Aliphatic Ketones as Solvents J. G. PARKAND H. E. HOFMANN, Stanco Inc., Elizabeth, N . J .
T
HE s t o r y of the rapid
A n o t h e r s o u r c e of ketones T H E P U R P O S E of this paper is to present a sysiemalic of aliphatic ketonesis described by Desparmet (5) P w t h of the use of nitrocellulose lacquers as in a recent article in which he acetone, methyl ethyl, m e W butyl, and methyl industrial finishes is one familiar also refers to the a d v a n t a g e s to every p r o t e c t i v e - c o a t i n g amyl-from the standpoint of inherent of ketones as n i t r o c e l l u l o s e chemist. From 1922 to 1929 properties. solvents. Mixtures of simple The properties discussed include the solvent and mixed ketones are obtain'ed t h e i n d u s t r y w a s constantly and resins, and evaporaby distilling the calcium salts faced with the specter of a SolPower, solubility of resulting from the fermentation vent shortage. Since 1929 this tion rates, together with suggested applications as apparition has disappeared, and of a l k a l i n e sugar s o l u t i o n s determined by practical tests. the demand is now for cheaper by butyric acid bacteria. These and b e t t e r s o l v e n t s in order sugar solutions are prepared that nitrocelIulose lacquer may enlarge its scope of usefulness from sawdust. The products, however, have an empyreuand enter new fields. matic odor, due to the presence of small quantities of pyridine I n discussing the relation of constitution to the properties bases which are quite difficult to remove. of lacquer solvents, Calvert (2) says, after pointing out the The ketones used in this work were chemically pure prod. . . ucts and were of a pleasant ethereal odor. Acetone and nature of nitrocellulose: "It should not be surprising that pyroxylin solvents of present commercial importance are methyl ethyl ketone, the first two members of the series, have oxy-compounds usually containing either a carbonyl group, been known and used in connection with nitrocellulose for as in an ester or a ketone, or an alcohol and ether group, as some time. The three higher members are newcomers in the mono-ethers of ethylene glycol." Other writers to the field of lacquer technology, and it is their properties have alluded to the fact that ketones as a class are excellent that are being studied here. These ketones were prepared nitrocellulose solvents, but individuals with the correct from the secondary alcohols, and therefore it may be stated that their availability is assured. The compounds are colorproperties have not been available. less mobile liquids having the physical properties shown in TABLE I. PHYSICAL PROPERTIES OF ALIPHATIC KETONES Table 1,
..
.
(Data taken mostly from International Critioal Tables) METHYL METHYLMETHYLMETHYL ETHYL PROPYL BUTYL AMYL ACETONEKETONEKETONE KETONE KETONE Moleoular weight 58 72 86 100 114 Boiling point (760 mm.), O c. 56.1 79.6 102 127.2 150.2 Specific gravity 0.7915 0 3 0 5 0 0 .So89 0.8209 0.8269 Refractive index (20" C.) 1.3587 1.3791 1.3895 1.4024 1.4110 Visoosity, centipoises (25' 0.318 0.401 0.473 0.584 0.766 C.) Vapor pressure (20' C.) 184.8 77.5 30 10 3.6 Flash point (closed oup), 2 19 45 73 106 (-16.7) (-7.2) (7.2) (22.8) (41.1) L s ~ e % ~heai, e % )oal.ygram c a l . /ram 125 83 0 . 5 2 7 106 0 . 5 5 0 91. 0 . 5 5 3 83 . Specific Dieleotrio oonstant 21.4 18.4 15.4 12.2 Surface tension (20' C.) 23.7 24.6 25.2 25.5 .. . .. .. No data are available for the spaoea indicated by leaders.
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The use of higher ketones as solvents in nitrocellulose compositions is described in a patent granted to Seher in 1892 (4). Mention is here made, among others, of methSrl ethyl, methyl propyl, methyl butyl, and methyl amyl ketones. Since that time many other patents have been issued, covering the use of a ketone or ketones in some special type of product, or covering the use as solvents of ketones obtained by various processes (1). Very few of these ideas appear to have been put into practice for one reason or another, except Tvith respect t o acetone and methyl ethyl ketone. Aliphatic ketones of higher boiling points have never been produced on a commercial scale. Several ketone solvents have been available in moderate quantities for some time, but each has a t least one distinct disadvantage which removes it from the consideration of lacquer manufacturers. These include principally: cyclohexanone, which is too high-boiling and too expensive; diacetone alcohol, which readily decomposes into acetone; and mesityl oxide, which contains an unsaturated bond, and is therefore unstable. The only other source of ketones has been the so-called acetone oils which have been discarded on account of their bad odors.
