherm after removal to air. The obtained crude product is not dispersed in hexane (ε = 1.9) and water (ε = 78.5), but toluene (ε = 2.4), chloroform (ε = 4.7), dichloromethane ( (ε = 8.9), dispersed in acetone (ε = 20.5), and methanol (ε = 32.6).

[0079] 2.0 g of the crude product was dispersed in 30 ml of chloroform. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant. The solvent of the supernatant was distilled off under reduced pressure and the dry weight was 1.21.
g of powder was obtained. The whole amount of this powder was again dispersed in 2.0 ml of chloroform to obtain a magnetic fluid. It was confirmed that the ferrofluid was a stable magnetic fluid without precipitation even after storage for 3 months at room temperature.

Production Example 10 Synthesis of CH ₃ CONH (CH ₂ ) ₁₁ COOH NH ₂ (CH ₂ ) ₁₁ COOH 10 was placed in a 1 l Erlenmeyer flask.
0 g and 400 g of acetic acid were added and replaced with nitrogen. At room temperature, 100 g of acetic anhydride was added dropwise over 1 hour. After the completion of the dropwise addition, the reaction was completed by continuing stirring at room temperature for 3 hours. Acetic acid and acetic anhydride were distilled off from the reaction solution under reduced pressure to obtain 120 g of a crude product.

20 g of the above crude product was purified by a column. 10 g of a white powder was obtained as a purified product.

1H-NMR of purified product (DMSO-d6 +
In CDCl ₃ , TMS is set as a standard (0.00 ppm). ) And IR analysis gave the following results.

1H-NMR: 1.0 to 1.8 ppm
(M; 18H, CH ₂ ), 1.9 ppm (S; 3H, C
H ₃ CON) 2.0-2.5 ppm (m; 2H, CH ₂ C)
OO) 2.7 to 3.3 ppm (m; 2H, NC
_{H 2), 7.2~7.6ppm (broad;} 1H, C
ONH).

IR: 1195, 1250, 1280, 1
350, 1370, 1460, 1560, 1610, 1
690, 2860, 2920, 3350 cm -1 From these analysis results, the purified product was CH ₃ CONH (C
It was confirmed to have a structure of H ₂ ) ₁₁ COOH.

Example 10 CH ₃ CONH (CH ₂ ) ₁₁ C
Preparation of Fe-Based Magnetic Fluid Using OOH as Surfactant Except that 4.05 g of CH ₃ CONH (CH ₂ ) ₁₁ COOH was used instead of H (C ₂ H ₄ O) ₃ (CH ₂ ) ₁₀ COOH as a raw material Prepared according to Example 7. 13.5 g of a black powder were obtained as a crude product. The crude product did not exotherm after removal to air. The obtained crude product is not dispersed in hexane (ε = 1.9) and water (ε = 78.5), but toluene (ε = 2.4), chloroform (ε = 4.7), dichloromethane ( (ε = 8.9), dispersed in acetone (ε = 20.5), and methanol (ε = 32.6).

2.0 g of the crude product were dispersed in 30 ml of methanol. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant.
The solvent of the supernatant was distilled off under reduced pressure to obtain 1.32 g of a powder by dry weight. The whole amount of the powder was dispersed again in 2.0 ml of methanol to obtain a magnetic fluid. It was confirmed that the ferrofluid was a stable magnetic fluid without precipitation even after storage for 3 months at room temperature.

Production Example 11 C ₄ H ₉ NHCO (CH ₂ ) ₁₀
Synthesis of COOH HOOC (CH ₂ ) ₁₀ COOH was placed in a 1 l Erlenmeyer flask.
_{100g, n-C 4 H 9} NH 2 47.6g, C 6 H 11 N =
C = NC ₆ H ₁₁ 134 g, tetrahydrofuran 40
0 ml was added and the mixture was stirred at 25 ° C. for 5 hours. By-product C ₆ H ₁₁ NHCONHC ₆ H ₁₁ was filtered off. The solvent was replaced with chloroform from tetrahydrofuran, and the resulting chloroform solution was washed with saturated saline. Chloroform was distilled off under reduced pressure to obtain 130 g of a crude product.

20 g of the above crude product was purified by a column. 6.1 g of a white powder was obtained as a purified product.

