I
B. W.
HOTTEN
California Research Corp., Richmond, Calif.
Metal Terephthalamates A New Class of Oil-Gelling Agents Versatility of terephthalamates as gelling agents suggests their use in solvents, fuels, plastics, elastomers, surface coatings, and lubricants
SOAPS
of animal and vegetable fatty acids are widely used as gelling agents, but they are deficient in some properties needed for such gels as lubricating greases. Bryant and Giordano ( 2 )found that salts of aliphatic amic acids had good gelling action in mineral oils. T h e author has found that the terephthalamate structure leads to a much better combination of many important gel properties.
The selective monosalt formation, as measured by potentiometric titration, was very sensitive to the water content of the ethanol used as a potassium hydroxide solvent:
Water Concn. in Ethanol, %
Direct amidation of dimethyl terephthalate yielded excessive diamide. Thus a more selective synthesis of an unsymmetrical intermediate was attempted. Monosaponification of Dimethyl Terephthalate. Saponification might be made selective if conditions could be found under which the monosalt precipitated as soon as formed. The solubility of dimethyl terephthalate was measured in several solvents. Results are in Table I. Benzene was selected for preliminary trial because of its solvent power, chemical inertness, and convenient boiling point. Sodium hydroxide in ethanol reacted slowly with dimethyl terephthalate in benzene a t the reflux temperature, and the product was too gelatinous for convenient handling. But potassium hydroxide in ethanol reacted rapidly to give an easily filterable, crystalline precipitate.
Experimental Procedures
Precipitate Equiv. Wt.
Monosalt Concn., yo
126 192 227
4- 5 67- 75 95-100
15 5
Synthesis
0
Toluene, xylene, and methanol also permitted selective monosalt formation. Methanol was less sensitive than the hydrocarbons to the disalt-promoting effect of water. Amidation. Two practical amidation methods were developed. I n one method thionyl chloride reacted with potassium methyl terephthalate to form methyl terephthaloyl chloride, which reacted with amines to form the methyl terephthalamate. I n the second method amines reacted directly with potassium methyl terephthalate in the presence of phosphorus trichloride. Synthesis of methyl terepthalamates is summarized in the following equations :
+
C H a 0 ~ C- a - C O ~ C H 3 K O H -+ CH~OZC-D-COZK
+ CH30H (1)
Table I. Solubility of Dimethyl Terephthalate Solubility,
CH~OZC-D-COZK
+ SOC12
+ KCl / I\
O
Solvent Isopropyl alcohol Ethanol Carbon tetrachloride Mixed xylenes Dimethyl sulfoxide Toluene Methyl ethyl ketone Acetone Dimethylformamide Nitromethane Benzene Chloroform a
40
50
.. 1 .. .. 6 6 4 8 8 8
8
10 10 26
8
8 6
11 11 13 12 13 14 40
-*
C H ~ O Z C - O - C O C ~ + SOZ
G./100 MI."
Solvent, C. 60
70
80
5 6 10 12 10 16 17
9 9 17 17 19 24 27
15 15
CHIO&-D-COC1
+ RNHz +
..
24
..
35 39
.. .. .. 29 42 30 ,. 32 44 .. .. ,.
18 20 22
Volume of solvent measured at 2 5 O C.
CONHR
+ (CzH5)3NHCl
(3)
or in place of Equations 2 and 3, 2 C H a O d 2 -\\ n-COzK
Properties of relatively pure methyl IVsubstituted terepthalamates made by the described methods are listed in Table 11. The N-alkyl derivatives had higher solubilities and lower melting points than the N-aryl derivatives.