SOLVENT POWER The most interesting property of a solvent is its solvent power. The first investigation made of the ketones was upon the solvent action of these compounds on the various types of cellulose compounds. Cellulose acetate is readily soluble in acetone. Some grades are soluble in methyl ethyl ketone, while practically all are soluble in a mixture of the ketone with a small proportion of ethyl alcohol. The ketones higher than methyl ethyl do not dissolve cellulose acetate even in the presence of alcohol, but are latent solvents when used in conjunction with certain solvent plasticizers. This action is similar to that of camphor and alcohol upon cellulose nitrate. The cellulose ethers are soluble in all of the ketones, but Probably not as readily as in the coal tar hydrocarbons. TABLE11. VISCOSITIES OF NITROCELLULOSE SOLUTIONS (20% solutions at 25O C . ) SOLVBNT Acetone Methyl ethyl ketone Methyl ropy1 ketone Methyl utyl ketone Methyl amyl ketone Ethyl acetate %-Butylacetate
g
VISCOSITY Poises 1.4 2.0 3.4 7.5 12.0 3.0 9.1
The ketones are excellent solvents for nitrocellulose, judged both from the viscosity of the nitrocellulose solutions they produce and their tolerance for hydrocarbons. As it is generally recognized that the viscosity of a nitrocellulose solution is indicative of the solvent power of the solvent, a 20 per cent solution of dry half-second R. S. nitrocellulose was prepared with each of the ketones under observation, as well as with butyl acetate. The viscosities were then determined a t 25" C. by means of a MacMichael viscometer, using solutions which had been allowed to stand for several weeks after being prepared.
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INDUSTRIAL AND ENGINEERING CHEMISTRY
It will be noted that in this series of ketones, as is the case in any homologous series of solvents, the solvent power decreases as the molecular weight increases. io 900 00
B700 M 6W SOD
4w 300
sB $
200
100 BD
23 ;i 44
133
It will be noted that the results obtained are parallel to those given in Table 11, and it is evident from these data that the ketones have higher dilution ratios than the regular esters of corresponding boiling points, with the exception that, when petroleum naphthas are used, the dilution ratios of the ketones are somewhat inferior to those of the esters. Investigation shows that the ketones are miscible in all proportions with the other solvents and diluents used in the lacquer industry. The solubility of the oils, waxes, and resins which are in common use are given in Table IV. Methyl butyl and methyl amyl ketones show good compatability with ester gum and amberol resins in the presence of nitrocellulose, that is, the solution of nitrocellulose and resin is clear and gives a clear film. With methyl propyl ketone a small amount of plasticizer is necessary to produce a clear film, while with acetone and methyl ethyl ketone, a plas-
4
30
20
0
0
/0
10
20
M
49
53
60 70 80 QO 103
140
120
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TfUPtffATURE , *C
FIGURE 1. VAPORPRESSURE OF ALIPHATIC KETONES
As a further test of the solvent power of the ketones, the dilution ratios were determined with toluene and with lactol spirits. Lactol spirits is a petroleum distillate boiling between 80" and 130" C. The method used for determining the dilution ratios is the classical one in which tne solvent and non-solvent are so adjusted just before the end point is reached that the final concentration of nitrocellulose lies between 5 and 7 per cent. As pointed out by numerous authors, it is necessary to adjust the final concentration of nitrocellulose to the same value in a series of tests so that comparative results will be obtained. The final ratios of nonsolvent to solvent, by weight are given in Table 111. rr4BLE
111. RATIOSOLVERT
SOLVENT Acetone Methvl ethvl ketone
n-Butyl acetate
TABLE Iv.
TO
NOWSOLVEAT
DILUTION RATIO Toluene Lactol spirits
4.75 4.5 4.1 4.0 3.5 3.6 3.1
SOLUBILITIES OF SOLVENTS .4ND
0.625 0.73 0.80 0 . so 0.80 :1 2
.
