INDUSTRIAL AND ENGINEERING CHEMISTRY
826 (8) (9) (10) (11) (12) (13)
Green, “Microscopy of Paint and Rubber Pigments” (1922). Grenquist, IND. ENG.CHEM.,20, 1073 (1928). International Critical Tables, Vol. 11, p. 272 (1927). Ibid., p. 273. Kitchin, Trans. Am. Insl. Elec. Eng., 48, 495 (1929). Nordenson, Koltoid-Z.. 16. 65 (1915).
(14) (15) (16) (17) (18) (19)
Vol. 22, No. 8
Xuttall, Chemistry 5 Industry, 41, 1359 (1928). Smoluchowski, Physik. Z.,6, 529 (1905). Svedberg, “Colloid Chemistry,” p. 238 (1928). Wbitney and Blake, J . Am. Chem. Soc., 26, 1385 (1904). Wiegand. Canadian Chem. J . , 4 (1920). Williams and Kemp, J . Franklin I n s f . , 203, 35 (1927).
Secondary Esters and Their Use in Lacquers’ J. G. Park and M. B. Hopkins STANCO DISTRIBUTORS, 2 PARK AvE., N E W YORK, N. Y.
regarding them have been published. It is the purpose of this paper to present a systematic study of their properties based on the use of experimental data scientifically obtained with special reference to use in lacquers. The investigation has been confined to the study of the secondary butyl, amyl, and hexyl acetates, as it is believed that these esters hold the greatest interest for lacquer manufacturers from the standpoint of both their inherent properties and their economic position. The secondary esters used in this work were practically chemically pure mixtures of 85 per cent ester and 15 per cent corresponding alcohol. Although the process of manufacturing secondary esters permits their production as single individuals or as any blend the lacquer manufacturer may desire, it was deemed advisable to determine the properties of the pure ester mixtures. For this reason in those cases where comparisons are made between secondary and other esters, the comparisons do not necessarily offer a basis for evaluation. The boiling ranges of the esters used, which are recorded graphically in Figure 1, will bear out the statement that the three secondary esters used are evidently purer chemical compounds than the three esters used as a basis of comparison. Of the latter, butyl propionate has the widest boiling range, no doubt owing to the presence of homologous compounds. The secondary esters are colorless mobile liquids having the properties listed in Table I. of Secondary Esters SP.GR. REFRACTIVE ESTER BOILING 15.5O/ INDEX CONCN. POINT 15.5’ C. (20.0’ C.) DEXSITY Lbs. per % O c. Rd. .” 0.861 1.3915 7.17 85-88 107-114 0.863 1.4021 7.18 85-88 128-134 1.4081 7.18 85-85 146-156 0.863
Table I-Properties SOLVECNT sec-Butyl acetate sec-Amyl acetate sec-Hexyl acetate
These compounds, as now commercially available, have characteristic clean ester odors quite different from the odors of normal esters. It is the general experience of those who work with secondary acetate that it does not seem to affect the lower part of the throat to the same extent as normal acetate, and consequently there is less “gagging” effect. The earlier production of secondary esters was not particularly satisfactory from the odor standpoint, but great improvement has been made in this respect and the present 1 Received April 27, 1930. Presented before the Division of Paint and Varnish Chemistry at the 79th Meeting of the -4merican Chemical Society, Atlanta, Ga., April 7 t o 11, 1930.