+
+ PC13 + CONHR + 2KC1 + RNHICl +
4RNHz
RNHIPOZ (2a)
Selective Saponification of Dimethyl Terephthalate. A potassium hydroxide solution of 760 grams (13.6 moles) in dry methanol (4330 ml. total) was added over a 5-minute period to a stirred dimethyl terephthalate (Hercules Powder Co.) solution of 2700 grams (13.9 moles) in 15,000 ml. of benzene in an iron kettle. T h e mixture was heated for 20 minutes at 65' to 70' C., cooled to room temperature, and filtered with a suction filter. The filter cake was washed in the kettle with 12,000 ml. of benzene at 50' C., and the mixture was refiltered. The washed filter cake, dried on a steam plate, yielded 2930 grams (96%) of fine, white, needle-shaped crystals; neutral equivalent determined by potentiometric titration was 213 (calculated for KO&C6H4C02CH,, 218). Part of the product was further purified by recrystallization from water; the neutral equivalent was 216 and sulfate ash 40.0 (calculated 39.9). Chlorination of Potassium Methyl Terephthalate. Thionyl chloride (58 ml., 0.8 mole) was added dropwise for 20 minutes to a stirred slurry of 139 grams (0.64 mole) of potassium methyl terephthalate in 200 ml. of benzene in a resin flask. The mixture was refluxed 11 hours. More thionyl chloride (50 ml.) was added. T h e mixture was refluxed 3 hours, cooled, and filtered. Opaque crystals of potassium methyl terephthalate were gradually replaced during the reaction by transparent crystals of potassium chloride. Excess thionyl chloride and benzene were distilled off the filtrate. The residue formed a brown solid on cooling; the yield was 102 grams (81%). Its equivalent weight, measured by adding excess aniline, extraction in water of the resulting aniline hydrochloride, and titration of the extract, was 224 and 225 (calculated for CH30&C6H,COC1, 199); the melting point was 130° C. VOL. 49, NO. 10
OCTOBER 1957
169 1
Table II.
Methyl N-Substituted Terephthalamates
Amidation Process, S a w n . Esuiv. Substituent Equation Calcd. Found n-Butyl 2a 235 244 246 n-Dodecyl 2a 335 331 333 n-Octadecyl 425 2,3 431 43 1 ;r\-
Di-n-hexyl
2, 3
347
362 360
Phenyl
2a
255
251 248
p-Tolyl
2aa
269
a
N Content, % Calcd. Found
M.P., O C.
Solubility
5.96
5.99
121
Sol. hot toluene
3.96
3.87 3.88
116
Sol. hot toluene, hot isopropyl alcohol
3.24
3.20 3.19
117
Sol. hot toluene, hot ethanol, hot isopropyl alcohol
s o
Liq.
Sol. toluene, isopropyl alcohol
5.41
193
Insol. toluene, sol. hot isopropyl alcohol
,. 5.49
256 5.2 5.06 206 Insol. toluene, sol. hot 256 5.09 isopropyl alcohol From methyl hydrogen terephthalate in place of potassium methyl terephthalate ( 4 ) .
The chlorination took about 8 hours when the higher boiling toluene was used. Triethylamine and pyridine (about 1%) served as catalysts to further reduce the reaction time. Amidation of Methyl Terephthaloyl Chloride. Methyl terephthaloyl chloride (107 grams, 0.5 mole) dissolved in benzene was added dropwise for 20 minutes to 138 grams (0.5 mole) of n-octadecylamine (Armour and Co., Armeen 18D) and 55 grams (0.54 mole) of triethylamine at a starting temperature of 70 'C., which increased to 120' to 130' C. from the heat of reaction. The mixture was stirred for 10 minutes at this temperature range. The product was fiashed with water in a Waring Blendor until free of chloride, crystallized from ethanol, and dried. The yield was 174 grams (79%) ; saponification equivalent 425, 431 (calculated for CH30&C,H4COh-HC18Ha7,4 3 1 ) ; and nitrogen content 3.20'%, 3.197, (calculated 3.24). The same procedure was used with calcium hydroxide as acid acceptor. A small amount (17 grams) of the methyl ester was hydrolyzed by refluxing with 100 ml. of concentrated hydrochloric acid and 100 ml. of Carbitol (Carbide & Carbon Chemicals Div.) for 8 hours. The product was cooled and filtered. The
Table 111. NSubstituent n-Butyl n-Dodecyl
Metal Na Na
filter cake was washed with hot water until free of chloride and was recrystallized from dioxane. The yield was 10 grams with neutral equivalent 432 (calculated for H O Z C C ~ H ~ C O N H C , ~ 41 H ,7) ~ , and with a melting point of 205" C. Direct Amidation of Potassium Methyl Terephthalate. Phosphorus trichloride (35.4 ml., 0.405 mole) was added dropwise for 20 minutes to a stirred suspension of 176.5 grams (0.81 mole) potassium methyl terephthalate and 150.5 grams (1.62 moles) aniline in 750 ml. of toluene in a resin flask between 24' and 65 'C. More toluene (250 ml.) was added to counteract solidification. The mixture was refluxed for 5 hours, cooled, and filtered. The filter cake was washed with hot water until free of chloride and recrystallized from isopropanol. The yield was 130 grams (63%) ; saponification equivalent was 251, 248 (calculated for CHIOzCCBH,CONHC6H5, 255); and nitrogen content was 5.41y0 (calculated 5.49).