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DILKJEXTS
SOLVESTMethyl Methyl propyl butyl ketone ketone
Methyl Methyl amyl ethyl SUBSTANCE Acetone ketone ketone S 8 S S 8 Nitrocellulose S 8" i i i Cellulose acetate Ethyl cellulose 8 S S S 8 Water 8 P8 ss VSS vss 95% alcohol 0 8 S 8 R Petroleum spirits S S S 8 s All other solvents S S 8 8 8 Linseed oil 8 S 8 J 9 Tung oil S 8 S 8 s Castor oil S 8 s 8 I Mineral oil (tech. white) i 8 8 8 S Essential oils, etc. 8 8 8 S S Ester gum pa s 8 3 8 Dammar (whole) PS Pa p8 f" PS PS PS 1 Bleached shellac Kauri (chips) 5 8 8 8 S Manila (hard) 8 S S 8 s Pontianao (nubs) S 8 8 8 S Glyptal-type resin S 8 8 S S Amberol-type resin i S 8 S 8 Cumarone resin i 8 9 5 R Vinyl acetate resin S 8 8 S S Rosin S 8 8 8 I Beeswax i i vss yas vss i 1 1 vsa Paraffin wax i Ceresin i ! yss YSS 1 1 Carnauba wax i i a-in presence of alcohol ps-partially soluble i-insoluble ss-slightly soluble s-aoluble vss-very slightly soluble
FIGURE 2. EVAPORATIOX RATES OF KETONES AND CERTAIN ESTERS (Temperature, 18.5-19.5' C.)
ticizer and another solvent or diluent are necessary. Methyl ethyl ketone is approximately equivalent to ethyl acetate in its behavior with resins. All of the ketones show good compatability with blown castor oils and the glycerol-phthalic anhydride resins. i7AP0R PRESSURE AND
RATEO F EVAPORA4TION
The vapor pressures of the ketones were obtained from actual experimental determinations by the dynamic method. The logarithms of the values obtained were then plotted against the reciprocals of the absolute temperatures in accordance with the modified form of the Clausius-Clapeyron equation, -K log P = -
T
and the curves obtained are shown in Figure 1. The evaporation rates of the five ketones under investigation, as well as three of the common esters, were determined in the usual way. The results obtained are plotted graphically in Figure 2 and indicate the following facts: 1. Each ketone evaporates approximately twice as slowly as the one just before it in the series.
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2. Methyl ethyl ketone matches ethyl acetate very closely in evaporation rate. 3. Methyl butyl ketone is a good match for n-butyl acetate. 4. Methyl amyl ketone evaporates very slowly, or about the same as sec-hexyl acetate. It is somewhat slower than butyl propionate or amyl acetate.
Vol. 24, No. 2
butyl acetate, which has been used in these tests as a standard for comparison. Acetone, which is miscible with water in all proportions, and methyl ethyl ketone, which dissolves considerable water, were not tested for blush resistance, as they are low boilers and have little or no bearing on the blush resistance of a solvent mixture. This property is usually investigated only in solvents boiling above 100" C. Five lacquers, three of which contained the higher ketones and the other two n-butyl acetate and sec-butyl acetate, respectively, were applied to tin panels and tested in a humidity cabinet in the usual manner. The results obtained are summarized in Table VI. TABLEVI. BLUSHINGTESTS ON I A ~ C Q U E R S CO\TAINING KETONES, ETC. ST~NDAR FORMULA D
SOLVENT by volume 14 grams (wet) sea R. S.nitrocellulose 60 toluene 5 grams ester gum 10 n-butyl alcohol 5 grams dibutyl phthalate 20 ethyl acetate 100 cc. solvent 10 other solvent RELA- BEHAVIORO F LACQUERWHEN TIYE OTHERSOLVENT Is: nwcDRY WET DIFFER-Hc- Me Pr Me Bu Me Am BULB BULB ENCE MIDITY kekekeButyl Butyl cone tone tone acetate acetate a F ( " C . ) ' F. (' C.) P. % 2 92 87 ( 3 0 . 6 ) 85 ( 2 9 . 4 ) 87 (30.6) 84 ( 2 8 . 9 ) 3 89 FIGURE 3. SOLUBILITY OF DRYHALF-SECOND R. S.NITROCEL- 86 (30) 83 ( 2 8 . 3 ) 3 89 LULOSE IN SYSTEM hlETHYL BUTYLKETONE-Sec-BUTANOL 82 ( 2 7 . 8 ) 79 ( 2 6 . 1 ) 3 88 i TOLUENE 87 ( 3 0 . 6 ) 83 ( 2 8 . 3 ) 4 85 86 (30) 82 ( 2 7 . 8 ) 4 85 i t + 8F, ( 2 9 . 4 ) 81 ( 2 7 . 2 ) 4 85 5. Methyl propyl ketone is an intermediate between ethyl 83 ( 2 8 . 3 ) 79 ( 2 6 . 1 ) 4 85 87 (30.61 82 127.8) 5 81 i f + . . and butyl acetates and somewhat faster than sec-butyl acetate. 85 i 2 9 . 4 ) 80 ( 2 6 . 7 ) 5 81 6 . The evaporation rates of all these compounds are in the 84 ( 2 8 . 9 ) 79 ( 2 6 . 1 ) 5 80 same order as their boiling points. 87 ( 3 0 . 6 ) 81 ( 2 7 . 2 ) 6 77 85 ( 2 9 . 4 ) 79 ( 2 6 . 1 ) 6 77 =t 8 70 87 ( 3 0 . 6 ) 79 ( 2 6 . 1 ) t BLUSHRESISTANCE - Bad bl ush; f slight blush: no blush.