precautions to prevent d e hydration of secondary alcohols during esterification has led some to the erroneous idea that secondary esters are unstable. This fact should not be overlooked when running saponifications to determine the ester content. The writers’ laboratories use regular saponification methods, but care is taken that the samples are refluxed with the alcholic potash at least 4 hours before titrating. Solvent Power
It is generally conceded that the dilution ratio is a reasonably accurate measure of solvent power of an ester; therefore this test was applied to the solvents under examination. Six solutions containing 20 per cent of dissolved nitrocellulose were prepared, and the non-solvent was slowly added, with thorough mixing, as long as the precipitated nitrocellulose would redissolve. The dilution ratios were then calculated as the ratio of non-solvent by weight at the end of the experiment. The values obtained are presented in Table 11. Table 11-Dilution SOLVENT
Ratios of Secondary Esters DILUTIOX RATIOBY WEIGHT With toluene With naphtha
sec-Butyl acetate sec-Amyl acetate sec-Hexyl acetate n-Butyl acetate %-Butylpropionate Pentacetate
The naDhtha used in these tests was the usual Detroleum distillate having a boiling range of approximateiy 80” to 130” C. These dilution ratios are plotted graphically in Figure 2, in descending order. It will be noted that practically the same order exists for both non-solvents. It will also be noted that the dilution ratio decreases with the increase in molecular weight of the solvent. As a further test of the solvent power of secondary esters, viscosity determinations were made of nitrocellulose solutions of the same concentration, in various solvents. It is generally recognized that viscosities of solutions of nitrocellulose are a measure of the solvent value of the solvents used. The viscosities of 20 per cent solutions of dry ’/zsecond R. S. nitrocellulose in the various solvents under examination were determined a t 25” C. by the means of a MacMichael viscometer. These values were determined on solutions which had been allowed to stand for approximately six weeks after being prepared. (Table 111)
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which may have been present, the results in Table V were obtained. T a b l e V-Solubility
of W a t e r S O L U B L E I N 100 CC. OF W A T E R A T 25'
c.
SOLVENT
cc. sec-Butyl acetate sec-Amyl acetate sec-Hexyl acetate n-Butyl acetate n-Butyl propionate Pentacetate
It will be noted that these figures are parallel to the results obtained by dilution ratios. The secondary acetates were found to be miscible in all proportions with the other solvents and diluents used in the lacquer industry and may be used in any combination the formulator desires. All the plasticizers, drying oils, and non-drying oils used in lacquer formulation are miscible withleach of these solvents in all proportions. T a b l e 111-Viscosity
of 20 P e r C e n t S o l u t i o n s of cellulose a t 25' C .
SOLVENT
I/n
-Second Nitro-
VISCOSITY
Poises n-Butyl acetate n-Butyl propionate sec-Butyl acetate Pentacetate sec-Amyl acerate sec-Hexyl acetate
9.12 9.12 10.49 13.22 15.03 50.13
Water Solubility of Secondary Esters It is generally known that the solubility of water in a solvent is an indication of the probable tendency of that solvent to permit blushing in humid weather. It has been shown by Reid and Hofmann (3) that it is this property, and not the rate of evaporation, which influences blushing in a lacquer. As a general rule the aliphatic esters boiling above 100" C. are not very miscible with water, and therefore have good blush resistances. Very little difference was observed in the solubility of water in the normal and secondary esters. Using commercial samples, without previous drying to remove traces of water
0.2
Evaporation Rate The evaporation rates of the various solvents were determined by placing equal volumes of each liquid in shallow vessels of equal size and then weighing them a t frequent intervals. The percentage of each solvent lost by evaporation was plotted against the time, and the curves in Figure 3 show a fairly uniform rate of evaporation for all but pentacetate and butyl propionate. These two solvents are, however, known to be mixtures of at least two components. The slight change in the rate of evaporation near the end of the test is due to the fact that as the vessels become nearly dry the area of the liquid is not the same as is the case when considerable of the solvent is present. By comparing the curves in Figure 3 with the boilingrange curves in Figure 1, it will be seen that the rate of evaporation of see-amyl acetate is nearer to that of butyl acetate than their boiling point curves would indicate. This emphasizes the fact that, except in homologous series, the rates of evaporation of solvents cannot be predicted satisfactorily from their boiling points. The slopes of curves such as those in Figure 3 indicate the rate of evaporation of a solvent and it is believed that this point should be further emphasized. The time required for a certain percentage to evaporate will obviously depend
f i G Z-DliUTlON
As would be expected with adjacent members of the same homologous series, the secondary esters were found to exhibit the same solvent power towards resins as that shown by the normal esters. The solubility of the gums which are used in the lacquer industry are given in Table IV. T a b l e IV-Solubility of R e s i n s in S e c o n d a r y Eisters RESIN sec-Burur, S ~ C - A M Y L sec-H BXYL Rosin S S 8 Ester gum S S 8 Dammar S S s Amberol S S s Albertol S S s Kauri S S 8 Cumar S S E Pontianac S S s Manila S S s Elemi S S s Shellac I I I Asphalt S S e Tars S S E Pitches S S E S-Soluble I-Insoluble
1.0 0.2