Metal N-Substituted Terephthalamates
Preparation. Most metal salts were made in a solvent or a n oil by saponifica-
Metal N-Substituted Terephthalamates
Sulfate Ash, % Calcd. Found 29.2 28.8 29.5
Calcd. 5.76
Found 5.13
20.0
3.94
3.62 3.69
I n HzO: 0.1 a t 60' C., 0.5 a t 80' C., 3.0 at 100' C.; gels on cooling from 1-396 soln. Insol. cold and hot HzOand other common solvents
20.6
N, %
21.0 n-Octadecyl
Na
16.2
16.9
3.19
3.10
n-Octadecyl
Ba
28.0
27.5
..
.,
Phenyl
Na
27.0
26.5
5.33
5.38 5.43
1 692
INDUSTRIAL AND ENGINEERING CHEMISTRY
Solubility, G./100 M1. In H20: 50 a t 20' C., 70 at 100' C. Sol. hot CHIOH
Insol. cold and hot H20 and other common solvents I n HzO: 4.0 at Oo C., 6.7 a t 40' C., 10 at 95" C.
tion of the methyl terephthalamate or by neutralization of the terephthalamic acid. Aluminum salts were made by precipitation with aluminum nitrate from a potassium terephthalamate solution or by the reaction between aluminum isopropoxide and a terephthalamic acid. Relatively pure salts, listed in Table 111, were prepared by adding metal hydroxide in a small amount of water to a solution of the methyl ester in dioxane, refluxing for 1 to 3 hours, and filtering; they were purified by washing with ether and water or, when possible, by recrystallization from water. Physical Properties. Sodium 11'octadecylterephthalamate is insoluble even in boiling water. Sodium soaps and sodium salts of aliphatic amic acids, such as N-octadecyladipamic acid, dissolve readily in hot water. The shorterchained sodium N-butylterephthalamate dissolved in hot water but gelled in cold water. The water-solubility curve of sodium N-phenylterephthalamate was low and rectilinear between 0' and 95' c, Ammonium and potassium terephthalamates derived from hydrogenated tallow amines gave opalescent solutions in hot water and had low solubility in cold water. Corresponding lithium, calcium, and barium salts were insoluble in cold and hot water, as are their stearate counterparts. All the metallic salts were infusible below their decomposition temperatures. Sodium hydrogenated tallow amine terephthalamate showed a phase change a t 150' C. in a differential calorimeter. Crystallographic Properties. An electron micrograph of sodium iVoctadecylterephthalamate is shown in Figure 1. This sample was prepared by adding sodium hydroxide in methanol to a solution of methyl N-octadecylterephthalamate in ethanol, followed by refluxing for several hours. A small portion of the gelatinous precipitate was washed with ethanol and shadowed with uranium ( 7 ) for the micrograph. The exceptional detail of surface structure in this micrograph indicates the molecular arrangement within the crystals. Longitudinal striations are visible in several places. The striation ridges are about 60 A. wide and may be made up of only two rows of molecules. An electron micrograph of the sodium hydrogenated tallow amine terepthalamate prepared similarly is in Figure 2. In contrast to the flat laths of the pure octadecyl salt, this salt forms long strings. The fibrils in some of the finer strings intertwine in a regular helical pattern and are about twice as wide as the ridges on the pure octadecyl salt and thus may be made up of four rows of molecules. Lithium salt crystals in Figure 3 contain undulating, but fascicular rather than intertwined, fibrils that tend
METAL TEREPHTHALAMATES Table IV. X-ray Diffraction (CuKcrl) Spacings of Sodium and Barium N-Octadecylterephthalamates Na Salt I (rel.)
Ba Salt I (rel.)
d , A.
57.3 (1)a 28.7 (2) 19.5 (3) 11.6 8.26 5.21 4.95
4.77
Figure 2.
Figure 1. Electron micrograph of sodium N-octadecylterephthalamate. Encircled striations are only about 60 A. wide
Electron micrograph of so-
dium hydrogenated tallow amine terephthalamate. Fine fibrils intertwined into strings are about 120 A. wide
to coil up when broken off the parent crystal. The calcium and barium salt crystals appear intertwined like the sodium salt. The aluminum salt crystals look like fine grains of rice. Information on the internal structure of two of the terephthalamates was obtained with x-ray diffraction. Diffraction data from sodium and barium N-octadecylterephthalamates are in Table IV and their diagrams are shown in Figure 4. The long spacing for the sodium salt is 57.7 A., nearly the same as the strlation ridge width of about 60 A. measured in the electron micrograph. If the molecules are arranged in layers of headto-head pairs, as they are thought to be in soaps, and if each pair of molecules is about 64 A. long, as calculated from normal bond radii and angles, this long
4.64 4.60 4.39 4.15 3.86 3.45 2.95 2.56 2.50 2.04 a
29 2 4 1 2 6 4 4 2
d , A. 58.1 56.0 29.4 28.5 19.6 19.0 14.7 14.2
(1) (1)
(2) (2) (3) (3) (4) (4)
100 100 40 46 21 30 3 4
3
14 3 23 17 4 2 2 1
Order of long spacing.
__
Figure 3. Electron micrograph of lithium hydrogenated tallow amine terephthalamate. Finest fibrils splitting out from main crystals areabout 130 A.wide I
'-
I
Na
/I
I\
ID
ll
I /
I
.
I/
Ba
n -
15
.
20
25
DIFFRACTION ANGLE, 2 0 Figure 4. X-ray diffraction patterns of sodium and barium N-octadecylterephthalamates
spacing indicates that they are tilted 25O from normal to the axis. The barium salt crystals were apparently oriented uniformly in the powder diagram sample, for only orders of two polymorphic long spacings appeared in the diffraction diagram. They indicate molecular tilts of 23' and 27' from normal to the axis. Gelling Power. The gelling power of terephthalamates was investigated from the viewpoints of three variables-the N substituent, the salt cation, and the nature of the liquid being gelled. The effect of the N-substituent on gelling power is shown in Table V. For gel preparation, the methyl terephthalamate was first heated in the oil until it dissolved; the solution cooled to room temperature; sodium hydroxide in water added; and the mixture heated to about 150' C., cooled to room temperature, and milled. Small samples were milled by being pumped through a highpressure, l/d-inch needle valve opened about a half turn. Consistency was measured with a grease penetrometer-the lower the penetration, the stiffer the gel. As the chain of the N-substituent was lengthened from butyl to octadecyl, the gelling power of the salt increased. Even the butyl salt had some gelling powersodium salts of acids below palmitic from natural fats have almost no gelling power under these conditions. The octadecyl salt was also a much stronger gelling agent than sodium stearate-almost twice as much sodium stearate is needed to gel oil to the same consistency. The phenyl salt had no gelling power, but addition of a methyl group to form the @tolyl salt led to good gelling power. All gels formed melted above 250' C., which is a t least 50' C. higher than that for sodium stearate gels. VOL. 49, NO. 10
OCTOBER 1957
1693
Table V. Effect of N-Substituent on Gelling Properties of Sodium Terephthalamates in Mineral Oil" Salt Concn. in Oil,
a
Gel Properties Texture Consistencyb
%
.\'-Substituent n-Butyl n-Decyl n-Octadecyl Di-n-hexyl Phenyl p-Tolyl
Smooth paste Granular gel Smooth, clear gel Separated Paintlike slurry Smooth gel
15 10 8.4 15 15 15
..
Conclusions
Liquid 254
Solvent-refined paraffinic oil; viscosity a t 100' F., 114 cs.; a t 210' F., 10.9 cs. ASTM worked penetration, Method D 217-52T.
Table VI.
Effect of Cation on Gelling Properties of Hydrogenated Tallow Amine Terephthalamates in Mineral Oil" Salt Concn. in Oil,
Cation Li Na Ca Ba A1 a
3 70 397 275
% 10 10 10 10 8.7
Gel Properties Consistencyb 286 264 401 296 263
Texture Smooth, clear Smooth, clear Mushy Smooth, clear Rubbery
M.P.,
c.c
2,21 2 60 65 226 155
Acid-treated naphthenic oil: viscosity a t 100' F., 98 cs.; at 210" F., 7.6 cs. ASTM worked penetration, Method D 217-52T. ASTM dropping point, Method D 566-42.
Cation variation was examined in a series of terephthalamates made from hydrogenated tallow amines. Gels (except from the aluminum salt) made as described above are listed in Table VI. The aluminum salt (monobasic) was formed by adding aluminum nitrate solution to potassium terephthalamate solution; the precipitate was heated in oil to 200' C. to form the gel. The lithium. sodium, barium, and aluminum salts, all except the calcium salt, had high gelling power. A barium tallow amine terephthalamate was also made and found to be an extremelv powerful gelling agentat 6.5% concentration gel penetration was 291. The gels melted at 30" to 50' C. higher than corresponding metal stearate gels. Gels in mineral oils are
primarily for use as lubricating greases. Greases made from the sodium salt had the water resistance, work stability in bearings, heat resistance, and pumpability required for a multipurpose lubricant (4)' When the liquid was varied, terephthalamates were much moreversatile as gelling agents than conventional soaps. Gels were formed by saponification of the methyl terephthalamate in the liquid being gelled, except when the liquid itself was easily saponifiable. In that case, the more reactive terephthalamic acid was used or the salt was preformed and heated to about 150" to 200° C. in the oil for dispersion. Results are in Table VII. Sodium hydrogenated tallow amine terephthalamate gelled hydrocarbons. etha-
Table VII. Gelling Power of Sodium Hydrogenated Tallow Amine Terephthalamate in Various Liquids Liquid
Method of Salt Dispersion
'Salt Concn.,
%
Appearance
Sapond. methyl ester Sapond. methyl ester Sapond. methyl ester
5 10 12
Smooth, opalescent Smooth, opalescent Smooth, rubbery
Bright stock mineral oilb White mineral oilc
Sapond. methyl ester Sapond. methyl ester
13 10
Smooth, tacky Smooth, white grease Smooth, white grease Smooth, white grease Smooth, brown grease Smooth, gray grease
15 Bis (2-ethylhexyl) Preformed terephthalate Sapond. methyl ester 15 Polypropylene glycol methyl butyl etherd 25 Di-(p-tolyl)-I-naphthyl Preformed phosphate 10 Polymethylphenylsiloxanee Sapond. methyl ester a ASTM worked penetration, LMethodD 217-52T. Viscosity at 100° F., 942 cs.; at 210° F., 41 cs. e Viscosity a t 100' F., 76 cs.; at 210' F., 7.7 cs. Molecular weight 500; viscosity at 100' F., 13.1 cs.; a t 210' F., 3.7 cs. e Daw Corning Fluid D C 550.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Dimethyl terephthalate dissolved in an inert solvent, such as benzene, toluene, or methanol, can be selectively saponified with potassium hydroxide in dry methanol to potassium methyl terephthalate. Potassium methyl terephthalate reacts with thionyl chloride to form methyl terephthaloyl chloride, which reacts with primary and secondary amines to form methyl AT-substituted terephthalamates. Methyl N-substituted terephthalamates can also be made directly from potassium methyl terephthalate and primary or secondary amines in the presence of phosphorus trichloride. Sodium Y-octadecylterephthalamate is insoluble in boiling water. Electron micrographs and x-ray diffraction patterns indicate that the molecules in sodium IV-octadecylterephthalamate crystals are in paired layers tilted about 25" from normal to the long axis of the crystals. Some terephthalamate salts form undulating and helical crystals. Salts of A'-substituted terephthalamic salts are generally more versatile and more efficient as gelling agents than conventional soaps.
Acknowledgment The author wishes to thank F. 0. Johnson for some of the solubility measurements on dimethyl terephthalate, ht. S. Williams for preliminary experiments on saponification of dimethyl terephthalate, Jay Cortes for electron micrographs. and R. E. Barieau for xray diffraction data.
Gel Properties
Ethanol Dioxane Toluene
1 694
nol, a polyether, an ester, and a polysiloxane with comparable efficiency; but it was less efficient in the phosphate oil. The versatility of terephthalamates as gelling agents suggests their use in solvents, fuels, plastics, elastomers, and surface coatings, as well as in lubricants.
Consistencya Fluid jelly Soft jelly Medium stiff jelly 269 280 223 246 225 292
References (1) Birdsall, D . H., Farrington, B. B., J . Phys. Chem. 52, 1415 (1948). ( 2 ) Bryant, W. C . . Giordano, A. (to SwanFinch Oil Corp.), U. s. Patent 2,604,449 (July 22, 1952). ( 3 ) Dreher, J. L., Hotten, B. W., Carter, C. F., NLGISpokesman 20, No. 11, 10 (1957). (4) Grimmel, H. W., Guenther, A., Morqan, J. F., J. Am. Chem. SOC.68, 539 (1946).
RECEIVED for review October 22, 1956 ACCEPTED
M a r c h 15, 19.57
Division of Industrial and Engineering Chemistry, 130th Meeting, ACS, Atlantic City, S . J., September 1956.