'* +'
It has been generally agreed that the two properties of a solvent which most affect its blush resistance are its miscibility with water, and the cooling effect upon evaporation. The solubility of water in each of the ketones and the solubility of each ketone in water are given in Table V as a percentage of the saturated solution a t room temperature (approximately 25' C.). The maximum depression of a wetbulb thermometer wet with the solvent a t a room temperature of 22.5' C. is also given. T.4BLE
1'.
SOLVENT PROPERTIES SOLVENT
AFFECTING BLUSH RESISTANCE
SOLUBILITY OF: H20 in Solvent in HzO solvent
WET-BULB DEPRESSIOS
c.
Acetone Infinite Infinite 30.5 Methyl ethyl ketone 22.6 9.9 21.5 Methyl propyl ketone 6.0 3.6 12.0 Methyl butyl ketone 3.44 3.70 6.5 Methyl amyl ketone 1.95 2.15 3.0 Ethyl acetate 7.9 3.OU 21.5 n-Butyl acetate 2.3 2.4 6.5 a For c . P . product containing no alcohol; commercial material dissolves more water than this.
Some practical tests were conducted Kith the blush-resisting properties of the ketones under examination upon lacquers having the following composition: STANDARD FORMUL.~ 14 grams (wet) 1,s' sec. R . S. nitrocellulose 5 gram8 ester gum 5 grams dibutyl phthalate 100 cc. solvent
SOLVENT by volume 60 toluene 10 n-butyl aloohol 20 ethyl acetate 10 other solvent
It is very difficult to obtain satisfactory data of an absolute nature concerning the actual blush resistance of a solvent. It is usually necessary to make comparative tests, using solvents of well-known properties as standards. The most universally used solvent having good blush resistance is n-
+
--
+
-
*+
++
++
--
++ + ++
+++
+++
++*
++
++
++
While the results obtained hold only for lacquers of the general formula indicated, they are cited as comparative data.
USE OF KETONESIN THINNERS The solubility of half-second nitrocellulose in ternary systems containing a solvent with sec-butyl alcohol and toluene was determined for methyl butyl ketone (Figure 3), as this solvent closely corresponds to n-butyl acetate. CONCLUSION In conclusion it may be stated that the uses of acetone are well known. Methyl ethyl ketone is recommended as a direct substitute for ethyl acetate in nitrocellulose lacquers, and as a medium-boiling solvent in cellulose acetate compositions, It might also well be used in paint removers, when a solvent is required of slower evaporation rate than acetone. Methyl butyl ketone is recommended as a substitute for n-butyl acetate in all kinds of nitrocellulose lacquers. The methyl propyl and methyl amyl ketones may be used when ingredients of other evaporation rates are required. All have high dilution ratios, good blush resistance, and are compatible with all the resins. They are also stable to light, heat, and moisture, and do not turn dark upon aging. LITERATURE CITED (1) Broxn a n d Crawford, "A S u r v e y of Nitrocellulose Lacquer," Chemical Catalog, 1928. (2) Calvert, IKD. EM. CHEX, 21, 213 (1929). (3) Desparniet, Cuir tech., 21, 56 (1928). (4) Seher, A , , U. S.P a t e n t 470,451 (March 8 , 1892). RECEIYED September 10, 1931. Presented before the Division of Paint and Varnish Chemistry at the 82nd Meeting of the American Chemical Society, Buffalo, N. Y., August 31 to September 4, 1931.