1H-NMR of purified product (DMSO-d6 +
In CDCl ₃ , TMS is set as a standard (0.00 ppm). ) And IR analysis gave the following results.

1H-NMR: 0.8 to 1.8 ppm
_{(M; 23H, CH 3,} CH 2), 2.0~2.5ppm
_{(M; 4H, CH 2 CON} , CH 2 COO), 2.7~
_{3.3ppm (m; 2H, NCH 2} ), 7.2~7.6
ppm (broad; 1H, CONH).

IR: 1195, 1250, 1280, 1
350, 1370, 1460, 1560, 1610, 1
690, 2860, 2920, 3350 cm-1 From these analysis results, the purified product was found to be C ₄ H ₉ NHCO (CH
₂ ) It was confirmed to have a structure of ₁₀ COOH.

Example 11 C ₄ H ₉ NHCO (CH ₂ ) ₁₀
Preparation of Fe-Based Magnetic Fluid Using COOH as Surfactant 4.49 g of C ₄ H ₉ NHCO (CH ₂ ) ₁₀ COOH instead of H (C ₂ H ₄ O) ₃ (CH ₂ ) ₁₀ COOH as a raw material
Was prepared according to Example 7 except that 12.8 g of a black powder were obtained as a crude product. The crude product did not exotherm after removal to air. The obtained crude product is not dispersed in hexane (ε = 1.9) and water (ε = 78.5), but toluene (ε = 2.4), chloroform (ε = 4.7), dichloromethane ( ε = 8.9), acetone (ε = 20.5), methanol (ε = 32.6)
Dispersed inside.

2.0 g of the crude product were dispersed in 30 ml of methanol. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant.
The solvent in the supernatant was distilled off under reduced pressure to obtain 1.25 g of a dry weight powder. The whole amount of the powder was dispersed again in 2.0 ml of methanol to obtain a magnetic fluid. It was confirmed that the ferrofluid was a stable magnetic fluid without precipitation even after storage for 3 months at room temperature.

Comparative Example 1 Synthesis of Magnetic Fluid Using Oleic Acid as a Surfactant The same procedure was carried out except that 3.70 g of oleic acid was used in place of H (C ₂ H ₄ O) ₃ (CH ₂ ) ₁₀ COOH as a raw material. Synthesized according to Example 1. The crude product obtained was 13.0 g,
It was a black non-viscous powder. The crude product exothermed upon removal from the dryer.

2.0 g of the crude product were dispersed in 30 ml of hexane. This dispersion was centrifuged under a centrifugal force of 8000 G for 20 minutes, and the precipitate was removed from the supernatant. The solvent in the supernatant was distilled off under reduced pressure to obtain 1.11 g of powder by dry weight. The whole amount of this powder was again dispersed in 2.0 ml of hexane to obtain a magnetic fluid. Storage for 3 months at room temperature resulted in precipitation in the magnetic fluid.

Comparative Example 2 Synthesis of a Magnetic Fluid Using Linoleic Acid as a Surfactant The procedure was performed except that 3.67 g of linoleic acid was used in place of H (C ₂ H ₄ O) ₃ (CH ₂ ) ₁₀ COOH as a raw material. Synthesized according to Example 1. 13.7g immediately after taking out from the dryer
However, severe heat generation occurred and the weight was reduced to 13.0 g. The color changed from a black, non-viscous powder to a black powder with a partial red color. From the result of X-ray diffraction, Fe ₃ O ₄
In addition, the presence of α-Fe ₂ O ₃ was confirmed. The obtained crude product did not disperse in any dispersion medium.

[0097]

The magnetic fluid obtained by the present invention can be prepared without taking special measures such as adding an antioxidant.
Stable against oxidation. Not only is there no danger of oxidation due to the production method, but also a stable and simple magnetic fluid can be obtained without precipitation even during long-term storage.

Claims (1)

(57) [Claims] 1. A compound represented by the general formula: ## STR1 ## R--X-(CH ₂ CHR'O) _n- (CH ₂ ) _m-
COOH (where R is an alkyl group having 1 to 18 carbon atoms, and X is -O
-, -COO-, -OCO-, -CONH-, or-
NHCO-, R 'represents a hydrogen atom or a methyl group, n represents an integer of 0 to 30 and m represents an integer of 8 to 12), a magnetic fine particle, and a dispersion medium. A magnetic fluid characterized by comprising: